Refractory Access Research Articles

Semantic Distance Abnormalities in Mild Cognitive Impairment: Their Nature and Relationship to Function

The authors sought to directly examine compromises in the semantic system in mild cognitive impairment and their possible relationship to everyday functional competencies. Study participants were 25 patients who met criteria for amnestic mild cognitive impairment, 27 patients with mild or moderate Alzheimer's disease, and 70 healthy comparison subjects. The authors administered a novel semantic distance task in which participants make decisions about word or image stimuli that correspond to real-world entities that differ in physical size. The authors also administered a performance-based measure of everyday functional competence. Participants in the mild cognitive impairment and Alzheimer's groups were consistently less accurate and slower than healthy comparison subjects in semantic decisions in which words were used as stimuli. When these participants had to make more fine-grained decisions about the semantic attribute of size, their performance in accuracy and reaction time disproportionately worsened relative to that of comparison subjects. In image-based conditions in which line drawings were used as stimuli, sensory-perceptual information (i.e., the size of the drawings themselves) had undue influence over semantic knowledge judgments in the mild cognitive impairment and Alzheimer's groups. Performance in the semantic distance task was a strong and significant predictor of everyday functional competence in the mild cognitive impairment and Alzheimer's groups. This study synthesized several distinct strands in the mild cognitive impairment literature by providing evidence for 1) compromises in the semantic system in mild cognitive impairment, not confounded by overt retrieval or refractory access; 2) intrusion of perceptual information on semantic processing; and 3) a robust relation between semantic corruption and difficulties in everyday functioning.

Refractory semantic access dysphasia resulting from resection of a left frontal glioma

The existence of semantic access disorders is now well established, however the precise cognitive and anatomical underpinnings are still debated. Here we describe the case of a patient that became aphasic after the resection of a left frontal glioma. Detailed lesion reconstruction indicates that the lesion was mostly restricted to the left dorsal and ventral prefrontal cortices and the underlying white matter, but sparing temporal lobes. Critically, the patient showed all the signs of refractory semantic access dysphasia, supporting the association between this syndrome and damage to left prefrontal areas likely to subserve retrieval and selection mechanisms for verbal material.

Contrasting Graded Effects of Semantic Similarity and Association across the Concreteness Spectrum

Evidence from healthy individuals and neuropsychological patients with deep dyslexia or semantic refractory access dysphasia suggests that abstract and concrete concepts have different dependencies upon associative and similarity-based representational frameworks. However, the importance of information about semantic similarity for concepts that lie across the full concreteness spectrum has not been investigated. Here we report the performance of healthy individuals on an odd-one-out task involving semantically related word triplets that showed continuous variation for the key variables of concreteness, similarity strength, and association strength. In addition, data from a stroke aphasic patient tested on a matching-to-sample task based on the same abstract, middle-concreteness, and concrete stimuli are also presented. The effects of similarity and association strength upon performance were both shown to interact significantly with concreteness, but in opposite directions. The effect of semantic similarity increased with concreteness but the effect of association decreased with concreteness. This research provides further evidence for the proposal that abstract and concrete words have different dependencies upon associative and similarity-based information. It also develops the proposal by providing data that are consistent with a graded and not binary or ungraded model of the relationship between concreteness and these two forms of semantic relationship.

Taxonomic and thematic organisation of proper name conceptual knowledge.

We report the investigation of the organisation of proper names in two aphasic patients (NBC and FBI). The performance of both patients on spoken word to written word matching tasks was inconsistent, affected by presentation rate and semantic relatedness of the competing responses, all hallmarks of a refractory semantic access dysphasia. In a series of experiments we explored the semantic relatedness effects within their proper name vocabulary, including brand names and person names. First we demonstrated the interaction between very fine grain organisation and personal experience, with one patient with a special interest in the cinema demonstrating higher error rates when identifying the names of actors working in a similar film genre (e.g. action movies: Arnold Schwarzenegger, Bruce Willis, Sylvester Stallone, Mel Gibson) than those working in different genres (e.g. Arnold Schwarzenegger, Gregory Peck, Robin Williams, Gene Kelly). Second we compared directly two potential principles of semantic organisation – taxonomic and thematic. Furthermore we considered these principles of organisation in the context of the individuals' personal knowledge base. We selected topics matching the interests and experience of each patient, namely cinema and literature (NBC) and naval history (FBI). The stimulus items were arranged in taxonomic arrays (e.g. Jane Austen, Emily Bronte, Agatha Christie), thematic arrays (e.g. Jane Austen, Pride and Prejudice, Mr Darcy), and unrelated arrays (e.g. Jane Austen, Wuthering Heights, Hercule Poirot). We documented that different patterns of taxonomic and thematic organisation were constrained by whether the individual has limited knowledge, moderate knowledge or detailed knowledge of a particular vocabulary. It is suggested that moderate proper name knowledge is primarily organised by taxonomy whereas extensive experience results in a more detailed knowledge base in which theme is a powerful organising principle.

Taxonomic and Thematic Organisation of Proper Name Conceptual Knowledge

We report the investigation of the organisation of proper names in two aphasic patients (NBC and FBI). The performance of both patients on spoken word to written word matching tasks was inconsistent, affected by presentation rate and semantic relatedness of the competing responses, all hallmarks of a refractory semantic access dysphasia. In a series of experiments we explored the semantic relatedness effects within their proper name vocabulary, including brand names and person names. First we demonstrated the interaction between very fine grain organisation and personal experience, with one patient with a special interest in the cinema demonstrating higher error rates when identifying the names of actors working in a similar film genre (e.g. action movies: Arnold Schwarzenegger, Bruce Willis, Sylvester Stallone, Mel Gibson) than those working in different genres (e.g. Arnold Schwarzenegger, Gregory Peck, Robin Williams, Gene Kelly). Second we compared directly two potential principles of semantic organisation – taxonomic and thematic. Furthermore we considered these principles of organisation in the context of the individuals' personal knowledge base. We selected topics matching the interests and experience of each patient, namely cinema and literature (NBC) and naval history (FBI). The stimulus items were arranged in taxonomic arrays (e.g. Jane Austen, Emily Bronte, Agatha Christie), thematic arrays (e.g. Jane Austen, Pride and Prejudice, Mr Darcy), and unrelated arrays (e.g. Jane Austen, Wuthering Heights, Hercule Poirot). We documented that different patterns of taxonomic and thematic organisation were constrained by whether the individual has limited knowledge, moderate knowledge or detailed knowledge of a particular vocabulary. It is suggested that moderate proper name knowledge is primarily organised by taxonomy whereas extensive experience results in a more detailed knowledge base in which theme is a powerful organising principle.

Refractoriness and the healthy brain: A behavioural study on semantic access

While many behavioural studies on refractory phenomena in lexical/semantic access have focused on the mechanisms involved in the oral production of names, comprehension tasks have been almost exclusively used in neuropsychological studies on brain damaged patients. We report the results of two experiments on healthy participants conducted by means of speeded word to picture matching tasks. They assess the effects of the same variables examined in the study of refractory access dysphasic patients: semantic distance and word frequency (experiment 1) and presentation rate and serial position effects (experiment 2). Semantic access patients usually show little effect of word frequency but a large semantic distance effect. However, critical in characterising the syndrome as ‘refractory’, effects of presentation rate and serial position should also be present. The experiments involved the use of a deadline response procedure. The critical manipulation was the absence of a Response Stimulus Interval (RSI) in the fast presentation rate conditions; slower presentation rates involved 1 s RSI. With these manipulations the typical behavioural pattern of performance provided by semantic access dysphasic patients was reproduced. Semantic distance effects were more powerful than word frequency effects (experiment1). Presentation rate effects were found and, most important for a “refractory” account of the effects, a serial position effect was obtained (experiment 2). These results provide the first evidence of such a broad range of refractory effects at the same time in comprehension tasks in healthy subjects and support a purely semantic account for the locus of refractoriness. Moreover, error analysis showed a predominance of perseverative errors with subsequent representations of the same target, supporting a failure of cognitive control mechanisms as the cause of refractory behaviour. The findings are discussed in the light of current models of lexical and semantic processing.

Inferring semantic organization from refractory access dysphasia: Further replication in the domains of geography and proper nouns but not concrete and abstract concepts

Patients with “refractory access dysphasia” have been a source of unique insight into the organization of previously unexplored domains of semantic knowledge (i.e., proper nouns, geography, concrete and abstract concepts). However, much of the relevant data have been based on the performance of a small number of patients. Here, we present 2 patients who both display a “refractory access” pattern of performance on spoken-word–written-word matching tasks and test their performance in the domains of famous people, geography, and abstract and concrete words. While these patients show performance similar to that for the previously reported patients in the domains of famous people and geography, they show a very different pattern of performance with abstract and concrete nouns. We discuss possible reasons why patients may differ in performance and evidence for and against the “differential frameworks” hypothesis for the organization of concrete and abstract concepts.

The Influence of refractoriness upon comprehension of non-verbal auditory stimuli

An investigation of non-verbal auditory comprehension in two patients with global aphasia following stroke is reported. The primary aim of the investigation was to establish whether refractory access disorders can affect non-verbal input modalities. All previous reports of refractoriness, a cognitive syndrome characterized by response inconsistency, sensitivity to temporal factors and insensitivity to item frequency, have involved comprehension tasks which have a verbal component. Two main experiments are described. The first consists of a novel sound-to-picture and sound-to-word matching task in which comprehension of environmental sounds is probed under conditions of semantic relatedness and semantic unrelatedness. In addition to the two stroke patients, the performance of a group of 10 control patients with non-vascular pathology is reported, along with evidence of semantic relatedness effects in sound comprehension. The second experiment examines environmental sound comprehension within a repetitive probing paradigm which affords assessment of the effects of semantic relatedness, response consistency and presentation rate. It is demonstrated that the two stroke patients show a significant increase in error rate across multiple probes of the same set of sound stimuli, indicating the presence of refractoriness within this non-verbal domain. The implications of the results are discussed with reference to our current understanding of the mechanisms of refractoriness.

Refractory access disorders and the organization of concrete and abstract semantics: Do they differ?

Patients with ‘refractory semantic access deficits’ demonstrate several unique features that make them important sources of insight into the organization of semantic representations. Here we attempt to replicate several novel findings from single-case studies reported in the literature. Patient UM-103 displays the cardinal features of a ‘refractory semantic access deficit’ and showed many of the same effects of semantic relatedness reported in the literature. However, when probing concrete and abstract words, this patient revealed very different patterns of performance compared to two previously reported patients. We discuss the implications of our data for models of semantic organization of abstract and concrete words.

The Semantic Organisation of Mass Nouns: Evidence from Semantic Refractory Access Dysphasia

The conceptual properties and organisation of mass noun concepts are examined in a patient (A.Z.) with a semantic refractory access disorder. A cardinal feature of this class of disorder is the build up of interference (refractoriness) between semantically similar concepts. In a series of written word identification tasks, a gradient of semantic relatedness is demonstrated within the broad domain of mass noun concepts but not between different word classes. More detailed examinations of semantic similarity effects within subcategories of mass concepts reveal a variable degree of fine-grain organisation, which may reflect the influence of premorbid personal knowledge and experience. Furthermore, it is demonstrated that common mass or count noun status did not lead to an enhancement of the refractory effects of semantic similarity.

Refractory access disorders and the organization of concrete and abstract concepts: An attempt to replicate

Refractory access disorders and the organization of concrete and abstract concepts: An attempt to replicate

The Different Frameworks Underlying Abstract and Concrete Knowledge: Evidence from a Bilingual Patient with a Semantic Refractory Access Dysphasia

We report the case of a bilingual patient (IRQ) who acquired a semantic refractory access dysphasia following a middle cerebral artery stroke. In a series of spoken word-written word matching tasks, the degree of semantic similarity between target and distractor items was found to affect the accuracy of IRQ's identification of concrete but not abstract words. By contrast, the degree of semantic association between target and distractor items was found to affect response accuracy when identifying abstract but not concrete words. These results provide further corroboration for the notion that abstract concepts are supported by an associative representational network whereas concrete concepts are supported by a categorical representational framework. We also demonstrate an equivalent refractory deficit of comprehension in both English and Arabic. In addition, we provide the first documented evidence of a category-specific refractory deficit of knowledge for abstract words. We would like to thank Dr. David Cohen and the therapists on the Harrow Stroke Unit at Northwick Park Hospital who allowed us to study patients under their care. We are grateful to Dr. Jason Warren for his opinion on the neuroimaging data. We are also indebted to Professor Martin Rossor for his continued support of all aspects of our work. This work was supported by an equipment grant from the Alzheimer's Research Trust.

Qualitatively Different Semantic Representations for Abstract and Concrete Words: Further Evidence from the Semantic Reading Errors of Deep Dyslexic Patients

This paper presents an investigation of the hypothesis that conceptual knowledge for abstract and concrete items is underpinned by qualitatively different representational frameworks (Crutch and Warrington, 2005a). A re-analysis of the semantic reading errors of four deep dyslexic patients is presented, examining the incidence of semantically associated and semantically similar errors in response to abstract and concrete target words. The results demonstrate that abstract target words elicit a greater proportion of associative than similar errors, while concrete words show the reverse pattern. These findings provide evidence which converges with that previously documented for a semantic refractory access dysphasic to suggest that abstract concepts are represented in an associative network while concrete concepts are represented in a categorical framework. The author would like to express his gratitude to Professor Elizabeth Warrington and Professor Max Coltheart for their helpful comments on an earlier version of this paper. He is also indebted to Mr. Chris Frost for his advice on the statistical analysis of the data, and to Professor Martin Rossor for his support of this work. The author is an Alzheimer's Research Trust Fellow.

Comparing and contrasting patients with refractory access and storage semantic impairments

Comparing and contrasting patients with refractory access and storage semantic impairments

Abstract and concrete concepts have structurally different representational frameworks

The architecture supporting our conceptual knowledge of abstract words has remained almost entirely unexplored. By contrast, a vast neuropsychological, neurolinguistic and neuroimaging literature has addressed questions relating to the structure of the semantic system underpinning our knowledge of concrete items (e.g. artefacts and animals). In the context of semantic refractory access dysphasia, a series of experiments exploring and comparing abstract and concrete word comprehension are described. We demonstrate that semantically associated abstract words reliably interfere with one another significantly more than semantically synonymous abstract words, while concrete words show the reverse pattern. We report the first evidence that abstract and concrete word meanings are based in representational systems that have qualitatively different properties. More specifically, we show that abstract concepts, but not concrete concepts, are represented in an associative neural network. Furthermore, our patient was found to have significantly greater difficulty in identifying high frequency than low frequency abstract words. This observation constitutes the first evidence of an inverse word frequency effect. Our results challenge the generality of many existing models of human conceptual knowledge, which derive their structure from experimental findings in the concrete domain alone.

A circumscribed refractory access disorder: A verbal semantic impairment sparing visual semantics

We report the case of a patient (AZ) with a semantic refractory access dysphasia. On matching-to-sample tests assessing comprehension of the spoken word, AZ shows all the hallmarks of a refractory access disorder, namely inconsistent performance on repeated testing and sensitivity to both presentation rate and the semantic similarity between competing responses. However, on tasks examining her visual knowledge, such as matching two structurally different exemplars of the same item, AZ's performance is quantitatively and qualitatively different. In a series of experiments testing her knowledge of animate and inanimate items, AZ demonstrated significantly worse performance with verbal-visual matching than with visual-visual matching. Furthermore, response accuracy was observed to decrease with successive probing of an item in the verbal conditions but not the visual conditions. We also demonstrate that this discrepancy cannot be explained on the basis of either task difficulty or presentation rate. We attribute our results to a build-up of refractoriness in the systems mediating verbal comprehension whilst those underlying visual comprehension remain unaffected. We argue that our data speak against a unitary amodal semantic system and in favour of at least partially separate verbal and visual semantic processing.

The semantic organisation of proper nouns: the case of people and brand names

We describe the performance of a patient (AZ) with a semantic refractory access disorder on a series of experiments probing comprehension of two broad proper noun categories, namely person names and brand names. By inducing and manipulating the semantic relatedness effects which are commonly observed in semantic refractory access patients, we demonstrate that famous person knowledge is primarily organised by occupation, whilst knowledge of brands is organised by product type. For instance, we show that AZ has significantly greater difficulty identifying a famous person from among distractor personalities who have the same occupation (e.g. composers: Beethoven, Mozart, Handel, and Bach) than those who have different occupations (e.g. Beethoven, Picasso, Shakespeare, and Jefferson). We also show that such semantic relatedness effects do not occur when stimuli are grouped by another variable such as nationality. We argue that these semantic distance effects reflect the greater build-up of refractoriness among concepts which are supported by shared neural circuitry. In psychological space, it seems natural that these individuals should be classified in this way. The strength of our findings lie in the fact that this organisation of psychological space is mirrored by neural organisation. Thus, we report a previously undocumented degree of fine-grain organisation within conceptual knowledge of these classes of proper nouns. We also interpret our data as providing the strongest empirical support to date for the semantic module of cognitive models of person recognition.

Further Experience With a Percutaneously Inserted Double-Lumen Silastic Catheter for End-Stage Renal Failure Patients With Refractory Vascular Access Problems

Further Experience With a Percutaneously Inserted Double-Lumen Silastic Catheter for End-Stage Renal Failure Patients With Refractory Vascular Access Problems

Further Experience With a Percutaneously Inserted Double- Lumen Silastic Catheter for End-Stage Renal Failure Patients With Refractory Vascular Access Problems

Further Experience With a Percutaneously Inserted Double- Lumen Silastic Catheter for End-Stage Renal Failure Patients With Refractory Vascular Access Problems

Maintaining the Patency of Double-Lumen Silastic Jugular Catheters for Haemodialysis

A system has been developed for maintaining the patency of double lumen silastic jugular catheters in patients with refractory vascular access problems. Most patients receive a small daily dose of aspirin. Selected patients also receive warfarin to maintain a prothrombin time (PT) of 15, 20, or 30 seconds. Inadequate blood flow due to thrombus obstruction can be overcome by the intravenous administration of urokinase, 250.000 units. This can be administered safely to outpatients provided that heparin is not given simultaneously. Occasionally a second dose may be required. By adopting this policy all catheter obstructions have been overcome. The danger of iatrogenic bleeding cannot be discounted. Warfarin therapy must be very closely monitored.