Do You Hear This Silent GIF?

The silent GIF generated by @IamHappyToast depicts a scene of electrical pylons playing skip-rope. As the playing pylon jumps over the swinging cables and lands, people are reporting hearing a thudding sound, despite the GIF being silent.

Twitter user @Lisa DeBruine, a researcher at Glasgow University's Institute of Neuroscience & Psychology polled followers of the thread to ask if other people also experienced the auditory hallucination. The poll is ongoing, but 68% of people that have responded to the poll so far are reporting hearing a thudding sound.

Why do we hear a sound that isn't there? 
Speaking to the BBC, Dr De Bruine was unable to answer this question: "I thought some of the vision scientists I follow would be able to explain it right away, but it seems like there are several plausible explanations and no clear consensus."

Also speaking to the BBC was Chris Fassnidge, a doctoral student in psychology at London's City University, who works in this area of neuroscience. He offered this insight: "I suspect the noisy gif phenomenon is closely related to what we call the Visually-Evoked Auditory Response, or vEAR for short,"

Adding: "This is the ability of some people to hear moving objects even though they don't make a sound, which may be a subtle form of synaesthesia - the triggering of one sense by another.

Chris explained this is like hearing someone across the street's foot-steps on the sidewalk, even though the likelihood of being able to perceive these sounds in a busy street, or from behind a shop window, is unlikely.

Virtual reality goggles fully immerse the wearer in a computed reality.

It is well known that the brain will make something seem real because it needs to make sense of its environment. If you have ever experienced virtual reality, you will have already experienced this phenomenon. Eyeglasses, headphones and some clever computing are all that is needed whisk you off for an immersive experience. Researchers and psychiatrists are now using these techniques to aid research and treatment of psychiatric conditions, like post-traumatic stress disorder or phobias. 

The neuroscience behind these hallucinations and the reasons why our brains make these scenarios - such as the jumping pylon - feel real is best described by Prof. Anil Seth in the following TED talk:

Credit: TED, YouTube.

Neuroscientists are still trying to understand the brain circuitry involved in forming our perception of the world. The brain continues to astound and astonish, and understanding and exploiting the mechanisms by which our brains compute and 'hallucinate' to interpret the world around us could enable better treatment and rehabilitation for a host of conditions ranging from debilitating phobias to depression.