Is bar-holding with negative reinforcement preparatory or perseverative.

Three of four white rats learned to press first one bar and then another to escape or avoid electric shocks. Cumulative bar-holding-time records showed that holding occurred frequently on the second bar but hardly ever on the first, indicating that bar-holding is more "perserverative" than "preparatory". The response chain, first-bar press second-bar press, was more easily established by a forward than by a backward chaining procedure.