Delwin T. Lindsey

Chromatic two-pulse resolution with and without luminance transients*

Two-pulse discrimination thresholds determined for homochromatic pulses presented as luminance increments or decrements are invariant with wavelength. Wavelength does affect two-pulse temporal resolution if chromatic pulses are presented in hue substitution, matched in luminance (with flicker photometry) to an achromatic background field. For relatively long pulses, the wavelength effect resembles trichromatic saturation discrimination, with poorest temporal resolution at 570 nm. For shorter pulses, temporal resolution for hue substitution stimuli appears related to saturation discrimination under conditions of artificial tritanopia. Under conditions of hue substitution, short-wavelength pulses yield good temporal resolution.

Structure-function relationships in human red/green color vision

The relationship between molecular structure of the visual pigment genes and red-green color vision was studied in 126 normal and 63 color-defective males. We found that the great majority of defects in red-green color vision are associated with the formation of 5′R-G hybrid genes (protan series), deletion of the G gene (deutan series), or the formation of 5′R-G hybrid genes (deutan series). Within these two series, however, dichromacy and trichromacy cannot always be predicted from the molecular patterns, particularly among protans. Amino acid residues in exon 5 largely determine whether a hybrid gene will be more R-like or more G-like in phenotype. We observed numerous genetic polymorphisms in the R and G pigment genes of both normal and color-defective subjects. These polymorphisms may account for some, but not all, of the observed variations in color vision phenotypes. A common Ser/Ala polymorphism at position 180 of the R pigment gene was found to be highly correlated with the bimodal distribution of Raleigh matches we observed among 50 color-normal Caucasian males.