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This study examined the influence of diazepam upon the successive positive contrast effect in one-way avoidance learning. The results showed that when injected with vehicle, a safety-time increment (from 1 to 30sec in the contrast group) during one-way avoidance learning led to a performance improvement, surpassing that of two control groups receiving the larger (30sec) or the lower (1sec) reward (safe time) from the beginning of training. However, when three similar groups were injected with diazepam, this contrast effect disappeared and learning was similar in all groups at the end of training. These results demonstrated a positive contrast effect in one-way avoidance learning and its attenuation by diazepam, bearing out previous findings about the joint influence of fear and relief upon acquisition and maintenance of the avoidance response. From an opponent process theory, the interaction between the motivational strength of fear and the incentive value of relief can explain not only positive and negative contrast effects, but also how anxiolytics attenuate both effects.
