Form identification in peripheral vision

Outlined and solid-surfaced metric histoforms and polygons we;e employed in an identification task where choice forms were fixed at 0 deg and target forms at six points along the temporal horizontal meridian in the periphery (nasal retina). Accuracy in the identification of solid-surfaced polygons in the far periphery (80 deg from the fovea) was much higher than has been previously reported. Polygons were identified more quickly than histaforms, but a significant difference was not obtained between the speed of identification of outlined and solid shapes. Combined speed and error data indicated that shape (histoform or polygon) is the most salient dimension of a form less than 50 deg from the fovea. whereas beyond 50 deg from the fovea the surface (outlined or solid) of a form is its most salient dimension. Finally. comparisons of the functional relations provided by these performance data with anatomical and physiological data produced the following hypothesis: Spatial summation of rod receptors beyond 20 deg of angular eccentricity in the nasal retina is directly proportional to the density of rod receptors.