Midsession reversal task with pigeons: Parallel processing of alternatives explains choices

Most models of choice assume a “tug of war” (ToW) between options present at the time of the choice, arguing that preferences are built in this process, and implying that adding options increases delay to act. In contrast, the Sequential Choice Model (SCM) proposes that choices are driven by parallel expression of the mechanisms that control action in sequential encounters, without comparative deliberation at choice time. Only the SCM predicts choice preferences based on latencies to respond in single-option encounters. SCM further predicts that latencies to choose should either be the same or shorter than those in sequential encounters. We contrasted these models using a midsession reversal task with pigeons. Responses to one alternative (S1) were rewarded in the first half of each session and those to the other (S2) in the second half. Single-option (sequential) and two-option (choice) trials were intermingled. In choice trials subjects strongly preferred S1 early in the session, showed intermediate preferences towards the mid-session, and preferred S2 late. These preferences were all predicted by changes in latency towards the presently negative alternative (S2 early and S1 late) in single-option trials. Latency towards presently positive stimuli were minimal throughout, in both single and two option trials, with no evidence of an evaluation time cost of choice. The ability to predict choice preference from latencies in sequential encounters and the absence of a choice delay support the SCM against ToW models, consistently with results from other protocols and species.