Shepard Tone Illusion

Background

Roger Shepard (1964) created an auditory illusion that produces the impression of a tone that endlessly ascends (or descends) in pitch, much like an auditory barber pole. The illusion works by layering sinusoids at octave intervals with a Gaussian spectral envelope — as one component reaches the top of the audible range and fades out, another enters at the bottom.

The Tritone Paradox

Diana Deutsch (1986) discovered that when two Shepard tones separated by a tritone (half octave) are played, some listeners hear an ascending pair while others hear descending — even though the stimulus is identical. This reveals that pitch perception has a circular component: it depends on where your internal pitch template is anchored.

This Experiment

You will hear pairs of Shepard tones and judge whether the second tone sounds higher or lower than the first. Some pairs are unambiguous; the tritone pairs are genuinely ambiguous.

References

Shepard, R.N. (1964). Circularity in judgments of relative pitch. Journal of the Acoustical Society of America, 36, 2346–2353.

Deutsch, D. (1986). A musical paradox. Music Perception, 3, 275–280.

Deutsch, D., Henthorn, T., & Dolson, M. (2004). Absolute pitch, speech, and tone language. Music Perception, 21, 339–356.

You will hear pairs of tones. After each pair, judge whether the second tone sounded higher or lower than the first.

Press ↑ or click Higher if the second tone sounds higher.

Press ↓ or click Lower if the second tone sounds lower.

Some pairs are obvious; others are genuinely ambiguous — there is no wrong answer for those!

There are 24 trials. Please use headphones if possible for the best experience.

Note: Click the button below to enable audio (browser requirement).

Shepard Tone Illusion

Your Results