Inside Your Brain

Want to improve your hearing? Have someone tickle your toes, or lightly stroke the palm of your hand. Sounds crazy, but it works, and things get even weirder.

Every day, in everything we do, our body collects information from our five senses and combines it into a coherent picture that helps to guide our actions and, in evolutionary terms, helps to keep us alive. It's a well-known phenomenon, but it has long been believed that this process, which scientists call "sensory integration," occurs in the brain at relatively high cognitive levels, in an area known as the associative cortex. But research from the Max Planck Institute in Tübingen, Germany, published in the 20 October issue of the journal Neuron, shows that at least in the case of hearing and touch, sensory integration occurs much further upstream. Indeed, it occurs in the part of the brain where hearing actually occurs: the auditory cortex.

The Tübingen scientists were trying to find out where in the brain sensory integration occurs. Functional magnetic resonance imaging (fMRI) revealed increased activity in the secondary auditory cortex when the auditory stimulus was combined with tactile stimulus—when hearing was combined with touch.

So what's that got to do with hi-fi? For one thing, it gives you something fun to try. You can't do the fMRI bit, but otherwise this is an experiment you can do at home. Tonight while you're listening to music, try adding a little tactile stimulation. See if it makes the music sound better. Let us know how it goes.

And when you're done with the experiment (assuming you're still awake), consider the implications. Most of us were already aware that the senses influence each other; that's why ventriloquism works as well as it does: the eye fools the ear into thinking the sound is coming from the dummy's mouth. But the Tübingen scientists have shown that it isn't just a matter of influence; the experience of hearing is directly affected, at the very earliest and most primitive stages, by the other senses. It isn't just that we think we hear something different when someone is tickling our toes with a feather. It's that we do hear something different. Hearing itself is different.

In a sensory context, there is no such thing as objective observation. Our ears—together with the related neurological plumbing—are wonderful information-gatherers, but they make lousy scientific instruments. Their response is too complex. The experience of hearing is too rich.

Does it work the same way with the other senses? Is what we hear affected at the same deep level by, for example, what we see? The Tübingen work doesn't address that question, but I see no reason to think that things would be any different for the other senses.

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