Monday, 25 February 2013

Can I have a reaction?

After broadcasting some terrible news the TV presenter in the studio would turn to me and say: Can I have a reaction? What sort of reaction? Should I burst into tears, faint, or perhaps punch him on the nose for juxtaposing a human tragedy with a banal question? The interviewer, of course, wants a thought, a comment, or an observation:  instant words of wisdom cast in the form of a spontaneous reply. They want something more than a mere reaction, at the speed of a reflex.

Perhaps, without intending it, they are making a fundamental point. The essence of a living organism is its ability to react to its environment. We test the injured and unconscious for their reactions. The extremely useful Glasgow Coma Scale (Teasdale and Jennet 1974) was created to measure the level of consciousness after head injury, and is now widely used in emergency medicine and intensive care. When I was doing my thesis on brain damaged children in the late sixties we simply recorded the period of unconsciousness, without specifying how that was established. The scale is very simple, and is based on motor reactions (“from makes no movements” to “responds to commands”) verbal production (“makes no sounds” to “converses normally”) and those windows into the soul, the eyes (“does not open eyes” to “opens eyes spontaneously”).

So, if we have the misfortune to be severely injured, the decision to switch off the machine keeping us “alive” will be based on our reactions, though nowadays that includes the reactions that can be determined by brain scans alone.  I think, therefore I am.

However, in ordinary healthy life we can do more than just react. We can react fast. Survival depends upon it. Had I the power, dear reader, to make the chair you are sitting in drop instantly by a mere one inch, you would show an almost instant startle response. In about a quarter of a second you would find that the message from your bottom (no chair present) was much more interesting than even my riveting comments. Your eyes would have widened in surprise, your arms extended and you would be ready for action, so ready that you would probably have stopped all the non-essential bodily systems, and have prepared yourself for extreme action. Useful things, rapid reactions.

How fast can we react? There are many ways to measure one’s reactions.  The BBC has a reaction time test amusingly based on firing tranquilizer darts into sheep:
but there are many others, and this one is based on a traffic light, which has more face validity:  
This morning my reactions (on the sheep test) have taken an average of 0.29 seconds, and the best I have achieved in the last two weeks is 0.2128

Before going further with the decimal points, I should warn you that my results were less good when using the standard laptop keyboard (perhaps the keys are getting worn out through over-use) and much quicker with a new wireless mouse, which is probably far more sensitive. So, be aware of measurement errors, and find the most sensitive system you can.

However, I can take only partial comfort from my reaction times, because my main interest is determining how quickly I can react as a driver. These computer game test results have to be corrected because of a historical decision taken at the beginning of the motor car age. Early horse drawn coaches had hand operated brakes, though they were hardly immediate. The operator had to wind a handle which applied the brake to the wheel. Apart from handle, the main “brake” was also hand operated, in the sense of the alarmed coachman pulling back on the horse’s reins. Much quicker, but not particularly effective if the coach was racing downhill.

When designers of horseless carriages tried to decide where to put all the controls on the new-fangled motor car, they found that drivers had their hands full with the steering wheel and the gears. Also, to get the braking effect it was far better for the driver to step with full force on the mechanical pedal.  Hence the brake pedal was put on the floor, where it has remained.

With the rise of servo-assisted systems that placement was almost irrelevant by the eighties, but cultural habits tend to persist.  Most studies of driver’s reaction times show that foot/pedal reaction times at about 0.4 or 0.5 are twice as long as hand/button reaction times.  To make things worse, even those times are achieved only when drivers know that their reactions are about to be measured. Real life emergencies come without warning. Under the more realistic conditions of sustained driving, it takes about 1.2 seconds for drivers to move their foot from accelerator to brake pedal.

It is time to provide a brake function on the steering wheel. The most ecologically valid system would probably be to measure the force with which drivers push down on the steering wheel when trying to stop, which is part of the startle response and the wish to push back from the approaching hazard.  It would be necessary to avoid false activations of the brake system, but that can be worked on by adjusting the sensitivity of the system. In brief, the emergency stop function must come back to the hand, where reactions are faster.

Away from the peculiarities of the motor car, what can be made of simple reaction times?  A great deal, seems to be the answer. It some ways it is one of the world’s simplest IQ tests. See a target: respond. Not too intellectually challenging. The task is easy to teach to just about any conscious person, without any fancy instructions. It is easy to administer rewards, encouraging even those with learning difficulties to participate. It is a real scale with a real zero, and every microsecond counts as much as any other microsecond, which in S.S.Steven’s (1946)  theory of scale types is a ratio scale, the most quantitative of quantitative scales.

So, how well does reaction time predict intelligence? Correlations of about 0.3 are found for simple reaction time, and a larger 0.49 for more complex choice reaction tasks. Why should the faster reactors be brighter, and the brighter participants faster? One simple unifying theme is that if you have a faster central processor you can solve simple problems (reaction time tasks) faster, and solve complex problems to a higher standard because you have more mental time to work through the solutions.

Faster reactors also live longer. It may be that they have solved the problem of living: don’t smoke, don’t overeat, don’t drink too much, and don’t take stupid risks. Perhaps so. Yet the most recent research suggests that, helpful as intelligence may be in life, it is not directly responsible for extending lifespans. Much of the intriguing correlation between intelligence and lifespan can be explained by simple reaction times.   It seems that if you have fast reactions you probably have a good nervous system, which means you probably have other bodily systems which are good as well. You have System Integrity. You are like a car which was made on a good day: all systems are present and correct, because all the operators were paying attention to their assembly tasks.

So, armed with my reaction times, I will now try to calculate my remaining lifespan. This may take some time, because searching the relevant literature for the predictive equations takes longer than shooting a dart at a BBC sheep.


  1. and the best I have achieved in the last two weeks is 0.2128

    Interesting. my reaction time is a pathetic 0.33 ms. I hope Woodley is wrong that reaction time correlates to g at -.6!

    1. Practice, practice! First thing to note is that you may be getting an artefactual delay due to the mouse clicker, etc. The other thing is that there is a practice effect to a minor degree (Woodley covers this) in that all proper testing allows the subject several trials so that they can get used to the equipment.

    2. Doubtful - when I took an IAT (I have a 'strong implicit bias' btw) I was tripping over the keyboard, and that's a pretty good CRT.