Average evoked responses were recorded from human vertex in response to tone pulses presented at intersignal intervals (ISI) ranging from 0.25 through 10 sec. Tone pulses were 20 msec in duration with 20-msec rise and decay times. Frequencies investigated were 500, 1000, and 2000 Hz. Response amplitude was found to be a linear function of logx0ISI. Response latency did not change significantly with ISI, except perhaps in component N,. of the response, which appeared to increase in latency as

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... increased. These relations obtained regardless of frequency. INTERSIGNAL INTERVAL AND EVOKED RESPONSES z Fii0 o Data for Curve B were taken from Davis et al. (1966).