The Journal of Neuroscience, June 8, 2005, 25(23):5651-5656; doi:10.1523/JNEUROSCI.1084-05.2005
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Behavioral/Systems/Cognitive
Neural Basis for a Powerful Static Motion Illusion
Bevil R. Conway,1,5
Akiyoshi Kitaoka,2
Arash Yazdanbakhsh,1,3
Christopher C. Pack,4 and
Margaret S. Livingstone1
1Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, 2Department of Psychology, Ritsumeikan University, Kita-ku, Kyoto 603-8577, Japan, 3Cognitive and Neural Systems Department, Boston University, Boston, Massachusetts 02215, 4Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada H3A 2B4, and 5Harvard Society of Fellows, Harvard University, Cambridge, Massachusetts 02138
Most people see movement in Figure 1, although the image is static. Motion is seen from black
blue
white
yellow
black. Many hypotheses for the illusory motion have been proposed, although none have been tested physiologically. We found that the illusion works well even if it is achromatic: yellow is replaced with light gray, and blue is replaced with dark gray. We show that the critical feature for inducing illusory motion is the luminance relationship of the static elements. Illusory motion is seen from black
dark gray
white
light gray
black. In psychophysical experiments, we found that all four pairs of adjacent elements when presented alone each produced illusory motion consistent with the original illusion, a result not expected from any current models. We also show that direction-selective neurons in macaque visual cortex gave directional responses to the same static element pairs, also in a direction consistent with the illusory motion. This is the first demonstration of directional responses by single neurons to static displays and supports a model in which low-level, first-order motion detectors interpret contrast-dependent differences in response timing as motion. We demonstrate that this illusion is a static version of four-stroke apparent motion.
Key words: directional; prestriate; receptive field; striate cortex; primate; visual motion
Received March 19, 2005;
revised May 3, 2005;
accepted May 7, 2005.