Attention Influences Surround Suppression:the Modulation Of Task Difficulty And Feature Process

Surround suppression is a mechanism of information integration existing across visual system levels.It refers that the appearance or sensitivity of the center target stimuli can be impaired by a similar background,which is important for edge detection,contour grouping and figure-ground segregation.As a top-down mechanism,attention also has a great effect on the information selection and integration.Does this high-level attention exert an impact on surround suppression?And is there some modulated factors?To answer the question,the study explored the effect of attention on the surround suppression in human vision through psychophysical and event-related potential experiments,and investigated the modulation of the task difficulty and feature process.In the first experiment,we measured the detection threshold for test grating after subjects adapted to the target(presented either alone or surrounded by stimuli)by adopting the contrast adaptation paradigm and two-interval forced choice task,and then obtained the surround suppression in different attentional states.We manipulated subject’s attentional state via central fixation task or target grating deflection task during adaptation,aiming to explore the effect of attention on the surround suppression.Based on this design,we found different results between skilled subjects and unskilled subjects.For the skilled subjects,attention weakened surround suppression,whereas for the unskilled subjects,attention enhanced surround suppression.As for these results,we proposed two hypotheses.One hypothesis is that the difference in subjective task difficulty between two groups affected the perception of the stimulus,and then influenced the surround suppression.The other one is that the difference in ability to resist the flicking in contrast while detecting the orientation deflection affected the process of contrast,and then influenced the suppression index.In the second experiment,we manipulated the task difficulty via staircase method,aiming to explore the modulation effect of task difficulty on surround suppression.The result showed that the increase in task difficulty reduced the surround suppression under attentional condition(attending to the target),and the change in task difficulty had on effect on suppression index under inattentional condition(attending to the fixation).In attentional condition,subjects were asked to detect the orientation change of the target,so the increase in attentional task difficulty may strengthen the process of orientation and then reduce the process of contrast.Therefore,the effect of task difficulty on surround suppression when subjects attended to the target may result from the difference in the contrast feature process under distinct sets of task difficulty.In the third experiment,we changed the attentional task in the stage of adaptation.We asked subjects to detect the target contrast change instead of orientation change,which was aimed to explore the modulation effect of contrast feature process on surround suppression.The result suggested that the reduction of surround suppression due to attention disappeared when the subjects attended to the target contrast change.Lastly,in the fourth experiment,we investigated directly the difference of target grating ERP signal under various attentional and surrounding conditions via event-related potential technique.We obtained two results.Firstly,attention weakened the surround suppression overall,manifesting the shortened time and reduced amplitude of C1、N1、P2 component in suppression signal.Secondly,comparing with the inattentional condition,the amplitude of P1 component in suppression signal was enhanced in attentional condition.In summary,our study made two conclusions.Firstly,attention had an impact on surround suppression,which was modulated by the subject’s familiarity in task,task type and contrast feature process.Secondly,when attention was directed to a dimension independent of contrast and interfered with contrast process,attention would weaken the surround suppression;while attention was directed to contrast feature,attention would not impair the surround suppression,and even strengthen the suppression index.