A Further Investigation of Apparent Size and Retinal Size as Determinants of the Figural After-Effect

Abstract

A figure which is more distant from the eye than another but subtends the same visual angle is usually seen as the larger. This phenomenon is called perceptual size constancy. Experiments have been reported which show that sometimes the apparent and sometimes the retinal sizes of the stimulus figures determine the direction of the figural after-effect. These experiments are reviewed and two further experiments are reported. In the first experiment two types of stimulus figure (discs and annuli) which subtended a visual angle of 1° 36′ resulted in figural after-effects, the direction of which would have been predicted by the retinal sizes of the figures. In the second experiment larger figures were used which subtended a visual angle of about 4° and which were the same as those used by Sutherland (1954). In this experiment the after-effects were generally in a direction which would have been expected if apparent size determined the direction of the after-effect. In the interpretation of the results attention is drawn to the “Central Tendency Effect” which has been observed in size judgements of stimulus figures of varying size. Two hypotheses are suggested; one is that the true figural aftereffect has been obscured by the “Central Tendency Effect” in successive judgements, and the other is that time error in successive judgements of size is essentially a figural aftereffect. Some supportive evidence for the latter hypothesis is reported. It is concluded that apparent size is not a critical determinant of the figural after-effect.