Do phonological neighbourhood density and phonotactic probability influence speech output accuracy in acquired speech impairment?

Abstract

Background: Among the many factors that may affect speech production, phonological neighbourhood density (ND) and phonotactic probability (PROB) have displayed effects on speech and language performance in healthy speakers. It is not clear if they show an effect in impaired speech output after stroke and if they do whether this is facilitatory or inhibitory. Aims: To determine whether ND and/or PROB play a role in speech production accuracy in acquired output impairment after stroke. Methods & Procedures: A total of 20 English native speakers with acquired spoken output impairment after stroke repeated 906 single-word stimuli. They included real and nonsense words varying in syllable structure, length, and complexity, as well as syllable and word frequency, ND, and PROB. Responses were transcribed phonetically and scored as either correct or incorrect. Logistic regression analyses were completed for each speaker separately to determine the effects of ND and PROB on repetition accuracy in relation to controlled variables. Outcomes & Results: A total of 14 speakers showed a positive effect of PROB on repetition accuracy. Only two individuals displayed a positive effect of ND. No double dissociations regarding the effect of ND and PROB were noted. Conclusions: ND does not appear to have a significant independent effect on repetition accuracy in speakers with acquired output impairment after stroke. By contrast PROB has a positive effect on repetition accuracy in impaired speakers, but does not appear to be a major determinant of output accuracy. Results are discussed in relation to study design and future work to further examine issues around ND and PROB and their possible role in clinical differential diagnosis of output disorders.