Identifying the mechanisms that generate choice and timing behavior in dynamic concurrent choice procedures

Cognitive theories of timing and conditioned reinforcement provide two different theoretical perspectives on choice between delayed rewards. The primary objective of this research was to identify the process that generates choice in the concurrent-chains procedure and to characterize its relationship with temporal control. Experiments 1-3 investigated the relationship between the dynamics of pigeons’ preference and temporal control in concurrent chains using an arrangement in which the delays to reinforcement changed unpredictably across sessions. To obtain convergent measures of choice and timing behavior, occasional ‘no-food’ terminal links lasted longer than the schedule values and ended without reinforcement. Measures of choice (log initial-link response ratios) and timing (start and stop times from no-food terminal links) stabilized within individual sessions. Sensitivity of log response ratios to relative immediacy increased as initial-link duration decreased or absolute terminal-link delays increased, but absolute initial- and terminal-link duration did not affect temporal control. Residual covariation analyses of log response ratios with log start and stop time ratios confirmed that measures of choice and timing were interdependent. Experiments 4 and 5 used concurrent-chains procedures in which immediacy, magnitude (and probability, in Experiment 5) ratios for left and right keys were 2:1 or 1:2, determined across sessions by independent, random series. Experiment 6 was a concurrent schedule in which relative reinforcement rate and magnitude were 2:1 or 1:2, determined the same way. Multiple regression analyses showed that pigeons’ response allocation in Experiments 4-6 was sensitive to multiple dimensions of reinforcement. Levels of preference within individual sessions and initial links or interfood intervals was more extreme when all dimensions favored the same key than when at least one dimension favored each key, consistent with assumptions of the generalized matching law. Within individual sessions, changes in response allocation in all experiments tended to be abrupt, consistent with the assumptions of Rate Estimation Theory (Gallistel & Gibbon, 2000). A decision model that posits a comparison between delayed outcomes with a criterion delay (Grace & McLean, 2006) described initial-link responding in Experiments 1-3. A modified decision model in which outcome expectancy is compared to an expectancy criterion described responding in Experiments 4-6