dorothea_round
Dorothea Wendt

Scientist, PostDoc

mail@eriksholm.com

The PUPILS project is taking pupillometry from group level to the individual level. The project aims to find out whether the method can be a diagnostic tool for hearing-aid fitting in the future.

The measurement of the pupil dilation, i.e. pupillometry, can be interpreted as a reliable index of listening effort. Within recent years, pupil dilations have been studied extensively as an indicator of the person’s listening effort mobilized for speech perception in a noisy environment. It has been demonstrated that listening effort is affected by speech intelligibility, masker type, hearing impairment, and hearing-aid signal processing. For instance, it was shown that noise-reduction schemes of hearing aids can reduce the listening effort that is spent in ecological valid listening situations. So far, the pupillometry method has mainly been evaluated on a group level, no attempts have been made to evaluate the individual listener’s effort.

 

Project Goals

The PUPILS project aims to examine whether the pupillometry method can be a suitable diagnostic tool for hearing-aid fitting and for testing the benefit of a hearing aid on an individual listener basis.
The transition from a group level towards an individual level of listening effort is not straightforward and provides some challenges since the underlying components affecting the pupillary response are not fully understood yet. To assess the individual pupillary response as an outcome measure of listening effort, the test–retest reliability of the pupillary method will be explored within this project. Different work packages are designed to develop the experimental paradigm and to examine the specificity and sensitivity of the method.

Furthermore, the focus will be on advanced analysis methods, the modeling of the pupillary response and the classification of individual pupil traces. The goal is to identify models that are ultimately feasible for an analysis on an individual basis using a few or even single pupil traces.

The project is performed at DTU, more specifically in close cooperation with Professor Torsten Dau (Hearing Systems) and Per Bækgaard (DTU Compute).

To project is supported by the Oticon Foundation and expected to be completed in 2022.
listenplusfig2_ramme

Figure 1: Example of normalized pupil curve averaged across a group of listeners. The pupil size was measured while people listening to sentences in noise. The PPD is calculated as the maximum pupil dilation during stimulus presentation. Figure from Wendt et al., (2017)

Measuring Peak Pupil Dilation

The Peak Pupil Dilation (PPD) is defined as the maximum pupil dilation during the time interval between sentence onset and the noise offset (see Figure 1). It is a commonly used indicator of listening effort in such an experimental paradigm. The larger the PPD, the higher the listening effort.

In adverse and noisy listening situations, listening effort is expected to be high, which would be reflected in an enlarged pupil dilation. By applying a NR scheme (including directional microphone use and NR), the hypothesis was that listening effort can be reduced for people with hearing impairment, as indicated by a significant decrease in pupil dilation.

A second study was performed that also focused on the impact of the signal processing on effort over a broader range of listening situations (i.e. broad range of SNRs). This study demonstrates that listening effort changes in a non-monotonic way as a function of the SNR with maximum effort occurring at approximately 50 percent intelligibility. Furthermore, reduced effort was observed again at ecological and high SNRs reflecting everyday communication (with speech intelligibility above 80 percent). Interestingly, in more adverse listening situations where speech intelligibility was reduced, listeners even mobilized more effort with the active NR scheme. This study was part of a PhD project within the LISTEN project. Learn more about the project and the findings here.

The PUPILS project is taking pupillometry from group level to the individual level. The project aims to find out whether the method can be a diagnostic tool for hearing-aid fitting in the future.

The measurement of the pupil dilation, i.e. pupillometry, can be interpreted as a reliable index of listening effort. Within recent years, pupil dilations have been studied extensively as an indicator of the person’s listening effort mobilized for speech perception in a noisy environment. It has been demonstrated that listening effort is affected by speech intelligibility, masker type, hearing impairment, and hearing-aid signal processing. For instance, it was shown that noise-reduction schemes of hearing aids can reduce the listening effort that is spent in ecological valid listening situations. So far, the pupillometry method has mainly been evaluated on a group level, no attempts have been made to evaluate the individual listener’s effort.

 

Project Goals

The PUPILS project aims to examine whether the pupillometry method can be a suitable diagnostic tool for hearing-aid fitting and for testing the benefit of a hearing aid on an individual listener basis.
The transition from a group level towards an individual level of listening effort is not straightforward and provides some challenges since the underlying components affecting the pupillary response are not fully understood yet. To assess the individual pupillary response as an outcome measure of listening effort, the test–retest reliability of the pupillary method will be explored within this project. Different work packages are designed to develop the experimental paradigm and to examine the specificity and sensitivity of the method.

Furthermore, the focus will be on advanced analysis methods, the modeling of the pupillary response and the classification of individual pupil traces. The goal is to identify models that are ultimately feasible for an analysis on an individual basis using a few or even single pupil traces.

The project is performed at DTU, more specifically in close cooperation with Professor Torsten Dau (Hearing Systems) and Per Bækgaard (DTU Compute).

To project is supported by the Oticon Foundation and expected to be completed in 2022.
listenplusfig

Figure 2: PPD (in mm) averaged across a group of people with hearing impairment. NoNR = noise reduction was turned off; NR = NR scheme was turned on. L50 = SNR corresponding to 50% intelligibility; L95 = SNR correspond to 95% speech intelligibility. Figure from Wendt et al., (2017).

Results

Figure 2 shows reduced PPD, and thus a reduced effort mobilization, at both 50 percent and 95 percent speech intelligibility with an active NR scheme. Interestingly, listening effort was reduced in a condition where speech intelligibility was at ceiling. In other words, listening effort was reduced in a situation where people were able to recognize most of the speech even without the hearing aid signal processing. This situation, which was tested at a signal-to-noise-ratio (SNR) that reflects everyday communication, is often referred to as ecological listening conditions. For more detailed information about the study and the results see Wendt et al. 2017.

A second study was performed that also focused on the impact of the signal processing on effort over a broader range of listening situations (i.e. broad range of SNRs). This study demonstrates that listening effort changes in a non-monotonic way as a function of the SNR with maximum effort occurring at approximately 50 percent intelligibility. Furthermore, reduced effort was observed again at ecological and high SNRs reflecting everyday communication (with speech intelligibility above 80 percent). Interestingly, in more adverse listening situations where speech intelligibility was reduced, listeners even mobilized more effort with the active NR scheme. This study was part of a PhD project within the LISTEN project. Learn more about the project and the findings here.

Main findings

Researchers developed a new approach for evaluating the extent to which hearing aids can reduce listening effort. Until now, pure-tone audiometry -sometimes combined with traditional speech recognition measures- has been used for the development of hearing aids. 
Since traditional speech recognition measures lack the sensitivity to be applied under these easier acoustical conditions, such as for speech understanding in quiet or at high Signal-to-Noise Ratios (SNRs), they cannot always adequately be used as an outcome for research on the benefit of a hearing aid. 
Within LISTEN, the pupillometry method was developed further as an alternative form of measurement revealing how listening effort is modulated across the entire range of day-to-day listening situations. From acoustically challenging towards easier listening situations.

Rather than utilizing conditions representing difficult and noisy listening situations in daily life, LISTEN provided knowledge and evidence for more realistic (that is easier and quieter) listening situations. A novel finding was that while hearing aids increase speech understanding in difficult listening situations, they also significantly reduce listening effort under easier listening conditions. 

The underlying mechanisms of the pupil dilation response were further unraveled in studies measuring the pupil light reflex. These studies revealed that an individual’s level of fatigue influences the level of effort one can exert, which revealed a breakthrough in our understanding of the mechanisms behind listening effort and the pupil dilation response.

Learn more

  • learnmore-poster

    Poster

    Analysis of the individual listening effort reflected by the pupillary responses during speech perception in noise
    See poster