This project will improve our understanding of how human infants come to appreciate the three-dimensional structure of the world by means of binocular disparity between the visual signals from the two eyes. This capability is exquisitely acute in normal adults, and it is known as "stereopsis". Stereopsis is the simplest emergent property of visual perception that cannot be performed using subcortical processes. Rather, stereopsis necessarily involves the cerebral cortex, not only in generating the final three-dimension stereoptic percept, but even in extracting the sensory information it is based upon, namely binocular disparity. Understanding the emergence and early development of stereopsis in human infants will improve our understanding of perceptual and cognitive development in infancy.
Infants are not capable of stereopsis at birth, but rather become capable of stereopsis sometime between ages 2 and 6 months. Individual infants acquire stereopsis very suddenly, whereas other visual functions, such as contrast sensitivity and grating resolution acuity, develop gradually over this age range. A central issue in the study of infant visual development is to account for the sudden postnatal emergence of stereopsis. It is well known from much previous work in anatomy, physiology, and psychophysics, as well as from clinical experience, that normal maturation of stereopsis depends critically on normal binocular visual experience. However, this dependency of continuing develop-ment on experience does not necessarily mean that experience is necessary to establish the physiological bases of stereopsis to begin with, or that experience controls the timing and manner of its emergence. Another possibility is that the anatomical and physiological substrate of human stereo vision appears automatically as the infant matures, and never imposes any serious limit on behavior. Perhaps the known immaturity of the infant's contrast sensitivity function limits infant stereo behavior without limiting the maturation of the stereo vision mechanisms. A third possibility is that the infant visual nervous system is "wired up" in a fundamentally different way from those of older infants, children and adults. The project will be made up of a series of experiments on infants and adults that are designed to explore the limitations on infant stereopsis over the first months of life, just as it emerges. The experiments will test these general explanations of why newborn infants do not have stereopsis.
