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.

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.

The effect of notch filtering on the waveform of the newborn auditory brainstem response.

OBJECTIVE: To identify whether the use of a notch filter significantly affects the morphology or characteristics of the newborn auditory brainstem response (ABR) waveform and so inform future guidance for clinical practice. DESIGN: Waveforms with and without the application of a notch filter were recorded from babies undergoing routine ABR tests at 4000, 1000 and 500 Hz. Any change in response morphology was judged subjectively. Response latency, amplitude, and measurements of response quality and residual noise were noted. An ABR simulator was also used to assess the effect of notch filtering in conditions of low and high mains interference. RESULTS: The use of a notch filter changed waveform morphology for 500 Hz stimuli only in 15% of tests in newborns. Residual noise was lower when 4000 Hz stimuli were used. Response latency, amplitude, and quality were unaffected regardless of stimulus frequency. Tests with the ABR stimulator suggest that these findings can be extended to conditions of high level mains interference. CONCLUSIONS: A notch filter should be avoided when testing at 500 Hz, but at higher frequencies appears to carry no penalty.

Provisional stimulus level corrections for low frequency bone-conduction ABR in babies under three months corrected age.

OBJECTIVE: To estimate bone-conduction stimulus level corrections by testing the auditory brainstem response (ABR) of normally-hearing newborns. The stimuli used were low frequency tone pips calibrated to reference levels derived from ISO 389 values. DESIGN: Tone pips were presented via supra-aural earphones and a B71 Radioear bone vibrator at 0.5 or 1 kHz. ABR thresholds from both transducers were compared at each frequency. STUDY SAMPLE: twenty-seven newborn hearing screening referrals (33 ears) who passed an ABR discharge criterion at 4 kHz. RESULTS: Median air- and bone-conduction ABR threshold differences were 30 dB at 0.5 kHz and 20 dB at 1 kHz. CONCLUSION: The 0.5 kHz data from this study and previous studies were compared. Previous studies suggested lower figures for the bone-conduction stimulus level correction. Likely sources of this discrepancy are discussed. The average 0.5 kHz bone-conduction correction value for infants < 3 months old is about 28 dB. The correction for 1 kHz is 20 dB. We recommend that calibration reference levels used in this study be adopted and that appropriate corrections be applied to bone conduction ABR thresholds in infants < 3 months old before calculation of any air-bone gap and subsequent clinical interpretation.

Comparison of ABR response amplitude, test time, and estimation of hearing threshold using frequency specific chirp and tone pip stimuli in newborns.

OBJECTIVE: To evaluate the auditory brainstem response (ABR) amplitudes evoked by tone pip and narrowband chirp (NB CE-Chirp) stimuli when testing post-screening newborns and to determine the difference in estimated hearing level correction values. DESIGN: Tests were performed with tone pips and NB CE-Chirps at 4 kHz or 1 kHz. The response amplitude, response quality (Fmp), and residual noise were compared for both stimuli. STUDY SAMPLE: Thirty babies (42 ears) who passed our ABR discharge criterion at 4 kHz following referral from their newborn hearing screen. RESULTS: Overall, NB CE-Chirp responses were 64% larger than the tone pip responses, closer to those evoked by clicks. Fmp was significantly higher for NB CE-Chirps. CONCLUSION: It is anticipated that there could be significant reductions in test time for the same signal to noise ratio by using NB CE-Chirps when testing newborns. This effect may vary in practice and is likely to be most beneficial for babies with low amplitude ABR responses. We propose that the ABR nHL threshold to eHL correction for NB CE-Chirps should be approximately 5 dB less than the corrections for tone pips at 4 and 1 kHz.

Cortical electric response audiometry hearing threshold estimation: accuracy, speed, and the effects of stimulus presentation features.

OBJECTIVES: A number of stimulus presentation features of the tone burst-evoked N1-P2 cortical response were investigated to identify any advantage over simple stimulation when the test is used for hearing threshold estimation. The speed of establishing objective thresholds at 1, 3, and 8 kHz in both ears was also measured in what was designed to be an efficient test protocol, together with the precision of the threshold estimates with reference to subjects' conventional audiograms. DESIGN: Twenty-four volunteer subjects were recruited and tested by both behavioral and electrophysiological methods. A low-intensity, 3-kHz stimulus was used when the stimulus features were studied. The parameter was the N1-P2 amplitude. RESULTS: Changing the side of presentation (randomly or by alternating ears), varying the interstimulus interval and inserting a 10-second recovery period midway though an averaging run had no demonstrable effect on response amplitude, both individually or in combination, contrary to earlier reports. Establishing the 6 threshold estimates took an average 20.6 minutes. The mean error in the N1-P2 threshold estimate was 6.5 dB, with no significant effect of frequency. After correcting for this bias, 94% of individual threshold estimates were within 15 dB of the behavioral threshold and 80% were within 10 dB. CONCLUSIONS: This study suggests that cortical electric response audiometry has a performance that is as good as or better than the auditory brain stem response for threshold estimation in adults and that sophisticated stimulation techniques do not appear to be required. An efficient test protocol that automates many laborious tasks reduces the test time to less than half that previously reported in the literature for this response.