UC Irvine

The sense of hearing depends on many physical and biological processes. Much research is focused on different aspects of hearing loss and ways to improve the lives of those with this disability. Auditory neuropathy (AN) is a relatively newly discovered hearing disorder and has been related to damage in the auditory nerve synapses, both pre- and post-synaptic transmission, and the nerve itself. This damage ranges from demyelination to axonal and cell loss. One of the significant deficits that people with AN suffer is their inability to understand speech in a noisy environment. Understanding speech depends on the listener’s ability to extract the temporal envelope of the spoken language. Since AN patients have a significant temporal processing deficit, it is difficult for them to understand speech despite the fact that they can hear it. Gap detection and temporal modulation transfer function (TMTF) have been the most common psychophysical tests that are used to measure the severity of impairment in patients with AN. These two subjective tests have frequently been used to evaluate the temporal acuity of patients with auditory neuropathy. However, these tests rely on subjects’ active responses to stimuli, which means that they are not feasible for examining infants and patients with some cognitive disabilities that limit their understanding of the task. Therefore, finding an alternative test that can reliably and objectively measure temporal acuity is crucial.

Recent studies suggest that cortical evoked potentials may be used to assess both the severity and lesion sites of AN. However, these cortical potentials are limited to adults and are not easily implemented in an everyday clinical setting.

The present research proposed a new technique that will allow clinicians to objectively measure the auditory temporal processing acuity for patients with auditory neuropathy. The auditory temporal processing acuity for five different groups has been studied using both the conventional subjective test and a newly proposed objective technique. The five groups included 12 younger normal-hearing subjects (18-28 years), 12 older subjects (41-63 years), 12 elderly subjects (67-82 years), two normal-hearing children (10-14), and seven subjects who have been diagnosed with auditory neuropathy (11-43). Some of the subjects in the older and elderly groups had normal hearing thresholds, and some had hearing loss. The newly developed objective technique used a modulated noise in which its amplitude or frequency rate was varied over time to elicit the envelope following response (EFR). Data from the five groups showed a significant correlation between the modulation detection threshold estimated by the EFR and that by behavioral modulation transfer function (MTF). This significant correlation suggests that the EFR can serve as an objective novel technique to evaluate the severity of auditory neuropathy. Together, the EFR-MTF profiles can be related to known sites of lesions in AN. The EFR profile can be used as a bio-marker to objectively diagnose auditory processing disorders and to help make treatment options.