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. © 1998 John Wiley & Sons, Inc. Dev Psychobiol 32: 199–214, 1998