Abstract
40 Ss assigned stimuli consisting of square grey patches of side lengths 1 in., 1½ in., 1½ in., 1¾ in. and 2 in., into 5 categories according to perceived size. The stimuli were viewed tachistoscopically under 4 conditions of duration—625, 125, 25, and 5 msec.—and two conditions of illumination—1.00 and 0.80 log ft-L. on white. Half the Ss experienced high illumination conditions and the other half low. Pre-test training in the correct assignment of the stimulus set to the appropriate categories was given under conditions of free inspection. Data obtained from the 5-msec. treatment for both high and low illumination conditions were scaled by the graphical method of Diederich, Messick, and Tucker. The resulting scale values were interpreted as showing a constant shift in perceived size toward the smaller end of the size scale. The differences in slope and position of the graph of scale values against real size for the two illumination conditions suggest that the size shrinkage effect is a function of the interaction of illumination and duration.