Discrimination of Temporal Same–Different Relations by Pigeons

To what extent are nonhumans capable of learning discriminations based upon abstract relations between stimuli (e.g., a same-different rule)? This question has generated a great deal of controversy over the years (e.g., Spence, 1937), and controversy continues to surround the issue of relational learning in animals (e.g., see Carter & Werner, 1978; D'Amato, Salmon, & Colombo, 1985; Premack, 1978, 1983). The evidence indicates that pigeons have considerable difficulty learning relational concepts such as the same–different rule (see Carter & Werner, 1978, for a review), whereas monkeys trained on tasks like those used with pigeons (e.g., matching-to-sample—MTS) appear to base discriminative responses upon a generalized conceptual rule (e.g., D'Amato & Salmon, 1984).