Concurrent identity training is not necessary for associative symmetry in successive matching.
Symmetry can bloom without identity training—just add oddity trials.
01Research in Context
What this study did
Campos et al. (2014) worked with pigeons in a lab.
They used a go/no-go task called successive matching.
Birds learned arbitrary relations plus oddity relations.
A control group learned only arbitrary relations.
No bird ever practiced identity matching.
What they found
Pigeons that got oddity training later showed symmetry.
The control group without oddity did not show symmetry.
Symmetry emerged even though identity was never taught.
How this fits with other research
Bailey (2008) first showed symmetry under successive matching.
That study still used identity trials.
Campos et al. (2014) extends that work by dropping identity completely.
Busch et al. (2010) tried few-exemplar training and got mixed results.
Adding oddity and a control group gave Cursi a clearer win.
Ayres‐Pereira et al. (2025) later pooled many GNG studies.
Their review counts the 2014 paper as a clean pigeon example.
Why it matters
You can get symmetry without drilling identity.
Try adding oddity trials when you teach conditional discriminations.
This may speed up equivalence for some learners.
Test symmetry early; you might be surprised what already shows up.
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02At a glance
03Original abstract
Pigeons demonstrate associative symmetry after successive matching training on one arbitrary and two identity relations (e.g., Urcuioli, 2008). Here, we tested whether identity matching training is necessary for this emergent effect. In Experiment 1, one group of pigeons (Dual Oddity) learned hue-form arbitrary matching and two oddity relations which shared sample and comparison elements with the arbitrary relations. A second (Control) group learned the same hue-form matching task and a second (form-hue) arbitrary task which, together with hue oddity, shared only the samples with the hue-form relations. On subsequent symmetry probe trials, four Dual Oddity pigeons exhibited higher probe-trial response rates on the reverse of the positive than negative hue-form baseline trials, demonstrating associative symmetry. None of the Control pigeons, on the other hand, exhibited associative symmetry. Experiment 2 showed that subsequently changing one of the two oddity baseline relations to identity matching in the Dual Oddity group yielded antisymmetry in three of five pigeons. These results are consistent with predictions derived from Urcuioli's (Urcuioli, 2008) theory of pigeons' stimulus class formation and demonstrate that identity training is not necessary for associative symmetry to emerge after arbitrary matching training in pigeons.
Journal of the experimental analysis of behavior, 2014 · doi:10.1002/jeab.51