Dark adaptation and increment threshold in rhesus monkey and man

Dark adaptation and increment thresholds were determined for a trained rhesus monkey and a human observer under identical conditions. The measurements were made with a 1.5' diameter, 100 ms target at 10 degrees and 40 degrees eccentricity along the temporal horizontal meridian. Qualitatively, the results are similar for the two species: Both rhesus monkey and man have photopic and scotopic branches, which cross at approximately the same time in the dark and at approximately the same background luminance.