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Davis M. Glasser, Duje Tadin; Lower temporal limit for generation of the motion after-effect. Journal of Vision 2008;8(17):56. doi: 10.1167/8.17.56.
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The motion after-effect (MAE) is generally observed after prolonged inspection of a moving stimulus. However, neurophysiological studies have reported adaptation effects following briefly presented stimuli (e.g., Müller et al., 1999). The putative functional roles of this rapid adaptation are improved coding efficiency and increased discriminability. Here, we investigated whether psychophysical adaptation effects can be observed at such brief timescales.
Observers viewed a large, high-contrast adapting grating presented for 67ms (1c/deg, 15deg/s, temporal sum of contrast was 0, precluding afterimage generation). This exposure duration was below the motion discrimination threshold, likely because of suppressive center-surround interactions (Tadin et al., 2003). Importantly, this ensured that observers did not know the expected direction of the MAE. Nevertheless, when presented with a stationary test stimulus, observers reported perceiving illusory motion opposite to the adapting motion. This was observed for adaptor-test ISIs of 0ms, 150ms, 400ms, but not for 1000ms.
In supporting experiments, we showed that this rapid MAE exhibits partial interocular transfer and spatial frequency tuning. Interestingly, removing the test stimulus and shortening adaptor duration (in order to generate a negative afterimage) also yielded a perceivable MAE for adaptor presentations as short as 25 ms. Finally, MAE was observed even when the adapting stimulus was completely suppressed during continuous flash suppression (CFS) although longer adaptation duration was required in this case.
In summary, we found that adaptation to brief moving stimuli yields perceivable MAEs, even when adaptation duration is below threshold. Evidently, the MAE is not merely a perceptual illusion that follows prolonged exposure to a moving stimulus, but rather a process that can occur essentially every time we experience motion.
MüllerJ. R.MethaA. B.KrauskopfJ.LennieP. (1999). Rapid adaptation in visual cortex to the structure of images. Science, 285, 1405–1408.
TadinD.LappinJ.S.GilroyL.BlakeR. (2003) Perceptual consequences of center-surround antagonism in visual motion processing. Nature, 424, 312–315.
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