Motion aftereffect

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The motion after-effect (MAE) is a visual illusion experienced after viewing a moving visual stimulus for about a minute and then looking at stationary stimulus. The stationary stimulus appears to move slightly for about 15 seconds, opposite to the direction of the original (physically moving) stimulus. The motion aftereffect is believed to be the result of motion adaptation.

For example, if one looks at a waterfall for about a minute and then looks at the stationary rocks at the side of the waterfall, these rocks appear to be moving upwards slightly. The illusory upwards movement is the motion aftereffect. This particular motion aftereffect is also known as the waterfall illusion.

Another example can be seen when one looks at the center of a rotating spiral for several seconds. The spiral can exhibit outward or inward motion. When one then looks at any stationary pattern, it appears to be moving in the opposite direction. This form of the motion aftereffect is known as the spiral aftereffect.

Media:Illusion_movie.ogg Example movie which produces distortion illusion after you watch it and look away.

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[edit] Explanation

Neurons coding a particular movement reduce their responses with time of exposure to a constantly moving stimulus; this is neural adaptation. Neural adaptation also reduces the spontaneous, baseline activity of these same neurons when responding to a stationary stimulus (see, for example, Barlow & Hill, 1963; Srinivasan & Dvorak, 1979). One theory is that perception of stationary objects, for example rocks beside a waterfall, is coded as the balance among the baseline responses of neurons coding all possible directions of motion. Neural adaptation of neurons stimulated by downwards movement reduces their baseline activity, tilting the balance in favour of upwards movement.

[edit] History

Aristotle (approx. 350 B.C.) reported illusory movement after viewing constant movement, but did not specify its direction. The first clear specification of the motion aftereffect was by Jan Evangelista Purkyně (1820) who observed it after looking at a cavalry parade. Robert Addams (1834) reported the waterfall illusion after observing it at the Falls of Foyers in Scotland. According to Verstraten (1996) the term waterfall illusion was coined by Thompson (1888).

[edit] See also

[edit] References

  • Addams, R. (1834). An account of a peculiar optical phænomenon seen after having looked at a moving body. London and Edinburgh Philosophical Magazine and Journal of Science, 5, 373–374
  • Aristotle (approx. 350 B.C.) Parva Naturalia.
  • Barlow, H. B., & Hill, R. M. (1963). Evidence for a physiological explanation of the waterfall illusion. Nature, 200, 1345-1347.
  • Purkinje JE (1820) Beiträge zur näheren Kenntniss des Schwindels aus heautognostischen Daten. Medicinische Jahrbücher des kaiserlich-königlichen österreichischen Staates, 6, 79–125.
  • Srinivasan, M. V., & Dvorak, D. R. (1979). The waterfall illusion in an insect visual system. Vision Research, 19, 1435-1437.
  • Thompson, P. (1880). Optical illusions of motion. Brain, 3, 289-298.
  • Verstraten, F. A. J. (1996). On the ancient history of the direction of the motion aftereffect. Perception, 25, 1177-1188.

[edit] Bibliography

  • Mather, G., Verstraten, F., & Anstis, S. (1998). The motion aftereffect: A modern perspective. Cambridge, Mass: MIT Press

[edit] External links

  • "Neave Strobe" - an example of this effect (enable javascript to view).