[Audiometric thresholds estimated by auditory steady-state responses. Influence of EEG amplitude and test duration on...

To examine the influence of electroencephalogram (EEG) amplitude, test duration, and residual noise on the definition of threshold criteria for auditory steady-state responses (ASSR) in three representative populations.

EEG recordings from 61 patients, 11 sedated babies, and 53 relaxed volunteers were used in an offline analysis that calculated the mean EEG amplitude and the time course of residual noise. Additionally, the time course of residual noise and the test duration for a fixed level of residual noise were estimated from the mean EEG amplitude using the "square root of N" law of averaging.

A strong correlation between measured and predicted residual noise was found in all three groups. The mean EEG amplitude as well as the predicted test duration for a fixed residual noise level differed significantly among the three groups, with EEG amplitudes in clinical patients being four times greater than in relaxed volunteers.

The strong correlation between EEG amplitude, test duration, and residual noise in ASSR recordings allows for the prediction of individual test duration or residual noise levels in advanced testing algorithms. This study found that high mean EEG amplitudes in awake patients considerably reduce the accuracy of hearing thresholds estimated by ASSR.