Spectral saturation curves for chimpanzee and man.

Abstract

Thresholds of spectral saturation were measured by finding the quantity of spectral light which when added to one of two white stimulus areas made it possible for the subject to choose this stimulus with 75% accuracy. Thresholds were measured at 17 spectral wavelengths for 2 chimpanzees and 2 human beings, and at 4 wave-lengths for 3 other human subjects. Curves were plotted of these thresholds as a function of wave-length. Results for chimpanzees and human beings proved to be very similar, both in magnitude of the thresholds and general shape of the curves. Curves for both types of subjects showed a high peak in the yellow-green region, with continuous dropping off toward the spectral extremes. For the comparison white used, 4029[degree] K. color temperature, the peak of the human curve was at 575 mu, and that of the chimpanzee curve at 570 mu, a difference found statistically reliable. For both chimpanzees and human beings the highest thresholds (lowest saturation) coincided with a radical color change in the spectrum (from reddish to greenish for the human subjects). The chimpanzees showed this by a reversal of their discrimination habit when testing reached wave-lengths below 570 mu. The 5 mu difference in point of lowest saturation for chimpanzees and man is consistent with other slight differences in color vision.