International Journal of Comparative Psychology

The effects of stimulus preexposure on conditioning and generalization of a taste aversion were evaluated in infant rats, manipulating stimulus similarity and duration, and the length and procedure (intermixed vs. blocked) of preexposure. Preexposure to simple tastes retarded conditioning and reduced generalization (Experiment 1a), whereas preexposure to compound tastes facilitated conditioning and increased generalization (Experiment 1b). Increasing the number of preexposure trials retarded conditioning and decreased generalization with compound tastes (Experiment 1c). These experiments failed to find a differential effect of intermixed vs. blocked stimulus preexposure. In Experiment 2, a 15 min exposure to the conditioned stimulus during conditioning resulted in a weak aversion, whereas a 60-min exposure resulted in a strong aversion. In Experiment 3, the strength of the aversion and the duration of the conditioned stimulus were directly related in nonpreexposed pups, but inversely related in preexposed pups. In infant rats, the level of generalization between stimuli is determined by how preexposure affects acquisition rate.