Long-term observations on achievement of gross motor functions such as head control and walking were made in ninety-one infants with severe sensorineural hearing loss. Infants associated with neurological diseases were excluded. For statistical analysis the 91 patients were classified into two groups; group A including 51 infants with profound hearing loss over 90dB, and group B including 40 infants with hearing loss less than 90dB. The infants with delay in walking were 67per cent in group A and 37per cent in group B. The difference of the percentage between the two groups was highly significant statistically. According to the mother's report, 71per cent of the delayed walking and 21per cent of the infants who started to walk at the normal age had delayed in achieving head control. Although the causes of hearing loss of the 91 infants were varied, 58per cent of the infants in group A and 82per cent of the infants in group B were etiologically genetic or unknown. From the etiological standpoint there was not a definite correlation between the retarded motor development and the causes of hearing loss. In conclusion, it may be said that slow acquisition of the control of head movement as well as walking in infants with severe sensorineural hearing loss may be mainly attributed to the vestibular hypofunction.
The present state of hearing aid use in three schools for the deaf in Japan was investigated. The hearing threshold measured with a hearing aid earphone, whose output sound pressure level was calibrated in a 2cm3 coupler, was compared with the hearing aid output for the 70dB input. With all the controls set to the position regularly used. The results showed that the amplification level of hearing aids was considerably less than that expected from hearing thresholds. In the group with hearing thresholds above 100dB SPL, the aided levels were below hearing thresholds in 60 percent of the ears at 1000Hz, 84 percent at 2000Hz, and in all the ears except one in 99 at 4000Hz. In the group with hearing thresholds below 100dB SPL, most of the aided levels were a little less than 10dB above the hearing thresholds except at 4000Hz. It was pointed out that the re-setting of volume controls of the hearing aids and the search for greater amplification at 4000Hz were urgently needed for better use of residual hearing in these children.
Round window membranes were experimentally incised, and electrophysiological consequences were measured by using an implanted electrode at 10 days interval in guinea pigs. Ten days after surgery, AP thresholds and CM detection thresholds raised at 20dB especially in high frequency. On the other hand, these electrophysiological parameters were as same as preoperative ones at 30 days after surgery. This suggests that a simple incision on the round window membrane makes no remarkable changes in cochlear functions after closing the membrane.