Project Descriptions
Recovery of sentence production
This work is focused on charting the course of recovery of sentence comprehension and production in individuals with agrammatic (Broca's) aphasia. Subjects are trained to produce certain sentence structures and generalization to other linguistically related structures - controlled for both lexical and syntactic properties - is examined. Linguistic theory (e.g., Chomsky, 1981, 1986, 1993) as well as results of psycholinguistic and neurolinguistic studies are used to predict patterns of language learning. We focus on (a) sentence structures (e.g., filler gap structures) in which noun phrases (NPs), and other elements (e.g., verbs and auxiliaries) have been moved out of their original d-structure positions, (b) functional categories (e.g., verb tense morphology and complementizers), and (c) verb and verb argument structure. Results indicate that generalized sentence production is enhanced when target structures are related along dimensions articulated by linguistic theory.
We also continue to test the hypothesis that training more complex rather than simple structures will result in greater improvement in aspects of sentence production and comprehension. We define sentence complexity in terms of the (a) type of movement involved in sentences, i.e., wh- and NP-movement, (b) phrasal tree structure and the relation between nodes in the syntactic tree, and (c) the number and type of embeddings. In addition, we consider the lexical properties of verbs and how they impact syntactic operations in determining complexity. We find that treatment of complex structures results in generalization to less complex ones when the less complex structures lie in a proper subset of the complex sentences (The Complexity Account of Treatment Efficacy (CATE)). This work is supported by the NIH: 3 R01 DC01948-01-14.
Verb production deficits
In this work we investigate the effects of form class (i.e., noun vs. verb) on single word comprehension and production in individuals with aphasia and other neurological impairments. In addition, production of various verb types (based on argument structure properties) is examined in both single word and sentence production tasks. Results have shown not only that nouns and verbs may be selectively impaired in aphasic subjects, but also that selective impairments across types of verbs is common. Verbs with a greater complexity in terms of both number and type of participant roles are more difficult to produce - both in single word and sentence production tasks - than verbs with less complex argument structure. Treatment studies examining the functional relation between verbs across types also are being conducted.
Lexical-semantic deficits and recovery
(forthcoming)
Online sentence processing
This work uses a variety of techniques -- including auditory anomaly detection, eyetracking during listening, and speeded picture verification -- to examine how individuals with aphasia comprehend complex sentences in real time. Of particular interest is the speed and accuracy with which normal and aphasic individuals resolve filler-gap (movement) dependencies. Results to dateindicate that linguistically-motivated treatment (TUF, Thompson, 2001) improves comprehension of movement structures. Agrammatic (Broca's) aphasic individuals who have received treatment are faster and more accurate in their comprehension of sentences with movement than aphasic individuals who have not. Work in progress examines the time-course of normal and aphasic processing using eyetracking measures, as well as the effect of treatment on the processing of different classes of movement dependencies.
fMRI investigations of sentence processing
This work uses functional magnetic resonance imaging (fMRI) to examine brain sites involved in aspects of word and sentence processing in normals and to examine the neurobiology of language recovery in aphasia. This work is supported by the NIH (3 R01 DC01948-01-14) and formerly by the McDonnell-Pew Foundation Program in Cognitive Neuroscience and is conducted in collaboration with the Cognitive Brain Mapping Group at Northwestern University. While neuroimaging studies have begun to elucidate the neural correlates of language, few have examined brain sites recruited by aphasic patients, and even fewer have studied the neural mechanisms supporting recovery. Results to date indicate that, in non-brain-damaged subjects, simple and complex sentence processing elicits activation in Broca's area, left posterior superior and middle temporal gyri, the left dorsolateral prefrontal cortex and the intraparietal sulcus. Complex sentences, however, elicit greater activation in a separate focus located in Broca's area. Studies examining recovery of language processing in aphasia show recruitment of right hemisphere homologues of Broca and Wernicke's areas as well as left peri-lesional areas.
Production of functional categories
Primary progressive aphasia
We also are engaged in work examining the decline of lexical and morphosyntactic aspects of production in individuals with dementia. This work is being conducted in collaboration with Dr. Sandy Weintraub and Dr. M-Marsel Mesulam.
