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.