The Chubb illusion is an optical illusion wherein the apparent contrast of a patterned object varies dramatically, depending on the context of the presentation.
The Chubb illusion, as well as numerous other visual and perceptual illusions, provide a valuable way to investigate how the eye and brain process visual information. Equally, they are used by artists for visual effect, entertaining and satisfying the endless fascination human beings have with novelty and creativity.
The phenomenon was first observed by Charles Chubb and colleagues Sperling and Solomon, who published their findings in the December 1989 edition of Proceedings of the National Academy of Sciences USA in an article entitled "Texture interactions determine perceived contrast".
To illustrate the Chubb illusion, a circle of low contrast texture or pattern is placed in two different fields. When placed in a plain gray field, the circle appears to have more contrast than when it is placed in a field that surrounds it with high contrast texture or pattern.
The lower contrast image is perceived to be higher contrast when placed in front of a gray background because the gray background is more ambiguous than the high contrast background. The brain is used to interpreting images that are subject to "imperfect transmittance"; viewing objects from a distance, through fog, or through water or glass are examples of imperfect transmittance. In these cases, the brain compensates for the lower levels of light that actually fall upon the retina in an attempt to judge the true colors or contrast of the object. When placed in front of a gray background, the contrast pattern seems more high contrast because the ambiguous gray background causes the brain to interpret the image using imperfect transmittance. With the high contrast background, it is more obvious that there is nothing hindering the transmittance of light from the image, and the brain perceives the image more accurately.
The study of the Chubb illusion is a useful tool that helps neuroscientists understand the relationship between vision and perception.
- Chubb C., Sperling G., and Solomon J.A. "Texture interactions determine perceived contrast." Proceedings of the National Academy of Sciences USA. 1989, 86(23):9631-5. PMID 2594791.
- Lotto, R.B. and Purves, D. "An Empirical Explanation of the Chubb Illusion" Journal of Cognitive Neuroscience, 2001. Vol. 13, Number 5. Retrieved October 30, 2007.
- Chubb C., Sperling G., and Solomon J.A. "Texture interactions determine perceived contrast." Proc Natl Acad Sci USA. 1989 Dec. 86(23):9631-5. PMID 2594791.
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