We all know how our eyes can easily be deceived, as there are a lot of visual illusions that trick our eyes. But, it turns out our ears can be deceived too. We can easily be fooled into hearing something that actually isn’t there. ASAPScience published an amazing video about audio illusions.
Should you believe your ears and the things they hear?
Here is another video, published by ASAPScience again. The “speaking piano” audio illusion is amazing!
What are audio illusions?
Audio illusions or Auditory illusions are false perceptions of a real sound or outside stimulus. These false perceptions are the equivalent of an optical illusion: the listener hears either sounds that are not present in the stimulus or sounds that should not be possible given the circumstances of how they were created.
Auditory illusions highlight areas where the human ear and brain, as organic survival tools, differentiate from perfect audio receptors; this shows that it is possible for a human being to hear something that is not there and be able to react to the sound they supposedly heard.
Audio illusions examples
McGurk Effect
The first audio illusion example in the video called McGurk effect is a perceptual phenomenon that demonstrates an interaction between hearing and vision in speech perception. The visual information a person gets from seeing a person speak changes the way they hear the sound. Like hearing “bar” or “far”, despite the audio isn’t changing.
The effect was first described in 1976 in a paper by the British cognitive psychologist Harry McGurk (23 February 1936 – 17 April 1998) and his colleague John MacDonald, titled “Hearing Lips and Seeing Voices” in Nature (23 Dec 1976). It discovered by accident when McGurk and his research assistant, MacDonald, asked a technician to dub a video with a different phoneme from the one spoken while conducting a study on how infants perceive language at different developmental stages. When the video was played back, both researchers heard a third phoneme rather than the one spoken or mouthed in the video.
Tritone paradox
The tritone paradox is an auditory illusion in which a sequentially played pair of Shepard tones (see notes 1) separated by an interval of a tritone, or half an octave, is heard as ascending by some people and as descending by others.
Different populations tend to favor one of a limited set of different spots around the chromatic circle as central to the set of “higher” tones. Roger Shepard in 1963 had argued that such tone pairs would be heard ambiguously as either ascending or descending. However, the British-American psychologist and psychology of music researcher Diana Deutsch (b. 1938) in 1986 discovered that when the judgments of individual listeners were considered separately, their judgments depended on the positions of the tones along the chromatic circle.
For example, one listener would hear the tone pair C-F♯ as ascending and the tone pair G-C♯ as descending. Yet another listener would hear the tone pair C-F♯ as descending and the tone pair G-C♯ as ascending. Furthermore, the way these tone pairs were perceived varied depending on the listener’s language or the dialect.
Shepard Tone illusion
A variant of the previous audio illusion, the tritone paradox, the Shepard Tone illusion also has many variations. In it, multiple sine waves are played on top of one another rising in pitch, while one quickly drops down an octave as the others continue rising. But, our brain doesn’t notice this drop, and so the clips sound like they are rising… forever!
Risset rhythm illusion
Jean-Claude Risset (13 March 1938 – 21 November 2016) was a French composer, best known for his pioneering contributions to computer music.
After the discrete Shepard scale, Risset created a version of the scale where the steps between each tone are continuous, and it is appropriately called the continuous Risset scale or Shepard-Risset glissando.
Risset has also created a similar effect with a rhythm in which the tempo seems to increase or decrease endlessly.
Like the Shepard Tone illusion, a beat starts relatively slow and starts to speed up. As it gets faster, another beat (beat 2) starts at exactly half the speed and both of them increase in speed together. Eventually, the faster one fades out as the slower one fades in, and the loop continues. Our brain can’t pick up this and as a result, it sounds like it’s speeding up forever.
Shepard tone illusion + Risset rhythm illusion combined
Here is a video of Shepard tone illusion + Risset rhythm illusion combined.
1) The “Shepard tone”, an auditory illusion in which a tone seems to rise (or lower) in pitch forever, without becoming inaudible.
2) The “Risset rhythm”, in which the beat’s tempo seems to speed up (or slow down) forever.
3) The “Mandelbrot set” fractal, a visual representation of a simple mathematical formula that produces a seemingly infinite variety of complex shapes and patterns, many of which are reminiscent of those found in Nature.
Notes
- A Shepard tone, named after the American cognitive scientist Roger Shepard (b. 1929), is a sound consisting of a superposition of sine waves separated by octaves. When played with the bass pitch of the tone moving upward or downward, it is referred to as the Shepard scale. This creates the auditory illusion of a tone that continually ascends or descends in pitch, yet ultimately seems to get no higher or lower.
Sources
- McGurk effect on Wikipedia
- Tritone paradox on Wikipedia
- Shepard tone on Wikipedia
- Auditory illusion on Wikipedia
- Jean-Claude Risset on Wikipedia
