Document Detail

Luminance-dependent hue shift in protanopes.
MedLine Citation:
PMID:  15518221     Owner:  NLM     Status:  MEDLINE    
For normal trichromats, the hue of a light can change as its luminance varies. This Bezold-Brücke (B-B) hue shift is commonly attributed to nonlinearity in the blue-yellow opponent system. In the present study, we questioned whether protanopes experience analogous changes. Two protanopes (Ps) viewed spectral lights at six luminance levels across three log steps. Two normal trichromats (NTs) were tested for comparison. A variant of the color-naming method was used, with an additional "white" term. To overcome the difficulty of Ps' idiosyncratic color naming, we converted color-naming functions into individual color spaces, by way of interstimulus similarities and multidimensional scaling (MDS). The color spaces describe each stimulus in terms of spatial coordinates, so that hue shifts are measured geometrically, as displacements along specific dimensions. For the NTs, a B-B shift derived through MDS agreed well with values obtained directly by matching color-naming functions. A change in color appearance was also observed for the Ps, distinct from that in perceived brightness. This change was about twice as large as the B-B shift for NTs and combined what the latter would distinguish as hue and saturation shifts. The protanopic analogue of the B-B shift indicates that the blue-yellow nonlinearity persists in the absence of a red-green signal. In addition, at mesopic levels (< or = 38 td), the Ps' MDS solution was two dimensional at longer wavelengths, suggesting rod input. Conversely, at higher luminance levels (76 td-760 td) the MDS solution was essentially one dimensional, placing a lower limit on S-cone input at longer wavelengths.
David L Bimler; Galina V Paramei
Publication Detail:
Type:  Case Reports; Journal Article    
Journal Detail:
Title:  Visual neuroscience     Volume:  21     ISSN:  0952-5238     ISO Abbreviation:  Vis. Neurosci.     Publication Date:    2004 May-Jun
Date Detail:
Created Date:  2004-11-02     Completed Date:  2005-01-11     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  8809466     Medline TA:  Vis Neurosci     Country:  England    
Other Details:
Languages:  eng     Pagination:  403-7     Citation Subset:  IM    
Department of Health and Human Development, Massey University, New Zealand.
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MeSH Terms
Color Perception / physiology*
Color Vision Defects / physiopathology*
Space Perception
Twins, Dizygotic

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