Impact of stimulus-related and listener-related factors on cognitive processing load as indicated by pupil dilation

This study investigated the influence of stimulus-related factors such as speech intelligibility level and masker types and listener-related factors, including cognitive abilities and hearing status, on the pupil dilation during speech perception. Pupil diameter was recorded during the speech recognition task across a wide range of intelligibility levels in hearing-impaired (N=29) and normal-hearing (N=34) listeners. Sentences were presented in quiet, in a stationary masker, and in the presence of a competing talker. Two aged-matched groups of listeners, one with symmetrical, sensorineural, mild-to-moderate hearing loss and one with normal-hearing thresholds, participated in this study. Hearing-impaired listeners received frequency-specific amplification to compensate for reduced audibility. We measured individual working memory capacity and linguistic abilities. Final results will be presented at the conference as this study is still ongoing. Based on findings from previous research, an interaction between speech-intelligibly, masker types, hearing status and peak pupil dilation relative to baseline (PPD) is expected (Kramer et al., 1997; Zekveld et al., 2011). A systematical increase in PPD with decreasing intelligibility is hypothesized. We expect hearing-impaired listeners to show larger pupil dilations for speech recognition in the interfering talker condition compared to the stationary noise background (such as Koelewijn et al., 2014). Moreover, a smaller task-evoked PPD is expected to be found for the hearing-impaired listeners compared to listeners with normal-hearing and for listeners with poorer cognitive abilities compared to those with better cognitive skills (as proposed by Grady, 2012; Zekveld et al., 2011). The results of this study will help to better understand how stimulus-related factors, such as speech intelligibility level and masker type, and listener-related factors, like cognitive skills and hearing abilities, influence cognitive processing load as indexed by the PPD.