Study On The Regulation Of Frontal Lobe And Parietal Lobe On Distractor Suppression In Visual Search

Visual search is one of the basic cognitive activities of human beings.The study suggests that the frontal cortex is involved in regulating visual search.Visual search mainly includes two different mechanisms of target enhancement and distractor suppression.Most of the previous studies focused on the target enhancement mechanism.We mainly studied the neural mechanism of distractor suppression with prior knowledge of distractor substances.In this study,Transcranial Magnetic Stimulation(TMS)and Magnetic Resonance Imaging(MRI)were used to investigate the modulation of the frontal and parietal cortex in visual search.We have designed visual search tasks with prior knowledge(cue)of distractor and no prior knowledge(uncued)of distractor.The tasks are mainly divided into Distractor location cue(DC)and Distractor location uncued(UC).In addition,the color of the distractor is divided into white or color(green and red).We found that the location of the distractor accelerated the response.TMS stimulation of the dorsolateral prefrontal cortex(DLPFC)increased the search response of the subjects under UC conditions during the online search,and the effect was stronger when the color of the distractor was white,but there was no influences of TMS stimulation to the DLPFC during search for DC conditions.Furthermore,when TMS stimulation was administered prior to the search screen presentation it did not affect the search response.TMS stimulation of posterior parietal cortex(PPC)did not affect the search response during the online search screen.Based on these results,we speculate that DLPFC is associated with distractor suppression which commences after the search screen is presented.Hence,a prior knowledge of distractor may reduce the activity of DLPFC.In this study,we did not find evidence supporting the role of PPC in visual search.In order to investigate the different influence of the prior knowledge of the distractor and the target on the search,this experiment adds the target location cue(Target location cue,TC)condition,to the previous conditions(DC and UC)in the initial experiment.While performing the task,we scanned the structure and functions of the frontal and parietal region using MRI in other to study the functions of the aforementioned regions during visual search.Hence,we observed that the response of DC and TC is faster than that of UC task,indicating that the prior knowledge of the location had effect on the distractor suppression and the target search.The sMRI data analysis showed that the gray matter density of the mid-frontal gyrus was positively correlated with the location effect of the distractor,but negatively correlated with the location effect of the target.The fMRI data showed that the frontal,occipital and marginal lobules had different degrees of activation under the three task conditions.Furthermore,the rate change of the signal in the right middle temporal gyrus under UC task,the left precuneus and the right middle frontal gyrus under the TC task was negatively correlated with behavioral performance.These findings suggest that the frontal and parietal region participates in visual search,and that the middle frontal gyrus may participate in the modulation of visual search by prior knowledge.In addition,DLPFC might be involved in distractor suppression which tends to commence work after the search screen is presented,but prior knowledge of the distractor may reduce the activity of the DLPFC.In summary,under the suppression of distractor substances,multiple brain regions participate in the modulation.