Cortical Electric Response Audiometry Hearing Threshold Estimation: Accuracy, Speed, and the Effects of Stimulus Presentation Features

Department of Clinical Engineering, Royal Liverpool University Hospital, Liverpool, United Kingdom.
Ear and Hearing (Impact Factor: 2.83). 11/2006; 27(5):443-56. DOI: 10.1097/01.aud.0000233902.53432.48
Source: PubMed

ABSTRACT 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.
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.
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.
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.

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    • "They found that speech identification abilities decreased when exposed to poorer signal-to-noise ratios with the performance decrement paralleled by both increased N1 latencies and decreased N1 amplitudes. More importantly, the latency and amplitude of the N1 significantly correlated with behavioral assessments of signal detectability (Martin et al., 1997) with electrophysiological thresholds closely approximating behavioral thresholds (Lightfoot and Kennedy, 2006). These findings suggest that AEPs provide a sensitive measure of signal audibility, which may prove useful at evaluating the effects of age-related hearing loss on central auditory processing. "
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    • "Also, rise times between 20 and 30 ms result in the largest N1 amplitudes with either no further change, or decrease, in amplitude with longer rise times [40, 41]. Perhaps different results may have been obtained using stimuli with more typical rise/fall times and overall durations, such as 20 ms rise time and 60 ms total duration [22, 23, 42–44], although a recent study by Easwar and colleagues [45] suggests little difference in SCPs to hearing-aid-processed stimuli with 7.5 ms versus 20 ms rise times. "
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    • "As an example, the N1-P2 amplitude was expected to be 5 uV for 1 k, and 3 uV for higher frequencies at CAEP threshold. If the amplitude was larger, then threshold was equal to the stimulus presentation level minus 5 dB (Lightfoot & Kennedy 2006). Given the challenges of electrophysiological response recognition by visual detection methods, automated or machine scoring techniques have been applied. "
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