Say it sounds like singing

by Peter W McOwan and Paul Curzon, Queen Mary University of London

All too often things get repetitive. Songs in the chart repeat their lyrics, comedy catchphrases begin to jar and friends can keep saying the same things over and over again. But strange things can happen when speech is repeated; yes when speech is repeated we can find it begins to sound like music. You can't believe everything you hear!

American speech researcher Diana Deutsch discovered this strange speech to music illusion by accident one day when she was editing a spoken sound track. She had the phrase 'sometimes behave so strangely' on a loop, and noticed that after a short while the spoken words sounded as if they were being sung. She experimented with changing the way the phrase was played and found that the change from speech to song only happened when the phrase was repeated exactly and regularly.

So it seems that the way our brain processes sound to perceive whether it is a song or speech requires that sound have particular characteristics. However, if we set it up correctly we can fool the brain into thinking that speech has some of the characteristics of a song.

If I didn't say that, who did?

Diana has been responsible for uncovering and exploring many of the strange ways our ears and brain play word tricks on us. Another illusion she discovered is a way that phantom words emerge from a babble of other words. It sounds a little spooky, but it's one of the illusions our auditory cortex, the part of the brain near our ears, can be tricked by. If you listen to a sequence of stereo overlapping repeating words and phrases, your brain starts to try and make sense of them. The auditory cortex's task is to make sense of the sounds arriving so even if it's a jumble it will work hard to pull something from the racket. The illusionary words that you hear are often dependant on what you're thinking about at the time, so if you are hungry you may hear words related to food. It's quite a creepy experience just before lunch. This strange phenomena is called the 'phonemic restoration effect', phonemes being the component sound that make up words.

Hearing like a human

One strand of computer science aims to understand how the brain works, by creating computer models that do the same thing. These kinds of illusions, both optical and auditory give good test cases. If you really understand how humans hear then you should be able to create programs that allow computers to hear the same way. If you get it right then the programs should be fooled in the same way that humans are and hear the same illusions. The fact that we hear sounds based on what we are thinking means to truly create a computer that hears like a human, you need to have modelled our thought processes too!

Hearing like a human is a lot harder than just recording sounds.