Prick up YOUR EARS

We know many animals can hear sounds we can’t, but can we train ourselves to tune into their private world? Peter Wohlleben – bestselling author of The Hidden Life of Trees – investigates

Let’s face facts: many animals would trump us in a routine hearing test. People can hear sound waves with a frequency of 20-20,000 vibrations per second (20,000 Hz), whereas dogs hear from 15-50,000 vibrations per second (50,000 Hz). Our hearing is not that much worse; it’s just that we can’t hear anything above 20,000 Hz, a threshold above which the world is still filled with noise for dogs.

If we’re going to make a comparison, however, volume would be a more meaningful measure than pitch. Dogs pick up on quieter sounds than we do simply because they have larger ear muscles and can point their ears towards the source. It’s easy to see how this works. Just cup your hands and place them behind your ears pointing forward. We often do this as a purely visual indication that we need someone to repeat themselves, but you’ll find it also makes a big difference to what you hear. Try it while walking in the woods and, even from far away, you’ll hear the quieter birds or a deer slipping through the undergrowth.

HEARING WITH YOUR EYES

Unlike dogs, only an estimated ten to 20 per cent of people can move their ears. The people who can can’t do much more than wiggle them – and certainly can’t point them forwards. Recent research, however, shows that we have been too focused on external features. In fact, you and

I can change the direction of our ears, but we make the adjustment internally. And to do this, we need our eyes.

Kurtis Gruters, a graduate student in the department of neuroscience at Duke University in North Carolina, set out to prove this with 16 subjects sitting in a completely darkened room. The darkness allowed them to concentrate on coloured LED lights that they were asked to track visually. However, the first thing that moved was not the subjects’ eyes but their eardrums, which oriented towards the points of light. It took just ten milliseconds for the subjects’ eyes to follow. You could say that the eyes and the ears were directed to an object at about the same time.

What’s important here is not the time lag but the fact that we line up our auditory apparatus at all, an alignment that had never been noticed before. Even more surprising is that the subjects’ ears were oriented not to a sound but to an object they wanted to observe with their eyes. Gruters’ studies show that we still have a thing or two to learn when it comes to our physical capabilities, and that