New research finds that the visual cortex – a part of the brain that receives and processes information from the eyes – also processes sound information, which can create visual imagery.

Led by Lars Muckli, a professor in the Institute of Neuroscience and Psychology at the University of Glasgow in the UK, the team reports its findings in the journal Current Biology.

The authors suggest processing auditory information enables the human visual system to predict incoming information, thus giving us a survival advantage, as Prof. Muckli explains:

“Sounds create visual imagery, mental images, and automatic projections. So, for example, 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. If it turned out to be a horse, you’d be very surprised.”

In their study report the team explains that the early visual cortex in humans was traditionally thought to process simple visual information such as orientation, contrast, and spatial frequency – relayed from the retina. It then feeds this information forward to processes further along the visual system.

However, the idea that the early visual cortex also receives “non-retinal” information has not been sufficiently investigated, say the authors, despite the fact that feedback connections from other parts of the brain “greatly outnumber feedforward connections.”

For their study, they carried out five experiments using functional magnetic resonance imaging to observe early visual cortex activity in 10 volunteers.

In one experiment, they observed what happened as blindfolded volunteers listened to three natural sounds: birdsong, traffic noise and a crowd of people talking.

They used a special algorithm that interprets different patterns of brain activity to show that different categories of sound were being processed in the early visual cortex, in a similar way to categories of imagery.