What influence our ear shape has on hearing?

The brain recognizes the shape of the ears through sound reflections

It is not difficult for people with intact hearing to locate sounds, to differentiate between speakers and to hide certain sounds or to focus attention on them. This is made possible in particular by the shape of the ears. The ear shape reflects the sound into the inner ear in a very special way that allows the brain to draw the appropriate conclusions and to calculate the position of the sound in the room.

How exactly this process runs was previously considered unclear. Now neuroscientists from the University of Leipzig and the University of Montreal have deciphered which processes take place in the brain. These findings could be used to develop better hearing aids, as the researchers announce in a press release from the University of Leipzig.

A Leipzig research team examined the processes in the brain, which occur during the hearing and found out that the shape of the ears is instrumental in the process. (Image: Brian Jackson / fotolia.com)

Big or small - the shape of the ear is crucial

The Leipzig research team found in his study to what extent the shape of the ears and their bulges influences how sound waves are transmitted to the inner ear. These reflection patterns are analyzed by the brain, which can be used to detect, for example, whether a sound is coming from above, below, left or right.

Sounds from above and below are harder to locate

In particular, how the sounds that come from above or below, are located by the brain was so far unclear. "Sounds from different directions affect the outer regions of our ears differently," explains Marc Schönwiesner, professor at the Institute of Biology at the University of Leipzig. The auricle reflects the sound in the auditory canal through its irregular shape. This creates a short echo that changes the timbre.

The brain learns from small differences

"Our brain can learn these small differences and associate them with different directions," says Schönwiesner. The tone is the property of a sound, which is determined by the volume of the individual frequencies contained in the sound. It is the reason why one and the same note, such as a high C, sounds different from a violin than from a recorder.

Course of the study

In the study, the ear shape was changed in 15 subjects with silicone inserts. These should then locate sounds in a sonic laboratory, both with and without silicone in the pinna. Although the tones always remained the same, there were clear differences in the tests. With the respective natural ear shape, the tones could be located quite precisely, whereas the subjects barely succeeded in using the silicone pieces.

Without the natural ear shape no sound location could take place

"When we played a note above their heads, they suddenly thought that it came from below," reports Schönwiesner. In subsequent tests without the Silkoneinsatz, the subjects were able to build on their previous listening services.

In further series of tests, the subjects were played sounds while they were in magnetic resonance imaging (MRI). Thus, the scientists were able to observe the processes in the brain while the sound is being processed. Neuroscientists focused on activities in the auditory cortex, the area of ​​the cerebral cortex that is responsible for hearing.

The higher the source of the sound, the worse the location

The scientists found that the lower the head of a sound, the less active the neurons are. The researchers were even able to read the source of the sound from the evaluation of the brain waves. MRI also showed that changes in the ear shape led to a significantly more disorganized behavior of the neurons.

The subjects got used to the new ear

After the participants of the study carried the silicone inserts for a longer period of time and thus moved through everyday life, the brain activities had returned to normal and reacted to the new ear shape as if it were their own. "We can hear with our own individually designed ears, because our brains know their form," summarizes Schönwiesner. If this changes, it will take some time to adapt. This is also the case, for example, when we grow.

A new generation of hearing aids?

"In Germany, about 17 percent of the population is currently affected by hearing deficits," said Schönwiesner. With increasing tendency, because our environment is getting louder and at the same time people are getting older. According to estimates by hearing aid manufacturers and doctors, up to 25 percent of hearing aids are currently not in use because patients often underestimate that the brain needs time to get used to it. Instead, many hearing impaired people expect immediate improvement. "If we understand the habituation process better, we may be able to speed it up, so that patients could be advised in a targeted manner," concludes Schönwiesner. (Vb)