Blutner/Philosophy of Mind/Consciousness



The greatest gift which humanity has received is free choice. It is true that we are limited in our use of free choice But the little free choice we have is such a great gift and is potentially worth so much that for this itself life is worthwhile living. (Isaac Bashevis Singer 1968)

In many cases we do not do what we will but we will what we do. (Modern Neuroscience)


1   Libet's 1979 experiments

In the 60s the brain surgeon Bertram Feinstein allows his friend Benjamin Libet to perform experiments with uncovered brains. In the breaks during Feinstein’s surgical work Libet amused the patients by performing simple experiments with electrical stimulations of certain brain areas, and the patients had to report what they felt. What is the inner experience of an outer stimulation? In some way, he began to replicate Wilder Penfield’s investigations about topographic maps (relating brain and body regions).


However, Libet's main interest was concentrated on the time characteristics of the relation between external stimulus and internal experience.


§         His first important finding was that it  needs at least a 500 ms  cascade of electrical stimulation  to trigger a conscious experience.

§         In a later experiment Libet and his colleagues found a very elegant experimental arrangement for investigating the timing of external stimulus and internal experience:

Libet et al. (1979): Subjective Referral of the Timing for a Conscious Sensory Experience. Brain 102, 193-224.


The Experiment


More or less simultaneously the experimenter

(1) stimulated a brain region such that the subject felt a tickle in her left hand.

(2) stimulated the right hand directly.

The subject had to decide where she felt the stimulation first, in the right hand or in the left hand or at the same time. It was possible for the experimenter to shift the onsets  of the stimulations

Libet’s expectation was that that in each case approximately a half second is necessary to prompt a conscious experience (since it needs always approximately a half second before a stimulation can trigger conscious experience). However, the outcome was completely unexpected:

The stimulation of the brain and the stimulation of the skin were experienced simultaneously if the stimulation of the brain started a half second earlier!


In case of the external stimulation of the skin our 'conscious mind' it subtracts a half second and predates subject's conscious experience.  In this way, we experience the outer world in the correct way. It takes a while until we experience  a event in the outer world. However, our 'conscious mind' dates it back and we think we experience the world in the temporally right moment. (The same phenomenon as with the Blind Spot: Our perceptual system is insufficient. However, we do not become aware of  its errors)


A direct test of this hypothesis is possible if the incommensurability of the two stimuli (i.e., the direct stimulation of the brain and the stimulation of the skin) can be overcome. In the critical experiment two different regions of the brain were  stimulated electrically:

(1) a brain region of the cortex such that the subject felt a tickle in her left hand.

(2) a brain region in the thalamus (phylogenetically old; so-called unspecific system; this system collects information from the whole body and sends it to the cortex)

The finding was that in this case very the same pattern is occurring:



2 Is an experimental approach to the question of free will possible?


§         Are we completely defined by the deterministic nature of physical laws? Are we essentially sophisticated automatons only, with our conscious feelings and intentions tacked on as epiphenomena with no causal power? (cf. Thomas H.Huxley) 

§         Or do we have some independence in making choices and actions, not completely determined by the known physical laws?

What we need first for approaching the problem in a experimental way is a good operational definition of free will. This approach should be in accord with common views.

That means

§         There should be no external control or cues to affect the occurrence or emergence of the voluntary act under study; i.e. it should be endogenous.

§         The subject should feel that he/she wanted to do it, on her/his own initiative, and feel he could control what is being done, when to do it or not to do it.
Many actions lack this second attribute. For example, when the primary motor area of the cerebral cortex is stimulated, muscle contractions can be produced in certain sites in the body. However, the subject (a neurosurgical patient) reports that these actions were imposed by the stimulator, i.e. that he did not will these acts. Clinical disorders with a similar effect are Parkinson and even obsessive compulsions to act.



Simple examples of 'self paced' voluntary acts are lifting a finger, closing an eye etc.

How can we measure the onset of such a voluntary act?

This question is the most important for performing serious experiments. Obviously, consciousness is private. It is a primary phenomenon. That means consciousness is only accessible to the subject that  has the experience. (The only criterion for consciousness is consciousness itself).  There is principally no way to reduce it to some measurable activities in he brain. Of course, there may be a correlation between consciousness and electrical activity in the brain. However, the primary phenomenon of consciousness is purely subjective.

Wundt's clock

Wund's clock


3 Benjamin Libet on consciousness and free will

Consider the following two description of the same situation, one time as our subjective report, the other time as from the perspective of modern neuroscience.


A Subjective report

On the journey. We are driving three hours already, and we have to drive another four hours. We see a sign indicating a place to rest. We think 'time for a break'. On the other hand, we have to drive another 400 km and we want to arrive not too late. However, it is dangerous to drive lacking in concentration. Consequently, we decide to make a stop. We indicate, brake, and drive on the place to rest.

B Modern Neuroscience

On the journey. Unconsciously our brain has registered that we are tired. And unconsciously our brain registers this sign indicating a place to rest. from earlier experience our brain knows that we can rest there. And it gives a signal to our body to indicate and to brake. At the same time another bundle of neurons becomes active. Unconsciously it has checked the plan for our journey and has doubts whether we will arrive in time if we make a break. Our brain has to come to a decision. What's better, to stop or not to stop? Within milliseconds the brain decides to stop, and it gives order to register and to brake. All that happens unconscious. Only 200 milliseconds later this decision becomes conscious (and - being trained philosophers - we deeply become convinced that this was our free will)


3.1  The readiness potential

In 1965, Hans H. Kornhuber and  Lüder Deecke investigated the correlation between arbitrary movements of hand and foot and electrical activities in the brain (EEG). The general question was this: It is possible to demonstrate by EEG that a person performs a certain action (for example, she opens or closes her hand).  Kornhuber  & Deecke found a rather strange phenomenon: already 1 second before the hand (or foot) is moved an activity in the EEG appears. They called it "Bereitschaftspotential" (readiness potential). Surprising is that the readiness potential starts so early.


readiness potential 

Readiness Potential: Changes of the electrical field of a certain brain region  already 1 second before an action begins.


Benjamin Libet from the Medical centre of the University of California (San Francisco) was fascinated by this finding and asked a very important question: If a simple action like moving our hand is prepared for more than a half second in our brain, at what moment do we consciously decide to perform this action? Intuitively, we feel it is much less that a half second. If this is right, and the preparation of an action begins much earlier as the conscious decision to perform this action, can we have a free will then. What about the freedom of our will?

3.2  Libet's 1983 experiment

The first experiments to address the timing of decisions directly were conducted by Benjamin Libet and his colleagues.

Libet et al. (1983): Time of conscious intention to act in relation to onset of cerebral activity (readiness potential): the unconscious initiation of a freely voluntary act. Brain 106, 623–642.

Their experiments asked questions about when people believed they made a decision versus when the brain began to make the decision. In one form of their experiment, they measured EEG activity while subjects voluntarily chose to lift a finger. During the task, subjects watched a rapidly moving clock hand and made a mental note of when they decided to lift their finger.

This yielded three types of data:

(1)  when the subject lifted her finger [electromyogram of the muscles]

(2)  when she believed she decided to lift her finger [Wund's clock]

(3)  what her brain activity was during this time. [EEG]

The EEG results demonstrated that the cortex became active with a ‘readiness potential’ 350 ms before the reported awareness of a ‘wish to move’. These experiments suggested that our subjective awareness of decisions occurs measurably later than the actual events of deciding





Our brain initiates a 'voluntionary act' unconsciously.  Not a conscious decision but unconscious processes are at the beginning. This conclusions directly contradicts our (conscious) common sense: Consciousness is unfaithful. It swindles people. Furthermore, from the voluntionary act to the action (lifting a finger) it takes about 200 ms (myogram of the muscles). Is this enough time for a conscious stop of the action?


3.3  Libet's conclusions concerning free will

§         Actually, only 100 ms is available in which the conscious function might affect the final outcome of the volitional process (the primary motor cortex needs some time to the spinal motor nerve cells).

§         Libet argues that this is enough time for stopping or voting the final progress of the volitional process. "Conscious-will could thus affect the outcome of the volitional process even though the latter was initiated by unconscious cerebral processes."

§         Indirect evidence of a veto possibility: Subjects in Libet's experiment reported that a conscious wish appeared but that they suppressed or vetoed that. Libet could show that in such cases a large  readiness potential proceeded the veto, signifying that the subject was indeed preparing the act, even thought the action was aborted by the subject.

§         Does the conscious veto have a preceding  unconscious origin? In this case we cannot consider the veto as action of free will. Libet proposes, instead, that  the conscious veto may not require preceding unconscious processes. The conscious veto is a control function different from a conscious wish to act. At the moment there is no experimental evidence against this possibility. 

§         Psychological implication: Consciousness is not a high level authority that gives orders to subordinated instances. Instead, its main role is a selective one: make a decision between the bulk of possibilities  that are proposed by unconscious processes.

§         Ethical implication: The role of conscious free will is not to initiate a voluntary act, but rather to control whether the act takes place.  "This kind of role for free will is actually in accord with religious and ethical strictures. These commonly advocate that you 'control yourself'. Most of the Ten Commandments are 'do not' orders"


4  Causality and the perception of time

Libet investigated the relation between the felt time of conscious actions/events and the time course of brain activity (a). Another important question concerns the perception of events in time dependent on the real time course, for example the timing judgment  of pressing a key and the (delayed) occurrence of a tone (b).

An especially interesting question concerns the interaction of time and causality. What is the relation between time and causality? Does our perception of when an event occurs depend on whether we caused it? A recent study by Haggard, Clark and Kalogeras (2002) suggests that when we perceive our actions to cause an event, it seems to occur earlier than if we did not cause it  (cf. David M. Eagleman and Alex O. Holcombe, in the reader)

In one condition, subjects judged the timing of an auditory tone by reporting the corresponding position of a rapidly moving clock hand. In the second, crucial condition, subjects pressed a key that caused a tone to follow 250 ms later. Again, subjects judged the time of the tone. Comparing the data across conditions, the perceived times of the tone when keypress and ton were causally linked were compared with the conditions in which the ton occurred by itself. Remarkably, when the tone was causally linked to the subjects’ keypress, subjects judged the tone to occur 46 ms earlier than if these events had occurred alone.

In a second experiment with different subjects, the delay between the keypress and subsequent tone was varied (to be 250, 450, or 650 ms), and subjects judged the time of the tone. Haggard et al. found that the further apart the keypress and tone, the more the temporal ‘attraction’ of the tone to the keypress was diminished (see Figure).


Tones perceived to be a consequence of one’s actions seem to occur earlier in time than solitary tones. More generally, when we perceive our actions to cause an event, it seems to occur earlier than if we did not cause it.

Eagleman & Holcombe's explanation

The philosopher David Hume pointed out that events that are close together in space and time are more likely than spatio-temporally distant events to be perceived as causally related. With certain assumptions about the prior probabilities, it follows from Bayes’ equation that events known to be causally related are more likely to be close in time and space than unrelated events.

P(Cause (e1, e2) | CloseTime(e1, e2)) >

P(Cause (e1, e2) | DistantTime(e1, e2))

==>  (with certain assumptions about the prior probabilities)

P(CloseTime(e1, e2) | Cause (e1, e2)) >

P(DistantTime(e1, e2) | Cause (e1, e2))