Cortical evoked potentials in response to brief modulation of signal amplitude. Experiments on auditory temporal resolution.

Human cortical evoked potentials were monitored with scalp electrodes as an indicator of the ability to resolve brief changes in an auditory signal. For a brief period in the middle of a noise pulse its intensity was increased or decreased. The magnitude and duration of this change was varied to establish (1) the threshold for the cortical evoked potential and (2) the effect on the evoked response (amplitude, latency) in the suprathreshold region. To evoke a stimulus-specific potential pattern, durations of about 16 ms were required for intensity changes of +3 dB. With an intensity step of +9 dB, the threshold duration was reduced to 4-6 ms. A brief increase in intensity was more associated with distinctly lower thresholds and larger response amplitudes than an equivalent reduction in intensity, duration being equal. These results confirm the critical durations found in psychoacoustic studies that offer valuable evidence as to the ability to resolve brief changes in an auditory signal.