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Thursday at 7.40pm
with Robyn Williams
26/05/2005
Richard Passingham
Summary:
Studies show that reactions of top people in sport are faster than consciousness can register. How can you get to such a lightning reflex? Richard Passingham, Professor of Psychology at Oxford describes some remarkable experiments.
Transcript:
Robyn Williams: Have you checked the whereabouts of your left leg recently? Does it have a mind of its own like Peter Sellers’ arm in Dr Strangelove, always trying to give the Nazi salute irrespective of its owner’s intentions. Intention, that’s the word for this evening’s conversation. It’s with Professor Dick Passingham who’s a psychologist at Oxford and who likes to play tricks on us and our limbs, to see how the brain controls them. Or doesn’t – like when you think your arm or leg belongs to someone else.
Do you believe for example that you could be tricked into thinking that a dummy arm is actually your own? It’s something Professor Passingham does all the time.
Richard Passingham: It’s an illusion that was discovered by a man called Bogunovic in America and he was interested as we are in how we know that our body belongs to ourselves because there are patients who actually with particular lesions in their brain think that the left hand side of their body belongs to somebody else.
The illusion involves the following. You have your arm, your right arm, under cover and on top of it a rubber arm. It’s a prosthetic arm so it looks very like a real arm and normally of course you would know perfectly well that the prosthetic arm doesn’t belong to you. And what he discovered is that if you use paint brushes, one to brush your real arm under the cover and one visibly to brush the rubber arm, after about ten seconds or so you get the illusion that the rubber arm belongs to yourself. And it’s so remarkable that you even think that if you were to move a finger that visible finger of the rubber arm would move.
Robyn Williams: And do you feel the tickle?
Richard Passingham: Oh you feel the tickle of course. It really feels as if it’s on your real arm. The illusion happens because there’s a conflict – on the one hand you can feel your real arm and you know where it is but on the other hand you see the brush on the rubber arm at the same time as you feel it on your real arm so there’s a conflict. And the brain resolves this conflict by actually making you think that the rubber arm belongs to yourself.
Robyn Williams: So how did you use this illusion as part of your investigation?
Richard Passingham: Well I was working with Henry Kerson who comes from the Karolinska Institute in Sweden who’s now one of the members of my group and as always I’m interested in letting young people follow their own course and he wanted to follow up how we have this self concept. Our belief that we know the difference between our arm and somebody elses. So what we did was we used scanners. These may well now be familiar to your listeners using a magnetic resonance scanner we can now image activity in the brain while somebody lies in our scanner. So what we did is we got hold of oh I think about 20 people and we found out how many of them actually felt the illusion strongly. We put them in the scanner and we arranged their heads so that they could see the rubber arm directly, we didn’t use a mirror, their head was slightly tilted up so that they could see their arm. And then we carried out the experiment exactly as Bogonovic had, that is we synchronously brushed both the real arm underneath the cover and the rubber arm which the person can see happening.
Now to do the experiment we made use of the fact that there are two conditions in which you don’t feel the illusion. One is if the brush doesn’t happen synchronously, if in other words, you’re brushing out of synch the real arm and the rubber arm then you don’t feel the illusion. And there’s another condition in which you don’t feel the illusion and that’s if you have the rubber arm pointing the wrong way so that its fingers are pointing towards your shoulders. So we could look for where is the activity in the brain when you do feel the illusion compared with these two control conditions.
Robyn Williams: And what did you find?
Richard Passingham: Well we found that the area that showed the strongest activity related to the illusion was an area called the pre-motor cortex which is part of your motor system and it’s an important area because it receives information from all the senses. So it receives both tactile information and about the position of your arm and it also receives visual information. And this area was active only in the condition in which you felt the illusion, only after you began to feel the illusion and remarkably the more strongly you felt the illusion the more strongly this area was active. We got the people to rate the strength of the illusion in various ways and as I say there was very close relation between how strongly they felt the illusion and how active this area was.
Robyn Williams: And when you were going outside the conventional reaction where you actually have a successful illusion when in fact you had the arm going the other way, what happened in the brain?
Richard Passingham: Then we found no activity in this area at all, these were controlled conditions in which as you say the subjects felt no illusion and there was no activity in the pre-motor cortex at all. And this is what tells us that the critical area for multi-sensory integration that is for the putting together of sensory information is in fact the pre-motor cortex. And we take it that the way in which you know that your arm belongs to you and not to somebody else is that you get both visual information about your arm and you get tactile or touch information about your arm and normally these are congruent. They tell you the same thing and they tell you that that’s your arm. But in this case where there’s a conflict then vision dominates.
Robyn Williams: OK, so bring in the people who’ve got this misfortune where they can’t actually recognise their limb how does your study affect understanding what’s going on with them?
Richard Passingham: Well the demonstration of people who think that their left arm belongs to somebody else has best been done by a method called the sodium amatol method. You inject sodium amatol into the right middle cerebral artery and this is done only in patients who are getting ready for surgery and it’s done not for experimental purposes but it’s done to tell you important things about where language is represented in these people’s brains. Now when you inject sodium amatol into the right hemisphere your left arm becomes paralysed and falls from a position as you are asked to hold it upright, it falls down onto the bed covers, you’re awake at the time. If you then ask the people if their arm is OK, they say yes, my arm’s fine. And then if you ask them whose arm is that many of them say it’s somebody else’s which is a quite remarkable finding.
Now in the sodium amatol case the amatol is injected into the blood supply and infuses through much of the right hemisphere of the brain. So that doesn’t tell you anything about the localisation of activity which is why you want to scan because if you scan, you can find out which are the critical areas for any particular phenomenon. Now in our experiments we found two areas in particular, the parietal cortex and the pre-motor cortex. The parietal cortex was more active both when the arm was pointing forwards and also when the brush strokes were synchronised. But the area that was most critical in the sense that it only showed up in the one condition in which you felt the illusion was as I say the pre-motor cortex. So what this adds is strong information about the location of areas, which are critical for the phenomena observed in the clinic.
Robyn Williams: Having found those locations can it enable you to help the patients so that they can find their limbs again?
Richard Passingham: We haven’t yet got anywhere on that. Now there are other examples where illusions have done that. The well-known neuroscientist Ramachandran has been interested in an allusion by which if your arm is cut off, let’s say from the elbow let’s say due to an accident you may go on feeling your forearm and you may think it’s there. And this is an illusion because the arm isn’t there and there’s been a lot of interest in why you feel this illusion. And he’s indeed scanned people using a method called magneto encephalography to see what’s happening in their brain under this illusion. But then being the ingenious man he is he’s gone on to think of ways in which he might treat people and he’s done this using mirrors.
Robyn Williams: And in those experiments Dick Passingham was just referring to Dr Ramachandran showed the patients themselves in a mirror and told them that their real arm, not the amputated arm, was the one that felt the pain and treated them normally and the pain went away. The brain in other words believed the mirror trick and you may have heard Rama as he’s know talking to Natasha Mitchell on All in the Mind on ABC Radio National a couple of weeks ago about this.
Well Professor Richard Passingham is using scanners to help solve another problem, that of intention. Imagine facing Bret Lee bowling super fast and how quickly you need to respond with a cricket bat. In fact it’s quicker than the brain seems to be able to handle yet it does so – how?
Richard Passingham: Well the interest of the difference between automatic actions and those that we think about is being central to our research. Philosophers have for a long time said that they think voluntary actions are preceded by an intention and the very well known psychologist and philosopher William James early in the century or at the end of the last century in his classic book talked about these as willed actions. The suggestion being that they are preceded by an act of will. Now it’s been very difficult to do research on that but in a classic experiment carried out in 1983 the neuroscientist Benjamin Libet thought of a way of actually timing when you feel the intention.
Now he did this using a clock face. So the person is sitting there and in front of them is a clock and a spot is going round the outside of the clock fairly quickly, rotating round. The person is then asked simply to move their forefinger whenever they want. They might do it after 15 seconds, or 9 seconds or 3 seconds it’s up to them; a typical voluntary action. What he then did was ask the people when they felt the intention to move they should remember where the spot was on the clock face and that tells you when they were first aware of their intention to move. Now his classic finding and the one that puzzled people was that you can record electrical activity from the brain from the scalp using either EEG or electro encephalograph about a second before a voluntary action – it can be more. But people normally report the intention to move about 200 milliseconds before they move. So the puzzle is that the brain seems to be getting ready to move really some time before we are aware that we are going to move and that we have the intention.
So that’s the phenomenon that we’ve made use of in an experiment working in Oxford. What we did was scan people and in our experiment on some trials they timed when they intended to move and on some trials they times when they actually made the movement. So now we can compare activity when the subject’s attention is directed to their intention with the activity when they are just attending to the movement itself. And what we found was that there was enhanced activity in an area called the pre-supplementary motor area which lies on the inner surface of the brain, increased activity there when you attended to your intention. Now the interesting thing is that it had been thought that the electrical activity that you can record using the EEG before movement has its origin in this area though that had never been proved. So what we’ve shown is that indeed your intention occurs in the same area in which the electrical activity occurs about a second before movement.
What it seems to show is this: Actually the origin of the movement is unconscious, you’re not aware of it, it’s occurring well before the time of which you’re aware. Now that you are aware about 200 milliseconds before movement appears to be because the activity is enhanced and there seems to be a rule that if we are to be aware of representations in the brain the activity needs to be enhanced. So it looks as if the original direction for the movement is unconsciously performed by the brain and then we become aware of it and that’s the time when we say we intend it. So you might then say well what’s the point of awareness? And it’s been suggested by many that the point might be that there’s still time to change the movement or indeed to veto it and that was proposed by Benjamin Libet.
But what really this is relevant for is the whole issue of how much of our mental activity we’re aware of? And if you consider for example sportsman, cricketers, a batsman reacting to a bowler or a tennis player reacting to a serve then actually it’s been shown that the activity that leads to them responding is activity of which they are not aware – they don’t know how they do it. And we now think that much of our mental activity occurs below the level of consciousness.
Robyn Williams: Now if you take Viv Richards who’s the quickest natural player I can think of to get to that point where your reaction is right, in other words it’s appropriate, long before you can know enough about where the bowler’s going to sling the ball, presumably you fine tune, you practice enables you to have an unconscious reflex if you like in advance so that you get it right more often than you get it wrong?
Richard Passingham: Well we’ve been interested in that and what we’ve done is take the case of piano playing. If you play the piano you’re aware that at first when you learn the piece you have to attend very hard and you’re aware of what you’re doing, you know which fingers you’re moving and you are sight reading and it takes a lot of your attention. But after practising for many, many hours you can now play the piece automatically and you can, in fact, play it while holding a conversation; you don’t have to attend to what your fingers are doing. So we’ve actually scanned people again using FMRI and we scanned people while they were learning a sequence of finger movements. And what we found was that at first the prefrontal cortex, which you could regard as the top of the hierarchy of information processing, the prefrontal cortex is very active indeed. But when the task has become automatic and the sequence is under your belt and you don’t have to think about it then there’s no longer activity in the prefrontal cortex. So that raises the question well what areas are active when the task has become automatic? And one of the areas that’s active, though not the only one, is the cerebellum which lies in the hind brain. Now the cerebellum is very enlarged in the human brain and is involved in the learning of skills and motor skills, there’s much evidence for that.
And what we found was that when the task had become very automatic there was activity in the cerebellum and the areas that are connected to it. So I assume that what Viv Richards has done over very, very many years is go from having activity in his prefrontal cortex as he thinks about what he’s doing until it becomes automatic and you no longer have to think about it and it’s then performed by other areas of the brain. And if you think Donald Bradman as I remember as a young man used to throw a cricket ball at a wire and this way by repeated practice he got to be able to throw without thinking and a cricketer can throw at the bails simply without thinking. And in the lab you can show that you’re not thinking by asking the person when they are carrying out the task to do another task at the same time. We’ve done that and when you learn the motor sequence you’re very disturbed in learning it if you have to carry out another task whereas when the task is automatic you can do something else at the same time without interference.
Robyn Williams: So that’s how we do it every day, almost without thinking. Aren’t we clever. Richard Passisngham is Professor of Cognitive Neuropsychology at Oxford.
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