Incentive processes and the peak shift.
Peak shift needs an operant contingency; classical conditioning alone keeps the peak where it started.
01Research in Context
What this study did
McGonigle et al. (1982) asked a simple question. Can peak shift happen without any response-rate change?
They used pigeons in two set-ups. One was operant: peck produced food. The other was classical: food just appeared no matter what the bird did.
Both groups saw the same lights. The goal was to see if the brain still "moved" the peak away from the trained color when only the food cue, not the peck, was linked to the stimulus.
What they found
Peak shift showed up only in the operant group. Birds pecked most to a color that was even farther from the old "no-food" color.
In the classical (autoshaped) group, the peak stayed put. Stimulus-reinforcer pairings alone were not enough to slide the peak.
How this fits with other research
Eckerman (1969) already showed that more reinforcers speed up simple discrimination. J et al. go deeper: the same reinforcer count can either shift the peak or leave it, depending on whether the response is operant.
Rutland et al. (1996) later tracked within-session patterns under autoshaping. They found flat, late peaks when food rate dropped. This seems to clash with J's "no shift" claim, but the tasks differ. F looked at response rate curves across time; J looked at the stimulus generalization gradient across colors. Both can be true.
LeBlanc et al. (2003) tied higher reinforcer rates to stronger, disruption-proof stimulus control. Their data fit J's: rich operant contingencies give both peak shift and tougher discrimination.
Why it matters
If you want a learner to "overshoot" and avoid a fault-line stimulus, make the target response operant and tightly tied to reinforcement. Classical pairings alone will not bend the gradient. Next time you shape intraverbal or tacts to fine shades (like "light blue" vs "blue"), keep the contingency response-based, not just exposure-based, to get that extra generalization push.
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02At a glance
03Original abstract
Intradimensional operant discrimination schedules were employed, which eliminated the covariation of response and reinforcement rates that are found on most operant baselines. In Phase 1, one keylight (S(1)) controlled an increase in pigeons' treadle pressing, relative to another keylight (S(2)), while being correlated with a decrease in frequency of reinforcement. In Phase 2 both treadle pressing and reinforcement increased in the presence of one keylight, relative to the second. In Phase 1 the relatively flat treadle-press generalization gradients peaked at S(1), whereas the peaks of those in Phase 2 were shifted from S(1) in a direction away from S(2). It was postulated that these positive and negative stimulus-reinforcement contingencies influence the likelihood of obtaining peak shift through the operation of a classically conditioned "central motive state." How response-reinforcement and stimulus-reinforcement contingencies might contribute to the development of inhibitory effects of S(2) is discussed. Autoshaped key pecking also was produced by these procedures. During manipulations of stimuli, the gradients obtained for autoshaped key pecking were narrow and sharply peaked at the food-correlated stimulus (S(2)) in Phase 1. This failure to obtain peak shift for an elicited response suggests a difference in discriminative processes operating in classical and instrumental learning.
Journal of the experimental analysis of behavior, 1982 · doi:10.1901/jeab.1982.37-441