Like dogs and cats: Humans also point their ears

The slightest rustle or crackle is enough — in a flash, the ears of dogs or cats point in the direction of the noise. Some species of monkeys can also direct their ears in a targeted manner.

Until now, science assumed that humans have never possessed this ability or lost it completely in the course of evolution. But researchers at the University of Saarland have now presented a study showing that humans do indeed unconsciously point their ears in the direction from which an interesting sound is coming. However, the ear movements are only minimal and practically undetectable.

Pricking up their ears

The muscles around the ear become active as soon as "novel, striking or task-relevant stimuli are perceived," say researchers from the "Systems Neuroscience & Neurotechnology Unit" (SNNU) headed by Prof. Daniel Strauss.

Strauss, a neuroscientist and computer scientist, explains that "the electrical activity of the ear muscles reflects the direction in which a person aims their attention when listening."

To detect the minimal movements, the researchers used sensors around the ear to record the electrical activity in the muscles that change the shape of the shell of the ear — the auricle — or move it, according to their report in the journal eLife. In addition, the test subjects were observed on special, high-resolution video recordings.

25 million-year-old 'neural fossil'

According to Strauss, humans have probably retained an orientation system that attempts to control the movement of their auricles.  He believes that the newly discovered ability is a kind of "neural fossil" that has persisted in the human brain for about 25 million years.

It remains unclear, however, why this alignment of the ears in the primate chain has been largely lost, said Strauss.

Two types of attention

While the test persons were reading a monotonous text, they were surprised by unfamiliar noises from various lateral positions. In this way, the researchers were able to test the "reflexive attention" that automatically occurs when unexpected noises occur.

In addition, the test subjects had to listen to a short story read aloud to them from one side while at the same time ignoring a "competing" story from the opposite side. This allowed the testing of "goal-oriented attention," as it occurs, for example, during active listening.

Both test setups showed that the movements of the vestigial muscles in the human ear indicate the direction of the sounds the test subjects are paying attention to.

Depending on the type of stimulus, the researchers recorded minimal, varying, upward movements of the ear or backward movements of the lateral edge of the auricle at varying degrees of intensity.

Basis for more targeted hearing aids?

The findings made by the Saarland research team are interesting not only with regard to the history of evolution or for basic research. They could possibly also be used to develop better hearing aids.

"These could amplify the sounds that the wearer tries to hear while suppressing the sounds that he or she tries to ignore. In this way, the function of the devices would virtually follow the hearing intention of the user," says Prof. Strauss.

A new type of hearing aid could detect the electrical activity of the ear muscles in milliseconds and thus determine the direction in which the ears are trying to align themselves. A built-in computer could then amplify the directional microphones in a targeted manner and suppress disturbing background noise.