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  • Title: Spectral sensitivity of the visual system as revealed by evoked potentials in normal and anomalous trichomats.
    Author: Yankov E, Nakova A, Tzekov R.
    Journal: Acta Physiol Pharmacol Bulg; 1999; 24(4):91-100. PubMed ID: 11098295.
    Abstract:
    The spectral sensitivity of the visual system upon adaptation by white light at intensity of 10,500 td was studied in Maxwellian view. The monochromatic stimuli had a size of 8 degrees and duration of 700 ms. They were superimposed on an adaptation field of 14 degrees. The spectral sensitivity was determined by the off-VEP amplitude measured from the negative peak with a latency of 75-80 ms to the positive peak with a latency of 100-110 ms. The EEG was led off monopolarly from the occipital scalp area. Eight normal trichomats, 2 protanomalous and 2 deuteranomalous subjects were investigated. Some specificity of the spectral sensitivity curve, determined by the VEP amplitude, were studied. Special attention was placed on the sensitivity decrease between lambda = 550 nm and lambda = 590 nm, which was much pronounced in the normal trichomats. Maximum sensitivity was observed at lambda = 527 nm. The sensitivity at lambda = 578 nm was lower than the maximum one by 0.8 logarithmic units or more. It is assumed that this sensitivity decrease is a manifestation of opponency between the middle wavelength and long wavelength mechanisms. In the anomalous trichomats the sensitivity decrease between lambda = 550 nm and lambda = 590 nm was much less pronounced. Maximum sensitivity was obtained at lambda = 551 nm. In the long wavelength range of the spectrum the deuteranomalous subjects showed a higher sensitivity as compared to the protanomalous ones. The obtained results suggest disturbances of color opponency in the anomalous trichomats.
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