Five experiments on the perception of lightness by human and subhuman (monkey) Os involved judgments of lightness intervals and discrimination of simultaneous contrast. (1) Both species responded comparably on discriminations that involved lightness contrast. (2) Differences in response to gradations of lightness by human and subhuman Ss were related to the artifact of human language, and when human Ss were provided with a response that did not conform to linguistic categories, they made a graded response to graded grays.
