Closing your eyes during a passionate kiss has long been revered as a symbol of true love, but now scientists have come up with a more clinical explanation for why people do it. The textbook answer – that it's hard to focus when close up to someone – is wrong.

Instead they found that the brain is unable to process visual data along with the sensations arriving from our lips and tongues.

Writing in the Journal of Experimental Psychology: Human Perception and Performance, Polly Dalton and Sandra Murphy, cognitive psychologists at Royal Holloway, University of London, said: "Tactile awareness depends on the level of perceptual load in a concurrent visual task."

Focusing strongly on a visual "will reduce our awareness of stimuli in other senses" Dalton said, adding that it was "important for designers to be aware of these effects, because auditory and tactile alerts are often used in situations of high visual demand, such as driving a car or flying an aircraft".

The pair's research however, did not involve the study of people kissing. Instead they got their subjects to carry out visual tasks while measuring whether they could detect something touching their hands at the same time.

The research showed that the ability to detect tactile sensations diminished as the visual task became more complex. Sometimes, however, people want to focus on the tactile sensations when dancing, kissing and making love, Dalton said.

She added: "These results could explain why we close our eyes when we want to focus attention on another sense," she added. "Shutting out the visual input leaves more mental resources to focus on other aspects of our experience."

Kissing – whether with eyes open or closed – is known to have health benefits for both men and women. It is known to release endorphins which increase happiness and adrenaline which can help to reduce pain.

Kissing also lowers cortisol levels which can help to release stress and although it is no substitute for exercise, it burns 2-3 calories per minute.