Apraxia of Speech: Impaired Access to Motor Programs or Damaged Motor Programs?

Definitions of apraxia of speech (AOS) describe this motor speech disorder as an impairment in planning and programming of speech movements (Duffy, 2005). The exact underlying mechanism of the impairment, however, is not well understood. The purpose of this investigation is to specify the speech planning impairment in AOS by testing two specific hypotheses framed in the DIVA model (Guenther, 2006)

Feedforward and feedback control in apraxia of speech: effects of noise masking on vowel production

PURPOSE: This study was designed to test two hypotheses about apraxia of speech (AOS) derived from the Directions Into Velocities of Articulators (DIVA) model (Guenther et al., 2006): the feedforward system deficit hypothesis and the feedback system deficit hypothesis. METHOD: The authors used noise masking to minimize auditory feedback during speech. Six speakers with AOS and aphasia, 4 with aphasia without AOS, and 2 groups of speakers without impairment (younger and older adults) participated. Acoustic measures of vowel contrast, variability, and duration were analyzed. RESULTS: Younger, but not older, speakers without impairment showed significantly reduced vowel contrast with noise masking. Relative to older controls, the AOS group showed longer vowel durations overall (regardless of masking condition) and a greater reduction in vowel contrast under masking conditions. There were no significant differences in variability. Three of the 6 speakers with AOS demonstrated the group pattern. Speakers with aphasia without AOS did not differ from controls in contrast, duration, or variability. CONCLUSION: The greater reduction in vowel contrast with masking noise for the AOS group is consistent with the feedforward system deficit hypothesis but not with the feedback system deficit hypothesis; however, effects were small and not present in all individual speakers with AOS. Theoretical implications and alternative interpretations of these findings are discussed.R01 DC002852 - NIDCD NIH HHS; R01 DC007683 - NIDCD NIH HH

Feedback and Feedforward Control in Speech Production in Apraxia of Speech and Aphasia

Apraxia of speech (AOS) is considered to be a speech motor planning impairment (e.g., McNeil et al., 2009), but the nature of this impairment remains poorly understood. The present study was designed to test two hypotheses about the nature of AOS, framed in the DIVA model (Guenther et al., 2006). The DIVA model assumes that speech targets are regions in auditory space, and combines two control mechanisms to reach those targets: feedback control and feedforward control. The feedback mechanism generates corrective motor commands when the actual speech sound deviates from the intended speech sound. The feedforward mechanism generates predictive motor commands based on past experiences with the speech target. In the context of the DIVA model, we developed two hypotheses about possible underlying deficits in AOS. The Feedforward Control Impairment (FF) hypothesis states that feedforward control is impaired in AOS, with consequently a greater reliance on feedback control (Jacks, 2008). The Feedback Control Impairment (FB) hypothesis states that feedback control is impaired in AOS; concurrent feedback may be disruptive (cf. Ballard & Robin, 2007). We tested these hypotheses by measuring acoustic vowel contrast in two conditions: normal listening and auditory feedback masking. Under masking conditions, unimpaired speakers maintain segmental contrast (suggesting adequate feedforward commands to support speech without auditory feedback) even though contrast is somewhat reduced (suggesting on-line use of auditory feedback) (Perkell et al., 2007). The FF hypothesis predicts a greater reduction of segmental contrast with feedback masking in speakers with AOS than in controls, because effective removal of the auditory feedback control strategy will reveal the impaired feedforward commands. The FB hypothesis, in contrast, predicts increased segmental contrast with feedback masking, because removal of auditory feedback will allow the intact feedforward commands to produce adequate contrasts. One previous study that used feedback masking in AOS examined vowel duration and found longer vowels with masking in AOS and controls (Rogers et al., 1996); the present study also examined vowel duration

Feedback and feedforward control in apraxia of speech: Noise masking effects on fricative production

The present study tested two hypotheses about apraxia of speech (AOS), framed in the DIVA model (Guenther, Ghosh, & Tourville, 2006). The DIVA model assumes that speech targets are regions in auditory space, and combines two mechanisms to reach those targets: feedback control and feedforward control. The Feedforward System Deficit (FF) hypothesis states that feedforward control is impaired in AOS, with consequently a greater reliance on feedback control (Jacks, 2008; Maas, Mailend, & Guenther, 2013). The Feedback System Deficit (FB) hypothesis states that feedback control is impaired in AOS; for example, self-generated auditory feedback may be disruptive (cf. Ballard & Robin, 2007). We tested these hypotheses by measuring acoustic fricative contrast in normal listening and noise masking conditions. The rationale is that noise masking effectively eliminates the self-generated auditory feedback signal, thus forcing a greater reliance on feedforward control. For unimpaired speakers, we predict a reduction in acoustic contrast, given evidence that speakers monitor and use auditory feedback on-line (e.g., Tourville, Reilly, & Guenther, 2008), though this reduction is expected to be small given the robust feedforward commands presumably available to unimpaired speakers (e.g., Perkell, 2012). For speakers with AOS, the FF hypothesis predicts greater reduction of contrast with masking in AOS patients than in controls, because removal of auditory feedback will reveal the impaired feedforward commands. The FB hypothesis predicts increased contrast with feedback masking, because removal of interfering auditory feedback enables intact feedforward commands to produce adequate contrasts

Individual Versus Small Group Treatment of Morphological Errors for Children With Developmental Language Disorder

Purpose: This study examines the effects of enhanced conversational recast for treating morphological errors in preschoolers with developmental language disorder. The study assesses the effectiveness of this treatment in an individual or group (n = 2) setting and the possible benefits of exposing a child to his or her partner's treatment target in addition to his or her own. Method: Twenty children were assigned to either an individual (n = 10) or group (n = 10, 2 per group) condition. Each child received treatment for 1 morpheme (the target morpheme) for approximately 5 weeks. Children in the group condition had a different target from their treatment partner. Pretreatment and end treatment probes were used to compare correct usage of the target morpheme and a control morpheme. For children in the group condition, the correct usage of their treatment partner's target morpheme was also examined. Results: Significant treatment effects occurred for both treatment conditions only for morphemes treated directly (target morpheme). There was no statistically significant difference between the treatment conditions at the end of treatment or at follow-up. Children receiving group treatment did not demonstrate significant gains in producing their partner's target despite hearing the target modeled during treatment. Conclusions: This study provides the evidence base for enhanced conversational recast treatment in a small group setting, a treatment used frequently in school settings. Results indicate the importance of either attention to the recast or expressive practice (or both) to produce gains with this treatment.acceptedVersio

Benefit of visual speech information for word comprehension in post-stroke aphasia

Aphasia is a language disorder that often involves speech comprehension impairments affecting communication. In face-to-face settings, speech is accompanied by mouth and facial movements, but little is known about the extent to which they benefit aphasic comprehension. This study investigated the benefit of visual information accompanying speech for word comprehension in people with aphasia (PWA) and the neuroanatomic substrates of any benefit. Thirty-six PWA and 13 neurotypical matched control participants performed a picture-word verification task in which they indicated whether a picture of an animate/inanimate object matched a subsequent word produced by an actress in a video. Stimuli were either audiovisual (with visible mouth and facial movements) or auditory-only (still picture of a silhouette) with audio being clear (unedited) or degraded (6-band noise-vocoding). We found that visual speech information was more beneficial for neurotypical participants than PWA, and more beneficial for both groups when speech was degraded. A multivariate lesion-symptom mapping analysis for the degraded speech condition showed that lesions to superior temporal gyrus, underlying insula, primary and secondary somatosensory cortices, and inferior frontal gyrus were associated with reduced benefit of audiovisual compared to auditory-only speech, suggesting that the integrity of these fronto-temporo-parietal regions may facilitate cross-modal mapping. These findings provide initial insights into our understanding of the impact of audiovisual information on comprehension in aphasia and the brain regions mediating any benefit

Benefit of Visual Speech Information for Word Comprehension in Post-stroke Aphasia

Aphasia is a language disorder that often involves speech comprehension impairments affecting communication. In face-to-face settings, speech is accompanied by mouth and facial movements, but little is known about the extent to which they benefit aphasic comprehension. This study investigated the benefit of visual information accompanying speech for word comprehension in people with aphasia (PWA) and the neuroanatomic substrates of any benefit. Thirty-six PWA and 13 neurotypical matched control participants performed a picture-word verification task in which they indicated whether a picture of an animate/inanimate object matched a subsequent word produced by an actress in a video. Stimuli were either audiovisual (with visible mouth and facial movements) or auditory-only (still picture of a silhouette) with audio being clear (unedited) or degraded (6-band noise-vocoding). We found that visual speech information was more beneficial for neurotypical participants than PWA, and more beneficial for both groups when speech was degraded. A multivariate lesion-symptom mapping analysis for the degraded speech condition showed that lesions to superior temporal gyrus, underlying insula, primary and secondary somatosensory cortices, and inferior frontal gyrus were associated with reduced benefit of audiovisual compared to auditory-only speech, suggesting that the integrity of these fronto-temporo-parietal regions may facilitate cross-modal mapping. These findings provide initial insights into our understanding of the impact of audiovisual information on comprehension in aphasia and the brain regions mediating any benefit

Speech Motor Planning in Apraxia of Speech and Aphasia

Apraxia of speech (AOS) is a motor speech disorder that poses significant obstacles to a person's ability to communicate and take part in everyday life. Agreement exists between current theories of AOS that the impairment affects the speech motor planning stage, where linguistic representations are transformed into speech movements, but they disagree on the specific nature of the breakdown at this processing level. A more detailed understanding of this impairment is essential for developing targeted, effective treatment approaches and for identifying the appropriate candidates for these treatments. The study of AOS is complicated by the fact that this disorder rarely occurs in isolation but is commonly accompanied by various degrees of aphasia (a language impairment) and/or dysarthria (a neuromuscular impairment of speech motor control). In addition, the behavioral similarities of AOS and its closest clinical neighbor, aphasia with phonemic paraphasias, undermine the usefulness of traditional methods, such as perceptual error analysis, in the study of both disorders. The purpose of this dissertation was to test three competing hypotheses about the specific nature of the speech motor planning impairment in AOS in a systematic sequence of three reaction time experiments. This research was formulated in the context of a well-established theoretical framework of speech production and it combines psycholinguistic reaction time paradigms with a cognitive neuropsychological approach. The results of the three experiments provide evidence that one component of the speech motor planning impairment in AOS involves difficulty with selecting the intended motor program for articulation. Furthermore, this difficulty appears to be intensified by simultaneously activated alternative speech motor programs that compete with the target program for selection. These findings may prove useful as a theoretically-motivated basis for improving diagnostic tools and treatment protocols for people with AOS and aphasia, thus enhancing clinical decision-making. Such translational and clinical research aimed at developing sensitive and specific diagnostic tools and improving treatment approaches is the ultimate long-term objective of this research program

Group and individual data for all variables; detailed information about individual children (Maas & Mailend, 2017)

Supplemental Material S2. Group and individual data for all variables.<div><br></div><div>Supplemental Material S3. Detailed information about individual children, including precise <i>p </i>values and effect sizes with 95% credible intervals. </div><div><br></div><div><div>"The focus of this study was on fricative contrast and anticipatory CV coarticulation, as indexed by acoustic measures obtained from the first spectral moment (m1) at three points during the fricative (onset, midpoint, offset). Acoustic measures were based on tokens in which both fricative and vowel were perceptually accurate. Accuracy was judged from audio recordings by a native English listener and verified by the first author (a near-native speaker with 20+ years of phonetic training). Acoustic analyses were performed using Praat (Boersma & Weenink, 2008)."</div><div><br></div><div>See also Supplemental Material S1: https://doi.org/10.23641/asha.5103070</div><div><br></div><div>Maas, E., & Mailend, M. L. (2017). Fricative contrast and coarticulation in children with and without speech sound disorders. <i>American Journal of Speech-Language Pathology, 26</i>(2S), 649–663.</div></div><div><br></div

Analysis results for error rate, duration, and spectral mean (Maas & Mailend, 2017)

Supplemental Material S1. Group means and standard deviations for error rate, duration median, and m1 median, by target and timepoint, are provided in a table; analysis results are described, including ANOVA interactions, <i>p </i>values, and significant/not significant effects. Provided figure shows group data for spectral mean, by target and timepoint, for adults vs. TD6 vs. TD9, TD6 vs. SSD6, and TD9 vs. SSD9.<div><br></div><div>"The focus of this study was on fricative contrast and anticipatory CV coarticulation, as indexed by acoustic measures obtained from the first spectral moment (m1) at three points during the fricative (onset, midpoint, offset). Acoustic measures were based on tokens in which both fricative and vowel were perceptually accurate. Accuracy was judged from audio recordings by a native English listener and verified by the first author (a near-native speaker with 20+ years of phonetic training). Acoustic analyses were performed using Praat (Boersma & Weenink, 2008)."<br></div><div><br></div><div>See also Supplemental Materials S2 and S3: https://doi.org/10.23641/asha.5106508</div><div><br></div><div>Maas, E., & Mailend, M. L. (2017). Fricative contrast and coarticulation in children with and without speech sound disorders. <i>American Journal of Speech-Language Pathology, 26</i>(2S), 649–663.</div