Urcuioli, P.J. (2008).
Associative symmetry, “anti-symmetry”, and a theory of pigeons’ equivalence-class formation.
Journal of the Experimental Analysis of Behavior, 90, 257-282.
Five experiments assessed associative symmetry in pigeons. In Experiments 1A, 1B and 2, pigeons learned
two-alternative symbolic matching with identical sample- and comparison-response requirements and with
matching stimuli appearing in all possible locations. Despite controlling for the nature of the
functional stimuli and insuring all requisite discriminations, there was little or no evidence for
symmetry. By contrast, Experiment 3 demonstrated symmetry in successive (go/no-go)
matching, replicating the findings of Frank and Wasserman (2005). In view of these results,
I propose that in successive matching, (1) the functional stimuli are stimulus Ð temporal
location compounds, (2) continual non-reinforcement of some sample-comparison combinations
juxtaposed with reinforcement of other combinations throughout training facilitates stimulus class
formation, (3) classes consist of the elements of the reinforced combinations,
and (4) common elements produce class merger. The theory predicts that particular
sets of training relations should yield “anti-symmetry”: Pigeons should respond more to a
reversal of the non-reinforced symbolic baseline relations than to a reversal of the
reinforced relations. Experiment 4 confirmed this counterintuitive prediction. These
results and other theoretical implications support the idea that equivalence relations
are a natural consequence of reinforcement contingencies.
Key words: associative symmetry, anti-symmetry, stimulus classes, equivalence relations, successive
matching, pigeons, key peck