Banking on predictability, the mind increases efficiency

Nov 22, 2010 by Chris Barncard

( -- Like musical compression saves space on your mp3 player, the human brain has ways of recoding sounds to save precious processing power.

To whittle a recording of your favorite song down to a manageable pile of megabytes, computers take advantage of reliable qualities of sounds to reduce the amount of information needed. Collections of neurons have their own ways to efficiently encode sound properties that are predictable.

"In perception, whether visual or auditory, has a lot of structure to it," said Keith Kluender, a psychology professor at the University of Wisconsin-Madison. "Your takes advantage of the fact that the world is predictable, and pays less attention to parts it can predict."

Along with graduate student Christian Stilp and assistant professor Timothy Rogers, Kluender co-authored a study published in this week's (Nov. 22) early online edition of the showing listeners can become effectively deaf to sounds that do not conform to their brains' expectations.

The researchers crafted an orderly set of novel sounds that combined elements of a tenor saxophone and a French horn. The sounds also varied systematically in onset — from abrupt, like the pluck of a violin string, to gradual, like a bowed string. These sounds were played in the background while test subjects played with Etch-a-Sketches.

After a little more than seven minutes, listeners completed trials where they were asked to identify one in a set of three that was unlike the other two.

Distinguishing sounds that varied in instrument and onset in the same way they had just heard was a simple matter. But sounds that didn't fit — with, say, more pluck and not enough saxophone — were completely lost to the listeners. They could not correctly identify one of the non-conforming sounds as the odd one among three examples.

"They're so good at perceiving the correlations between the orderly sounds, that's all they hear," says Kluender, whose work is funded by the National Institute of Deafness and Other Communication Disorders. "Perceptually, they've discarded the physical attributes of the sounds."

The results jibe well with theoretical descriptions of an efficient brain, and the researchers were able to accurately predict listener performance using a computational model simulating brain connections.

"The world around us isn't random," Stilp says. "If you have an efficient system, you should take advantage of that in the way you perceive the world around you. That's never been demonstrated this clearly with people."

To avoid having to carefully take in and remember every last bit of visual or audible stimulus it encounters, the mind quickly acquaints itself with the world's predictability and redundancy.

"That's part of why people can understand speech even in really terrible conditions," Kluender says. "You can press your ear to the wall in a cheap apartment and make out a conversation going on next door even though the wall removes two-thirds of the acoustic information. From just small pieces of sounds, your brain can predict the rest."

Explore further: Conceptual representation in the brain: Towards mind-reading

Related Stories

Where the brain makes sense of speech

Dec 19, 2007

Researchers have identified regions of the brain where speech sounds are perceived as having abstract meaning, rather than as just a stream of sensory input. They said their identification of the regions demonstrates that ...

Lend me your ears -- and the world will sound very different

Jan 14, 2008

Recognising people, objects or animals by the sound they make is an important survival skill and something most of us take for granted. But very similar objects can physically make very dissimilar sounds and we are able to ...

Adults with dyslexia have problems with non-speech sounds too

Jun 01, 2010

( -- Dyslexia is usually associated with persistent reading, spelling, and sometimes speech difficulties that are hard to overcome. One theory proposed to explain the condition is that people with dyslexia suffer ...

Recommended for you

Conceptual representation in the brain: Towards mind-reading

1 hour ago

Your measured brain signals can reveal whether you are thinking about an animal or a tool. That's what neuroscientist Irina Simanova discovered during her PhD at Radboud University, where she investigated the conceptual representation ...

Researchers track down cause of eye mobility disorder

17 hours ago

Imagine you cannot move your eyes up, and you cannot lift your upper eyelid. You walk through life with your head tilted upward so that your eyes look straight when they are rolled down in the eye socket. ...

How kids' brain structures grow as memory develops

19 hours ago

Our ability to store memories improves during childhood, associated with structural changes in the hippocampus and its connections with prefrontal and parietal cortices. New research from UC Davis is exploring ...

User comments : 0

More news stories

Bionic ankle 'emulates nature'

These days, Hugh Herr, an associate professor of media arts and sciences at MIT, gets about 100 emails daily from people across the world interested in his bionic limbs.

Smoking's toll on mentally ill analyzed

Those in the United States with a mental illness diagnosis are much more likely to smoke cigarettes and smoke more heavily, and are less likely to quit smoking than those without mental illness, regardless ...

Net neutrality balancing act

Researchers in Italy, writing in the International Journal of Technology, Policy and Management have demonstrated that net neutrality benefits content creator and consumers without compromising provider innovation nor pr ...