The illumination required for a criterion latency of the scotopic VECP was compared with the sensory threshold in a number of situations where the area and the spatial distribution of the test stimulus was altered. Plots of the log area versus log illumination derived from both VECP (criterion latency) and psychophysical (threshold) measurements allowed the determination of slopes indicating summation indices. Areal summation was shown to be present within the whole area stimulated (up to 18° in diameter). It was found that the slopes in both sets of measurements probably reflect lack of retinal homogeneity rather than areal summation as such. Qualitatively, the slopes of both types of measurements are similar; quantitatively there are small systematic discrepancies.

Keywords:
Visual evoked cortical potential, Central retina, Rod organization, Spatial summationtion, Scotopic vision, Sensory threshold
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© 1973 S. Karger AG, Basel
1973
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