Verb deficits in Alzheimer's disease and agrammatism: implications for lexical organization

This study examined the nature of verb deficits in 14 individuals with probable Alzheimer's Disease (PrAD) and nine with agrammatic aphasia. Production was tested, controlling both semantic and syntactic features of verbs, using noun and verb naming, sentence completion, and narrative tasks. Noun and verb comprehension and a grammaticality judgment task also were administered. Results showed that while both PrAD and agrammatic subjects showed impaired verb naming, the syntactic features of verbs (i.e., argument structure) influenced agrammatic, but not Alzheimer's disease patients' verb production ability. That is, agrammatic patients showed progressively greater difficulty with verbs associated with more arguments, as has been shown in previous studies (e.g., Kim & Thompson, 2000; Thompson, 2003; Thompson, Lange, Schneider, & Shapiro, 1997), and suggest a syntactic basis for verb production deficits in agrammatism. Conversely, the semantic complexity of verbs affected PrAD, but not agrammatic, patients' performance, suggesting "bottom-up" breakdown in their verb lexicon, paralleling that of nouns, resulting from the degradation or loss of semantic features of verbs.     

A psychometric analysis of functional category production in English agrammatic narratives

Hierarchical models of agrammatism propose that sentence production deficits can be accounted for in terms of clausal syntactic structure [Friedmann, N., & Grodzinsky, Y. (1997). Tense and agreement in agrammatic production: Pruning the syntactic tree. Brain and Language, 56, 397-425; Hagiwara, H. (1995). The breakdown of functional categories and the economy of derivation. Brain and Language, 50, 92-116]. Such theories predict that morpho-syntactic elements associated with higher nodes in the syntactic tree (complementizers and verb inflections) will be more impaired than elements associated with lower structural positions (negation markers and aspectual verb forms). While this hypothesis has been supported by the results of several studies [Benedet, M. J., Christiansen, J. A., & Goodglass, H. (1998). A cross-linguistic study of grammatical morphology in Spanish- and English-speaking agrammatic patients. Cortex, 34, 309-336; Friedmann, N. (2001). Agrammatism and the psychological reality of the syntactic tree. Journal of Psycholinguistic Research, 30, 71-88; Friedmann, N. (2002). Question production in agrammatism: The tree pruning hypothesis. Brain and Language, 80, 160-187], it has also been challenged on several grounds [Burchert, F., Swoboda-Moll, M., & De Bleser, R. (2005a). Tense and agreement dissociations in German agrammatic speakers: Underspecification vs. hierarchy. Brain and Language, 94, 188-199; Lee, M. (2003). Dissociations among functional categories in Korean agrammatism. Brain and Language, 84, 170-188; Lee, J., Milman, L. H., & Thompson, C. K. (2005). Functional category production in agrammatic speech. Brain and Language, 95, 123-124]. In this paper the question of hierarchical structure was re-examined within the framework of Item Response Theory [IRT, Rasch, G. (1980). Probabilistic models for some intelligence and attainment tests (Expanded ed.). Chicago: University of Chicago Press]. IRT is a probabilistic model widely used in the field of psychometrics to model behavioral constructs as numeric variables. In this study we examined production of functional categories (complementizers, verb inflections, negation markers, and aspectual verb forms) in narrative samples elicited from 18 individuals diagnosed with nonfluent aphasia and 18 matched controls. Data from the aphasic participants were entered into an IRT analysis to test (1) whether production of clausal functional categories can be represented as a variable on a numeric scale; and (2) whether production patterns were consistent with hierarchical syntactic structure. Pearson r correlation coefficients were also computed to determine whether there was a relation between functional category production and other indices of language performance. Results indicate that functional category production can be modeled as a numeric variable using IRT. Furthermore, although variability was observed across individuals, consistent patterns were evident when the data were interpreted within a probabilistic framework. Although functional category production was moderately correlated with a second measure of clausal structure (clause length), it was not correlated with more distant language constructs (noun/verb ratio and WAB A.Q.). These results suggest that functional category production is related to some, but not all, measures of agrammatic language performance.     

The quantitative analysis of agrammatic production: procedure and data

Despite the long-standing interest in structural aspects of aphasic production, no method has emerged for the systematic analysis of aphasic speech. This paper attempts to address that need by outlining a procedure for the quantitative assessment of narrative speech which yields measures for both morphological and structural characteristics of aphasic production. In addition to complete instructions for carrying out this analysis, data for three groups of subjects are presented: agrammatic aphasics, aphasics who are similarly nonfluent but not clinically judged as agrammatic, and normal controls. While the agrammatics were distinguishable from the nonagrammatic patients on most measures, both nonfluent groups showed comparable reductions in the structural complexity of their propositional utterances. Other findings include indications from individual patient data that aspects of grammatical morphology may dissociate in agrammatism.     

Variation in the pattern of omissions and substitutions of grammatical morphemes in the spontaneous speech of so-called agrammatic patients

We describe the patterns of omissions (and substitutions) of freestanding grammatical morphemes and the patterns of substitutions of bound grammatical morphemes in 20 so-called agrammatic patients. Extreme variation was observed in the patterns of omissions and substitutions of grammatical morphemes, both in terms of the distribution of errors for different grammatical morphemes as well as in terms of the distribution of omissions versus substitutions. Results are discussed in the context of current debates concerning the possibility of a theoretically motivated distinction between the clinical categories of agrammatism and paragrammatism and, more generally, concerning the theoretical usefulness of any clinical category. The conclusion is reached that the observed heterogeneity in the production of grammatical morphemes among putatively agrammatic patients renders the clinical category of agrammatism, and by extension all other clinical categories from the classical classification scheme (e.g., Broca's aphasia, Wernicke's aphasia, and so forth) to more recent classificatory attempts (e.g., surface dyslexia, deep dysgraphia, and so forth), theoretically useless.     

Verb and auxiliary movement in agrammatic Broca's aphasia

Verb production in agrammatic Broca's aphasia has repeatedly been shown to be impaired by a number of investigators. Not only is the number of verbs produced often significantly reduced, but verb inflections and auxiliaries are often omitted as well (e.g., Bastiaanse, Jonkers, & Moltmaker-Osinga, 1996; Saffran, Berndt, & Schwartz, 1989; Thompson, Shapiro, Li, &Schendel, 1994, 1997). It has been suggested that these problems are, in part, caused by the fact that finite verbs need to be moved from their base-generated position to inflectional nodes in the syntactic tree (e.g., Bastiaanse & Van Zonneveld, 1998). Others have suggested that production deficits in agrammatism can be predicted based on the position that certain structures take in the syntactic tree (Friedmann & Grodzinsky, 1997; Hagiwara, 1995). If the former theory is correct, several predictions can be made. First of all, the discrepancy between production of finite verbs in the matrix and embedded clause that has been found for Dutch (Bastiaanse & Van Zonneveld, 1998) should not be observed in English, since the word order of the matrix and embedded clause are the same in the latter language. Second, if verb movement (including movement of auxiliaries) is problematic for speakers with agrammatic aphasia, then a hierarchy in the production of auxiliaries in yes/no questions, auxiliaries, and finite verbs in declarative sentences in English would be expected, since the former has been moved and the two latter are in base-generated position. In the present paper, these hypotheses were tested in a cross-linguistic study of Dutch and English. Results showed the position in the syntactic tree does not predict deficit patterns; rather the critical factor appears to relate to whether or not verb or auxiliary movement is required.     

Semantic weight and verb retrieval in aphasia

Individuals with agrammatic aphasia may have difficulty with verb production in comparison to nouns. Additionally, they may have greater difficulty producing verbs that have fewer semantic components (i.e., are semantically "light") compared to verbs that have greater semantic weight. A connectionist verb-production model proposed by Gordon and Dell (2003) learns through error correction to "divide the labor" between syntax and semantics. Verbs that are semantically heavier come to depend less on syntax and more on semantics. For lighter verbs, the reverse is true. We performed this study to clarify the role of semantic weight in aphasic verb production and to test the prediction from Gordon and Dell that a brain lesion that impairs the syntactic input to verb retrieval will impair lighter verbs more than heavier ones. Consistent with this prediction, we found that the decrement for lighter verbs was present in a group with agrammatic aphasia but not in a matched group without agrammatism.     

Functional categories in agrammatism: evidence from Greek

The aim of this study is twofold. First, to investigate the use of functional categories by two Greek agrammatic aphasics. Second, to discuss the implications of our findings for the characterization of the deficit in agrammatism. The functional categories under investigation were the following: definite and indefinite articles, personal pronouns, aspect, tense, subject-verb agreement, wh-pronouns, complementizers and the mood marker na (=to). Based on data collected through different methods, it is argued that the deficit in agrammatism cannot be described in terms of a structural account but rather by means of difficulties in the implementation of grammatical knowledge.     

Bound morpheme loss errors in normal and agrammatic speech: One mechanism or two?

Loss errors involving bound morphemes in normal and agrammatic speech are examined to determine if all errors can be due to a single processing problem. It is concluded that two problems are present. First, there is a general problem with accessing bound morphemes (or forms containing bound morphemes), leading to the production of the base form. Second, there is a syntactic problem involving agreement. In agrammatism, the first problem is differentially exacerbated. Implications for normal and agrammatic speech are examined.     

The linguistic interpretation of aphasic syndromes: Agrammatism in Broca's aphasia,an example

One of the most striking characteristics typical of the speech of Broca's aphasics is its agrammatism — the omission of ‘function’ words and inflectional morphemes. Agrammatism is generally viewed as being symptomatic of a syntactic deficit. We argue here that such an account lacks grammatical systematicity, and that the only uniform and systematic interpretation of this deficit is in terms of phonological structure. A natural class consisting of ‘function’ words and some bound morphemes can be defined with reference to the junctural properties of sentences which characterize phonological words. It is this class of elements which tend to be omitted in agrammatic speech. The goal of this paper is not only to provide an hypothesis for the interpretation of one aphasic syndrome, but also to test and illustrate the efficacy of paying close attention to substantive universals of grammatical structure in proposing accounts of linguistic deficits.     

Patterns of comprehension and production of nouns and verbs in agrammatism: implications for lexical organization

This study examined the relationship between verb retrieval and verb-argument-structure properties in seven agrammatic aphasic patients using tasks requiring access to the verb's lexicon for both comprehension- and productionlike processes. Results showed intact comprehension of both nouns and verbs and noun naming, but impaired naming of verbs. Subjects also demonstrated near-normal performance on a grammaticality judgment task involving verb-argument-structure violations but were impaired in categorizing verbs by type (based on number of obligatory arguments). In both naming and categorization conditions, a hierarchy of verb difficulty emerged. Subjects were more accurate in naming/categorizing one-place verbs than two-place verbs and more accurate in naming/categorizing two-place verbs than three-place verbs. The pattern of selective impairment in lexical access/retrieval supports the hypothesis that one dimension of normal lexical organization is by form class. The results also suggest that no necessary relationship exists between production difficulties and comprehension of nouns/verbs in agrammatism. Further, the performance pattern noted supports the claim that verb-argument-structure properties, an important component of the verb lexicon, influence verb production at the single-word and at the sentence level. Subjects' performance on different tasks suggests that the locus of breakdown in the verb-retrieval processes for productionlike tasks may be in accessing information at the lemma level of representation as per Bock's model (1995) of sentence production.     

Competition in lexical processing of Italian noun/verb homographs

The study investigates the lexical representation of Italian noun/verb homographs, introducing a factor which has been analysed in production studies: the specific-word frequency (SWF). The SWF parameter allows to understand whether the grammatical class information is specified within the lexical knowledge or it is selected during post-lexical stages. We ran six lexical decision tasks employing the priming paradigm and a grammatical decision task to investigate the lexical representation of noun/verb homographs. In addition, we sought to determine the role played by the frequency of representations and the temporal activation of the grammatical class information. Our findings support the claim that these forms have independent representations for each syntactic role they can play. We interpreted these findings in the light of what we call the “Nominal Dominance” effect, which affects the lexical access of noun/verb homographs. We also discuss the relation between nominal dominance and lexical frequency.     

Verb inflection and verb diversity in three populations: agrammatic speakers, normally developing children, and children with specific language impairment (SLI)

The present study focuses on the relation between a grammatical and a lexical-semantic aspect of verb production. The spontaneous speech of three different populations (normally developing children, agrammatic aphasics, and children with a specific language impairment) has been analyzed with respect to the proportion of finite clauses and the diversity of the produced lexical verbs. The group results show that in the three populations both the proportion of finite verbs and the variability of the lexical verbs is low. When the individual scores are considered, differences between the normally developing children and the language-impaired subjects show up. Whereas in normally developing children verb finiteness and verb variability go hand-in-hand, the reverse relationship between these variables is observed in the agrammatic aphasics and the children with a specific language impairment. Given this reverse relationship, it is probable to assume two separate disorders. We therefore suggest an impairment at the interface level where lexical information and syntactic structure are integrated during sentence production.     

Training agrammatic subjects on passive sentences: implications for syntactic deficit theories

We trained two subjects with chronic agrammatic aphasia on production of passive sentences using a computerized, iconic-based communication system. After training, one of the subjects demonstrated significant improvements in his abilities to comprehend and verbally produce English passive voiced sentences, including sentences with conjoined subjects and objects. These results suggest that agrammatism does not represent a fixed syntactic deficit.     

Grammatical encoding in aphasia: evidence from a "processing prosthesis"

Agrammatic aphasia is characterized by severely reduced grammatical structure in spoken and written language, often accompanied by apparent insensitivity to grammatical structure in comprehension. Does agrammatism represent loss of linguistic competence or rather performance factors such as memory or resource limitations? A considerable body of evidence supports the latter hypothesis in the domain of comprehension. Here we present the first strong evidence for the performance hypothesis in the domain of production: an augmentative communication system that markedly increases the grammatical structure of agrammatic speech while providing no linguistic information, functioning merely to reduce on-line processing demands.     

Regular and irregular morphology and its relationship with agrammatism: evidence from two Spanish-Catalan bilinguals

We report the performance of two aphasic patients in a morphological transformation task. Both patients are Spanish-Catalan bilingual speakers who were diagnosed with agrammatic Broca's aphasia. In the morphological transformation task, the two patients were asked to produce regular and irregular verb forms. The patients showed poorer performance with irregular than regular morphological transformations in both of their languages. These results are at odds with the proposal that agrammatic speech is always or even preponderantly associated with poorer performance in processing regular versus irregular verb form. Instead, these results support the view that a major component of agrammatic production is a deficit in morphosyntactic processing, independently of whether this processing ultimately involves regular or irregular forms.     

Representation of grammatical properties of Italian verbs in the mental lexicon

The present study focuses on the representation of verbs in the Italian mental lexicon and investigates some grammatical properties: inflectional class, mood, tense, and person. Two experiments based on free recall of single inflected forms are reported. The patterns of recall and error are taken as evidence for the grammatical and morphological information exploited in the access to the verb forms. The pattern of results provides support for the hypothesis that in the mental lexicon the information about conjugation and mood is an organizational criterion for the representation of verbal forms. An interaction between mood and conjugation, likely to arise from the difference in productivity between conjugations, is also observed.     

Verb movement in acquisition and aphasia: same problem, different solutions-evidence from Dutch

This paper focuses on verb movement in agrammatism and child language. We present data from a sentence completion experiment with 6 Dutch agrammatic aphasics and 21 Dutch-speaking children. The experiment compares completion of matrix clauses (which require verb movement) and embedded clauses (where such movement is not required) in these two populations. The results reveal a clear asymmetry: Both agrammatics and children do very well with embedded clauses but fail in 50% with the matrix clauses. It is concluded that the problem which both populations are facing is one of verb movement rather than verb inflection. An error analysis of the responses reveals that, although both agrammatics and children try to avoid movement, they apply different strategies to achieve this goal.     

Finiteness and verb-second in German agrammatism

This study presents results from sentence-completion and grammaticality-judgement tasks with seven German-speaking agrammatic aphasics and seven age-matched control subjects examining verb finiteness marking and verb-second (V2) placement. The patients were found to be selectively impaired in tense marking in the face of preserved mood and agreement marking. Moreover, our results revealed that V2 scores varied across our patients, with some showing impaired and others preserved V2 performance. These findings will be discussed in the light of different syntactic accounts of agrammatism.