Detection and direction discrimination performance with flicker gratings in peripheral vision

Detection and direction discrimination experiments were conducted with luminance and flicker gratings. The flicker gratings had bars made up of static random pixels interspersed between other bars with flickering random pixels. All experiments were carried out in peripheral vision with grating images centered at 8 deg eccentricity in the superior retina. Detection of flicker gratings (i) was independent of pixel size, (ii) declined with spatial frequency in the range 1-4 c/deg, and (iii) improved with stimulus area (number of grating cycles). Detection performance with a flicker grating was comparable to that obtained with a low-contrast (0.01) luminance grating, and the results suggest that the spatial structure of a flicker-domain stimulus is based upon signals which are weak compared to the maximum signals attainable with a luminance-domain stimulus. With the detectability of flicker and luminance gratings equated, d' for discriminating the direction of motion of a luminance grating increased with step size (1/12 to 1/4 cycle) whereas direction discrimination performance with a flicker grating remained unchanged and at chance levels. Under the conditions tested, there was no evidence that the motion of a flicker-domain stimulus could be processed peripherally. Constraints on alternative models of motion processing are discussed.