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William Curran, Christopher P. Benton; The dynamic motion aftereffect is driven by local motion adaptation. Journal of Vision 2005;5(8):149. doi: 10.1167/5.8.149.
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© ARVO (1962-2015); The Authors (2016-present)
The motion aftereffect (MAE) takes two forms - the static and dynamic MAE. Differences in their characteristics point to separate mechanisms underlying the static and dynamic MAE (dMAE), leading to speculation that they reflect neural adaptation in areas V1 (which encodes local motion) and MT/V5 (which encodes global motion), respectively. We tested whether the dMAE is driven solely by adaptation of global motion detectors, or whether local motion detector activity contributes to the effect. Our first experiment measured the speed tuning of the dMAE. Observers adapted to two displays on either side of fixation - a random dot pattern moving upwards, and a noise pattern in which all dots took a random walk (0% motion coherence). Following adaptation the stimuli were replaced with a 0% motion coherence and a 35% motion coherence stimulus moving upwards, respectively. The task was to judge which stimulus - the resultant dMAE or the 35% motion coherence stimulus - had the greater apparent speed. Dot speed was identical in both the adapting and test stimuli, and observers were tested over a range of speeds. The results revealed an inverted U-shaped speed tuning function. We repeated the experiment, but this time kept dot speed in the dMAE test stimulus constant while varying speed in the adapting stimuli and vice versa. If perceived speed of the dMAE is driven solely by adaptation of global motion detectors, then speed of the adapting stimulus - but not the test stimulus - will be responsible for the MAE's speed tuning. This is because the adapting stimulus is rich in global motion information. The test stimulus, on the other hand, does not contain any global motion information, but is rich in local motion information. Our data reveal that dMAE speed is determined solely by the characteristics of the test stimulus. We conclude that the dMAE is driven by neurons involved in local-motion processing, activity that is primarily associated with area V1.
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