Interaural discrimination test using dichotically presented different speech sounds (digits) was investigated for the differential diagnosis of retrocochlear deafness. In this paper, some points to be considered in performing interaural discrimination test were discussed.
The different speech were presented to subjects through a dual-channel tape-recorder with stereophonic ear phones. Each pair of digit sounds was recorded to start as synchronous as possible.
To decide the level presented to subjects, articulation scores of all word-lists were tested. It was most suitable that test words were presented at 40dB above the threshold.
Articulation score of interaural discrimination test was better in hearing the second list than the first list. However, there was no significant difference between the score of the second list and the third list. Then subjects was demanded training only one list beforehand.
This test could be performed without regard to cerebral dominance of hemisphere, because difference of discrimination score between two ears was not detected in normal subjects.
This test was inapplicable to subjects having monaural discrimination loss for digit sounds at 40dB above the threshold.

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A series of 12 cases of bilateral sudden deafness was reported. 7 cases of them had simultaneous loss of hearing in both ears and the other 5 cases had alternate onsets in certain intervals ranging from 10 months to 42 years.
The former cases showed severe deafness and similar audiograms in both ears and their prognosis was bad. On the other hand hearing of the latter cases recovered at least in the recently affected side.
The pathogenesis of bilateral sudden deafness was discussed and it was considered that sudden deafness could always be bilateral and the rare bilateral case might be the severer type of the unilateral one.

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We observed clinically on 274 cases who visited the Hearing and Speech Clinic for children in Tokyo University Hospital from July 1965 to June 1966.
The following results were obtained.
1) Of 274 cases 156 cases were male and 118 cases were female. Sixty-two per cent of them were under three years of age.
2) The grade of hearing impairments was measured by conditioning orientation reflex, play audiometry, E. E. G. audiometry, and standard audiomotry. Percentage of the slight hearing loss cases (hearing loss of 20 to 40dB) was 22%, that of the medium hearing loss cases (hearing loss of 40 to 70dB) was 39% and that of the severe hearing loss cases (hearing loss of 70dB over) was 25%.
Our deaf children of 28per cent had mental retardation. These children with double handicaps (hearing impairment and mental retardation) should be paid attention to at their diagnosis and treatment.
3) Speech development of children with hearing disorders was delayed one or two years of age if not educated, as compared with that of normal children. Particularrly, its delay of the severly impaired deaf children was great.
4) Analysing the causes of impaired hearing of 274 cases, hereditary predispositions, convulsion, disturbances of pregnancy, brain damage on delivery and premature were significant factors.

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