Abstract
This investigation emphasized that brain stem response (BSR), can be used as a clinical test for determining hearing threshold in mentally disturbed children.
The subject were 18 mentally retarded children aged 3-7 years. Many subjects were neither testable by COR (Conditioned Orientation Reflex) audiometry nor by play audiometry, but were testable by BOA (Behavioral Observation Audiometry) such as startle response and eye movement response. From the results of these test, all subjects were supposed to have normal hearing.
BSR audiometry were performed in all mentally disturbed subjects and fifteen normal subjects whose age ranged between 3 and 25 years. The stimulus sound used, was one cycle sinusoidal wave at a frequency of 2 kHz and 4 kHz. The sinusoidal wave clicks were presented at a rate of 25 per second with alternately reversing the polarity of the acoustic stimuli. The 1, 000 clicks generated by means of a sinusoidal- wave click generator were transduced by a condenser earphone applied to the subject. The electrode sites were the vertex and the ear lobe. The electrical responses were amplified with a preamplifier, filtered with a frequency range of 300-5, 000 Hz. The BSR audiometry was performed under general anaesthesia in all mentally disturbed subjects. We measured the latencies of wave 1 and 5 as a function of stimulus intensity from 25 to 95 dB peak equivalent SPL.
In this experiment, the response thresholds obtained from mentally disturbed subjects were close to those obtained from normal subjects. When measured with 4 kHz sinusoidal wave clicks, the latencies of wave 1 and 5 obtained from mentally disturbed group increased with decreasing sound intensity, and the same results were obtained from the normal group also.When measured with 4 kHz sinusoidal wave clicks, there were no differences in the latency of wave 1 in both groups. However, mean latency of wave 5 at each intensity became significantly longer in mentally disturbed group than in the normal group as sound intensities approach hearing threshold. We are at present unable to explain this discrepancy.
