Aural Illusions

Grey_square_optical_illusionMany of us are familiar with visual illusions that trick your eyes (or rather, your brain) into thinking it’s seeing something different than what’s really there (for example, square A and square B are exactly the same color in the image to the right). But are you familiar with some of the aural illusions that have been discovered? Meara O’Reilly has a bunch up on her web site.

Meara O’Reilly is a sound artist and educator, in residence at the Exploratorium. Current ongoing projects include a curated collection of auditory illusions as found in indigenous folk music traditions, as well as adapting more scientifically established auditory illusions to be presented on homemade acoustic instruments.

The Shepard tone is one of the best known aural illusions. Because each pitch consists of multiple octaves when a continuous scale is played it creates the illusion that the scale isn’t going higher or lower.

The Wessel Illusion was a new one to me.

The Wessel Illusion demonstrates how timbre can determine the way in which we perceptually group notes in a melody.

Three notes, rising in pitch but alternating in timbre, are played slowly. When this sequence is played faster, it’s possible to hear the trajectory of the melody change.

There are a whole bunch of other aural illusions and other neat things to explore over at O’Reilly’s web site. Some neat musical examples as well as the basic illusions. Check them out further here.