Eye movements of younger and older adults decrease during story listening in background noise

Assessments of listening effort are increasingly relevant to understanding the speech-comprehension difficulties experienced by older adults. Pupillometry is the most common tool to assess listening effort but has limitations. Recent research has shown that eye movements decrease when listening is effortful and proposed indicators of eye movements as alternative measures. However, much of the work was conducted in younger adults in trial-based sentence-listening paradigms during concurrent visual stimulation. The extent to which eye movements index listening effort during continuous speech listening, independently of visual stimuli, and in older adults, is unknown. In the current study, younger and older adults listened to continuous stories with varying degrees of background noise under free and moving-dots viewing conditions. Eye movements decreased (as indexed by fixation duration, gaze dispersion, and saccade rate) with increasing speech masking. The reduction in eye movements did not depend on age group or viewing conditions, indicating that eye movements can be used to assess effects of speech masking in different visual situations and in people of different ages. The pupil size was only sensitive to speech masking early in the experiment. In sum, the current study suggests that eye movements are a potential tool to assess listening effort during continuous speech listening.