SCIENCE / Shots faster than the speed of thought: A player returning a fast serve can only really know about it after the event. John McCrone looks at evidence that the conscious mind is rarely on the ball

BIFF, BANG, wallop. That sums up a lot of the rallies at Wimbledon this year. Yet with serves from the likes of Boris Becker regularly reaching speeds of 125mph, it is a wonder that the players even manage to make a return - let alone get a semblance of a rally going.

What makes a lengthy rally at Wimbledon seem all the more remarkable is recent brain research which shows that players are actually swinging at balls before they can have conscious knowledge of them. Experiments by a University of California physiologist, Ben Libet, suggest it takes up to half a second for our conscious impressions of the world to 'form'. This means that the impression we have of living in the present is just a clever illusion and a player returning a fast serve can only really know about it after it has already happened.

It seems tennis players - or competitors in any other fast reaction sport - rely on subconscious motor routines when they make their shots. Rather than waiting the half-second it takes for events to reach consciousness, the decision where and how to hit the ball is made by a set of well-drilled, preconscious processes.

Yet even here, in the zone of subconscious reactions, there is still a lag between the brain and reality. It takes at least a tenth of a second (100 milliseconds) for nerve impulses to travel from the eye to the brain and another tenth of a second for correcting messages to fan back out to the muscles. This creates an unbridgeable fifth of a second lag for players. (So much for the old coaching adage of keeping your eye on the ball).

The research into such neural time-lags is proving hugely controversial among those who study human consciousness. Some psychologists, such as Anthony Marcel of the Medical Research Council at Cambridge, flatly refuse to believe that awareness is forever following half a second behind events. 'The implication of this is that you could never co-ordinate with the world. You would always be unconscious of the last half-second. So I just can't accept Libet's interpretation of his results,' Dr Marcel says.

But Professor Libet stands firm, saying that while the idea seems paradoxical, it does square with some of the intuitive beliefs that sports people have about what it takes to play sports well. He has been working on the timing of mental events for well over a decade, and one of his most clear-cut experiments was published last year.

In this test, a light touch on the hand of a subject was followed by a second stimulus, an electrical pulse, direct to the part of the brain that maps sensations for touch. Libet found that if the direct pulse followed 400 milliseconds after the touch, the two stimuli merged and were experienced as a single exaggerated response. Crucially, not only was the lapse in time between the two events not noticed, but the combined event felt as if it had happened half a second earlier. Subjectively, the experience was timed to the moment the hand was first touched rather than to when the brain was directly stimulated.

Libet says: 'The brain seems to be able to compensate for the lag in its processing. It can refer everything that happens backwards in time to the moment it first arrived at the brain so that, subjectively, it feels as if we are living in the immediate present. Of course, this can lead to some pretty strange situations. A sprinter will tell you that he waited until he heard the starter's gun before he took off. But the truth seems to be that proper consciousness of what happened could not have occurred until after he had got at least a few yards down the track. His initial reaction must have been unconscious.'

In another experiment, Libet found that our minds seem to need time even to become aware of their own internally generated impulses. He wired up a group of subjects to a brain-wave monitor and asked them spontaneously to flex their wrists at any moment they got the urge to during an experimental trial.

What Libet discovered was that the subjects showed a readiness potential - a sharp drop in electrical activity that acts to clear the decks for a neural event - a full half-second before any wrist flexions occurred. Even more surprisingly, this readiness potential appeared a good 300 milliseconds before subjects reported conscious experience of any impulse to make a move. Again, it seems to take time for brain events to brew up and form a settled conscious picture.

There is considerable confusion among scientists and philosophers about how to interpret Libet's findings. Many of those with a philosophical background, such as a Tufts University professor, Daniel Dennett, and Anthony Marcel of the MRC, believe he must be wrong in thinking that consciousness suddenly switches on after half a second of neural activity: 'Seeing consciousness as a punctate event in the brain, with a particular time and position, just can't be the right approach,' Dr Marcel says.

But neurologists find it easier to stomach the bizarre implications of Libet's results. They point out that even if we became conscious of events the instant they reached the brain, we would still lag 100 milliseconds behind reality, because of the time it takes for nerve traffic to arrive from the senses. To then organise this information - putting it through the dozens of filtering processes involved in perception and making the connections with memory that allow sensations to be understood - must take a bit of extra time. In this light, a half-second lag seems quite reasonable. All the brain needs is a clever compensating mechanism - a way of papering over the time gap - so that the illusion of instantaneous consciousness is preserved.

If Libet is correct, it seems that the mistake philosophers are making is to assume that it is consciousness that does all the work in our mental lives. Instead, his work implies, much of our thinking and reacting takes place at a subconscious level. Consciousness only feels as if it happened to be there at the time.

Libet believes this view fits neatly with what is known about sports performance. There has been much research into how athletes react to fast-moving events. In Britain, most of this has been done with cricketers. Peter McLeod of Oxford University's department of experimental psychology has tested the reactions of several top-class batsmen - including Allan Lamb and Wayne Larkin - to see how they could cope with medium-fast balls from a bowling machine. The balls were pitched at a mat with wooden rods hidden under it, a set-up designed to simulate the unpredictable bounce of a good seam bowler's delivery.

Dr McLeod says people assume that elite athletes can do what they do because they have a quicker eye or superior reaction times to the rest of us. But he found none of the batsmen could react to a sharp deviation in flight in less than 200 milliseconds. If the ball turned off the wicket this quickly, they were beaten every time. McLeod says it seems that the raw reaction times of the best athletes are much the same as those of ordinary people. What makes the difference with an athlete is the quality of the subconscious decision-making processes which follow once information reaches the brain.

McLeod says part of the skill lies in anticipating where a ball will end up. From long experience, a top-class batsman will develop a feel for exactly where a ball will be during the final 200 milliseconds when he is blind to its path. He will then be able to deliver a smoother swing to connect with the ball, having better fine muscle control than the average person. Finally, a batsman at this level will have learnt a larger repertoire of motor routines - different kinds of shot, such as the hook or the late cut - to cope with different situations. A Gower or a Gooch sees the ball no more quickly than a weekend knockabout player, but is simply better equipped to deal with what he (subconsciously) sees.

Philosophers of the mind find it a dilemma that the brain should seem capable of so much intelligent action prior to the emergence of full conscious awareness. Yet just the same principle of subconscious skill seems to apply to such an everyday action as driving a car. Many people have had the experience of coming to with a start, having driven several miles through busy traffic on automatic pilot. Any well-practised skill comes to be performed subconsciously, conscious attention being saved for when something unexpected or surprising happens.

Indeed, when it comes to skilful action, ponderous conscious thinking often seems more of a hindrance. Tennis players frequently talk of being 'in the zone' or 'pumped', where their minds achieve a Zen-like wordlessness and their shots flow with a fluid grace. What they appear to be doing in this state is blocking the distracting chatter of conscious thought, relegating consciousness to the back seat and allowing their brains to be given over fully to subconscious processing.

There is support for this idea from an experiment by a University of California psychologist, Arthur Jensen. He asked a group of subjects to deliberately delay their responses in a reaction-time test by as short an interval as possible. Their reaction times were found to increase not by a small fraction, but by a giant leap - from 250 milliseconds to 600 or 700 milliseconds. Libet says it now seems obvious that the need to wait on a lagging consciousness for a decision is what causes this disjointed delay - a result which suggests that allowing consciousness to control a skilled action like a tennis return will lead to a clumsy, jerky response.

At last it seems that science has an explanation to another of those great mysteries of tennis - why people so often swat a tempting sitter wildly out of court or into the bottom of the net. With the ball left hanging in the air, consciousness has time to catch up with events and then, like a wildly enthusiastic amateur, crashes in and makes a complete hash of what otherwise would have been the simplest of triumphant shots. -

(Photograph omitted)