Most of us are familiar with optical illusions. They make our eyes and brain question whether they are seeing things as they really are or creating our own version of what we see.
Likewise, an auditory illusion can trick your brain and ears into believing they are hearing certain things. They are false perceptions of real sounds generated by an external stimulus.
One such auditory illusion is called Shepard’s tone, a sound named after cognitive scientist Roger Shepard, who created it in addition to an optical illusion called Shepard’s Table.
What is Shepard’s Tone?
A Shepard tone, also known as a Shepard scale, is a sound design or set of sine waves that create the illusion of a constant and infinite tone that will rise or fall.
It is achieved by overlapping notes that rise or fall only one octave but vary in volume. As each cliff fades and diminishes, the beginning and end of each become indiscernible and seem to begin to continuously ascend or descend.
Shepard’s tone creates a way to build conflict or heighten tension. In the film, it is meant to create a sense of discomfort or show that trouble is brewing.
This is one of the sound effects that creates foreboding that turns into a haunting effect, building anticipation and anxiety.
A great example can be found in the 1996 video game Super Mario 64.
Shepard’s visual creation of scale would create an image that looks like a staircase that goes on forever. It is also called the “Musical Barber’s Pole” or “Sound Barber’s Pole” due to comparisons with the endless diagonal lines.
Like a barber’s pole, the scales give the illusion that they are constantly moving up or down, but in reality they just go around and around.
The French composer Jean-Claude Risset created an alternative form, which he coined the Shepherd-Risset glissando. In his version, the sounds smoothly transition from one to the next to create a more haunting version.
How does Shepard’s tone work?
The Shepherd’s Tone is one of the most popular audio illusions known.
The series of notes spaced an octave apart and the differences in volume give the listener the impression that it is an endless sound when played in a loop.
Its tones entice our brains to make perceptual errors. Although it’s just a series of short, repeating patterns, we hear it as a continuous single pattern that keeps changing pitch.
Why does Shepherd’s tone cause anxiety and panic?
The effects of music on human emotions are still being studied, but life experience tells us that it has a profound impact.
Music has been shown to increase blood flow to the areas of the brain where our emotions reside. Our limbic systems are very responsive to music. Music also gives listeners dopamine.
Music is used to help regulate moods, so it stands to reason that Shepherd’s tone, which is intended to make listeners anxious or panicky, does exactly what it’s intended to do.
Some TikTokers have subjected themselves to what they consider “audio torture” by playing Shepherd’s tone for hours.
TikToker Sean Andrew documented his experience listening to the audio for 10 hours.
Andrew reported experiencing chest tightness, anxiety, racing thoughts, increased heart rate and ringing in the ears after playing the sound for 5 hours.
Shepard’s tone in music and movies
Christopher Nolan used Shepard’s 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, Shepherd’s 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, namely by pop groups like Pink Floyd and The Police. It is usually used to increase the tension just before a kick.
Nairi Ausler is a writer from Seattle, Washington and the author of seven books. It covers lifestyle, entertainment and news, as well as navigating the workplace and social issues.