Abstract:

We live in a three-dimensional (3D) space and operate objects that lie at different depth plane in the space. It seems natural to assume that our visual system is able to direct attention to object located at different depths. Although it has been well documented that the human brain reconstructs a 3D world from two-dimensional (2D) retinal images by extracting 3D structures and depth positions of objects, it remains poorly understood how visuospatial attention is shifted in depth, especially in the later inhibitory phase (inhibition of return, IOR). In the present study, by constructing a virtual 3D environment and presenting the target either closer to or farther from the participants in an adapted version of the Posner spatial-cuing paradigm, we aimed to investigate the location-based IOR along depth plane in 3D space. The cue-target correspondence in depth of target (closer depth plane vs. farther depth plane) was crossed with the cue-target correspondence in cue validity (cued vs. uncued), forming a 2 by 2 factorial design in the two experiments. Attention was oriented and reoriented along the diagonal trajectory in experiment 1, dditionally, in order to further control for the confounding effect of attentional orienting/reorienting across hemispace, attention was oriented and reoriented along the straight trajectory in experiment 2. If the two experiments revealed different patterns of results, the hemispace, rather than the pure depth, might have caused the results. In contrast, if the patterns of results were similar in the two experiments, the result most likely be attributed to the depth. At the beginning of each trial, one of four locations in either the closer or farther depth plane was cued for 300 ms (The cue was uninformative for the coming target), and was followed by a 200 ms inter-stimulus interval. Subsequently, the spatial location of the central fixation cross was cued for 300 ms to attract attention away from the previous cued location either in the closer or farther depth plane. After another period of 150 or 250 ms, the target was presented for 250 ms at one of four locations of either the cued or the uncued location with equal probabilities. Results showed that RTs to targets at the cued location were significantly longer than RTs to targets at the uncued location in both closer, t (24) = 7.89, p < 0.001, and farther, t (24) = 5.68, p < 0.001, depth planes in experiment 1, i.e., typical IOR effect. IOR effects in closer depth plane (30 ms) were larger than in farther depth plane (15 ms). Similarly, in experiment 2, RTs to targets at the cued location were significantly longer than RTs to targets at the uncued location in both closer, t (25) = 8.27, p < 0.001, and farther, t (25) = 4.36, p < 0.001, depth planes. IOR effects in closer depth plane (27 ms) were larger than in farther depth plane (15 ms). Results of the two experiments showed similar pattern, suggesting that the location based IOR effect found in experiment 1 should be attributed to attentional orienting across depth rather than hemispace. In conclusion, attention could be oriented/reoriented effectively along depth plane in 3D space to induce location based inhibition of return, which was not “depth blindness”.

Key words: three-dimensional (3D) space, attentional orienting/reorienting, spatial inhibition of return (IOR)