Contrast effect
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A contrast effect is the enhancement or diminishment, relative to normal, of perception, cognition and related performance as a result of immediately previous or simultaneous exposure to a stimulus of lesser or greater value in the same dimension. (Here, normal perception or performance is that which would be obtained in the absence of the comparison stimulus - i.e., one based on all previous experience.)
Contrast effects are ubiquitous throughout human and non-human animal perception, cognition, and resultant performance. A hefted weight is perceived as heavier than normal when "contrasted" with a lighter weight. It is perceived as lighter than normal when contrasted with a heavier weight. An animal works harder than normal for a given amount of reward when that amount is contrasted with a lesser amount and works less energetically for that given amount when it is contrasted with a greater amount. A person appears more appealing than normal when contrasted with a person of less appeal and less appealing than normal when contrasted with one of greater appeal.
Simultaneous contrast identified by Michel Eugène Chevreul refers to the manner in which the colors of two different objects affect each other. The effect is more noticeable when shared between objects of complementary color.[1]
In the image here, the two inner rectangles are exactly the same shade of grey, but the upper one appears to be a lighter grey than the lower one due to the background provided by the outer rectangles.
This is a different concept from contrast, which by itself refers to one object's difference in color and luminance compared to its surroundings or background.
Successive contrast occurs when the perception of currently viewed stimuli is modulated by previously viewed stimuli.
For example, when one stares at the dot in the centre of one of the two colored disks on the top row for a few seconds and then looks at the dot in the centre of the disk on the same side in the bottom row, the two lower disks, though identically colored, appear to have different colours for a few moments.
One type of contrast that involves both time and space is metacontrast and paracontrast. When one half of a circle is lit for 10 milliseconds, it is at its maximum intensity. If the other half is displayed at the same time (but 20-50 ms later), there is a mutual inhibition: The left side is darkened by the right half (metacontrast), and the center may be completely obliterated. At the same time, there is a slight darkening of the right side due to the first stimulus; this is paracontrast.[2]
[edit] See also
[edit] References
- ^ Colour, Why the World Isn't Grey, Hazel Rosotti, Princeton University Press, Princeton, NJ, 1985, pp 135-136. ISBN 0-691-02386-7
- ^ "eye, human."Encyclopædia Britannica. 2008. Encyclopædia Britannica 2006 Ultimate Reference Suite DVD
