PURPOSE: A salient feature contrast between a target item and many background items results in perceptual pop-out of the target from the background. However, when the feature contrast is small the target may not be salient initially, but sufficient training on the detection task can also result in a pop-out e?ect. Previous studies suggest that the pop-out effect induced by simple feature contrast is mediated by primary visual cortex (V1) through creating a saliency map, which is thought to be a bottom-up process. In the current study we examine whether the saliency map in V1 can be enhanced by perceptual learning.
METHODS: Two monkeys were trained to detect a line segment whose orientation was deviated by varying extents from a background of iso-oriented lines. Over the course of training we recorded V1 neuronal responses with implanted microelectrode arrays. We used support-vector-machine (SVM) classifier to decode V1 responses.
RESULTS: The animals' performance in the detection task, measured as percent correct and reaction time, was signi?cantly improved with training for targets with small orientation contrasts. By comparing neurons with different preferred orientations relative to the target, we dissociated two distinct neural response components that signal the pop-out e?ect. One component is stimulus-driven and little affected by training; it relies on orientation-dependent contextual modulation mechanisms, which create a saliency map from neural response outset. The other component is mainly task- and experience-dependent; it signals the perceptual saliency of the target, independent of the preferred orientations of neurons. The latter mechanism generates a delayed saliency map (40 ms after visual response onset), which is enhanced by perceptual training and correlated with improved behavioral performance.
CONCLUSIONS: V1 is involved in detection of local-feature contrast through two separate saliency maps. Perceptual learning enhances the late saliency map but not the early, bottom-up, saliency map.
Purpose: Humans can learn to abstract and conceptualize the shared visual features defining an object category in object learning. Therefore, learning is generalizable to transformations of familiar objects and even to new objects that di?er in other physical properties. In contrast, visual perceptual learning (VPL), improvement in discriminating ?ne di?erences of a basic visual feature through training, is commonly regarded as speci?c and low-level learning due to its speci?city to the trained stimulus conditions. Such location and orientation speci?city is taken as evidence for neural plasticity in V1 or improved readout of V1 signals. However, new training methods have shown complete VPL transfer across stimulus locations and orientations, suggesting the involvement of high-level cognitive processes. Here we report that VPL bears similar properties of object learning.
Methods & Results: Speci?cally, we trained human observers to discriminate the explicit orientation of luminance gratings encoded by V1 neurons; or the implicit orientation of bilaterally symmetric dot patterns encoded by higher cortical areas. We compared the mutual transfer of learning between these two distinct stimuli. Learning in orientation discrimination of the symmetric dot patterns transferred completely to the gratings. In contrast, learning in orientation discrimination of the gratings transferred only partially to the dot patterns; but subsequent exposure to the same-oriented dot patterns in an irrelevant task (a Training-Plus-Exposure technique) further markedly reduced orientation thresholds for the dot patterns, achieving a complete learning transfer from the gratings to the dot patterns. Similarly, motion direction discrimination learning is transferable between the ?rst- and second-order motion signals, replicating the same patterns of learning transfer.
Conclusion: These results suggest that perceptual learning can take place at a conceptual level and generalize to stimuli with different physical properties. Our findings thus reconcile perceptual and object learning into a uni?ed framework.
PURPOSE: Anisometropic amblyopia, one type of lazy eye, is a neuronal vision disorder accompanied with weak or strong spatial vision loss in the amblyopic eye (AE) when compared to normal eyes. While the plausible neural substrates and consequences on visual perception have been studied, its relation to changes of monocular early neuronal processing remains unclear.
METHODS: Here we used the monocular tilt illusion as a probe of primary visual cortex inhibitory interactions and we modeled amblyopic low-level perception disturbances through network modi?cations at monocular V1 stages.
RESULTS: We found that the amount of orientation misperception was higher in AEs when compared with non-amblyopic (NAEs) and neurotypical eyes (NTEs). Importantly, it was highly correlated to subject's AE peak contrast sensitivity. Near the peak of contrast sensitivity, the model predicted from the tilt data a broader orientation tuning width of AEs than NAEs and NTEs without any relation to subjects' contrast sensitivity functions (CSF).Additionally, for subjects with stronger loss of peak CSF, these correlations could be explained by stronger lateral inhibition in AEs.
CONCLUSIONS: Through psychophysics experiments in humans and computational modeling of V1, our study provides new fundamental insights into visual neuronal disorders through inhibitory prevalence.
Purpose: Although numerous studies have shown that perceptual learning can improve deficient visual functions in adults with amblyopia, the efficacy of perceptual learning in treating children with amblyopia has rarely been investigated. Here, we designed a child-friendly, individualized adaptive vision training (iAVT) based on a visual training procedure originally developed to train adults with amblyopia (Zhou et al., 2006) to evaluate e?ects of perceptual learning in children with amblyopia.
Methods: Nineteen amblyopic children (7.78±2.73 yrs) were trained with the iAVT in a filtered letter E orientation identification task near their individual cutoff frequency for 8 sessions, with 300 trials or 30 minutes per session. Contrast sensitivity function (CSF) and visual acuity in both the amblyopic and fellow eyes, and stereo acuity were assessed before and after training. CSF was measured using the qCSF procedure (Lesmes, Lu, Baek, & Albright, 2010). Each qCSF assessment took less than ?ve minutes.
Results: Training signi?cantly improved visual acuity (2 lines) and contrast sensitivity (53.9%, from 13.01 to 20.02, p< 0.0001) in the amblyopic eye, stereo acuity (80.8%, from 606 to 116.2, p< 0.0001), and contrast sensitivity (24.7%, from 28.4 to 35.4, p< 0.01) in the fellow eye. The magnitudes of improvements were correlated with pre-training visual deficits: The worse the pre-training measure was, the greater the improvements. Interestingly, we found no significant correlation among the magnitudes of improvements in visual acuity, contrast sensitivity, and stereo acuity (all p > 0.39).
Conclusions: These results demonstrate the merit of perceptual learning in treating children with amblyopia. Consistent with results in adults with amblyopia (Xi, Jia, Feng, Lu, & Huang, 2014), the lack of correlation among improvements in visual acuity, contrast sensitivity, and stereo acuity suggests that structured monocular and binocular treatments are necessary to fully restore de?cient visual functions in amblyopia.
PURPOSE: Two theories explain visual perceptual learning (VPL): Early cortical neural plasticity (e.g., Karni & Sagi, 1991; Stoups et al., 2001) and neuron-specific response reweighting (Dosher & Lu, 1987; Law & Gold, 2008), as motivated by observed learning specificities. However, our double training studies (Xiao et al., 2008; Zhang et al., 2010; Wang et al., 2016) demonstrate that VPL often shows complete transfer to untrained locations, orientations/directions, and physical properties, indicating that VPL is primarily a rule-based high-level process operating at a conceptual level. Here we test a hypothesis that VPL requires neither early cortical neural plasticity nor neuron-speci?c response reweighting.
METHODS: In a peripheral orientation-discrimination learning task, training took place with the Gabor stimulus either rotated in 12 locations (anti-clockwise) and 4 orientations 90-deg apart (clockwise), or in a random order. Each location/orientation combination received 2 trials per block of trials, 6 blocks per session, for a total of 60 trials over 5 daily sessions. A staircase controlled the orientation di?erence from condition to condition. The pre/post condition was never practiced.
RESULTS: Both rotating and random training conditions produced significant orientation learning, indicating that the observers can learn orientation discrimination with multiple conditions that minimize neural plasticity in early visual areas and neuron-speci?c response reweighting. Learning transferred to the untrained pre/post location/ orientation condition, so that the improvement was comparable to that in a control group that only practiced the pre/post condition for an equal number of trials. Therefore, orientation learning with multiple stimuli is genuine and unspecific to the more difficult multiple stimulus task. Similar results were seen in a motion-direction learning task with 6 rotating locations and 8 rotating directions 45-deg apart, but without direction/location speci?cities.
CONCLUSIONS: These results indicate that early cortical plasticity and neuron-speci?c input reweighting are unnecessary for VPL. Instead sensory inputs can be reweighted at a later stage in a neuron unspeci?c manner.
PURPOSE: We perceive a stable visual world despite the retinal image is constantly shifted rapid eye movements (saccades), which normally occur 3-4 times a second. It has been suggested that the brain maintains a stable visual representation by predictively mapping objects to their future retinal loci. Because remapping related neural activation is observed when visual objects are no longer visible before saccades, it is believed that the memory trace of visual objects can also be remapped around saccades. The remapped memory trace has been linked to increased neuronal discharge or enhanced behavioral performance. Here we show that it also generates an inhibitory attentional effect—inhibition of return (IOR)—that is of great importance to e?cient orienting.
METHODS: The participant first fixated a central dot. This dot was then displaced 8 degrees to the left or right, and the participant initiated a saccade to follow it. Around the time of saccade onset, an onset cue was flashed for 30 ms. Eight-hundred milliseconds after the cue onset, a target appeared at either the cued location, the cued retinal locus, or two distance matched control locations, and the participant quickly saccaded to the target. The memory trace of the onset cue was remapped around the first saccade; the behavioral consequence of this memory trace was later revealed by the target. Of great interest to us is whether the memory trace of the cue will also generate an IOR effect, as in tasks in which the cue is presented long before the intervening saccade.
RESULTS: To reveal how IOR evolves as the cue onset time approaches the the ?rst saccade, the time intervals between the cue and the onset of the ?rst saccade were split into four bins. IOR was observed at the cued location in all four bins, including the one in which the cue disappeared only 14 ms before the ?rst saccade.
CONCLUSIONS: The results of the present study show that the remapped memory trace of obejcts can generates not only facilitatory but also inhibitory effects. These effects are both critical to the e?cient sampling of visual information.
PURPOSE: Previous studies demonstrated that fusiform face area (FFA) is the core region of face processing, which is largely innate and tuned by visual experience. However, the degree to which the face-selectivity of FFA was genetic determined remains unclear. Moreover, evidence is still lacking on elucidating the neural plasticity of the FFA in other sensory modalities (e.g. tactile).
METHODS: To investigate these questions, we studied 38 eyesight obstacle disabled subjects, who consist of four sub-groups: congenital blind, early blind, late blind and low vision. All subjects were trained ~3 hrs on perceiving man-made tactile faces and other complex object categories. Functional magnetic resonance imaging (fMRI) was performed both before and after training.
RESULTS: We found robust face-selective activation in the FFA in both the early blind and low vision subjects after training. In contrast, this was not seen in the congenital blind or late blind subjects.
CONCLUSIONS: Our results suggest that even after more than 14 years of absence of visual face exposure, the FFA can still quickly become engaged in processing face information, and even from a different sensory modality. However, despite of strong genetic determined, the specialization of face processing requires an initial visual driven start.
PURPOSE: Perceptual learning (PL) can transfer completely to an orthogonal orientation if the latter is exposed through an irrelevant task (Zhang et al., 2010). PL thus is more likely rule-based cognitive learning. However, it is unclear why PL is orientation specific in the first place and why exposure to the transfer orientation enables learning transfer. Here we used a continuous ?ashing suppression (CFS) paradigm to answer these questions.
METHODS: Foveal orientation discrimination was always trained at one orientation. In other blocks of trials ?ashing white noise was presented to one eye, which suppressed the awareness of an orthogonal Gabor (sometimes a letter C) presented to the other eye.
RESULTS: In bottom-up orientation exposure condition, observers reported the color of a dot centered on the noise in the dominant eye, without knowing the presence of the subconscious orthogonal Gabor in the non-dominant eye. This bottom-up exposure produced partial transfer. In a top-down “exposure” condition, observers were required to report, or guess is they had to, whether an orthogonal Gabor/letter-C was presented to the non-dominant eye even though it was suppressed by the ?ashing noise in the dominant eye. However, during actual experiment neither the Gabor nor the letter C was presented. This top-down "exposure" also induced partial transfer. In a third condition, when observers performed the Gabor/C task and the orthogonal Gabor was actually present, this combined bottom-up and top-down exposure induced complete learning transfer.
CONCLUSIONS: These results suggest that learning speci?city may result from under-activations of untrained visual neurons due to insufficient bottom-up stimulation and/or top-down attention during training. High-level perceptual learning thus may not functionally connect to these neurons for learning transfer.
PURPOSE: Memory for actions in recognition memory is usually better in a subject performed task (SPT, self-performing actions on verbal commands) than after verbal encoding (verbal task, VT), which is known as “SPT effect”. In the current study, we aim to investigate whether the SPT e?ect and memory processes during associative recognition were influenced by the strength of the pre-existing associations between action and object.
METHODS: During the study phase, participants studied ordinary verb-object pairs (e.g., “cut the watermelon”) and bizarre verb-object pairs (e.g., “plant the hammer”) in a SPT or VT condition. During testing, they discriminated between intact (old), recombined, and new items and made Remember/Know judgments; in addition, their EEGs were recorded.
RESULTS: Associative recognition was better following SPT than VT. The interaction between type of phrases and encoding condition suggested that only in the VT condition, bizarre phrases were better recognized than ordinary phrases. For ordinary phrases, early frontal ERPs (the signature of familiarity) to intact phrases were more positive than recombined and new phrases (intact > recombined = new) following SPT, but no such e?ects were found after VT. Late parietal ERPs (the signature of recollection) were graded following SPT (intact > recombined > new), whereas these late e?ects were smaller and did not di?er between intact and recombined items following VT. For bizarre phrases, both early frontal ERPs and late parietal ERPs to intact phrases were more positive than those to new phrases following both SPT and VT. However, following VT, late parietal ERPs to intact phrases were more positive than recombined phrases.
CONCLUSIONS: These results demonstrate that enactment unitized the action and object so that familiarity further enhances associative recognition for ordinary phrases in the SPT condition. Bizarreness encourages familiarity only after VT, which led to bizarreness e?ect in the VT condition.
PURPOSE: To deal with a crowded visual scene, it is important that attention is allocated over time and space efficiently. Previous studies suggest that attention acts as a moving spot light dwelling on each location serially, whereas other studies reveal that attention can stay on multiple locations simultaneously. Interestingly, recent behavioral findings demonstrate rapid temporal fluctuations in attentional behavior, suggesting that attention shifts between two spatial locations rhythmically. However, the neural mechanism underlying the space-time distribution of attention remain largely unexplored.
METHODS: In the present study, we combined covert atten-tional paradigm and temporal response function techniques (TRF) to address the issue. EEG was recorded from fifteen human subjects as they were presented with 5-sec dynamic sequences at two spatial locations and were asked to attend to one of them. Notably, the visual sequences at the two locations were randomly modulated in luminance and independently manipulated, so that we can estimate the TRFs for attended and unattended visual sequences separately (Att vs. Unatt) from the same EEG response.
RESULTS: First, compared to Unatt condition, TRFs for Att condition showed an alpha-band (~10 Hz) power inhibition around 100ms, commensurate with previous findings that alpha activities represent inhibitory processes during attention. Second, the alpha inhibition did not display spatial specificity as found before (e.g., decrease on contralateral side and increase on ipsilateral side), suggesting that it may represent an object-level attention independent of space. We further examined TRFs when both visual sequences are in motion and revealed similar alpha inhibition, confirming its nature of object-based attention. Finally, the alpha inhibition was followed by a subsequent alpha enhancement, indicating attentional switching from attended to unattended object. Interestingly, this alpha switching pattern was modulated by task context. Specifically, the Att-Unatt alpha switching pattern became stronger with the decrease in attentional cuing validity (from 100% to 75% and 50%).
CONCLUSIONS: Our findings suggest that attention e?ciently and flexibly distributes over space and time to accommodate changing task demands. We propose that attention samples multiple visual objects in a rhythmic manner, by modulating and coordinating inhibitory alpha-band neuronal activities.
PURPOSE: Attention-deficit/hyperactivity disorder (ADHD) is a prevalent neurodevelopmental disorder with prominent impairments in directing and sustaining attention. The current study sought to identify the neurophysiological bases of attention deficits in ADHD, focusing on electroencephalographic (EEG) markers of attentional selection (N2pc) and suppression (PD).
METHODS: EEG data were collected from 135 children with and without ADHD, ages 9–15 years, while they searched for a shape target either in the absence (Experiment 1) or presence (Experiment 2) of a salient-but-irrelevant color distractor.
RESULTS: In Experiment 1, the shape target elicited a smaller N2pc in children with ADHD (n = 38) compared to typically developing (TD) children (n = 36). The smaller N2pc amplitude predicted higher levels of inattentive symptomatology in children with ADHD. Moreover, the target-elicited N2pc was followed by a positivity in the TD children, but not in children with ADHD. In Experiment 2, the salient-but-irrelevant color distractor elicited a smaller PD component in children with ADHD (n = 32) than in TD children (n = 29). The smaller PD predicted higher inattentive symptom severity as well as lower behavioral accuracy in children with ADHD.
CONCLUSIONS: The correlation between N2pc/PD amplitudes and ADHD symptom severity suggests that these signals of attentional selection and suppression may serve as potential candidates for neurophysiological markers of ADHD. Our findings provide a neurophysiological basis for the subjective reports of attention deficits in children with ADHD and highlight the importance of spatial attention impairments in ADHD.
PURPOSE: Motion direction learning (MDL) showed less location specificity when trained with a staircase method (Zhang & Li, 2010) than with a single-level method of constant stimuli (MCS) (Ball & Sekuler, 1982). Learning also transfers to an untrained direction with a TPE (training-plus-exposure) procedure when staircases are used (Zhang & Yang, 2014), but the transfer fails with the single-level MCS (Liang et al., 2015). We suspect that training with a single-level MCS, which uses a pair of fixed motion stimuli with a single-level direction difference, may allow learning specific local cues for direction judgments.
METHODS: MDL were trained with the single-level MCS using a pair of moving dot patterns. To disturb the potential local cues in training, we slightly jittered the directions of the stimulus pair every presentation within a small range while keeping the dificulty constant.
RESULTS: When trained with fixed stimuli (?dir = 10°), peripheral MDL transferred little to contralateral and diagonal quadrants with transfer indices (TI) of 0.27 ± 0.06 and 0.25 ± 0.09 respectively. However, when the directions of the stimulus pair were slightly jittered within a range of ± 4°, the transfer significantly increased (TI = 0.65 ± 0.10 & 0.63 ± 0.13). Similarly, when trained with fixed stimuli pair, fovea MDL (?dir = 3°) failed to tranfer to an orthogo-nal direction even with TPE paradigm(TI = 0.25 ± 0.16), again if the stimulus directions were jittered within ± 2°, significantly more-transfer was enabled by TPE training(TI = 0.82 ± 0.24).
CONCLUSIONS: These results are consistent with the local-cue learning hypothesis regarding MDL with the single-level MCS, which is responsible for part of the specificity in motion direction learning literature. They also demonstrate the importance of using appropriate psychophysical methods in training to reduce specificity in perceptual learning.
PURPOSE: Mental rotation of complex 3D structure is an important visuospatial ability. To examine the plasticity of this ability, traditional laboratory approaches rely on laborious data collection involving multiple training sessions, and thus are normally limited to small sample size and sometimes insuffcient training. Our study presented an innovative approach combining the advantages of game-based assessment and Internet-based data collection, and demonstrated the potential of this approach in providing new insights on the plasticity of visuospatial ability.
METHODS: In each session of a game-like assessment, participants were presented with a mental rotation problem in each trial, and the difficulty of each trial increased gradually. The number of successfully completed trials in a session was recorded as a score indexing the participants’ visuospatial ability. This game was distributed in a social-networking mobile application (i.e., WeChat), and a large sample (N = 119,662) of participants voluntarily played the game more than once. The changes in scores between sessions were used to illustrate the learning effeciency, or the plasticity, of the visuospatial ability. We asked how the plasticity of the visuospatial ability changed as a function of age.
RESULTS: The performance in visuospatial ability peaked at the age of 26-30, whereas the improvement of the performance was observed over repetitive participation in all ages, which peaked at the age of 15-20 and dramatically reduced over 50s. In short, the present study demonstrated that the visuospatial ability can be improved by training, and its plasticity varied across ages.
CONCLUSIONS: The present study was a ?rst attempt of using game-based assessment and large-scale internet-based data collection in cognitive plasticity, and illustrated the potential of this approach in large-scale data collection, especially in research fields requiring large sample size and repetitive participation.
PURPOSE: The goal of the present study was to elucidate the neural mechanisms underlying processing global and local features in a non-human primate model.
METHODS: Monkeys were trained to make a saccade to an odd-ball target, which was different from the distractors (white circle) in color (red circle), local features (square), a global feature (ring) or their combinations. Saccade latencies were used to assess monkeys’ sensitivity to distinctions in color, local features and the global feature.
RESULTS: In the first experiment, the odd-ball target was presented simultaneously with the distractors. Contrary to predictions based on the general model, we found that detecting the global feature took less time than detecting the local features, but took about the same time as detecting color. In the second experiment, the distractors were presented first and one of them was replaced by the odd-ball target. Thus, monkeys were asked to detect a change in color, local features or a global feature in absence of target onset. Again, contrary to predictions of the general model, we found that detecting a change in the global feature (i.e., no hole vs. one hole) is faster than detecting a change in either color or local features. In the third experiment, we examined how distinctions in local and global features affect detecting distinction in color. We found that detecting distinction in color was facilitated by distinction in the global feature, but not in the local features. In the fourth experiment, we further examined interactions between detecting distinctions in local and global features. We found that distinction in local features of the ring-outside shape may facilitate detecting the ring, but distinction in local features of the ring-inside shape may slow detecting the ring.
CONCLUSIONS: These results not only challenge the general model of visual information processing by demonstrating monkeys’ sensitivity to a global feature over local features, but also provide insights into a new model, which features differential processing of local and global properties.
Purpose: Primates frequently make saccadic eye movements to receive acute visual information, which causes blur and displacement of visual inputs on retina. However, despite the instable visual inputs our visual perception remains stable. One possible neural mechanism underlying the visual stabilization is so called perisaccadic receptive field (RF) remapping, i.e., around the time of saccade, visual neurons in many cortical areas become sensitive to spatial locations that will be covered by the neurons’ classical retinotopic RF after a saccade. This theory, however, is charged recently by findings that, just before saccade, neurons' RF in monkey’s frontal eye field converged to the location of saccadic target instead of future RF. To understand neural mechanisms of visual stability further, we systematically studied the dynamic change of visual RF in macaque posterior parietal cortex.
Methods: We recorded extracellular activity of single neurons while monkeys were performing a visually-guided delay saccade task, and mapped neuron’s visual RF at four periods ( fixation, delay, just before saccade and long after saccade) to get current RF, delay RF, perisaccadic RF and future RF. Then, we compared the spatial properties of them to analyze the dynamic change of a neuron’s visual RF.
Results: We recorded 119 visual neurons in total from the posterior parietal cortex of two monkeys. Among them, some (41/119) show constant retinotopic RF throughout the four task epochs, but another show significant change of receptive field just before saccade (37/119) or during delay period (19/119). Remarkably, the change of receptive field for most neurons tend toward the location of the future rather than saccadic target.
Conclusion: These results indicate that, inconsistent with frontal eye field, posterior parietal cortex integrates pre and post saccadic visual information through a mechanism of receptive field remapping rather than receptive field convergence.
PURPOSE: Recent studies show that visual motion information is processed in a distributed fashion in the primate brain. However, properties and functions of motion-sensitive neurons outside the traditional V1-MT motion pathway are largely unknown. As a step towards full understanding of motion processing in the brain, we studied the functional role of motion-sensitive neurons in area V2 in macaque monkeys.
METHODS: With the guidance of optical imaging maps, we recorded from direction-selective (DS) neurons in anesthetized monkey V2.
RESULTS: Compared with DS neurons in area MT, V2 DS neurons have a much smaller receptive field center (~1.1deg) and a stronger antagonistic surround. Unlike MT neurons, they show weak motion integration (i.e. not selective to plaid directions). These features make V2 DS neurons suitable for detecting precise spatial locations of motion contrast in the visual scene. Consistently, both imaging results and single cell responses show that these neurons were preferentially activated when motion boundaries were presented in the visual scene.
CONCLUSIONS: We propose that the main functional role of V2 DS neurons is detection of local motion contrast, and this contrast information is used for shape-from-motion integration that also occurs in V2.
PURPOSE: While retinal dopamine (DA) has been long implicated in myopia development, current studies demonstrate that retinal DA levels are unaltered in C57BL/6 mice with form-deprivation myopia. This work was undertaken to explore whether and how refractive development is perturbed in this mouse strain when retinal DA levels are reduced by 6-hydroxydopamine (6-OHDA) administration.
METHODS: 6-OHDA of different doses was intravitreally applied. Retinal DA levels were measured by HPLC and TH levels analyzed by quantitative Western blotting. To choose appropriate 6-OHDA doses that significantly reduce retinal DA levels, but caused minimal disturbance of overall retinal physiology, ERG analysis was performed. Refractive errors were measured using a photorefractor, and ocular biometry assessed with optical coherence tomography and photokeratometry.
RESULTS: 6-OHDA of 6.25 μg and 12.5 μg significantly reduced retinal levels of DA and TH, but did not significantly affect ERG a- and b-wave amplitudes. With normal visual experience, 6-OHDA induced myopic refractive shifts in a dose-dependent fashion. Form-deprivation induced further myopic shifts in 6-OHDA injected eyes, but did not cause further decline in retinal DA. Furthermore, 6-OHDA administration resulted in a shorter axial length and a steeper cornea, while form-deprivation led to a longer axial length, without changing the corneal radius of curvature.
CONCLUSIONS: Reducing retinal DA levels by 6-OHDA led to myopic refractive shifts in C57BL/6 mice, which mainly resulted from a steeper cornea. We propose that, in addition to the DA-independent mechanism for form-deprivation induced myopic refractive shifts, there is a DA-dependent mechanism in parallel that underlies myopic refractive shifts in this mouse strain.
PURPOSE: The neural mechanism underlying face processing involves both bottom-up sensory processing of a face stimulus and top-down modulation. Face stimuli can elicit specific event-related potentials (ERPs), including N170, vertex positive potential (VPP), and P2, which are based on different bottom-up and top-down interactions at different processing levels. The specific top-down face processing without bottom-up contamination remains largely unknown. Particularly, it is unclear what neural responses manifest the top-down face-specific modulation while bottom-up inputs of physical features of faces are eliminated.
METHODS: This study was to examine the ERP components that are specifically modulated by the face imagery when random ambiguous visual stimuli are presented. Sixteen participants received two blocks of ambiguous stimuli, in which they were instructed to imagine either faces or houses upon looking at the ambiguous stimuli. The waveforms of VPP at the fronto-central sites, and N170 and P2 at the occipito-temporal sites were measured and analyzed.
RESULTS: Both VPP and P2 responses were enhanced by the face imagery compared to the non-face (house) imagery, and N170 disappeared when eliminating the physical face features.
CONCLUSIONS: Ambiguous-stimulus-induced VPP and P2, but not N170, can be modulated by the top-down face-imagery processing when bottom-up face-signal inputs are eliminated.
PURPOSE: Bisphenol A (BPA), a common environmental endocrine disrupter, has been implicated in the induction of anxiety-like behavior and decrease of synaptic plasticity in amydala, mPFC and hippocampus. The neural activities of primary visual cortex (area 17) of cats are directly related with the perception of movement direction and line orientation. To date, there is not any report about the effect of BPA exposure on the visual receptive field properties on area 17 of adult cats. Since fluctuations of population have a great weight on processing of specific percepts and behavior, we analyzed changes occurring over the response fuctuations of population after BPA exposure.
METHODS: In the present study, BPA was administrated intravenously (i.v.) as saline solution (0.2mg/ml/h) for two hours. Using multiple-channel recording technique, we recorded responses of population and single neuron to different direction stimulation before and after BPA exposure.
RESULTS: The results showed that two key indexes of response fluctuations, noise correlation and signal correlation, were markedly upregulated after BPA exposure. We also found that BPA declined the direction discrimination capability of population after two hour exposure. These changes exhibited BPA exerted a negative effect on visual perception. To further study the alteration mechanism, response properties of single unit were examined based on orientation tuning. The results showed that BPA weakens the direction discrimination capacity and orientation selectivity capacity of the single neuron. Simultaneously, there is also a worse performance of information extraction capacity (signal to noise ratio) after dosing BPA.
CONCLUSIONS: Our present findings demonstrate that acute BPA exposure interferes the orientation perception in visual sensory system of adult cats due to decrease of orientation tuning in single neuron. Moreover, these results provide a new insight into BPA-induced brain function deterioration, revealing a more broad picture of its effect on cerebral cortex.
PURPOSE: Lambertian surfaces, which are used to model matte appearance, have been reported to present illusory gloss under special conditions: the surface is of high-magnitude RMS height deviation and is viewed fronto-planar while being illuminated with collimated light originating from directly behind the observer (Wijntjes et al, 2010, Journal of Vision, 10(9), 13). We conducted two psychophysical experiments to examine whether this illusory gloss is perceived in the same manner as those of real glossy surfaces, and whether observers can recognize the surfaces are of unordinary RMS height.
METHODS: In the first experiment, observers adjusted the parameters of a glossy reflection model applied on surfaces with ordinary RMS height, and they successfully matched the perceived gloss of these real glossy surfaces to the perceived gloss of the high-RMS-height Lambertian surfaces. Then the observers participated in a 2AFC experiment, in which they were asked to choose the bumpier one from a pair of surfaces used in the first experiment.
RESULTS: The results support the previous finding that glossiness and bumpiness inter-influence the perception of each other (Ho et al, 2008, Psychological Science, 19, 196-204). We also find that the perceived bumpiness of the high-RMS-height Lambertian surfaces are not significantly different from those of the ordinary-RMS-height glossy surfaces.
CONCLUSIONS: This indicates that the high-RMS-height Lambertian surfaces are perceived by observers as low-RMS-height glossy surfaces. Similar to the bas-relief ambiguity, the literature and our current work show that under certain surface geometry, lighting and viewing conditions, the perception of surface property is puzzled by a kind of “bump-gloss” ambiguity.
PURPOSE: Tilt aftereffect (TAE) is the phenomenon that the perceived orientation of a test stimulus is altered after prolonged exposure to an oriented adaptor. This phenomenon has been widely considered to result from adaptation of orientation-selective neurons in the early visual cortex. In this study, we investigated whether the TAE could be induced from a perceived illusory orientation of adapting stimulus dissociated from its physical orientation, by taking advantage of a new illusion— the flash grab effect.
METHODS: Subjects viewed a physically vertical line that was repeatedly and briefly flashed on top of a patterned disk that oscillated clockwise and counterclockwise, with the flashed line presented at the moment of the rotation reversals. Importantly the adapting line was perceived as tilted away from vertical. Following adaptation to 11 cycles of the flashed line, a test line was briefly presented near vertical orientation at the corresponding location without the background disk.
RESULTS: Results showed that a significant TAE was induced by the perceived orientation. In contrast, when the physical orientation of the titled adapting line was adjust by each individual subject so that the adapting line was perceived to be vertical, no TAE was observed. Thus when perceived and physical orientations of the adapting lines are pitted against each other, the TAE is dependent on the perceived rather than the physical orientation. In separate experiments using multimodal neuroimaging methods, we have shown that the perceived tilt from flash grab effect is primarily due to feedback processing in the brain.
CONCLUSIONS: Our results suggest that higher-level processes and feedback signals play an important role in the TAE.
PURPOSE: Ambiguous stimulations can induce involuntary alternation between exclusive subjective perceptions. Numerous studies have demonstrated that a number of brain regions was involved in bistable perceptual processing. Though that top-down information processing has been proposed to interpret perceptual switching, the studies so far have been limited in providing spatial or temporal information about neural activity.
METHODS: In this study we investigated neural circuits associated with bistable perception in epileptic patients who are invasively implanted electrodes to clinically localize seizure onset zones. The electrophysiological and behavioral data were simultaneously recorded from ten patients while they performed a structure-from-motion (SFM) task. Three regions of interests (hMT+, PPC and LPFC) were extracted via either individual anatomy (PPC and LPFC) or a functionally probabilistic map (hMT+).
RESULTS: During performance of the SFM task, the LPFC and PPC showed significantly increased high-gamma (HG) activity (70-150Hz) about 300ms and 200ms, respectively, before perceptual switching, while the hMT+ showed increased HG activity even after perceptual switching. The increased HG activity in the LPFC and PPC was also validated not induced by the action. During a monostabile replay task, only hMT+ area, without the PPC and LPFC, showed significantly increased HG activity about 500ms before perceptual switching.
CONCLUSIONS: The temporal difference relative to the action between top-down and bottom-up pathway may be related to the underlying neural projections, which has been proposed by recent studies. Taken together, the findings suggest that the increased lateral prefrontal cortex itself can trig the alternative bistable perception, which did not rely on hMT+ activity, thereby providing a fundamental evidence for the top-down processing model of bistable perception.
PURPOSE: In a horizontal pattern consisting of zigzagging strips of phase-shifted abutting line gratings, strong diagonal and lateral illusory motion is perceived when the pattern is moved up or down at moderate speed. We wished to study how different configurations affect the saliency of apparent motion and find out the how the illusory motion is induced.
METHODS: We performed psychophysical experiments on nine subjects to test the salience of apparent motion when changing the spacing, length of the inducing lines, width of zigzags as well as their luminance contrast.
RESULTS: The apparent motion is strongly influenced by the spacing, length of the inducing lines, width of zigzags as well as the luminance contrast. With isoluminant color defining the pattern and background, apparent motion is largely abolished. No motion is seen when the zigzagging grating strips are separated by a gap, when the grating lines are interleaved or when the grating strips are delineated at the interface by a continuous line.
CONCLUSIONS: Two types of motion were distinguished according to their directions, (i) motion along the diagonal interface between the zigzagging grating strips and (ii) collinear motion in the direction of the horizontal grating lines. We hypothesized, based on the equiluminant findings that the apparent motion could be dominantly processed by the magnocellular pathway, which encodes motion signals while being largely insensitive to color. The endpoints of grating lines is crucial for the existence of the illusory motion. The neural mechanisms underlying this illusion require further investigation.
PURPOSE: Visual environment changes at multiple timescales. It is thus hypothesized that adaptation mechanisms operate at differing timescales to accommodate the environmental changes. This has been demonstrated in recent work. However, neural substrates of these adaptation mechanisms remain unclear. To address this issue, two psychophysical experiments were conducted.
METHODS: Using the interocular suppression paradigm, in Experiment 1a and 1b we firstly investigated the timescales of adaptation before and after cortical processing stage by tracking the time courses of contrast adaptation effects under different viewing conditions(monocular, binocular, and dichoptic). To compare the timescales of mechanisms spanning wider in the visual processing hierarchy, in Experiment 2 we further tracked the decay of tilt aftereffect after adaptation to either a compound grating pattern (curvature) or its component gratings.
RESULTS: Results of Experiment 1a demonstrated that slower adaptation mechanisms were more predominant for the monocular condition than for the binocular condition. Results of Experiment 1b also showed that the residual adaptation effects were larger in the monocularly adapting condition and the dichoptically orthogonal adapting condition than that in the binocular adapting condition. Considering that interocular suppression is stronger in the binocular condition, and it mostly occurs on the cortical level, results of Experiment 1a and 1b might indicate that adaptation mechanisms at the binocular processing stages were longer-term. Further, the results Experiment 2 revealed a slower decay for the compound [mid-level (e.g. V4)] than for the component (early visual areas) adaptation condition, suggesting longer-term mechanisms in the mid-level (e.g. V4) than the early visual areas.
CONCLUSIONS: Our findings indicate that neural mechanisms controlling visual adaptation may become more sluggish along the visual processing stream, at least from low- to mid-level processing stages.
PURPOSE: To explore the topological properties of brain functional networks derived from resting-state functional magnetic resonance imaging in patients with amblyopia.
METHODS: Seventeen amblyopic subjects and twenty control subjects were recruited to undergo a resting-state functional magnetic resonance imaging scan. The whole-brain functional networks were constructed for each subject, and topological properties such as small-worldness, network effciency and nodal centrality were quantitatively analyzed with graph theoretical analysis.
RESULTS: Both the amblyopic and control groups exhibited small-world properties in brain functional networks, which means a balance between local segregation and global integration for visual information processing. However, compared with control subjects, patients with amblyopia showed altered quantitative values of brain functional networks, characterized with decreased clustering coefficient, lower characteristic path length and decreased network effciency. Topological properties are also significantly altered in some brain regions. These alterations support the disrupted topological organization of brain functional networks in patients with amblyopia.
CONCLUSIONS: Amblyopia is partly resulted from the deficits of visual information transmission. Detection and estimation of altered brain functionl networks can help to further understand the pathophysiological mechanism underlying amblyopia.
PURPOSE: Figure–ground segmentation is a fundamental task for biological and artificial visual systems. The visual figure is many multiples greater in size than the receptive fields/filters of early visual areas. Computing figure-ground must therefore involve a cascade of bottom–up & top–down processes across multiple visual areas and spatial scales. We previously observed figure–ground enhancement at long latency (~100ms) at the earliest stage of central vision, the lateral geniculate nucleus (dLGN). Here we ask how large saccadic eye movements affect figure-ground modulation in dLGN. Critically, we wished to evaluate how figure-ground representations were affected across the saccade.
METHODS: We performed tetrode recordings of spiking and local field potentials (LFP) in behaving macaque dLGN. We used speeded reaction–time where the subject had to find, and then saccade to a moving-dot defined visual figure against a background. Spiking and LFP responses were analysed by aligned them to either the stimulus onset, or the target–saccade onset.
RESULTS: We found strong and robust saccadic modulation of neural responses in macaque dLGN across all locations analysed. Saccadic modulation was seen for parvo–, magno– and konio–cellular streams. Time-frequency analysis showed that saccadic modulation is largely driven in the α-band. In the trials where a figure stimulus was in the receptive field, a continued figure-ground specific enhancement was maintained even after the saccade terminated.
CONCLUSIONS: We found figure-ground selective enhancement is amplified across saccades (i.e. even after the stimulus has left the receptive field), showing that trans-saccadic continuity of representation may have significant implications for the stability of visual perception.
PURPOSE: Under a noisy “cocktail-party” condition with multiple-people talking, listeners often ask the talker to repeat the attended sentence for their better recognition. The “say-it-again”-induced improvement of speech recognition is partially caused by visual-speech priming (VSP), based on working memory of lipreading signals of previously-presented sentences. This study was to discover the most specific brain substrates underlying the unmasking effect of VSP.
METHODS: Using functional magnetic-resonance imaging and psychoacoustic methods, this study investigated the brain substrates underlying the unmasking effect of VSP in 16 healthy subjects.
RESULTS: The results showed that two categories of brain regions were activated by the listening condition with VSP: (1) the unmasking-correlated regions, including the left inferior temporal gyrus (ITG), left middle cingulate cortex and right putamen, whose VSP-induced activation was significantly correlated with VSP-induced improvement of target-speech recognition; (2) the regions without the correlation between brain activation and speech-recognition improvement, including the right ITG, right fusiform cortex, and right caudate. The brain structures with VSP-related functional connectivity to the unmasking-correlated regions were those involved in semantic priming, speech production, or irrelevant-signal suppression, including the right pars triangularis of the inferior frontal gyrus (IFG), left pars orbitalis of the IFG, left putamen, right caudate, left and right insular cortices, and right anterior cingulate cortex.
CONCLUSIONS: the speech-unmasking effect of VSP is based on the functional integration of two brain networks: (1) the unmasking-correlated network that specifically mediates perceptual integration and motor representation of visual-speech and auditory-speech signals, and (2) the unmasking-nonspecific network that generally suppresses irrelevant masking-speech signals. This two-network strategy for speech unmasking may be generally applicable to scene analyses under noisy “cocktail-party” conditions.
PURPOSE: Human subjects are more sensitive to luminance decrements than luminance increments, as is evident by a lower threshold and shorter latency for dark stimuli. This asymmetry can be explained by the results of neurophysiological recordings in dLGN and V1 of cat and monkey. Specifically, V1 population responses demonstrate that black stimuli elicit a higher level of activation than white stimuli, while the response latency of OFF cells in dLGN is shorter than that of ON cells. The removal of a black or white spot often generates the perception of a negative afterimage. Here we ask whether increment and decrement stimuli also elicit asymmetrical negative afterimages? If so, can these asymmetries be attributed to the asymmetries for ON- and OFF-channels?
METHODS: To answer these questions, we performed psychophysical experiments in human observers and single-cell recordings in cat dLGN.
RESULTS: Psychophysically, we found that bright afterimages elicited by luminance decrements (darker flash spots) are stronger and last longer than dark afterimages elicited by luminance increments of equal size; yet the perceptual latency of the latter is shorter than that of bright afterimages. Neurophysiologically, we found that ON cells in dLGN (and retina by analyzing S-potentials) responded to the removal of a dark spot with higher ?ring rates and longer latencies than OFF cells to the removal of a bright spot.
CONCLUSIONS: We suggest that subcortical differences in ON- and OFF-channels can explain asymmetries between bright and dark negative afterimages which is consistent with a subcortical origin of negative afterimages.
PURPOSE: When a line is flashed on a patterned disk rotating back and forth at its turnaround point, the perceived location of the line is often dramatically displaced, known as the flash grab effect (Cavanagh & Anstis, 2013). Like other illusions in the motion induced position shift family, the neural mechanism of the flash grab effect remains unclear.
METHODS: We conducted a combined fMRI and ERP study to investigate the spatial and temporal neural correlates of this perceptual effect. In different sessions, participants viewed the visual display showing the flash grab illusion repeatedly in the fMRI scanner and with ERP recording sessions. The physical flashes were presented at the vertical meridian, while the perceived locations of the flashes were either to the left or the right of the vertical meridian.
RESULTS: Following the localization of the retinotopic visual areas in each participant, results clearly show that the distribution of fMRI BOLD signals in V1, V2, and V3 could be well predicted by the perceived, but not the physical, positions of the flashes. In the ERP signals, while a robust and clearly lateralized C1 was seen from physically displaced flashed lines, no such lateralized signal was observed in the typical time window of C1 from the perceptually displaced flashes, suggesting that the perceptual illusion was unlikely a result of feedforward processing. For the perceptually displaced flashes, there was a hint of a lateralized signal in the occipital area about 20ms later than C1, and significantly lateralized ERP signals emerge only at the later N1 component.
CONCLUSIONS: Taken together, the combined spatio- temporal imaging results suggest that the perceived displacement of the flashed target in the flash grab effect is instigated by feedback signals from high-level areas to early retinotopic visual cortex.
PURPOSE: Visual scenes contain local and global properties. Numerous behavioral studies demonstrate that the global features are processed more rapidly than local features, namely global precedence effect. However, the neuronal temporal dynamics underlying the global and local processing as well as their interactions remains largely unknown.
METHODS: To address the issue, we recorded magnetoencephal-ography (MEG) from 20 human subjects as they viewed 5-sec long glass pattern stimuli, the luminance of which was randomly modulated continuously. Critically, the form coherence of glass pattern was also randomly and independently modulated simultaneously. Based on the two random sequences (luminance and form coherence) within one trial, we were able to calculate and separate the brain response that specifically tracks changes in local and global property from the same MEG responses, by employing a temporal response function technique (TRF).
RESULTS: The TRF for local and global property processing showed quite distinct spatiotemporal patterns. Specifically, local feature changes elicited activations in early visual area (EVA) around 100 msec. Global features, on the other hand, elicited much earlier responses (< 50 msec), which first developed in orbitofrontal cortex (OFC), then in V3A, V1, and TPJ. We further examined the interactions between global and local processing and found a two-stage course. In particular, within 100~200 msec, the OFC activations in global processing negatively correlated with EVA activities in local processing, suggesting a global-local competition relationship, whereas within 200-300 msec, OFC and TPJ responses in global processing and EVA responses in local processing showed a positive relationship, implicating a global-local integration process.
CONCLUSIONS: Our experiments, by employing a new technique, successfully enables the dissociation of global and local processing within the same trial response. Commensurate with previous findings, our results support that OFC initiates the coarse-to-?ne process in visual perception. The global and local process undergoes competition and then integration.
Drifting ramped gratings or shaded diamonds brighter when the direction of movement produces fast-OFF relative to fast-ON luminance profiles. The neural mechanism and locus remain unclear. We recorded DC-electroretinograms from toad eyecups presented with sequential epochs of sawtooth, sine-wave, and square-wave gratings drifting horizontally across the retina with drift temporal frequencies of 2.5 - 20Hz. A sustained DC increase in trans-tissue potential during drift (plateau region), plus a peak at drift offset were observed. Consistent with human perceptual experience, the DC plateau was greater for fast-OFF cf fast-ON sawtooth stimuli. All gratings produced an increase in DC potential as a function of temporal frequency. Modelling suggested that changes in root mean square (RMS) temporal luminance contrast contributed to these effects, but could not explain the divergence in response amplitudes for the two sawtooth profiles. Pharmacological dissection of retinal responses indicated that the response differences for the two sawtooth profiles remained following suppression of post-photoreceptoral activity with Tetrodotoxin (TTX), 2-Amino-4-Phosphonobutric acid (APB), and cis-Piperidine-2,3-dicarboxylic Acid (PDA). This points to a photoreceptoral locus as the origin of DC potential differences resulting from asymmetries in the response to fast-ON and fast-OFF sawtooth profiles, and as the likely locus for the drifting sawtooth brightness illusion.
Purpose: Identifying tilted objects is harder than identifying upright objects using image structure information . However, motion generates optic flow that calibrates image structure. Calibrated image structure preserves spatial layout despite image distortion . Thus, if the tilting process and the tilting objects are continuously perceptible, then the interaction of optic flow and image structure should allow accurate perception of object locations despite orientation change.
Methods and results: We tested this hypothesis by simulating two surfaces separated in depth, with cutout holes in the front surface through which targets and distracters on the rear surface were visible. Both surfaces first rotated and processed rigidly to review depth structures (structure-from-motion), then the front surface translated to occlude targets. Next, the two surfaces tilted rigidly. After some time delays, participants identified locations of hidden targets. We found that: (1) when tilting was perceptible, participants identified object locations equally well with or without orientation change; (2) when tilting process was imperceptible, identifying object locations from a tilted scene after orientation change worsened; and (3) when observers did not see but were told about the amount of tilting, identification was worse than with no orientation change.
Conclusion: Therefore, combined optic flow and image structure information, not mere knowledge about the tilt, enables accurate perception despite orientation change.
PURPOSE: The contrast sensitivity function (CSF) provides a comprehensive assessment of spatial vision in both normal and clinical populations. The shape of the CSF provides important information about the modulation transfer function and internal noise of the visual system (Chen et al., 2014; Hou, Lu, & Huang, 2014). Several visual diseases have been shown to differentially affect CSFs under different light conditions. In this study, we tested two hypotheses: (1) the shape of the CSF is invariant for each individual observer across different light conditions, and (2) the shape of the CSF is invariant across all the individuals.
METHOD: CSFs of 112 college students with normal or corrected-to-normal vision were measured using the quick CSF procedure (Lesmes, et al, 2010) in three light conditions (2.65, 20.2 and 95.4 cd/m2). The detailed experimental procedure is described in Hou et al, 2016. CSF is modeled by a truncated log parabola with four parameters: peak gain, peak frequency, bandwidth, and truncation level (Watson & Ahumada, 2005).
RESULT: To test hypothesis 1, we fit a model lattice to each observer’s data using a maximum likelihood procedure. We found that the model holding CSF shape parameters (bandwidth, truncation level) invariant across light conditions, but freely varied peak gain and peak spatial frequency across conditions, provided statistically equivalent fits as the most saturated model for 89.3% of the observers.To test hypothesis 2, we fit the aggregate data with a CSF model that held CSF shape invariant across all observers. This model, with 2 × 3× 112 + 2 parameters, is statically inferior to a model that allowed the shape parameters to vary across observers (with (2 × 3 + 2) × 112 parameters).
CONCLUSION: The results suggest that the shape of the CSF is invariant under different light conditions, but not invariant across observers.
PURPOSE: Aging-related declines in vision can decrease well-being of the elder. Concerning early sensory changes as in the primary visual cortex, physiological and behavioral reports seem contradictory. Neurophysiological studies on orientation tuning properties suggested that neuronal changes might come from decreased cortical local inhibition. However, behavioral results either showed no clear deficits in orientation processing in the elder, or proposed stronger surround suppression. We try to resolve these discrepancies by combining psychophysical, modeling and neurophysiological data re-analysis techniques.
METHODS: The current study firstly used psychophysical experiments to probe the age-related inhibition systems changes refected by behavioral performance. Secondly, a computational modeling was applied to identify the detail parameters changes underlying these age-related phenomenon. Finally, we also re-analyzing published neurophysiological data of senescence macaque, which confirmed our behavioral and modeling findings.
RESULTS: We resolved these discrepancies by demonstrating stronger lateral inhibition in the elder while neuronal orientation tuning widths, related to local inhibition, stayed globally intact across age. We confirmed this finding by re-analyzing published neurophysiological data that showed no systematic tuning width changes, but instead a higher neuronal noise with aging.
CONCLUSIONS: These results suggest a stronger lateral inhibition and mixed effects on local inhibition during aging, revealing a more complex picture of age-related effects in the central visual system than previously thought.
PURPOSE: The N170 and the RP are both negative-going deflections in ERP that exhibit preferential activity to visually recognizable objects; occurring at ~170 and ~250 ms, respectively. Despite their similarities, there is very little overlap in the study of these two components. Also, the paradigms associated with each are different: The RP is usually obtained by a rapid stream stimulation procedure (RSS) (Rudell, 1992), while the N170 is observed with a single presentation of visual stimuli. Studies of RP often claim that RSS can enhance activity that is preferential to recognizable objects. However, no study has ever demonstrated that RSS results in stronger preferential activity than the N170 paradigm. By testing the same subjects in RSS and N170 paradigms that are designed to be comparable, we show the first evidence in favor of RSS enhancements of preferential activity.
METHODS: This study comprises two experiments. The RP has a longer latency. Therefore, in the first experiment, we determine if the N170 and RP signals are, in fact, comparable. A parametric increase in the temporal gap between a forward mask and target produces a continuum between RSS and N170 paradigms. The second experiment addresses the main question: Does RSS enhance preferential activity to recognizable objects, compared to the N170 paradigm? In that experiment, object recognizability was manipulated by image inversion. And for generality, we test 2 different categories of recognizable object: faces, and Chinese characters.
RESULTS and CONCLUSIONS: Experiment 1 shows that, along our gap-continuum, there is also a gradual shift between RP and N170 waveforms: systematic relations between potentials evoked by mask and target, topographic similarities across gap, and associations with the vertex positive potential. Our Experiment 2 results clearly show that the RSS paradigm does enhance preferential activity. For both categories of object, inversion effects for both characters and faces were greatly enhanced.
PURPOSE: Perception and action are interdependent. How visual information guide movements has been extensively studied, while how movements affects vision is understudied. We postulate that moving in an altered visual environment can modify well-established representations of the world such as visual perspective.
Methods: Here we invert the rules of perspective in virtual reality by modifying the size-distance relation from distant objects appearing smaller, the normal case, to distant objects appearing larger. In the pretest and posttest, we measured the magnitude of Ponzo illusion as a quantification of perception of perspective.
During adaption, subjects wore a head-mounted display and a data glove. Subjects were divided into 3 groups. For the active group, subjects actively engaged with the special virtual scene for 30 mins: they were required to push a virtual ball. The ball rolled and stopped at a target gate. Before each push, subjects adjusted the gate width to predictively minimize the discrepancy between the gate and the ball. For the passive group, visual manipulations remained the same but subjects passively watched the ball rolling away. For the control group, subjects performed the same task as the active group but with a normal perspective.
RESULTS: We computed the reduction of illusion size between pretest and posttest to examine how VR exposure affected perception. Both active and passive groups had significant changes (paired t-test, p<0.05) with significant difference between groups (ANOVA, p<0.05). Post-hoc tests only detected that the active group had larger effect than the control group (p<0.05). This shows that actions in VR can facilitate the change in perception of perspective.
CONCLUSIONS: Our study suggests that immersion in an altered visual environment can change our well-established perceptual representation and motoric interaction can facilitate this change. Immersive VR offers an effective tool to study the interaction between perception and action by quickly reshaping their existing relations.
PURPOSE: Many behavioral and neuroimaging studies have shown that human decisions are sensitive to the statistical moments (mean, variance, etc.) of reward distributions. However, little is known about how reward distributions—or, probability distributions in general—are represented in the human brain. When the possible values of a probability distribution is numerous (infinite for a continuous distribution), it would be unrealistic or at least cognitively costly to maintain the probability for each possible value. Here we explored potential heuristic representations of probability distributions and tested them on human subjects. In particular, we tested a recently developed hypothesis that human representations of probability distributions are mixtures of a small number of non-overlapping basis distributions.
METHODS: In two experiments, we constructed a variety of multimodal distributions of spatial positions. On each trial, 70 vertical lines—the horizontal coordinates of which were samples independently drawn from the distributions—were briefly presented, one at a time on the computer screen. Human subjects were asked to locate (on the axis where stimuli were presented) the mean and the mode of the samples. A total of 19 naive subjects participated and completed 144–162 trials each.
RESULTS: All subjects’ mean and mode responses were highly correlated with the true mean and mode of the samples. Interestingly, all subjects’ mean and mode responses had systematic deviations from the true means and modes. The deviation patterns could be well predicted by computational models that assume a division of samples into a small number of clusters following the k-means clustering algorithm. Only the centroid and the relative weight of each cluster were necessary for the further calculation of mean and mode responses.
CONCLUSIONS: Humans represent probability distribution as k-means clusters, and use the centroid and relative weight of each cluster to calculate concerned statistics of the distribution.
PURPOSE: Cooperation and competition usually induce different mental construal processes, leading to assimilation and contrast effects. The present study investigated whether the state and trait cooperation/competition modulate the representations in visual working memory (VWM).
METHODS: In Expriment1, after an online cooperative/competitive priming task, participants completed a working memory task individually to remember several colors and then recall one of the item by reproducing it on a continuous color wheel. In Experiment 2, we recruited participants who were cooperation/competition oriented to take part in the visual WM task identical to that in Experiment1.
RESULTS: In Expriment1, results showed no significant difference on WM capacity and resolution between the two priming conditions. In Experiment 2, we found that cooperation-oriented participants showed higher VWM resolution than those competition-oriented, but there was no significant difference on the VWM capacity.
CONCLUSIONS: Taken together, these results suggest that cooperation personality selectively boosts VWM resolution. In addition, our results found no assimilation and contrast effects, which are usually revealed in the previous studies about cooperation and competition, implying the mechanism that competition and cooperation modulate mental representations is likely to be more complicated than merely assimilating or contrasting.
PURPOSE: Although visual perceptual learning is often location specific, learning can transfer to a new location if the new location is additionally trained with an irrelevant task (Xiao et al., 2008). Here we characterized this double training effect on Vernier learning and its transfer at various levels of external noise.
METHODS: A 2-Gabor Vernier was imbedded in five levels of white noise (rms contrast 0%～29%) and centered in a visual quadrant at 5o eccentricity.
RESULTS: When training was at zero noise, Vernier thresholds were reduced at both zero and high noise at the trained location, but only at high noise at a diagonal quadrant location. However, if orientation discrimination with a Gabor at zero noise was also practiced at the diagonal location, Vernier thresholds at the diagonal location were improved at all noise levels. When training was at high noise, Vernier thresholds were only reduced at high noise at both trained and diagonal locations. Additional orientation training at zero noise, but not at high noise, at a diagonal location reduced Vernier thresholds at lower noise levels at both locations.
CONCLUSIONS: Fitting TvC functions of Vernier learning revealed that: 1) Training at zero noise enhances the sensitivities of perceptual mechanisms, which can transfer to untrained location with double training. 2) Training Vernier at high noise reduces the effect of external noise only, but additional orientation training at zero noise at a different location enhances the sensitivities to Vernier differences at lower noise levels at both locations. These results suggest that training a fine discrimination task enhances the sensitivity of perceptual mechanisms, which appears to be a high-level cognitive process.
Purpose: Experience is known to facilitate our ability to extract regularities from simple repetitive patterns to more complex probabilistic combinations (e.g. as in language, music, navigation). However, little is known about the neural mechanisms that mediate our ability to learn hierarchical structures.
Methods: Here we combine behavioral and functional MRI measurements to investigate the brain circuits involved in learning of hierarchically organized structures. In particular, we employed variable memory length Markov models to design temporal sequences of increasing complexity. We trained observers with sequences of four di?erent symbols that were determined first by frequency statistics (i.e. occurrence probability per symbol) and then by context-based statistics (i.e. the probability of a given symbol appearing relates to the context provided by the preceding symbol). Observers performed a prediction task during which they indicated which symbol they expected to appear following exposure to a sequence of symbols.
Results: Our results demonstrate that cortico-striatal mechanisms mediate learning of behaviorally-relevant statistics that are predictive of upcoming events. Importantly, we show that individual variability in learning relates to two di?erent learning strategies: fast learners adopt a maximization strategy (i.e. learning the most probable event per context) while slower learners focus on matching (i.e. memorize all presented combinations). Correlating fMRI activation with individual learning strategy demonstrates that learning by matching engages the visual cortico-striatal loop including hippocampal regions. By contrast, learning by maximization involves interactions between executive control and motor cortico-striatal loops.
Conclusion: Thus, our findings suggest dissociable cortico-striatal routes that promote structure- outperforms rote- learning and facilitate our ability to extract predictive statistics in variable environments.
PURPOSE: In primates, vision is the most important sensation to collect information from the environment and guides the behavioral performance. In some occasions, the fast response is needed, such as express saccade, i.e. saccade with extremely short reaction time (latency). Express saccade has been considered to be generated through a short-cut visual-oculomotor pathway, which is usually not functioning. Previous studies suggest that the generation of express saccade requires advanced motor preparation. Motor preparation is a covert cognitive processing and might be contributed by many brain areas. Here we employed the ?xational saccade (micro-saccade) as a behavior probe to study this processing in express saccades.
METHOD: We compared the fixational saccade rate under express saccade condition and regular saccade condition. We also analyzed the fixational saccade rate under gap tasks with di?erent gap duration.
RESULTS: The results showed that the fixational saccade rate changed differently between express saccade and regular saccade: in short gap duration, the fixational saccade rate decreased much earlier in express saccade than in regular saccades; in medium and long gap durations, it decreased at similar time, but with a following rebound only in the regular saccade. Moreover, comparing between di?erent gap durations, the timing of ?xational saccade rate decrease was more related to the saccade initiation in express saccades, but more related to the physical disappearance of ?xation point in regular saccades. This suggests that the decrease of fixational saccade rate was closely related with saccade preparation in express saccade, but with visual transient in regular saccade.
CONCLUSIONS: Fixational saccade rate reflected that there was advanced motor preparation for express saccade.
PURPOSE: The current study sought to identify the neurophysiological bases of development in covert spatial attention, focusing on electroencephalographic (EEG) markers of attentional selection (N2pc) and suppression (PD).
METHODS: EEG data were collected from healthy young adults (aged 19–29 years) and typically developing children (ages 9–15 years), while they searched for a shape singleton target either with the absence (Experiment 1) or presence (Experiment 2) of a task-irrelevant color singleton distractor.
RESULTS: The results showed that the lateral shape target elicited a prolonged and smaller N2pc in children (n = 25) compared to adults (n = 28) in Experiment 1. Moreover, the target-elicited N2pc was followed by a similar positivity in both children and adults. In Experiment 2, we replicated the reduced target-elicited N2pc in children. Counterintuitively, the lateral salient-but-irrelevant color distractor elicited a larger PD in children (n = 22) than in adults (n = 31). We found no evidence for a correlation between the reduced target-elicited N2pc and the increased distractor-elicit PD in children.
CONCLUSIONS: Our results provide neurophysiological evidence that covert spatial attention in children of 9-15 years old is still undergoing significant development. Compared to adults, children deploy insufficient attention resources to the targets and use more attentional suppression to resist to the silent-but-irrelevant distractors. However, the development of target selection and distractor suppression might depend on distinct cognitive mechanisms.
PURPOSE: Whereas attention readily facilitates the detection and discrimination of objects, it is unknown whether it aids in forming the vast voluminous visual space that contains the objects. Conventional wisdom suggests not, given the e?ortless ease in which we perceive 3D-scenes. Here, we asked if a di?erential allocation of an ambient attention resource to either the lower visual field (ground) or upper visual field (ceiling) a?ects space perception.
METHODS: In Experiment 1, the observer judged the location of a brie?y presented target (1 sec) placed either on the textured ground or ceiling surface (2x4 LED array spanning 1.4x3m area, 0.15 sec). Prior to target presentation and to ensure proper ?xation, a dimly lit LED was randomly turned o? for 0.1 sec, 1-3 times within a 3-6 sec ?xation period. The observer had to correctly report each time the LED ?ickered. Meantime, he/she attended to either the upper or lower ?eld.
RESULTS: We found judged location was more accurate for a target on the ground, provided the ground was visible plus the observer directed ambient attention to the lower visual field and not the upper ?eld. This reveals attention facilitates space perception with reference to the ground. Our second experiment found judged location of a midair target with both ground and ceiling surfaces present was more accurate when the observer attended to the lower visual field, indicating that the ambient attention e?ect extends to visual space above the ground.
CONCLUSIONS: These ?ndings underscore attention's role in anchoring visual orientation in space, arguably, a primal event that enhances one's ability to interact with objects within the space. That the ambient attention's e?ect was contingent on the ground being visible suggests that our terrestrial visual system is best served by its ecological niche.
The smile expression is reported to significantly enhance the perceived facial attractiveness. However, little is known about how the facial physical attractiveness influence expression dimension, conversely. Here we investigated the in?uence from facial physical attractiveness on perception and expressing habit of smiling and angry expressions.. By rating the uncontrolled expressions on 60 female image persons, we found that impression strength of anger in attractive group was perceived stronger than that in unattractive group, while impression strength of smile expression between two groups was perceived approximately the same. However, when we used the controlled expressions constructed by expression templates on computer-morphing technology, we observed the reversed results that smile expression rather than angry expression was perceived as the stronger impression strength in the attractive group than unattractive group. The discrepancy between these two observations re?ects an increase of physical smiling strength and decrease of physical anger strength on unattractive persons in contrast with attractive persons. Our results provided the further insight into unconscious inclination of emotional expression (expressive habit) in?uenced by facial attractiveness.
PURPOSE:The research of visual working memory (VWM) has been a hot topic in the cognitive and cognitive neuroscience fields during the past decade years. It focused on the storage mechanism and capacity especially. Three different theories have been proposed to explain the storage mechanism of visual working memory. Luck & Vogel (1997) indicated that the object stored in the VWM in an integrated unit, regardless of the number of features containing in individual objects, and regardless of the features belonging to one or more dimensions. And that was the object-based storage theory, which was also called "strong object" hypothesis. However, many subsequent researches found that VWM for conjoined objects was worse than for objects made of single features when feature heterogeneity was controlled(Olson & Jiang, 2002; Wheeler & Treisman, 2002). Based upon these results, Olson & Jiang put forward the "weak object" hypothesis, suggesting that VWM is limited by both the number of objects and the composition of those object features. And Wheeler & Treisman put forth dual-storage mechanism, assumed features from the same dimension compete for capacity and cannot be bound together, whereas features from different dimensions can be stored in parallel. More researchers identified the dual-storage theory, but there is controversy, especially on the multi-feature stimuli. So we aimed to study the storage mechanism of VWM with 3-D graphs containing two kinds of features, and to test which hypothesis of above are more reasonable.
METHODS: Using single change-detection paradigm, we carried out two experiments to investigate the units of storage of visual object working memory and visual spatial working memory for the 3-D graphs with features of double dimensions. The stimulus graphs in experiment 1 consist of basic features of color and shape, and the memory materials in experiment 2 were presented by different colors and textures. Participants were asked to judge whether the test item varied to the item in sample display. The memory performance was checked by varying the test items in four conditions: color change, shape or texture change, feature exchange(binding change), and location. The ?rst three conditions belong to object WM task and the last belongs to spatial WM task.
RESULTS: The results of 2 (memory set size: 3 vs. 4) × 4(change condition of test item) within-subject repeated measures ANOVA on mean percent correct from two experiments both showed: (1) There was no signi?cant di?erence between the memory performance of feature exchange condition and the worst accuracy of single feature change conditions. (2) There was a signi?cant main e?ect on memory set size, which the memory performance of 3 graphs was higher than that of 4 graphs. (3) The performance of visual object working memory task was signi?cantly higher than that of visual spatial working memory task.
CONCLUSIONS: These findings of two experiments revealed that:（1）The 3-D graphs with basic features of color and shape were stored as an integrated manner in VWM. (2) The 3-D graphs with one basic feature and one detailed feature also could be stored as a binding form. In conclusion, the 3-D graphs with features from different dimensions were stored as integrated units in object working memory and spatial working memory.
PURPOSE: The present study aimed at investigating the relationship between emotion cognition and attention and the possible neuromechanism. It aimed to probe whether emotion cognition is an automatic process and independent of attention or it is modulated by attentional resource and belongs to a kind of controlled processing.
METHODS: The present research adopted eye tracking technology and dual-task paradigm. The subjects’ attention was manipulated to fixate at the central task to study whether subjects could detect the emotional faces presented in an area with a decrease of near-absence of attention.
RESULTS: The results revealed that since emotional stimuli had higher cognitive priority, its cognition required very little attentional resource. Also, the attentional dependence of emotion cognition varied with the competing task. When the central and peripheral tasks were both emotional faces discrimination, the subjects could not perform well in the peripheral task, showing that the attentional resource a?ected emotion cognition. However, when the peripheral task was emotional face discrimination but the central task was different, the subjects performed well in the peripheral task.
CONCLUSIONS: The processing of emotional information required very little attentional resource and it is a kind of controlled processing. Emotional information can be processed parallelly with other stimuli and there may be a speci?c channel in human brain to process emotional information, supporting multiple resource theory.
PURPOSE: The understanding of the information-processing mechanism of human visual system is a major cognitive neuroscience and physiology research topic. The insight of the structure and function of human visual cortex might also help us explain the state-of-art performances of recent deep neural networks.
METHODS: The human subject looked at a sequence of natural images whose content includes animals, buildings, food, humans, indoor scenes, manmade objects, outdoor scenes and textures. We analyzed the functional Magnetic Resonance Imaging (fMRI) data of both the ventral pathway (V1-V2-V4-LO) and the dorsal pathway (V1-V2-V3-V3a/b) on the visual cortex, and performed PCA-SVM on the basis of voxel activities of di?erent regions to conclude the trend of classi?cation accuracy. The canonical correlation analysis (CCA) was also used to estimate the linear correlationship among considered regions.
RESULTS: We found that the classification performance improved hierarchically from lower-level regions to higher-level regions in both pathways, among which the LO, V3a and V3b BOLD signals were good classification basis no worse than the widely-used features such as GIST, HOG and LBP. Simultaneously, the performances of V3a and V3b voxels were very close to those of LO voxels. CCA results also showed relatively strong linear correlationship between V3a/b and V4/LO.
CONCLUSIONS: Primarily, the visual cortex disposes visual information hierarchically. When we tracked the information stream in the visual system, the representations of the stimulus grew more and more abstract and global for recognition, so the layer-stacked deep neural networks were better models for visual cortex than traditional shallow ones. Moreover, V3a and V3b located at the dorsal pathway were also involved in object recognition, which was further confirmed by CCA results. Consequently, when it comes to object recognition, we should consider the coordination mechanism between the two pathways rather than focusing on the ventral pathway alone.
PURPOSE: One paradox in primate vision concerns the increasing complexity of encoded features while spatial frequency (SF) selectivity decreases drastically along the visual hierarchy. We know V1 holds the highest SF selectivity for ?ne spatial analysis, however the comparative SF processing in di?erent functional stripes of V2 as well as in the downstream V4 is less clear.
METHODS: By simultaneous intrinsic optical imaging of macaque V1, V2 and V4, we quantitatively measured the population responses across these visual areas to sine-wave gratings with various SFs. The population responses of V1, V2, and V4 were subsequently con?rmed by single-unit recordings in awake macaques.
RESULTS: As expected we found that the SF selectivity was the highest in V1 while most regions in V4 exhibited the lowest SF selectivity. Compared with V1 and V4, V2 exhibited the strongest population response magnitude. We further investigated the SF selectivity across V2 functional stripes and found that the SF selectivity in thick stripes were lower than that in both thin and pale stripes. No signi?cant SF di?erence was found between the thin and pale stripes.
CONCLUSIONS: Our findings on the distinct SF selectivity across simultaneously imaged V1, V2, and V4 sheds lights on the spatial analysis along the visual hierarchy, which help to further our understanding and electrophysiological studies as well as computational modelling of the integration of local spatial features to form global representations.
PURPOSE: To investigate the changes of resting-state interhemispheric functional connectivity in the brain of the ametropic amblyopia patients.
METHODS: 13 ametropic amblyopia patients (age: 11-16years) and 10 normal controls (ages: 11-16 years) were recruited for the study. The functional magnetic resonance imaging (fMRI) images of both normal controls and ametropic amblyopia patients were obtained in Beijing Tongren Hospital and preprocessed. And then, voxel-mirrored homotopic connectivity (VMHC) method was used to assess the homotopic resting-state functional connectivity (RSFC), which is a sensitive index for detecting the inter-hemispheric alterations of the amblyopia. Group comparisons were conducted and Pearson correlations were used to explore the correlationship between mean VMHC values in the abnormal regions and the clinical parameters.
RESULTS: We performed two-tailed two sample t test to assess the differences of VMHC between amblyopia patients and normal controls. As we used the symmetric T1 mash, the result showed symmetric abnormal regions in the brain. Amblyopia patients exhibited decreased VMHC in middle temporal gyrus (MTG), inferior temporal gyrus (ITG), precuneus, precentral gyrus (PreCG), posterior cingulate gyrus (PCG) and supplementary motor area (SMA) regions. Meanwhile, the increased VMHC were located in the insula and putamen. The Pearson correlation analysis showed that the mean VMHC values in MTG were positively correlated (r = 0.728, p = 0.011) with the visual acuity in amblyopia patients.
CONCLUSIONS: Significant differences between amblyopia patients and normal controls in VMHC showed that the alterations of inter-hemispheric functional connectivity in the brain, indicating the changes of the inter-hemispheric coordination and functional homotopy in amblyopia.
PURPOSE ：Motion perception is important for human beings to interplay with environment, such as walking through the street to avoid moving vehicles. Psychophysical researches on human beings reveal that the old people show accumulating deficits in motion perception. Previous studies suggesting decreased neuronal inhibition in visual system accounts for some of the de?cits. However, some visual functions in the old remain the same or even better than young people, suggesting aging a?ect di?erent inhibitory mechanisms di?erently. This research want to prove this assumption.
METHODS: Here we used motion repulsion and drifting gabor direction discrimination paradigms to investigate inhibitory machanism. Motion repulsion refers to the phenomenon observers overestimate the perceived angle when two superimposed dot patterns moving at an acute angle. The misperception has been interpreted as mutual inhibition between nearby direction-tuned neurons within the same cortical area. At high contrast, the drifting gabor direction discrimination threshold increases with the enlargement of the gabor size. This is considered as behavioral manifestation of surround suppression and directed by feedback inhibition from higher cortical regions to primary visual cortex.
RESULTS: We found motion repulsion in elder people was much larger than younger ones. But the increase of motion discrimination threshold with enlargement of drifting gabor size in older group was much less than younger group
CONCLUSIONS: We suggest that the altered motion repulsion in the aged may result from enhanced mutual inhibition in the same area. The decreased change of threshold in the old group is consistent with previous findings. We interpret this result as attenuated feedback inhibition from higher level area to lower level area. Our data indicates that aging a?ect intra-areal inhibition and inter-areal inhibition in visual motion system di?erently.
PURPOSE: Binocular rivalry arises when incompatible images are presented one to each eye. If the two eyes’ con?icting information were invisible with identical perceptual interpretations, does rivalry competition still occur? The current study investigated whether binocular rivalry can be induced from con?icting but invisible spatial patterns.
METHODS & RESULTS: A chromatic grating counter-phase ?ickering at 30 Hz appeared uniform, but produced signi?cant TAE and orientation-selective adaptation. The invisible pattern also generated significant BOLD activities in the early visual cortex, with minimal response in the parietal and frontal cortical areas. A monocularly presented invisible chromatic grating, compared to perceptually matched uniform stimuli, enhanced the rivalry competition with a low contrast visible grating presented to the fellow eye. Furthermore, switching from a uniform ?eld to a perceptually matched invisible chromatic grating produced interocular suppression at about 200 ms following the onset of the invisible grating. Experiments using briefly presented monocular probes revealed evidence for sustained rivalry competition between two invisible gratings during continuous dichoptic presentations.
CONCLUSIONS: These findings indicate that even without visible interocular conflict, and with minimal engagement of fronto-parietal cortex and consciousness related top-down feedbacks, perceptually identical patterns with invisible con?ict features produce rivalry competition in the early visual cortex.
PURPOSE: Recent studies have shown that information from peripherally presented images can be obtained from foveal retinotopic cortex, presumably due to feedback signals. The current study is designed to investigate whether such a feedback processing is temporally ?exible.
METHODS: We investigated this potential feedback signal by presenting noise in fovea at di?erent object-noise SOAs while subjects performed a discrimination task on peripheral objects.
RESULTS: First, we found a selective impairment of performance when a foveal noise was presented around 250 ms following the onset of the peripheral presentation of objects. Then we tested whether foveal processing is automatically engaged as soon as peripheral object information reaches higher levels of cortex. If so, we would predict a rather fixed temporal window for the foveal noise to be effective (i.e., around 250 ms); however, when the two peripheral objects were oriented differently and mental rotation was required for the discrimination task, the engagement of foveal processing was delayed as revealed by a systematic shift of the effective temporal window of foveal noise.
CONCLUSIONS: During processing spatially detailed object information in the periphery, the foveal retinotopic cortex is engaged at a ?exible time point when ?ne detail information is needed.
PURPOSE: It has been suggested that processing of global and local properties is associated with neuronal oscillations at different rhythms. Recently, by employing a time-resolved behavioral measurement, several visual attentional studies have revealed neurophysiologically relevant rhythms directly in behavioral performances, suggesting that the underlying neuronal dynamics might be manifested directly at the behavioral level. Here we applied this time-resolved behavioral approach to access the temporal dynamics of global/local processing.
METHODS: The stimuli are a big arrow (global) composed of small arrows (local). The global and local properties are either congruent or incongruent. After cued by a text of 'Global' or 'Local', subjects reported the global or local properties of the target as fast as possible and their reaction times were recorded. The cue-to-target SOA varied from 110 to 600ms in steps of 10ms.
RESULTS: First, we replicated typical global precedence e?ects (global faster than local) in slow trends of the time-resolved behavioral time courses. Second, with the slow trends removed, the global processing demonstrated a rhythmic fluctuation at alpha band (~10 Hz), which are in phase between the congruent and incongruent conditions, suggesting that the global property is sampled in an alpha-band rhythm, not influenced by local properties. Relatively in contrast, the local processing demonstrated a rhythmic fluctuation at beta band (~26 Hz), which showed an ‘out-of-phase’ relationship between the congruent and incongruent conditions, which suggest a global precedence e?ect in oscillation, implicating that local processing is largely driven and modulated by the global property.
CONCLUSIONS: Our results provide behavioral evidence supporting the central role of neuronal oscillations in global/local processing. Our study also speaks for a dynamic framework within which global and local.
Can playing action video games improve visuomotor control? If so, can these games be used in training people to perform daily visuomotor-control tasks, such as driving? We found that action gamers have better lane-keeping and visuomotor-control skills than do non–action gamers. We then trained nongamers with action or nonaction video games. After they played a driving or ?rst-person-shooter video game for 5 or 10 hr, their visuomotor control improved signi?cantly. In contrast, nongamers showed no such improvement after they played a nonaction video game. Our model-driven analysis revealed that although different action video games have different effects on the sensorimotor system underlying visuomotor control, action gaming in general improves the responsiveness of the sensorimotor system to input error signals. The ?ndings support a causal link between action gaming (for as little as 5 hr) and enhancement in visuomotor control, and suggest that action video games can be bene?cial training tools for driving.
PURPOSE: When multiple stimuli are present in the visual ?eld, competitive interactions between stimuli could be biased by stimulus-driven and attention-driven processes. To study the neural mechanisms underlying multiple-stimulus encoding, we used fMRI with decoding and encoding model to estimate the orientation-selective responses in human visual cortex to parafoveally presented Gabor arrays.
METHODS: In an array, a center Gabor (eccentricity = 2.5°) was surrounded by eight ?anking Gabors (0.75° from the center Gabor). By manipulating the configuration of the flankers, we introduced crowding effect in the multi-stimulus displays at di?erent levels (non-crowded, less-crowded, and more-crowded condition). In the scan, observers performed tasks unrelated to orientation. Using forward encoding model, we decomposed the multivoxel response in each visual area into responses of a hypothetical set of orientation-selective channels.
RESULTS: For non-crowded condition, when selective attention was on the entire array, the orientation response to the array was dominated by the orientation of the flankers. However, when selective attention was directed to the center Gabor, the orientation response began to reflect the orientation of the center Gabor in extrastriate areas: the orientation selectivity for the center Gabor was strongest in V4 while weakest in V1. For less-crowded condition, with directed attention, orientation information was encoded in V1 as an ensemble, which could not be retrieved in downstream visual areas. For more-crowded condition, attention had little e?ect in recovering the orientation information in all the visual areas.
CONCLUSIONS: These ?ndings suggest that attention resolves the competition among multiple stimuli by counteracting the in?uences of nearby stimuli, resulting in enhanced information processing at the attended location. This process of biased competition appears to be cumulative along the visual-processing hierarchy and became most significant in V4. However, crowding signi?cantly diminished this role of attention on image processing.
Purpose: To determine whether bright light (BL) inhibits form deprivation myopia (FDM) via the dopamine receptor D1 (D1R)-linked signaling pathway localized in specific retinal neuronal cell types in mice.
Methods: D1R antagonist SCH39166 was daily intraperitoneally injected to evaluate if BL mediates declines in FDM development through D1R. Refraction changes were evaluated with an eccentric infrared photorefractor. Optical coherence tomography evaluated ocular axial components. Electroretinography monitored retinal function. c-Fos and p-TH (phosphorylated tyrosine hydroxylase) immunofluorescent staining evaluated D1R receptor activity and dopamine synthesis, respectively. Six different biomarkers of retinal neuronal types delineated di?erential distribution of D1R expression.
Results: BL (2500-5000 lux) exposure for 4 weeks (6 hours per day) inhibited FDM development by reducing ocular elongation and shifting refraction towards hyperopia compared to that in normal light (NL, 100-200 lux ). SCH39166 injections completely reversed the inhibitory effects of BL on both refraction and ocular elongation. BL increased the number of cells expressing p-TH and c-fos expression in D1R+ BCs, especially in D1R+ON-BCs as well as horizontal cells (HCs).
Conclusions: BL increases D1R activity in the bipolar cells (BC) of the ON pathway and HCs, which is associated with less myopic shift and ocular elongation than that occurring in NL. This di?erence suggests that BL-induced increase in the activity of D1R in the ON pathway contributes to the suppression of FDM development in mice.
Purpose: To compare psychophysical performance and brain activation during a motion salience task and voluntary saccadesin adult strabismicamblyopes and controls.
Methods: The motion salience task involved discrimination and detection of a target of coherently moving dots. The second task required voluntary saccades to horizontal stimulus position changes. fMRI activation and functional connectivity between parieto-frontal attention network ROIs, and V1 and V5 were compared for the two tasks.
Results: Behavioural thresholds were higher for detection ofthe moving stimuli by the strabismic amblyopic eye compared to the fellow eye or control eyes. BOLD activation in IPS, FEF and V5 for both tasks, through the amblyopic eye was weaker than that to fellow eye or control subject eyes though no di?erence was seen in V1 activation to the motion task under any eye-viewing condition. Correlational connections between key nodes of the visual attention network activated by the amblyopic eye were abnormal in the motion task, with the FEF ipsilateral to the amblyopic eye the most isolated node.By contrast, the functional connections of this network were relatively normal for the voluntary saccade task.
Conclusions: Amblyopic eyes require slower speed and longer exposure for the detection of moving targets.Overall our results suggest that strabismic amblyopia is associated with reduced attention network activation during motion-driven attention tasks independent of V1.
PURPOSE: Dichoptic training is becoming a popular tool in amblyopia treatment. Here we investigated the effects of dichoptic training on juvenile amblyopia no longer responsive to patching treatment (PT group) or never patch treated (NPT group).
METHODS & RESULTS: Training consisted of three stages. (1) 10 PT and 10 NPT amblyopes (8-17 years, 11-anisometropic, 4-ametropic, 1-strabismus, 4-mixed) received dichoptic de-masking training for 40 hours. They used AEs to practice contrast discrimination of Gabors that were dichoptically masked by a band-filtered noise pattern simultaneously presented in NAEs. Dichoptic learning is indexed by the increase of maximal tolerable noise contrast (TNC) for AE contrast discrimination. Training improved maximal TNC by 600% in PT and 700% in NPT, which translated to stereoacuity improvements by 5.4-lines in PT and 3.6-lines in NPT, and AE visual acuity improvements by 1.1-lines in PT and 2.2-lines in NPT. (2) The amblyopes further received stereopsis training for another 40 hours. Training improved stereoacuity by 3.3-lines in PT and 0.3-lines in NPT, and AE acuity by 0 line in PT and 0.4 lines in NPT. Seven PT amblyopes regained normal stereoacuity (20~50 arcsec) after two stages of training. (3) Extra monocular AE grating acuity training (30 hours) failed to improve grating acuity in both groups. Neither did it produce further AE acuity and stereoacuity gains. Altogether, the stereoacuity gain was associated with pre-training interocular suppression but not with a reduction of interocular acuity di?erence in most amblyopes.
CONCLUSIONS: Dichoptic training can improve and even restore some juvenile amblyopes’ stereoacuity, especially those with mild amblyopia. The dissociation of stereoacuity gain and change of interocular acuity difference suggests that the stereoacuity gains may not result from reduced interocular suppression in most amblyopes, rather the amblyopes may have learned to better readout the stimulus information to improve stereopis.
PURPOSE: Microsaccades have been associated with a variety of functions such as eliminating visual fading, supporting detailed visual search, indicating covert attention and in?uencing motor preparation. Although the direction of microsaccades could be modulated by the spatial location of covert attention, there is no elaborate study about the change of microsaccades direction along time.
METHODS: Two monkeys were trained to perform two spatial choice tasks in which the monkeys needed to ?gure out one from two stimuli as saccadic goal based either on the spatial location of a visual cue or the color of stimuli.
RESULTS: The direction of microsaccades of two monkeys began to rotate shortly after the onset of the cue (spatial or color) and continued until a response saccade was allowed in both tasks. The speed of the rotation of microsaccades direction di?ered between two di?erent saccade choices. In contrast, no rotation of microsaccades direction was observed in a memory guided saccade task in which no competing choice was provided.
CONCLUSIONS: The rotation of microsaccades direction in spatial choice tasks represents the motor choice of monkeys. In addition, this rotation phenomenon of microsaccades might indicate that the mental process conducting a saccade response from a saccade choice is continuous rather than saltatory.
PURPOSE: The present study aimed to examine whether two visual working memory (VWM) representations can simultaneously guide attention and automatically interfere with concurrent visual search when participants are required to memorize two items with feature conjunctions. In addition, we tested whether collective representations of multiple features or representations of integrated objects with feature conjunctions guide attention.
METHODS: The present study adopted the typical dual-task paradigm, participants were required to memorize two objects before starting a visual search task which was completely irrelevant to the memory task.
RESULTS: The present study showed that two VWM representations can involuntarily capture attention and interfere with concurrent visual search. In addition, each of two VWM representations can interfere with concurrent visual search as much as can a single cued VWM representation, irrespective of whether the cue validity is 75% (Experiment 3), or 100% (Experiment 4). Moreover, each of two VWM representations can also produce a large memory-driven capture e?ect, whether or not there is a short (800msec) or long (3000msec) SOA between memory display and visual search.
CONCLUSIONS: Thus, two VWM representations can simultaneously control attention. Furthermore, when participants are required to memorize two objects de?ned by a conjunction of color and texture, a distractor that matches the color of one memorized item and the texture of the other memorized item (such that it is not fully matching either memorized item) can also capture attention. This might suggest that features of the memorized object are free-?oating in VWM.
PURPOSE: A visual search for targets is facilitated when the target objects are on a di?erent depth plane than other masking objects cluttering the scene.
METHODS: The ability of observers to determine whether four letters, presented stereoscopically at four symmetrically-located positions on the fixation plane, were the same or di?erent, was assessed when the target letters were masked by other randomly positioned and oriented letters appearing on the same depth plane as the target letters, or in front, or behind it. Three additional control maskers, derived from the letter maskers, were also presented on the same three depth planes: 1) random-phase maskers (same spectral amplitude composition as the letter masker but with the phase spectrum randomized); 2) random-pixel maskers (the locations of the letter maskers’ pixel amplitudes were randomized); and 3) letter-fragment maskers (the same letters as in the letter masker but broken up into fragments).
RESULTS: Performance improved with target duration when the target-letter plane was in front of the letter-masker plane, but not when the target letters were on the same plane as the masker, or behind it. A comparison of the results for the four di?erent kinds of maskers indicated that maskers consisting of recognizable objects (letters or letter fragments) interfere more with search and comparison judgments than visual noise have the same spatial frequency profile and contrast. In addition, performance was poorer for letter maskers than for letter-masker fragments, suggesting that the letter maskers interfered more with performance than the letter-fragment maskers because of the lexical activity they elicit.
CONCLUSIONS: The degree of binocular unmasking is greater when the target appears to be in front of rather than behind the masker in the letter discrimination task. These results contrast with those that indicate that when the target is presented foveally (at the point of fixation) its detectability appears to be independent of whether it is perceived in front of or behind the masker. Hence pattern recognition but not target detection is sensitive to the perceived spatial relationships of maskers to targets. The fact that similar results were obtained for meaningful (whole letters) as for meaningless (letter fragments) maskers indicates that the interference from the masker occurs at a pre-lexical stage of processing.
PURPOSE: Our visual world is rich in spectral information, and the evolution of separate L / M cone and resultant L—M opponent channels in catarrhine and some platyrrhine primates is indicative that distinguishing "red" from "green" serves a critical purpose. Psychophysical studies in humans, and electrophysiology in both human and non-human primate visual cortices suggests a red dominance in driving neural responses in comparison to other colors. The purpose of this study is to test if there is a neural basis of red dominance at the level of local ?eld potentials (LFP) and multi-unit activity (MUA).
METHODS: Here we used 16-channel laminar probes to record LFP and MUA across the cortical depth for full-field isoluminant color stimuli in both V1 and V4. We computed band-limited power from the LFP during stimulation induced by seven isoluminant colors (red, orange, yellow, green, cyan, blue, purple). As the gamma (γ) band is commonly assumed to be related to attention and stimulus awareness in visual cortex, we hypothesized that red may di?erentially drive gamma band power during visual perception.
RESULTS: Isoluminant red stimulation induced significantly higher power at both the γ–low (30–50Hz) and γ–high bands (50–100Hz) across all laminar depths in both V1 and V4. Even when recording within V4 color domains whose color preference was other than red, or V4 form domains with little color preference, red still drove a higher γ–band power response.
CONCLUSIONS: Red drives a significantly enhanced γ–band response invariant to color or form domain preferences, which is consistant with the perceptual preference to red shown in other studies perceptually.
PURPOSE: The primary visual cortex (V1) in primates performs a fine spatial analysis of the visual world, with the highest visual acuity in the cortical area corresponding to the fovea of the retina. Electrophysiological single-unit recordings have revealed an inverse proportionality between the receptive ?eld size, spatial frequency (SF) selectivity of V1 neurons and their eccentricities. As eccentricity is measured as the distance (degrees) from the fovea whereas cortical magnification factor (CMF) is calculated as cortical surface distance/visual angle (mm/degree), the correlation between the neural SF selectivity and CMF in macaque V1 has not yet been quantitatively de?ned.
METHODS: In this study by using intrinsic optical imaging, the SF selectivity of each pixel of the imaged area was measured in response to sinewave gratings with various combinations of orientation and SF. We quantitatively measured the relationship between CMF and SF selectivity, eccentricity as well as orientation domain size in macaque V1.
RESULTS: The ?ne cortical representation of the visual space was mapped and analyzed by using fast Fourier intrinsic optical imaging before the acquisition of the eccentricity and CMF maps with high spatial resolution. A physiometric function for SF selectivity and CMF was thus determined in the imaged areas of macaque V1. We also quantitatively measured the inverse proportionality between eccentricity and CMF and between the size of orientation domains and CMF.
CONCLUSIONS: These quantitative measurements of relationship among SF selectivity, eccentricity, orientation domains and CMF will be highly informative for future electrophysiological recording, other brain imaging studies and computational modeling in primates.
PURPOSE: Binocular rivalry occurs when dichoptic images presented to the two eyes are too dissimilar to be fused. Research of Wolfe & Franzel, (1988) describes a series of binocular visual search experiments, in which they claim that luster is e?cient for visual search while spacing is not. Does spacing stay ine?cient when interference factors increase?
METHODS: A verification experiment is implemented with a polarized 3D display presenting the stimulus and an SMI eye-tracker recording the eyes’ fixation trace. Three groups of luminance of (100 250), (125 200) and (150 225) are designed to present lustrous and matte with the background of 175. Stimuli size is 1.5° and set size is held constant at 2 while the spacing of items varies from 1 to 7. On target trials, one item is lustrous and the other is matte. On distractor trials, both are matte. Subjects are asked to observe whether luster appears and make a judgement. Each subject is tested with 1500 trials.
RESULTS: The average reaction time of target trials (0.612s) is obviously less than that of distractor trials (0.649s). For target trials, average RTs of spacing varies from 1 to 7 are 0.605s, 0.617s, 0.613s, 0.623s, 0.616s, 0.599s, 0.611s. For distractor trials, average RTs are 0.642s, 0.654s, 0.661s, 0.646s, 0.652s, 0.619s, 0.667s. Fixation trace of target trials show that subjects observe items from one to the other while subjects observe in the direction of items in distractor trials.
CONCLUSIONS: The design of three groups of luminance reduces the in?uence that white and black colors impose on the judgements of target. The results suggest that there is no obvious effect of spacing and spacing does not seem to be a major in?uence of this experiment. For this luster based visual search experiment, space is not e?cient.
PURPOSE: In a pair-of-pairs comparison experiment, Clarke et al.  showed human observers two pairs of textures and required them to decide on which pair was more similar. Dong and Chantler  further examined 51 sets of computational image features for estimating the humans’ perceptual judgements but they found that none performed well. A question hence arises: do humans estimate texture similarity in a consistent way? In this study, we conduct an experiment in order to answer it.
METHODS: The top 80 most inconsistent pairs of pairs of textures between humans’ judgements and the results obtained using features were selected. Only the pair that the majority of the 51 feature sets chose as dissimilar but the observers [Clarke et al., 2012] disagreed with this in each pair of pairs was used. An experiment was conducted using eight native English speakers. Given a pair of textures, the observer was required to describe the similarity of these using at least one of the 98 English words that Bhushan et al.  used.
RESULTS: The occurrence frequencies of the 98 words were accumulated into a histogram. Since these words were divided into eleven clusters by Bhushan et al. , the frequencies of the words in the same cluster were collapsed into a single bin. Considering the size of each cluster was di?erent, the collapsed frequency of each cluster was then normalized using its size. It was found that four clusters of words were more frequently used than the others, including “regular”, “lined”, “netlike” and “bumpy” (only one word was listed for each cluster).
CONCLUSIONS: Experimental results show that regularity, directionality and bumpiness mainly account for the perceptual judgements that human observers chose the 80 pairs in the pair-of-pairs comparison experiment [Clarke et al., 2012]. This finding suggests that humans estimate texture similarity in a consistent manner.
PURPOSE: The human fovea serves both as the locus for ?xations and the ocul?omotor reference for saccades. Training normally sighted adults with occluded central vision can reliably induce a preferred retinal locus (PRL) in peripheral vision for ?xation with re-referenced saccades. Does the development of a PRL in peripheral vision alter the neural processing of the visual inputs? Crowding, the impediment of object recognition by clutter, is a hallmark of form-vision de?cits in peripheral vision. Here we asked if the spatial extent of crowding can be altered as a consequence of the training-induced PRL.
METHODS: We trained nine human subjects using the object-following-and-visual-search task with a simulated central-?eld scotoma and a prescribed PRL. Before and after training, we measured the spatial extent of crowding at two locations: the prescribed PRL location in the upper-left visual ?eld and a symmetric “sideways” location in the upper-right ?eld.
RESULTS: After training, subjects’ saccades were re-referenced to the prescribed PRL location in the presence of the simulated central scotoma. Training led to a shrinkage of the crowding zone along the radial axis at the PRL location, causing the crowding zone to become roundish. The crowding zone along the radial axis at the sideways location was also reduced. With fMRI measurements before and after training, we found a radial-specific reduction of crowding-related suppression across visual areas V1-V4, which was only observed at the PRL location.
CONCLUSIONS: These ?ndings suggest that human crowding zones dynamically reorganize relative to the reference point of saccade, which is consistent with the saccade-confounded image-encoding theory (Nandy & Tjan, 2012). By demonstrating that training with a simulated central-field scotoma facilitates peripheral vision via reshaping the crowding zones, this study reveals the residual plasticity in adult peripheral vision and sheds light on new mechanisms of rehabilitations for patients with central ?eld loss.