Unsignalled avoidance in a shuttlebox: a rapid acquisition, high-efficiency paradigm.

Detailed descriptive data are provided on the free-operant avoidance behavior of rats in a shuttlebox during both acquisition and terminal performance. Initially, eighteen 21-min acquisition sessions were given. Each hurdle-cross postponed the next shock 20 sec (response-shock interval) and shocks were scheduled every 5 sec (shock-shock interval) in the absence of a response. All eight subjects avoided over 70% of the shocks due (12/min) in Session 1. Maximum response rates were reached by the third session and declined slowly while shock rates continued to drop slowly through Session 15. Three subjects were run an additional five months with a response-shock interval of 20 sec and their terminal response rates were all under five responses per minute and shock rates were 0.07 per minute. Interresponse time distributions for terminal performance showed that over 95% of all responding by all three subjects occurred in the last half of the response-shock interval.