Differences between fovea and periphery in the detection and discrimination of spatial offsets.

Previous work has shown that the ratio between the thresholds for detecting a spatial (vernier) offset and discriminating its direction is about two, if the targets are presented to the fovea, whether at a fixed, vertical, orientation, or a variable orientation. In the present study, vernier detection and discrimination thresholds were measured at the fovea and at two retinal eccentricities (3 and 10 deg), two presentation durations (300 and 1000 msec), and three lengths (25, 50 or 100 min) with the targets either vertical or in a variable orientation. For vertical targets, thresholds rose at similar rates in the two tasks, so that their ratio was constant with eccentricity. For variable-orientation targets, thresholds rose with eccentricity at different rates in the two tasks, and more steeply for discrimination, so that at 10 deg, unlike in the fovea, detection performance was superior to discrimination performance. The implications for estimates of cortical magnification and possible differences in the specializations of foveal and peripheral vision are discussed.