A clue to why listening to multiple talkers is harder with hearing loss

2 December 2008

New research shows that hearing-impaired listeners have a reduced ability to select and pay attention to just one voice when there are multiple talkers. The research, conducted at Boston University in the USA, sheds light on why listening becomes more difficult for people with hearing loss in many everyday settings.

Dr Virginia Best and colleagues simulated a situation in which five different people were talking at once, each standing in a different location. The aim was to understand whether actively paying attention can make speech more intelligible.

Participants in the study were asked to identify target sequences of speech. Each sequence could come at any time and from any of five places, during a background babble of speech played from the other positions. In some tests the listeners were given a visual cue to where and/or when the target speech would occur, so they knew when and/or where to pay attention. In other tests, no information was given at all.

Results, reported in The Journal of the Association for Research in Otolaryngology, showed – unsurprisingly – that listeners did better if they received a cue  to help them pay attention. However, the listeners with sensorineural hearing loss (affecting the inner ear) received less benefit overall than normal hearing participants.

Perhaps surprisingly, knowing when to pay attention was of about equal benefit to all participants, whether or not they had hearing loss. In contrast, knowing where to pay attention was of significantly less help to the hearing-impaired group than it was to those with normal hearing.

Importantly, this was true even if normal hearing listeners heard the target speech at a lower volume level to mimic the effect of hearing loss. This indicates that the problem was not just due to difficulty in hearing, but was also because the hearing-impaired group had trouble attending to the right voice.

The results suggest that a reduced-quality input caused by damage in the ear makes it harder for the brain to separate sounds out into ‘objects’, such as one person’s voice. This in turn suggests that there is no clear object to pay attention to, making the task very difficult.

“This study is just one example of where a high-level function (directing spatial attention) can be negatively affected by a peripheral impairment. I think further research might reveal many more of these 'downstream consequences' of hearing loss, and help explain why even a mild hearing loss can affect communication when the listening environment is complex” says Dr Best.

The study has helped to identify a new area for researchers to target in order to develop rehabilitation strategies that will improve communication in everyday situations for hearing-impaired people.