Do you hear what I hear?: A still from the moving dots movie that the researchers used to discover synaesthetes. Watch the video via the link at the end of the story and see if you hear anything unusual.
Credit: Caltech
Only in their minds
However, when asked, all of the synaesthetes could name examples of daily visual events that caused sounds that they logically knew to be only in their minds, such as seeing a fluttering butterfly or watching television with the sound turned off.
Saenz and Koch now suspect that as much as one per cent of the population may experience auditory synaesthesia.
In fact, they believe that the brain may normally transfer visual sensory information over to the auditory cortex, to help predict the associated sound. And it could be this process that results in actual perception of sounds in synaesthetes, perhaps due to stronger than normal connections, says Saenz.
"We might find that motion processing centres of the visual cortex are more interconnected with auditory brain regions than previously thought, even in the 'normal' brain," she adds.
"At this point, very little is known about how the auditory and visual processing systems of the brain work together. Understanding this interaction is important because in normal experience, our senses work together all the time."
With the California Institute of Technology.
