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Libet's delay


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A period of approximately half a second between a person's skin being touched and the resulting conscious experience of being touched, although the brain receives the signal and responds to the stimulus with an evoked potential after a little more than a hundredth of a second (15 milliseconds), and a reflex response can occur within about a tenth of a second (100 milliseconds). In research with fully conscious patients during brain surgery under local anaesthetic, Libet found a half-second delay between the beginning of continuous electrical stimulation of the exposed somatosensory cortex and the patient's report of a conscious sensation, such as a tingle in the right hand during electrical stimulation of a point in the left somatosensory cortex. In contrast, even a brief stimulus applied directly to the skin is consciously experienced, but not immediately—if it is followed within less than half a second by stimulation of the somatosensory cortex, then backward masking stops the skin stimulus from being felt, confirming that the conscious experience of a skin stimulus is delayed by about half a second. According to Libet, the reason why we do not notice the half-second delay is that our conscious experiences of sensations are antedated to the time of the evoked potentials, creating the illusion that the sensations are almost immediate. Also called the antedating of consciousness, backward referral of sensation, half-second delay in consciousness, or time delay in consciousness. See also readiness potential. [Named after the US physiologist Benjamin Libet (1916–2007) who reported the delay first in an article in the journal Perspectives in Biology and Medicine in 1965 and subsequently in numerous publications, notably an article in the journal Brain in 1979 (co-authored with three colleagues) and in Behavioral and Brain Sciences in 1985]

Subjects: Psychology.


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