Abstract

The phenomenon of size constancy is defined as the apparent perceptual invariance of the linear dimensions of a seen object as this approaches the eye or recedes from it. It has been interpreted as resulting from the application by the brain of a size correction, made possible by the subject's apprehension of distance cues present in the image. We present several observations which, by dissociating accommodation from distance of the seen object and by suppressing the optic effects of accommodation on the visual image itself, show that this interpretation is incorrect, and that in fact the size correction of the visual image is a function of the central effort of accommodation, not of the distance of the seen object.