The structure of pigeon multiple-class same-different learning.
Keep the response mapping fixed while you teach same-different relations; pigeons (and probably people) only form a general rule when the link stays the same.
01Research in Context
What this study did
Cook (2002) taught pigeons to peck 'same' or 'different' keys after seeing two colors. One group always saw the same color pair linked to the same key. A second group saw the pair-key link shuffle every day.
Birds got food only for correct choices. After many trials the team tested the birds with brand-new colors they had never seen.
What they found
Pigeons with the fixed mapping learned fast and scored about a large share correct on new colors. Birds with the shuffled mapping stayed near chance even after thousands of trials.
The fixed group had formed a broad 'same-different' rule. The shuffled group had not.
How this fits with other research
Howard (1979) and Cohen (1969) saw the same thing in matching-to-sample: consistent links let pigeons transfer to new stimuli. Cook (2002) now shows the rule holds even for the harder same-different task.
Ayres‐Pereira et al. (2025) recently moved the idea to humans. They found that adults only formed equivalence classes with almost-identical pictures when the items were shown side-by-side. Cook (2002) used colors instead of shapes and pigeons instead of people, but both papers say: keep the display format steady if you want broad learning.
Collier et al. (1986) warns that moving a stimulus around the screen can break some discriminations. Cook (2002) kept color pairs in the same spots, so the good transfer may hinge on that hidden consistency.
Why it matters
When you teach conditional discriminations—same/different, bigger/smaller, or matching—lock the response to the relation, not to the individual picture. Use one key, one gesture, or one spoken word for each relation across all examples. After the learner masters the first set, test with totally new stimuli right away. If accuracy jumps, you have built a concept, not just rote memory.
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02At a glance
03Original abstract
Three experiments examined the structure of the decision framework used by pigeons in learning a multiple-class same-different task. Using a same-different choice task requiring the discrimination of odd-item different displays (one or more of the display's component elements differed) from same displays (all display components identical), pigeons were concurrently trained with sets of four discriminable display types. In each experiment, the consistent group was tested such that the same and different displays of four display types were consistently mapped onto their choice alternatives. The inconsistent group received a conflicting mapping of the same and different displays and the choice alternatives that differed across the four display types but were consistent within a display type. Experiment 1 tested experienced pigeons, and Experiment 2 tested naive pigeons. In both experiments, the consistent group learned their discrimination faster and to a higher level of choice accuracy than did the inconsistent group, which performed poorly in general. Only in the consistent group was the discrimination transferred to novel stimuli, indicative of concept formation in that group. A third experiment documented that the different display classes were discriminable from one another. These results suggest that pigeons attempt to generate a single discriminative rule when learning this type of task, and that this general rule can cover a large variety of stimulus elements and organizations, consistent with previous evidence suggesting that pigeons may be capable of learning relatively unbounded relational same-different concepts.
Journal of the experimental analysis of behavior, 2002 · doi:10.1901/jeab.2002.78-345