Abstract
The N200 amplitude of the motion-onset VEP evoked by a parafoveal grating of variable contrast (0.5-64%), constant speed (2degrees/ s), direction (horizontally rightward), and spatial frequency (2 cpd) was studied before and after adaptation to a stationary or drifting grating (1, 2, or 4degrees/s rightward or leftward). These results are compared to those for the pattern-appearance VER ...
Abstract
The N200 amplitude of the motion-onset VEP evoked by a parafoveal grating of variable contrast (0.5-64%), constant speed (2degrees/ s), direction (horizontally rightward), and spatial frequency (2 cpd) was studied before and after adaptation to a stationary or drifting grating (1, 2, or 4degrees/s rightward or leftward). These results are compared to those for the pattern-appearance VER Psychophysical measurements were made simultaneously of the perceived speed. While iso-directional (rightward) adaptation leads to a mean amplitude reduction of 39%, the decrease after counter-directional adaptation has a size of 20%. The post-adaptation matches of perceived speed differ in dependence on the iso-directional adapting speed and decrease on average to 98%, 85%, and 69% of the pre-adapt perceived speed after 1, 2, and 4degrees/s adapting speeds, respectively. The perceived speed is moderately reduced (83% of the pre-adapt value) after counter-directional adaptation nearly independently of the adapting speed. A model of velocity processing is presented, which enables us to predict the trends of the experimental motion VEP and perceived speed data. (C) 2004 Elsevier Ltd. All rights reserved.
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