Polydipsia's Contribution to the Temporal Discrimination of Rats in the Development of Fixed Interval Behavior and as a Function of Fixed Interval Length

A two-phase experiment was undertaken to study the contribution of polydipsia, excessive water drinking, to the temporal discrimination of rats on fixed internal schedules of 60, 120, 180, and 300 seconds. In the first phase of the experiment, the timing accuracy of 12 rats who had access to water was compared to 12 rats who had no water. The rats were trained for 25 sessions on an FI 60-second schedule. In early sessions, before polydipsia was fully developed, no differences emerged between the timing accuracy of the water and no-water groups. As the amount of water drunk by the water group increased over sessions, a parallel increase was noted in the timing accuracy of that group. In the final sessions of Phase I, a significant difference emerged between the timing accuracy of the water and no-water rats. It was concluded that polydipsia facilitated the development of temporal discrimination. The second phase of the experiment was undertaken to study the effects of increased interval length on timing accuracy and water intake. Four rats from each of the water and no-water groups were changed to FI schedules of 120, 180, and 300 seconds and trained for 20 days. Three main conclusions were drawn from Phase II: (1) timing accuracy declined as a function of increased interval length; (2) water rats exhibited more accurate timing ability than their no-water counterparts but only for groups operating under the 180- and 300-second lengths; no differences emerged between the 120-second water and no-water groups; (3) the amount of water drunk during the longer schedules did not substantially change from the amount drunk under the 60 second schedule; therefore, changes in the amount of water drunk could not be used to account for changes in timing accuracy. Changes in the rate of water drunk, however, were suggested as an alternative explanation. In summary, the facilitating role of polydipsia in the temporal discrimination of rats was supported over a range of fixed interval lengths. Timing accuracy was found to decline over longer interval lengths, while parallel changes in the amount of water drunk were not found.