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A PHYSICIST WRITES . . .
(May 2011)
I have pointed out several times in these columns that much of what your eyes detect is ignored by the brain — and that much of what you think you see is invented by it! Concentrate (when you’re driving) too hard on the car in front, and you will overlook things happening at a different distance, or in a different direction. Fail to go for regular eye-tests, in middle age at least, and you could discover (possibly too late to hang on to your driving licence) that an insidious disease such as glaucoma has been nibbling away at the peripheral field of view, while your brain was working hard to disguise the effects by ‘filling in’ for the blank areas of retina.
But it’s not just your awareness of the here and now that you can’t trust: a programme on Radio 4 last month (Mind Changers: click here to listen to it) said much the same about memories of past events — both recent and distant ones. You may think you have a clear recollection or picture of something that happened to you, or in front of you, but all sorts of influences can modify it.
In the programme an experiment was described in which people were shown a film of a road accident. Some were then asked: “How fast were the cars going when they hit each other?” Others were asked the same question but with the word “hit” replaced by “smashed into”. The second group were found to produce significantly higher estimates of speed!
As if this wasn’t enough evidence of memory being controlled by simple words, a week later all the subjects were contacted again and asked: “Did you see any broken glass?” In reality there was none shown in the film — but the second group proved more likely to say yes, being still under the influence of the “smashed into” phrase.
Later research established that witnesses in court are at risk of having their memories corrupted not only by the way questions are put, but also by any ‘new’ information they may have heard (eg, from other people or from the media). The problem is that nothing’s more convincing to a jury than someone in the box who says categorically: “I was there, and I saw what happened.” So psychologists, we were told, have been testifying to the unreliability of such evidence, in countless trials in the US (which is where the research was done).
Over here too, it’s becoming recognized by the police that when there are several witnesses to an incident, they all need to be questioned early (and in an unbiased way) before their memories have had a chance to be modified. And such changes can happen without any outside influence: even the simple act of telling friends about something you saw can alter your ‘genuine’ recollection of it!
In short, memories of past events are far from being the fixed ‘video-recordings’ in the mind that they might seem to be. We’ve all had the experience of finding out that we were in error about something we thought we remembered clearly, but the message of the Mind Changers programme was that this is the rule rather than the exception. Which rather casts doubt on some of the content of my previous columns...
Let’s continue with this one, even so. Just occasionally on the road I meet low-slung tricycles on which the rider is lying almost flat (with feet forwards). Could any method of travel be less safe, you think. And what is their attraction? Well, after some investigation I can answer the second question. Apart from the obvious advantage over a bicycle — stability — a recumbent tricycle with its long seat is much more comfortable to be on, it can corner more quickly (if you remember to lean in), it has better aerodynamics and so it’s at least as fast as a bike on the level, and it allows you to take in the view all around without neck-strain.
Recumbent trikes are also attractive to those with a disability (such as a bad back) that would keep them off a bicycle. Although the machines are slow going uphill, with a sufficiently low gear engaged they can cope with a gradient that would bring a two-wheeled rider to an ungainly halt. And if you do want to stop for a rest half-way up, a hill-restart is no problem at all! The bad news is that being low-production items, recumbents are expensive to buy.
They and their riders still look horribly vulnerable to me. But this turns out to be one of their safety features: drivers give them a wide berth. Overall they are said to be markedly safer than bicycles — lower centre of gravity, little risk of being sent flying if a tyre loses its grip, not far to fall if you do come off, and in the event of a frontal collision your feet take the impact rather than your head.
Going back to my second sentence at the beginning, however, I would say there’s a significant risk that a driver concentrating on something else on the road may not recognize a recumbent tricycle for what it is (even with the little flag they sometimes carry), simply because they are so rarely seen. By which I mean that his or her brain might fail to make the essential leap from detecting the outline of the machine in the distance, to Think Trike!
A question, to end with. The driving regulations say, in effect, that at traffic lights an amber means red if you can stop safely behind the line, or green if you can’t. (Why doesn’t the Highway Code print this same clear message, instead of the rather different instructions in Rule 175? But that isn’t my question.) In a similar vein, the first rule of advanced driving is to ensure you can brake to a halt safely in the distance you can see to be clear. But both these precepts imply that you need to have a proper feel for your own minimum stopping distance at different speeds.
What I would like to know is: how can you acquire this feel — even just in the dry and on the flat, let alone in other conditions — except by carrying out a considerable amount of emergency-stop testing yourself? Please don’t say: study the stopping-distance table in the Highway Code! It hasn’t been revised in 65 years. Its numerical distances are not easy to apply to your view along the road, especially at different speeds. And anyway the thinking-distance components are too short (in my view), hence the overall figures are surely too optimistic. So forget about practising on a skid-pan: what we need is access to a whole layout of road surfaces and gradients, where we can brake non-stop.
Peter Soul
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