Chapter 12. The psychophysics of olfaction in the human newborn
Until the early 1960s, little was known about the human newborn’s ability to detect odors. At that time, the modern study of newborn olfaction was introduced by Trygg Engen in collaboration with Lewis Lipsitt, colleagues in the Psychology Department of Brown University. In two seminal studies, they demonstrated that newborns could not only detect pure olfactory stimuli, as opposed to odorous trigeminal irritants, but also could habituate to them over repeated presentations. These studies introduced numerous now-standard control procedures and compound stimuli to the habituation literature. In another series of experiments on newborn olfactory psychophysics, infants directly scaled the subjective intensity of a log2 dilution series of concentrations of five members of an homologous series of aliphatic alcohols, which differ only in the number of carbons in their chemical chains. Newborn’s data were described by power functions that were inversely related to chain length. These functions permitted the role of chain length in newborn sensory adaptation to be examined. Two alcohol pairs, each composed of different chain lengths, were formed from concentrations that were equated for magnitude of responding within pairs. Members of each pair served as both the adapting stimulus and the test stimulus after two adapting intervals. Newborns exhibited either selective cross-adaptation or selective cross-facilitation, depending on the physical properties of odorants with different chain lengths, their order of presentation, and the adapting interval within each odor pair. This body of work exemplifies Engen’s innovations in the science of olfaction with the human newborn. The systematic studies of Engen and his colleagues were the first to document the newborn’s highly developed and acute sense of smell and the significant effect of olfactory experience on newborn learning.