Stimulus representations in human Pavlovian conditioning: implications of missing negative transfer across response systems.

Three Pavlovian conditioning experiments with human participants are reported, which investigated whether common or separate stimulus representations are involved in solving nonlinear discrimination tasks in different response systems. In our experiments we made use of a negative transfer effect between positive and negative patterning. Experiment 1 specified the conditions under which such a negative transfer effect occurs in human eyelid conditioning. Experiments 2 and 3 investigated whether a similar effect also occurs if two response systems--the eyelid and the skin conductance response system--are trained with trials of both types being randomly interleaved. The presence or absence of a negative transfer effect indicates whether or not the stimulus representations involved in the two conditioning processes overlap. The findings are discussed within the framework of a neuropsychological model of hippocampal function. The results suggest that the representations are distinct and thus support the idea of acquired equivalence and distinctiveness of stimulus representations.