Effect of tone-burst frequency on fast and slow components of auditory brain-stem response.

By means of digital filtering, averaged auditory brain-stem responses (ABR) were divided into slow and fast components with frequency compositions of 50-300 Hz and 400-1 500 Hz, respectively, and the relation of the two components to stimulus frequency was investigated. Tone bursts with a rise-decay time of two periods of the chosen frequency with no plateau (2-0-2) and with a 4 ms rise-decay time with no plateau (8 ms duration) were used as acoustic stimuli. Tone-burst frequencies were 0.5, 1, 2, 4 and 8 kHz at an intensity level of 40 dB nHL. The amplitude ratio of wave V of the fast component to the slow component decreased with decreasing stimulus frequency, and it remained almost unchanged at each stimulus frequency regardless of the rise-decay time of the stimuli. From these results, it became clear that the frequently-mentioned audiometric difficulties for lower frequency stimuli in ABR testing are related mainly to the low amplitude of the fast component for the frequency range below 1.0 kHz. The slow component, with relatively large amplitude for the low-frequency stimuli, is regarded as the most useful index in the ABR for threshold estimation of hearing.