Human auditory evoked potentials to frequency-modulated tones

Three experiments evaluated steady state and transient auditory evoked potentials (EPs) to tones that were sinusoidally modulated in frequency and to tones that alternated between two frequencies with a linear ramp. The steady state responses to sinusoidal FM were small and difficult to record at both the first and second harmonics. Ramp FM evoked larger and more consistent second harmonic steady state responses than the sinusoidal FM. Only the ramp FM stimuli elicited transient EPs and these only at low modulation rates. These responses were larger to upward ramps than to downward ramps. The response to two simultaneously presented ramp FM tones differed from the sum of responses to the individual tones, indicating some interaction in the processing of the two stimuli.