Infants perceive two-dimensional shape from horizontal disparity.

Previous studies observed that responsiveness to horizontal disparity as such emerges at approximately 2 months of age. Moreover, 3- to 4-month-old infants utilize stereoscopic information to perceive object variations in depth. The present study investigated infants' ability to respond to crossed horizontal disparity information that defines two-dimensional shape. Infants 4 and 5 months of age were habituated to either a cross or the outline of a square. During the posthabituation period, they were presented with both shapes. The stimuli were dynamic random dot stereograms shown on an autostereoscopic monitor. The participants 5 but not 4 months of age displayed significant novelty preferences for the unfamiliar shape during the posthabituation period. Five-month-old infants are hence sensitive to horizontal disparity information that specifies shape.