title: Distortion-Product Otoacoustic Emission Measured Below 300 Hz in Normal-Hearing Human Subjects.
abstract: Physiological noise levels in the human ear canal often exceed naturally low levels of otoacoustic emissions (OAEs) near the threshold of hearing. Low-frequency noise, and electronic filtering to cope with it, has effectively limited the study of OAE to frequencies above about 500 Hz. Presently, a custom-built low-frequency acoustic probe was put to use in 21 normal-hearing human subjects (of 34 recruited). Distortion-product otoacoustic emission (DPOAE) was measured in the enclosed ear canal volume as the response to two simultaneously presented tones with frequencies f1and f2. The stimulus-frequency ratio f2/f1was varied systematically to find the "optimal" ratio evoking the largest level at 2 f1-f2frequencies 87.9, 176, and 264 Hz. No reference data exist in this frequency region. Results show that DPOAE exists down to at least 87.9 Hz, maintaining the bell-shaped dependence on the f2/f1ratio known from higher frequencies. Toward low frequencies, however, the bell broadens and the optimal ratio increases proportionally to the bandwidth of an auditory filter as defined by the equivalent rectangular bandwidth. The DPOAE phase rotates monotonously as a function of the stimulus ratio, and its slope trend supports the notion of a lack of scaling symmetry in the apex of the cochlea.
authors.affiliation: Section for Signal and Information Processing, Department of Electronic Systems, Fredrik Bajers Vej 7B5, 9220, Aalborg, Denmark. atc@es.aau.dk.
authors.forename: Anders T
authors.initials: AT
authors.lastname: Christensen
authors.affiliation: Section for Signal and Information Processing, Department of Electronic Systems, Fredrik Bajers Vej 7B5, 9220, Aalborg, Denmark.
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Ordoñez
authors.affiliation: Section for Signal and Information Processing, Department of Electronic Systems, Fredrik Bajers Vej 7B5, 9220, Aalborg, Denmark.
authors.forename: Dorte
authors.initials: D
authors.lastname: Hammershøi
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D017084:Otoacoustic Emissions, Spontaneous; D055815:Young Adult
keywords: DPOAE phase; auditory filter; cochlear mechanics; distortion-product otoacoustic emission; low-frequency hearing; optimal stimulus ratio