Stimulus comparison and stimulus association processes in the perceptual learning effect.

In four experiments rats were given preexposure to two flavoured fluids, presented simultaneously in separate bottles. A conditioned aversion was then established to one flavour and the generalization of this aversion to the other was tested. Experiments 1a and 1b demonstrated that, in contrast to the effect obtained when the two flavours are presented at separate times during preexposure, such preexposure enhances generalization. Experiments 2a and 2b examined the hypothesis that this enhanced generalization was a consequence of the formation of an excitatory association between the two flavours during preexposure. In these experiments, the preexposure phase was followed by a phase of training (in which each flavour was presented alone on separate occasions) designed to extinguish the postulated association. It was found, however, that the enhancement of generalization survived the introduction of this procedure. Implications for the perceptual learning effect (the observation that certain forms of preexposure can restrict generalization between preexposed stimuli) are discussed.