The best case scenario is no more than a massive surge of adrenaline for both parties, a shouted “What’s the matter with you? Are you blind?”
Followed by some late-night soul-searching as we struggle to understand how and why we hadn’t seen them.
And while we’re all capable of momentary lapses in concentration and judgement, the reality is that you might not have seen them. You might well have been blind.
The first problem is something called saccadic masking or chronostasis, which is a fancy way of saying that your brain sometimes makes stuff up. No, seriously, it does and it does it all the time.
Because, while we like to think of our eyes as a video camera, the truth is much more complex; when we move our eyes from side to side, shifting our point of focus from one area to another, there is a risk that our brain would be overloaded by information – and the way we deal with this is to shut down our vision for the duration of the time we’re moving our eyes. We then fill in the blank period with the thing we’re actually seeing at that moment. In other words, we make stuff up. This is saccadic masking.
You can easily test this for yourself: simply look in a mirror and shift your focus from one eye to the other; you won’t be able to see your eyes moving from left to right, no matter how much you concentrate. Your brain is filling in the gap with what it thinks is there, rather than what actually is.
This can be hugely dangerous. Imagine reaching a junction in your car. You move your head from left to right to see what’s coming and think you can see everything that’s there but, because you are only getting a series of snapshots of the scene, not what’s actually there, you may well be missing some important stuff.
If, for example, a cyclist is in the space that is concealed by the saccadic masking, you simply won’t see them - and, the faster you move your head, the larger the resulting blind spots.
Scary, isn’t it? And it gets worse…
John Sullivan, an RAF pilot with 4,000 flight hours and a keen cyclist, has written a wonderfully eloquent explanation of these issues - and one of the most serious is the difficulty our peripheral vision has in detecting some approaching objects.
If two objects are on a collision course, but are travelling at roughly the same speed, the brain won’t be able to detect any relative movement. This is probably an evolutionary hang-up from a time when it was more important to have our attention drawn to fast-moving objects that were coming towards us than slow-moving objects that weren’t.
This arises because only the centre of our eye generates high resolution images, to prevent the brain being overloaded with data – the rest is just low resolution peripheral vision that is very good at noticing movement but less good at seeing anything else. In fact, your peripheral vision is so bad that just 20-degrees from the centre your visual acuity is one tenth of what it is in the middle, where you enjoy the benefits of foveal vision.
This wasn’t a problem when we were evolving millions of years ago because a flicker of motion in our peripheral vision – caused by something like a fast-moving predator running towards us – would have been enough to make us turn our heads towards it, and so bring our full range of visual acuity into play.
However, this causes problems now that we’re moving much, much faster than we’ve evolved to cope with. A common scenario might be the approach to a crossroads or a T-junction; if both vehicles are travelling at the same speed there is no speed differential, so the brain doesn’t notice it very well and won’t prompt you to turn your head to focus on the approaching vehicle. You may well simply not see the bike, car, or even lorry and pull out straight into its path.
10 tips for eye health
We have a fairly large blind spot in our vision because of the way our optic nerve is attached to the back of the eye. This junction effectively masks about 6-degrees of our vision, so if something is in this blind spot, we literally can’t see it.
You can see this effect for yourself by undertaking a Scotoma Test.
The problems don’t end there. Because your brain knows that you can’t see through solid objects, it frequently over-compensates and creates a further blind spot around stuff it knows it can’t see through. This is a real problem in cars because your brain will often ignore an area around the vertical metal A-pillars that sit either side of your car’s windscreen.
Tips for driving at night
Working around these problems
The good news is that none of these problems are insurmountable.
The first stage is to slow down as you approach a junction or a roundabout. Travelling more slowly will have the effect of creating a differential speed between you anything that is approaching, which will help your peripheral vision notice it – and when it does you’ll move your head automatically to bring your full foveal vision into effect.
The next thing is to look left and right more deliberately. John Sullivan suggests focussing on three points on each side, in the far distance, middle distance and near distance, pausing for a fraction of a second at each point – and to do the whole thing at least twice in each direction. Pilots call this the ‘lookout scan’ and it will more than double your chances of seeing an approaching vehicle when combined with point one (above).
The third solution is to move your head when you’re scanning for traffic, to overcome the problem of that blind spot around your car’s A-pillars and the one in your eye. Simply moving your head towards the windscreen increases the area you can see by a good amount. RAF pilots have a saying: ‘Move your head or you’re dead’, which might be a bit melodramatic in your local Tesco car park but is good advice, nonetheless.
Finally, when you’re changing lanes on a dual-carriageway or motorway, check – and double-check – your mirrors but take a final look at the space you would like to move into to make sure that you haven’t overlooked anything because of saccadic masking or the inadequacies of your peripheral vision.
It all sounds pretty complicated, doesn’t it? The reality is that it isn’t and it will soon be second nature if you practise it regularly.
You could also take an IAM RoadSmart assessment and test. If you fancy improving your driving – and you should, if only because it’s huge fun and will transform the way you approach driving and the risks that come with it – it’s offering free taster sessions at the moment.