Hearing the sound of silence. In 2008 at Caltech, we discovered that about 1 in 100 people hear sounds when they see images flash or move, even when no physical sound is present. The sound is all their heads, but it’s not imagination. This experience is due to a cross-activation of sensory centers in the brain – a benign neurological trait called synaesthesia. People with “hearing-motion” synesthesia describe their sound perceptions with words like whirring, buzzing, wobbling, tapping, or beeping. It happens automatically, doesn’t require effort or attention, and is typically experienced since childhood – as far back as can be remembered. Someone with hearing-motion synesthesia may not even realize that he or she hears sounds that other people do not. Test yourself for hearing-motion synesthesia by viewing the video on the right.

Our study of hearing-motion synesthesia began when a student visiting the lab noticed a silent movie on a computer screen and asked, “Does anybody else hear that?”. Surprisingly, it wasn’t difficult to find other people who “heard motion” once we started to ask! People with hearing-motion synesthesia have an enhanced soundtrack in life hearing sounds associated with all types of seen movement. In the video above, the student describes the sounds of birds hopping in the distance.

How can we verify this? Published experiments from our lab provide objective evidence for hearing-motion synesthesia. We devised a task in which people with hearing-motion synesthesia would performed better than others if their sound perceptions were real. Normally, people find it easier to judge rhythmic temporal patterns like Morse code with sound (beeps) compared to vision (flashes). So, we asked subjects to judge whether pairs of Morse-like patterns of visual flashes were identical or not (in actuality 50% were identical, and 50% subtly different). For subjects without synesthesia this task was very hard, but people with synesthesia found it much easier. They reported that they heard a sound each time they saw a flash – transforming the difficult visual task into an easier auditory task. This synesthetic translation of vision to sound kept up with a rapid pace of visual flashes that were spaced as little as 150 ms apart.

Commentary in Current Biology by Ed Hubbard

Media coverage: Nature News, New Scientist, BBC News, Scientific American Mind, Caltech Press Release, ABC News, MSNBC, MSN Health, YouTube, BoingBoing Video News coverage at ScienCentral.

Hearing-motion synesthesia is not known to be associated with any other behavioral traits or conditions and is best thought of as a neurological “idiosyncrasy”. Some people who hear-motion are surprised or relieved to know that this phenomenon has been scientifically documented.

Testimonial from a reader:
“I have this and it is a huge pain in the ass, LOL! Most of the time I don’t notice it, but when I do it really drives me nuts. The sound is in my head too, not something I physically hear with my ears. I hear my eyelids when I blink. I hear a woosh sound when I pass my hand in front of my face. If I twirl my finger I hear a sound like “woo woo woo woo”. It doesn’t matter what the movement is, If I catch it in my vision, I hear it move. Anyway, I just wanted to say thanks for proving i’m not crazy!!! :)”