Context and Audition

For each sequence, please try and decide:
Do you hear the pitch go up or down between the two final tones?

What did you hear?

Most people report an upward shift at the end of Sequence A, and a downward shift at the end of Sequence B.
Do you agree?

What was played?

In fact, the two final tones of Sequence A are physically identical to the two final tones of Sequence B.
Only the preceding melodies are different.

Do not take our word for it: use the controls above to listen only to the two final tones of Sequence A and Sequence B (without any note from the preceding melodies). You will hear that they really are the same in both cases.

Want to know more?

We believe that the illusion reveals potent and ubiquitous contextual processing in audition, perhaps explaining why people are so incredibly good at dealing with the complex auditory scenes we navigate everyday (a conversation in a noisy place, a music concert...).

In a few words, everytime you hear two successive sounds, like two speech sounds in a sentence, or two musical notes in a melody, you need somehow to bind them over time to realise that e.g. pitch went up. In our examples, we designed the final two tones as a carefully-balanced situation: there were as many "up" transitions than "down" transitions between the frequencies that make up the tones. What the context did was to favor some of these transitions, by biasing you towards one possible binding between tones, the binding that minimized the overall frequency distance (after all, real sounds do tend to evolve smoothly over time).

This is only part of the story! For a lot of behavioral data, some brain imaging, and a probabilistic model explaining why this may be important for everyday sounds, please see: Prior context in audition informs binding and shapes simple features', by Claire Chambers, Sahar Akram, Vincent Adam, Claire Pelofi, Maneesh Sahani, Shihab Shamma, and Daniel Pressnitzer, Nature Communications, 2017.

This work has been done at the Laboratoire des Systèmes Perceptifs (CNRS & Ecole normale supérieure, PSL Research University, Paris), in collaboration with U. Maryland (USA) and the Gatsby Unit in London.

Wait, it did not really work for me...

The illusion was found to be highly robust, in a series of psychophysical and online experiments involving 150+ participants. But, interestingly, sometimes there were also strong biases towards one direction, peculiar to each listener and the acoustic details of each sound. Maybe the example above was heavily biased for your particular ears? Try those instead.

Website by Daniel Pressnitzer (daniel.pressnitzer at