Voluntary acts are preceded by electrophysiological (RPs). With spontaneous acts involving no preplanning, the main negative RP shift begins at about200 ms. Control experiments, in which a skin stimulus was timed (S), helped evaluate each subject's error in reporting the clock times for awareness of any perceived event.

Over a long career, Libet has conducted experiments that have shown, in clear and concrete ways, how the brain produces conscious awareness.

Evidence that led to the hypothesis of a backwards referral of conscious sensory experiences in time, and the experimental tests of its predictions, is summarized. Criticisms of the data and the conclusion by Churchland that this hypothesis is untenable are analysed and found to be based upon misconceptions and faulty evaluations of facts and theory. Subjective referral in time violates no neurophysiological principles or data and is compatible with the theory of "mental" and "physical" correspondence.

It is widely accepted in science that the universe is a closed deterministic system in which everything can, ultimately, be explained by purely physical...

It is widely accepted in science that the universe is a closed deterministic system in which everything can, ultimately, be explained by purely physical causation. And yet we all experience ourselves as having the freedom to choose between alternatives presented to us — ‘we’ are in the driving seat. The puzzling status of volition is explored in this issue by a distinguished body of scientists and philosophers.

The major findings by Libet et al. are briefly summarized. The criticisms and alternative proposals by Trevena and Miller, Pockett, and Gomes are analyzed and found to be largely unwarranted.

The critical reinterpretations of Libet's research by G. Gomes make speculative, unwarranted, and untested assumptions. These assumptions and arguments are analyzed and their status relative to Libet's findings is criticized.

In this “Reply” paper, the arguments and experimental findings by Pockett, Pollen, and Haggard et al. are analyzed. It had been shown that a 0.5 s duration of repetitive activations of sensory cortex is required to produce a threshold of sensation. The view that this is due to a facilitatory buildup in excitatory state to finally elicit neuronal firing is shown to be incompatible with several lines of evidence. Objections to the phenomenon of subjective referral backwards in time are also (...) untenable. Haggard, Cartledge, Dafydd, and Oakley report that a self-initiated act can, under hypnotic suggestion, appear to the subject to be “involuntary.” The act under hypnosis is better viewed as one initiated unconsciously, not as an act of conscious will. (shrink)

In lieu of an abstract, here is a brief excerpt of the content:Commentary on “Free Will in the Light of Neuropsychiatry”Benjamin Libet (bio)Is Free Will Incompatible with Neuroscience?Sean Spence sets forth some interesting approaches to the issue of free will. His concepts are provocative and his marshalling of related quotations is informative.However, I shall argue with some of his crucial assumptions, in a way that affects the validity of some of Spence’s major conclusions. The latter are that “conscious experience is (...) always temporally postneural activity and thus... ‘caused’ not causal. Our ‘control’ is a sense which may be lost.... Our sense of agency is apparently illusory.”I have, of course, no quarrel with the view that even a fully voluntary act is initiated unconsciously (non-consciously). That condition was in fact demonstrated experimentally by us (Libet et al. 1983) when we found that cerebral neural activity (“readiness potential”) precedes the subject’s awareness of his/her intention or wish to act by at least 350 msec. This applied to fully self-initiated acts that occurred without “pre-planning” by the subject of when to move. (Incidentally, those finding have been replicated by others—see Keller and Heckhansen, 1990 with commentary thereon by Libet 1992, and Wong et al. 1988).However, we also found that conscious intention did precede that actual motor act by about 200 msec. That left open the potentiality for the conscious function to control the outcome of the process that was initiated in the brain unconsciously (see Libet 1985). We have all had the experience of consciously suppressing or vetoing the performance of an urge or intention to act. The 200 msec interval provides sufficient time in which the voluntary process could be stopped, before final activation of the motor area about 50 msec before the act. We were able to show that subjects could veto an act in the 100–200 msec interval before the expected time for the action.Spence dismisses this free will potentiality in the control or veto of a voluntary process. He says: “It is flawed because the ‘decision’ (in consciousness) to act or not to act is itself the ‘result’ of preceding neural activity.” This argument is based on my own evidence that a period of up to 500 msec of cerebral activity is required to produce a conscious sensory experience (Libet 1993, for review).But conscious control of a process is not the same as becoming aware of the volitional intent (Libet 1985, 563–564). Control implies the imposing of a change, in this case after the appearance of the awareness of intention to act. Conscious control may not necessarily require the same neural “time-on” feature that precedes the appearance of awareness per se. There is presently [End Page 95] no directly applicable evidence against the appearance of a conscious control function without prior neural processes specific to its initiation.In short, one cannot cavalierly dismiss the possibility of a conscious free will function on the basis of a belief that such a control function must be itself initiated unconsciously by prior specific neural processes. The argument that conscious free will control is simply a useful delusion must still be regarded as a philosophical belief, not a scientifically demonstrated proposition.Spence goes on to suggest that “Consciousness is necessary for purposeful (intentional) action but it is not the initiator.” But if Spence is consistent in his view that all conscious functions are preceded by specific neural activities that initiate the function, then his putative role for consciousness would have been itself initiated unconsciously. How, then, would consciousness be “performing (purposeful, intentional) actions with subtlety and invention” if it is simply an after-effect of the responsible cerebral process? It would appear that Spence is postulating an active role for consciousness in directing the course of neural activities carrying out purposeful, intentional actions. That is the kind of potentiality I was suggesting must be kept open, but one that Spence dismissed elsewhere as “flawed.”On a technical point: The Grey Walter experiment is cited as evidence for postulated effects of timing, in the “illusion” of self-initiation of an act. However, that experimental result was simply due to the fact that the motor cortex initiates the command... (shrink)

In previous research Libet discovered that a critical time period for neural activation is necessary in order for a stimulus to become conscious. This necessary time period varies from subject to subject. In this current study, six subjects for whom the time for neural activation of consciousness had been previously determined were administered a battery of psychological tests on the basis of which ratings were made of degree of repressiveness. As hypothesized, repressive subjects had a longer critical time period for (...) neural activation of consciousness, suggesting the possibility that this neurophysiological time factor is a necessary condition for the development of repression. (shrink)