Document Detail

Normal and dichromatic color discrimination measured with transient visual evoked potential.
MedLine Citation:
PMID:  16962005     Owner:  NLM     Status:  MEDLINE    
It would be informative to have an electrophysiological method to study, in an objective way, the effects of mercury exposure and other neurotoxics on human color vision performance. The purpose of the present work was to study human color discrimination by measuring chromatic difference thresholds with visual evoked potential (VEP). Six young normal trichromats (24 +/- 1 years old) and one deutan (26 years old) were tested. The stimuli consisted of sinusoidal isoluminant chromatic gratings made from chromaticity pairs located along four different color directions centered on two reference points. Heterochromatic flicker photometry (HFP) protocol was used to obtain the isoluminance condition for every subject and for all chromaticity pairs. Spatial frequency was 2 cycles/deg. Presentation mode comprised onset (300 ms)/offset (700 ms) periods. As previously described, we found a negative deflection in the VEP which was related to the chromatic difference: as chromatic difference increased, amplitude increased and latency decreased. VEP response amplitude was plotted against distance in the CIE 1976 color space between the grating chromaticities and fitted with a regression line. We found color thresholds by extrapolating the fitting to null amplitude values. The thresholds were plotted in the CIE 1976 color space as MacAdam ellipses. In normal trichromats the ellipses had small size, low ellipticity, and were vertically oriented. In the deutan subject, the ellipses had large size, high ellipticity, and were oriented towards the deutan copunctal locus. The VEP thresholds were similar to those obtained using grating stimuli and psychophysical procedures, however smaller than those obtained using pseudoisochromatic stimuli (Mollon-Reffin method). We concluded that transient VEP amplitude as a function of contrast can be reliably used in objective studies of chromatic discrimination performance in normal and altered human subjects.
Bruno D Gomes; Givago S Souza; Anderson R Rodrigues; Cézar A Saito; Luiz Carlos L Silveira; Manoel da Silva Filho
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Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Visual neuroscience     Volume:  23     ISSN:  0952-5238     ISO Abbreviation:  Vis. Neurosci.     Publication Date:    2006 May-Aug
Date Detail:
Created Date:  2006-09-11     Completed Date:  2006-10-18     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  8809466     Medline TA:  Vis Neurosci     Country:  England    
Other Details:
Languages:  eng     Pagination:  617-27     Citation Subset:  IM    
Departamento de Fisiologia, Universidade Federal do Pará, Pará, Brazil.
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MeSH Terms
Color Perception / physiology*
Contrast Sensitivity / physiology*
Discrimination (Psychology) / physiology*
Evoked Potentials, Visual / physiology*
Pattern Recognition, Visual / physiology
Photic Stimulation / methods
Psychophysics / methods
Reaction Time / physiology

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