Generalization peak shift for autoshaped and operant key pecks.
Peak shift shows up under both operant and respondent learning, and respondent alone can drive the biggest bend.
01Research in Context
What this study did
The team worked with two groups of pigeons. One group earned food only if they pecked the key. The other group got food no matter what—food just followed the light.
After training, both groups saw a row of lights that looked like the training color. The birds pecked most at a color that was not the original. This bend is called peak shift.
What they found
Both groups showed the same bend, but the autoshaped birds pecked even harder. Their top rate was one-third to four-fifths higher than the operant group.
The result shows peak shift is not just an operant trick. Respondent learning can push the bend even farther.
How this fits with other research
Hayes et al. (1975) saw the same bend in rats that heard tones. Food came no matter what the rat did. Their peak shift looked like the pigeons here, so the effect crosses species and senses.
Semb (1974) watched tiny steps—head turns and near pecks—before the bird ever struck the key. Those small moves were reinforced and grew into the final peck. Rasing et al. (1992) now show that once the peck exists, respondent learning can still bend the generalization curve.
Pickering et al. (1985) warn that elicited pecks can fake operant choices. The new data agree: autoshaped pecks are real, measurable, and can outrun operant rates.
Why it matters
If you run stimulus discrimination lessons, watch for peak shift in either direction. The bend can come from reinforcement history, from simple pairings, or both. When you see a learner respond strongest to a cue that was never directly taught, do not rush to retrain. Check if the shift is respondent—just a learned gut reaction—and use it or block it as needed.
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02At a glance
03Original abstract
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.
Journal of the experimental analysis of behavior, 1992 · doi:10.1901/jeab.1992.57-127