EFFECT OF WINDOW SIZE ON DETECTION ACUITY AND RESOLUTION ACUITY FOR SINUSOIDAL GRATINGS IN CENTRAL AND PERIPHERAL-VISION

Detection and resolution of square patches of sinusoidal gratings were measured in central and peripheral vision (30 degrees horizontal temp oral visual field) for high-contrast gratings as a function of the num ber of cycles in the stimulus. We determined performance in a forced-c hoice paradigm for a fixed number of stimulus cycles by arranging for stimulus diameter to vary inversely with spatial frequency. For both p sychophysical tasks and for both target locations, the psychometric fu nction relating performance to log spatial frequency shifted to higher frequencies without changing slope significantly as the number of cyc les in the stimulus was increased. Thus the entire effect could be cap tured by an analysis of spatial acuity, which increased with increasin g number of grating cycles over the range 0.5-6 cycles but remained co nstant over the range 6-14 cycles. In the central field, resolution ac uity and detection acuity were equal regardless of the number of cycle s in the stimulus. In the peripheral field, detection acuity exceeded resolution acuity and perceptual aliasing occurred for stimuli in the range 1-14 cycles. From this result we conclude that resolution acuity is sampling limited in the periphery, provided that the stimulus cont ains at least one full cycle of the grating. Essential features of the results could be accounted for by Fourier analysis of the stimulus. ( C) 1996 Optical Society of America