How Does Attention Influence Contrast Surround Suppression

Surround suppression is a common visual perceptual phenomenon.At the level of perception,it means the contrast of the central stimulus is suppressed by the peripheral stimulus and its subjective contrast is reduced.The effect size of the surround suppression is related to the orientation,contrast,spatial frequency and visual field position of the stimuli.In the visual system,attention helps us extract target information from complex visual background information.Some studies have found that attention is also a factor that affects the effect size of surround suppression.However,due to the differences among these studies,such as different types of attention and experimental stimuli,their conclusions are inconsistent.Thus,we ask the questions:Does attention influence surround suppression?If so,how?It is the first study to combine two different methodologies-psychophysics and event-related potential(ERP)-to explore how spatial attention influences contrast surround suppression in humans,using gratings with a sinusoidal change in brightness as the visual stimuli.In this study,attention was manipulated by means of different attentional tasks and we compared the effect size in three visual environments which the target was isolate,with two flankers that had the same orientation as the target,and were orthogonal to the target.Answering this question helps us understand the mechanism of attention towards the visual information.The results of experiment 1a and experiment 1b showed that compared with the unattended condition,the suppression index was closer to one when the flankers had the same orientation as the target,indicating that the parallel flankers had a weaker suppression effect on the target in the attended condition.But in experiment 1b,when the flankers were orthogonal to the target,there was no significant difference between attended and unattended condition.The results of experiment 2 showed that the significant differential period of ERP amplitude between two visual environments which the target was isolate and with two orthogonal flankers was shorter and the average value of differential amplitude in those two condition was lower in the attended condition.Both experiments consistently showed that attention reduced the contrast surround suppression.