Further comparisons of ABR response amplitudes, test time, and estimation of hearing threshold using frequency-specific chirp and tone pip stimuli in newborns: Findings at 0.5 and 2 kHz

Abstract

Objective: To compare auditory brainstem response (ABR) amplitudes evoked by 0.5 and 2 kHz tone pip and narrowband chirp (NB CE-Chirp) stimuli when testing post-screening newborns. To determine the difference in ‘estimated hearing level’ correction values. Design: Tests were performed with tone pips and NB CE-Chirps at 0.5 or 2 kHz and the ABR threshold for each stimulus defined. Response amplitude, response quality (Fmp), and residual noise were compared for both stimuli. Study sample: Thirty-nine babies (42 ears) who passed our ABR discharge criterion at 4 kHz following referral from their newborn hearing screen. Results: NB CE-Chirp responses were, on average, 31% larger than the tone pip responses at 0.5 kHz and were 52% larger at 2 kHz. Fmp was significantly higher for NB CE-Chirps. Conclusions: The advantages of NB CE-Chirps over tone pips we previously identified at 4 and 1 kHz extends to 0.5 and 2 kHz, which supports the use of NB CE-Chirps when testing newborns. We propose that ABR nHL threshold to eHL corrections for NB CE-Chirps should be approximately 5 dB less than corrections for tone pips at 0.5 and 2 kHz, mirroring our recommendation at 4 and 1 kHz.

Key Words::

• Auditory brainstem response; test time; tone pip; narrowband chirp; neural synchrony; amplitude; Fmp; corrections

Notes

Acknowledgements

A preliminary version of this work was presented as a poster, ‘Further comparisons of ABR response amplitudes, test time, and estimation of hearing threshold using frequency specific chirp and tone pip stimuli in newborns’, at the International Conference on Newborn Hearing Screening, Cernobbio (Lake Como), Italy, June 2014; and at the British Academy of Audiology Annual Conference, Bournemouth, November 2014. The authors would like to thank Sungtak Hong, PhD student, Department of Marketing, London Business School, for performing the main statistical analysis of this study.

Declaration of interest: The authors alone are responsible for the content and writing of this paper. There were no conflicts of interest.

Notes

1. The dBeHL to dBnHL corrections have two components: (1) a transducer correction to compensate for the increased stimulus level associated with the use of insert earphones and bone vibrators when used in newborns, and (2) a correction that predicts the ‘true’ or behavioural threshold from the ABR threshold. The use of these corrections allows ABR results to be compared to, and used as if they were, the results of conventional pure-tone audiometry. A full explanation of their derivation is available in the English guidelines for early audiological assessment (2013).

2. The corrected age is the difference between the chronological and gestational age of the baby.

3. When using TDH-39 earphones 30 dBeHL corresponds to 40 dBnHL. When using ER-3A inserts 30 dBeHL corresponds to 30 dBnHL.

4. Bayesian averaging is a method of preventing noise from contaminating the average. More weight is placed on low noise periods and less on high noise periods. Each sub-average is weighted according to an estimate of the inverse of its average residual noise. For a more detailed explanation of the method employed by the Interacoustics Eclipse ABR system see Lightfoot and Stevens (2014).

5. Fmp is a measure of the quality of the response using the F statistic of the response to noise variance ratio, with the noise variance estimated from the EEG values at multiple points. Fmp is a more accurate extension of the Don and Elberling (1994) Fsp measure. The degrees of freedom chosen for the calculation were suggested by the individual distribution of the values acquired from testing a group of adults.

6. The medium level was taken as the baseline level plus 10 dB, and the high level was the baseline plus 20 dB.