Henke, Peter G.

The purpose of this study was to determine the extent to which preadaptation to differential brightness magnitude affects responses to a constant postadaptation stimulus. Twenty-four male albino rats, one hundred and tweny days old, were divided into four groups and differentially preadapted in Skinner-boxes to 236.90, 77.25, 22.87, and 1.27 apparent foot-candles for 10 minutes, without access to a bar. Immediately following this period the Ss were allowed to respond under continuous reinforcement to a postadaptation stimulus of 236.90 apparent foot-candles. Measurement in terms of bar pressing indicated that the four groups extinguished differentially over six days. The control group, for whom the discrepancy bwtween preadaptation magnitude and postadaptation stimulus remained zero, was found most resistant to extiction during this period. Additionally, increases in the discrepancy between the pre- and postadaptation magnitudes led to experimental groups. The implications of these data for the proposition of stimulus definitions in terms of behaviorally effective magnitudes were discussed.