Investigating the Effects of Rhythm and Entrainment on Fluency in People With Aphasia

Aphasia is an acquired language disorder, most commonly due to stroke. It can affect an individual's ability to speak, understand spoken language, read, and write. Many treatments designed to improve spoken language in persons with aphasia (PWAs) use unison speech, having the person with aphasia speak along with the clinician or with a recording. One goal of this study is to determine who benefits from speaking in unison, and what characteristics of speech help them the most. Another goal is to investigate a possible mechanism for this benefit: why does speaking in unison help? 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 so it can be as effective and efficient as possible. 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: each speaker must plan their own speech motor commands before having heard the other speaker say the words they are planning. Natural conversational timing requires the speaker to make use of knowledge about language, particularly grammar, to align with the other person. In contrast, a metrical pattern allows a speaker to predict speech timing without relying heavily on language-based knowledge. Given that many PWAs have impaired grammar, we hypothesize that most PWAs will benefit more from speaking in unison to sentences with metrical vs. conversational timing patterns. However, there is great variation in linguistic, motor speech, and timing skills across PWAs, so metrical and conversational timing patterns are likely to have different degrees of effectiveness for different 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. Results will also indicate whether a speaker's ability to predict speech timing is necessary for a benefit of unison speech. Prediction ability will be measured by how closely the speaker aligns their speech with a spoken model.