New York, April 16 (IANS): People who are heavy drinkers -- those that drink between 10 and 40 alcoholic drinks per week -- may perceive that they can handle the alcohol, as it leads people to judge that they are not impaired.

The findings showed that tolerance to alcohol of men who take more than five drinks at one time and women taking more than four drinks, is not protective against accidents or injuries.

While heavy drinkers showed less impairment than light drinkers on a rote fine motor test over time, they did not perform better on a test involving more short-term memory, motor speed, and more complex cognitive processing.

Thus making decisions to attempt more difficult tasks when drunk may be highly risky, because it is based on faulty information, the researchers said.

"Overall, there is a common belief among heavy drinkers that they can 'handle their alcohol' and that many common daily tasks may not be affected by their alcohol use," said Ty Brumback researcher at the Veterans Affairs San Diego Healthcare System in California, US.

Some heavy drinkers' extensive experience with alcohol may cause increased speed of metabolism, and lower self-perceived impairment.

This behavioural tolerance in heavier drinkers may be a result of cellular adaptation within the brain, changing the sensitivity to alcohol.

Contextual factors also play a part, as when people learn a task while drunk, they adapt to performing that task while under the influence, the researchers said.

"The results have implications for our understanding of alcohol-induced impairments across neurobehavioural processes in heavy drinkers and their ongoing risks for alcohol-related consequences over time," Brumback added.

For the study, published in the journal Psychopharmacolog, 155 young adult volunteers were tested on two cognitive and motor coordination tests at the beginning of the study and again five years later.