Function of the pupil in vision and information capacity of retinal image

Abstract

AbstractThe light–pupil reflex system has been the object of study in physiological engineering, as a typical example of involuntary biological systems. As regards the variable that actually controls the pupil, however, there has been little discussion of its role in vision. This study notes that the pupil is closely related to the spatial frequency response of the eye's optical system, and discusses the relation between the quality of the retinal image and the pupil size, as determined by the external image and the characteristics of the eye's optical system. By defining the information capacity of the retinal image as the evaluation measure, the quality of the retinal image is represented quantitatively. The relation between the pupil size and the information capacity of the retinal image is examined for various conditions. It is shown that the human pupil is controlled so that the quality of the retinal image is optimized, in the sense of the information capacity of the retinal image for each luminance level, when the external image is a natural image. On the other hand, when the external image is not a natural image, or when the characteristic of the eye's optical system or the relation between the visual cell arrangement and the pupillary diameter differs from the actual situation, it is not necessarily true that the pupil optimizes the quality of the retinal image. The above results suggest that the function of the pupil in vision is optimization of the quality of the retinal image. It is also suggested that the adjustment function of the pupillary diameter is acquired under the constraints of the external image and the hardware of the eye. © 2003 Wiley Periodicals, Inc. Syst Comp Jpn, 34(9): 48–57, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.10344