Measuring listening effort tells us about the benefits of a hearing aid

How do you test whether a hearing device actually makes a difference for the user? The level of brain capacity spent on understanding a conversation – listening effort - is one way to do that. In a new study, listening effort was used as the measurement for the benefit of a hearing aid.

Being part of a conversation in a noisy environment can be quite a challenge. For everybody really, but especially if you are hearing impaired. To understand what someone is saying, you will need to focus your energy and concentration on that one person. That is called spending listening effort.

The effort spent when trying to understand speech offers a new means of testing whether a hearing device is actually doing it’s job.

“Usually audiologists use a speech recognition test where the hearing impaired person repeats words. But if you can show that listening effort is reduced because of the hearing device, you also show that listening may be less exhausting,” explains Postdoc Dorothea Wendt. She is researching listening effort in the Cognitive Hearing Science group at Eriksholm Research Centre.

A recent study from Eriksholm Research Centre and VU University medical center in Amsterdam showed that a programme inside a hearing aid designed to reduce the noise around the user actually made a difference to the listening effort.

“When we measure listening effort in different test situations, we can see that in the situations closest to reality, listening effort is significantly reduced for the hearing aid user. That is really interesting and relevant, because it means that the noise reduction in the hearing aids actually helps people,” says Dorothea Wendt about the study.

The study is published in the journal Hearing Research.

Pupil size reveals listening effort

In the test setup 25 different listeners with hearing-impairment were asked to focus on a voice coming from a loudspeaker in front of them while competing talkers were presented from the back and the side through other loudspeakers. By means of a test, where the listeners repeat the sentences from the loudspeaker in front of them, the researchers were able to see how much of the speech the listeners heard through the noise.

The listening effort was measured simultaneously with an eye-tracking camera that measured the pupil size of the test subjects while they were concentrating on being able to repeat the speech. A greater pupil dilation during this speech recognition test indicates an increase in listening effort.

The ratio between the volume level of the talker and the level of the noise, called the signal-to-noise ratio (SNR), changed during the test. When the SNR was positive (speech level higher than noise level) – it was easier for the listeners to recognize the speech. In these situations, less effort needed to be spent compared to listening in a situation with negative SNR.


Noise reduction makes it easier to understand

As the difference in volume between talker and noise becomes smaller, the more listening effort is needed (the black line in figure 1). However, this is only until a certain point after which the effort drops. The researchers assume that this is the point where hearing and recognizing the speech gets so difficult and demanding that the listeners disengage and may give up.

The results also indicate that this point of giving up moves when the noise reduction in the hearing aids is turned on (the dotted line). The listener stays engaged and allocate resources in those more difficult listening situations, when supported by activated noise reduction.

“What is very interesting is that people still try to listen even in more adverse listening situations when they have the hearing aids and the noise reduction on. With inactive noise-reduction, they would get disengaged earlier and more likely miss the conversation in noise,” says Dorothea Wendt.

She also takes note of the fact that the difference between listening with or without noise reduction is significant in the listening situations that are considered ‘ecologically valid conditions’ – the listening situations most likely to mirror reality. These have on average a difference between talker and noise of 5 dB.

Tests on listening effort could be valuable in the clinic

The study deals with a specific hearing aid but according to Dorothea Wendt, measuring listening effort could be used as a way to evaluate the benefit of hearing devices on a more general level as well. It could be an important addition to the more traditional speech recognition tests in audiological practice.

“We still need the traditional measure of speech recognition, but adding tests on listening could give more information on how people understand speech and how they allocate their cognitive resources to perform a task. This is information that you wouldn’t measure otherwise,” says Dorothea Wendt and adds:

“However, the pupillometry method has to be developed further, and more research is needed, before it might be applicable and provide clinical value. So far, the methods are only used to examine changes in listening effort for a group of hearing-impaired listeners and not for individuals.”

Read about another way of measuring listening effort - the SWIR test – here: Worldwide interest in SWIR: An increasingly popular method for measuring listening effort

Introducing the newest listening effort project: HEAR-ECO

This study was part of Barbara Ohlenforst’s PhD thesis, which again was part of the EU funded LISTEN project.

The LISTEN project aimed at developing the pupillometry method for measuring listening effort further in order to better show the benefits of a hearing device
But research usually leads to more questions, so even though LISTEN has now come to an end, the work on listening effort is now continuing in the international HEAR-ECO project.

“In HEAR-ECO we’ll combine pupillometry with other techniques, such as EEG, to measure listening effort. We aim to examine the listening effort with those different techniques beyond the typical lab situation. The long-term goal is to investigate the benefit of hearing devices, for the user in those ecological valid listening scenarios,” says Dorothea Wendt.

Read more news from Eriksholm Research Centre here.