Two experiments are described whose aim was to investigate whether perception of size at birth is determined solely by proximal (retinal) stimulation, or whether newborn babies have the ability to perceive an object's real size across changes in distance. In Experiment 1, preferential looking between pairs of stimuli which varied in real size and viewing distance was found to be solely determined by retinal size, suggesting that changes to proximal stimulation can have profound effects on newborns' looking behavior. However, in Experiment 2 newborns were desensitized to changes in distance (and retinal size) during familiarization trials, and subsequently strongly preferred a different sized object to the familiar one, suggesting that the real size had been perceived as constant across the familiarization trials. These results confirm Granrud's (1987) findings that size constancy is present at birth. o 1990 Academic press. 1~.One organizing feature of perception which contributes to the perceived stability of the visual world is size constancy, that is, seeing an object as its real size despite changes that occur to the size of its retinal image as its viewing distance from an observer varies. It seems certain that size constancy is present at some point in infants' visual perception, but exactly when, and whether learning and experience are required for its development, are not fully known. Evidence for size constancy in early infancy was reported by Bower (1964Bower ( , 1966. Eight-week-old infants were conditioned to give head turns when a 30-cm cube was presented 1 m away; and they subsequently gave more conditioned responses to the same-size cube at a distance of 3 m, whose retinal image was onethird the size of the training stimulus, than to a 90-cm cube at 3 m, whose retinal image size was the same as the training stimulus. The data

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