Towards the preferred stimulus parameters for distortion product otoacoustic emissions in adults: A preliminary study

Comparison of Two Clinical Devices for the Measurement of Distortion Product Otoacoustic Emissions in Normal-Hearing Adults

BACKGROUND AND OBJECTIVES

Otoacoustic emissions (OAEs) are low-intensity sounds generated by the cochlea and associated with the function of the outer hair cells. Since OAE measurements do not require active participation of a listener, OAEs are considered an objective measure of cochlear function. While distortion-product OAEs (DPOAEs) are commonly used in clinical practice, limited information is available on the performance of various clinical devices. This study compared two commercial clinical devices, Titan and Eclipse from Interacoustics, and collected normative data for DPOAEs in people with normal hearing. The data collection and analysis were focused on signal and noise amplitudes as well as signal-to-noise ratios (SNRs).

SUBJECTS AND METHODS

Sixty-three participants with normal hearing (age 23.2±2.0 years) were included in the study. DPOAEs were measured at 31 frequencies ranging from 500 to 10,000 Hz.

RESULTS

DPOAE amplitude differed across frequencies. Additionally, a high number of unreliable responses were observed at the edge frequencies (<828 Hz and >6,072 Hz). There were no significant differences between the two devices in terms of DPOAE amplitudes, but the recorded-noise levels (amplitude) differed significantly. SNRs of the recorded OAEs were frequency dependent (higher frequencies showed larger SNRs), and significant differences in terms of SNR were found between the two devices.

CONCLUSIONS

Despite the above-mentioned differences, the OAEs recorded with both devices met the pass criteria for the SNR (≥6 dB) consistently across frequencies, and thus the differences do not compromise the test outcomes. The frequency dependence of the OAE amplitudes and the corresponding SNRs may be relevant for clinical practice.

Audiologic characterization using clinical physiological measures: Normative data from macaque monkeys

Clinical auditory physiological measures (e.g., auditory brainstem responses, ABRs, and distortion product otoacoustic emissions, DPOAEs) provide diagnostic specificity for differentially diagnosing overt hearing impairments, but they remain limited in their ability to detect specific sites of lesion and subtle levels of cochlear damage. Studies in animal models may hold the key to improve differential diagnosis due to the ability to induce tightly controlled and histologically verifiable subclinical cochlear pathologies. Here, we present a normative set of traditional and clinically novel physiological measures using ABRs and DPOAEs measured in a large cohort of male macaque monkeys. Given the high similarities between macaque and human auditory anatomy, physiology, and susceptibility to hearing damage, this normative data set will serve as a crucial baseline to investigate novel physiological measures to improve diagnostics. DPOAE amplitudes were robust at f2 = 1.22, L1/L2 = 65/55, increased with frequency up to 10 kHz, and exhibited high test re-test reliability. DPOAE thresholds were lowest from 2-10 kHz and highest < 2 kHz. ABRs with a standard clinical electrode montage (vertex-to-mastoid, VM) produced Waves I-IV with a less frequently observed Wave-I, and lower thresholds. ABRs with a vertex-to-tympanic membrane (VT) electrode montage produced a more robust Wave-I, but absent Waves II-IV and higher thresholds. Further study with the VM montage revealed amplitudes that increased with stimulus level and were largest in response to click stimuli, with Wave-II showing the largest ABR amplitude, followed by -IV and -I, with high inter- and intra-subject variability. ABR wave latencies decreased with stimulus level and frequency. When stimulus presentation rate increased or stimuli were presented in close temporal proximity, ABR amplitude decreased, and latency increased. These findings expand upon existing literature of normative clinical physiological data in nonhuman primates and lay the groundwork for future studies investigating the effects of noise-induced pathologies in macaques.