Abstract
Recently, marked progress has been noticed in the field of hearing test for young children. The authors discussed it at three points.
1) Evoked response audiometry
The evoked responses of EEG to sound are often very small and buried in the much greater spontaneous electrical activity. The methods of superimposion of traces were devised by Dawson (1954), and then Asawa and others applied these methods to the clinical examination. The computer is the best equipment to extract the evoked responses. This extracting method is done by repeated sampling of the EEG output at fixed intervals following sound stimulation. The constant latency of the evoked responses makes the averaging possible for the computer. This method seems to be promising in the field of objective audiometry for young children.
The authors studied the V-potentials of EEG response to auditory stimuli in awake state and found that 1) the evoked potential consists of 3 or 4 phasic waves, 2) the largest responses are obtained at the vertex, 3) the responses' can be induced by any other type of stimulus and 5) the responses are recognized within 20 dB above the hearing threshold of adults, but need stronger stimulation in case of children. The authors also studied the audiometry in newborn babies, all sedated, with a computer, and found that a five-phasic wave was seen.
It was discovered that the evoked potential could be induces during sleep as well as in awake state. It follows that the audiometry in children w ill better be done while a sleep.
2) Hearing test for newborn infants
It has been said that newborn infants have various kinds of aural responses to tonal stimuli soon after birth. Many authors have previously reported on the auditory tests of newborn babies.
The authors made the auditory examination of newborn infants with pure tones and an artifical sounds of cow's mooing by means of the pneumogram and the macroscopically observed change. The responses were recognized in the inten sity level of stimulating tone from 40 to 90 dB, the average threshold value being 62.8 dB.
3) Response of fetus to and stimuli
Recently, much attention has been paid to the hearing test for fetus.
Peiper (1924) observed the signs of activity of a fetus responding (to tonal stimuli. Murphy and Smyth (1962) reported the change of heart-rate of the fetus due to sounds.
With further study, the reliability and validity of the audiometry for the fetus will increased.
