Associative symmetry in a spatial sample-response paradigm.

Symmetry has been difficult to observe in nonhumans mainly because they seem to perceive stimuli as a conjunction of visual, spatial, and temporal characteristics. When such characteristics are controlled, symmetry does emerge in nonhumans (cf. Frank and Wasserman, 2005; Urcuioli, 2008). Recently, however, Garcia and Benjumea (2006) reported symmetry in pigeons without controlling for temporal order. The present experiments explored their paradigm and the ingredients for their success. Experiments 1 and 2 sought to replicate their findings and to examine different symmetry measures. We found evidence for symmetry using non-reinforced choice probe tests, a latency-based test, and a reinforced consistent versus inconsistent manipulation. Experiment 3 adapted their procedure to successive matching to evaluate their contention that a choice between at least two comparisons is necessary for symmetry to emerge. Contrary to their prediction, symmetry was observed following go/no-go training. Our results confirm Garcia and Benjumea's findings, extend them to other test and training procedures, and once again demonstrate symmetry in the absence of language.