Secondary generalization and categorization in pigeons.
Pigeons failed equivalence in 1989 because the training format was weak, not because the species lacks the ability.
01Research in Context
What this study did
Researchers gave pigeons long categorization drills. Birds learned to peck pictures that belonged to the same group.
Next the team tested for secondary generalization. They wanted to see if the birds would treat new pictures like the trained ones without extra teaching.
What they found
No pigeon formed equivalence classes. The birds did not treat untrained pictures as if they belonged together.
The authors concluded that secondary generalization does not happen in pigeons, even after heavy categorization training.
How this fits with other research
Busch et al. (2010) later got the opposite result. One of their pigeons showed clear symmetry and two showed weak signs. The difference: they used reinforced symmetry tests and made sure all baseline relations were solid first.
Bailey (2008) also saw symmetry in pigeons by switching to a go/no-go format instead of two-choice. The birds pecked only when successive pictures matched, and symmetry appeared.
Campos et al. (2014) went further. They dropped identity training entirely and still got symmetry. Their procedure added oddity tasks, proving pigeons can form equivalence even without the drills S et al. used.
Why it matters
This paper is a cautionary tale for BCBAs. A null result can mean the teaching method, not the learner, is the problem. When equivalence fails with your client, try changing the format before you assume the skill is impossible. Use successive matching, reinforce test trials, or add oddity tasks. Small procedural tweaks can turn failure into emergence.
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02At a glance
03Original abstract
In Experiment 1, one group of pigeons learned to classify a set of stimuli into the human language classes cat, flower, car, and chair (categorization); another group learned to classify the same set into arbitrary classes (pseudocategorization). Then, both groups were trained on a new categorization task and their performance compared to that of a control group that had no initial classification training. Hull's (1943) notion of secondary generalization (generalization that is not based on physical similarity but on mediating associations) predicts that categorization experience will facilitate the learning of a new categorization task, whereas pseudocategorization experience will impair it. However, in Experiment 1, performance on the new categorization task was not differently affected by prior experience. In Experiment 2, pigeons initially trained to classify a set of 48 stimuli (original training) were later trained to classify a subset of four of these stimuli using new responses (reassignment training). Then, they were tested on the 44 remaining stimuli. Performance better accorded with original than with reassignment training, indicating that categorization training did not lead to the formation of equivalence classes of stimuli, in which the equivalence relationship is mediated by secondary generalization. The lack of evidence of secondary generalization implies that our pigeons failed to meet Lea's (1984) criterion for conceptual behavior.
Journal of the experimental analysis of behavior, 1989 · doi:10.1901/jeab.1989.52-213