Fine orientation discrimination and shape constancy in young infants.

The present study aimed to investigate simultaneously fine orientation discrimination and shape constancy in young infants. The design employed two variants of the habituation paradigm. Infants in one group were habituated to a single orientation (5 or 15 degrees) of a single stimulus presented repeatedly, and they were then tested with the complementary orientation (15 or 5 degrees). Infants in a second group were habituated to several orientations (5, 10, and 15 degrees) of the same stimulus, and they were then tested with a familiar orientation of the stimulus, with two novel orientations of the same stimulus, and with a new stimulus. Between-groups comparison showed that infants habituated more efficiently to re-presentations of a single orientation than to multiple orientations of the same stimulus, providing evidence of fine orientation discrimination; posthabituation comparison within the single-orientation group confirmed that infants discriminated small orientation changes. Posthabituation comparison within the multiple-orientation group showed that infants generalized over novel orientation changes of the familiar stimulus though they discriminated change to a novel stimulus. Cumulatively, the results of this study demonstrate that under one set of conditions young infants show sensitivity to relatively fine variations in pattern orientation, but that under a different set of conditions young infants give evidence of shape constancy with the same patterns.