They are big, small, pointed, long. But all human ears have one characteristic in common – they have a rather bulky structure. The cartilaginous auricle is not smooth, but has striking ribs, depressions and thickened areas. What is this shape all about? Markus B. made us aware of this question – thank you for that.
The shape of the ears is important for our ability to locate a sound source in the room. The beaded structures determine how the sound is reflected in our inner ear. This creates acoustic effects through which our brain can calculate where a sound comes from in the room. A German-Canadian team of scientists has impressively illustrated this system through experiments: Accordingly, the brain “knows” the individual shape of each person’s ears: if you artificially change them, our thinking organ can no longer correctly locate sound sources.
As the researchers explain, the shape of the ear is particularly important when assigning sound that comes from close range and from above or below. On the other hand, whether a tone sounds on the right or left has to do with the distance between our two ears: If a telephone rings to the right of us, the sound waves first reach the right ear, then with a delay the left. This delay enables our brain to understand where a sound is coming from.
The irregular shape is used for vertical sound localization
In the case of vertical locations, however, the beaded structures then come into play, the scientists explain: “Tones from above or below strike the outer areas of our hearing organs in slightly different ways. The irregular shape of the ear cup reflects the sound in the ear canal. This creates a short echo that changes the timbre, ”says Marc Schönwiesner from the University of Leipzig. The timbre is the property of a tone, which is determined by the volume of the individual frequencies contained in the tone. “Our brain can learn these small differences and associate them with different directions,” says the scientist.
He and his colleagues examined this system by slightly changing the outer ear shape of 15 volunteers. The participants were given a small piece of silicone that was not visible from the outside. Before and afterwards, the scientists played sounds to the participants in a sound laboratory, from which they should assign whether they came from above or below.
The brain knows its ears
It turned out that before changing their ear shape, the test subjects were able to locate the tones quite precisely – but they could hardly do that with the silicone pieces used. “When we played a note above their heads, they suddenly believed that it came from below,” says Schönwiesner.
That changed, however, after the test subjects had moved through everyday life with their new ears for some time. After a few days, they were able to continue their original listening successes with repeated hearing tests. The brain had accordingly adjusted to the new acoustic characteristics. That means: “We can hear with our own individually designed ears because our brains know their shape,” summarizes Schönwiesner.