Early-session increases in responding during extinction.

After training under a variable-interval 60-s schedule of reinforcement, four rats were exposed to 30-min extinction tests, which occurred either at the start or at the end of the session (each session being 50-min long). Response rate in extinction decreased when the extinction test occurred at the end of the session, but first increased and then decreased when the extinction test occurred at the start of the session. Consistent with other recent results, this finding suggests that some variable, other than reinforcement, contributes to early-session increases in responding.