The Influence of Speech Material, Intelligibility, and Masker Type on the Pupil Dilation Response in Cochlear Implant Users

The intelligibility conditions in this study did not result in any measurable differences in listening effort, as indicated by the pupil dilation responses of unilateral or bimodal postlingually deafened CI users for everyday sentences or CVC words. A main effect of intelligibility condition on PPD was only found for digit triplets. Speculatively, this may be because the relative simplicity and low cognitive load evoked by this speech material allowed intelligibility effects to become apparent in this specific group of listeners. Subjective ratings indicated greater listening effort, difficulty, and a tendency to give up at lower intelligibility levels. When sentences were masked with an interfering speaker, both PPD and subjective listening effort increased compared with masking with continuous noise. These findings suggest that manipulating masker type can alter the pupil dilation response and perceived listening effort in CI users, even when using everyday sentences.