Spatial and Chromatic Visual Efficiency in Human Neonates
Martin S. Banks Elizabeth Shannon University of California at Berkeley
The early stages of vision are primarily serial. Visual stimuli pass sequentially through the eyes' optics, which are responsible for forming the retinal image; the photoreceptors, which sample and transduce the image into neural signals; and two to four retinal neurons, which transform and transmit those signals to the optic nerve and eventually to the central visual pathways. Considerable information is lost in these early stages of the visual process as evidenced by the close correspondence between the filtering properties of the optics and receptors, and some measures of visual sensitivity (e.g., Banks, Geisler, & Bennett , 1987; Coletta, Williams, & Tiana, 1990; Pelli, 1990). In this chapter, we examine how immaturities among these early stages of vision limit the spatial vision and the color vision of human neonates.
It is well established that human neonates see poorly. In the first month of life contrast sensitivity (a measure of the least luminance contrast required to detect a visual target) and visual acuity (a measure of the finest detail that can be detected) are at least an order of magnitude worse than in adulthood (reviewed by Banks & Dannemiller, 1987). Chromatic discrimination (the ability to distinguish targets on the basis of their wavelength composition) is much reduced, too (reviewed by Teller & Bornstein, 1987). One would think that the anatomical and physiological causes of such striking functional deficits would have been identified, but the specific causes are still debated. Some investigators have proposed that optical and retinal immaturities are the primary constraint ( Jacobs & Blakemore, 1988; Wilson, 1988), whereas others have emphasized immaturities in the central nervous system ( Bronson, 1974; Brown, Dobson, & Maier,