It used to be thought that people closed their eyes while sharing a kiss because their vision could not focus on something as close as the other person's face.
But according to a study published in the Journal of Experimental Psychology: Human Perception and Performance on vision and tactile sensory experience by cognitive psychologists Polly Dalton and Sandra Murphy at Royal Holloway, University of London, the brain finds it difficult to process other senses if it's concentrating on visual stimuli. So, by closing our eyes when we kiss, we can more easily focus on other sensations, like touch.
The study, which did not involve people kissing, suggests that, to focus on a tactile sensation, people might instinctively close their eyes.
However, these conclusions, published in the Journal of Experimental Psychology: Human Perception and Performance, were reached without studying couples kissing.
Study participants were instead assigned visual tasks to complete while their tactile sense was measured. To measure visual sense, participants completed letter-searching tasks of varying difficulty. The tactile response was measured by responding to a small vibration applied to one of their hands.
It is 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.