Survey of attempts to use auditory evoked potentials to obtain an audiogram

Click stimuli have been used to elicit ABR in auditory diagnosis but the ABR response is dominated by the activity of high-frequency nerve fibres and it is therefore impossible to deduce hearing at lower frequencies from ABR to clicks. Short tone pips or filtered clicks are also inadequate since the response is still dominated by basal turn, high-frequency nerve fibres. In order to attempt to obtain an audiogram by means of ABR, various noise-masking techniques have been used to restrict the response to more specific regions along the basilar membrane. These included presenting click or filtered click stimuli together with either different high-pass noises in order to obtain a derived ABR or notched noise. Though these techniques have been tested on small groups of normal subjects, they have not been adequately clinically validated on sufficient numbers of hearing-loss patients with various audiogram shapes. When tested on patients with low-frequency hearing loss, inappropriate thresholds have been obtained indicating problems with lower frequencies. Alternatively, other types of auditory evoked responses based on less synchronous neural activity have been studied including the SN10 response and the 40 Hz-MLR. These responses have not been adequately clinically tested. In conclusion the evoked potential techniques have not been completely tested in the clinical situation and several studies have indicated problems with the evaluation of lower frequencies.