The effects of unison production on speech fluency in people with aphasia

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Many treatments designed to improve spoken output in persons with aphasia (PWAs) incorporate unison speech, having the person with aphasia speak along with the clinician or with a recording. The goal of this study is to determine the individual and stimulus characteristics that predict the degree of benefit from speaking in unison, and to investigate a possible mechanism for this benefit. This knowledge is important because understanding who benefits from this commonly used and potentially powerful therapy component, under which conditions they benefit, and why they do, is critical for customizing therapy for maximum therapeutic efficiency. Unison speech is conducted using one of two different timing patterns: (1) a natural conversational pattern, which is used in everyday conversations, or (2) a metrical pattern, which follows a beat-based timing framework, as in songs or some poems. In either case, precisely aligning one’s speech with that of another person (i.e., entraining one’s speech) requires prediction: motor commands must be formulated before the corresponding input from the other person has been heard and processed. While natural conversational timing requires the speaker to make use of syntactic knowledge to align with the other person, a metrical pattern allows a speaker to predict speech timing without relying heavily on syntactic knowledge. Given that many PWAs have an impaired ability to process syntax (i.e., agrammatism), we hypothesize that most PWAs will benefit more from speaking in unison to sentences with metrical vs. conversational timing patterns. However, there is great heterogeneity in linguistic, motor speech, and timing skills across PWAs, so metrical and conversational timing patterns are likely to have different degrees of effectiveness across individuals. Results from this study will demonstrate how individual characteristics and speech timing affect whether or not a person with aphasia benefits from speaking in unison, and will test whether predictive processing, as evidenced by true speech entrainment, is necessary for a benefit of unison speech production to be realized.