| IntroductionAt the moment the clicks - evoked auditory brain stem response ( ABR) has been developed as the most widely application for the objective assessment. However, the ABR evoked by clicks has some limitations, as it evaluates hearing sensitivity only at higher frequencies above 2000Hz and its thresholds for lower frequencies is not frequency - specific. Tone pips are frequency - specific stimuli, and it is very important significance that auditory evoked potentials ( AEP) to tone pips is applied to assessing objective hearing thresholds in forensic medicine research.In this study we investigated the relationship among the behavioural pure tone thresholds, behavioural tone pips thresholds and AEP thresholds evoked by tone pips and got their relationship in order to predict the behavioural pure tone thresholds through AEP thresholds evoked by tone pips.Subjects and methodsForty undergraduates (80 ears) at China Medical University participated in our experiment. All had normal hearing sensitivity at all frequencies from 500 to 8000 Hz ( <25dBHL).After pure tone auditory thresholds had been obtained at 1000, 500, 2000 and 4000Hz, behavioural thresholds and AEP thresholds to tone pips were determined. AEP to tone pips was recorded with a Nicolet Compact Four Electrodiag-nostic System. For the tone pips,rise - plateau - fall times of 3 —4—3 msec werepresented at repetition rates of 29. 1/sec. The earphone (TDH -39P) produced tone pips. The responses were amplified 2000 times and were filtered between 1 and 500Hz. Data were collected in time windows of 20ms. The electrodes were placed at the vertex ( positive input) , ipsilateral mastoid ( negative input) and forehead (ground). Individual impedances were less than 5k and inter - electrode impedance was below 3k. The subjects reclined comfortably on an examination couch in an audiometric room. AEP to tone pips testing was started at 80dBnHL. The stimulus level was decreased with lOdBnHL until no AEP waveforms could be detected. The responses were written out on a X - Y plotter at last.Results1. A positive wave was obtained from all the subjects for each frequency. The latency of the component was between 7 and 15 ms,so we called it positive response 10 (PI0).2. Mean differences and standard deviations between P10 wave thresholds to tone pips and behavioural tone pips thresholds at 500, 1000, 2000 and 4000 Hz were 8.31 ±4.50,10.19 ±3.37,9.69 ±3.12 and 10.31 ±3.53dBnHL,respectively. Differences between behavioural tone pips thresholds and behavioural pure tone thresholds over the same frequency range were 15. 06 ±9. 29,13. 44 ±5. 60,7. 69 ±6. 56 and 6. 19 ±5. 75dBnHL. Differences between P10 wave thresholds to tone pips and behavioural pure tone thresholds over the same frequency range were 23. 38 ± 10. 09,23. 63 ± 8. 23,17. 38 ± 8. 86 and 16. 50 ± 7. 04 dBnHL.3. Mean differences of the differences between P10 wave thresholds to tone pips and behavioural pure tone thresholds at 500, 1000, 2000 and 4000Hz were approximately near 20dBnHL. Therefore,when P10 thresholds are used to predict behavioural pure tone thresholds,a conservative estimation should be equal to P10 wave thresholds subtracting 0 -20dBnHL,it is,the prediction range of behavioural pure tone thresholds.4. As the frequency of tone pips increases, the latency of Pi0 wave decrea-... |
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