The discrimination between lights of different wave lengths in the cat.

Abstract

The ability of cats to discriminate between lights of 8 different spectral regions was examined by a method of behavior, using a Y-shape discrimination box. In order to ensure that the discrimination was not based on brightness, but on differences in wave-length, the various relative amts. of different spectral lights which, in a previous investigation on the animals''s photopic spectral sensitivity, were of equal stimulus value to the animals, were used as stimuli, and projected in pairs onto the stimulus panels. By definition, color vision can only be assumed to exist in an animal, if it has shown to exercise a choice between different spectral lights, depending on wave-length. The conclusion that color discrimination seems absent in this sp. is based on the following observations: The 4 exptl. animals were unable, after 950 trials, to discriminate between lights of different wave-lengths when these had been matched in brightness by the animals themselves. An additional 500 trials to 3 selected spectral regions also produced no evidence of learning. Four control animals, untrained in any sort of discrimination were introduced into the stimulus situation to determine if they could discriminate, on the basis of wave-length, between spectral lights which had been matched in brightness by the exptl. group. No learning was evident after 950 trials. When the learning ability of these animals was tested in an intensity discrimination, all animals learned to discriminate a low intensity spectral stimulus from a white light of relatively high intensity within 200 trials. In order to test the effect of pupil constriction (due to light intensity) on the response of the animals, 4 cats (2 from the exptl. group and 2 from the control group) were run for 900 trials to 2 sets of spectral stimuli with their pupils dilated by local application of homatropine. The responses of these animals did not differ significantly from their discriminations without the drug. It is suggested that, in spite of the cat''s possession of a peripheral "color vision" mechanism, the behavioral method employed in the present expt. has produced no evidence of an ability on the part of the animal to respond differentially to lights of different wavelengths which are of equal brightness to the animal.