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

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)

Phonological priming in apraxia of speech and aphasia

This study investigated speech planning in people with aphasia, people with apraxia of speech (AOS), and control speakers using a priming task in which participants name pictures in sets that do or do not share form properties. Two hypotheses were tested: (1) patients with AOS have an impairment in retrieving metrical frames (number of syllables, stress pattern); (2) patients with aphasia have an impairment in retrieving segments. Findings to date (from one patient with AOS and aphasia) suggest interference rather than facilitation. Theoretical and clinical implications will be discussed

A process-oriented approach to differential diagnosis and treatment planning of pediatric speech sound disorders

De classificatie en differentiaaldiagnose van spraakontwikkelingsstoornissen is nog altijd een controversieel thema. De verschillende diagnostische categorieën zijn gedefinieerd op procesniveau, in termen van het cognitieve proces waar de kern van de onderliggende stoornis zich bevindt, en ook de meeste behandelmethoden zijn gericht op verschillende delen van het spraakproductieproces. In de klinische praktijk wordt de differentiaaldiagnose echter gebaseerd op gedragssymptomen, met methoden die bovendien vaak niet gestandaardiseerd en/of genormeerd zijn.Het diagnostische dilemma is dat het onderzoek naar de gedragskarakteristieken van de verschillende subtypes afhankelijk is van ‘zuivere’ casussen geselecteerd op basis van niet-ambigue, helder afgebakende criteria, die echter alleen gedefinieerd en beschikbaar gemaakt kunnen worden als resultaat van onderzoek naar a priori ongedefineerde casussen. In dit paper bespreken we een procesgerichte aanpak van differentiaaldiagnose en indicatiestelling gebaseerd op drie onderzoekslijnen waarmee die circulariteit doorbroken kan worden. De kern van de aanpak bestaat uit drie belangrijke punten/inzichten:Waar gedragssymptomatologie onduidelijk is, is het wel mogelijk om op procesniveau specifieke problemen in deelprocessen helder te definiëren. (Een focus op onderliggende processen in plaats van classificatie op basis van gedragssymptomen.)Processen beïnvloeden elkaar: een stoornis op één procesniveau beïnvloedt het functioneren en de ontwikkeling van andere processen. (Een focus op procesprofielen met gradaties van betrokkenheid.)Spraakproductiesysteem en -stoornis ontwikkelen zich. (Een focus op het veranderen van procesprofielen.)Op basis van deze inzichten opperen we een model van differentiaaldiagnose en therapieplanning voor spraakstoornissen bij kinderen dat ─naast vloeiendheidsstoornis─ bestaat uit twee algemene diagnostische categorieën: spraakachterstand en spraakontwikkelingsstoornis. Binnen deze categorieën worden vervolgens op procesniveau de behandeldoelen geformuleerd. Deze procesgeoriënteerde aanpak van diagnose en therapieplanning heeft belangrijke voordelen. In tegenstelling tot diagnostische classificatie op basis van gedragssymptomen biedt het directe aanknopingspunten voor een dynamisch behandelplan op maat; een behandelplan afgestemd op de specifieke tekortkoming(en) van het individu dat continue wordt geëvalueerd en bijgesteld gedurende het verloop van de spraakstoornis. Aan de hand van een voorbeeld wordt geïllustreerd hoe een dergelijke aanpak er in de praktijk uit kan zien.The classification and differentiation of paediatric speech sound disorders (SSD) remains a controversial issue. The definitions used in classifying childhood SSD and motor speech disorders (MSD) refer to speech production processes, and accordingly a variety of methods of intervention has been developed aiming at different parts of the speech production process. However, diagnosis in clinical practice is primarily based on behavioural speech symptoms rather than the underlying deficits. The diagnostic dilemma is that the ability to investigate the characteristics of subtypes of SSD requires &amp;#39;pure&amp;#39; cases selected on the basis of unambiguous/clear-cut criteria. These criteria can only be defined and made available as a result of research (into a priori undefined /undetermined cases). In this paper we propose a process-oriented approach to diagnosis and treatment planning of paediatric SSD based on three pillars of research that will allow us to break through this circularity. The core of this approach comprises three important notions: 1. Although the behavioural symptomatology of paediatric SSD&amp;#39;s is not completely clear, it is possible to precisely define a specific core problem in terms of processes. (A focus on underlying processing deficits rather than classification based on symptoms.) 2. Developmental interaction between processes: a specific underlying impairment on one level or domain also affects the development on adjacent levels or domains. (A focus on process profiles with degrees of involvement.) 3. The speech production system and -disorder develop/evolve in time. (A focus on changing profiles.) Based on these three notions,we propose a model of differential diagnosis and treatment planning for childhood speech disorders that - besides &amp;quot;fluency disorder&amp;quot; - comprises two general diagnostic categories labelled &amp;quot;speech delay&amp;quot; and &amp;quot;developmental speech disorder&amp;quot;. Within these categories, treatment goals are formulated on the level of processes. This process-oriented approach to diagnosis and treatment planning holds important advantages. In contrast to diagnostic classification based on a description ofbehavioural symptoms, it offers direct leads for treatment aimed at the specific underlying impairment tailored to the specific needs of the individual that is evaluated and adjusted in the course of the speech disorder. The approach is illustrated with an example.</p

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