ABR-MLR-SVR are all far-field potentials generally recorded at the surface of the head, at the vertex. Each response has a certain characteristics and its recording parameters need different modalities. With the objective of observing the acoustically evoked sequential response pattern from the lower auditory pathway to the so-called auditory cortex, we have been trying conducting logarithmic time-scalerecordings, and our understanding of the clinical evaluation of these recording maneuver is excellent. Clinically applied data together with the results of some basic researches on sequential recording are demonstrated. The modalities of ABR-MLR-SVR have been applied to cases of hydrocephalus, several kinds of central lesions, and senile dementia. The results in these cases are also demonstrated. Wireless recording of SVR in infants is available to obtain information from higher levels of the auditory pathway. Not only ABR, but also MLR and SVR might yield more precise information concerning hearing, if these responses are re-examined using current sophisticated analyzing devices. Especially, AEPs are effective to estimate the hearing level in infants, objectively and multilaterally.
In 1999, Tanaka proposed a new method of language education, namely, a top-down approach, for young profoundly hearing-impaired children who were candidates for cochlear implantation. In this method, language education was first imparted prior to the surgery, by combined use of residual hearing as well as signed Japanese and manual codes of Japanese. As soon as steady progress of language development and the degree of hearing loss in the candidates were confirmed, the surgery for cochlear implantation was planned. In order to transfer manual communication to auro-oral communication, the implanted children who have already acquired knowledge of the Japanese language through vision, are shown manual codes, characters or written words which they already know, and asked to imitate the therapist's or parents' pronunciation of the teaching materials. By this method, these children gradually come to understand spoken words mainly through audition. Since April, 2004, 17 young deaf children with cochlear implants were followed up for over two years. In fifteen of the 17 children, manual communication was successfully transferred to auro-oral communication, while in the remaining two cases, this has not been possible because of auditory hypofunction due to hypoplasia of the auditory nerve or difficulty in learning the language. These findings suggest that careful use of manual communication does not interfere with the development of auro-oral communication in children received undergoing cochlear implant surgery.
Seven Subjects with normal hearing level (NORM) and five with moderate sensorineural deafness (DEAF) were subjected to a speech discrimination test using both 4-mora highly familiar syllabic words and meaningless monosyllabic words in a sound-free field with artificial speech noise (SNR-27dB, -18dB, -9dB). The following results were obtained in relation to the discrimination scores: The NORM group showed a high discrimination score for both 4-mora syllabic words and monosyllabic words when the artificial noise level was efficient (phonemic restoration). A perceptual synthesis for the missing speech sounds was observed in both the NORM and DEAF groups. We concluded that the top-down mechanism for speech recognition in the human brain will affect the discrimination score when the word familiarity is high enough in both NORM and DEAF subjects. However, two cases of DEAF showed a poor discrimination score due to the auditory deprivation.
An opinion poll was conducted among the teachers of schools for the hearing-impaired or deaf students in Hokkaido, with the purpose of clarifying the present state of the educational environment of children with cochlear implants and to identify any problems that they might have. The results suggested the existence of adequate cooperation between the schools for deaf students, including students with cochlear implants, and medical institutions. The periodic meetings, which were started pre-surgically, were thought to be particularly effective. On the other hand, poor cooperation existed between the schools for hearing-impaired students who were not deaf, and medical institutions. When children with cochlear implants try to enter regular schools, special support from those schools and institutions is necessary and classes need to be prepared to accept children with cochlear implants. It is important not only to continue the cooperation with schools for deaf students, but also to create better cooperation with the schools for hearing-impaired students. In addition, we need to establish a system for supporting those children with cochlear implants who wish to enter ordinary schools.
Eighty cases of hearing impairment detected by a newborn screening program were referred to our hospital for a complete audiometric re-examination between January 2000 and December 2004. Fifty-two of the 80 cases were boys and 28 were girls. In 20 cases, the referral forms were inadequate, so that we could not ascertain what kind of equipment had been used for the screening test or which side was involved. We finally diagnosed bilateral hearing impairment in 24 cases (30%), and unilateral hearing impairment in 22 cases (28%). There was one case in which unilateral hearing impairment had been diagnosed at the time of the newborn screening test, but in which we finally diagnosed bilateral severe sensorineural hearing impairment. Ten cases, including three with bilateral hearing impairment, did not attend their scheduled ABR appointments, hence the diagnosis in these cases remains uncertain. One of these cases was diagnosed to have bilateral hearing impairment at a health checkup conducted two years later. Those diagnosed to have bilateral hearing impairment wore the hearing aid from an early stage and were provided information about rehabilitation institutions. However, in some cases, the patients stopped visiting the examining institutes before the final diagnoses were given. We think that it is necessary to review the procedures at the examining institutes, especially those related to the observation methods and the explanations given to the parents.