Two-step acquisition: Modification of an internal clock's criterion.

10 male albino Norway rats were trained on a discrete-trial peak procedure in which food, if available, occurred following the 1st response after a signal had been present for 10 sec. 10 other Ss were trained on the same procedure with a 20-sec criterion. When the time of reinforcement was reversed between groups, Ss adjusted their temporal criterion in 2 abrupt steps. During the intermediate state of the 3-step function, Ss used a temporal criterion that was near the geometric mean of the initial and terminal times of reinforcement. It is concluded that the intermediate transition state reflects an internal structure in the animal's information processing system not readily accounted for by stimulus–response models of behavior. (35 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)