Cortical processes underlying metacontrast masking across different contrast polarities

Aydın, Alaz
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.


Visual object representations: effects of feature frequency and similarity
Eren Kanat, Selda; Hohenberger, Annette Edeltraud; Department of Cognitive Sciences (2011)
The effects of feature frequency and similarity on object recognition have been examined through behavioral experiments, and a model of the formation of visual object representations and old/new recognition has been proposed. A number of experiments were conducted to test the hypothesis that frequency and similarity of object features affect the old/new responses to test stimuli in a later recognition task. In the first experiment, when the feature frequencies are controlled, there was a significant increas...
Visually impaired can watch films, too: assessing the effects of audio description via film narrations
Zengin Temırbek uulu, Zeynep; Sağın Şimşek, Sultan Çiğdem; Department of English Language Teaching (2019)
This study aims to assess the efficiency of audio description which is a tool for visually impaired individuals while watching live or recorded performances. This tool enables these individuals to gain more from what they encounter as a voice describes settings, characters as well as events and some simple actions that are important. This unique research not only provides a first assessment of a tool generated for better learning and understanding but also is important in the way that it provides an insight...
Cortical processes underlying the effects of static sound timing on perceived visual speed
Kaya, Utku; Kafaligönül, Hulusi (Neuroimage, 2019-10-01)
It is well known that the timing of brief static sounds can alter different aspects of visual motion perception. For instance, previous studies have shown that time intervals demarcated by brief sounds can modulate perceived visual speed such that apparent motions with short auditory time intervals are typically perceived as faster than those with long time intervals. Yet, little is known about the principles and cortical processes underlying such effects of auditory timing. Using a speed judgment paradigm ...
Evaluation of visual quality metrics
Ölgün, Ramazan Ferhat; Akar, Gözde; Department of Electrical and Electronics Engineering (2011)
The aim of this study is to work on the visual quality metrics that are widely accepted in literature, to evaluate them on different distortion types and to give a comparison of overall performances in terms of prediction accuracy, monotonicity, consistency and complexity. The algorithms behind the quality metrics in literature and parameters used for quality metric performance evaluations are studied. This thesis also includes the explanation of Human Visual System, classification of visual quality metrics...
Acute effects of local vibration on muscle performance at different durations and frequencies
Yıldırım, Ahmet; Korkusuz, Feza; Department of Physical Education and Sports (2010)
The purpose of the present study was to investigate the acute effects of local vibration on muscle performance at different durations and frequencies. Fifteen male handball players participated in the study voluntarily. University’s Ethics Committee approved the study and the informed consent forms were filled by all participants. Different vibration durations, (10 sec, 1 min, 10 min), different frequencies (40 and 80 Hz), dominancy (dominant and non-dominant) and conditions (vibration and no-vibration) wer...
Citation Formats
A. Aydın, “Cortical processes underlying metacontrast masking across different contrast polarities,” M.S. - Master of Science, Middle East Technical University, 2018.