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| Paper IPM / Cognitive / 8974 |
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| Abstract: | |||||||
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Topographic organization of the motion aftereffect was measured on small
test stimuli after adaptation to motion. The stimuli were random dots
embedded in a 969 grid. In each adaptation trial, the dots in the central 565
grid holes were coherently moving in one direction for 5 s. After adaptation, a
small random dot pattern filling one of the randomly selected grid holes was
presented moving at various speeds for 0.2 ms. the subjects' task was to
report perceived direction of the test stimulus by pressing one of two keys on
the keyboard. The subjects' accuracy in direction discrimination was plotted
as a function of test stimulus speed. Psychometric function shift in adapted
trials compared to the non-adapted control condition was measured with fitted
logistic curves. The shift value was defined as the strength of the motion
aftereffect (MAE). To provide a fine topographic map of MAE we measured its
strength for all grid holes. We found that this strength is highest in the internal
edge of the adaptation area, parallel to the motion direction (p < 0.03). We
also found a small positive aftereffect in background areas adjacent to the
adaptation area. This background effect was asymmetrically stronger in areas
in the direction of motion.
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