Spatiotemporal visual response to suprathreshold stimuli

The spatiotemporal visual response to an inducing bar of a short duration was studied by a brightness-matching procedure. The apparent brightness of a test line, presented in the centre of an inducing bar, exhibited a U-shaped dependence of the inducing-bar width with a minimum at about 4.5' width. The temporal response to a 4.5'-wide inducing stimulus consisted of three alternating phases, the middle one being the largest. The spatial spread of the response to this stimulus was initially restricted in the area of the inducing bar, later it was extended to adjacent positions achieving a triphasic form and still later faded away. These findings indicate that the response to a spatiotemporal impulse of suprathreshold luminance is triphasic in time and the spatial spread of the response depends on the time after the stimulus onset. A model was presented assuming that the spatiotemporal weighting function might be described by a spherical harmonic function modulated by a Gaussian function. The model predictions agreed with the data obtained.