LIFE SCIENCES How cochlear implants can influence speech interpretation

From: EUROPA - Brussels,Belgium - Apr 2, 2007

Quiet environments provide a good setting for the human brain when it needs to interpret speech. But noisy environments, say researchers at University College London and Imperial College London, prove taxing on the brain because the speech it must make sense of seems incomprehensible. In their latest study, funded by the Wellcome Trust and the Medical Research Council, researchers aimed to simulate the everyday experience of people who need cochlear implants and to assess how these experiences with the devices can be improved. Their findings were published in the February issue of the Journal of Neuroscience.

People who are either deaf or who have serious hearing problems use cochlear implants, but these surgically implanted electronic devices can make speech garbled and have a high level of background noise. While it will not restore a person's hearing, the device should provide useful sensations of sounds.

"In a noisy environment, when we hear speech that appears to be predictable, it seems that more regions of the brain are engaged," Dr Jonas Obleser, who conducted the research at the UCL's Institute of Cognitive Neuroscience. "We believe this is because the brain stores the sentence in short-term memory. Here it juggles the different interpretations of what it has heard until the result fits in with the context of the conversation."

The clarity of a person's speech and the level of background noise will influence how well the left and right temporal lobes of the brain interpret speech. If background noise does in fact impair a person's hearing, other regions of the brain jump into action, like the angular gyrus, which is involved in several language- and cognition-related processes. In this study, the researchers identified the key role the angular gyrus plays by using MRI scans of the brain.

Working out how the brain interprets distorted speech will help the researchers to make the experience of people with cochlear implants better.

"The idea behind the study was to stimulate the experience of having a cochlear implant, where speech can sound like a very distorted, harsh whisper," explained Professor Sophie Scott, a Wellcome Trust Senior Research Fellow at ICN. "Further down the line, we hope to study variation in the hearing of people with implants. Why is it that some people do better at understanding speech than others? We hope that this will help inform speech and hearing therapy in the future."