Phonological Working Memory Limitations and Agrammatism: Is There a Causal Relationship between the Two?

Syntactic processing in sentence comprehension requires some form of Working Memory (WM) resources. However, the nature of the relation between WM and sentence comprehension is controversial. One of the questions is whether WM for language is a single resource, or, alternatively, it consists of different components, each entrusted with a different linguistic function (Caplan & Waters, 1999). The aim of the study is to investigate the nature of the relation between WM and sentence comprehension by comparing sentence comprehension abilities with performance on WM tasks of four Greek-speaking patients with Broca’s aphasia. The experimental hypothesis is that patients with different performance patterns in sentence comprehension will present with different verbal WM capacity

Short-term and working memory treatments for improving sentence comprehension in aphasia: a review and a replication study

Although the roles of verbal short-term and working memory on spoken sentence comprehension skills in persons with aphasia have been debated for many years, the development of treatments to mitigate verbal short-term and working memory deficits as a way of improving spoken sentence comprehension is a new avenue in treatment research. In this article, we review and critically appraise this emerging evidence base. We also present new data from five persons with aphasia of a replication of a previously reported treatment that had resulted in some improvement of spoken sentence comprehension in a person with aphasia. The replicated treatment did not result in improvements in sentence comprehension. We forward recommendations for future research in this, admittedly weak at present, but important clinical research avenue that would help improve our understanding of the mechanisms of improvement of short-term and working memory training in relation to sentence comprehension

Lesion correlates of auditory sentence comprehension deficits in post-stroke aphasia

Auditory sentence comprehension requires coordination of multiple levels of processing: auditory-phonological perception, lexical-semantic comprehension, syntactic parsing and discourse construction, as well as executive functions such as verbal working memory (WM) and cognitive control. This study examined the lesion correlates of sentence comprehension deficits in post-stroke aphasia, building on prior work on this topic by using a different and clinically-relevant measure of sentence comprehension (the Token Test) and multivariate (SCCAN) and connectome-based lesion-symptom mapping methods. The key findings were that lesions in the posterior superior temporal lobe and inferior frontal gyrus (pars triangularis) were associated with sentence comprehension deficits, which was observed in both mass univariate and multivariate lesion-symptom mapping. Graph theoretic measures of connectome disruption were not statistically significantly associated with sentence comprehension deficits after accounting for overall lesion size

Effects of lexical processing deficits on agrammatic sentence comprehension: An eyetracking study

Individuals with Broca’s aphasia show lexical processing deficits, such as deficits in lexical access or lexical integration. Although studies have implicated lexical processing as areas of impairment in Broca’s aphasia, few studies have looked at the effects of these deficits on sentence comprehension. We conducted a series of eyetracking experiments to test whether Broca’s aphasic individuals are impaired in lexical access or lexical integration and whether such deficits affect sentence comprehension. Results showed that while lexical access and lexical integration are both impaired in Broca’s aphasia, only the deficit in lexical integration affects sentence comprehension

The brain structure during language development: neural correlates of sentence comprehension in preschool children

Language skills increase as the brain matures and language specialization is linked to the left hemisphere. Among distinct language domains, sentence comprehension is particularly vital in language acquisition and, by comparison, requires a much longer time-span before full mastery in children. Although accumulating studies have revealed the neural mechanism underlying sentence comprehension acquisition, the development of the brain’s gray matter and its relation to sentence comprehension had not been fully understood. This thesis employs structural magnetic resonance imaging and diffusion-weighted imaging data to investigate the neural correlates of sentence comprehension in preschoolers both cross-sectionally and longitudinally. The first study examines how cortical thick- ness covariance is relevant for syntax in preschoolers and changes across development. Results suggest that the cortical thickness covariance of brain regions relevant for syntax increases from preschoolers to adults, whilst preschoolers with superior language abilities show a more adult-like covariance pattern. Reconstructing the white matter fiber tract connecting the left inferior frontal and superior temporal cortices using diffusion-weighted imaging data, the second study suggests that the reduced cortical thickness covariance in the left frontotemporal regions is likely due to immature white matter connectivity during preschool. The third study then investigated the cortical thickness asymmetry and its relation to sentence comprehension abilities. Results show that longitudinal cortical thick- ness asymmetry in the inferior frontal cortex was associated with improvements in sentence comprehension, further suggesting the crucial role of the inferior frontal cortex for sentence comprehension acquisition. Taken together, evidence from gray and white matter data provides new insights into the neuroscientific model of language acquisition and the emergence of syntactic processing during language development

Structured Access in Sentence Comprehension

This thesis is concerned with the nature of memory access during the construction of long-distance dependencies in online sentence comprehension. In recent years, an intense focus on the computational challenges posed by long-distance dependencies has proven to be illuminating with respect to the characteristics of the architecture of the human sentence processor, suggesting a tight link between general memory access procedures and sentence processing routines (Lewis & Vasishth 2005; Lewis, Vasishth, & Van Dyke 2006; Wagers, Lau & Phillips 2009). The present thesis builds upon this line of research, and its primary aim is to motivate and defend the hypothesis that the parser accesses linguistic memory in an essentially structured fashion for certain long-distance dependencies. In order to make this case, I focus on the processing of reflexive and agreement dependencies, and ask whether or not non-structural information such as morphological features are used to gate memory access during syntactic comprehension. Evidence from eight experiments in a range of methodologies in English and Chinese is brought to bear on this question, providing arguments from interference effects and time-course effects that primarily syntactic information is used to access linguistic memory in the construction of certain long-distance dependencies. The experimental evidence for structured access is compatible with a variety of architectural assumptions about the parser, and I present one implementation of this idea in a parser based on the ACT-R memory architecture. In the context of such a content-addressable model of memory, the claim of structured access is equivalent to the claim that only syntactic cues are used to query memory. I argue that structured access reflects an optimal parsing strategy in the context of a noisy, interference-prone cognitive architecture: abstract structural cues are favored over lexical feature cues for certain structural dependencies in order to minimize memory interference in online processing