Auditory Illusions – The Science behind the Magic of Hearing

The human mind is an amazingly complicated computer, capable of interpreting data given to it, extrapolating from that data to accurately predict the most likely outcome and making decisions on the fly based on that data. In most cases, even incomplete data provided by sensory perception is enough for the brain to accurately calculate missing gaps or excess information that is not meant to be there. Although sometimes, for some reason, this is not the case. The brain either fails to perceive something that is actually there, incorrectly interprets sensory information or even falsely perceives something that does not exist. This results in auditory illusions.

What is an auditory illusion?

An auditory illusion is a distortion in the sense of hearing, revealing how the brain actually organizes and interprets aural stimulation. Auditory illusions are the aural equivalent of optical illusions, where the listener hears either sounds which are not present in the stimulus, or “impossible” sounds. Auditory illusions are a clear example of how the human ear and brain are more fine-tuned to be organic survival tools and less to being perfect audio receptors.

Examples of auditory illusions and how they work

1. Binaural Beats

This particular illusion is perceived when two pure tones are presented to the brain dichotically (one through each ear) and the brain seems to identify a third beat that is not actually there.

How binaural beats work

The third beat is perceived when two pure-tone sine waves with frequencies lower than 1500Hz and a difference of less than 40Hz between them are presented to one ear each. The third beat, known as the binaural beat, has a perceived pitch that correlates to the difference between the two presented tones. For instance, if a 650 Hz pure tone is presented to the left ear and a 630 Hz pure tone is presented to the right ear, the brain detects the phase difference between these two tones and interprets this as an actual beat corresponding to the 20 Hz difference between them.

2. McGurk Effect

This particular phenomenon is an excellent example of how the brain integrates sensory input. The illusion is perceived when the visual component of one sound is paired with the auditory component of another, resulting in the perception of a third sound.

Speech perception is multimodal, meaning it combines input from different sensory inputs to enhance detection. In this case, it combines visual perception with auditory perception to reduce the likelihood of hearing something ambiguous. However, when the brain is presented with visual information for one sound and the auditory information for another, slightly different sound, it attempts to reconcile the two and a third sound is perceived instead.

Contrary to popular belief, speech perception is not an auditory process. The brain perceives speech as multiple sensory inputs all working together and more often than not, we do not separate visual input and auditory input when we are listening to a person speak. In other words, when you are listening to a person you can see, the brain cannot differentiate between what it can “see” a person say from what it can hear.

3. Yanny or Laurel

One of the most popular internet sensations in 2018 was a low-quality looping sound clip that had most people hearing either “laurel” or “Yanni”. It had a lot of people entertained, even drawing the attention of celebrities.

People generally pay attention to three frequencies when listening to speech and the lowest of these three is key for hearing the letters l and r, which are the consonants that make up the word Laurel. Most people listening to a decent quality recording on a decent device would not have misheard the clip.

Our ability to hear allows us to experience the beauty of the world around us. The human ear and brain have developed the ability to hear even in the most unfavourable conditions, provided ears are taken care of and kept healthy.

Make a booking at Hearing Works to receive professional ear-care and keep yourself from hearing the wrong thing.