A differential outcomes effect using biologically neutral outcomes in delayed matching-to-sample with pigeons

The differential outcomes effect (DOE) pertains to enhanced conditional discrimination performance if each correct stimulus-choice sequence is always followed by a different outcome (e.g., food vs. water) compared to when each correct sequence is followed equally often by either outcome. The present experiments sought evidence of a DOE in pigeons, using biologically neutral outcomes. Experiment 1 replicated findings with rats demonstrating that a DOE can occur when one outcome is a biologically neutral light and the other is the absence of that light. Experiment 2 extended these findings by demonstrating a DOE when two biologically neutral outcomes of similar sensory and associative properties were employed.