TIMING PROCESSES IN THE REINFORCEMENT-OMISSION EFFECT

A comparison was made of the effects of long-term exposure to fixed-in terval reinforcement with unsignaled and with signaled reinforcement o missions. When successive fixed-interval cycles ended in reinforcement , subjects showed a clear ''scalloped'' response pattern. When reinfor cement was omitted, but a brief signal was given in lieu of reinforcem ent, responding in the next cycle started earlier than it did after re inforcement. When reinforcement was omitted without exteroceptive cues , response rates peaked near the time of reinforcement and then declin ed to a flat but substantial level. The classic reinforcement omission effect was observed, in that total responding was greatest after uncu ed omission, somewhat less after cued omission, and least after reinfo rcement. However, response rate plotted as a function of time showed t hat the uncued-omission condition had a very different function from t hat of the cued-omission or reinforcement conditions. A failed-discrim ination account of the omission effect might accommodate the three fun ctions if the discrimination is considered to be a temporal one. The t emporal-discrimination account argues that high-rate responding reflec ts the accumulation of subjective time proximal to the memory of the t ime of reinforcement. The accumulation resets completely with food rei nforcement, incompletely with cues in lieu of reinforcement, and not a t all in the absence of cues.