CONTRAST SENSITIVITY OF THE HUMAN PERIPHERAL RETINA 1

THE CAPACITY of the eye to appreciate detail in a distant object is dete~ined by both the size and contrast of the detail. The effects of contrast on visual resolution are conveniently measured in terms of the threshold contrasts for detecting sinusoidal gratings. These variable contrast targets, first used by SCHADE (1956) to measure visual acuity, have an intensity distribution that varies sinusoidally with distance across the bars of the pattern. Recently, ENROTH-CUGELL and ROBSON (1966) have recorded the responses of single ganglion cells of the cat’s retina to sinusoidal gratings that drifted across the cell’s receptive field. The contrast sensitivity functions of single units were determined by adjusting the contrast so that the drifting grating evoked a criterion response. Superficially, the contrast sensitivity measured on individual cells appears imilar to the psy~hophysically determined contrast sensitivity of the human eye. Both show a spatial frequency of optimum sensitivity with a fall in sensitivity at higher and lower spatial frequencies. Detailed comparisons between the psychophysical and the single unit contrast sensitivity functions indicate important differences (ENROTH-CUGELL and ROBSON, 1966). Firstly, they occupy very different positions along the spatial frequency axis. The ca