Visual sensitivity and color vision in ground squirrels

Abstract

Several measures of visual capacity were obtained from ground squirrels ( Citellus mexicanus and Citellus tridecemlineatus) in discrimination tests. These measures included: (a) spectral sensitivity functions for conditions of achromatic and chromatic adaptation, (b) dark-adaptation functions, (c) tests for a neutral point, (d) wavelength discrimination, and (e) chromaticity confusion lines. The all-cone character of vision in these animals is expressed in the lack of any shift in relative spectral sensitivity as achromatic adaptation state is altered and also in the rapid and relatively small increase in sensitivity during dark adaptation. More than one process was found to underlie the spectral sensitivity function. These squirrels have color vision of the dichromatic variety with a well-defined neutral point. Their wavelengthdiscriminating abilities are also characteristically dichromatic. Measurements of chromaticityconfusion loci suggest that the dichromacy of these squirrels is closest to that shown by protanopic humans. No differences were found between these two species of ground squirrel on any of the measures of visual capacity.