The Visual Cortex Also Processes Sound

New research has revealed that the portion of the human brain that is responsible for processing information from the eyes also helps process sound information to create visual imagery.

A study published in the journal Current Biology details how researchers determined that the visual cortex of the brain also sees extensive activity associated with sounds.

Lead researcher Lars Muckli, of the Institute of Neuroscience and Psychology at the University of Glasgow, explained that scientists have long assumed that hearing and images are associated with one another because it is very clear that sounds can lead to visual imagery.

"if you are in a street and you hear the sound of an approaching motorbike, you expect to see a motorbike coming around the corner," Muckli said in a statement. "If it turned out to be a horse, you'd be very surprised"

That surprise comes from the fact that we would visualize a bike even before seeing it. It can be quite a shock for a practiced mind when a visualized image and an actual image don't match up.

However, according to Muckli, very little research has looked into precisely where sound-born images are created in the brain and how they link up with what is actually seen.

In order to find out, Muckli and his colleagues used function magnetic resonance imaging to observe visual cortex activity in 10 volunteers as they completed five different activities.

In one experiment, the volunteers were blind-folded so there was no retinal information to be interpreted by the visual cortex. They were then asked to listen to natural sounds such as birdsong, or people talking. They found that the early-visual cortex showed similar activity as it would if it were interpreting information from the eyes.

Interestingly, even when sound and visual information was cut off, the visual cortex still showed signs of early processing based off imagined images alone.

"In [the] future we will test how this auditory information supports visual processing, but the assumption is it provides predictions to help the visual system to focus on surprising events which would confer a survival advantage," Muckli said.

The study was published in Current Biology on May 22.