Some people see colour when listening to music
US scientists have discovered people who can "hear" what they see.
The rare form of synaesthesia - a condition where senses intermingle - came to light after a student reported "hearing sounds" from a screensaver.
Researchers at the California Institute of Technology then found three more people with the same condition, New Scientist magazine reported.
Those affected performed better in tests of recognising visual patterns than those without the condition.
A more common form of the condition is being able to perceive numbers or letters as colours.
Several artists have been linked with the condition, including David Hockney who is able to see colour when listening to music.
Dr Melissa Saenz discovered the phenomenon when a group of students were being shown around her lab and one asked if anyone else could hear a pattern of moving dots on a computer screen.
When she questioned him further she realised he matched the criteria for synaesthesia - he had experienced it all his life and it happened with lots of different moving images.
By sending the moving dots image to hundreds of other volunteers, she found three others who could also hear sounds, such as tapping, whirring or whooshing, when watching it.
To double check they did have synaesthesia she tested their ability to recognise a series of visual patterns.
They either heard a pair of series of beeps or watched a pair of a series of flashes and had to say whether they matched.
Both groups were accurate 85% of the time when they heard the pattern, the results published in Current Biology show.
Can you hear these dots?
But when watching it, the individuals with synaesthesia remained 85% accurate while the others dropped to only 55% accuracy.
Dr Saenz said: "I was surprised to realise this particular form had not been reported before and I wanted to see how common it was.
"The goal of the study was to objectively determine if the sound perception was real."
Dr Julia Simner, who researches synaesthesia at the University of Edinburgh said some forms of the condition were more common than others.
"It's common to find people who have it the other way round - so they see colour when they hear music.
"The very nice thing about this paper is they have been able to document a kind which we knew was out there but for which we only had hazy knowledge."