Free operant avoidance behavior in hooded rats: IRTs and response chains

Twenty-five hooded rats were given 50 avoidance training sessions with leverpress IRTs obtained during as well as between sessions. Five qualitatively different shapes to the IRT profiles were found: single- or double-peaked shapes, positively or negatively accelerated shapes, and U-shaped distributions. Both the specific shape of the profile and the stability of that shape during a session were related to the avoidance proficiency of an individual rat. Six rats received two additional training sessions, with the final 30 min of each videotaped to obtain frequency counts of nine behavior categories. The observational data showed that avoidance-proficient rats typically incorporated the leverpress requirement into repetitive response chains.