A psychometric analysis of functional category production in English agrammatic narratives

Abstract

Hierarchical models of agrammatism propose that sentence production deficits can be accounted for in terms of clausal syntactic structure (Friedmann & Grodzinsky, 1997;Hagiwara, 1995). 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, Christiansen, & Goodglass, 1998;Friedmann, 2001Friedmann, , 2002, it has also been challenged on several grounds (Burchert, Swoboda-Moll, & De Bleser, 2005a;Lee, 2003;Lee, Milman, & Thompson, 2005). In this paper the question of hierarchical structure was re-examined within the framework of Item Response Theory (IRT, Rasch, 1980). 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 neural correlates of agrammatism: Evidence from aphasic and healthy speakers performing an overt picture description task

“…The percentage of open class words was significantly lower than in the 3W-condition. This result reveals that the aphasic speakers did use function words, unlike many aphasic speakers with severe agrammatism (De Roo et al, 2003 ; Milman et al, 2008 ). However, the data do not convey any information about the correctness of the closed class words used.…”

The relation between content and structure in language production: An analysis of speech errors in semantic dementia

“…The view that closed class items are especially related to syntactic processing is also considered in explorations of agrammatism, in which special problems with these items are cited, amongst other deficits (e.g. Bates & Wulfeck, 1989;Druks & Froud, 2002;Mesulam et al, 2003;Milman, Dickey & Thompson, 2008;Gordon & Dell, 2003). Closed class items have been divided into those with some semantic content like locative prepositions (up, down, above etc.)…”

Rasch Model and Its Extensions for Analysis of Aphasic Deficits in Syntactic Comprehension

“…The dichotomous Rasch model (Rasch 1961) has been widely applied in many areas (Wright 1977;Bond and Fox 2007, to mention a few). One application of this model in aphasic studies was used to examine if different clausal functionals inflict the same level of difficulty on all patients and whether clausal structure difficulty can be ordered hierarchically (Milman, Dickey, and Thompson 2008). Another application in aphasia research investigated whether the Rasch model can be used to construct and analyze a test of auditory language (Hula et al 2006).…”