Psychology professor Diana Deutsch also discovered various “ musical illusions“.
The McGurk effect, for example, highlights to what extent visual triggers can affect what we hear. This relationship can explain in part how our senses activate in relation to one another, as well as how they are affected by the brain. Neurologists continue to explore the relationship between our primal survival instincts and our physical perception of the world around us. The study of psycho-acoustics relates to how we perceive sound. Ever felt like you have heard a noise that wasn’t really there or mistakenly heard someone calling your name in a crowd? Well, you’re not alone, and there are various reasons that can explain such phenomena. Just like visual illusions, our brain can interpret audio information in an unusual way. At the higher speed, the changing notes linger in your perception long enough to be linked into a melody, but at the lower speeds they’re too widely separated.The aural equivalent of an optical illusion, auditory illusions also highlight the influence of neurological reflexes on our perception of reality. The melody disappears if the piece is played slowly.Ĭompare these recordings of Christian Sinding’s Frühlingsrauschen (“Rustle of Spring”). If they’re played fast enough, the brain picks up on the occasional notes that change, and links them together to form a melody.
Some pieces of music consist of high-speed arpeggios or other repeating patterns, which change only subtly. Right-handed people tend to hear the high melody in the right ear, and the low one in the left, while left-handers show a more diverse response. In other words, the brain reassigns some of the notes to a different ear in order to make a coherent melody. Rather than hearing the two scales, people hear a descending and re-ascending melody in one ear, and an ascending and descending melody in the other. There are several ways in which people perceive these sounds, but the most common is to group the high and low notes together. However, the notes alternate from ear to ear – for instance, the right ear hears the first note of one scale, and then the second note of the other (see diagram, top right). Two major scales are played: one ascending, one descending. The scale illusion is an example of our brains grouping similar notes togetherĤ Scale illusion (Listen through stereo headphones, or stereo separated loudspeakers, best placed some distance apart)Īnother effect first demonstrated by Diana Deutsch, this is an example of our brains “grouping” similar notes together. If the phoneme is replaced by a period of silence, rather than a cough, the deletion is very obvious. But not only do most people hear the complete sentence, they generally find it very difficult to work out which phoneme has been deleted. One of the phonemes has actually been completely removed by the cough. In this recording by Richard Warren from the University of Wisconsin in Milwaukee, a spoken sentence is interrupted by a cough. This means that if a part of an audio recording is missing, our brains will often work out what should have been there. Much of human perception is the result of the brain filling in gaps in the data from our senses. Indeed, you may find that the phrases you hear are related to what’s on your mind – for example, people who are dieting often hear phrases associated with food. Your brain is constructing them, in a bid to make sense of a meaningless noise. However, none of the phrases are really there. As you listen to it, you’ll start to pick out specific phrases. Building on the stereo effect described above, the recording features overlapping sequences of repeating words or phrases, located in different regions of stereo space. This illusion was first demonstrated by Diana Deutsch at the University of California, San Diego. The illusion demonstrates our ability to locate sounds in space by comparing the inputs to the two ears, we can work out where a sound is coming from.Ģ Phantom words (Listen through stereo separated loudspeakers, best placed some distance apart) Similarly, increases in the volume of sound from the clippers give the impression that he is bringing them closer and closer to each ear. As the barber “moves” to your right, the volume increases slightly in the right channel and decreases in the left. Listening to it, you feel as though you are in a barber’s chair, with the barber moving around you, clipping away at your hair. This is a demonstration of the stereo effect. 1 Barber’s shop illusion (Listen with headphones)
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