On the role of US expectancies in avoidance behavior.

In studies on avoidance learning, a warning signal is followed by an aversive outcome (US) unless the participant makes a particular response. Several theories have been developed to try to explain the mechanisms underlying avoidance learning. Surprisingly, stimulus-response (S-R) theories and cognitive theories of avoidance learning have rarely been compared experimentally. These theories differ in the role they assign to the US representation in avoidance learning. We used a method often used to investigate the contribution of the US representation-namely, US revaluation. Participants first learned to avoid two different negative USs. In a revaluation phase, the value of one US became positive, whereas the value of the other US remained the same. The results indicated that after the revaluation phase, participants avoided the positive US less than the negative US. These results cannot be explained by S-R theories of avoidance learning.