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Davis M. Glasser, James Tsui, Kevin C. Dieter, Christopher C. Pack, Duje Tadin; Psychophysics and neurophysiology of the rapidly generated MAE. Journal of Vision 2009;9(8):676. doi: 10.1167/9.8.676.
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© ARVO (1962-2015); The Authors (2016-present)
Previously, we reported that 67ms of motion adaptation is sufficient to generate perceivable static MAEs, even when subjects are unable to discriminate the adapting motion direction (Tadin & Glasser, VSS2008). This finding indicates that the MAE is not merely an illusion that follows prolonged motion exposure, but rather a process that can occur every time we see motion. Here, our aims are to (1) test whether the rapid MAE exhibits the same stimulus tuning as the conventional MAE and (2) investigate whether MT neurons exhibit adaptation on the same brief timescale as the rapid MAE.
(1) Psychophysics: To obtain stimulus tuning of the rapid MAE (200ms adaptation), subjects rated perceived MAE strength for various combinations of adapting and stationary test stimuli. Notably, we found that for high-contrast adapting stimuli, MAE strength decreased with test contrast, increased with adaptation speed and exhibited partially low-pass tuning to the adaptor spatial frequency. Size tuning was relatively flat except for the smallest sizes.
(2) In parallel experiments, we measured perceived MAE duration using conventional adapting stimuli (30s adaptation, 10s top-ups). Except for the adapting duration, all stimulus parameters were identical to the rapid MAE measurements. Results revealed that, despite a 100-fold difference in adaptation duration, tuning of the rapid MAE mirrored that of the conventional MAE. This finding suggests that conventional and rapid MAEs likely share underlying neural correlates.
(3) Neurophysiology: Motion adaptation was measured for a population of MT neurons in alert macaques. Adapting stimulus was a high-contrast Gabor patch presented for 67ms, with speed, spatial frequency and size set to each neuron'
s preferred values. Adaptation was followed by a 400ms stationary test stimulus (3% contrast). We found that neural responses following null-direction adaptation were significantly stronger than following preferred-direction adaptation; a result suggesting a possible neural correlate for rapidly generated static MAEs.
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