Here or There, Now or Then? Relative Reinforcement and Divided Stimulus Control in Space and Time

Abstract

Stimuli that signal the consequences that are likely to follow behaviour control how, when, and where organisms behave. When more than one stimulus provides such information, each may exert some control over behaviour. Recent research suggests that such divided stimulus control depends on the relative ability of each stimulus to predict future reinforcers. The present thesis extended this finding in four experiments with pigeons. Experiment 1 showed that relative reinforcer rates determine divided control between separately trained stimuli that signalled the location of future reinforcers if the stimuli were spatially separated, but not if they were combined together. Experiment 2 was an extension of Experiment 1, and showed that reinforcer rates determine divided control between spatially separated stimuli that were trained together. In Experiment 3, relative reinforcer probabilities divided control between stimuli that signalled the time of future reinforcers, but such effects were small and time-dependent, probably because elapsed time also competed for behavioural control. Experiment 4 investigated divided control between elapsed time and a visual stimulus in a concurrent choice schedule, and showed that this division depends on elapsed time and the reliability with which visual stimuli signalled future reinforcer availability, but not on the reliability with which elapsed time signalled future reinforcer availability. Therefore, in general, stimuli that were better predictors of future reinforcers exerted stronger control over behaviour. These experiments extend the relation between relative reinforcer predictability and divided stimulus control to (1) separately trained stimuli, (2) spatially separated stimuli, (3) temporal discriminations, and (4) temporal and non-temporal stimuli. However, the effects of relative reinforcers on divided stimulus control were modulated by several factors, including the spatial configuration of the stimuli, the type of training procedure, changes in previously learned contingencies, elapsed time, and contingency discriminability. Therefore, the present thesis helps to establish the generality of the relation between relative reinforcers and divided stimulus control, but also highlights some of the potential limits of this generality. This thesis is a step towards a more comprehensive understanding of the complexities of stimulus control, and provides a platform for future research to investigate further the mechanisms underlying divided stimulus control.