Spatially extended instrumental responses are organized in functional bouts

Instrumental behavior is typically organized into bouts, with distinct behavioral processes seemingly governing within-bout response rate, bout-initiation rate, and bout length. This organization, however, may instead arise simply from the spatial proximity of the organism to the operandum at the end of each response. Two experiments used rats to test the organization of spatially extended instrumental responses into bouts and the sensitivity of bout parameters to critical manipulations. In Experiment 1, rats consecutively pressed two levers located on either side of an operant chamber, reinforced on a tandem variable-time (VT) 150-s fixed-ratio (FR) 1 schedule (Phase 1). The FR requirement was then increased (Phase 2) before food restriction was reduced (Phase 3). In Experiment 2, reinforcement was contingent on pressing a single lever or alternating between two levers in alternating multiple-schedule components. Lever pressing was then extinguished in both components. Regardless of topography, responses were organized in bouts (Experiments 1 and 2). Higher FR requirements increased bout length (Experiment 1), and the response-alternation requirement reduced within-bout response rate (Experiment 2). Both manipulations, along with reduced deprivation and extinction, reduced bout-initiation rates. These results rule out the possibility that bouts of responses emerge from the spatial proximity of terminating and initiating operants.