Seminar "Surround suppression effect in human early visual cortex contributes to illusory contour processing: MEG evidence"

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Centre for Cognition & Decision Making invites you to a seminar on 05.03.2015:

«Surround suppression effect in human early visual cortex contributes to illusory contour processing: MEG evidence»
by Boris Chernyshev, Ph.D., Laboratory of Cognitive Psychophysiology, National Research University Higher School of Economics, Department of Higher Nervous Activity, Lomonosov Moscow State University.

Illusory contours have been extensively used for the investigation into the internal nature of visual processing. A large body of evidence demonstrates that lateral occipital complex is the most critical node responsible for the IC detection. Yet presently there is no agreement on the role of the early visual cortices in detection of illusory contours such as Kanizsa figures, and the sign of their potential involvement is not clear. Collateral luminance borders, which are present in Kanizsa figures, may evoke iso-orientation surround suppression in V1 leading to the reduction in the initial response to Kanizsa figures compared with controls. We attempted to find the direct evidence, as well as localisation and timing of early suppression effect produced by Kanizsa square in adult non-clinical human participants. We used two sizes of stimuli in order to test the validity of the effect at two different levels of eccentricity; the stimuli sized 4.5° and 9.0° were presented to the participants centrally in passive viewing conditions. By applying strict spatial and temporal restrictions as well as using threshold-free cluster enhancement technique followed by permutation statistics, we were able to detect the inverted illusory contour effect – relative suppression of the response to the Kanizsa figure compared with the control stimulus within the 40-120 ms time window after the stimulus onset, which was located mostly in V1. In view of the current literature, the current finding is highly compatible with the explanation involving iso-orientation surround suppression to collinear borders. The effect may be related to the principle of "sparse" coding, according to which V1 suppresses representations of inner parts of collinear assemblies as being informationally redundant. Such a mechanism is likely to be an important step preceding shape recognition.

Date: 05.03.15
Time: 15.00
Address: Volgogradsky Prosp., 46B
Room: 109

If you need a pass to the HSE, please contact Anastasia Plotnikova via email: aplotnikova@hse.ru
mobile +7 (963) 767-60-70

Дата

5 марта, 2015 г. 15:00

В статье упомянуты

Департамент психологии