Heather Murphy in the NYTimes:
This week, in an improbable turn of events, the sound of silence went viral.An animated GIF showing an electrical tower jumping rope over delightfully bendy power lines began to spread. The frenzy started when Lisa Debruine, a researcher at the Institute of Neuroscience and Psychology at the University of Glasgow, posed this question:
Does anyone in visual perception know why you can hear this gif? pic.twitter.com/mcT22Lzfkp— 𝙻𝚒𝚜𝚊 𝙳𝚎𝙱𝚛𝚞𝚒𝚗𝚎 🏳️🌈 (@lisadebruine) December 2, 2017
When she asked Twitter users in an unscientific survey whether they could hear the image — which actually lacks sound, like most animated GIFs — nearly 70 percent who responded said they could.Once you “heard” it, it was hard not to start noticing that other GIFs also seemed to be making noise — as if the bouncing pylon had somehow jacked up the volume on a cacophonous orchestra few had noticed before.
It turns out that this phenomenon has ha name, visual-evoked auditory response or visual EAR, and has been under investigation:
The ability to “vEAR” is not limited to scenes where one would expect to hear a noise, they say. One lab study found that more than 20 percent of people could hear flashing lights in silent videos. A range of motions, abstract patterns and even colors evoke sound for some.The act of hearing a visual highlights the trippy fact that our senses do not operate the way we often assume, with crisp boundaries between them. Smelling, hearing and tasting all “speak to each other and influence each other, so little things like the color of the plate you’re eating on can influence how food tastes,” said Mr. Fassnidge.
We know, in general, that our senses are constantly involved in predicting or "guestimating" what's next. In the case of vEARing the guestimation crosses sensory borders so that we hear where there is, in fact, no sound, but there should/could be.
Using electrical brain stimulation, we have also found tentative signs that visual and auditory brain areas cooperate more in people with vEAR, while they tend to compete with each other, in non-vEAR people,” Dr. Freeman said in an email. “So people who claim to hear visual motion have brains that seem to work slightly differently.”
Individuals with frequent or advanced vEARing may have a form of “synesthesia,” a neurological phenomenon in which one sense feeds into another, he said. In other types of synesthesia, sounds might be linked to colors or words with tastes.