April 25, 2010

Auditory Illusions

Two classic auditory illusions. Try them out! Christie Nicholson reports

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Every now and then we present auditory illusions on 60-Second Psych. Being an audio podcast about human perception, it's sort of the perfect match.

First up a classic illusion from Diana Deutsch at the University of California, San Diego. It's a recording of repeating sounds, which our brains perceive as specific words. Listen to this[audio sample]. What words did you hear? Well none of them are actually there. In an effort to make sense of the repeated gibberish our brains actually perceive real words or phrases. Often the words are related to whatever is on our mind at that time. Recently I've been driving in New York City a lot, so I heard the words "road rage" repeated over and over.

Here's one more illusion. This is an example of the Shepard scale, created by cognitive psychologist Roger Shepard. The tones are separated by octaves, meaning each successive frequency doubles and this creates the fascinating effect of a constantly descending tone, but really it goes absolutely nowhere; it stays at the same level. Listen to this [audio sample].

It's the auditory equivalent of the barber shop pole that appears to be moving but isn't. Or like the artist M.C. Escher's lithograph of a never-ending staircase called Ascending and Descending. Any way you hear it, it's kinda creepy.

—Christie Nicholson

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