Find in Library

Introduction: It is known that an intact cortical left hemisphere is crucial for language production. Recently, more credit is given to the right hemisphere and subcortical areas in the production of non-novel language, including formulaic language. John Hughlings Jackson (1874/1958), first described how propositional and non-propositional speech are differentially affected by neural impairment. Non-propositional language is often preserved following left hemisphere stroke even when aphasia is present (Code, 1982; Sidtis et al., 2009; Van Lancker Sidtis & Postman, 2006). With right hemisphere and subcortical stroke, formulaic language is reduced (Sidtis et al., 2009; Van Lancker Sidtis & Postman, 2006; Speedie et al., 1993). The dual process model of language competence states that propositional and non-propositional speech are processed differently in the brain, with novel speech controlled by the left hemisphere, and a right hemisphere/subcortical circuit modulating formulaic language (Van Lancker Sidtis, 2004; 2012). Two studies of formulaic language will be presented as further evidence of the dual process model: a study of formulaic language in Alzheimer’s disease, and a study of recited speech in Parkinson’s disease. Formulaic language includes overlearned words, phrases or longer linguistic units that are known to the native speaker, occur naturally in discourse, and are important for normal social interaction (Fillmore, 1979; Pawley & Syder, 1983; Van Lancker, 1988; Van Lancker Sidtis, 2004; Wray, 2002). Formulaic expressions include conversational speech formulas, idioms, proverbs, expletives, pause fillers, discourse elements, and sentence stems (stereotyped sentence-initials). Longer units of linguistic material, such as prayers, rhymes, and poems, termed recited speech, is another subtype of formulaic language that is learned in childhood and recited periodically throughout life. Cortical disease: Alzheimer’s disease and formulaic language Alzheimer’s disease (AD) is a bilateral cortical degenerative disease that affects communication. Anecdotal reports suggest the preservation of common, conversational formulaic expressions even when novel language is reduced. Qualitative studies have also documented formulaic language preservation in AD (Maclagan, Davis, & Lunsford, 2008). In an attempt to confirm qualitative and anecdotal evidence, quantitative analysis of monologues from 11 people with AD was performed (Bridges & Van Lancker Sidtis, 2013a). AD participants fell into two groups: 5 early-onset (EO, M age = 53.8) and 6 late-onset (LO, M age = 85.5), all approximately 3 years post-onset. Five age-matched neurologically-healthy controls (HC; M age = 63.6) were also interviewed. Participants talked about family, friends, hobbies, or employment. Syntactic complexity and lexical characteristics were analyzed to assure language characteristics were similar to traditional description of AD speech. Formulaic expressions were categorized [using Van Lancker Sidtis and Rallon’s (2004) criteria] into conversational speech formulas, idioms/proverbs, expletives, pause fillers, discourse elements, sentence stems, or formula errors. Both EO and LO people with AD produced more words in formulas than HC; however, the EO and LO groups did not differ on the overall percent of words in formulas. Roughly 37% of words of the EO group were formulaic, 34% in the LO group, and 22% in the HC group. Also observed in the speech of the AD group were formula errors, which were not similar to errors expected by healthy adults; instead, they were distorted, “If I can’t say anything pleasant, just keep quiet.” From this study, quantitative support is provided for the anecdotal and qualitative reports of preserved production of formulaic language in AD. In fact, formulaic language is produced excessively and may compensate for the lack of novel speech. As AD is a cortical degenerative process, results suggest that the production of formulaic language is at least partially modulated by the intact subcortical region, supporting the dual process model. Subcortical disease: Parkinson’s disease and recited speech Evidence of the involvement of subcortical structures in the production of formulaic language also comes from studies of subcortical injury. An examination of the spontaneous speech of people with basal ganglia stroke found fewer formulaic expressions than healthy adults or people with left hemisphere lesions (Sidtis et al., 2009; Illes et al., 1988). Similarly, a case study of a man post-subcortical stroke described deficits in the ability to recite prayers, a longer form of formulaic language (Speedie et al., 1993). A study of individuals with Parkinson’s disease (PD), a progressive disease causing dysfunction of the basal ganglia circuitry, sought to extend Speedie et al.’s (1993) findings with group data (Bridges et al., 2013b). Two groups of people with PD (M age = 60.9), 6 with deep brain stimulation of the subthalamic nucleus (STN-DBS), and 7 without STN-DBS, and another 7 healthy participants (HC) were asked to recite familiar poems, prayers and rhymes (Humpty Dumpty, Twinkle Twinkle Little Star, Mary Had a Little Lamb, Jack and Jill, Roses are Red, Sticks and Stones, The Lord’s Prayer, and The Pledge of Allegiance). Groups were compared for the percent of error words produced (out of all non-target words produced) during the task. The STN-DBS group in the OFF condition (a more severe state of subcortical dysfunction) produced significantly more error words (37.13%) than HCs (17.44%). The STN-DBS group in the ON condition (33.34%) and the PD group without STN-DBS (21.53%) fell between the STN-DBS OFF condition and HCs. These results provide further support for the dual process model of language production, as individuals with the most severe state of subcortical dysfunction perform poorly on recited speech tasks when compared to healthy adults, indicating the importance of intact subcortical areas for accurate production. Conclusions: Formulaic speech is a specific type of non-novel language that is common in conversation. Longer formulaic sequences that are overlearned, memorized, and recited include prayers, rhymes and poems. The production of these formulaic structures relies on different neural regions than the production of novel language, as we see preservation in this ability with cortical impairment (AD) and reduced production with subcortical (PD) and right hemisphere impairment. The studies reviewed provide additional support for the dual process model of language production, which suggests formulaic speech requires subcortical (and right hemisphere) involvement and novel speech is dependent upon the left hemisphere cortical areas. As formulaic language is a common component of clinical evaluation and treatment of language disorders, it is important to understand the neural underpinnings of production to better inform clinical practice.