AFTERIMAGE (Aftersensation)

A sensation that arises out of another sensation immediately after the original stimulation ceases. A positive afterimage is a continuation of the original sensation. A negative afterimage is its opposite in hue or brightness. Negative afterimages are the more commonly observed type, since they are usually more intense and lasting than positive afterimages (COLOR PLATE 3).Positive afterimages are most vividly experienced in a relatively dark surrounding after intense stimulation. One way to produce them is to look directly at the setting sun for a moment, then immediately close your eyes. Another way is to switch off a brightly lighted television program and keep looking at the tube. A positive afterimage is only fleetingly observed, and is automatically replaced by the comparatively long-lasting negative afterimage.Negative color afterimages are the complementary of the original stimulus. If you stare at a small square of yellow paper until the borders take on a bluish tinge and the yellow begins to fade, then look at a sheet of white paper, a patch of blue color will be clearly visible, since blue is complementary to yellow. The duration and vividness of the afterimage depends on the intensity of the color and the area it covers as well as the time spent in viewing it. It is also affected by the illumination and composition of the second surface. If we quickly turn our eyes from one surface to another, the afterimage will move with our gaze. Its size will depend on the location of the surface we fixate. If the surface is nearby, the image will appear small; if it is at a distance, the image will be larger.A negative afterimage will mix with color according to the regular laws of color mixture—for example, a blue afterimage projected onto orange paper will produce a red-purple hue. Moreover, if we look at a surface of a particular hue and then gaze at its complementary, this color will appear more saturated than it would normally be. In fact, this is believed to be the only way to obtain the fullest possible saturation.Negative afterimages can sometimes have disturbing effects. If we look briefly at a brilliant light while driving a car, we may experience a distracting and dangerous blackout for a moment. If we wear a bright-hued sweater while reading, the book may take on an annoying complementary hue. Aftereffects can be so pronounced that artists, decorators, and house painters must be careful not to let them interfere with their judgment in selecting and mixing colors.