Carolina Abdala, PhD

Professor of Otolaryngology-Head and Neck Surgery

Co-Division Chief

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Human Cochlear Function: A Continuum of Maturation and Aging.
This project studies changes in cochlear function throughout the human lifespan, defining the timeline for these age-related shifts and the mechanisms driving the changes. We use primarily otoacaoustic emissions, a noninvasive ear canal probe of cochlear mechanics to learn about the human peripheral system. We apply both distortion- (DPOAE) and reflection-source (stimulus frequency OAEs and the reflection-component of the DPOAE) emissions using custom-algorithms, innovative swept-tone methodology and advanced analysis schemes. We disentangle the origin of age-related effects by separating distortion product OAEs into their dual components, distortion and reflection; and studying how each component’s phase and amplitude is impacted throughout the human lifespan. In our lab it is important to study both apical and basal halves of the cochlea to yield a more comprehensive understanding of how the cochlea codes low and high-frequency sounds. The apex has been minimally studied in humans, and wholly unexplored during maturation. Yet, we have recently reported striking immaturities in DPOAE phase for low-frequency signals coded in the apex of neonates. Our exploration of human cochlear function from base to apex using multiple OAE sources establishes a normative framework, provides detailed information about newborn cochlear maturation, and probes how the elderly cochlea ages into senescence. These findings contribute to more comprehensive cochlear models and toward the development of more innovative probes of cochlear function for human application. This project is funded by the NIH-NIDCD.

Exploiting Dual OAE Sources to Study the Normal and Impaired Human Cochlea.
This project attempts to exploit the distinct information embedded in reflection- and distortion-source OAEs to create a more comprehensive and descriptive joint test of cochlear function. At present, OAEs are used in a categorical sense, simply to detect hearing loss. However, once hearing loss is detected, we wish to learn about the underlying deficit and etiology. The ample information provided by the two OAE types (i.e. linear reflection and nonlinear distortion) can offer distinct clues about different aspects of cochlear function. We wish to exploit this distinct information to describe (not just detect) sensorineural hearing loss (SNHL). At present, SNHL is a catch-all term, defined by degree of loss and audiometric configuration. However, two hearing losses with identical audiograms can produce varying perceptual difficulties and varied success with hearing aids. By recording a combined reflection and distortion OAE profile over broad level and frequency ranges, we may be able to learn more about the underlying deficits that comprise the broad and vague category of SNHL. When used in combination, the properties embodied by each OAE can be considered in one joint metric. We are currently developing and testing this joint OAE protocol by recording stimulus frequency OAEs and the distortion component of DPOAEs in ears with normal and impaired hearing. This project is conducted in collaboration with fellow USC faculty member Dr. Christopher Shera.



  • Does Endolymphatic Hydrops Shift the Cochlear Tonotopic Map? AIP Conf Proc. 2024 Feb 27; 3062(1).. View in PubMed
  • Characterizing a Joint Reflection-Distortion OAE Profile in Humans With Endolymphatic Hydrops Ear Hear. 2023 Nov-Dec 01; 44(6):1437-1450. . View in PubMed
  • The Remarkable Outer Hair Cell: Proceedings of a Symposium in Honour of WE. Brownell. J Assoc Res Otolaryngol. 2023 04; 24(2):117-127. . View in PubMed
  • Characterizing the Relationship Between Reflection and Distortion Otoacoustic Emissions in Normal-Hearing Adults J Assoc Res Otolaryngol. 2022 Oct; 23(5):647-664. . View in PubMed
  • Weakened Cochlear Nonlinearity During Human Aging and Perceptual Correlates Ear Hear. 2021 July/Aug; 42(4):832-845. . View in PubMed
  • Extended low-frequency phase of the distortion-product otoacoustic emission in human newborns JASA Express Lett. 2021 Jan; 1(1):014404. . View in PubMed
  • J Acoust Soc Am. 2020 09; 148(3):1585. . View in PubMed
  • Effects of Forward- and Emitted-Pressure Calibrations on the Variability of Otoacoustic Emission Measurements Across Repeated Probe Fits Ear Hear. 2019 Nov/Dec; 40(6):1345-1358. . View in PubMed
  • Variable-rate frequency sweeps and their application to the measurement of otoacoustic emissions J Acoust Soc Am. 2019 11; 146(5):3457. . View in PubMed
  • Morphological Immaturity of the Neonatal Organ of Corti and Associated Structures in Humans J Assoc Res Otolaryngol. 2019 10; 20(5):461-474. . View in PubMed
  • Swept-Tone Stimulus-Frequency Otoacoustic Emissions in Human Newborns Trends Hear. 2019 Jan-Dec; 23:2331216519889226. . View in PubMed
  • Probing Apical-Basal Differences in the Human Cochlea Using Distortion-Product Otoacoustic Emission Phase AIP Conf Proc. 2018 May 31; 1965(1). . View in PubMed
  • Reflection- and Distortion-Source Otoacoustic Emissions: Evidence for Increased Irregularity in the Human Cochlea During Aging J Assoc Res Otolaryngol. 2018 10; 19(5):493-510. . View in PubMed
  • Swept-tone stimulus-frequency otoacoustic emissions: Normative data and methodological considerations J Acoust Soc Am. 2018 01; 143(1):181. . View in PubMed
  • Role of Neuropilin-1/Semaphorin-3A signaling in the functional and morphological integrity of the cochlea PLoS Genet. 2017 Oct; 13(10):e1007048. . View in PubMed
  • Towards a joint reflection-distortion otoacoustic emission profile: Results in normal and impaired ears J Acoust Soc Am. 2017 08; 142(2):812. . View in PubMed
  • Characterizing spontaneous otoacoustic emissions across the human lifespan J Acoust Soc Am. 2017 03; 141(3):1874. . View in PubMed
  • Changes in the Compressive Nonlinearity of the Cochlea During Early Aging: Estimates From Distortion OAE Input/Output Functions Ear Hear. 2016 Sep-Oct; 37(5):603-14. . View in PubMed
  • Frequency shifts in distortion-product otoacoustic emissions evoked by swept tones J Acoust Soc Am. 2016 08; 140(2):936. . View in PubMed
  • Optimizing swept-tone protocols for recording distortion-product otoacoustic emissions in adults and newborns J Acoust Soc Am. 2015 Dec; 138(6):3785-99. . View in PubMed
  • Stability of the medial olivocochlear reflex as measured by distortion product otoacoustic emissions J Speech Lang Hear Res. 2015 Feb; 58(1):122-34. . View in PubMed
  • Stimulus-frequency otoacoustic emissions in human newborns J Acoust Soc Am. 2015 Jan; 137(1):EL78-84. . View in PubMed
  • Exploiting Dual Otoacoustic Emission Sources AIP Conf Proc. 2015; 1703. . View in PubMed
  • Distortion-product otoacoustic emission reflection-component delays and cochlear tuning: estimates from across the human lifespan J Acoust Soc Am. 2014 Apr; 135(4):1950-8. . View in PubMed
  • Aging of the medial olivocochlear reflex and associations with speech perception J Acoust Soc Am. 2014 Feb; 135(2):754-65. . View in PubMed
  • Maturation of the human medial efferent reflex revisited J Acoust Soc Am. 2013 Feb; 133(2):938-50. . View in PubMed
  • Maturation and aging of the human cochlea: a view through the DPOAE looking glass J Assoc Res Otolaryngol. 2012 Jun; 13(3):403-21. . View in PubMed
  • The relationship between MOC reflex and masked threshold Hear Res. 2011 Dec; 282(1-2):128-37. . View in PubMed
  • The breaking of cochlear scaling symmetry in human newborns and adults J Acoust Soc Am. 2011 May; 129(5):3104-14. . View in PubMed
  • Breaking away: violation of distortion emission phase-frequency invariance at low frequencies J Acoust Soc Am. 2011 May; 129(5):3115-22. . View in PubMed
  • Level dependence of distortion product otoacoustic emission phase is attributed to component mixing J Acoust Soc Am. 2011 May; 129(5):3123-33. . View in PubMed
  • Distortion-product otoacoustic-emission suppression tuning in human infants and adults using absorbed sound power J Acoust Soc Am. 2011 Apr; 129(4):EL108-13. . View in PubMed
  • Deviations from Scaling Symmetry in the Apical Half of the Human Cochlea AIP Conf Proc. 2011; 1403:483-488. . View in PubMed
  • Differences in distortion product otoacoustic emission phase recorded from human neonates using two popular probes J Acoust Soc Am. 2010 Jul; 128(1):EL49-55. . View in PubMed
  • Distortion product otoacoustic emission phase and component analysis in human newborns J Acoust Soc Am. 2010 Jan; 127(1):316-25. . View in PubMed
  • Considering distortion product otoacoustic emission fine structure in measurements of the medial olivocochlear reflex J Acoust Soc Am. 2009 Mar; 125(3):1584-94. . View in PubMed
  • Changes in the DP-gram during the preterm and early postnatal period Ear Hear. 2008 Aug; 29(4):512-23. . View in PubMed
  • A comparative study of distortion-product-otoacoustic-emission fine structure in human newborns and adults with normal hearing J Acoust Soc Am. 2007 Oct; 122(4):2191-202. . View in PubMed
  • Distortion product otoacoustic emission suppression tuning and acoustic admittance in human infants: birth through 6 months J Acoust Soc Am. 2007 Jun; 121(6):3617-27. . View in PubMed
  • Theory of forward and reverse middle-ear transmission applied to otoacoustic emissions in infant and adult ears J Acoust Soc Am. 2007 Feb; 121(2):978-93. . View in PubMed
  • Effects of middle-ear immaturity on distortion product otoacoustic emission suppression tuning in infant ears J Acoust Soc Am. 2006 Dec; 120(6):3832-42. . View in PubMed
  • Effects of aspirin on distortion product otoacoustic emission suppression in human adults: a comparison with neonatal data J Acoust Soc Am. 2005 Sep; 118(3 Pt 1):1566-75. . View in PubMed
  • Distortion product otoacoustic emission (2f1-f2) suppression in 3-month-old infants: evidence for postnatal maturation of human cochlear function? J Acoust Soc Am. 2004 Dec; 116(6):3572-80.. View in PubMed
  • A longitudinal study of distortion product otoacoustic emission ipsilateral suppression and input/output characteristics in human neonates J Acoust Soc Am. 2003 Dec; 114(6 Pt 1):3239-50. . View in PubMed
  • Ipsilateral distortion product otoacoustic emission (2f1-f2) suppression in children with sensorineural hearing loss J Acoust Soc Am. 2003 Aug; 114(2):919-31. . View in PubMed
  • Progressive hearing loss in mice lacking the cyclin-dependent kinase inhibitor Ink4d Nat Cell Biol. 2003 May; 5(5):422-6. . View in PubMed
  • DPOAE suppression tuning: cochlear immaturity in premature neonates or auditory aging in normal-hearing adults? J Acoust Soc Am. 2001 Dec; 110(6):3155-62.. View in PubMed
  • Cochlear receptor (microphonic and summating potentials, otoacoustic emissions) and auditory pathway (auditory brain stem potentials) activity in auditory neuropathy Ear Hear. 2001 Apr; 22(2):91-9. . View in PubMed
  • Distortion product otoacoustic emission suppression in subjects with auditory neuropathy Ear Hear. 2000 Dec; 21(6):542-53. . View in PubMed
  • Distortion product otoacoustic emission (2f1-f2) amplitude growth in human adults and neonates J Acoust Soc Am. 2000 Jan; 107(1):446-56. . View in PubMed
  • Maturation of medial efferent system function in humans J Acoust Soc Am. 1999 Apr; 105(4):2392-402. . View in PubMed
  • Gender distinctions and lateral asymmetry in the low-level auditory brainstem response of the human neonate Hear Res. 1998 Dec; 126(1-2):58-66. . View in PubMed
  • A developmental study of distortion product otoacoustic emission (2f1-f2) suppression in humans Hear Res. 1998 Jul; 121(1-2):125-38. . View in PubMed
  • Auditory threshold sensitivity of the human neonate as measured by the auditory brainstem response Hear Res. 1997 Feb; 104(1-2):27-38. . View in PubMed
  • Distortion product otoacoustic emission (2f1-f2) amplitude as a function of f2/f1 frequency ratio and primary tone level separation in human adults and neonates J Acoust Soc Am. 1996 Dec; 100(6):3726-40. . View in PubMed
  • Hearing threshold as measured by auditory brain stem response in human neonates Ear Hear. 1996 Oct; 17(5):395-401. . View in PubMed
  • The development of cochlear frequency resolution in the human auditory system Ear Hear. 1996 Oct; 17(5):374-85. . View in PubMed
  • Distortion product otoacoustic emission suppression tuning curves in human adults and neonates Hear Res. 1996 Sep 01; 98(1-2):38-53. . View in PubMed
  • The development of frequency resolution in humans as revealed by the auditory brain-stem response recorded with notched-noise masking J Acoust Soc Am. 1995 Aug; 98(2 Pt 1):921-30. . View in PubMed
  • Frequency contribution to the click-evoked auditory brain-stem response in human adults and infants J Acoust Soc Am. 1995 Apr; 97(4):2394-404. . View in PubMed
  • Perceptual features from normal-hearing and hearing-impaired children’s errors on the NST Ear Hear. 1986 Oct; 7(5):318-22. . View in PubMed
  • Statistical models for predicting Edgerton-Danhauer NST scores from pure-tone thresholds J Aud Res. 1986 Jul; 26(3):167-75. . View in PubMed
  • A survey of speech and other auditory perception assessment materials used by cochlear implant centers J Aud Res. 1986 Apr; 26(2):75-87. . View in PubMed