High-Level Language Production in Parkinson's Disease: A Review <s> Complex Language Production in PD <s> Speech and language alterations were assessed in 51 patients with Parkinson9s disease (PD) and 10 patients with dementia of the Alzheimer type (DAT). Thirty-five of the PD patients had no evidence of intellectual impairment on a conventional mental status questionnaire and 16 of the PD patients had dementia syndromes of comparable severity to the DAT patients. DAT produced significantly greater language disturbances, including anomia, decreased information content of spontaneous speech, and diminished word list generation. PD patients had significantly decreased phrase length, impaired speech melody, dysarthria, and agraphia. The results suggest that the dementia of PD is distinguishable from that of DAT: PD patients have prominent motor speech abnormalities, whereas DAT patients exhibit more profound language alterations. <s> BIB001 </s> High-Level Language Production in Parkinson's Disease: A Review <s> Complex Language Production in PD <s> Abstract The hypokinetic dysarthria of Parkinson's disease (PD) has been described extensively. In contrast, patterns of hesitation and the language structure in spontaneous speech of the PD patient have not been investigated, although several studies have shown language-related abnormalities in word naming, word generation, and verbal recall. In the present study, 10 male Parkinson's patients and 10 normal male speakers were compared in a reading and spontaneous speaking paradigm for acoustic and linguistic features. Among acoustic measures, fundamental frequency and relative intensity differentiated PD from control subjects, consistent with reported features of hypokinetic dysarthria. The striking observations among linguistic measures differentiating PD from control subjects were an increase in the number of (a) silent hesitations per minute, (b) abnormally long silent hesitations, (c) words per silent hesitation, (d) open class phrases, and (e) optional open phrases per speech sample, and a decrease in the number of modalizations and interjections. An increase in the number of filled hesitations occurring per minute, as well as a decrease in syntactic complexity separated moderate from mild Parkinson's patients. Our interpretation of the data favors the hypothesis that changes in the structure of spontaneous language production with increasing severity of dysarthria reflect PD patients' adaptation to their disease. <s> BIB002 </s> High-Level Language Production in Parkinson's Disease: A Review <s> Complex Language Production in PD <s> Abstract An analysis of the temporal (prospective) form (silent and filled hesitations, repetitions, incomplete phrases, context-related comments, interjections), syntactic form, and lexical (retrospective) form (verbal deviations, open and closed class phrases) of spontaneous language production of early and middle stage Alzheimer's, Huntington's, and Parkinson's patients was made. Results showed that the language structure was disrupted in each disease, but in different ways. Temporal interruptions of varying types were frequent in the language of Alzheimer's and Huntington's Disease patients; only long-duration silent hesitations were frequent in Parkinson's language samples. Syntactic complexity was reduced in Huntington's Disease. Verbal paraphasias were found in both the language of Alzheimer's patients, as well as moderately advanced Huntington's patients. Closed class phrases were predominant in the language of Alzheimer's patients and Huntington's patients, and open class phrases in the language of Parkinson's patients. Taken together, the results suggest that (1) there is a unique neurolinguistic profile for spontaneous language production for each neurodegenerative disease, (2) pathology of the neostriatum disrupts syntactic organization, (3) adaptive strategies are used to cope with verbal and speech-motor difficulties, and (4) adaptive strategies fail to be effective with increasing disease severity. <s> BIB003 </s> High-Level Language Production in Parkinson's Disease: A Review <s> Complex Language Production in PD <s> Methodological problems have been a longstanding barrier to the systematic exploration of issues in language production. Recently, however, production research has broadened beyond traditional observational approaches to include a diverse set of experimental paradigms. This review surveys the observational and experimental methods that are used to study production, the questions to which the methods have been directed, and the theoretical assumptions that the methods embody. Although tailored to the investigation of language production, most of the methods are closely related to others that are widely employed in cognitive research. The common denominator of these procedures is verbal responding. Because the processing complexities of verbal responses are sometimes overlooked in research on memory, perception, attention, and language comprehension, the methodological assumptions of production research have implications for other experimental procedures that are used to elicit spoken words or sentences. <s> BIB004 </s> High-Level Language Production in Parkinson's Disease: A Review <s> Complex Language Production in PD <s> Abstract This study examined the grammatical content of written sentences elicited from 96 Parkinson's patients, 30 Parkinson's with dementia patients and 167 control subjects. Parkinson's patients without dementia or with mild dementia presented no impairments in sentence length, syntactic complexity or amount of information content. Moderately demented Parkinson's patients showed reduced sentence length and information content but normal syntactic complexity. This pattern of results provides evidence that lexical-semantic content is more susceptible to decline than syntactic structure with the progression of dementia in Parkinson's disease. <s> BIB005 </s> High-Level Language Production in Parkinson's Disease: A Review <s> Complex Language Production in PD <s> Language comprises a lexicon for storing words and a grammar for generating rule-governed forms. Evidence is presented that the lexicon is part of a temporal-parietalhnedial-temporal “declarative memory” system and that granlmatical rules are processed by a frontamasal-ganglia “procedural” system. Patients produced past tenses of regular and novel verbs (looked and plagged), which require an -ed-suffixation rule, and irregular verbs (dug), which are retrieved from memory. Word-finding difficulties in posterior aphasia, and the general declarative memory impairment in Alzheimer's disease, led to more errors with irregular than regular and novel verbs. Grammatical difficulties in anterior aphasia, and the general impairment of procedures in Parkinson's disease, led to the opposite pattern. In contrast to the Parkinson's patients, who showed sup pressed motor activity and rule use, Huntington's disease patients showed excess motor activity and rule use, underscoring a role for the basal ganglia in grammatical processing. <s> BIB006 </s> High-Level Language Production in Parkinson's Disease: A Review <s> Complex Language Production in PD <s> Deficits in verbal fluency and naming, memory and comprehension of verbal information, as well impairment in verbal and logical reasoning are frequently associated with linguistic performance in Parkinson's disease, a neurodegenerative disorder primarily involving subcortical structures and the depletion of dopaminergic neurons in the substantia nigra. Impairment is more pronounced in more complex aspects of language processing as in sentence comprehension, understanding of relational terms and relative clauses, and in aspects of logical reasoning. It is believed that constraints in accessing the cognitive resources needed to implement the processing of syntactic and semantic information, as well as the disruption of reciprocating neural connections between the basal ganglia with the prefrontal cortex, may explain these observed deficits. <s> BIB007 </s> High-Level Language Production in Parkinson's Disease: A Review <s> Complex Language Production in PD <s> Previous research suggests that lexical and semantic verbal fluency are differentially sensitive to the effects of cortical and subcortical dementias, but little is known about action fluency performance in dementias. The present study compared lexical, semantic, and action fluency in groups of patients with Parkinson's disease (PD) with and without dementia and an elderly control group. Findings revealed an interaction between fluency type and subject group. Although the demented PD (PDD) group performed significantly more poorly than their non-demented counterparts and normal controls on all three fluency tasks, a disproportionate disparity in scores was noted on the action fluency task. The findings suggest that action fluency may be particularly sensitive to PD-associated dementia and may be an early indicator of the conversion from PD to PDD. As reported elsewhere, PD without dementia was not associated with significant impairment on any of the fluency tasks. <s> BIB008 </s> High-Level Language Production in Parkinson's Disease: A Review <s> Complex Language Production in PD <s> The purpose of this study was to investigate the presence and nature of spoken language deficits in Huntington's (HD) and Parkinson's (PD) diseases. Specifically, the study examined whether (a) the... <s> BIB009 </s> High-Level Language Production in Parkinson's Disease: A Review <s> Complex Language Production in PD <s> Abstract Sentence processing in Alzheimer's disease (AD) has been found to be influenced by several grammatical and extragrammatical factors, including phrase structure and verb–argument relations, number of propositions/verbs, and processing resource capacity. This study examines the effects of these variables on sentence production in AD. Normal control and AD subjects were asked to repeat six types of sentences varying along the above dimensions of complexity. Subjects' processing resource capacity was measured using several verbal working memory tests. AD subjects' sentence-repetition performance was impaired compared to the normal control group. Significant effects were observed for branching direction of phrase struc- ture, canonicity of verb–argument relations, and serial position of errors. Sentence-repetition performance significantly correlated with working memory scores. The findings are interpreted within a resource capacity theory of sentence processing. <s> BIB010 </s> High-Level Language Production in Parkinson's Disease: A Review <s> Complex Language Production in PD <s> This study examined syntactic changes in the spoken discourse of patients with Huntington's (HD) or Parkinson's disease (PD) and explored possible relationships between their syntactic changes and concomitant cognitive and motoric symptoms. Patient and control groups participated in a conversational discourse activity and completed a battery of standardized speech and cognitive tests. The HD group used shorter and fewer grammatically complete utterances than their healthy, age-matched peers, whereas there were no significant syntactic differences between PD patients and their healthy, age-matched peers or between PD and HD patients. Productive syntax abilities in HD and PD were meaningfully related to both neuropsychological and motor speech changes. These findings indicate that patients with subcortical disease, at least those with HD, may present with language production deficits and that these deficits are most likely the product of not only motor speech limitations (i.e., dysarthria) but also underlying cognitive impairments. <s> BIB011 </s> High-Level Language Production in Parkinson's Disease: A Review <s> Complex Language Production in PD <s> Four language sample measures as well as measures of vocabulary, verbal fluency, and memory span were obtained from a sample of young adults and a sample of older adults. Factor analysis was used to analyze the structure of the vocabulary, fluency, and span measures for each age group. Then an extension analysis was performed by using structural modeling techniques to determine how the language sample measures were related to the other measures. The measure of grammatical complexity was associated with measures of working memory including reading span and digit span. Two measures, sentence length in words and a measure of lexical diversity, were associated with the vocabulary measures. The fourth measure, propositional density, was associated with the fluency measures as a measure of processing efficiency. The structure of verbal abilities in young and older adults is somewhat different, suggesting age differences in processing efficiency. <s> BIB012 </s> High-Level Language Production in Parkinson's Disease: A Review <s> Complex Language Production in PD <s> Twenty-six subjects with idiopathic Parkinson's disease (PD) and normal cognitive status (as measured by the Mini-Mental State Examination) were examined with a battery of tests selected to reveal subtle and/or high-level language impairments. The test battery included 'repetition of long sentences', 'recreating sentences', 'making inferences', 'comprehension of logico-grammatical sentences', 'comprehension of ambiguous sentences' and 'comprehension of metaphors', 'word definitions', 'word fluency', 'naming', 'sentence analysis' and 'morphological completion'. Comparisons were made between the PD subjects and 26 control subjects matched for age, gender and level of education. Significant differences in performance between the PD subjects and the control subjects were found in the ability to make inferences and to analyse sentences (state the correct number of words in a read sentence). An additional four subjects with different degrees of cognitive dysfunction were also investigated and were found to have... <s> BIB013 </s> High-Level Language Production in Parkinson's Disease: A Review <s> Complex Language Production in PD <s> Clinical and neuroimaging studies have shown that verb processing suggests a preferential participation of a prefrontal network, which is dysfunctional in Parkinson's disease (PD). To assess a verb processing deficit in PD, we compared noun- and verb-generation tasks for 34 nondemented PD patients (according to the Dementia Rating Scale) with 34 matched normal subjects, using two intracategory tasks (noun/noun and verb/verb generation) and two intercategory tasks (noun/verb and verb/noun generation). PD patients were significantly impaired in the two tasks involving verb production, i.e., verb/verb and noun/verb generation, whereas their performance was similar to those of controls in the two tasks requiring noun production. For the two impaired tasks, we assessed 1) the influence of lexical competition that corresponds to the presence of several candidate words for a given stimulus; 2) the influence of slight cognitive dysfunction; and 3) the influence of motor deficit. Significant correlations were found between DRS scores and performance on the noun/verb task, and no significant correlations were found between lexical competition or motor deficit and performance. The specific deficit for verb production in PD patients is discussed in relation to deficits affecting either action or grammatical representations. © 2002 Movement Disorder Society <s> BIB014 </s> High-Level Language Production in Parkinson's Disease: A Review <s> Complex Language Production in PD <s> The structure of the brain and the nature of evolution suggest that, despite its uniqueness, language likely depends on brain systems that also subserve other functions. The declarative/procedural (DP) model claims that the mental lexicon of memorized word-specific knowledge depends on the largely temporal-lobe substrates of declarative memory, which underlies the storage and use of knowledge of facts and events. The mental grammar, which subserves the rule-governed combination of lexical items into complex representations, depends on a distinct neural system. This system, which is composed of a network of specific frontal, basal-ganglia, parietal and cerebellar structures, underlies procedural memory, which supports the learning and execution of motor and cognitive skills, especially those involving sequences. The functions of the two brain systems, together with their anatomical, physiological and biochemical substrates, lead to specific claims and predictions regarding their roles in language. These predictions are compared with those of other neurocognitive models of language. Empirical evidence is presented from neuroimaging studies of normal language processing, and from developmental and adult-onset disorders. It is argued that this evidence supports the DP model. It is additionally proposed that “language” disorders, such as specific language impairment and non-fluent and fluent aphasia, may be profitably viewed as impairments primarily affecting one or the other brain system. Overall, the data suggest a new neurocognitive framework for the study of lexicon and grammar. q 2004 Elsevier B.V. All rights reserved. <s> BIB015 </s> High-Level Language Production in Parkinson's Disease: A Review <s> Complex Language Production in PD <s> The present study investigates the production of regular and irregular verbs in the past tense and the comprehension of passive sentences by Greek-speaking PD patients, and compares their behavior to that of normal speakers. Although the two groups manifest large scale differences at all the above constructions, the behavior of PDs is not different at regular vs. irregular past tense formation neither did we obtain strong evidence that they do not comprehend passives, most importantly, they certainly do not perform at chance. On the basis of the above, we conclude that there are no indications for a clearly linguistic deficit of the PD group, hence, their difference with the control group should be attributed to other factors, such as the computational demands of the tasks. <s> BIB016 </s> High-Level Language Production in Parkinson's Disease: A Review <s> Complex Language Production in PD <s> The Declarative/Procedural Model of Pinker, Ullman and colleagues claims that the basal ganglia are part of a fronto-striatal procedural memory system which applies grammatical rules to combine morphemes (the smallest meaningful units in language) into complex words (e.g. talk-ed, talk-ing). We tested this claim by investigating whether striatal damage or loss of its dopaminergic innervation is reliably associated with selective regular past tense deficits in patients with subcortical cerebrovascular damage, Parkinson's disease or Huntington's disease. We focused on past tense morphology since this allows us to contrast the regular past tense (jump-jumped), which is rule-based, with the irregular past tense (sleep-slept), which is not. We used elicitation and priming tasks to test patients' ability to comprehend and produce inflected forms. We found no evidence of a consistent association between striatal dysfunction and selective impairment of regular past tense morphology, suggesting that the basal ganglia are not essential for processing the regular past tense as a sequence of morphemes, either in comprehension or production, in contrast to the claims of the Declarative/Procedural Model. All patient groups showed normal activation of semantic and morphological representations in comprehension, despite difficulties suppressing semantically appropriate alternatives when trying to inflect novel verbs. This is consistent with previous reports that striatal dysfunction spares automatic activation of linguistic information, but disrupts later language processes that require inhibition of competing alternatives. <s> BIB017 </s> High-Level Language Production in Parkinson's Disease: A Review <s> Complex Language Production in PD <s> The current study examines whether young and older adults have similar preferences for animate-subject and active sentences, and for using the order of activation of a verb's arguments to determine sentence structure. Ninetysix participants produced sentences in response to three-word stimuli that included a verb and two nouns differing in animacy. Dependent variables included accuracy, sentence structure produced, and production times for active vs. passive sentences. Neither group shows a strict preference for active sentences, but the two groups are differentially sensitive to animacy and the order of noun activation. Results suggest that sentence structure choice is a probabilistic, constraint-satisfaction process during which these factors interact. <s> BIB018 </s> High-Level Language Production in Parkinson's Disease: A Review <s> Complex Language Production in PD <s> Nine early non-demented bilingual (L1 – Friulian, L2 – Italian) patients with Parkinson’s disease and nine normal controls matched for age, sex and years of education were studied on a spontaneous language production task. All subjects had acquired L1 from birth in a home environment and L2 at the age of six at school formally. Patients with PD evidenced more phonological, morphological and syntactic errors in L1 than in L2. The opposite pattern was observed in normal controls as far as grammar was concerned. These findings suggest that implicit language processing is more impaired than explicit language processing in Parkinson’s disease. <s> BIB019 </s> High-Level Language Production in Parkinson's Disease: A Review <s> Complex Language Production in PD <s> Experimental studies of sentence production in Parkinson disease (PD) are rare. This study examined the relationship between cognitive abilities and performance on two sentence production tasks, sentence repetition, and sentence generation, in which complexity was manipulated. Thirty-eight older adults aged 60 to 85, half with PD, completed the two language tasks plus a cognitive battery. Participants with PD performed more poorly in the repetition task overall, especially in fluency, but differences were no longer significant once cognitive ability was controlled. In contrast, on the sentence generation task the PD group was significantly impaired on all language dimensions and overall performance. Although cognitive ability accounted for significant variance in all measures of sentence generation, the PD group remained significantly impaired when these factors were controlled. These findings suggest that, although language production is influenced by cognitive abilities, it can be significantly impaired in PD over and above the effects of differences in cognitive abilities. <s> BIB020
Studies investigating high-level, complex language in PD are relatively rare and have employed a variety of methodologies. Cummings and colleagues BIB001 were among the first to address deficits in complex expressive language in PD. These researchers compared individuals with PD but no dementia (n = 35), PD plus dementia (n = 16), and individuals with dementia of the Alzheimer's type (n = 10) on the Boston Diagnostic Aphasia Examination  and Western Aphasia Battery  . Those with dementia of the Alzheimer type performed more poorly on language tasks than participants with PD at comparable levels of dementia severity, demonstrating decreased information content and more impairment of word list generation and word finding. Nondemented persons with PD were reported to have "spared" language with lower information content and less complex syntax than expected in individuals of the same age, based on clinical observation. In another early study, Illes et al. BIB002 reported that the language production of people with PD differed both acoustically and linguistically from healthy older adults. They examined speech rate, fluency, syntactic complexity, lexical production, and the relative distribution of content and grammatical phrases in 10 persons with PD (5 mild, 5 moderate) and 10 age-matched controls while reading the Grandfather passage and producing spontaneous speech. In this study, people with PD tended to produce longer sentences than healthy older adults due to a tendency to list several events within a single sentence, leading to a greater proportion of content word phrases (i.e., noun, verb, and adjective phrases) than in the healthy older adult group. However, only the moderately impaired PD group produced sentences with lower syntactic complexity. Illes et al. also reported that the speech of the PD group was disfluent, marked particularly by more pauses and more pauses per word than the speech of the healthy older adult group. In addition, syntactic complexity correlated with dysarthria severity (motor speech impairment) and PD severity, as measured by the Webster scale. These researchers attributed the disfluencies and unusual syntactic constructions to difficulties with concept formulation as well as compensation for motor speech impairment. In a companion study, Illes BIB003 analyzed responses to open-ended, autobiographical questions from individuals with PD (n = 10), Huntington's disease (HD) (n = 10), and Alzheimer's disease (n = 10) along with health older adults (n = 10). This study analyzed several temporalacoustic, syntactic, and lexical dependent variables, including words per minute, location of pauses, number of fluency disruptions of several types (nonword fillers, pauses, false starts, and word repetitions) per word, syntactic complexity, and proportion of open class words. Illes reported that the PD groups overall did not differ from healthy older adults on most of these measures. However, the PD group included more pauses in their responses than controls, with perceptible silent hesitations at the initiation of sentences and between main clauses and optional clauses. These hesitations were reported to be followed by "a certain press of speech (p. 635)" in both the Huntington's and Parkinson's disease groups. The author described this pattern as a type of motor speech, or perhaps cognitive, "cogwheel" phenomenon (p. 635), leading to short periods of freezing or rigidity followed by a limited burst of action, speech in this case. Thus, Iles attributed the disfluencies within and between utterances in the PD group to difficulty activating concepts and formulating sentences, as well as to adaptation to the motor impairments of PD. In contrast, she described the complexity of syntax in PD as "relatively intact" and stated that their speech was highly informative relative to individuals with Alzheimer's or Huntington's disease. Lewis et al. BIB007 used standardized testing to examine high level, complex language production in PD. They tested 20 persons with PD, half with dementia, and 20 healthy age-matched adults on a battery of tasks, including the Boston Naming Test, the WORD test, Test of Language Competence, Word Fluency Test, and Dementia Rating Scale, that assessed both cognitive and linguistic performance. In contrast to the tests used by Cummings et al. BIB001 , the tests chosen in this study examined a number of more complex aspects of language, including the ability to identify synonyms and antonyms, incorporate specific words into a grammatical sentences, define words, and interpret complex and figurative language. Compared to the healthy adults, those with PD performed worse on tests of complex language production, such as providing definitions for words and generating sentences that included specified target words. In addition, more severe dementia was associated with increasing impairment in picture naming, interpreting metaphors, processing ambiguous sentences, defining words, and generating sentences. Lewis et al. argued that the "operational functions (p.200)" of language were intact in PD. Instead, they attributed the observed deficits in language use to cognitive impairment associated with frontal lobe dysfunction. This argument was based on face validity of the tasks used; the language tasks on which the PD group scored most poorly were those that required organization, planning, abstract thought, and integration of information, functions associated with the frontal lobe. Berg and colleagues BIB013 assessed complex language production in 26 persons with PD and 26 control subjects with a test battery modeled after that used by Lewis et al. BIB007 . They tested sentence repetition, sentence production, and the ability to define words along with several receptive language tasks, using an instrument designed to test subtle impairments of complex language function in Swedish adults. Findings specific to complex language production were consistent with those of Lewis et al. BIB007 . Participants with cognitive dysfunction demonstrated significant impairments in the comprehension of metaphors and ambiguous sentences as well as in generating sentences; however, they performed similarly to controls when repeating sentences. Berg et al. also reported that overall performance on their test battery correlated with overall cognitive ability as measured by the mini-mental status exam (MMSE)  , demonstrating that language impairment increased with increasing dementia severity. While Illes BIB003 analyzed fluency and syntactic complexity, their use of unusual dependent variables for these, especially syntactic complexity, makes it difficult to directly compare their findings to other studies. Generalization from the studies by Lewis et al. BIB007 and Berg et al. BIB013 is limited by a lack of information about the actual language production output of the people with PD. These standardized tests did not yield any information about whether the language output was, for example, coherent, grammatical, or syntactically complex. Thus, although these studies provided converging evidence that complex language production (and comprehension) were impaired in PD, exactly how the impairment manifested was not addressed. Furthermore, attributing language impairments to frontal lobe impairments based on task analysis has face validity, and correlations with dementia severity are somewhat better. However, several researchers have begun to measure more detailed characteristics of the language output of individuals with PD as well as the component cognitive abilities underlying performance on dementia scales, using tasks that provide a better estimate of different types of cognitive abilities (e.g., working memory, inhibition, set shifting, and speed of processing). Studies adopting these approaches are discussed below. Small et al. BIB005 analyzed written sentence generation using sentences produced as part of the MMSE  . Sentences from 167 healthy older adults, 96 Nondemented individuals with PD, and 30 individuals diagnosed with PD plus dementia (14 mild and 16 moderate) were analyzed for grammaticality, syntactic complexity, and information content. Small et al. reported that only the PD group with moderate dementia produced shorter, less grammatically complex sentences with reduced information content (i.e., fewer propositions per word) as well as more sentence fragments compared to healthy older adults. However, they found no difference in sentence complexity or information content between healthy older adults and nondemented or mildly demented individuals with PD. Thus, while Small et al. provided a more complete characterization of the sentence generation capabilities of individuals with PD at different levels of dementia, they did not relate these patterns to more specific underlying cognitive deficits. Murray BIB009 took a more advanced approach and compared the cognitive profiles (e.g., memory, attention, and lexical retrieval) and language functioning of 10 persons with PD, 10 with Huntington's disease, and 18 age-matched control subjects. Participants described the cookie theft [69] and grocery scene pictures [70] . Dependent variables included total number of utterances, grammaticality of sentences, syntactic complexity (proportion of simple sentences and the number of embedded clauses per utterance), and informativeness (proportion of Correct Information Units and proportion of informative utterances). Groups did not differ in total number of utterances produced or overall syntactic complexity; however, participants with PD in this study produced a smaller proportion of grammatical sentences and less information than control subjects. Murray also reported that individuals with PD who had better shortterm memory and better attention produced longer, more syntactically complex utterances. Further, participants with PD who were more cognitively intact overall, as measured by dementia ratings scale scores (DRS)  , produced more information. In a companion study, Murray and Lenz BIB011 examined the conversational discourse of 10 persons with PD, 9 with Huntington's disease, and 17 controls, and reported no impairments in syntax among those with PD. However, they observed significant positive relationships between DRS, length of utterances and sentence complexity in the PD group. The authors attributed the difference in findings between this study and Murray's previous study BIB009 to differences in the degree of constraint the task put on responses. They suggested that individuals with PD performed more poorly in more constrained tasks (e.g., picture description) than in open ended tasks like conversation. The findings in Murray and Lenz are consistent with previous findings in the aging literature that syntactic complexity and sentence length are related to cognition, particularly working memory ability, in healthy older adults BIB012 , and further suggest that these characteristics of language will be vulnerable as overall cognitive abilities decline. In an interesting study examining spontaneous speech in bilingual individuals with PD, Zanini et al. BIB019 reported significantly more grammatical errors in 9 individuals with PD compared to age and education matched healthy adults. Furthermore, this difference was limited to performance in the first language of participants, Friulian, while performance in the second language, Italian, did not differ between groups. Interestingly, the number of grammatical errors produced in the first language correlated significantly with executive function tasks assessing task-switching ability. The authors attribute the grammatical impairments in the first language to differences in the representations of the two languages resulting from differences in the age of acquisition. Because the first language was learned from birth, the authors argued that the first language was more likely to be processed using implicit, procedural processing which engages basal ganglia structures BIB015 . In contrast, the second language, which was typically learned in these individuals when the person entered school, would be subject to more explicit processing which would tap neocortical representations. Thus, Zanini et al. argued that basal ganglia deficits such as in PD would be more likely to impair first language grammar which was learned and processed implicitly, rather than second-language grammar, which was learned explicitly in school. The correlations between grammatical errors and task switching are also consistent with other studies BIB020  that have also reported correlations between grammatical errors and executive function tasks. Recently, Colman et al.  examined the effects of cognitive abilities and task switching on language production in 28 persons with PD and 28 age matched healthy participants. The experiment required participants to provide an inflected form of a verb within a sentence context. Participants also completed a battery of cognitive tests. Those with PD performed more poorly than healthy adults on cognitive measures of task switching (the Trail Making Task, Odd Man Out) and, marginally, on action fluency (P = .06), but not on tasks assessing sustained and divided attention, working memory, inhibition, semantic fluency, or phonemic fluency. In the verb production task, participants saw a picture and read the sentence context aloud to activate the grammatical context and then generated the inflected form of an appropriate verb. Participants were instructed to produce a past tense verb when the context sentence included a time biasing adverb like "yesterday" and had to remember to produce a present tense verb elsewhere if there were no adverbial cue. Errors primarily consisted of participants producing past tense verbs when there was no cue, (i.e., when a present tense verb was required). The authors concluded that the verb production deficits in PD were due to cognitive deficits exaggerated by task specific demands, specifically, having to switch from past to present tense when no cue appeared in the sentence  . This conclusion was supported by the finding that accuracy in the choice of tense in the verb generation task correlated with performance on working memory and task switching measures. Unfortunately, the experiment did not include a condition in which tense switching was signaled by including a present tense adverb such as "now," which would have helped distinguish the relative strength of the effects associated with memory for instructions versus tense switching. The findings of Colman et al. suggest that increasing experimental task demands (e.g., frequently switching between tenses with no overt cue in one condition) can reveal vulnerabilities in language production in PD. Additionally, they suggest that measures of working memory and task switching may index the degree to which grammatical sentence production will be affected in difficult tasks that specifically tax these abilities. The study by Colman et al. raises an import issue: difficulties with verb access could seriously impact sentence production due to the centrality of the verb to the sentence construction process BIB018 BIB004  . In fact, verb production in action fluency tasks seems to be particularly impaired in persons with PD whether they have dementia BIB008 or not BIB014  , while noun generation is relatively unimpaired. Individuals with PD also have been reported to have difficulty learning new verbs  and producing regular past tense forms of verbs BIB006 . However, this latter finding has been difficult to replicate (e.g.,  BIB016 BIB017 ). These findings suggest that verb activation and use may be particularly challenging for individuals with PD. The relationship between verb access deficits in PD and findings of diminished information content, impaired grammaticality, decreased syntactic complexity and impaired fluency has yet to be explored in the literature. Very recently, we BIB020 examined the effects of differences in task demands and stimulus complexity on sentence production in PD. We compared 20 Nondemented individuals with PD to 20 age and education matched healthy older adults in two tasks, sentence repetition and sentence generation, in which the complexity of the stimuli was manipulated. Participants also completed a battery that included tests of set shifting (the Trail Making Test), inhibitory processing (Stroop), verbatim and working memory (digit span forward and backward), and the DRS in order to assess the impact of individual differences cognitive abilities on language production performance in the two tasks. Groups' scores did not differ in the resultant executive function or working memory factors, but the PD group's scores were significantly lower on the DRS, while still being within the Nondemented range. Composite variables were created from these measures using principle components analysis, because they were all significantly intercorrelated with each other. Set-shifting and inhibition tasks loaded on an executive function factor, and the memory tasks loaded on a working memory factor. Residualized DRS scores from which working memory and executive function were partialled out were also computed for use in the regression analyses. Language production in each task was assessed using three language dimensions: fluency of production, grammaticality, and completeness. A fluent response was defined as being a sentence that was free of false starts, wholly or partially repeated words, and filled or unfilled pauses. Grammaticality was defined simply as being a grammatical utterance. Due to the nature of the tasks, completeness, our measure of information content, was defined differently in each task. In the repetition task, completeness referred to verbatim repetition; if a sentence was repeated verbatim, it was complete, and if there was any change, it was not. In the sentence generation task, participants were specifically asked to describe the event in the picture without using pronouns. Therefore, for this task, completeness required that a sentence mention each actor in the stimulus picture plus an appropriate action. Initial analyses consisted of group by complexity by language dimension multivariate analyses of variance. The research questions in this study went beyond those addressed in previous studies. Not only did we ask whether the two groups differed in language production across tasks and whether cognitive abilities accounted for significant variance in these tasks, we also asked whether the two groups still differed when effects associated with cognitive variables were controlled. To address this final question, we employed hierarchical, stepwise, multivariate regression models, which are described in more detail in the Appendix. Regression models were only computed for dependent variables showing significant group main effects or interactions. In the repetition task, participants repeated 20 sentences from Small et al. BIB010 that were controlled for word frequency and number of words, in which the complex sentences contained a relative clause (e.g., The tornado that swept through the town destroyed several homes) and the simple sentences contained a prepositional phrase (e.g., The circus at the convention center attracted thousands of children). The main effect of complexity was not significant; however, there was a significant main effect of group and a significant language dimension by group interaction. The two groups did not differ in the proportion of sentences repeated that were grammatical and complete, but the group with PD produced more disfluent responses and overall fewer acceptable sentences (sentences that were fluent, grammatical and complete) than the healthy adults, regardless of the complexity of the sentence. Moreover, the regression analyses revealed that 47% of the variance in fluency of production was accounted for by differences in working memory, executive function and DRS scores. Importantly, while group accounted for an additional 5% of the variance in both fluency and overall acceptability, these effects were not significant (P > .06 and P < .09, resp.). In other words, when the effects of cognitive ability were controlled, there were no longer significant group differences in performance on sentence repetition. In the sentence-generation task, the same individuals produced a single sentence to describe each of 20 pictures that differed in the number of actors. Half of the pictures contained 2 actors (simple condition), and half included 3 actors (complex condition). Pictures showed scenes with people or animals doing common actions (e.g., a boy and a girl climbing a tree, a dog chasing a cat that was chasing a girl). The 3-actor picture was considered more complex than the 2-actor picture because additional concepts (i.e., the third actor and its associated activity) needed to be activated and integrated with the other information in the output sentence. All main effects were significant. Complexity interacted with language dimension; complexity of stimuli had significant effects on grammaticality and fluency but not completeness in both groups. The interaction between group and language dimension was also significant. In the group with PD, fluency was disproportionately impaired relative to the healthy older adults, grammaticality was somewhat less impaired, and completeness was most preserved although the group differences were significant in all three dimensions. The regression analyses examining performance in each language dimension demonstrated that both working memory and executive function contributed significantly to fluency and completeness of responses as well as to overall performance, while grammaticality was only predicted by executive function scores. Furthermore, in each of these analyses, the effect of group remained significant, accounting for 10%-27% of the variance in performance, when cognitive variables were controlled. Therefore, our study found significant predictive relationships between working memory, executive function and different aspects of language production, illustrating the strong impact of these cognitive abilities on language production performance; however, cognitive abilities did not fully account for the group differences in language performance. Thus, our findings present the additional, unexpected possibility that the deficits in PD language production extend beyond what can be explained by standard tests of working memory and executive function. This unanticipated finding suggests that more sophisticated statistical techniques than simple correlations may be necessary to determine whether the language impairments in PD are wholly attributable to cognitive impairments (e.g.,  ), or whether deficits exist in PD that are specific to language processing as well. In summary, the studies described here provide converging evidence regarding the types of language impairment found in individuals with PD. First, information content is reduced. Second, grammatical sentence production is impaired, particularly in complex conditions or tasks. Third, fluency of production is impaired. The findings are mixed only with respect to complexity of sentences. An additional common theme is that most studies have found (or infer) that differences in cognitive abilities contribute to these deficits. Consistent with this, it also appears that language production in individuals with PD is particularly vulnerable to differences in the complexity of the eliciting task. In the section below, we situate this pattern of findings within the most commonly cited model of language production.