Biomedical subjects

Keith R Laws

Publications and source records attributed to Keith R Laws.

At least 19 recordsLinked to original sources

PubMed2006

An attenuation of the 'normal' category effect in patients with Alzheimer's disease: a review and bootstrap analysis.

There is a consensus that Alzheimer's disease (AD) impairs semantic information, with one of the first markers being anomia i.e. an impaired ability to name items. Doubts remain, however, about whether this naming impairment differentially affects items from the living and nonliving knowledge domains. Most studies have reported an impairment for naming living things (e.g. animals or plants), a minority have found an impairment for nonliving things (e.g. tools or vehicles), and some have found no category-specific effect. A survey of the literature reveals that this lack of agreement may reflect a failure to control for intrinsic variables (such as familiarity) and the problems associated with ceiling effects in the control data. Investigating picture naming in 32 AD patients and 34 elderly controls, we used bootstrap techniques to deal with the abnormal distributions in both groups. Our analyses revealed the previously reported impairment for naming living things in AD patients and that this persisted even when intrinsic variables were covaried; however, covarying control performance eliminated the significant category effect. Indeed, the within-group comparison of living and nonliving naming revealed a larger effect size for controls than patients. We conclude that the category effect in Alzheimer's disease is no larger than is expected in the healthy brain and may even represent a small diminution of the normal profile.

Aged↗

PubMed2006

The impact of colour, spatial resolution, and presentation speed on category naming.

Studies of neurological patients with category-specific agnosia have provided important contributions to our understanding of object recognition, although the meaning of such disorders is still hotly debated. One crucial line of research for our understanding of category effects, is through the examination of category biases in healthy normal subjects. This approach has, however, led to contradictory findings with advantages both for natural kinds and for man-made things being documented in healthy subjects. It has been proposed that task conditions may influence the direction of advantage (Gerlach, 2001) and in particular, that sub-optimal viewing conditions underpin natural kinds advantages, while man-made advantages emerge under more optimal viewing conditions. In two experiments with normal subjects, we examined the roles played by spatial resolution (blurring), stimulus type (colour and texture), and speed of presentation in picture naming across category. In both experiments, healthy subjects showed a natural kind advantage for original stimuli and for blurred colour stimuli (at slow and fast presentation speeds), while an advantage for man-made things emerged for line-drawings that were blurred and presented slowly. The implications for category-specific object recognition deficits are discussed.

Adult↗

PubMed2006

Formal thought disorder is characterised by impaired lexical access.

Recent studies have proposed that difficulty with accessing the lexical-semantic memory store may underpin some of the specific linguistic problems associated with formal thought disorder (FTD). We examined the consistency of name retrieval as an indicator of the ability to access lexical-semantic knowledge in patients with and without marked FTD to see if problems are specific to the former or common to schizophrenic patients in general. A graded naming test was administered on two separate occasions 8-16 weeks apart to 48 participants in three groups: 16 schizophrenic patients with high ratings of FTD, 16 schizophrenic patients with low ratings of FTD and 16 healthy controls. We compared the groups for naming consistency across time and the relationship between naming consistency and specific symptoms of FTD. Both patient groups had impaired naming and this was significantly greater in high than low FTD patients. The high FTD patients showed a profile that differed from both low FTD patients and healthy controls insofar as their naming was inconsistent across time, characteristic of an access disorder. Specifically, the FTD symptoms of derailment, tangentality and incoherence were related to the ability to access the lexical-semantic store. In conclusion, most patients with schizophrenia show an impaired semantic memory store. Nevertheless, FTD is associated with additional lexical-semantic difficulties that are quantitatively different to those seen in patients without FTD, and which may reflect disorganized semantic access.

Adult↗

PubMed2006

Category-specificity can emerge from bottom-up visual characteristics: evidence from a modular neural network.

The role of bottom-up visual processes in category-specific object recognition has been largely unexplored. We examined the role of low-level visual characteristics in category specific recognition using a modular neural network comprising both unsupervised and supervised components. One hundred standardised pictures from ten different categories (five living and five nonliving, including body parts and musical instruments) were presented to a Kohonen self-organising map (SOM) which re-represents the visual stimuli by clustering them within a smaller number of dimensions. The SOM representations were then used to train an attractor network to learn the superordinate category of each item. The ease with which the model acquired the category mappings was investigated with respect to emerging category effects. We found that the superordinates could be separated by very low-level visual factors (as extracted by the SOM). The model also accounted for the well documented atypicality of body parts and musical instrument superordinates. The model has clear relevance to human object recognition since the model was quicker to learn more typical category exemplars and finally the model also accounted for more than 20% of the naming variance in a sample of 57 brain injured subjects. We conclude that purely bottom-up visual characteristics can explain some important features of category-specific phenomena.

Female↗

PubMed2006

Name relearning in elderly patients with schizophrenia: episodic and temporary, not semantic and permanent.

INTRODUCTION: Recent reports of lexical-semantic deficits in patients with schizophrenia (Laws, Al-Uzri, & Mortimer, 2000; Laws, McKenna, & Kondel, 1998) suggest that younger patients have problems accessing intact memories and older patients show apparent "loss" of the lexical-semantic memory representations themselves. METHODS: Picture naming for everyday items was examined in a unique series of elderly patients with schizophrenia (n = 10) with a mean illness duration of 45.5 years; and compared with that in patients with probable Alzheimer's disease (n = 18) and elderly healthy controls (n = 27). Naming consistency across time was used as an indicator of whether the schizophrenic patients had difficulty accessing representations or a loss of the representations themselves. Finally, we examined the ability of the schizophrenic patients to relearn the names of unnamed items across four weekly retraining sessions and to retain them at a one month follow-up. RESULTS: The elderly schizophrenic patients were as anomic as patients with probable Alzheimer's disease. Consistency analysis revealed that the patients had storage deficits. Analysis of patient error types was consistent with a semantic deficit. Finally, the schizophrenic patients showed significant improvement with relearning, but this was not maintained at follow-up. CONCLUSIONS: Elderly patients with schizophrenia show a profound and stable anomia. Although name relearning induced some significant gains in naming, these were short-term and reflect episodic rather than semantic reinstatement of representations. Implications for cognitive remediation are discussed.

Aged↗

PubMed2006

Cognitive function and social abilities in patients with schizophrenia: relationship with atypical antipsychotics.

Although atypical antipsychotics have been associated with improvements in cognitive function in schizophrenia, the neurochemical basis for such effects is not well understood. Candidate neurotransmitter systems primarily involve dopamine and serotonin. The current study explored this issue by examining the cognitive abilities, social function and quality of life in patients with schizophrenia who were medicated with atypical antipsychotics. Comparisons were done for matched schizophrenia patients who were on antipsychotics with (i) an affinity for multiple receptors (olanzapine, clozapine, quetiapine) versus those that have preferential affinity for dopamine receptors (risperidone, amisulpride); and patients on medication with (ii) a high affinity for serotonin (5HT-2A) receptors (risperidone, olanzapine, clozapine) versus those with a low (or no) affinity for 5HT-2A receptors (quetiapine, amisulpride). No differences emerged between groups on any cognitive or social variable when the groups were compared for the dopaminergic properties of antipsychotic medication. By contrast, differences did emerge when patients were compared on the 5HT-2A affinity of their antipsychotic medications. Patients on low 5HT-2A-affinity antipsychotics exhibited a better performance on a measure of selective attention and adjustment to living. These findings accord with the notion that serotonergic mechanisms are important determinants of both the cognitive and the social effects of the atypical antipsychotics.

Adult↗

PubMed2005

Crowded and sparse domains in object recognition: consequences for categorization and naming.

Some models of object recognition propose that items from structurally crowded categories (e.g., living things) permit faster access to superordinate semantic information than structurally dissimilar categories (e.g., nonliving things), but slower access to individual object information when naming items. We present four experiments that utilize the same matched stimuli: two examine superordinate categorization and two examine picture naming. Experiments 1 and 2 required participants to sort pictures into their appropriate superordinate categories and both revealed faster categorization for living than nonliving things. Nonetheless, the living thing superiority disappeared when the atypical categories of body parts and musical instruments were excluded. Experiment 3 examined naming latency and found no difference between living and nonliving things. This finding was replicated in Experiment 4 where the same items were presented in different formats (e.g., color and line-drawn versions). Taken as a whole, these experiments show that the ease with which people categorize items maps strongly onto the ease with which they name them.

Adult↗

PubMed2005

Testing for a deficit in single-case studies: effects of departures from normality.

In neuropsychological single-case research inferences concerning a patient's cognitive status are often based on referring the patient's test score to those obtained from a modestly sized control sample. Two methods of testing for a deficit (z and a method proposed by Crawford and Howell [Crawford, J. R. & Howell, D. C. (1998). Comparing an individual's test score against norms derived from small samples. The Clinical Neuropsychologist, 12, 482-486]) both assume the control distribution is normal but this assumption will often be violated in practice. Monte Carlo simulation was employed to study the effects of leptokurtosis and the combination of skew and leptokurtosis on the Type I error rates for these two methods. For Crawford and Howell's method, leptokurtosis produced only a modest inflation of the Type I error rate when the control sample N was small-to-modest in size and error rates were lower than the specified rates at larger N. In contrast, the combination of leptokurtosis and skew produced marked inflation of error rates for small Ns. With a specified error rate of 5%, actual error rates as high as 14.31% and 9.96% were observed for z and Crawford and Howell's method respectively. Potential solutions to the problem of non-normal data are evaluated.

Bias↗

PubMed2005

Executive inhibition and semantic association in schizophrenia.

Research indicates that some patients with schizophrenia display aberrant inhibition of semantic memory, which may underpin formal thought disorder (FTD). We administered a novel Stroop-like paradigm to three groups of participants: 15 schizophrenic patients with formal thought disorder (FTD), 16 with low FTD ratings, and 15 healthy matched controls. They were required to inhibit a prepotent response for a (previously instructed) required response. Four conditions examined the effect of executive demands by manipulating the relatedness between prepotent and required responses (i.e., identical, semantically related, or unrelated). Two further conditions examining executive function working memory demands required the naming of real or abstract pictures that did and did not necessitate inhibition, respectively. Patients with and without FTD experienced increased difficulty when executive function working memory was required. Moreover, those with FTD also showed increased executive inhibition, but the pattern of errors suggested that the result of this was an automatic activation of semantically related representations. The findings support the notion that increased inhibition underpins the disorganised access to semantic memory in patients with FTD.

Association↗

PubMed2005

When is category specific in Alzheimer's disease?

Mixed findings have emerged concerning whether category-specific disorders occur in Alzheimer's disease. Factors that may contribute to these inconsistencies include: ceiling effects/skewed distributions for control data in some studies; differences in the severity of cognitive deficit in patients; and differences in the type of analysis (in particular, if and how controls are used to analyse single case data). We examined picture naming in Alzheimer's patients and matched elderly healthy normal controls in three experiments. These experiments used stimuli that did and did not produce ceiling effects/skewed data in controls. In Experiment 1, we examined for category effects in individual DAT patients using commonly used analyses for single cases (chi2 and z-scores). The different techniques produced quite different outcomes. In Experiment 2a, we used the same techniques on a different group of patients with similar outcomes. Finally, in Experiment 2b, we examined the same patients but (a) used stimuli that did not produce ceiling effects/skewed distributions in healthy controls, and (b) used statistical methods that did not treat the control sample as a population. We found that ceiling effects in controls may markedly inflate the incidence of dissociations in which living things are differentially impaired and seriously underestimate dissociations in the opposite direction. In addition, methods that treat the control sample as a population led to inflation in the overall number of dissociations detected. These findings have implications for the reliability of category effects previously reported both in Alzheimer patients and in other pathologies. In particular, they suggest that the greater proportion of living than nonliving deficits reported in the literature may be an artifact of the methods used.

Aged↗

PubMed2005

"Illusions of normality": a methodological critique of category-specific naming.

Category-specific disorders are perhaps the archetypal example of domain-specificity--being typically defined by the presence of dissociations between living and nonliving naming ability in people following neurological damage. The methods adopted to quantify naming across categories are therefore pivotal since they provide the criterion for defining whether patients have a category effect and necessarily influence the subsequent direction and the interpretation of testing. This paper highlights a series of methodological concerns relating to how we measure and define category (or any) dissociations. These include the common failure to include control data or the use of control data that is inappropriate e.g. at ceiling, unmatched. A review of past cases shows that the overwhelming majority suffers from these problems and therefore challenges conclusions about the purported empirical demonstrations of dissociations and double dissociations in the category specific literature. This is not a refutation of category deficits, but skepticism about the current existence of any convincing empirical demonstrations of category specific double dissociations. As a potential solution, certain minimal criteria are proposed that might aid with the attempt to document category effects that are more methodologically convincing.

Anomia↗

PubMed2005

What happens to semantic memory when formal thought disorder remits? Revisiting a case study.

INTRODUCTION: Laws, Kondel, and McKenna (1999) previously reported a case study analysis of a schizophrenic patient (TC) with severe formal thought disorder (FTD). Examining consistency across item and modality of input, Laws et al. documented an impairment of access to semantic knowledge in TC. METHOD: Following substantial improvement in his FTD, we readministered the same extensive battery of neuropsychological tests tapping semantic memory functioning. RESULTS: Whilst TC's naming remained relatively good, it also became more consistent across both time and modality. Tasks tapping language comprehension and understanding of semantic association revealed some significant improvements. Nevertheless, TC showed a residual propensity to verify false information. CONCLUSION: Improvement in FTD in schizophrenia was accompanied by a better and more stable semantic memory performance in TC. The findings are consistent with, and expand upon the original suggestion that thought disorder reflects disorganised access to semantic memory.

Journal Article↗

PubMed2005

Storage and access procedures in schizophrenia: evidence for a two phase model of lexical impairment.

Evidence has accumulated to show that schizophrenia is characterized by lexical-semantic difficulties; however, questions remain about whether schizophrenics have problems in accessing intact representations or a loss of the representations themselves. Both access and storage types of disorder have been reported and it has been speculated that this may reflect a transition from the former to latter with increasing length of illness. This study investigated whether illness duration, age or estimated premorbid IQ predict the size and accessibility of the lexical store. Fifty-six schizophrenic patients (chosen to represent a wide range of illness duration from 3-40 years) and 24 matched healthy controls were asked to name 120 pictures on two occasions. Estimates of store size and retrieval probability were derived from a two parameter stochastic Markov chain model. This revealed that even early in the course of illness, schizophrenics appear to have suffered a reduction in lexical store size and that those with longer length of illness show deficits in both their store size and their ability to retrieve names from that store.

Adult↗

PubMed2005

Category deficits and paradoxical dissociations in Alzheimer's disease and Herpes Simplex Encephalitis.

Most studies examining category specificity are single-case studies of patients with living or nonliving deficits. Nevertheless, no explicit or agreed criteria exist for establishing category-specific deficits in single cases regarding the type of analyses, whether to compare with healthy controls, the number of tasks, or the type of tasks. We examined two groups of patients with neurological pathology frequently accompanied by impaired semantic memory (19 patients with Alzheimer's disease and 15 with Herpes Simplex Encephalitis). Category knowledge was examined using three tasks (picture naming, naming-to-description, and feature verification). Both patient groups were compared with age- and education-matched healthy controls. The profile in each patient was examined for consistency across tasks and across different analyses; however, both proved to be inconsistent. One striking finding was the presence of paradoxical dissociations (i.e., patients who were impaired for living things on one task and nonliving things on another task). The findings have significant implications for how we determine category effects and, more generally, for the methods used to document double dissociations across individual cases in this literature.

Aged↗

PubMed2004

Stability of set-shifting and planning abilities in patients with schizophrenia.

Patients with schizophrenia have deficits in executive function that involve attentional set-shifting and planning ability. It is unclear, however, whether such deficits are stable during the course of the illness or if they fluctuate in response to medication effects or symptom changes. Patients with a DSM-IV diagnosis of schizophrenia (n=28) and healthy control subjects (n=17) were tested on computerised measures of attentional set-shifting and planning at baseline and 9-month follow-up. The measures used were the Intra/Extradimensional Shift test (ID/ED) and the Stockings of Cambridge test (SoC) from the Cambridge Automated Neuropsychological Testing Battery (CANTAB). On both tests, the patients were poorer than controls at baseline; however, there was no evidence of change over the 9-month follow-up. Additionally, there was little evidence of a relationship between executive test performance and medication or length of illness. This study accords with the presence of executive processing deficits in schizophrenia that are stable across time.

Adolescent↗

PubMed2004

An early marker for semantic memory impairment in patients with schizophrenia.

INTRODUCTION: Semantic memory impairment is now a well-documented phenomenon in patients with schizophrenia. Nevertheless, the characteristics of this deficit and any early markers remain contentious. METHODS: In this preliminary study, 12 schizophrenic patients underwent longitudinal assessment using a battery of semantic memory tests. Patient performance was compared to 12 matched controls. Using set criteria (derived from Warrington & Shallice, 1979), we examined whether the patients had a disorder affecting access to intact representations, or a degradation/loss of the representations themselves. The criteria were: consistency across time and modality, level of attribute information, and responsiveness to cueing. Finally, we compared patient naming for the same items across two naming tests (naming-to-description and picture naming) to determine cross-modality consistency. RESULTS: As expected, normal controls outperformed the patients on all tests. Naming-to-description was the most significant differentiator between patients and controls. Patients were inconsistent across both time and modality, showed minimal attributional knowledge impairment, and improved significantly with cueing on two naming tests. CONCLUSION: The profile of results indicates an access-type semantic deficit in this cohort of patients with schizophrenic. Finally, on a naming-to-description task, the patients failed to name up to 20% of items that they could name to picture. This suggests that naming-to-definition may act as an early marker of semantic memory impairment.

Journal Article↗

PubMed2003

Visual object processing in schizophrenia: evidence for an associative agnosic deficit.

Early studies suggested visual form perception impairment in schizophrenia. To re-examine this claim and characterise the deficit neuropsychologically, 41 schizophrenic patients were administered tests sensitive to different levels of visual object perception and recognition. Intellectually well-preserved patients were examined separately on these and additional tests. Single case analysis was also applied to four patients showing varying degrees of general intellectual impairment. As a group, the patients showed little impairment on tests of early visual object perception, but greater impairment on higher-level visual processing tests, in particular object recognition and naming. This held true for patients with preserved general intellectual function. Single case analysis suggested that patients with schizophrenia have a selective deficit affecting object recognition and identification, with a pattern similar to visual associative agnosia in neurological patients.

Adolescent↗

PubMed2003

Basic-level visual similarity and category specificity.

The role of visual crowding in category deficits has been widely discussed (e.g.,;; ). Most studies have measured overlap at the superordinate level (compare different examples of 'animal') rather than at the basic level (compare different examples of 'dog'). In this study, we therefore derived two measures of basic-level overlap for a range of categories. The first was a computational measure generated by a self-organising neural network trained to process pictures of living and non-living things; the second was a rating of perceived visual similarity generated by human subjects to the item names. The computational measure indicated that the pattern of crowded/uncrowded does not honour a living/non-living distinction. Nevertheless, different superordinates showed varied degrees of basic-level overlap, suggesting that specific token choice affects some superordinates more than others e.g., individual fruit and vegetable tokens show greater variability than any other items, while tools and vehicles produce more reliable or overlapping basic-level visual representations. Finally, subject ratings correlated significantly with the computational measures indicating that the neural model represents structural properties of the objects that are psychologically meaningful.

Humans↗