关键词: 视觉工作记忆, 注意选择, 精度负载, 容量负载, N2

Abstract:

Selective attention plays an important role in processing relevant information and ignoring irrelevant distractors. The relationship between visual working memory (VWM) and visual selective attention has been extensively studied. VWM is a complex system consisting of not only visual maintenance functions, but also executive control functions. High load on visual maintenance functions drains the capacity for perception and prevents distractors from being perceived, while high load on executive control functions drains the capacity available for active control and results in increased processing of irrelevant distractors. There are two types of load in VWM: capacity load referring to the number of items to be stored, and resolution load emphasizing the precision of the stored representations. It has been found that these two types of load exert opposite effects on selective attention. However the mechanism underlying the effects of different types of VWM load on selective attention is still unclear. In the present study, four experiments were designed to investigate how different types of VWM load affect selective attention.
Thirty-six participants were enrolled in Experiment 1, 2 and 3, respectively, and 14 participants were enrolled in Experiment 4. Participants were asked to perform both a VWM task and a visual search task. In the VWM task, participants had to retain colors in VWM to perform a change detection task. There were three levels of VWM load: baseline load, high-capacity load and high-resolution load. In the baseline load condition, participants were required to retain two colors and the change between the memory colors and the probe colors was large. In the high-capacity load condition, participants had to retain four colors and the change between the memory colors and the probe colors was also large. In the high-resolution load condition, participants had to retain two colors and the change between the memory colors and the probe colors was small. In Experiment 1 and 2, the visual search task was a Flanker task that was presented either in the periphery or in the center of the memory array. The Flanker task was presented with the memory array simultaneously in Experiment 1 and sequentially in Experiment 2. In Experiment 3, the visual search task was a Navon task. It was presented after the memory array and only in the center of the memory array. In Experiment 4, a Flanker task was presented after the memory array and only in the center of the memory array. EEG data during the memory interval were recorded by a 64-channel amplifier using a standard 10-20 system.
The results showed that high-capacity load and high-resolution load reduced Flanker interference, compared with baseline load, when the VWM task and the Flanker task were presented simultaneously, regardless of whether the Flanker task was presented in the periphery or in the center of the memory array. High-capacity load and high-resolution load also reduced Flanker interference, compared with baseline load, when the VWM task and the Flanker task were presented sequentially and the Flanker task was presented in the periphery of the memory array. Compared with baseline load, high-capacity load increased Flanker interference and high-resolution load reduced Flanker interference when the VWM task and the Flanker task were presented sequentially and the Flanker task was presented in the center of the memory array. Under the high-capacity load condition, the Navon interference for attending to global level was larger than that for attending to local level; under the high-resolution load condition, the Navon interference for attending to global level was smaller than that for attending to local level. ERP results showed that relative to the baseline load condition, the high- capacity load condition elicited smaller N2, whereas the high-resolution load condition elicited larger N2.
In conclusion, when the Flanker task is presented during encoding stage of VWM, high-capacity load and high-resolution load reduce interference. When the Flanker task is presented in the periphery of the memory array during maintaining stage of VWM, high-capacity load and high-resolution load reduce interference. These findings support the load theory of selective attention. However, when the Flanker task is presented in the center of the memory array during the maintenance stage, high-capacity load and high-resolution load lead to opposite effects. High-resolution load reduce interference, while high-capacity load increase interference. The underlying mechanism is that the different patterns of neural activity associated with the two types of VWM load may result in different distribution of cognitive control resources to selective attention.

Key words: visual working memory, selective attention, capacity load, resolution load, N2