Human Neonatal Cardiac Acceleration to Sound: Habituation and Dishabituation

The importance of early learning for the normal development of perception has been emphasized in studies reviewed by Hebb (1949, 1958), Riesen (1958), and Dember (1960). Nonetheless, adequate data on the human newborn are lacking, perhaps in part because the human newborn's relatively poor neuromuscular development poses serious barriers to behavioral studies (Harlow, 1959). W e have suggested that physiological measures could provide the basis for a program formulated to investigate ontogenetic development of functions involving specific and diffuse projection systems (Bartoshuk, 1962). To this end, we have been investigacing the occurrence of arousal habituation in human newborns, its selectivity or generalization, and the possibility of differentiating fatigue and learning interpretations of habituation. An auditory stimulus reliably eliciced cardiac acceleration in human newborns and iterative scimulation produced a significant response decrement across crials (Bartoshuk, 1962 ) . When responses on lacer trials were expressed as per cent of initial response, the response decrement curves did not vary with the intertrial intervals used ( 15, 30, and 60 sec.). The latter resulc argues against attributing the response decrement to fatigue or reactive inhibition, which should have been greater with shorter intertrial intervals. The author suggested that the response decrement may be similar to the habituation of arousal reported by Sharpless and Jasper (1956), which has been interpreted as involving some form of learning (Hebb, 1958; Rosvold, 1959). A learned discrimination is more obviously implicated in the demonstration of EEG responses in sleeping human adults to a tape recording of their own name, except when played backwards, but not to other names equated for intensity (Oswald, et al., 1960). Our previous studies (Bartoshuk, 1959, 1962) employed an identical stimulus on all trials and therefore they did not provide any data on the selectivity or generalization of habituation. The main purpose of the present research was to investigate dishabiruation under condicions designed to facilitate the evaluation of fatigue and learning interpretations of the response decrement seen in human newborns.