The neurologist Benjamin Libet performed a sequence of remarkable experiments in the early 1980's that were enthusiastically, if mistakenly, adopted by determinists and compatibilists to show that human free will does not exist. His measurements of the time before a subject is aware of self-initiated actions have had a enormous, mostly negative, impact on the case for human free will, despite Libet's view that his work does nothing to deny human freedom. Since free will is best understood as a complex idea combining two antagonistic concepts - freedom and determination, "free" and "will," in a temporal sequence, Libet's work on the timing of events can also be interpreted as supporting our "two-stage model" of free will. Indeed, Libet himself argued that there was still room for a veto over a decision that may have been made unconsciously over 300 milliseconds before the agent is consciously aware of the decision to flex a finger, but before the action of muscles flexing. In his 2004 book, Mind Time: The Temporal Factor in Consciousness, he presented a diagram of his work.
Libet says the diagram shows room for a "conscious veto."
The finding that the volitional process is initiated unconsciously leads to the question: Is there then any role for conscious will in the performance of a voluntary act (Libet, 1985)? The conscious will (W) does appear 150 msec before the motor act, even though it follows the onset of the cerebral action (1W) by at least 400 msec. That allows it, potentially, to affect or control the final outcome of the volitional process. An interval msec before a muscle is activated is the time for the primary motor cortex to activate the spinal motor nerve cells, and through them, the muscles. During this final 50 msec, the act goes to completion with no possibility of its being stopped by the rest of the cerebral cortex.) The conscious will could decide to allow the volitional process to go to completion, resulting in the motor act itself. Or, the conscious will could block or "veto" the process, so that no motor act occurs.
We don't know what specific unconscious mental processes the RP might represent....The position of conscious will in the time line suggests perhaps that the experience of will is a link in a causal chain leading to action, but in fact it might not even be that. It might just be a loose end — one of those things, like the action, that is caused by prior brain and mental events.Does the compass steer the ship? In some sense, you could say that it does, because the pilot makes reference to the compass in determining whether adjustments should be made to the ship's course. If it looks as though the ship is headed west into the rocky shore, a calamity can be avoided with a turn north into the harbor. But, of course, the compass does not steer the ship in any physical sense. The needle is just gliding around in the compass housing, doing no actual steering at all. It is thus tempting to relegate the little magnetic pointer to the class of epiphenomena — things that don't really matter in determining where the ship will go. Conscious will is the mind's compass. As we have seen, the experience of consciously willing action occurs as the result of an interpretive system, a course-sensing mechanism that examines the relations between our thoughts and actions and responds with "I willed this" when the two correspond appropriately. This experience thus serves as a kind of compass, alerting the conscious mind when actions occur that are likely to be the result of one's own agency. The experience of will is therefore an indicator, one of those gauges on the control panel to which we refer as we steer. Like a compass reading, the feeling of doing tells us something about the operation of the ship. But also like a compass reading, this information must be understood as a conscious experience, a candidate for the dreaded "epiphenomenon" label. Bernard Baars says there are two important time scales of consciousness
Sensory events occurring within a tenth of a second merge into a single conscious sensory experience, suggesting a 100-millisecond scale. But working memory, the domain in which we talk to ourselves or use our visual imagination, stretches out over roughly 10-second steps. The tenth-of-a-second level is automatic, while the 10-second level is shaped by conscious plans and goals.The kinds of deliberative and evaluative processes that are important for free will involve longer time periods than those studied by Benjamin Libet. Note also that the abrupt and rapid decisions to flex a finger measured by Libet bear little resemblance to the kinds of two-stage deliberate decisions for which we can first freely generate alternative possibilities for action, then evaluate which is the best of these possibilities in the light of our reasons, motives, and desires - first "free," then "will."
The premovement buildup of neuronal activity apparent in the RP and the assumption of causality invested in it have become a cornerstone in the study of volition. Notably, Benjamin Libet (9, 15) tried to measure the temporal relationship between the onset of the RP and the feeling of an “urge” to move. The results of Libet et al.’s experiments (9, 15) suggested that the objective neural events in the brain that cause movement precede the urge to move by 300 ms or more. A recent experiment, using Libet’s paradigm, confirms the same preurge buildup at the single-neuron level (16). Such demonstrations have had an unrivaled influence on the prevailing view that movement is initiated preconsciously and the feeling of intending to move is grafted on after the fact.Many philosophers have called free will "unintelligible" because of the internal contradiction and the presumed simultaneity and identity of free and will. Specifically, they mistakenly have assumed that "free" is a time-independent adjective modifying "will." A careful examination of ordinary language usage shows that free will is actually a temporal sequence of two opposing concepts - first "free" and then "will." First comes the consideration of alternative possibilities, which are generated unpredictably by acausal events (simply noise in neural network communications). This free creation of possible thoughts and actions allow one to feel "I can do otherwise." Next comes de-liberation and determination by the will, the unfreeing of possibilities into actuality, the decision that directs the tongue or body to speak or act. After the deliberation of the will, the true sentence "I can do otherwise" can be changed to the past tense and remain true as a "hard fact" in the "fixed past," and written "I could have done otherwise." Thus we have the temporal sequence which William James saw so clearly well over a century ago, with chance in a present time of random alternatives, leading to a choice which grants consent to one possibility and transforms an equivocal future into an inalterable and simple past. Free undetermined alternatives are followed by willed, determined choices. As John Locke knew more than three hundred years ago, "free" is an adjective that describes not the will, but the human mind.