Reliability and stability of the metrical stress effect on segmental production accuracy in persons with apraxia of speech

Abstract

Background: Acquired apraxia of speech (AOS) involves speech-production deficits on both the segmental and suprasegmental levels. Recent research has identified a non-linear interaction between the metrical structure of bisyllabic words and word-production accuracy in German speakers with AOS, with trochaic words (strong-weak stress) being resistant to errors compared with iambic words (weak-strong). Aims: To replicate previous findings in English speakers with AOS, to measure the test-retest reliability of the effect, and to examine the potential impact of different methods of word scoring. Methods & Procedures: Speech samples were collected from 27 speakers with AOS and aphasia. Participants were at least 12 months post-stroke or penetrating brain injury, and represented a large range of AOS and aphasia severities. Productions were elicited via verbal model. Sampling was conducted on three separate occasions: the initial data-collection session and then repeated samplings at 1-and 4-week intervals. Bisyllabic words with a CVCVC segmental structure were selected. The list was divided into sublists representing differing lexical stress patterns: A list of 42 trochees, and one of 37 iambs. All speech samples were phonetically transcribed and then aligned with canonical transcriptions via an edit distance algorithm that followed transcription alignment principles. Phonetic-level errors (distortions) were penalized less severely than phonemic-level errors. Per cent consonants correct and whole-word accuracy were also examined. Trochee and iamb lists were analysed separately. Outcomes & Results: Paired samples t-tests indicated that the modified edit distance was significantly lower for the trochee lists than for the iamb lists. There was a lack of a significant effect of time on the absolute difference between modified edit distance for both lists. Intraclass coefficients suggested the list and procedures used are appropriate as an outcome measure for group research. Conclusions & Implications:The results suggest that in English, as in German, the trochaic structure is more resistant to segmental errors in persons with AOS and aphasia, providing replication of the findings of Aichert et al. in 2016. Further, this effect is stable over repeated sampling occasions. Implications for clinical management of AOS include possible ways to scaffold item difficulty and potentially improve stimulus generalization. What this paper addsWhat is already known on the subject Research has previously shown a metrical stress effect on segmental production accuracy in German speakers with AOS. Such non-linear influences on segmental production accuracy provide insight into the speech-production process.What this paper adds to existing knowledge This paper shows a metrical stress effect in bisyllabic word repetition of English speakers with AOS, replicating previous work done with German speakers with AOS. Further, it provides measurements of the test-retest reliability of the measurement tool and the stability of the behaviour across r...

In Time with the Beat: Entrainment in Patients with Phonological Impairment, Apraxia of Speech, and Parkinson’s Disease

“…The effect was small in the healthy participants and the Parkinson’s patients and much larger in the two patient groups with AOS or phonological impairment after left hemisphere lesions, and it was independent of the regularity of the prime sentences. For patients with AOS, this result confirms earlier investigations based on repetition tasks, which revealed an advantage of trochaic over iambic patterns [ 35 , 36 , 37 ]. Furthermore, the results are in agreement with the error data reported from the same experiment for patients with AOS and PI [ 76 ].…”

“…They therefore seemed to exploit natural rhythmic cues in heard speech for the segmental realization of the target words. Furthermore, our study confirmed earlier results showing that the symptoms of AOS can be modulated positively by a regular (trochaic) stress of words to be produced [ 35 , 36 ]. The benefit from the regularity of target words could, for the first time, also be demonstrated in individuals with PI.…”

“…The regular metrical pattern of German (i.e., the trochee) had a facilitating effect on word production in apraxic speakers, with trochees being produced with greater articulatory accuracy and fluency than iambs. This effect was replicated in a more recent study of English-speaking patients with AOS [ 36 ]. Therefore, the vulnerability of speech segments to apraxic impairment strongly interacts with word-level prosody—an observation that is compatible with the NLG model described above [ 37 ].…”

A neurophonetic approach to articulation planning: The case of apraxia of speech

“…Most notably, the iambic patterns led to greater numbers of segmental errors, which pointed at an interlacing of segmental with supra-segmental levels of speech motor planning. This effect has meanwhile been replicated for American English (Bailey, Bunker, Mauszycki, & Wambaugh, 2019). By inference, although most apraxic speech errors surface as segment-bound symptoms, as in the examples (1) above, the source of these errors does not necessarily have to be assigned to the affected phonemes themselves, but can also lie at some higher, e.g., syllabic or metrical level of articulation planning.…”