Recently, University of Glasgow psychologist and researcher Lisa DeBruine created a mini-sensation on social media when she tweeted a playful animated GIF in which an electrical transmission tower appears to be jumping rope and asked, "Does anyone in visual perception know why you can hear this gif?" In a subsequent nonscientific poll of more than 315,000 Twitter users, 67 percent said they heard "a thudding sound" when they watched the animation, and another 3 percent said they heard "something else." Only 20 percent said they heard nothing at all.
That's seven out of 10 people who think they heard a sound accompanying a silent image. So what's up with that?
The explanation, according to research, is that while we think of sound as being generated by the world around us, the experience of hearing sounds actually happens in the auditory cortex, which is located in the temporal lobe of the brain. When something actually occurs — for example, the honk of an automobile horn — that creates sound waves in the air, it causes our eardrums to vibrate, which transfers the information through a complex anatomical path. That eventually generates an electrical signal, which the auditory nerve carries to the auditory cortex, which processes the information and tells us that we're hearing a loud noise.
Interestingly, though, in the absence of sound waves in the air, your brain will try to fill in the silence. In this study published in the Aug. 4, 2011 online edition of Nature Scientific Reports, researchers showed subjects hundreds of different still images, such as a man playing a saxophone or using a power saw, and also images that suggested silence, such as a woman sitting on a sofa reading a book. When the scientists measured the electrical activity in the subjects' brains, they found that the brain's auditory cortex was stimulated by pictures associated with sounds, in less than 200 milliseconds. Back in 2008, Radiolab's Jad Abumrad spent time in an aneochoic chamber, a space designed to be super-quiet. He discovered that in the absence of actual sound, his brain soon began imagining sounds, ranging from the buzz of a swarm of bees to the vocals from a Fleetwood Mac song.
In a study published in the March 2017 issue of Consciousness and Cognition, University College London researchers found that 21 percent of subjects reported being able to hear faint sounds when viewing flashes of light, a phenomenon known as visually-evoked auditory response.
Chris Fassnidge, the lead author of that study, joined in the Twitter fun by posting this animated GIF of Bamm Bamm from "The Flintstones" and asking, "Who hears this one?"