Dr. Jennifer Groh

So if you know how far apart your ears are and you know what the speed of sound is, then you can figure out what's the delay for the sound to get to reach this ear after this ear.

I often take off my glasses to measure the distance between my two ears that way.

And it's something like about a half a millisecond is the largest delay you can experience.

Half a millisecond.

So this is tiny, and that is for the difference between a sound here versus a sound here.

Exactly.

We can obviously detect much smaller sound separations than just totally left versus totally right.

So there's, you know, it's an incredible feat.

of computational power by the brain, I think maybe we should tell the audience why your brow is furrowed and I'm excited about this because half a millisecond is less than the duration of a single action potential.

It's the fundamental medium of communication in the nervous system, as you say.

So it would seem totally weird for us to be able to process sensory information that is faster than the duration of that minimum increment of firing.

You know, there's some research about how exactly this can be done, and it involves things like lots of neurons firing together and really precise synapses that cause minimal delay and very high temporal precision as the signals are going from one neuron to the next.

Absolutely.

So if you have hearing loss in one ear and one ear only, then it's very difficult to localize sound.

It's not completely impossible.

You would imagine that it would be completely impossible if the hearing loss was complete and if this timing difference and level difference were the only cues that we use.

But actually, the ear has these little folds in them, and the folds filter the sound as it comes in.

And in particular, it alters the frequency content of the sound.

They're useful and your ears are different than my ears.

And so you are going to be expecting a slightly different kind of fingerprint of what the sound sounds like as a function of location than I would be.