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“Dependence of visual evoked potentials on discrimination task difficulty and stimulus presentation time”

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The aim of the research was to find electrophysiological correlates of the discrimination of a new class of images and to estimate the temporal characteristics of this process. Three types of matrices differing in the number of Gabor patches with vertical and horizontal orientation were used in our study. The stimuli were presented for 30, 60, 130, 250, 500, 1000 ms against a background of the random matrices. The subject’s task was to discriminate the predominant orientation of Gabor elements in the matrix. Subjects differed in their ability to discriminate the predominant orientation of the stimuli. One group of participants recognized stimuli of all durations including stimuli shown for 30, 60 ms. The other group of subjects began to discriminate stimuli at a presentation time of 130 ms. The amplitude of the late positive component P300 recorded from the occipito-temporal area was greater for the stimuli with short duration, from 30 to 130 ms, for the group of participants that recognized short presented stimuli. The total amplitude of all components of visual evoked potentials (VEP) recorded from the occipital area for this group was also greater. We found an increase of latency of early components P90 in occipito-temporal area and P180 in fronto-central area for participants who didn’t recognize stimuli with short duration in comparison with the other group. The analysis of VEPs indicates that early stages of image processing can provide later a successful pattern recognition.

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