Weak lead stimulation can modify the human startle reflex It is proposed that, with the aid of physiological measures taken in the interval between lead and startle stimuli, this paradigm offers a promising method of investigating different levels of central processing, the operation of a short time‐constant as opposed to a long time‐constant system, and the operation of an orienting‐Attentional as apposed an Intensity dependent activational system.

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It is generally assumed that either heart rate or heart period can be used to measure phasic cardiac activity changing either from beat to beat or from second to second. However, only rate analyzed in real‐time units and only period analyzed in cardiac‐time units have the important property that the arithmetic mean of the unit estimates is free to vary and yields an average equal to the definitional estimate based on all units.

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In three experiments, the human blink response to 50-msec 105-dB white noise was markedly reduced by prior stimulation with weak tones, either 20 msec long or coextensive with lead intervals of 30 to 240 msec. Although the inhibitory effect was greater with a 70-dB than with a 60-dB lead tone, it was not affected by increasing the lead-tone duration beyond 20 msec. At lead intervals of 30 and 60 msec, the latency of blink onset was also reduced by prestimulation, and this effect was greater with the longer lead tones. Neither effect was an artifact of responding to the lead tone itself. The simultaneous occurrence of an inhibitory change in magnitude and a facilitatory change in latency, and the differential influence of lead stimulus duration, suggest that the magnitude and latency modifications involve different neural mechanisms with different time constants.