FIGURAL AFTEREFFECTS

There are two principal types of aftereffect: the apparent distortion of a figure following prolonged inspection, and the effect of inspection of one figure on the perception of a subsequent figure. A single experiment will illustrate both of these phenomena. If you stare at a curved line for several moments it will tend to appear less curved than it was at first; and if you look at a straight line immediately afterward, it will appear to be curved in the direction opposite to the original curved line (Gibson, 1933). The extent of figural aftereffects increases with the amount of exposure to the first figure, beginning with an exposure of two to five seconds anTEShing a maximum after about one minute. Under certain conditions the effects of prolonged exposure to the first stimulus have lasted for several months.Figural aftereffects are not easy to explain. One theory holds that the brain area which deals with the original stimulus becomes “satiated” or “fatigued” through prolonged inspection, and another area comes into play. The figure then appears to be different because a different part of the brain decodes the message. There is conclusive evidence that figural aftereffects are a function of a brain mechanism rather than a product of activity occurring in the retina: when the first figure is viewed by one eye and the second viewed by the other, the effect is still obtained. Aftereffects have been demonstrated in sense modalities other than vision. If you pass your hand over a curved surface a number of times and then stroke a straight surface it will appear to be curved in the opposite direction. This is termed tactile-kinesthetic aftereffect.