Functional class formation in the context of a foraging task in capuchin monkeys

Functional class formation via repeated reversals of simple discriminations was investigated in a foraging task in captive capuchin monkeys (Cebus cf. apella). Two capuchin monkeys were given simultaneous simple discrimination training and reversals with two (Phase 1), four (Phase 2), and six (Phase 3) visual stimuli (wooden boxes) in the context of searching for food in an apparatus. One different kind of food for each potential stimulus class was used as a reinforcer. After repeated functional reversals of two stimulus sets, multiple tests for functional class formation were performed (Phase 4). Evidence of class formation was found in all of the tests. Next, the same monkeys were given simultaneous simple discrimination training with variations of the stimulus locations between sessions (Phase 5). The class-specific reinforcement procedure was suspended. Tests for functional class formation were again performed. Evidence of class formation was found in all tests. The data suggest that some of the procedural difficulties in documenting class formation in nonhumans can be overcome with procedures that take advantage of the natural skills of the subjects.