Explanations of simultaneous brightness contrast consistent with traditional nativistic and empiricistic points of view have been presented. Evidence relevant to these views has been cited from experiments employing the techniques of electrophysiology of the retina and from experiments based on psychophysical methods. Inasmuch as the evidence is not conclusive and the theoretical issues remain controversial, this experiment was designed in an attempt to aid in clarification of these issues. A nativistic, or peripheral, explanation of simultaneous brightness contrast is based on a visual response mechanism in the retina; and an empiricistic, or central, explanation is based on past experience and learning; therefore, the experimental question here was whether instructions given the S would effect the degree of simultaneous brightness contrast. These instructions were designed to instill a "whole-perceiving attitude," on one hand, and an "analytical attitude," on the other
