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Albert Yonas, Carl E. Granrud, John Grittner; Size-distance perception based on ocular convergence angle in 3- to 5-year-old children. Journal of Vision 2006;6(6):733. doi: 10.1167/6.6.733.
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Changes in convergence angle affect the perceived size and distance of objects whose actual size and distance remain constant. With increased convergence angle, observers consistently perceive decreased object size and distance. With decreased convergence angle, observers perceive increased object size and distance. Although these effects are well established in adults, they had not been investigated previously in children. This study tested 3- to 5-year-old children and college-aged adults. Participants viewed a stimulus object, whose size and distance remained constant, through a mirror stereoscope, whose mirrors could be rotated to manipulate convergence angle. Each participant received 8 trials: 4 in which convergence angle increased and 4 in which it decreased. Convergence angle had similar effects on perceived size and distance in children and adults. Participants in both age groups consistently reported that the object appeared to move closer and become smaller when convergence angle increased, and appeared to move farther away and grow larger when convergence angle decreased. In addition, magnitude of change in perceived size was similar in the two age groups. These results suggest that an unconscious inference-like process, that takes distance cues into account in perceiving size, operates in young children as well as in adults. Previous studies have found substantial differences between children and adults in size constancy performance. This study's findings are consistent with the hypothesis that the same perceptual mechanisms govern size perception in children and adults, and that age-related changes in size constancy performance result from cognitive, not perceptual, development.
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