Development of intersensory function: age-related differences in stimulus selection of multimodal compounds in rats as revealed by Pavlovian conditioning.

Preweanling and adult rats were exposed to Pavlovian stimulus pairings with lights, tones, and light-tone compounds as conditional stimuli (CSs). Tone intensity was varied. As was found in previous studies using flavor CSs, odor CSs, or both, in which significant overshadowing or potentiation occurred to an element of a compound, overshadowing was less likely and potentiation more likely for preweanlings than for adults. Several experiments supported the view that these effects reflect an age-related difference in the controlling properties of stimuli: Young rats are more disposed to encode multimodal compounds on the basis of amodal intensity, whereas their elders are more likely to encode modality-specific properties of light and sound. Differential reinforcement in the presence of lights, tones, and light-tone compounds made preweanlings' stimulus selection appear more adultlike and may be a cause of development of intersensory function.