Most of us are familiar with optical illusions. They make our eyes and brain wonder if they are seeing things as they really are or if they are creating our own version of what we see.
Similarly, an auditory illusion can trick your brain and ears into believing that they are hearing certain things. They are false perceptions of real sounds generated by external stimuli.
One of these audible illusions is called the Shephard tone, a sound named after cognitive scientist Roger Shepard, who created it in addition to an optical illusion called the Shepard table.
What is a Shepard tone?
The Shepard tone, also known as the Shepard scale, is a sound design or set of sine waves that creates the illusion of a consistent, endless tone that will rise or fall.
It is obtained by superimposing notes which go up or down an octave but whose volume varies. As each ladder fades, the beginning and end of each become indistinguishable and seemingly begin to rise or fall continuously.
The Shephard tone creates a way to create conflict or increase tension. In movies, it is meant to convey a sense of discomfort or to indicate that trouble is brewing.
This is one of the sound effects that creates an eerie feeling that turns into a haunting effect, creating anticipation and anxiety.
A good example can be found in the 1996 “Super Mario 64” video game.
Visually creating a Shepard ladder would produce an image that looks like a staircase that goes on forever. It is also called “Musical Barber Pole” or “The Sonic Barber Pole” due to comparisons with the infinite diagonal lines.
Like a barber pole, the scales have the illusion of continuously moving up or down, but in reality they are simply spinning in a loop.
French composer Jean-Claude Risset created an alternative form, which he coined as the Shepard-Risset glissando. In his version, the sounds transition smoothly from one to the other to create a more haunting version.
How does the Shepard tone work?
The Shepard tone is one of the most popular audio illusions known.
The series of notes spaced an octave apart and the variations in volume give the listener the impression that it is an endless sound when played on a loop.
Its tones encourage our brain to make errors of perception. Although it is simply a series of short, repeated patterns, we hear it as a single, continuous pattern that constantly changes in pitch.
Why does a Shepard tone cause anxiety and panic?
The effects of music on human emotions are still being studied, but life experiences tell us that it has a profound impact.
What has been proven is that music increases blood flow to areas of the brain that house our emotions. Our limbic systems are very sensitive to music. Music also gives listeners a dopamine boost.
Music is used to help regulate moods, so it stands to reason that the Shepard tone, which is supposed to make listeners feel anxious or panicked, does exactly what it was meant to do.
Some TikTokers have subjected themselves to what they consider “audio torture”, playing the Shepard tone on repeat for hours on end.
TikToker Sean Andrew documented his experience of listening to audio for 10 hours.
Andrew reported that he experienced chest pressure, anxiety, racing thoughts, elevated heart rate and ringing in his ears after playing the sound for 5 hours.
The Shepard tone in music and movies
Christopher Nolan used the Shepard tone in his 2008 film, “The Dark Knight.” The sound of Batman’s motorcycle, the Batpod, has sound effects that demonstrate the constant rise and fall of a single note.
In Hans Zimmer’s 2017 film “Dunkirk”, the Shephard tone was used to create the rising and falling sound of an orchestra to create drama and heighten tension.
The Shephard tone is used a lot in music, especially by pop groups like Pink Floyd and The Police. Typically it is used to increase tension just before a kick.
NyRee Ausler is a writer from Seattle, Washington, and author of seven books. It covers lifestyle, entertainment and news, as well as workplace navigation and social issues.