Speech intelligibility in ALS and HD dysarthria: Everyday listener perspectives of barriers and strategies

The purpose of this study was to examine the barriers and strategies that listeners identify as they attempt to understand specific types of dysarthric speech. Speech samples were collected from speakers with dysarthria associated with amyotrophic lateral sclerosis (ALS) and dysarthria associated with Huntington Disease (HD). Samples included sentences ranging from 5–15 words in length and were between 60–90% intelligible. Focus groups of everyday listeners hear the samples and after transcribing them were asked to share their experiences regarding barriers to intelligibility and strategies for listening. Content analysis suggested that barriers and strategies fell into four distinct groups, segmental barriers and strategies (phonetic information), suprasegmental barriers and strategies (prosodic information), linguistic barriers (contextual information) and cognitive barriers and strategies (listener attention and effort). Based on this analysis, two scales (one for barriers and one for strategies) each containing 24 items were developed. These scales were presented to 37 everyday listeners who rated ALS and HD speech samples on a four-point equal interval scale. Scale scores reflecting level of item endorsement were averaged across listeners to ascertain the most prominent barriers and strategies for each type of dysarthria.; Results indicated that barriers to intelligibility vary as a function of the dysarthria type. Listeners indicated stronger endorsement for segmental, linguistic, and cognitive barriers for the ALS sentences as compared to the HD sentences. Strategies for listening also vary as a function of dysarthria type. The level of strategy endorsement was consistently high for both dysarthria types. In addition, results suggested that barriers and strategies vary as a function of sentence length and intelligibility. The longer more intelligible sentences received higher levels of endorsement of both barriers and strategies than the shorter less intelligible sentences, indicating that shorter sentences may be inadequate of listeners to identify barriers to intelligibility and strategies for listening. Results support the early perceptual descriptions of dysarthria (Darley, Aronson, & Brown, 1975) in that listeners distinguished various types of dysarthria based on barriers to intelligibility. In addition, results indicate that both bottom-up (phoneme-based) and top-down (linguistically based) processing are endorsed as strategies to understand distorted speech in dysarthria.