Acquisition of shuttlebox avoidance by rats was recorded under four CS conditions: (1) light as CS always in one compartment, tone as CS always in the other (LTF), (2) 50% light CS and 50% tone CS but randomly occurring in either compartment (LTR); (3) light CS in both compartments (LL); (4) tone CS in both compartments (TT). In per cent avoidance, LL was superior to the other three groups, which did not differ from each other. The hypothesis that discriminably different stimuli used as CSs

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... d reduce conflict and consequently facilitate avoidance acquisition was rejected. The factors which differentiate unidirectional and shuttle situations were discussed in light of these results.