Subjective Referral of the Timing for a Conscious Sensory Experience

Abstract

PREVIOUS studies had indicated that there is a substantial delay, up to about 0.5 s, before activity at cerebral levels achieves `neuronal adequacy' for eliciting a conscious somatosensory experience (Libet, Alberts, Wright, Delattre, Levin and Feinstein, 1964; Libet, 1966). The delay appeared necessary not only with stimulation of medial lemniscus, ventrobasal thalamus, or postcentral cortex, but even when the stimulus was a single electrical pulse at the skin (Libet, Alberts, Wright, and Feinstein, 1967, 1972; Libet, 1973). The present investigation began with an experimental test of whether there is in fact also a subjective delay in the conscious experience for a peripheral sensory stimulus. That is, is there a delay in the subjective timing of the experience that would correspond to the presumed delay in achieving the neuronal state that `produces' the experience? The results of that test led to a modified hypothesis ; this postulates (a) the existence of a subjective referral of the timing for a sensory experience, and (b) a role for the specific (lemniscal) projection system in mediating such a subjective referral of timing. Experimental tests of the new proposal were carried out and are reported here.