Dyslexia can impair a driver鈥檚 reactions as much as a moderate drinking session. That is the conclusion of a small study which compared how quickly dyslexic and non-dyslexic drivers react to traffic signs.
Those with dyslexia, which is characterised by difficulties with reading and writing, took on average 30% longer to react. The controversial finding will raise questions about whether people with dyslexia should have extra tests before being allowed behind the wheel. Drivers just over the UK鈥檚 alcohol limit, which can be exceeded by drinking two pints of beer, are typically 10% slower than normal to react.
In the study, Hermundur Sigmundsson at the Norwegian University of Science and Technology in Trondheim gave 17 volunteers, six of whom were dyslexic, two different tests. The first involved a 4-minute drive along a simulated country road at 50 to 80 kilometres per hour. In the second task, the volunteers drove through a city at lower speeds for 10 minutes.
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The simulator flashed up traffic signs in the drivers鈥� field of view and measured how quickly they responded by pushing a button or saying 鈥渘ow鈥�. In the rural drive, the signs appeared directly ahead, while in the city they appeared in a variety of places.
Slow in the city
The six dyslexic drivers took on average 0.13 seconds longer to react during the rural drive than the non-dyslexic controls and were 0.19 seconds slower in the city, where the simulated environment was more complex. In both tests the controls took around 0.6 seconds to respond, so the dyslexic drivers were experiencing a delay of 20 to 30%.
The results fit with other studies which suggest that dyslexia may affect the way the brain processes sensory information. For example, people with the condition were often clumsy as children, and passed childhood milestones such as crawling, walking and riding a bicycle later than other children.
Some activities that slow drivers鈥� reactions have been outlawed. Drink-driving is illegal and so, in the UK, is talking on hand-held cellphones, which was found in past studies to slow reactions by 45%. Such drastic action is not being suggested for dyslexic drivers. 鈥淩ather than banning them, it would be better to warn them,鈥� says Oliver Carsten, an expert on driving impairment at the University of Leeds in the UK. Sigmundsson says his results need to be confirmed by larger studies before any action is taken.
Having quick reactions does not automatically lead to good driving. 鈥淩eaction time is only one of the cognitive functions needed for driving, and it has not been consistently shown to be a good predictor of driving performance,鈥� a spokeswoman at the UK鈥檚 Department for Transport told 麻豆传媒. 鈥淵oung drivers have shorter reaction times but they have more accidents because they are overconfident,鈥� Carsten says.
And drivers who are drunk are impaired in other ways, too. They are typically more likely to miss objects in their peripheral vision, for example, and may drive more aggressively, Carsten says.
Journal reference: Brain and Cognition (DOI: 10.1016/j.bandc.2004.11.007)
