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Abstract: Convergence of the eyes was controlled by means of polaroids as in a previous experiment. 22 subjects made size judgments of 5 stimuli presented at various distances in a 5 m long light-tight box. The results indicated:1. With stimulus distance held constant and varying only convergence, perceptual size increases with increasing converged distance and decreases with decreasing converged distance. But the perceptual size caused by convergence changes does not fully correspond to the predicted size which subtends a constant visual angle at various converged distances.2. With convergence held constant and varying only stimulus distance, changes in perceptual size mainly follows the law of retinal image, thus the break down of size constancy can be observed. This has been verified both with stimuli of the same physical size and stimuli subtending the same visual angle at various distances.3. Monocular observation yielded results that lie between normal binocular observation and observation with convergence held constant.4. Size judgments of one-eyed persons follows the law of retinal image, i.e., they show no size constancy. This result is consistent with the result of normal subjects with convergence held constant.5. It is suggested, when an object approaches the observer, under normal observation, inflation of the retinal image is being counter-balanced by a size reduction process due to Convergence. Probably, kinesthetic impulses from the eye muscles fed back into the brain furnish a cue for distance which reflexively modulated size perception and make size constancy possible.

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