Some people can detect silent sounds through visual stimulation

Researchers at City University London have discovered that approximately 20 percent of people have the ability to hear sounds associated with silent light flashes and inaudible movements.

Synaesthesia is a mysterious condition in which sensations that are typically experienced separately occur at the same time. For example, the most common type of synaesthesia called vEAR causes people to hear sounds when they see motion or flashing lights.

“The survival of this association may explain links between sound and vision, such as why we like to listen to music synchronized with flashing lights or dance,” said the study authors.

“The effect also provides a good way to learn about what’s happening in the brain in people with synaesthesia, with vEAR’s high prevalence making it easier to investigate the mechanisms behind such cross-sensory perception.”

The research team conducted an online survey with over 4,000 participants. More than 20 percent of the individuals reported that they had experienced vEAR prior to the study.

The participants were instructed to watch video clips that featured people engaging in different types of movement, ranging from slow and smooth to fast and sudden.

The researchers found that meaningless visual stimuli often caused the subjects to hear sounds.

“It was seen that correspondents who had answered ‘yes’ to experiencing vEAR were specifically sensitive to the pure motion energy present in videos such as swirling or patterns that were not predictive of sounds.”

An association was also noted between vEAR and musical imagery, suggesting that the effect may be a natural physiological response that occurs when certain areas of the brain are stimulated.

“Some people hear what they see. Car indicator lights, flashing neon shop signs and people’s movements as they walk may all trigger an auditory sensation,” said study co-author Dr. Elliot Freeman.

“Ours is the first large-scale survey of this ability. We found that as many as 21 percent of people may experience forms of this phenomenon, which makes it considerably more prevalent than other synaesthesias.”

According to the researchers, the cross-sensory phenomena may also be caused by a “leakage” of information from visual regions of the brain into areas that regulate hearing.

The research is published in the journal Cortex.

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By Chrissy Sexton, Earth.com Staff Writer