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Anthony M. M. Norcia, Chuan Hou; Random-dot stereopis is highly immature in infants. Journal of Vision 2005;5(8):771. doi: 10.1167/5.8.771.
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© ARVO (1962-2015); The Authors (2016-present)
The visual cortex contains cells that are selective for both horizontal and vertical binocular disparity, but only horizontal disparities give rise to a sense of depth in the central visual field. Here we used Visual Evoked Potentials (VEPs) and dynamic random dot stereograms to study disparity processing in adults and in 63 infants between 2 and 6 months of age.
METHODS. We compared VEP disparity response functions for horizontal and vertical disparities. The use of dynamic random dot patterns ensured that no monocular cues were visible. Disparities were modulated sinusoidally across a 50 deg field over a wide range of disparities (0.25–64 arcmin). In the case of horizontal disparity, a corrugated depth surface was visible binocularly. No depth was seen with vertical disparities, rather a weak sense of banding was present for disparities larger than about 5 arcmin. The disparity corrugations were presented either in appearance/disappearance mode or in disparity reversal mode where the disparity sign of the corrugation was inverted.
RESULTS. In adults, the response to the appearance of a horizontal-disparity corrugation was much larger than to its disappearance or to the reversal of disparity. In infants these responses were all comparable in amplitude. In adults the threshold for horizontal disparity was about 0.25–0.5 arc min, but infant thresholds were much higher (4–10 arcmin). Critically, infant disparity response functions for vertical disparities were very similar to those for horizontal disparities. In adults, there was no measurable response to vertical disparities smaller than about 5 arcmin, but horizontal disparities produced a robust response that extended down to 0.25–0.5 arcmin.
CONCLUSIONS: Infants are sensitive to horizontal and vertical disparity, but we find no evidence for the greater sensitivity to horizontal disparity that is characteristic of adults. On this criterion, infants lack stereopsis, suggesting that they may perceive depth on the basis of other cues.
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