Samena Chaudhry Birmingham

Counting sheep is a useless way of dropping off to sleep, scientists have found. Instead, you should have been dreaming up a mental image of somewhere relaxing, such as a waterfall or a holiday.

Sleep researchers at Oxford University found that among a group of 50 people with insomnia those who were told to think of relaxing images fell asleep more than 20 minutes before they normally did. Those who tried "distraction" techniques, such as counting sheep, fell asleep even later than normal.

Allison Harvey from the department of experimental psychology at Oxford University suggested that relaxing images push away the worries that keep people awake, "Picturing an engaging scene takes up more brain space than the same dirty old sheep," she told New Scientist magazine (2002;173:17). "Plus it's easier to stay with it because it's interesting," she added.

One in ten people has chronic insomnia, which is thought to cost billions of pounds every year in sick days and accidents caused by tiredness.

Dr Harvey also found that people have been advised for many years to try to put their worries out of their heads to relax and get to sleep . Those who tried to suppress their worries take longer to fall asleep than those who let them run their course.

She said that this mirrors the classic psychological study called the "polar bear test" or "elephant test." This involves telling someone not to think about polar bears or elephants. It has the opposite effect. The forbidden image immediately pops into the head. So the suppression technique is guaranteed to fail.