[Objective frequency-specific measurement of hearing threshold using narrow-band chirp stimuli with level-adaptive simultaneous masking].

BACKGROUND

In the past, various simulation and measurement paradigms have been introduced and evaluated in order to improve frequency-specific measurement of the hearing threshold using early auditory evoked potentials (EAEP). A promising approach for improvement of detection of stimulus response is the usage of frequency-modulated chirp signals, which optimize the temporal synchrony of neuronal responses along a region of the basilar membrane.

AIM OF THE STUDY

This study validated the performance of three generated narrow-band chirp stimuli in combination with a level-adaptive simultaneous masker on a collective of normally hearing subjects.

MATERIAL AND METHODS

In this study 25 normal hearing subjects took part after undergoing pure tone audiometry as well as an objective estimation of the auditory threshold using low, middle and high chirp stimuli. The characteristic EAEP parameters were visually identified before statistical analysis. The characteristic latency level function was conducted using measurements within a stimulus level range from 80 to 0 dB HL. Afterwards a comparison of objectively verified auditory threshold and subjective auditory threshold was conducted.

RESULTS

All objectively determined thresholds of the frequency-specific evoked EAEP were on average below 10 dB HL: low chirp at 8.2 dB HL, middle chirp at 5.8 dB HL and high chirp at 5.4 dB HL. The mean difference compared to subjectively determined auditory thresholds at all frequencies was below 3 dB and was not significant.

CONCLUSION

Brainstem evoked response audiometry (BERA) using a band-limited and level-specific masked chirp stimulus is an efficient method for the determination of frequency-specific excitation thresholds in the clinical routine. The small, insignificant difference compared to the subjectively determined auditory thresholds makes usage of correction factors mostly redundant. Confirming the study results concerning low chirp stimuli so far, the low chirp BERA currently seems to be the method of choice for estimation of auditory threshold at low frequency ranges around 500 Hz.