A Study of Frequency Specificity of the Auditory Fast Responses

Abstract

In order to establish the application of action potentials (AP) of the cochlear nerve and brain stem auditory evoked response (BSR) in clinical audiology, the frequency specificity of them was studied using the special masking techniques.The change of AP and BSR latencies and amplitudes of white noise evoked responses were observed using the high and low pass filtered masking noise. Secondaly the band stop (reject) noise was produced during the tone pip stimuli by the frequency selective masking.According to the first examination, AP responses depended on the frequency range of cochlear partitions higher than 2kHz, while those responsive for BSR extended to a octave lower range.It is considered that the latencies of responses are dependent to the most basal part of the cochlear partition, which is stimulated when the stimulus conditions are held constant. The amplitudes of AP are decided by the length of the stimulated cochlear partition, when the stimlus conditions areheld constant and the lower frequency bands of masking are changed.The following results were obtained from the second examination. The thresholds of responses were 5dB above subjective ones to the 4kHz and 81kHz tone pip stimuli.On the other hand AP and BSR thresholds to the 2kHz tone pips were 20dB and 15dB above subjective threshold respectively. The AP responses were not obtained and BSR were unstable to the the tone pips at 1kHz.The intensity-latency curves of AP and BSR were shifted in parallel with the frequency from high to low.It is concluded that the effective frequency of the tone pips were 4kHz or higher for AP, and 2kHz or higher for BSR in clinical application. The frequency selective masking of the band stop noise is necessary for us to obtain the responses from more restricted part of the cochlear partition.