Temporal visual mechanisms may mediate compensation for macular pigment

Abstract

Macular pigment (MP) is a pre-receptoral filter that is diet-derived and deposited in relatively high optical density in the foveal region of the retina. Due to its yellow coloration, MP absorbs short-wavelengths from 400-520 nm (which appear blue). Despite the spectral and spatial non-uniformity imposed upon the sensory retina by MP, perception appears to be uniform across the visual field. MP therefore offers an opportunity to determine experimentally potential mechanisms responsible for mediating this uniformity. After assessing, in 14 subjects, MP’s effects on the temporal sensitivity of both the short-wavelength- and middle / long-wavelength-sensitive visual pathways, it appears that the visual system compensates for absorption of short-wavelength light by MP by slowing short-wavelength-cone signals, and by increasing the processing speed of middle- / long-wavelength-sensitive cones. This mechanism could work via temporal summation or a temporal neural code, whereby slower response dynamics would amplify relatively weak signals.