Symmetry in the pigeon with sample and comparison stimuli in different locations.

Pigeons typically do not show evidence for symmetry in two-alternative matching-to-sample but do demonstrate this emergent relation in successive (go/no-go) matching-to-sample. Because the sample and comparison stimuli are presented in the same spatial location (viz., on one key) during successive matching training and testing, this may be one reason why pigeons pass tests for symmetry in this paradigm. To evaluate this, one group of pigeons received successive matching training with hue-sample stimuli on the center key and form-comparison stimuli on the left key of a three-key chamber. A control group was trained with all stimuli appearing on the same (left) key. Training also involved concurrent hue- and form-identity successive matching with the same spatial location arrangement as each group's respective hue-form task. Later, nonreinforced form-hue (symmetry) probes structured in the same way as the baseline trials were given. Of the six birds in each group, five trained with different locations and two trained with constant location responded more to the reverse of baseline positive hue-form combinations than to negative ones in testing. Results confirm the prediction from Urcuioli's (2008) theory that symmetry should emerge even with varying spatial locations, as long as functional stimuli are held constant. © Society for the Experimental Analysis of Behavior.