For dangerous roads, keep a sweet bouquet handy

Smell can have a marked effect on the ability to carry out tasks, recall memories and concentrate, writes G. Neil Martin

If you had to relinquish one of your senses, which would it be? Vision? Probably not. Hearing? Unlikely. Taste? Possibly. Smell? Almost certainly.

Yet, about 80 per cent of food flavour is down to smell. Supermarkets cash in on this by pumping the odour of bread through their stores. Other businesses use smell to enhance mood - most notably to relieve the stress of travel. The arrivals lounge at Heathrow airport carries the scent of freshly mown grass, and platforms on the London Underground have been scented with perfume.

Middlesex is one of the few universities with a psychology department researching odour's effects on mood, cognition and physiology. In 1998, we reported the world's first systematic study of the effects of food odour on electrical activity in the human brain. We found that the smell of chocolate reduced attention-related brain activity more than odours such as coffee, lemon, rotting meat and garlic, and that the brain responded to types of odour rather than specific smells.

Other research shows that odours can affect behaviour. Earlier this year, we found that exposure to the odour of the bergamot pear reduced people's ability to stay vigilant. In experiments, participants performed vigilance exercises similar to those undertaken by air traffic controllers. Bergamot made people significantly less attentive than peppermint (or no odour). The message seemed to be that exposure to a pleasant, relaxing scent is not always good for you; its positive effect on mood may be outweighed by its negative effect on other mental processes.

Exposure to an unpleasant smell might also aid some types of thinking. In an experiment where participants completed easy and difficult versions of the same verbal and non-verbal tasks amid a pleasant scent (air-freshener), a bad smell (sour milk) or a control (no odour), those exposed to air freshener did better at the difficult tasks while those exposed to sour milk did better at the easier tasks.

A study of men's and women's driving ability, using a PlayStation game, showed how gender and smell interact to affect some behaviours. Women's ability to do easy tasks improved with exposure to a pleasant smell, while men exposed to it did significantly better at intermediate and difficult tasks.

Studies of odour, which encompass psychology, neuroscience, neurology and business studies, are becoming increasingly common. Research at Liverpool University, for example, has found that smells evoke more memories from childhood than words. There is evidence that odour can generate more emotional memories than words or pictures, although this evidence is not conclusive.

There may also be implications for some forms of learning: research at Cardiff University has found that people are more likely to recall accurate memories of an exhibition when in the presence of an odour that formed part of the exhibition.

Exposure to pleasant smells seems also to encourage some kinds of social behaviour, such as helping (we are more likely to lend someone small change in the presence of nice smells). And there is evidence that smell may have an effect on female sexual arousal.

Ever more fascinating discoveries are promised as we begin to expand our knowledge of what has been dubbed the Cinderella of the senses.

G. Neil Martin is principal lecturer in psychology at Middlesex University and associate editor of The Psychologist .