On-effect in brainstem electric response audiometry. Consequences for the use of tone-bursts

The nature of the auditory brainstem potentials is studied, referring to the theory of the on-effect. The following stimuli are used: a click, a tone-burst of 3 kHz with a rise-decay time of 2 ms and a plateau of 1 ms, and finally different initial parts of the former tone-burst (the first 8, 4, 2, 1 cycles). Together with the electrical waveforms, the acoustic forms of the stimuli are described and the frequency spectra are measured. The auditory brainstem potential appears to be a pure onset response with a very short integration time. Only the initial part of the tone-burst (mainly the first oscillation) is responsible for eliciting the response. The consequences for the audiometric use of short tonal stimuli are discussed. Measurements of intensities or frequency spectra, technically or subjectively, of the whole tone-bursts are inappropriate, because the intensity and frequency content of the effective stimulus must be considered. The real frequency specificity then becomes much poorer and differs little from the click stimulation.