Attentional Mechanism Of Nonsalient After Perceptual Learning And Physical Salient Stimuli

Salient stimuli are stimuli with unique feature in a homogeneous scene,while the corresponding nonsalient stimuli refer to stimuli where the target and background of the search are similar.Previous studies have shown that nonsalient trained stimuli could capture attention and would be actively suppressed when served as distractors.However,previous studies rarely discussed the attentional mechanisms of nonsalient stimuli in different visual processing stages before and after visual search training from the perspective of eye movement,and few studies compared the differences in attentional cognitive mechanisms between salient and nonsalient stimuli.Therefore,it was unclear that attentional mechanism of nonsalient stimuli in different stages of visual processing and whether nonsalient trained stimuli and physically salient stimuli operate through the same attentional neural mechanism.Study 1 explored the mechanism of attention by dividing the eye movement metrics into three visual processing stages:search initiation time(the early visual processing stage),which represents the cognitive process that the time of processing the current location and selecting the next search location;scanning time(the middle visual processing stage),which includes the number and processing time of fixation positions;verification time(the late visual processing stage),which represents determining whether the current stimulus is the target and making a verification.The results showed that the perceptual learning effect of trained triangle was not transferred to the untrained triangle,suggesting that perceptual learning may occur in the primary visual cortex.Moreover,the search initiation time increased after training,while the number of fixation and the fixation time decreased.Study 2 investigated the question by recording event-related potentials(ERPs)of searching for the two stimuli separately after matching the difficulty.The present results provided additional evidence for the function of the suppression is that it may terminate a shift of attention.For N1 component,the nonsalient trained stimuli had a shorter latency and larger amplitude than the physical salient stimuli whether presented as targets or distractors.It indicated that the nonsalient trained stimuli had an earlier sensory processing and greater visual attention orienting.The N2pc amplitude of the physical salient target was larger than the nonsalient trained target.This suggested that physical salient stimuli had a stronger ability to capture attention.However,when they presented as distractors,only the nonsalient trained stimuli could elicit the P_D component.Therefore,active suppression of the physical salient stimuli was more difficult than the nonsalient trained stimulus with the same difficulty.For P3component,the amplitude of physical salient stimuli was larger than nonsalient trained stimuli,both as targets and distractors,which indicated that the top-down controlled process of outcome evaluation for salient triangle was stronger.In summary,the attentional mechanism of nonsalient stimulus can improve search performance by searching for fewer locations and processing each location faster in the early and middle visual processing stages.The salient stimulus and nonsalient stimulus were processed via different neural mechanisms in the early sensory processing,attentional selection,active suppression,and the outcome evaluation process.The attention mechanism of nonsalient stimulus focuses on the relatively early cognitive processing of attention,while the attention mechanism of salient stimulus is more reflected the higher level of cognitive processing.