Associative symmetry by pigeons after few-exemplar training.
Reinforced symmetry testing with all prerequisites can produce equivalence in some pigeons, but inter-subject variability remains high.
01Research in Context
What this study did
Four pigeons learned a two-choice matching game. First they mastered AB and BC relations. Then the team tested if the birds could flip the relations (BA and CB) without extra teaching.
Every test trial paid off with grain. The birds saw a sample in the center and two side keys. Pecking the correct comparison ended the trial with food.
What they found
One pigeon showed clear symmetry. Two birds gave weak signs of flipping the relations. The last bird never got it.
Even with food for right answers and all prerequisites trained, most pigeons still struggled.
How this fits with other research
Bailey (2008) saw the same mixed picture. That study used a go/no-go setup and also found symmetry only in some birds. Together the two papers warn that pigeons need very specific formats before symmetry shows up.
Ayres‐Pereira et al. (2025) pooled many studies. Their review shows humans hit 87 % symmetry, while non-humans stay low and spotty. The target data sit right inside that low band.
Murphy et al. (2010) gives a bright contrast. Three teens with autism learned derived mands after the same kind of match-to-sample training. Same year, same method, different species, opposite outcome.
Why it matters
If you work with learners who struggle with symmetry, check the training format first. Successive go/no-go or extra prerequisite drills can help. Remember that even perfect reinforcement may not be enough for some individuals. Track each learner separately and be ready to add more baseline relations or switch modalities.
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Join Free →Run a quick symmetry probe after each baseline relation and note which learners fail; keep the probe short and reinforced so you can spot who needs more training nodes.
02At a glance
03Original abstract
The present experiment investigated whether pigeons can show associative symmetry on a two-alternative matching-to-sample procedure. The procedure consisted of a within-subject sequence of training and testing with reinforcement, and it provided (a) exemplars of symmetrical responding, and (b) all prerequisite discriminations among test samples and comparisons. After pigeons had learned two arbitrary-matching tasks (A-B and C-D), they were given a reinforced symmetry test for half of the baseline relations (B1-A1 and D1-C1). To control for the effects of reinforcement during testing, two novel, nonsymmetrical responses were concurrently reinforced using the other baseline stimuli (D2-A2 and B2-C2). Pigeons matched at chance on both types of relations, thus indicating no evidence for symmetry. These symmetrical and nonsymmetrical relations were then directly trained in order to provide exemplars of symmetry and all prerequisite discriminations for a second test. The symmetrical test relations were now B2-A2 and D2-C2 and the nonsymmetrical relations were D1-A1 and B1-C1. On this test, 1 pigeon showed clear evidence of symmetry, 2 pigeons showed weak evidence, and 1 pigeon showed no evidence. The previous training of all prerequisite discriminations among stimuli, and the within-subject control for testing with reinforcement seem to have set favorable conditions for the emergence of symmetry in nonhumans. However, the variability across subjects shows that methodological variables still remain to be controlled.
Journal of the experimental analysis of behavior, 2010 · doi:10.1901/jeab.2010.94-283