The relative effectiveness of different stimulus waveforms in evoking VEMPs: significance of stimulus energy and frequency.

We compared the effectiveness of a series of different sound stimulus waveforms in evoking VEMPs in normal volunteers. The waveforms were clicks (0.1-0.8 ms), biphasic clicks (0.8 ms) and sine waves (1250 Hz, 0.8 ms and 500 Hz, 2 ms) with different peak intensity and duration but similar root mean square area. VEMP amplitudes varied widely (corrected values 0.35 to 1.06), but when the amplitudes were plotted against the physical energy content and A-weighted intensity (L(Aeq): a measure of acoustic energy) of the waveforms, the relationship was found to be highly linear. However, when the stimuli were matched for their A-weighted energy, a 500 Hz 2 ms sine wave was the most effective waveform, suggesting that frequency tuning in the vestibular system is also an important factor. VEMP amplitude is thus determined by three stimulus-related factors: physical energy, transmission through the middle ear and vestibular frequency tuning. Use of a 500 Hz stimulus will maximise the prevalence and amplitude of the VEMP for a given sound exposure level.