Clearer Sounds From Picky Ears

Consonants are critical for telling words apart, and everyone occasionally mishears them--sometimes with comical results. But such confusion is no laughing matter for the 3.5 million children in the United States who suffer from language disorders and have trouble speaking and understanding even the simplest sentences. Now researchers say that training kids to pick out sounds from a noisy background might help overcome at least some of their difficulties.

Despite perfectly normal hearing, some children have trouble distinguishing the sound "ka" from "ba" or "da," for example, because those consonants last only 20 to 40 milliseconds. Last year researchers discovered that hissing noise would wipe out the memory of tones about this short in affected children (ScienceNOW, 9 May 1997). Team member Beverly Wright, a speech communication researcher at Northwestern University, wanted to find out if such elusive short-lived tones--a proxy for consonants--could be heard simply with more practice.

Wright and her colleagues began their experiment with 14 adults--none of whom had language disorders--to see if their perception could be improved. They asked the people to pick out extremely short-lived tones that were immediately followed by noise; such conditions are very difficult for children with language impairments. These conditions were meant to simulate what language disabled children experience in normal conversations. After about 10 practice sessions lasting an hour each, almost all the people improved in their ability to identify the tone correctly. Moreover, training people at one frequency improved their performances equally at several different frequencies, Wright reported this week at the Acoustical Society of America's annual meeting in Seattle. Wright says that children with language disorders have also improved in detecting sounds during practice sessions.

Some researchers speculate that such training rewires neurons that help perceive sound. Not everyone agrees on that theory or its promise for treating language disorders. Charles Watson of Indiana University, for instance, believes a simpler explanation is possible: Practice might simply teach people what to listen for, much like being able to spot easily a face in a crowd once it has been pointed out. "We have found remarkable abilities to hear out the details of complex sounds among musicians," he says. But that's not because their brains have been rewired, he suspects; rather "they simply know what to listen to."