A search for symmetry in the visual conditional discrimination of a bottlenose dolphin (Tursiops truncatus)

After conditional discrimination training in which stimulus A served as the sample and stimulus B as the comparison stimulus, it is sometimes observed that the reverse relation, where B is presented as the sample and A as the comparison stimulus, emerges without explicit training. This phenomenon is referred to as the emergence of symmetry. The present study investigated this phenomenon in a bottlenose dolphin (Tursiops truncatus) using a matching-to-sample task involving both figures and objects. Tino was first trained on an arbitrary matching task in which figures served as samples and objects as comparison stimuli (F–O). Following this acquisition phase, baseline training was conducted in which object–object (O–O) and figure–figure (F–F) identity matching trials, along with F–O trials, were presented in random order and with equal frequency within each session. Tino then participated in 24 test sessions, each of which included a single symmetry test trial (object–figure, O–F), in which an object was presented as the sample and figures as the comparison stimuli. On these O–F trials, he demonstrated significantly above-chance accuracy. These results suggest that prior differential reinforcement training involving identity matching, in which all stimuli were used both as samples and as comparison stimuli, combined with the low frequency of nonreinforced test trials, may have contributed to the successful emergence of symmetry without degradation in performance.