Advantages and disadvantages of human dichromacy.
We compared the visual detection thresholds for cone-isolating stimuli of trichromats (those with normal color vision) with those of X-linked dichromats, who lack either the long-wavelength-sensitive (L) cones (protanopes) or middle-wavelength-sensitive (M) cones (deuteranopes). At low (1 Hz) temporal frequencies, dichromats have significantly higher (twofold) thresholds for all colored stimuli than trichromats; whereas at high (16 Hz) temporal frequencies, they perform as well or better than trichromats. The advantages of dichromats in detecting high temporally modulated targets can be related to an increased number, through replacement, of the remaining L- or M-cone type. However, their disadvantages in detecting low temporally modulated targets, even in directions of color space where their increased number of cone photoreceptors might be expected to be beneficial, are best explained in terms of the loss of L-M cone opponency and the inability of the visual pathways to reorganize to allow the detection of low-frequency luminance modulation.
Sharpe
Lindsay T
LT
Institute of Ophthalmology, University College London, London, United Kingdom. ltsharpe@cvrl.org
de Luca
Emanuela
E
Hansen
Thorsten
T
Jägle
Herbert
H
Gegenfurtner
Karl R
KR
D016022:Case-Control Studies; D041321:Chromosomes, Human, X; D003118:Color Perception; D003117:Color Vision Defects / Q000235:genetics / Q000503:physiopathology*; D015350:Contrast Sensitivity; D005260:Female; D008040:Genetic Linkage; D006801:Humans; D008297:Male; D010775:Photic Stimulation / Q000379:methods; D017949:Retinal Cone Photoreceptor Cells / Q000503:physiopathology; D017299:Rod Opsins / Q000235:genetics; D012684:Sensory Thresholds; D013997:Time Factors
D017299:Rod Opsins