Benjamin Libet is a researcher in the physiology department of the University of California, San Francisco, and a pioneering scientist in the field of human consciousness.
In the 1970s, Libet was involved in research into neural activity and sensation thresholds. His initial investigations involved determining how much activation at specific sites in the brain was required to trigger artificial somatic sensations, relying on routine psychophysical procedures. This work soon crossed into an investigation into human consciousness; his most famous and controversial experiment demonstrates that unconscious electrical processes in the brain (called 'readiness potential') precede conscious decisions to perform volitional, spontaneous acts, implying that unconcious neuronal processes precede and potentially cause volitional acts which are retrospectively felt to be consciously motivated by the subject. If unconscious processes in the brain are the true initiator of volitional acts, as Libet's experiments suggest, then little room remains for the operations of free will. If the brain has already taken steps to initiate an action before we are aware of any desire to perform it, the causal role of consciousness in volition is all but eliminated. Researchers also analyzed EEG recordings for each trial with respect to the timing of the action.
It was noted that brain activity involved in the initiation of the action, primarily centered in the secondary motor cortex, occurred, on average, approximately five hundred milliseconds before the trial ended with the pushing of the button. In other words, apparently conscious decisions to act were preceded by an unconscious buildup of electrical charge within the brain. Libet himself finds room for free will in the interpretation of his results, but in a massively reduced role to that which we are used to. This is in the form of 'the power of veto', in which conscious acquiescence is required to allow the unconscious buildup of readiness potential to be actualised as a movement. Thus, while consciousness plays no part in the instigation of volitional acts, it retains a part to play in the form of suppressing or withholding from certain acts instigated by the unconscious. Libet's book on the subject is called Mind Time: The Temporal Factor in Consciousness.
- Benjamin Libet's evidence examined
- Benjamin Libet's Wikipedia page
- Do We Have Free Will? by Benjamin Libet
- Commentary of Benjamin Libet's Mind Time (158 kb PDF)
- Susan Blackmore's review of Mind Time
Benjamin Libet Quotes
I have taken an experimental approach to this question. Freely voluntary acts are preceded by a specific electrical change in the brain (the 'readiness potential', RP) that begins 550 ms before the act. Human subjects became aware of intention to act 350-400 ms after RP starts, but 200 ms. before the motor act. The volitional process is therefore initiated unconsciously. But the conscious function could still control the outcome; it can veto the act. Free will is therefore not excluded. These findings put constraints on views of how free will may operate; it would not initiate a voluntary act but it could control performance of the act. The findings also affect views of guilt and responsibility. But the deeper question still remains: Are freely voluntary acts subject to macro-deterministic laws or can they appear without such constraints, non-determined by natural laws and 'truly free'? I shall present an experimentalist view about these fundamental philosophical opposites.