Spatial interaction in the human retina during scotopic vision.

Abstract

The eye's sensitivity to light decreases with increasing background luminances. It was once thought that this could be simply explained by the decrease in the reservoir of available photolabile pigments in the receptors, but recent measurements have shown that changes in sensitivity are far too large to be accounted for by a simple theory involving concentration of visual pigments. A limit to the performance of the eye in detecting differences in brightness is set by quantum variability; but this existence of a theoretical limit tells us how well the eye could do in distinguishing brightness differences, not how it in fact achieves this.

The role of spatiotemporal edges in visibility and visual masking

“…The spatial edges of stimuli produce the strongest excitatory neural signals (2, 4-6). Ratliff (22) moreover suggested that physiological inhibition should also be strongest at the edge of a stimulus, and several perceptual studies have suggested that inhibition is stronger near the edge of a mask rather than within the mask's interior, at least when the mask and the target are presented simultaneously (3,(23)(24)(25). Here, we expand on these experiments by testing the suppressive effect of a mask stimulus that varies in size and onset time relative to the onset of the target, while using high-contrast suprathreshold stimuli in a two-alternative forced choice discrimination task.…”

“…Previous studies have shown that excitatory signals for a stimulus are localized at its edges (1, 2, 4-6, 28). It has also been suggested that inhibitory signals are strongest at the spatial edges (21)(22)(23)(24)(25)29). We expanded on the previous psychophysical studies concerning inhibition at the edge by carrying out visual masking experiments, perceptually and physiologically, in which we increased the distance of the mask's edge from the target, using both overlapping and nonoverlapping masks (Figs.…”

Stimulus determinants of dynamic visual acuity: I. Background and exploratory data.

“…Westheimer (50,51) investigated the effects of the brightness and siz, of a stimulus surround upon the increment threshold for a small flashing spot in the center of the surround area. In the peripheral retina (10' temporal) he found that the scotopic increment threshold for a small, brief stimulus was progressively raised by increasing the size of a surround stimulus up to a size of 45 minutes of arc.…”

“…DVA was measured for each of the three subjects, using five target angalar velocities (20,50,80,110, and 124°/sec) and two levels of target contrast (-.67 and -. 35).…”

The Specificity of Interactions Among the Visual Photopic Mechanisms as Revealed by Spatial Sensitization Effects

“…Crawford (1940) was the first to find that effect, but systematic studies were made much later. Westheimer (1965Westheimer ( , 1967 has made a series of experiments in which a small, brief test flash was superimposed on a steadily illuminated concentric background of variable diameters. As the diameter of the background increased, the amount of light to detect the test flash showed an initial increase followed by a decrease and reached a final steady level.…”