Retroactive interference effects of surprising reward omission on serial spatial memory

Reward omission was used to produce retroactive interference in a serial delayed-alternation task. Rats were given forced choices in 3 T mazes presented in succession followed by free choices in which the alternate arm in each maze was rewarded. Nonreward during the delay between forced- and free-choice runs produced a decrement in performance (i.e., retroactive interference) in comparison to reward during the delay. Interference in retention of the first maze in a list occurred when the second maze contained surprising reward or omission (i.e., an outcome contrary to previous training in that maze) in comparison to expected reward or omission. In addition to producing retroactive interference, omission sometimes increased alternation in the maze in which it occurred. These results support a differential rehearsal hypothesis of spatial memory.