INTENSITY EFFECT ON AMPLITUDE OF AUDITORY BRAIN-STEM RESPONSES IN HUMAN

Click intensity effect (90 to 0 dB HL) on amplitude of the auditory brainstem responses (ABAR) was studied in 152 normal children from birth to 6 years and 16 adults. All age groups showed similar amplitude-intensity functions for waves I and V. Wave I amplitude exhibited a 'transitional' response at 60 dB HL intensity, whereas wave V exhibited a more gradual change. As the clicks were decreased from 90 to 60 dB HL, amplitude reduction was much more dramatic for wave I (mean 57%) than for wave V (mean 30%), and the V/I amplitude ratio more than doubled (mean 70%). At moderate intensity range, the reduction in amplitude with the decrease in intensity is only slightly more for wave I than for wave V, and the V/I ratio continued to increase, but more slowly. Wave V amplitude changed linearly with click intensity at the rate of 0.024-0.042-mu-V/dB for different age groups. The older the children, the larger the decrement of wave V amplitude with decreasing intensity, which was accompanied by an age-related difference in the absolute amplitude at equal click intensities. The V/I amplitude ratio increased with decreasing intensity at a rate of about 0.01/dB, showing no apparent age-related difference.