Abstract
Infants' sensitivity to kinetic-depth develops earlier than sensitivity to binocular (and pictorial) depth and might serve as the foundation for cortical depth-processing networks. Previous studies on the development of depth-from-motion have used shape (i.e., rotating KDE figures), which is depth-sign ambiguous. Here we assess the unambiguous perception of depth from motion parallax (MP) which relies on the slow eye movement system which is developing at the same time as motion sensitivity. In this longitudinal study of the development of depth from MP, we used a Rogers and Graham random dot MP stimulus, which appears as a corrugated surface as it translates across a monitor at 0.2 Hz. Using the infant control habituation paradigm, looking time for the translating stimulus was recorded for each 10-sec trial until the infant reached habituation criterion. Then two test trials were presented: a depth-reversed MP stimulus, and a flat depthless stimulus. Dishabituation (recovery of looking time) to a test stimulus indicates the infant perceived the stimulus change. Four infants were followed from six- to twenty-four weeks-of-age, and tested monocularly to prevent binocular cues. By 20 weeks-of-age, three infants showed dishabituation to both the depth-reversed and flat test stimuli. One additional 20 week-old, tested cross-sectionally, also dishabituated to both test stimuli. One infant less than 20 weeks-of-age showed no dishabituation to the depth-reversed stimulus, but did dishabituate to the flat stimulus at 14 weeks. These results provide evidence for the development of unambiguous depth from MP between 14 and 20 weeks.