Mihaela-Beatrice Neagu1, Abigail Anne Kressner1,4, Torsten Dau1, Per Bækgaard3, Helia Relaño Iborra3, Dorothea Wendt1,2
1Department of Health Technology, Technical University of Denmark, Kgs. Lyngby, Denmark
2Eriksholm Research Center, Oticon, Snekkersten, Denmark
Department of Applied Mathematics and Computer Science, Technical University of Denmark, Kgs. Lyngby, Denmark

4Copenhagen Hearing and Balance Center, Rigshospitalet, Copenhagen, Denmark.

The reliability of pupillometry as an indicator of listening effort (LE) has previously been shown to be higher than that of other physiological and subjective measures (e.g., NASA Task Load Index – NASA TLX) of LE. Previous studies have examined pupil dilation during a speech-in-noise test as a function of signal-to-noise ratio (SNR) on a group level, reporting an increase in pupil size with decreasing SNR (indicating an increase in LE) until very challenging SNRs are reached, after which the pupil size then decreases (indicating disengagement). However, most of these studies analyzed the effects on a group level rather than individually, and furthermore, none have actually reported the dynamic range of the pupil response with changing SNR. The present study examined the change in the pupil response for a given change in SNR (ΔSNR) at the individual listener level. Specifically, the pupil dilation of 31 normal-hearing listeners was recorded while performing a speech-in-noise test at SNRs ranging from -12 dB to 4 dB in two separate visits, while 11 of the listeners were also tested in a third visit. The dynamic range of different pupil features (peak pupil dilation, PPD, and mean pupil dilation, MPD) are subsequently analyzed as a function of ΔSNR using logistic regressions and compared to the dynamic range of a subjective measure (NASA TLX) as a reference. Additionally, this study examines the reliability of the observed dynamic range across visits. Overall, the results of this study aim to provide insights into changes in individuals’ LE by assessing the dynamic range of the pupil response for a given ΔSNR as compared to a more subjective measure of LE. Understanding these aspects is important for the development of pupillometry towards a standardized tool to assess individual LE for rehabilitation purposes.