Abstract

Contributions to the theory of image processing in the human visual system frequently attempt to relate psychophysical performance on a particular visual task to the supposed dimensions of receptive fields in specific groups of neurons. The existence of models of optical degradation for the human eye will enable such experiments to be conducted with an improved degree of precision. Although at present the most detailed information on the optical transfer function of the eye has been mainly limited to studies with monochromatic light (Artal,1989), the parametric model of Deeley, Drasdo and Charman (1989) provides a means of investigating contrasts with white light for central vision. According to this model the modulation transfer (MT) in the retinal image of a sinewave grating of spatial frequency (SF) formed by an eye of pupil size (P) in mm., is given by the following equation: This model must of course be applied with due caution because the inclusion of the effects of the phase transfer function become relevant with pupil sizes exceeding 4mm at large peripheral angles (Walsh and Charman, 1992). Nevertheless it is already possible to apply this model to psychophysical data obtained for example at the fovea and at 100 eccentricity in the temporal visual field. According to classical studies and schematic eyes the MTF would in fact be identical at these two points because they are symmetrical around the optic axis of the ocular components. In reality however this may not be quite correct and increased retinal scatter may occur, but the corresponding asymmetry is visible in most studies on the MTF in peripheral vision, and MT does not decline very signifiantly at this point.

© 1993 Optical Society of America