Ontogenesis of learning: VI. Learned and unlearned responses to visual stimulation in the infant hooded rat.

A Pavlovian fear conditioning procedure was used to examine the ontogeny of the hooded rats' learned responses to visual stimulation. The data suggests a dissociation in the emergence of the processes required to detect visual events and those necessary for learning an association between visual stimulation and shock. Pups did not condition to a visual conditioned stimulus (CS) paired with a shock unconditioned stimulus (US) until they were 17 days old, even though 15-day-olds were clearly able to detect the visual CS. Although 15-day-olds failed to condition to the visual CS, they conditioned successfully when an auditory CS was paired with shock. Thus, the 15-day-olds' failure to condition to the visual CS was not due to a performance deficit or to a general ineffectiveness of shock as an US. These data suggest that the components of the visual system that mediate detection and those required for associative learning mature sequentially.