Abstract
Auditory brain stem responses (ABR) were examined on 121 individuals with normal hearing in special reference to the developmental changes. The following nine age groups were tested: 8 neonates, 10 two-month-olds, 10 four-month-olds, 10 six-month-olds, 15 one-year-olds, 17 two-year-olds, 18 three-year-olds, 18 eight-yearolds and 15 adults.
Under our test conditions wave components of ABR were well differentiated even in neonates. Although there were considerable developmental changes in the latency and the amplitude of each ABR component, the fundamental characteristics of the wave patterns were retained withn the same individual. This was found in 7 subjects who were studied longitudinally from birth to 2 years of age. Also a remarkable resemblance was observed between the wave patterns of a pair of monozygotic twins.
Mean values for the peak latency and the amplitude of each ABR component were obtained for all age groups. The peak latencies of all components showed a steady decrease with age toward the adults. Although the decrease was more remarkable with the slower component, the peak latency of the faster c9mponent reached the adult value more rapidly. Thus, the latency of wave I reached that of the adult at 2 months of age, wave III at 2 years and wave V at 3 years of age.
The amplitude of each ABR component showed larger individual variability than the peak latency. Until 3 years of age the amplitude of wave III was the largest of all waves, but thereafter wave V became the largest.
The application of ABR to objective audiometry was examined and discussed. The delay of wave V peak latency was considered to be the most suitable index for that purpose. Our results showed that 0.7 msec prolongation of wave V latency at 85 dB corresponded to 30 dB hearing loss.
