Properties of the brain-stem response slow-wave component.

A slow-wave component of the brain-stem response recordable to signals at low sensation levels shows some promise for estimating hearing thresholds at low frequencies. This study describes several properties of this slow-wave response (SWR) in 30 normal hearing subjects and examines correlations with psychophysical thresholds. Acoustic signals were tone pips at 0.25, 0.5, 1, 2, and 4 kHz with 3-ms rise-fall times and no plateau. Repetition rate was 40/s. The EEG was filtered at 20 to 1,500 Hz before averaging. Results showed SWR thresholds were on the average about 15 dB higher than behavioral thresholds, however, the range was 0- to 35-dB sensation level. A large decrease in SWR amplitude and a 20-dB increase in threshold could occur in states of deep sleep. The SWR appears to be useful for estimating low-frequency thresholds, but the 35-dB threshold range in normal hearing subjects should be considered when interpreting some SWR results.