The Intriguing World of Visual and Auditory Illusions: When Your Senses Deceive You

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.

Visual Illusions

Flying can mess with your senses in ways you wouldn’t expect. When your body’s sensory inputs send confusing or misleading signals to your brain, your brain will misinterpret them (i.e., cause an illusion). Each one can throw you off course if you’re not careful. The knowledge of these illusions, however, is not enough. And the key to doing so? Trust your instruments!

Common Visual Illusions in Flying

The Inversion Illusion: The inversion illusion happens when a pilot quickly transitions from a climb to straight-and-level. During an abrupt change from climbing to level flight, the fluid in the vertical canals of your inner ear continues to move. This false perception of your body’s position - thinking you’re in a climb when you’re not - leads to the inversion illusion.
The Coriolis Illusion: Imagine you’re turning steadily in one direction for a while (say, to the left). Your aircraft gets a quick boost, and your inner ear tells your brain that you’re in a climb. So how do you keep the Coriolis Illusion in check?
The False Horizon Illusion: You’re flying at night or in poor visibility conditions with no distinct horizon. The antidote to the False Horizon Illusion? You’ve got it - rely on your instruments! To further arm yourself against this illusion, enhance your understanding of your aircraft’s attitude indicator.
Autokinesis: Imagine you’re flying at night, and there’s a stationary light in the distance. The light isn’t moving at all, but your brain insists it is. This illusion can lead to misjudging the movement of other aircraft at night. You might think another airplane is moving when it’s not, or you might misinterpret its speed and direction. The countermeasure to autokinesis? Don’t stare at a single point of light for too long.
The Graveyard Spiral: Say you’ve unknowingly entered a slow, gentle bank. You’ve entered a gentle turn that has gone unnoticed. When you finally notice and correct the turn, it feels like you’ve started turning in the opposite direction. This deadly descent is what we call a graveyard spiral. The same can happen in reverse during deceleration.

Auditory Illusions

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.

What is the McGurk Effect?

Examples of Auditory Illusions

Binaural Beats: 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.
Speech Perception: This particular phenomenon is an excellent example of how the brain integrates sensory input. 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. 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.
The "Laurel" or "Yanni" Phenomenon: 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”. 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.

Visual Capture and the McGurk Effect

Visual capture is the dominance of your vision over your other senses. In regard to sound, when your vision dominates your hearing, what you see will determine what you hear, instead of hearing what is actually there. In ventriloquism, we see the puppets mouth moving, and the human’s mouth looks as if it is not moving, so it seems as if we are hearing the sound from the puppet.

Darci Lynne, a ventriloquist

A really popular example of visual capture in the science world is the McGurk Effect. This is a sound illusion that is caused by your brain listening to your eyes rather than your ears. A continuous stimulus sound is played over and over again, however each time the person on the screen move their mouth a different way when mouthing the sound. In order for this phenomenon to occur, there must be some kind of audio-visual integration (Alais 2004). According to a study done using BOLD fMRI, the superior temporal sulcus is believed to be responsible for the integration of auditory and visual cues (Burr 2009). People who lack this region are not able to experience the McGurk effect.

It is really cool to study all of the interesting things our brain does, but how is this possible?

References:

Alais D, Burr D (2004) “The ventriloquist effect results from near-optimal bimodal integration”.
Burr, D., Banks, M.S. & Morrone, M.C. (2009)“Auditory dominance over vision in the perception of interval duration”. Exp Brain Res 198, 49.