Imagine your life was like one of those old-school kung fu movies where the sound and video are out of sync. A group of English researchers have recently come into contact with a man who experiences life in exactly this way.
The man, a retired pilot known as “PH”, experiences sound 200ms (1/5th of a second) before his other senses. He hears things slightly before he sees them, and even hears his own voice slightly before he feels himself speak! We might feel as if PH’s condition is very strange indeed, but hang on a minute, why is it that we experienced our senses in sync in the first place?
Clap your hands together. You seem to see, hear and feel this happen all in perfect synchronicity. But is that really natural? After all light travels faster than sound, and these various signals are processed at different rates in the brain- so why is it that we don’t see, hear and then feel our hands clap one after the other?
The leading theory has been that our brain uses some sort of syncing mechanism to help us understand the world. This seems like a pretty crucial part of how we interpret our experiences, as our brains are constantly cross-referencing our sensory information in an effort to paint a clearer picture. We know for example that we use visual cues of people’s mouth movements to help us interpret speech, as demonstrated by the McGurk effect:
BBC Horizon: Episode 4 – Is Seeing Believing? (2010)
Because PH hears before he sees, audio must be delayed to seem in sync with video. So when researchers tried the McGurk effect on PH they assumed they would have to delay the audio by 200ms in order for the effect to kick in. They were shocked to find that the opposite was true; they actually had to speed up the audio by 200ms to achieve the effect. So even though PH subjectively experiences sound first, his brain seems to be processing sight before sound. What’s more, when 37 normal subjects were tested they showed similar patterns, though not to an extent they’d notice in daily life. Yep, that’s right, you could be slightly out of sync right now and have no idea.
So what do we make of all this? The researchers believe that their work supports the idea that our brains do attempt to synchronize the experience of our sensory input. We seem to average out the timing of our various brain functions in order to unify our experiences; things don’t sync up perfectly, but most of us are unable to notice.
PH says that he has learned to live with his condition. “It’s not life-threatening,” he says. “You learn to live with these things as you get older. I don’t expect my body to work perfectly.”
All images produced by the author unless otherwise specified.
- Freeman, E. D., Ipser, A., Palmbaha, A., Paunoiu, D., Brown, P., Lambert, C., … Driver, J. (2013). Sight and sound out of synch: Fragmentation and renormalisation of audiovisual integration and subjective timing. Cortex; a Journal Devoted to the Study of the Nervous System and Behavior, 49(10), 2875–2887. http://doi.org/10.1016/j.cortex.2013.03.006