Imagine you’ve been locked in a dark room for a very long time with no sound, no light, and no clue of what might be going on outside your room. Once in a while a man called McGurk would come into the room and tell you about what was going on in the outside world.
“It’s raining outside,” McGurk said. You nod.
“Your wife says she loves you,” he tells you. It’s kind of him, you think. A few days pass.
“The moon is as big as my thumb,” said the stranger on his return. Uh… okay. It’s new.
“Crayons bend when placed in water,” says McGurk. Well it sure ain’t right.
It goes on and on. McGurk usually tells you reasonable things – boring and mundane, even. But, very occasionally, he tells you something really strange: the unbelievable, the ridiculous or the patently untrue.
The question is, would you trust McGurk? How long should it be before you start to doubt his honesty? What kind of success rate should McGurk have before you consider him reliable or not.
This is the philosophical problem of perception. A phenomenon known as the McGurk Effect reveals just how pernicious this is.
‘Scuse me while I kiss this guy
Everything we know about the world comes through our senses. Our senses are the messenger or relay station through which we access everything around us. In the opening thought experiment, McGurk acts as our eyes and ears. In real life, we also don’t have direct knowledge of the world, but rather rely on our senses to paint an accurate picture of the world. And how do they do it?
Not very well. Our treacherous senses will lie to us almost daily. Place your thumb in front of you and it will be as tall as a building or taller than someone’s head. Or, in a favorite example of the philosophers, when you put a stick in water, it will appear bent or distorted. Our senses are small deceptive organs of fallibility. And yet, in these examples, we to know that our perceptions are wrong. We use our intelligence and our experience to correct what our senses tell us wrongly. We have the notions of perspective and refraction to account for the defects of our eyes.
But the question is not so easily answered. There are many times in our lives when we are unknowingly fooled by what we see or hear. It may take several days or weeks later for us to realize our mistake. We might never realize at all. Suppose the dog you saw walking past your house earlier was actually a fox. Or maybe the keys you took from the table earlier, thinking they belonged to you, actually belonged to your partner. You might assume that Jimmy Hendrix purple mist the lyrics are “Excuse me while I kiss this guy” instead of “Excuse me while I kiss the sky”. All these interpretations are justified by the weight of your senses. All are wrong.
One of the most fascinating instances where our senses trick us is known as the McGurk Effect.
“bah” is not “gah”“
The McGurk effect is a curious phenomenon that emerges from the confusion between our visual and auditory perceptions. It was first recorded in the 1970s by British cognitive psychologists Harry McGurk and John MacDonald. They observed it by accident after a puzzling incident they experienced while working with a technician while dubbing phonemes (speech sounds) on a video.
The McGurk effect is produced when you have a video of a speaker speaking one phoneme, then dub a completely different phoneme. In this case, the speaker makes the lip movements of “gah, gah, gah”, but the sound “bah, bah, bah” is substituted. Oddly, what happens is that you will hear the phoneme “dah, dah, bah.” It is the particular result of a dissonance in your perceptions. Your eyes expect a certain noise, but your ears provide another. So, with a cartoonish roar of gears, the brain implodes and produces a third sound – even though it was never actually included in the audio track.
The doubly strange thing about the McGurk effect is that it is quite resistant to correction. That is to say even knowing that the McGurk effect is one thing won’t prevent you from hearing the wrong sound. Try it yourself.
Never trust a liar
As philosophers have suspected, and neuroscientists prove time and time again, our brain constructs the world around us. He paints in details that we don’t see. It assumes, invents, hides, modifies and ignores large parts of the world around us. Our eyes actually only have a very small area of focus; the rest is peripheral or totally ignored. If this concentration were greater, the amount of visual sensory input would require a much larger brain than our skulls can hold. So it makes sense that the brain is a little loose with the details. The McGurk effect is the brain doing what it needs to do.
The result is that our senses are structurally designed to fool us a bit. The problem with this was described by the French philosopher René Descartes, who wrote: “It is prudent never to fully trust those who have deceived us even once.
Our senses are serial liars. So how much should we rely on them? Some philosophers, notably the Greek skeptics, have concluded that we should not trust our senses. Instead, we should treat everything with a pinch of “well, that could be able be the case.” In the Advaita school of Hindu Vedanta, the world is called “maya” or illusion. the truth.
Of course, there’s not much we can do about it. There is no way to live without our senses, and no other way to access the world. In many cases, education and experience allow us to recognize when our eyes or ears are deceiving us. In many others we have no hope of distinguishing right from wrong. But that’s all we have – the brain’s biological and evolutionary survival heuristic.
And so, as long as our understanding remains locked in its dark and cloistered tower, we will have to accept what the stranger tells us.
Jonny Thomson teaches philosophy at Oxford. He runs a popular Instagram account called Mini Philosophy (@philosophyminis). His first book is Mini Philosophy: A Little Book of Big Ideas.