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.

Stimulus intensity modulates associative and nonassociative responding in preweanling rats.

The purpose of the present study was to determine whether preweanling rats respond differentially to the intensity and energy source of a stimulus. Previous studies have suggested that infants process compound stimuli based on net stimulus intensity regardless of the energy source of the compound's elements, but more direct tests have been needed of the infant's response to the stimulus attributes of intensity and energy source. This response was tested for auditory and visual stimuli that had been equated (Experiment 1) in terms of perceived intensity (low and high). Intensity level and energy source of the stimuli were varied independently within nonassociative (Experiment 2) and associative (Experiment 3) procedures. The overall results indicate that stimuli of a low-perceived intensity were processed in terms of their intensity, whereas high-intensity stimuli were processed on the basis of energy source. These results are relevant to contemporary issues of cognitive development in humans and animals.