It’s coming from over there

I was walking up one of San Francisco’s many hills when I heard the shouting and laughing of children behind me.

Behind me? How did I know that?

Oh, right: I have two ears now.

I stopped and looked around. They sounded loud, and close. But I couldn’t see them.

Where were they?

I slowly pivoted in a circle to see what I heard in every direction. I had done this before with one ear, without success. Months ago, walking down Elizabeth Street , I had heard music on the air – perhaps a band practicing in a garage or backyard. It had sounded live, somehow. I’d stopped and looked around, trying to find it. But I couldn’t. The music was everywhere and nowhere at once. Placeless, undefined, omnipresent.

But now, today, the laughter and shouts sounded different at every point of the compass. I could feel it increasing in one ear at the same time that it diminished in the other ear. And there came a point, in one particular direction, that both ears came into synchrony. My body said: There. It’s there.

There are two different ways the brain uses to locate a sound. One is loudness difference, since one ear is further from the source than the other and “shadowed” by the head. The other is timing difference, since the sound arrives at the ears at different times. Was I hearing loudness difference, timing difference, or both?

An academic question, at the moment. I walked on, and five steps later, as I reached a crest, I saw them. Down the hill, two blocks away, the local schoolyard was full of children.

I was right.

Well, almost right: I’d been about ten degrees off.

I’m still working on balancing my ears. At the same spot on the volume wheel, they hear different loudnesses. So I was probably thrown off by that.

But just a bit. They were there, and I knew it.

(N.B. Check out this just-published study showing that people with one CI do much worse at localization than people with two CIs. Thanks to Ulf Nagel’s blog for pointing me to it.)