Effect of context salience on heart rate orienting and habituation in preweanling and periadolescent rats.

Previous research indicates that target learning is facilitated in the presence of strong extraneous sensory cues (e.g., salient contextual cues) in infant, but not adult, rats (McKinzie & Spear, 1995). The present study assessed whether such facilitation of conditioning is due to age-related differences in the effect of a salient context on processing of the conditioned stimulus (tone in this case). Preweanling and periadolescent rats were presented with a tone in either the presence (salient context) or absence (plain context) of a potent odorant. Magnitude of the heart rate orienting response to the target stimulus and its subsequent rate of habituation served as dependent variables. The results revealed that preweanling, but not periadolescent, rats showed greater cardiac orienting to the auditory stimulus in the salient than in the plain context. The results suggest that a salient context may influence stimulus processing by increasing the perceived salience and, perhaps in terms of perceived intensity, of the target stimulus.