Acoustic relations of the human vertex potential

The average amplitude of the slow, diffuse, nonspecific electrical response of the human cortex, called the V potential, evoked by tone pips or by tactile stimuli to thumb and forefinger, follows a power law with exponent about 0.24 (re sound pressure). The variability of the responses is great, across both trials and subjects. If auditory or tactile stimuli are judged equally strong, across frequency or modality, the V potentials tend to be equal. Both the latency and the amplitude of the V potential are independent of the rise time of a tone burst, at least up to 100 msec. The amplitude also remains nearly constant as the duration of the plateau of a burst, with rise and fall times of 5 msec, is varied from 2 to 320 msec. An off response that closely resembles the on response in waveform, latency, and amplitude appears at the end of any burst that is long enough, but an off response that follows an on response by 1 sec or less is much reduced in amplitude, and so is an on response that too closely follows an off response. The V potential is a response to change in stimulation either on or off.