|Institution:||University of Manchester|
|Keywords:||ASSR; Dead Regions; Dead Region Diagnosis; Auditory Steady-state Response; Hearing-impaired; Response Amplitude Curve|
|Full text PDF:||http://www.manchester.ac.uk/escholar/uk-ac-man-scw:121573|
The current behavioural dead region (DR) diagnosis methods such as psychophysical tuning curves and the threshold-equalising noise test require extensive subject co-operation. These present methods cannot be applied to infants. The work presented in the thesis aimed to develop a fast objective DR diagnosis method that could be applied to sleeping hearing-impaired infants. A novel fast objective electrophysiological method of recording response amplitude curves (RACs) which could enable objective DR diagnosis was developed.RACs were derived by recording auditory steady-state response amplitudes using modulated signals in the presence of narrow-band maskers. Two RAC methods were investigated. In the swept method, RACs were recorded in a single test run by recording the response amplitudes across the frequency range of a continuously swept-frequency narrow-band masker. In the fixed method, response amplitudes of eight separate test runs, each in the presence of differing fixed-frequency narrow-band maskers, were recorded.RACs were recorded in normally hearing adult subjects. The results showed that for normally hearing subjects in condition 1 (swept masker), the mean recorded RAC tip for a 2-kHz signal was 2250 Hz and the repeatability coefficient of two repeated recordings in each subject was 389 Hz; in condition 2 (fixed masker), the respective values were 2251 Hz and 342 Hz. These results indicated that the swept masking method is a viable and fast way to record RACs in normally hearing adults.RACs and psychophysical tuning curves (PTCs) were recorded in hearing-impaired adult subjects in order to asses the tip-frequency agreement between the tests. In some cases there were difficulties in using the required signal and masker levels due to maximum sound level limits. The RACs were poorly shaped and had poor repeatability. These findings indicate that the RAC method that was successfully applied to normally hearing subjects requires further development for use with the hearing impaired. The possible causes for the differences in the accuracy of the method between normally hearing and hearing-impaired subjects are discussed. The work presented in this thesis provides the basis upon which further research can be taken forward. It is envisaged that this work, together with further research, will lead to a clinically-effective objective DR diagnosis method. Attached CD containing Matlab scripts and technical documentation.