The role of inhibition in the suboptimal choice task.

Given a choice, pigeons prefer an initial-link stimulus that is followed by reliable signals that food will be delivered (S+) or not (S-) after a delay, over an alternative initial-link stimulus that is followed by unreliable signals of food, even when the former yields a lower overall probability of food. This suboptimal preference has been attributed to the combination of a biased attraction to the S+ and ignoring the S-. We evaluated the inhibitory properties of the S- in three experiments to investigate its role in suboptimal choice. In Experiment 1, pigeons were trained in an autoshaping procedure with the four terminal link stimuli of the suboptimal choice task; S+ was continuously reinforced, S3 and S4 were each partially reinforced on a 50% schedule, and S- was never reinforced. Summation tests showed that S- acquired inhibitory properties during training. Experiment 2 replicated the summation tests after training on the full suboptimal choice procedure and found that S- inhibition was not attributable to external inhibition. In Experiment 3, pigeons were trained on the suboptimal choice procedure and the development of inhibition was assessed throughout training. An analysis of individual differences across birds revealed that the response rates to S- were negatively correlated with the strength of suboptimal preference, both within subject as each bird acquired suboptimal preference, and across subjects once all birds had reached asymptotic levels of suboptimal preference. Thus, rather than ignoring the S-, we found evidence that birds attended to S- as an inhibitory stimulus. Future models explaining performance in the suboptimal choice task should consider inhibition to the S- as a factor in suboptimal choice. (PsycInfo Database Record (c) 2021 APA, all rights reserved).