Developmental Changes in the Olfactory Threshold of the Neonate1

This paper reports the results of a study in olfaction related to a general program of sensory and learning studies carried out in the neonate psychological laboratories of the Providence Lying-In Hospital. A recent study by Engen, Lipsitt, and Kaye (4), utilizing a technique for the psychophysical assessment of odor perception in the newborn, has reported on (a) the differential responsiveness of neonates to different olfactory stimuli and (b) the changing characteristics of babies' responses to successive stimulations with single odors, i.e., adaptation. The present experiment seeks to discover whether there are developmental changes in odor perception with increasing age over the first 4 days of life. Lipsitt and Levy (7) have previously reported increasing sensitivity over the first 4 days to electrotactual stimulation, and Kaye (5) has found basal skin conductance to increase over the same period. Previous studies of olfaction in infants (see reviews of Disher [3] and Pratt [8]) have tended to infer odor perception from the judged presence or absence of response to odorants of ungraded intensity. Pratt, Nelson, and Sun (9) obtained no age differences in percentage of response to several ungraded odors between birth and 4 days of age, or even to i i days of age. Disher (3) seems to have been the only worker to use different intensities of odorants in the study of neonatal response. She studied infants from 3 hours to Io days of age and, although an increasing percentage of response from 5I per cent to 71 per cent to four intensities of stimulus was obtained,