Distributed Sources of Otoacoustic Emissions Stephen Neely Michael Gorga Boys Town National Research Hospital Omaha, Nebraska

Story of OAE sources History of OAE-source theories Observations of multiple temporal peaks DPOAE IFFT Cochlear reflectance Clinical utility of DPOAEs Benefits of multivariate analysis DPOAE suppression

Where do OAEs originate? Kemp (1978) Kim, Siegel, Molnar (1979) Neely, Norton, Gorga, Jesteadt (1988) Prieve, Abbas (1989) Zweig, Shera (1995) Stover, Neely, Gorga (1996) Talmadge, Tubis, Long (1998) Shera, Guinan (1999) Konrad-Martin et al. (1999) Choi et al. (2003)

1978: Kemp Stimulated acoustic emissions from within the human auditory system First OAE measurements “…probably of cochlear origin”

1979: Kim, Siegel , Molnar Cochlear nonlinear phenomena in two-tone responses 2f1-f2 distortion component is present at the f2 place at the 2f1-f2 place Neural data (not a cartoon) As a graduate student in Kim’s lab, these data strongly influenced by thinking about otoacoustic emissions.

1988: Neely, Norton, Gorga, Jesteadt Latency of auditory brain‐stem responses and otoacoustic emissions using tone‐burst stimuli ABR latency remarkably consistent OAE latency twice ABR, but difficult to define Cochlear origin!

1995: Zweig, Shera Modeling otoacoustic emission and hearing threshold fine structures Introduced coherent reflection theory.

1996: Stover, Neely, Gorga Latency and multiple sources of distortion product otoacoustic emissions Pioneered IFFT analysis of DPOAEs Associated IFFT peaks with sources Sometimes more than two peaks

1998: Talmadge, Tubis, Long Modeling otoacoustic emission and hearing threshold fine structures Developed theory of two-source model

1999: Shera, Guinan Evoked otoacoustic emissions arise by two fundamentally different mechanisms: A taxonomy for mammalian OAEs Two mechanisms Linear reflection Nonlinear distortion Two broad classes of OAEs Reflection source Distortion source Taxonomy widely accepted and influential

2001: Konrad-Martin, Neely, Keefe, Dorn, Gorga Sources of distortion product otoacoustic emissions revealed by suppression experiments and inverse fast Fourier transforms in normal ears Further developed IFFT analysis of DPOAEs Observed multiple DPOAE peaks Demonstrated suppression of secondary DPOAE peaks Associated unsuppressed peaks with distortion sources and suppressed peaks with reflection sources

2008: Choi, Lee, Parham, Neely, Kim Stimulus-frequency otoacoustic emission: Measurements in humans and simulations with an active cochlear model Salient features of human SFOAEs were simulated with an active cochlear model. “…in the model, an SFOAE consists of a long-delay component generated by irregularity in the traveling-wave peak region and a short-delay component generated by irregularity in cochlear regions remote from the peak.”

Summary of OAE sources Consensus on cochlear origin SFOAEs contributions probably from multiple locations DPOAE contributions definitely from multiple locations: stimulus place, distortion place, and (possibly) basal locations Multiple sources represent not a problem, but an opportunity

Multiple Temporal Peaks DPOAE inverse FFT (Stover et al., 1996) Cochlear contribution to time-domain ear-canal reflectance (Rasetshwane & Neely, 2012)

DPOAE IFFT f1 sweep with fixed f2 Inverse FFT reveals multiple peaks (Stover et al., 1996) f1 sweep with fixed f2 Inverse FFT reveals multiple peaks

DPOAE IFFT: Peak latency vs. level Latency of individual peaks remains constant Peaks with longer latency become relatively smaller Group delay decreases (Stover et al., 1996)

Cochlear reflectance Cochlear contribution to ear-canal reflectance Wide-band noise stimulus IFFT -> waveform Similar to SFOAE, but normalized to forward pressure (Rasetshwane & Neely, 2012)

Cochlear reflectance Bandpass filtered (4 kHz) Latency of temporal envelope peaks remains constant as stimulus level increases (Rasetshwane & Neely, 2012)

Cochlear reflectance: Peak latency vs. level Latency of individual peaks remains constant Peaks with longer latency become relatively smaller Group delay decreases (Rasetshwane & Neely, 2012)

Summary of temporal peaks DPOAEs and SFOAEs similarly possess multiple peaks in temporal envelopes with intensity-invariant latency Group delay decreases because relative amplitudes of peaks with longer latency decrease Temporal peaks may be associated with distinct locations within the cochlea

Clinical Utility of DPOAEs Shaffer et al. (2003) Dorn, Piskorski, Gorga, Neely, Keefe (1999) Kirby, Kopun, Tan, Neely, Gorga (2011) Thorson, Kopun, Neely, Gorga (2012) Gorga et al. (2011) Johnson et al. (2007) Neely, Gorga, Kopun, Tan (2011)

2003: Shaffer, Withnell, Dhar, Lilly, Goodman, Harmon Sources and Mechanisms of DPOAE Generation: Implications for the Prediction of Auditory Sensitivity “The interactions of multiple sources of OAEs arising by distinct mechanisms complicate the simple interpretation that OAE frequencies and hearing test frequencies assess the integrity of the same cochlear locations.”

1999: Dorn, Piskorski, Gorga, Neely, Keefe Slow down. The parameter is F2. Example F2=2 kHz. DPOAE amplitude depends on hearing status at frequencies above f2 Suggests that DPOAEs have basal contributions

Predicting Audiometric Status from DPOAEs Using Multivariate Analyses Information from DPOAE measurements at multiple f2 frequencies can be combined via multivariate analysis Pass/fail test performance is improved by multivariate analysis (Dorn et al., 1999)

Do “Optimal” Conditions Improve Distortion Product Otoacoustic Emission Test Performance? Eleven years later, Kirby et al. (2011) confirmed the benefit of multivariate analysis on pass/fail test performance Still no commercial implementation of multivariate pass/fail decisions

2012: Thorson, Kopun, Neely, Gorga Multivariate analysis of DPOAE I/O functions have been shown to predict categorical loudness functions

DPOAE suppression tuning curves (Gorga et al., 2011) Group means eliminate variability due to multiple sources DPOAE STC quality is outstanding

Attempts to eliminate “reflection source” from DPOAE measurements have been disappointing Johnson et al. (2007): “…controlling source contribution with a suppressor did not improve diagnostic accuracy and frequently resulted in poorer test performance compared to control conditions.” Neely et al. (2011): “…averaging DPOAE measurements across closely spaced f2 frequencies not an effective way to reduce within-subject variability.”

Summary of Clinical Utility Multivariate analysis of DPOAEs at multiple f2 frequencies improves pass/fail test performance Multivariate analysis of DPOAE I/O functions may predict categorical loudness DPOAE suppression tuning curves best available Attempts to eliminate reflection source have been disappointing

Conclusions Multiple locations in the cochlea probably contribute to both DPOAEs and SFOAEs Distinction between distortion source and reflection source is useful in theory, but less useful in practice Elimination of reflection source from DPOAEs not necessary to achieve high-quality results: Pass/fail test performance Tuning curves Loudness prediction

Acknowledgements Co-authors Funding from NIH/NIDCD Grants R01 8318, R01 2251, and P30 4662

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2007: Johnson et al. Distortion product otoacoustic emissions: Cochlear-source contributions and clinical test performance “…controlling source contribution with a suppressor did not improve diagnostic accuracy and frequently resulted in poorer test performance compared to control conditions.”

2011: Keefe et al. Detecting high-frequency hearing loss with click-evoked otoacoustic emissions Various OAE types have similar pass/fail test performance