Abstract
Abstract: :
Purpose: This study investigated the effect of stimulus intensity on perceptive field sizes under rod bleach and no–bleach conditions. Results from these two adaptation conditions enable a better understanding of the influence of rod input on perceptive field sizes in the peripheral retina. Methods: Perceptive field sizes for the four elemental hues (blue, green, yellow, red) were measured under two adaptation conditions: 1) after 30 min dark adaptation, and 2) using a rod bleaching procedure. The size (.098 to 5°) and intensity (–0.2 to 3.3 log td) of the stimuli were manipulated and all measurements were made at 10° temporal retinal eccentricity. Using the ‘4+1’ color–naming paradigm observers described the color appearance of a series of monochromatic stimuli ranging from 440 to 660nm in 10 nm steps. Results: Mean hue responses as a function of stimulus size were determined for each wavelength at each intensity level and were fitted with the Michaelis–Menton function to estimate perceptive field sizes. Initial results indicate that under both adaptation conditions, as intensity increases perceptive field sizes decrease and converge to the same value. At each intensity level, perceptive field sizes differ for the four elemental hues, with the largest differences occurring at the lowest intensity level. The greatest difference between the two adaptation conditions also occurs at the lower intensity levels where some perceptive field sizes are larger under the bleach condition than under the no–bleach condition. Conclusions: Sizes of perceptive fields vary depending upon stimulus intensity and adaptation condition. Rod signals may be implicated for some of our results, though other factors (e.g. cone receptor densities, neural summation) are also being evaluated.
Keywords: color vision • perception • photoreceptors: visual performance