Listening effort under three types of auditory masking conditions, as measured by pupillometry, in young normal-hearing listeners
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Auditory maskers, whether intelligible speech or unintelligible noise, can make it difficult to hear and/or process a target sentence. These maskers can present challenges to peripheral processing as well as central processing. Change in pupil size is a physiological index of listening effort and can be measured using eye tracking technology. The aim of the study was to compare listening effort, as measured by changes in pupil size in individuals with normal hearing, between the conditions of Intelligible Speech Masker (ISM), Speech Shaped, Speech Envelope-Modulated Noise Maskers (SSSNM), and Stationary Noise Masker (SNM). Spatial separation between target and maskers was used throughout all conditions. The study design used adaptive tracks that varied the Target to Masker Ratios (TMRs) in each of the 3 conditions in order to identify the TMR corresponding to the 75% correct point on the psychometric function for each participant. Once the TMR corresponding to the 75% correct point was identified, this TMR was held constant for 24 trials while pupil size was recorded. The results show that the ISM condition elicited a higher degree of listening effort compared to either of the noise conditions (SNM and SSSNM). These results reveal that more effort is required to ignore background speech than to ignore background noise at equivalent TMRs. Understanding the amount of effort that young, normal-hearing listeners must exert in these different types of situations will provide a foundation for later measuring the amount of effort that individuals with hearing loss and/or cognitive-linguistic deficits (e.g., aphasia) must exert in the same situations.