Intelligibility is Just a Piece of the Communication Puzzle: Increased Listening Effort During Dysarthric Speech Perception

Purpose: The research aims of this study are to determine whether listening effort, as measured by pupil dilation and perceived listening effort (PLE) ratings, depends on whether the speech is produced by a speaker with dysarthria versus a neurotypical speaker, and whether the listener successfully perceived the spoken phrase.Method: Thirty-four listeners completed a speech perception task while an eye-tracking camera tracked their pupil dilation. Phrases in the speech perception task were produced by a speaker with dysarthria secondary to amyotrophic lateral sclerosis (ALS) and a neurotypical speaker. After hearing each phrase, listeners repeated what they heard and rated PLE on a 7-point Likert scale. Phrase repetition accuracy (accurate vs. inaccurate) was determined from their verbal response. Generalized additive mixed-models (GAMMs) were used to evaluate the relationship of the speaker type (dysarthria vs. neurotypical), phrase repetition accuracy and their interaction with pupil dilation. PLE ratings were similarly evaluated using linear mixed-effects (LME) models.Results: Both pupil dilation and PLE ratings were greater when presented with the phrases produced by speaker with dysarthria relative to the neurotypical speaker, even when the phrase was accurately perceived by the listener. Inaccurately perceived phrases, compared to accurately perceived ones, were also associated with greater pupil dilation and PLE ratings. Interaction effects were revealed between speaker type and phrase repetition accuracy for pupil dilation but not for PLE ratings. Additionally, pupil dilation results indicated that the allocation of effort over time differed between the trials produced by the dysarthric and neurotypical speakers.Conclusions: The results suggest listening effort is increased overall when listening to dysarthric speech compared to neurotypical speech, even when intelligibility is preserved. Although there was some overlap in the results for the pupil dilation and PLE ratings, notable differences suggest these measures are likely sensitive to distinct factors influencing listening effort.