Sentence production and processing speakers with aphasia
Many speakers who present with ‘agrammatic aphasia’ after left-hemisphere brain damage
show problems with building complex sentence structures in production. At the same
time, any impairment to their sentence comprehension may be much more subtle and masked
by strategies that use extrasyntactic information to derive meaning, such as knowledge
of the world and pragmatics, but also sentence intonation. Healthy speakers also use
such information to derive meaning from sentences and do not rely exclusively on word
order and the syntactic relations between words and phrases in natural language use.
The Neurolinguistics Lab is interested in the interplay between sentence structure
(syntax) and extrasyntactic factors in sentence parsing and particularly in how the
brain supports this complex process, in healthy and impaired language systems. If
we know which brain areas contribute to ambiguity resolution, and how these areas
work together, we may use this knowledge to stimulate and enhance language comprehension
in language-impaired speakers.
Phonological versus phonetic planning disorders in aphasia and apraxia of speech
This line of research goes back to Dirk den Ouden’s doctoral dissertation and aims to investigate the nature and source of word form errors in speakers with aphasia and/or apraxia of speech. To what extent is it possible to distinguish speech errors that are caused by impaired lexical access, phonological planning, or phonetic planning? One way in which to approach this question is to study how word form errors may be constrained by abstract phonological domains, such as syllables and phonemes, rather than by purely articulatory or perhaps even auditory factors. Related to this is the question to what extent hypothesized abstract phonological domains and elements are constrained by articulatory, auditory or general cognitive factors that are peripheral to the language domain (or are they?). Progress in this field will benefit from the identification of the neural correlates of phonological processing at different stages of word form generation. How can formal linguistic and psycholinguistic models of speech production be mapped onto the neurophysiology of language production? The long-term goal of this research is to lead to the development of treatment methods that target specific phonological units, in combination with neurophysiological interventions that stimulate post-stroke brain plasticity.
Neural correlates of verb representations and retrieval
Verbs form the core of sentence frames and problems with verb retrieval may underlie
deficits in sentence processing and production. The Neurolinguistics Lab is interested
in the types of information that are accessed during verb retrieval, automatically,
as an integral part of verb representation, or by association with verb semantics.
For example, a verb’s subcategorization frames, in terms of its argument structure
and the types of complements that a verb can take, affect the processing load that
is associated with its retrieval from the mental lexicon, as evident from reaction-time
and functional imaging experiments, including our own. Also, there is a question about
the extent to which a verb’s mental representation includes information on semantic
associations and pragmatic aspects of how such a verb is used in daily language. Does
the retrieval of verbs that are typically ‘hand actions’ (to grab) automatically activate
motor cortex areas that subserve the execution of such hand actions? And what if they
do? Does that mean this co-activation is a necessary part of the verb’s mental representation?
Predictors of response to naming treatment in aphasia
Within the Center for the Study of Aphasia Recovery (C-STAR), we collaborate on studies into the identification of biographical, cognitive, behavioral
and neurological predictors of response to phonological and semantic approaches to
therapy for the improvement of lexical access and production in speakers with aphasia.
Dr. Den Ouden is Principal Investigator on one of C-STAR’s subprojects, Telerehabilitation for Aphasia (TERRA; NIH P50 DC014664, project 1), in which we study whether outcomes after remote
naming intervention delivered virtually by a clinician are comparable to responses
to the same intervention delivered in the clinic. In addition, we hope to learn more
from this study about the factors that may make people better responders to (or better
suited for) telerehabilitation. What works for one person may not necessarily be ideal
for the next person and, of course, “we are all individuals” (Monty Python)!
Functional Communication Outcomes for speakers with aphasia
Functional communication assessments examine the extent to which an individual is
able to convey messages, or communicative goals, in daily-life situations. This ability
strongly impacts life participation and quality of life in people with aphasia. Changes
to functional communication skills should therefore be a core outcome measure for
aphasia intervention research. However, designing a reliable and comprehensive test
that allows researchers and clinicians to quantify ‘functional communication’ abilities
in speakers with aphasia has remained a challenge. The Neurolinguistics Lab is working
on the assessment of functional communication in speakers with aphasia, based on realistic
scenarios in an adaptive format that allows informative testing at different skill
levels, from speakers with severe to mild aphasia.
Drama intervention for speakers with aphasia
Aphasia is a language disorder that affects communication abilities, but communication is not limited to verbal expression. Since 2018, an aphasia group that is led by Dirk den Ouden and collaborator Prof. Peter Duffy, relies on actors who have aphasia to use verbal as well as nonverbal communication in expressing themselves. Speech-pathology students and drama students are actively involved with the group as well, so this is a very positive experience for all! While the aphasia drama group did not start out as a research project, the Neurolinguistics Lab is now investigating what specific aspects of drama participation drive the positive effects on living with aphasia and communication confidence that the actors themselves report. This work may ultimately lead to a more formalized program of drama intervention for people who have aphasia. Meanwhile, however, we are having a jolly good time rehearsing!