Auditory Illusions


auditory illusions

Most people are familiar with visual illusions, but did you know that our brains can also perceive auditory illusions?
Here are 4 examples of common auditory illusions.

The McGurk Effect

This illusion occurs when a sound is presented with conflicting visual stimuli. For instance, a person may look like they are saying /fa/ but the sound presented is the sound /ba/. This can either result in the person perceiving the third sound like /ga/ or they may hear the sound that was presented to them visually, which in this example is /fa/.

Here you can watch a video about the McGurk Effect and try it out for yourself!

Why does this illusion occur?

The simple answer is that the hemispheres of the brain work together to combine the information from the visual and hearing senses. When the messages are conflicting the brain gets confused and picks up on the sound normally associated with the visual signal and it is perceived rather than the true sound.

The Tritone Paradox

This illusion works best if you have a number of people around to compare your results with. In this illusion, two sounds are played one after the other. Each sound has a definitive pitch (so you could find it on a keyboard) but the octave of the pitch is in is unclear. The second sound also has a definitive pitch that is a tritone (specific measurement in music) away from the first sound. When the two sounds are played one after the other they will either be perceived as ascending or descending sounds. Whether you hear them as ascending depends on where you grew up and what language you speak.

This video shows a few different illusions including the tritone paradox. Try it yourself!

Shepard Tone Illusion

In this illusion, the sound will seem to continuously increase or decrease forever! This isn’t actually occurring of course! It is a bit like singing, “The Song That Never Ends”. It is actually a continuous loop of 8 notes that are made up of a combination of high and low parts that tricks your brain into creating continuous movement.

You probably saw this in the last video, but here it is again, in case you missed it!

The Doppler Effect

Have you ever noticed that as a firetruck goes by the sound seems to change? Most sirens alternate between two pitches giving it a wee-ooo sound. Since the object that is making the sound is moving towards you the firetruck is essentially driving through the sound waves and these waves bunch up making the sound higher and faster. Once the truck moves past you the waves spread out again and so the sound becomes slower and lower in pitch.

Here is a video of a firetruck where you can hear this effect happen:

If you are still interested in learning more about this amazing effect, this is another video that explains it in more detail:

Isn’t it cool how our brains can hear magic too?

We hope you enjoyed learning about a few auditory illusions!!!