Stereopsis Development in Human Infants: Sensitivity to Relative Versus Absolute and Horizontal Versus Vertical Disparity Using Sweep SSVEPs

摘要

Stereopsis is the primary cue underlying our ability to make fine depth judgments. In adults depth is perceived only for horizontal rather than vertical disparities, and depth discriminations are supported primarily by relative rather than absolute disparity. Although human infants begin to exhibit disparity responses between three and five months of age (Norcia & Gerhard, in press), it is not known how sensitivity profiles to the different types of disparity develop. Two possibilities are: 1) like adults, even young infants already rely primarily on relative and horizontal disparities, 2) infants are first sensitive to absolute disparities of either orientation and only later develop an adult-like reliance on relative and horizontal disparities. Here we use a sweep steady state visual evoked potential paradigm and dynamic random dot stereograms to measure disparity sensitivity in human infants (3a??7 months) and in adults. The core conditions were: 1) a relative disparity sweep, 2) a sweep changing from absolute to relative disparity. Each condition was run with both vertical and horizontal disparities yielding four conditions total. Our results suggest that infants do not have the strong preference for horizontal over vertical disparities that adults do and do not demonstrate adult-like relative disparity responses. Our results are consistent with several behavioral studies showing that stereoacuity thresholds improve over an extended developmental course reaching beyond preschool, e.g. (Birch & Salomao, 1998; Ciner, Schanel-Klitsch, & Herzberg, 1996; Ciner, Schanel-Klitsch, & Scheiman, 1991).