Generalization peak shift for autoshaped and operant key pecks

Pigeons acquired discriminated key pecking between 528- and 540-nm stimuli by either a response-reinforcer (operant group) or a stimulus-reinforcer (autoshaped group) contingency, with other training-schedule parameters comparable over groups. For the birds in the operant group, key pecks intermittently produced grain in the presence of one hue on the key (positive stimulus) but not in the other (negative stimulus). For the birds in the autoshaped group, pecking emerged when grain was intermittently presented independently of key pecking during one key color but was not presented during the other key color. Two independent contingency assays, peck-location comparisons and elimination of differences in reinforcement rate, confirmed the effectiveness of the two training procedures in establishing operant or respondent control of key pecking. After reaching a 10:1, or better, discrimination ratio between key pecks during the two key colors, the birds received a wavelength generalization test. Criterion baseline key-peck rates were comparable for operant and autoshaped groups prior to testing. On the generalization test, performed in extinction, all birds pecked most at a stimulus removed from the positive training stimulus in the direction away from the negative stimulus. In testing, autoshaped "peak" rates (24.5 to 64.9 pecks per minute) were from 33% to 80% higher than rates in the presence of the training stimuli. Respondent peak shift rarely has been reported heretofore, and never this consistently and robustly. These results further confirm the similarity of perceptual processing in classical and operant learning. They are discussed in terms of Spence's gradient-interaction theory and Weiss' (1978) two-process model of stimulus control.