BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Talks.cam//talks.cam.ac.uk// X-WR-CALNAME:Talks.cam BEGIN:VEVENT SUMMARY:“Dependence of visual evoked potentials on discrimination task d ifficulty and stimulus presentation time” - Tatiana Selchenkova\, I. P. Pavlov Institute of Physiology\, St. Petersburg DTSTART:20100224T130000Z DTEND:20100224T140000Z UID:TALK22977@talks.cam.ac.uk CONTACT:John Mollon DESCRIPTION:The aim of the research was to find electrophysiological corre lates of the discrimination of a new class of images and to estimate the t emporal characteristics of this process. Three types of matrices differing in the number of Gabor patches with vertical and horizontal orientation w ere 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 pred ominant orientation of the stimuli. One group of participants recognized s timuli 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 t he 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 occipi to-temporal area and P180 in fronto-central area for participants who did n't recognize stimuli with short duration in comparison with the other gro up. The analysis of VEPs indicates that early stages of image processing c an provide later a successful pattern recognition. LOCATION:Kenneth Craik Room\, Craik-Marshall Building\, Downing Site END:VEVENT END:VCALENDAR