Human auditory steady state potentials.
The auditory steady state potentials may be an important technique in objective audiometry. The effects of stimulus rate, intensity, and tonal frequency on these potentials were investigated using both signal averaging and on-line Fourier analysis. Stimulus presentation rates of 40 to 45/sec result in a 40 Hz sinusoidal response which is about twice the amplitude of the 10 and 60/sec responses. No significant effects of subject age or sex were seen. The 40/sec response shows a linear decrease in amplitude and a linear increase in latency when stimulus intensity is decreased from 90 to 20 dB normal hearing level. This response is recordable to within a few decibels of behavioral threshold. Stimuli of different tonal frequency give similar amplitude/rate functions, with absolute amplitude decreasing with increasing tonal frequency. Signal averaging and Fourier analysis provide nearly identical amplitude/rate, amplitude/intensity, and latency/intensity functions. Both methods of analysis may be used, therefore, to record the 40 Hz steady state potential. Fourier analysis, however, may be the faster and less expensive method. Furthermore, techniques ("zoom") are available with Fourier analysis to study the effects of varying stimulus parameters on-line with the Fourier analysis procedure.