Libet's Experiment on Consciousness

Astonishing Experiments

Some of the most-discussed experiments in the field are those carried out by Benjamin Libet, which appear to demonstrate that supposedly conscious decisions are already settled before we become aware of them.

Libet asked his experimental subjects to move one hand at an arbitrary moment decided by them, and to report when they made the decision (they timed the decision by noticing the position of a dot circling a clock face). At the same time the electrical activity of their brain was monitored. Now it had already been established by much earlier research that consciously-chosen actions are preceded by a pattern of activity known as a Readiness Potential (or RP). The surprising result was that the reported time of each decision was consistently a short period (some tenths of a second)after the RP appeared. This seems to prove that the supposedly conscious decisions had actually been determined unconsciously beforehand. This seems to lend strong experimental support both to the idea that free will is an illusion (at most, it would seem, there is scope for a last-minute veto by the conscious mind - a possibility which has been much debated since) and to a form of epiphenomenalism .

There are many different ways of challenging Libet's conclusions. We could still question whether RPs really have the significance attributed to them. We could question whether the unusual circumstances of the experiment, with subjects thinking in advance about making a decision, and then making one for no reason whatever, properly represent normal thought processes. We could take the view that the experiments involve at least two mental reporting processes, one to do with the occurence of the decision, one to do with the state of the clock, which makes any judgement of simultaneity highly problematic .

Libet himself proposed in 1994 that the diverse neural events which contribute to consciousness are drawn together by a conscious mental field (CMF): a phenomenon which emerges from certain kinds of brain activity. The experiments he proposed to test this idea have not been carried out, and arguably it raises more problems than it solves. Libet's research, in any case, remains challenging and interesting.

If you ask me, the key point is that consciousness is not a simple, unitary phenomenon. There's a difference, for example, between just saying what you think, and carefully planning in advance the words you're going to say. But nobody would claim that just saying what you think wasn't a conscious activity. Libet's experiment requires two different levels of consciousness. First you have to make an unreflecting decision to move. Then you have to consciously think about having made the decision - second-order consciousness - in order to notice the time. It's not at all surprising that the conscious decision represented by the RP comes first, and the second-order thought about that decision a fraction of a second later. In no way does this show the decision wasn't conscious, or any of the rest of it. More generally, it's obvious that the simpler processes which together constitute conscious thought can't themselves be conscious, or we should be stuck with an infinite regress. There's nothing in that which ought to worry us.

A fuller account of Libet's experiments and theory.

Damage to certain areas of the brain may leave a patient blind in one eye, or in one area of their visual field. Although they have normal vision elsewhere, such patients are unable to report what is going on in the 'blind spot' and say that they see nothing there. However, experiments have shown that when asked to guess the location of an object or a light in the blind patch, some of them perform well. Although they continue to say they cannot see the object in question, they consistently point in right direction. This phenomenon is known as 'blindsight'.

Blindsight appears to challenge the idea that we know what's going on in our minds and what motivates our behaviour, and it can therefore be seen as evidence in favour of some variety of epiphenomenalism. The experiments which reveal it can perhaps be seen as related to others which show that subliminal or unnoticed details can nevertheless influence our subsequent behaviour, as can post-hypnotic suggestions or information given only to one side of a 'split-brain' patient. A striking fact about all these cases is the patient's failure to be aware of what is going on. They may say they are acting at random, or they may invent reasons for their behaviour after the fact. This does suggest that we do less by way of controlling our behaviour than we think, and more by way of rationalising it.

Ramachandran has suggested that blindsight arises from the fact that there are two pathways from the eye into the brain - one to the cortex, assumed to be the home of consciousness, one to the 'older' instinctive parts. It's conceivable that blindsight represents survival of the 'old' pathway after destruction of the 'new' one to conscious functions. But this solution would be specific to vision.

A more general explanation might come from the idea that perception involves distributed activity in several different parts of the brain. Suppose, let's say, that seeing object A over there involves the activation of neurons (or neural groups) 1, 3, 7, and 9. Now suppose that the residual pathways of vision, the subliminal stimulus, the post-hypnotic suggestion, or whatever, are enough to activate 1 and 3, but not 7 or 9. As a result, there is no conscious experience of object A. But when it comes to pointing at random, or choosing what to do next, the fact that 1 and 3 are still 'reverberating' from the earlier stimulus predisposes us towards the choice of A over there, rather than say, B down there which would require activation of 2, 4, 6 and 8

Here is Dr.Jill Taylor on how she suffered a massive stroke and how she managed only with the right hemisphere for a long time !!

Here is the latest on Consciousness and how decisions were made seven seconds before the conscious mind registered it.

Brain Scanners Can See Your Decisions Before You Make Them

Reported by Brandon Keim

This schematic shows the brain regions (green) from which the outcome of a participant's decision can be predicted before it is made. Courtesy John-Dylan Haynes.

You may think you decided to read this story -- but in fact, your brain made the decision long before you knew about it.

In a study published Sunday in Nature Neuroscience, researchers using brain scanners could predict people's decisions seven seconds before the test subjects were even aware of making them.

The decision studied -- whether to hit a button with one's left or right hand -- may not be representative of complicated choices that are more integrally tied to our sense of self-direction. Regardless, the findings raise profound questions about the nature of self and autonomy: How free is our will? Is conscious choice just an illusion?

"Your decisions are strongly prepared by brain activity. By the time consciousness kicks in, most of the work has already been done," said study co-author John-Dylan Haynes, a Max Planck Institute neuroscientist.

Haynes updated a classic experiment by the late Benjamin Libet, who showed that a brain region involved in coordinating motor activity fired a fraction of a second before test subjects chose to push a button. Later studies supported Libet's theory that subconscious activity preceded and determined conscious choice -- but none found such a vast gap between a decision and the experience of making it as Haynes' study has.

In the seven seconds before Haynes' test subjects chose to push a button, activity shifted in their frontopolar cortex, a brain region associated with high-level planning. Soon afterwards, activity moved to the parietal cortex, a region of sensory integration. Haynes' team monitored these shifting neural patterns using a functional MRI machine.

Taken together, the patterns consistently predicted whether test subjects eventually pushed a button with their left or right hand -- a choice that, to them, felt like the outcome of conscious deliberation. For those accustomed to thinking of themselves as having free will, the implications are far more unsettling than learning about the physiological basis of other brain functions.

Caveats remain, holding open the door for free will. For instance, the experiment may not reflect the mental dynamics of other, more complicated decisions.

"Real-life decisions -- am I going to buy this house or that one, take this job or that -- aren't decisions that we can implement very well in our brain scanners," said Haynes.

Also, the predictions were not completely accurate. Maybe free will enters at the last moment, allowing a person to override an unpalatable subconscious decision.

"We can't rule out that there's a free will that kicks in at this late point," said Haynes, who intends to study this phenomenon next. "But I don't think it's plausible."

That implausibility doesn't disturb Haynes.

"It's not like you're a machine. Your brain activity is the physiological substance in which your personality and wishes and desires operate," he said.

The unease people feel at the potential unreality of free will, said National Institutes of Health neuroscientist Mark Hallett, originates in a misconception of self as separate from the brain.

"That's the same notion as the mind being separate from the body -- and I don't think anyone really believes that," said Hallett. "A different way of thinking about it is that your consciousness is only aware of some of the things your brain is doing."

Hallett doubts that free will exists as a separate, independent force.

"If it is, we haven't put our finger on it," he said. "But we're happy to keep looking."