Hack 25. See Movement When All Is Still
2.14.3. Hacking the Hack
Originally some people thought that adaptation in the motion aftereffect may have been caused by simple fatigue of the motion-sensitive cells. We know now that this isn’t the case. Instead, the mechanism is far more interesting and far cleverer. To demonstrate, simply try the original waterfall effect, but before watching the static pattern, close your eyes for 20 seconds. Now if the effect were due to fatigue and the effect itself lasted for 10 seconds, a wait of 20 seconds should remove the effect completely. But instead, you get an aftereffect nearly as long as you would have if you hadn’t waited for 20 seconds with your eyes closed. The motion-sensitive neurons should have had time to recoverwhy are they still adapted?
They are still adapted because your baseline for motion perception hasn’t been reset (because you’ve had your eyes closed). Adaptation worked as a kind of gain control, adjusting the sensitivity of your motion perception to the new expected level of input provided by the constant motion of the waterfall.
Aftereffects are common illusions; they don’t occur just for motion. The relative activation and habituation of neurons are general features of the brain. The reason aftereffects are built into neural processing is to adjust our sensations to cancel out continuousand therefore uninformativeinformation. It operates to make us sensitive to changes around the adapted-to baseline, rather than being overwhelmed by one dominant level of input. Think about how your eyes adjust to the dark for a good example of useful adaptation that can result in an unpleasant aftereffect. Adaptation is discussed further in [Hack #26] .
2.14.4. See Also
A motion aftereffect with scrolling text (http://www.naturalhighs.net/waterfalls/illusion.htm).
A good demo and good explanation of the effect (http://psylux.psych.tu-dresden.de/i1/kaw/diverses%20Material/www.illusionworks.com/html/motion_aftereffect.html).
Mather, G., Verstraten, F., & Anstis, S. (1998). The Motion Aftereffect: a Modern Perspective. Cambridge, MA: MIT Press.
Grunewald, A., & Mingolla, E. (1998). Motion after-effect due to binocular sum of adaptation to linear motion. Vision Research. 38(19), 2963-2971.
Rees, G., Frith, C. D., & Lavie, N. (1997). Modulating irrelevant motion perception by varying attentional load in an unrelated task. Science, 278(5343), 1616-1619.
Taken From : Mind Hacks
