Various characteristics of auditory steady-state responses (ASSRs), including their history, stimulus tones, detection techniques, and the change in response amplitude caused by the arousal state, were described in this report. Concerning the clinical application of ASSRs, the threshold difference between normal and hearing-impaired subjects, the variability of threshold estimates among articles, the reason for the difficulty in predicting the 500-Hz hearing level using an 80-Hz ASSR threshold, the maturation of infant responses, and the problems in bone conduction stimuli were discussed. Regarding future developments, the SSR evoked by electrical stimulation and the ASSR to actual speech sounds were described. ASSRs contribute to the different components of a newborn hearing screening program. The most important benefit is that they can provide an accurate assessment of hearing at different audiometric frequencies in a frequency-specific manner. Their advantage is that they provide these thresholds more rapidly than ABR using a multiple simultaneous stimulation technique. In addition, the ASSR to clicks may provide a rapid screening technique. Finally, they may be helpful in assessing suprathreshold hearing using ASSRs to sounds that sweep their intensity (sweep technique) or to actual speech sounds. In this respect, they may contribute to the objective fitting of hearing aids. The SSR evoked by electrical stimulation (ESSR) may contribute to the mapping of cochlear implants in young children and the ASSR to speech sounds may be useful in the diagnosis of dyslexia and dysphasia.
The causes of sudden deafness are discussed based on our own temporal bone studies and on those reported in the literature, focusing specifically on the pathology of the tectorial membrane. Changes in the tectorial membrane in patients with sudden deafness are similar to those observed in patients with known viral diseases, such as measles and mumps. It is noteworthy that the absence of interdental cells is a common finding. Inoculation of the guinea pig cochlea with herpes simplex virus I results in similar pathological changes of the tectorial membrane. Immunofluorescence studies demonstrated the presence of viral antigen in the tectorial membrane as well as in the interdental cells. One of our own cases, published in 1976, was reviewed. The patient developed bilateral sudden deafness immediately after undergoing severe psychological stress, which appeared to trigger the condition. While the tectorial membrane of both sides exhibited different features, the findings were suggestive of viral infection. The interdental cells were absent. The most likely etiology of sudden deafness in patients who do not show recovery of hearing is probably viral infection. It is conceivable that a latent viral infection is reactivated in these cases.
The etiology of idiopathic sudden deafness is still unknown, and it is difficult to estimate its prognosis. We focused on the patients classified as having Grade 2 to 3 deafness in this study. The patients with idiopathic sudden deafness were separated into two groups; those treated within 7 days and those treated later than 7 days after the onset. The cure rate of the patients treated within 7 days of the onset was 52.9%, while that in the group treated between 8 and 14 days after the onset was 36.6%. There was no significant difference in the cure rate between the Grade 2 and Grade 3 cases in either group. We concluded that the complete recovery rate in clinical cases depended on the following five factors, 1) the number of patients treated within 7 days of the onset, 2) the number of patients treated between 8 and 14 days after the onset, 3) the number of patients with Grade 3a deafness (accompanied by vertigo), 4) recovery rate on the 7 th day after treatment in the patients treated within 7 days, 5) the natural course. Future reports on this disease should include the five components listed above.
For some patients with conductive hearing loss, a bone conduction hearing aid (BCHA) remains the only choice for amplification. However, quantitative estimation of hearing improvement based on the physical characteristics of BCHAs has not yet been established. In this study, we examined the validity of a formula for estimating the aided threshold of a BCHA from pure-tone bone conduction thresholds of the wearer and the output characteristics of the BCHA. In 11 normal-hearing adults in whom the ear canals of both sides were plugged to simulate hearing loss, the aided thresholds for two types of BCHA were measured in sound fields and compared with the threshold estimated using the above formula. There were no significant differences between the two thresholds, except at 4000Hz, where the amplification was overestimated. The estimation errors in SD were from 2.3 to 6.5dB depending on the frequency and type of hearing aid. Although somewhat greater than that reported for the air-conduction hearing aid, this variability is sufficiently small to indicate the possibility that the aided threshold or functional gain for BCHAs can be estimated and their characteristics prescribed. To make such a prescription clinically possible, it is necessary for hearing aid manufacturers to provide the data of the acousto-mechanical characteristics of their BCHAs in hearing level representation.
Nine hearing-impaired children with cochlear implants were subjected to the confusion matrix analysis by the 57S monosyllable speech discrimination test. The mean monosyllable discrimination score was 85.1% and its confusion pattern with cochlear implants themselves was generally better or equivalent to that with hearing aids, except for poorer discrimination of voiced plosives. Discrimination of voiceless consonants was better than that of voiced consonants, except for that of /j/ and /w/. Fricatives, with the exception of the glottal fricative /h/, could be perceived better by cochlear implantees. The lowest monosyllable discrimination was observed for the palato-alveolar affricate /t∫/. As the source of the articulation moved farther, poorer discrimination of fricatives and affricates was observed. Fine frequency- and time-resolution provided by cochlear implants play an important role in the improvement of monosyllable speech perception.