Fixed interval performance in weanling rats: a comparison with adult and senile subjects.

Weanling (21 days), adult (100 days) and senescent (26 months) albino rats were submitted for 8 days to a fixed interval 60 second schedule, at a pace of 5 half-hour sessions a day. Temporal regulation indices (Curvature Index of Fry, Kelleher and Cook), overall response rates and running rates depend upon the age of the subjects and rank orderly (weanling greater than adult greater than senile). No significant difference was found for post-reinforcement pause durations. Two weeks after the end of the FI 60 second sessions, the senile subjects were submitted to a FI 120 second schedule for 10 days. The inverse relationship between age and temporal regulation accuracy evidenced in FI 60 seconds is discussed in relationship with classical FI data, factors involved in developmental studies and models for time regulated behavior.