Most people know that you cannot always rely on your senses. Optical illusions are well-known phenomena in which the illusion of spatiality or size relationships play a role. Beautiful representations like those by MC Escher are so popular that they are widely used as art postcards or calendars. What is less well known is that there are also auditory illusions. Our ears perceive the sounds of the environment, but these are sometimes interpreted differently than they really are. Here are some interesting examples.
- The obscuration of tones
- Shepard scale
- A mysterious melody
- Stereophony for a spatial effect
- McGurk effect
- Ringing in the ears - tinnitus
The obscuration of tones
If you hear two tones at the same time, which differ only slightly in their height, you only consciously perceive the louder stimulus. To do this, one of the tones must be significantly louder than the other. The ingenious inventors of the MP3 format took advantage of this auditory illusion. They discovered that you can simply leave out some of the tones when playing music, since humans hardly notice these tones anyway. This process plays a major role in digitization and data transfer – the smaller files can be saved with minimal space requirements and transferred faster on the Internet.
The Shepard scale describes an auditory phenomenon in which several different tones are played at the same time. By changing the volume at different times, the audience feels as if a musical scale is being played. You always hear the same tones, but everyone has a different volume. There are very nice sound samples for it and the effects have something futuristic about them. The Hungarian composer György Ligeti imitated this deception in one of his piano pieces. The floating sound experience can also occur with certain melodies from organ pipes.
A mysterious melody
The American music psychologist Diana Deutsch discovered during her research that it is usually not possible to recognize arbitrarily selected fragments of a melody without a suitable context. However, if the entire piece of music has been played once, the entire melody can be put together from the fragments at once. Our brain completes the missing passages so that you can hear the whole song in your head, although only individual tones are perceptible.
Stereophony for a spatial effect
With stereophony it is possible to create a spatial sound effect. Although you may only have two loudspeaker systems from which the sounds are reproduced. With clever control it is possible to create the illusion that the sound source is in a different place in the room than the loudspeakers. This effect is used at concerts or in the cinema. It becomes particularly interesting with 3D animations, which add the optical illusion of a spatial image to the spatial sound experience. The fact that the noises are placed in the right places makes the whole thing even more realistic, so that sometimes you hardly want to distinguish between the film and the real environment.
Are you always sure that you can hear exactly what someone is talking about? Then try out the McGurk effect. With this auditory illusion, optical perceptions are superimposed on the listening experience. Depending on the movements the person speaking makes with their mouth, it is believed that they are hearing different words. The stored sound sequence is always the same. You find that you can read lips unconsciously with it, even if it certainly still takes a lot of practice to accurately recognize the words without sound.
Ringing in the ear - tinnitus
Tinnitus is a very unpleasant auditory
illusion. This effect describes phantom noises, which can be heard by someone who is suffering from it, but these noises in reality do not exist in the environment. Tinnitus can be perceived as very annoying if it has become permanently lodged. Stress, hearing trauma due to short or long-term overload or accidents are seen as triggers. Tinnitus can be treated with psychological, physiological and drug therapies. Hearing aids also help treat tinnitus.