Tuning out: researchers make sense of background noise
6 March 2007
Scientists have worked out how the brain helps us make sense of each other in noisy places such as in a pub or train station. The researchers have found that when dealing with a conversation drowned out by a barrage of sound, the brain ‘juggles’ the different possible meanings of a sentence until it decides which is the most likely.
Dr Jonas Obleser, of the Institute of Cognitive Neuroscience (ICN) at University College London, who led the study, explained:
"In a noisy environment, when we hear speech that appears to be predictable, it seems that more regions of the brain are engaged. We believe this is because the brain stores the sentence in short-term memory. It juggles the different interpretations of what it has heard until the result fits in with the context of the conversation."
The scientists hope that by understanding how the brain interprets distorted speech, they will be able to improve the listening experiences of people who have cochlear implants. These electronic devices are surgically implanted and aim to give a sense of sound to a person who is profoundly deaf or who has severe hearing problems. However, sounds heard through an implant are crude and distorted, like listening to a harsh whisper or having a lot of background noise. The findings are published in the current issue of the Journal of Neuroscience.
This research, funded by the Wellcome Trust and MRC, used MRI scans to look at the workings of the brain when they simulated the experiences of people who rely on cochlear implants to interpret speech. Professor Sophie Scott of the ICN explained:
“The idea behind the study was to simulate the experience of having a cochlear implant, where speech can sound like a distorted, harsh whisper.”
The team discovered that a region of the brain called the angular gyrus appeared to play a role in decoding distorted sentences.
This image is of MRI scans that show the different parts of the brain activated depending on the speech heard. Brain activation occurs in the red areas if the words are highly predictable and in the blue areas if what is heard is unpredictable. The areas highlighted in purple show where activity overlaps.
When background noise is minimal and a person's speech is clear, it is mainly the left and right temporal lobes of the brain that are involved in interpreting speech. However, the researchers have found that when hearing is impaired by background noise, other regions of the brain are engaged, such as the angular gyrus, the area of the brain also responsible for short term memory – but only when the sentence is predictable.
Professor Scott concluded:
“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."
Scientists at the MRC Clinical Sciences Centre contributed to this research.
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