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

Syntactic predictions and asyntactic comprehension in aphasia: Evidence from scope relations

People with aphasia (PWA) often fail to understand syntactically complex sentences. This phenomenon has been described as asyntactic comprehension and has been explored in various studies cross-linguistically in the past decades. However, until now there has been no consensus among researchers as to the nature of sentence comprehension failures in aphasia. Impaired representations accounts ascribe comprehension deficits to loss of syntactic knowledge, whereas processing/resource reduction accounts assume that PWA are unable to use syntactic knowledge in comprehension due to resource limitation resulting from the brain damage. The aim of this paper is to use independently motivated psycholinguistic models of sentence processing to test a variant of the processing/resource reduction accounts that we dub the Complexity Threshold Hypothesis. According to this hypothesis, PWA are capable of building well-formed syntactic representations, but, because their resources for language processing are limited, their syntactic parser fails when processing complexity exceeds a certain threshold. The source of complexity investigated in the experiments reported in this paper is syntactic prediction. We conducted two experiments involving comprehension of sentences with different types of syntactic dependencies, namely dependencies that do not require syntactic prediction (i.e. unpredictable dependencies in sentences that require Quantifier Raising) and dependencies whose resolution requires syntactic predictions at an early stage of processing based on syntactic cues (i.e. predictable dependencies in movement-derived sentences). In line with the predictions of the Complexity Threshold Hypothesis, the results show that the agrammatic patients that participated in this study had no difficulties comprehending sentences with the former type of dependencies, whereas their comprehension of sentences with the latter type of dependencies was impaired

Why is it difficult to predict language impairment and outcome in patients with aphasia after stroke?

One of the most devastating consequences of stroke is aphasia. Communication problems after stroke can severely impair the patient's quality of life and make even simple everyday tasks challenging. Despite intense research in the field of aphasiology, the type of language impairment has not yet been localized and correlated with brain damage, making it difficult to predict the language outcome for stroke patients with aphasia. Our primary objective is to present the available evidence that highlights the difficulties of predicting language impairment after stroke. The different levels of complexity involved in predicting the lesion site from language impairment and ultimately predicting the long-term outcome in stroke patients with aphasia were explored. Future directions and potential implications for research and clinical practice are highlighted

Verbal memory and sentence comprehension in aphasia: a case series

This case series explores the relationship between verbal memory capacity and sentence comprehension in four patients with aphasia. Two sentence comprehension tasks showed that two patients, P1 and P2, had impaired syntactic comprehension, whereas P3 and P4’s sentence comprehension was intact. The memory assessment tasks showed that P1 and P2 had severely impaired short-term memory, whereas P3 and P4 performed within the normal range in the short-term memory tasks. This finding suggests an association between short-term memory deficit and sentence comprehension difficulties. P1 and P3 exhibited impaired comparable working memory deficits, suggesting a dissociation between working memory and sentence comprehension

Processing of syntactic dependencies in agrammatism: The role of predictability

The aim of this thesis is to explore the role of Predictability, that is, whether or not a dependency can be identified at an early stage of derivation on the basis of syntactic cues, in the sentence comprehension deficits in agrammatism. To that end, I investigate the comprehension of sentences with scope relations by Greek-speaking patients with agrammatic and non-agrammatic aphasia. Three different structures are investigated, namely sentences with contrastive focus in the object DP, ambiguous doubly quantified sentences and double object constructions with quantified object DPs. More specifically, sentences with contrastive foci provide an appropriate minimal pair to explore the role of Predictability. The reason is that in Greek object contrastive foci can either appear pre-verbally after A’-movement, resulting in predictable dependencies, or remain in situ. In situ contrastive foci require covert movement operations in order to be interpreted contrastively, resulting in unpredictable dependencies. My experimental hypothesis is that the agrammatic patients will exhibit a dissociation in processing predictable and unpredictable dependencies, with the former being impaired compared to the latter. To provide further evidence that successful processing of sentences with in situ contrastive foci reflects patients’ intact knowledge of covert movement mechanisms I examine the comprehension of ambiguous doubly quantified sentences, whose inverse scope interpretation requires the establishment of a covert movement dependency. The reason for examining double object constructions with quantified DPs is to further explore whether agrammatic patients are able to construct complex syntactic representation. The results indicate that problems with syntactic processing in agrammatic patients are largely confined to predictable dependencies, with performance on unpredictable dependencies relatively unimpaired