Infant vision research provides an interesting model for the neurobiology of development. It highlights a set of well-understood techniques for measuring the visual capacities of infants, basic descriptions of the development of many visual functions, and a behaviorally established animal model for asking causal questions. Quantitative anatomical and physiological data are becoming available; and quantitative visual theory is being imported into the discipline and used to evaluate hypotheses about the dependence of visual behavior on visual physiology and visual substrate in the developmental context.
And yet, there is work to be done at the metatheoreti-cal level. Coincidences of time scale and similarities of curve shape between psychophysical, anatomical, and physiological data are the beginning, not the end, of theoretical explanations; and the concept of critical immaturity (Brown, 1990), like that of critical locus (Teller, 1980), will require continuing scrutiny, both at the abstract level and when imbedded implicitly or explicitly in causal stories intended to relate visual function to visual substrate. Similar analyses might be useful in other domains of cognitive neuroscience.
One final question can be raised: Why do vision and the visual system bootstrap themselves in the particular sequence that they do? Why is a visual world with poor visual acuity and contrast sensitivity, poor sensitivity to color differences, and no stereopsis sufficient for young infants, while excellent representation of the temporal properties of stimuli is apparently required? Which of these developmental time courses are direct products of natural selection acting on infant behavior, and which are accidental consequences of other evolutionary pressures? It is easy to speculate that natural selection favors infants who perceive depth and distance before they can crawl; but beyond this, we know little about the reasons for the pattern of emergence of different visual functions over the course of infancy.
ACKNOWLEDGMENTS Portions of this paper are excerpted with permission from Teller, D. Y., 1997. First glances: The vision of infants. The Friedenwald Lecture. Investigative Ophthalmology and Visual Science 38: 2183-2203.
Preparation of this review was partially supported by NIH grant EY 04470. I thank David Corina, J. Anthony Movshon, and Yuzo Chino for comments on an earlier version of the manuscript, and Barry Lia for continuing discussions of the developmental neurobiology of primate vision.
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