Tuning of SFOAEs Evoked by Low-Frequency Tones Is Not Compatible with Localized Emission Generation

Karolina K. Charaziak*, Jonathan H. Siegel

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

19 Scopus citations

Abstract

Stimulus-frequency otoacoustic emissions (SFOAEs) appear to be well suited for assessing frequency selectivity because, at least on theoretical grounds, they originate over a restricted region of the cochlea near the characteristic place of the evoking tone. In support of this view, we previously found good agreement between SFOAE suppression tuning curves (SF-STCs) and a control measure of frequency selectivity (compound action potential suppression tuning curves (CAP-STC)) for frequencies above 3 kHz in chinchillas. For lower frequencies, however, SF-STCs and were over five times broader than the CAP-STCs and demonstrated more high-pass rather than narrow band-pass filter characteristics. Here, we test the hypothesis that the broad tuning of low-frequency SF-STCs is because emissions originate over a broad region of the cochlea extending basal to the characteristic place of the evoking tone. We removed contributions of the hypothesized basally located SFOAE sources by either pre-suppressing them with a high-frequency interference tone (IT; 4.2, 6.2, or 9.2 kHz at 75 dB sound pressure level (SPL)) or by inducing acoustic trauma at high frequencies (exposures to 8, 5, and lastly 3-kHz tones at 110–115 dB SPL). The 1-kHz SF-STCs and CAP-STCs were measured for baseline, IT present and following the acoustic trauma conditions in anesthetized chinchillas. The IT and acoustic trauma affected SF-STCs in an almost indistinguishable way. The SF-STCs changed progressively from a broad high-pass to narrow band-pass shape as the frequency of the IT was lowered and for subsequent exposures to lower-frequency tones. Both results were in agreement with the “basal sources” hypothesis. In contrast, CAP-STCs were not changed by either manipulation, indicating that neither the IT nor acoustic trauma affected the 1-kHz characteristic place. Thus, unlike CAPs, SFOAEs cannot be considered as a place-specific measure of cochlear function at low frequencies, at least in chinchillas.

Original languageEnglish (US)
Pages (from-to)317-329
Number of pages13
JournalJARO - Journal of the Association for Research in Otolaryngology
Volume16
Issue number3
DOIs
StatePublished - Jun 1 2015

Keywords

  • acoustic trauma
  • chinchilla
  • compound action potential
  • suppression tuning curve
  • two-tone suppression

ASJC Scopus subject areas

  • Otorhinolaryngology
  • Sensory Systems

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