Cortical processes underlying metacontrast masking across different contrast polarities

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Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Enformatik Enstitüsü, Bilişsel Bilimler Anabilim Dalı, Türkiye

Tezin Onay Tarihi: 2018

Öğrenci: ALAZ AYDIN

Danışman: MURAT PERİT ÇAKIR

Özet:

In this study a metacontrast masking experiment is conducted together with electroencephalography (EEG) recordings in order to investigate the neural mechanisms underlying visual masking phenomena. We employed a contour detection task under same and opposite target-mask contrast polarity conditions, together with varying stimulus onset asynchronies (SOA). Behavioral experiments resulted in unimodal type-A and type-B backward masking functions for opposite and same contrast polarity conditions, respectively. Relying on this difference as an indication of non-identical neural mechanisms, we collected EEG data under specific SOAs for an analysis of activation patterns under different contrast polarity masks. The behavioral results provided further evidence for sustained-transient dual-channel models of masking, specifically suggesting inhibition of on-sustained activity by off-transient activity, in accordance with previous research (Breitmeyer, 1978). Moreover, EEG analysis revealed significant differences in evoked potentials due to a change in mask contrast polarity at a short SOA of 10 ms, and compared polarity effects at two other critical SOA values of 50 ms and 200 ms.