The discrimination of relative frequency by pigeons.
Stimulus control weakens fast when the target is rare or the lag is long, so keep key cues frequent and tests quick.
01Research in Context
What this study did
Researchers taught pigeons to peck the picture that had shown up least often in a string of images. Each session flashed a mix of colors and shapes in a row. Birds earned grain only if they picked the rare one at the end.
The team varied how many pictures came between repeats of the rare target. They wanted to see if accuracy dropped as the gap grew longer.
What they found
Pigeons picked the least-frequent picture well above chance. Accuracy fell the longer ago that picture had last appeared. Birds also made more errors when the rare item sat in the middle of the list instead of at the start or end.
The data traced a clean forgetting curve: memory weakened as lag increased, just like in delayed-matching tasks.
How this fits with other research
Bacon-Prue et al. (1980) saw the same lag effect when pigeons recalled two-item sequences. Both studies show stimulus control fades after only a few seconds.
Griffin et al. (1977) added that pigeons can use a quick mnemonic strategy to fight the fade. Together the papers say: expect decay, but know you can slow it with rehearsal cues.
Adams (1980) and Rapport et al. (1982) push the idea further. They proved pigeons can count their own pecks or notice their own pauses. The current study widens the lens: birds can also track how often outside events happen, not just their own actions.
Why it matters
When you teach a new discrimination, remember that the learner's brain is tallying how often each cue shows up. If a target stimulus is rare or the lesson drags on, control weakens. Keep critical cues frequent and tests immediate. When you must space things out, give the learner a quick mediating response—like a rehearsal prompt—to bridge the gap.
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02At a glance
03Original abstract
Five experiments addressed the issue of how pigeons learn to discriminate the relative frequency of stimuli. During a sampling period, three different stimuli (keylights) were presented serially, in mixed order, and with different frequencies. During a choice period, the stimuli were presented simultaneously, and reinforcement was arranged for choosing the stimulus that was presented the least number of times during the sample. The results showed that (a) the overall proportion of correct choices was always above chance levels; (b) the likelihood of a correct choice decreased with the serial position of the correct stimulus, a negative recency effect; (c) when the last three stimuli of the sample were constrained to be one of each kind, the negative recency effect decreased but errors became more likely when the correct stimulus occurred early in the sample, a negative primacy effect; (d) accurate performance generalized to new and larger samples; and (e) under some conditions the probability of a correct choice was independent of the serial position of the correct stimulus. The serial position curves suggest that in a least frequent discrimination task, two processes determine how the least frequent stimulus controls behavior: a passive decay process (the stimulus loses its effectiveness with time since its last occurrence), and a residual salience process (when the stimulus occurs in the first position it may decay to a higher asymptote than when it occurs in later positions.
Journal of the experimental analysis of behavior, 1997 · doi:10.1901/jeab.1997.67-11