Senescent changes in parafoveal color appearance: saturation as a function of stimulus area

Abstract

The chromatic content (saturation) of monochromatic stimuli (480, 505, 577, and 650 nm) was scaled as a function of field size at three different retinal locations by 58 observers ranging from 18 to 83 yr of age. The different retinal locations (6 deg nasal, 2.5 deg inferior and 6 deg temporal eccentricity) were chosen according to anatomical studies demonstrating different degrees of senescent losses of cones or ganglion cells. Nine field sizes were tested, ranging from 0.0096 to 0.96 deg in diameter. The subjects used a percentage scale to judge the saturation of the flashed stimulus presentations (2 s on, 5 s off). The data analysis demonstrated that older observers require larger field sizes than younger observers to perceive hue as well as larger field sizes to reach the same level of scaled saturation. The spatial dependency of color appearance for younger and older observers was not correlated with senescent losses in retinal cells reported for the different retinal locations. The data were modeled by using an impulse-response function (i.e., Naka-Rushton equation) so that perceptive fields could be compared to electrophysiological measures of receptive fields or dendritic fields of retinal and cortical cells.

Chromatic-Spatial Vision of the Aging Eye

“…For example, color sensitivity varies with retinal eccentricity and is influenced by spatial variations in macular pigment density. Color appearance also varies with retinal eccentricity when probed with small spots, 56,59 yet during fixation and eye movements, the color of objects viewed naturally does not seem to change under most conditions. This may imply some compensation processes to normalize perception across retinal eccentricity.…”

“…This hypothesis was tested by Knau and Werner. 59 Fifty-eight observers (18-83 years) scaled the chromatic content (saturation percentage) of monochromatic stimuli (480, 505, 577, and 650 nm) that were equated for each observer to a 2.6 log troland, 560-nm standard by heterochromatic flicker photometry. Nine field sizes ranging from 0.0096 to 0.96 deg in diameter were tested at each of three retinal locations: 2.5° inferior, where there is known to be age-related loss in cone numbers, 8 6° nasal, corresponding to a location with significant age-related loss in ganglion cell density, 10 and 6° temporal as a control, a location with no significant age-related cone or ganglion cell loss.…”

Changes in hue and saturation of chromatic lights presented in the peripheral visual field

“…In contrast, Abramov et al 5 and Knau and Werner 13 have shown that desaturation in the periphery does not appear if the stimulus is suitably scaled in size. They compared the critical perceptive field size for the hue component or saturation of red, yellow, green, and blue monochromatic lights with monkey and human dendritic and receptive field sizes of ganglion cells and cells in the LGN and visual cortices V1 and V4 as a function of retinal eccentricity.…”

“…5,13 In real life, signals, warning lamps, or signboards rarely change their physical size and/or luminance. Of course when we move, the retinal size of objects changes continuously as well as the retinal position.…”

“…However, based on previous studies on peripheral color vision, scaling the stimulus size so that it maintains constant saturation could be considered. It should be noted that the retinal region where desaturation can be reduced by size scaling is from fovea to 10 -20 degrees 5,13 indicating that this compensatory property functions in a limited portion of the retina. Furthermore, if the size scaling is employed, then the stimulus size should be appropriately scaled for individual observers for the entire visual field before the measurement of color zone maps.…”