The peak shift in stimulus generalization: equivalent effects of errors and noncontingent shock.
Peak shift can be created or enlarged simply by pairing aversive stimulation with the non-reinforced stimulus—no errors required.
01Research in Context
What this study did
Pigeons learned to peck one line tilt for food and to skip a second tilt. The birds never received shocks for mistakes. Instead, mild shocks arrived at random times while the non-reinforced tilt was on screen.
The team then tested how the birds responded to many tilts between the trained ones. They wanted to know if shock alone could push the peak of responding away from the non-reinforced stimulus.
What they found
Shocks paired with the non-reinforced tilt created or widened a peak shift. The birds pecked most on a tilt that sat farther from the shock-linked one, even though they had never been shocked for pecking.
In short, errors were not needed to drive the shift. Aversive stimulation alone did the job.
How this fits with other research
Bloomfield (1967) had already shown peak shift with line tilts one year earlier. Grusec (1968) adds that shock can enlarge that same effect, giving clinicians a second lever.
Périkel et al. (1974) later proved that lowering the reinforcement rate on the non-reinforced tilt also widens peak shift. Together the studies show two ways to nudge stimulus control: make the S- less valuable by fewer reinforcers or by added aversives.
Griffin et al. (1977) found peak shift without any errors by signalling upcoming food. Their result and Grusec (1968) agree that shifts can arise from procedures that never let the bird make a mistake, broadening our tool kit for errorless teaching.
Why it matters
If you want a learner to respond more strongly to a target stimulus and less to a similar one, you can pair mild aversives with the look-alike stimulus instead of waiting for errors. This gives you an errorless path to sharper discrimination. Try pairing a brief neutral sound or mild timeout with the non-target stimulus during acquisition and then probe generalization. You may see the peak of correct responding drift farther from the unwanted cue, just like the pigeons did.
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Join Free →Pair a brief mild aversive with the non-target stimulus during discrimination training, then probe generalization to see if responding peaks farther from that cue.
02At a glance
03Original abstract
Terrace suggested that the peak shift in stimulus generalization occurs because the training stimulus not correlated with reinforcement has become aversive. This hypothesis is plausible in the light of instances where the peak shift is obtained compared with those where it fails to appear. The present experiment attempted to test implications of this hypothesis. Two groups of pigeons learned the same two-stimulus discrimination between colors by different training methods in a free-operant situation. When the discrimination was trained with many errors, a large peak shift was obtained in a subsequent generalization test of wavelength; after discrimination training with few errors, a negligible shift was observed. Half of each group then received noncontingent aversive shock during presentations of the stimulus not correlated with reinforcement in continued discrimination training. After this treatment, the errorless-shock subgroup showed a large peak shift and the error-shock subgroup tended to show a larger shift than before. Nonshocked control groups showed little change in the peak shift. It was concluded that pairing aversive shock with a stimulus not correlated with reinforcement is sufficient to produce or enhance a peak shift. In their effect on the peak shift, aversive shock and large amounts of nonreinforced responding appear to be equivalent.
Journal of the experimental analysis of behavior, 1968 · doi:10.1901/jeab.1968.11-239