Psychophysical measurements of perceived intensity of single-point and multiple-point cutaneous stimuli in humans and subhuman primates.

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Abstract
To study the magnitude of cutaneous sensations produced by air-puff stimuli of different spatial and intensive patterns, 2 rhesus monkeys [M. mulatta] and 5 human subjects were trained in a reaction-time (RT) task. The subject (human or monkey) initiated each trial by depressing a telegraph key. An air-puff stimulus was delivered to the forearm skin at a random time 0.5-4 s later, and the subject was required to release the key as soon as the stimulus was felt. RT was defined as the time interval between air puff and key release and was measured in 121 sessions with monkeys and in 72 with humans. Number, spacing and peak force of the air puffs were varied in different sessions. Mean RT ranged from 228-287 ms in monkeys and from 247-315 ms in humans, depending on the intensity and number of air puffs delivered to the skin. RT were narrowly distributed around the mean, with SD as small as 30 ms. The wider distribution of activity recorded in somatosensory cortex of monkeys in response to 3 air puffs is related to a parallel increase in sensation magnitude. Increasing the number and degree of activity of cortical neurons results in perception of a more intense sensation. The RT task provides a powerful tool for measuring the magnitude of sensory experiences in experimental animals.