This illusion was discovered by Diana Deutsch, and is an example of our brains “grouping” similar notes together. Two major scales are played: one ascending, one descending. However, the notes alternate from ear to ear – for instance, the right ear hears the first note of one scale, and then the second note of the other.

Some pieces of music consist of high-speed arpeggios or other repeating patterns, which change only subtly. If they’re played fast enough, the brain picks up on the occasional notes that change, and links them together to form a melody. The melody disappears if the piece is played slowly.

This is a recording of Shepard’s paradox synthesized by Jean-Claude Risset. Pairs of chords sound as if they are advancing up the scale, but in fact the starting pair of chords is the same as the finishing pair. If you loop this sample seamlessly then it should be impossible to tell where the sample begins and ends.