Audiological study of hearing impaired infants and young children
A hearing test for young children is one of the difficult problems which an otolaryngologist meets daily.
Both subjective and objective methods of testing have been devised.
Among the subjective tests are applications of reflex audiometry, play audiometry and response audiometry while the objective test mothods include psychogalvanic skin resistance test, evoked response audiometry and electrocochleography.
Historically, Ewing & Ewing(1944) began to develop the pediatric audiometry by conducting investigations into 2-3 year old children, using a set of toys capable of attracting their attention, which was so called play audiometry.
Dix & Hallpike(1947) introduced into clinical practice a method of instrumental conditioning for examining deaf children using a device called peep-show.
Since then, various proposed modifications for Dix & Hallpike's peep show have been suggested.
Bordley and Hardy(1949) reported on a electrophysiological device: a study in objective audiometry with the use of psychogalvanometric response.
Psychogalvanometric reflex audiometry and instrumental conditioned reflex audiometry did not allow sufficiently demonstrable data to be obtained in children under 3 years of age.
Suzuki & Ogiba(1960) invented an investigation method enabling the number of failures in the P.G.R. and I.C.R. to be reduced.
This method is based on the finding that children, when subjected to a sudden light stimulus, turn their heads instinctively towards the light source. This is evidantly a wholly unconditioned oriented reflex.
It can however be conditioned by making a sound stimulus precede the luminous one, a conditioned oriented reflex(C.O.R.) can thus be achieved for the auditory stimulus.
The C.O.R. audiometry of Suzuki & Ogiba also has other handicaps in that it is not capabling of testing unilateral hearing acuity nor loss of interest in the test on the part of older children.
Here, the author investigated 180 young deaf children from one to six who come to Yonsei Medical Center during the last four years.
By means of subjective audiometry as mentioned above, the author studied ways of building a more simple and accurate testing method for the very young child and infant in Korea.
A series of tests were performed using a pure tone, speech babbling, broad band noise, musical sound and calling of patients name as acoustic signals and the following results were obtained.
1. Speech babbling was used most commonly for the acoustic signal followed by pure tone, broad band noise and music etc., in that order.
2. Before 3 age, responses of the children were reflex responses such as head turning or startle and natural response such as a smile, but after 3 age, cooperative behavior such as block-dropping and hand-raising were used for auditory response.
3. The success rate of each signal is high in general for the age group over 3 but the age group below 3 shows a high success rate only where broad band noise, music sound and calling of patient's name are used as signals.
4. The number of trials to determine the sound detection threshold and pure tone threshold are in general below 3 times, but four or five times are needed on occasion to determine the threshold.
5. The etiology of the cases where the author failed to determine the sound detection threshold are due in most cases to unconditioning of the children in 40 cases(60.6%) and next those referred for speech therapy and no return cases in descending order.
6. 75% of the cases of children who received pure tone tests successfully could wear ear phones to determine the type of hearing impairment and they are above 4 years of age in most cases.
7. 60.4% of the patients tested by pure tone signals showed hearing impairment from moderate to severe form, all these and more severe cases need special auditory training.
8. Of the 66 children tested with ear phones, sensori-neural hearing impairment 66.7% and next mixed type in 22.7%.
9. The Average of the sound detection thresholds were in general 10-20 dB below the average of the pure tone thresholds and the difference becoming greater as the degree of the hearing impairment increased.