Objective measurements such as auditory evoked responses are often useful in the diagnosis of hearing disorders. In addition to conventional evoked responses measured by electroencephalography (EEG), auditory evoked functional imaging modalities such as functional magnetic resonance imaging (fMRI), positron emission tomography (PET) and magnetoencephalography (MEG) have been applied recently. Among these three methods, only MEG can measure synchronized neuronal activity directly, with a precision of within 1 ms. Assessment of the neural activity in the auditory cortices is an important application of MEG. The greatest benefit of MEG as compared to EEG is that activation of the auditory cortices can be evaluated, with division separately into the right and left hemispheres. MEG is anticipated as a useful method to evaluate the plastic changes in the auditory cortices induced by disorders in the auditory pathway, although some limitation exists in the measurement of such cases with an artificial hearing device such as a cochlear implant. To date, the averaged auditory evoked fields of auditory cortical responses such as N100m and ASSRs have been used mostly to assess the function of the auditory cortex. Nevertheless, it is expected that another aspect other aspects? of auditory processing in the cortices can be elucidated using the recently available analytic methods for time-frequency analysis as well as coherence analysis.
The aim of the present study was to investigate the music perception skills of adult cochlear implant (CI) users in comparison to hearing aid (HA) users. A music test battery was designed of a pitch ranking test and identification of familiar melodies test, and stimuli were presented via speakers connected to a PC at levels comfortable for each individual. The results revealed good pitch discrimination and melody identification in patients with mild or moderate hearing impairment wearing HAs, but the ability for both decreased as the hearing loss became severe. In the CI group, although there were many subjects who could discriminate more than 10-12 semitone in the pitch discrimination test, melody identification differed significantly among individuals with 10-90% of correct answers. In the HA group, the hearing threshold level and speech perception scores were positively correlated with the music perception. In the CI group, the relationship between the age and speech perception scores was strong. Even subjects with wearing HAs or CIs with profound hearing loss who had difficulty in pitch discrimination appeared to be able to distinguish known music by top-down processing, indicating the possibility of ability for music perception.
No simple objective test is available yet to evaluate tinnitus. We developed a simplified portable electroencephalographic (EEG) device to objectively detect tinnitus. We used it to measure and analyze the EEG recorded at Fp1 in chronic tinnitus patients and healthy volunteers. Fp1 is located on the left forehead, reflecting the function of the ventromedial prefrontal cortex, the brain area involved in higher cognitive processes. Each frequency from the EEG was separated by the Fourier transform and these data were analyzed by principal component analysis to validate this test. There was a significant difference of the EEG amplitude, except at the frequency of 10-11Hz, between patients with and without tinnitus. Therefore, we could objectively evaluate whether patients had tinnitus or not. This device is expected to be useful for discriminating feigned illness and for evaluating the efficacy of therapy. Further study is necessary to refine accurate detection of tinnitus and to determine its pathophysiological basis.
In 191 patients (298 ears) who visited the Hearing Aid Clinic at Kitasato University Hospital, in whom a functional gain test of a hearing aid was performed, we investigated the need for sound attenuation and masking of the non test ear to prevent cross hearing. In the unaided threshold test, there was a possibility of cross hearing only with sound attenuation by wearing an insert earphone in the non test ear at least in one frequency in 66 cases (34.6%). The hearing thresholds were elevated by masking in about a half of the cases. In cases of bilateral hearing aid fitting, contralateral masking tended to be more frequently indicated (51.4%) in the fitting for the worse hearing ear, while in cases of unilateral fitting, contralateral masking was necessary for only 11 cases (13.1%) in which hearing aid was fitted to the worse hearing ear. The incidence of cases in which unmasked thresholds were obtained by cross hearing was high at low frequencies under both unaided and aided conditions. Possible causes of this result were considered to be poor sound attenuation of the insert earphone, a large hearing difference between the two ears, and low gain of the candidate hearing aid. If reducing the test time is necessary, substitution of the audiometric threshold using an earphone for unaided sound field threshold, real ear insertion gain measurement, or use of double sound attenuation using an ear plug and an ear muff could be considered.
Hearing impairment is known to exaggerate cognitive deficits. We assessed the characteristics and effects of hearing aids in 59 elderly patients with hearing and cognitive impairment. There were 3 aims of this study. The first aim was to clarify the difference in hearing impairment between elderly patients with or without cognitive impairment seeking hearing aid fitting. The second aim was to highlight the difference between patients with hearing and cognitive impairment choosing and not choosing to use hearing aids. The third aim was to assess the effects of hearing aids in patients who cannot use hearing aids over for more than? 6 months. The speech discrimination ability of patients with cognitive impairment was significantly lower than that of patients without cognitive impairment, even after adjustment for the age, sex and hearing thresholds in pure-tone-audiometry (p<.0001). There was no significant difference between patients who chose and did not choose to use hearing aids. Only 48% of patients could use hearing aids continuously for over more than 6 months, however, there were positive effects such as reduction of tinnitus and hearing? disturbance, and improvement of communication.