Impaired speech production is a major obstacle to full participation in life roles by stroke survivors with aphasia and apraxia of speech. The proposed study will demonstrate the short-term effects of auditory masking on speech disfluencies and identify individual factors that predict a positive response, enabling future work to develop auditory masking as a treatment adjuvant targeting long-term improvement in speech. Providing an additional treatment option for adults with aphasia and apraxia of speech will have the clear benefit of improving quality of life and allowing individuals to participate more actively in their health care decisions through improved communication.

The objective of this research is to test the short-term effects of listening to noise (i.e. auditory feedback masking) on speech fluency in stroke survivors with aphasia and apraxia of speech. People with nonfluent types of aphasia frequently have apraxia of speech, which affects the motor programming of speech movements, causing distortions, slow rate, and speech disfluencies that impede the forward flow of communication. Speaking while listening to noise (e.g. auditory masking) is known to reduce disfluencies and increase speech rate in people who stutter. This method has been tested in people with aphasia, resulting in positive effects on speech production for a subset of those tested. The investigators contend that individuals who have apraxia of speech in addition to aphasia are most likely to benefit from auditory masking, but most previous studies did not test participants for apraxia of speech. In addition, though masking is most likely to affect speech disfluencies, previous studies did not measures disfluencies. The proposed work has two specific aims. Aim 1 will determine the short-term effect of auditory masking, provided on a single day, on speech fluency in stroke survivors with aphasia and apraxia of speech. Aim 2 will identify individual factors that predict a positive response, including presence of apraxia of speech, lesion characteristics, and type of aphasia (e.g. Broca's, Wernicke's). Voxel-based lesion analysis techniques will be used to determine sites of lesion associated with positive and negative response to auditory masking. Completion of this study will remove barriers to studying auditory masking as a technique for clinical intervention, but also as a research tool for behavioral neuroscientists probing the speech motor control system in speakers with aphasia and apraxia of speech.

Inclusion Criteria for Aphasic/Apraxic Participants:

• Single left-hemisphere cerebrovascular accident
• Speech errors are present, but participant is able to produce approximations of words or sentences by reading or repetition; < 90% and > 10% on Chapel Hill Multilingual Intelligibility Test (Haley, 2011)
• Right-handed prior to stroke by report
• Normal visual attention, acuity, and color vision
• Pure-tone threshold <= 40 decibels in at least one ear

Exclusion Criteria for Aphasic/Apraxic Participants:

• Predominating disorders of cognition or hearing (e.g. dementia, hearing impairment).
• Presence of degenerative neurological illness (e.g. Parkinson's disease, amyotrophic lateral sclerosis, primary progressive aphasia).

Inclusion Criteria for Neurologically Healthy Participants:

• Matched in age and sex to a participant with aphasia
• score of 90% or higher on the single-word intelligibility test
• Right-handed prior to stroke by report
• Normal visual attention, acuity, and color vision
• Pure-tone threshold <= 40 decibels in at least one ear

Exclusion Criteria for Neurologically Healthy Participants:

• History of stroke
• History of developmental speech or language disorder

Participants with aphasia (PWA) will be referred from existing referral sources (e.g. UNC Stroke registry, Triangle Aphasia Project), clinicians in the community, and the Carolina Data Warehouse for Health.