Reaction time measurement of receptive field properties in the human fovea.

A Westheimer -like function has been obtained for simple reaction time (RT) to target luminance increments superimposed upon homogeneous background fields. RT to a constant-luminance target progressively increases as the outer diameter of a constant-luminance background is increased up to approximately 6'-8'. Further increases in background diameter up to approximately 10'-22' then result in progressive decreases in RT. Beyond this background diameter RT remains relatively constant. The magnitude of this effect diminishes rapidly as target luminance is increased beyond a near-threshold value.