Effect of local density of water delivery on the overall frequency of responding in a signalled temporal schedule

Abstract

Two experiments were conducted, each with 12 male albino Wistar rats. The effect of delivering water in the 20 initial or final cycles of a temporally defined schedule upon the total number of responses per session was evaluated, regardless of the total number of obtained water deliveries. Water delivery was contingent to the first response during the tD period of each cyle and, in addition to that, if animals did not respond in the selected first or final blocks of cycles, water also was delivered noncontingently at the end of its tD period. tD and tΔ periods were signaled by different exteroceptive stimuli. Experiment 2 was similar to Experiment 1, except that a retractable lever was withdrawn right after water delivery when animals responded during the tD periods of the selected cycles and was not reinserted until the beginning of the next cycle. Results show that the total number of responses in a session seems to depend both on the frequency of responses associated to local water deliveries and on the total number of water deliveries, regardless of its distribution within a session. Results are discussed according to the intruded stimulus paradigm.