Acoustic emissions from the ear: a summary of results from humans and animals.

As mentioned in Saunders et al. [J. Acoust. Soc. Am. 78, 299-311 (1985)] an understanding of the transduction of sound into the auditory neural code is a major goal of the hearing scientist. A variety of tools has been and is being used to achieve that goal. The recent discovery of physical acoustic emissions from the ear provides both new insight into possible transduction mechanisms and a useful new tool for research. The existence of narrow-band spontaneous acoustic emissions from the ear suggests the possibility of active cochlear processes that were not seriously considered a decade ago. Acoustic emissions, both spontaneous and evoked, also provide a simple and noninvasive means of monitoring a by-product of cochlear-mechanical activity. In the present paper, results of studies of acoustic emissions from human ears are briefly summarized and compared to results obtained with animals. Differences between human and animal emissions are noted and the implications of these differences and hypotheses to explain them are discussed.