| Purpose:Concentric visual field defects directly affect the input of visual information and then affect the high-level processing of the brain.Based on the analysis of the electroencephalogram activity that simulated different concentric visual field defects,the characteristic changes of concentric visual field defects are revealed from two perspectives:time domain and frequency domain,to provide feasible indicators for objective forensic identification of visual field defects.Methods:Forty healthy subjects were recruited from Soochow University to perform a target stimulus discrimination task based on the visual oddball paradigm.The standard stimulus was a high contrast black and white checkerboard stimulus.The target stimulus was a black disk superimposed on the center of the black and white checkerboard stimulus,which was used to simulate the concentric visual field defect.The radii of the black disks varied from 5,10,20,and 30 degrees in visual angle.The distractor stimulus was a checkerboard disk with a radius of 10 degrees superimposed on the center of the black disk.The subjects were required to identify the target stimulus in a series of stimulus streams and make responses to the target stimulus by pressing buttons.Meanwhile,the behavioral data were recorded and the event-related electroencephalogram data were collected.Results:Concentric visual field defects significantly affected the visual discrimination task of the subjects,especially when the 30-degrees concentric visual field defect,the subject’s reaction time significantly increased and the accuracy rate significantly decreased.Event-related potential(ERP)results showed as follows:(1)The standard stimuli only induced the early exogenous ERP components,and P1,N1,and P2 components were mainly located in the tempo-occipital region;(2)The target stimuli not only induced the exogenous ERP components,but also induced the endogenous ERP components,and the average amplitudes of the target-elicited P1,P2,and P3 components decreased as the degree of concentric visual field defect increased;(3)The deviation between the standard stimuli and the target stimuli elicited a significant vMMN component,and its average amplitude increased as the degree of concentric visual field defect increased.Event-related oscillation(ERO)results showed as follows:(1)The target stimuli that simulated the concentric visual field defects elicited the significant power changes in the theta band(4-8Hz)and alpha band(8-12Hz),in which the alpha band was subdivided into the low alpha band(8-10Hz)and high alpha band(10-12Hz);(2)Different degrees of concentric visual field defects had the significant effects on the total,induced and phase power in the theta band.Total and induced power were mainly closely related to the 30-degrees visual field defects,while phase power was mainly related to the 20-degrees visual field defects;(3)Different degrees of concentric visual field defects had a significant impact on the total and induced power in the low alpha band,which was mainly related to the 10-degrees visual field defects;(4)Different degrees of concentric visual field defects had significant effects on the total,induced and phase power in the high alpha band,which was mainly related to the 5-degrees visual field defects.Conclusion:Concentric visual field defects not only affected the behavior of simple visual discrimination but also affected the brain processing of visual information.Event-related potential characteristics mainly revealed the time process of the different concentric visual field defects,from the early perception processing based on visual features to the late cognitive process based on attention resource allocation.Event-related oscillation characteristics highlighted the close connection between the different concentric visual field defects and the brain oscillatory activity in various frequency bands,to some extent,providing a feasible indicator for the assessment of the magnitude of different concentric visual field defects. |
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