Phonological simplifications, apraxia of speech and the interaction between phonological and phonetic processing

Abstract

Research on aphasia has struggled to identify apraxia of speech (AoS) as an independent deficit affecting a processing level separate from phonological assembly and motor implementation. This is because AoS is characterized by both phonological and phonetic errors and, therefore, can be interpreted as a combination of deficits at the phonological and the motoric level rather than as an independent impairment. We apply novel psycholinguistic analyses to the perceptually phonological errors made by 24 Italian aphasic patients. We show that only patients with relative high rate (>10%) of phonetic errors make sound errors which simplify the phonology of the target. Moreover, simplifications are strongly associated with other variables indicative of articulatory difficulties - such as a predominance of errors on consonants rather than vowels - but not with other measures - such as rate of words reproduced correctly or rates of lexical errors. These results indicate that sound errors cannot arise at a single phonological level because they are different in different patients. Instead, different patterns: (1) provide evidence for separate impairments and the existence of a level of articulatory planning/programming intermediate between phonological selection and motor implementation; (2) validate AoS as an independent impairment at this level, characterized by phonetic errors and phonological simplifications; (3) support the claim that linguistic principles of complexity have an articulatory basis since they only apply in patients with associated articulatory difficulties.

Identification and Remediation of Phonological and Motor Errors in Acquired Sound Production Impairment

“…From a clinical perspective, this issue has primarily been addressed in the literature on the differential diagnosis of apraxia of speech (AOS) and phonemic paraphasia (McNeil, Robin, & Schmidt, 2009;Wambaugh, Duffy, McNeil, Robin, & Rogers, 2006a) and in studies on the treatment of these deficits (Ballard et al, 2015;Wambaugh, Duffy, McNeil, Robin, & Rogers, 2006b). From a neurocognitive perspective, the focus has been on identifying the mechanisms involved in phonological processing and motor planning (Buchwald & Miozzo, 2011, 2012Galluzzi, Bureca, Guariglia, & Romani, 2015;Laganaro, 2012;Levelt, Roelofs, & Meyer, 1999;Ziegler & Aichert, 2015;Ziegler, Staiger, & Aichert, 2010).…”

Integrating SLAM with existing evidence: Comment on Walker and Hickok (2015)

“…A number of studies have documented individuals that violate this prediction (Galluzzi, Bureca, Guariglia, & Romani, 2015;Goldrick & Rapp, 2007;Romani & Galluzzi, 2005;Romani, Galluzzi, Bureca, & Olson, 2011;Romani, Olson, Semenza, & Granà, 2002). Furthermore, the errors of individuals exhibiting this pattern are strongly influenced by the acoustic/articulatory complexity of phonological structures (e.g., exhibiting errors on less-frequent sequences of consonants), but relatively uninfluenced by lexical properties (e.g., word frequency).…”

Complexity in articulatory and segmental levels of production

“…These errors are then compared with the errors made by individuals with phonological (but not articulatory) deficits, as well as the measures of age of acquisition and within- and cross-language frequency. Their participant data came from Galluzzi et al (2015; also see Romani, Galluzzi, Bureca, & Olson, 2011) in which they characterized individuals who make high rates of phonetic errors (i.e., slurred or distorted productions; visible or audible articulatory groping) as having apraxia of speech (AOS). In this series of studies, individuals were labelled as having AOS if they made at least 10% phonetic errors.…”

“…In addition, for sounds that do appear in clusters, the composition of the cluster may affect the accuracy of each of the components (Miozzo & Buchwald, 2013). From the description in the Romani, Galluzzi, Guariglia, and Golsin (2017) (as well as Galluzzi et al, 2015; Romani et al, 2011, both reporting on the same dataset), it appears that the stimuli were controlled for a number of critical lexical properties, but that the contexts in which the sounds occurred were not part of the stimulus design. By not controlling for the position a sound appears in, or whether it appears in a cluster, it is problematic to compare overall performance on different segments.…”

“…First, I discuss the operationalization of articulatory complexity as coming from errors of individuals diagnosed as having apraxia of speech by Galluzzi, Bureca, Guariglia, and Romani (2015), including both the approach to classifying patients and the structured (Staiger, Finger-Berg, Aichert, & Ziegler, 2012; Ziegler & Aichert, 2015) variation among the patients in this population. Second, I discuss the issue of articulatory complexity more generally and question whether the segmental accuracy measures are sufficient and even whether typological markedness patterns follow principles of articulatory complexity.…”