Publications
57 results found
Leeson VC, Barnes TR, Harrison M, et al., 2010, The relationship between IQ, memory, executive function, and processing speed in recent-onset psychosis: 1-year stability and clinical outcome., Schizophr Bull, Vol: 36, Pages: 400-409, ISSN: 1745-1701
Studies commonly report poor performance in psychotic patients compared with controls on tasks testing a range of cognitive functions, but, because current IQ is often not matched between these groups, it is difficult to determine whether this represents a generalized deficit or specific abnormalities. Fifty-three first-episode psychosis patients and 53 healthy controls, one-to-one matched for sex, age, and full-scale current IQ, were compared on Wechsler Adult Intelligence Scale (WAIS) subtests representing indices of perceptual organization, verbal comprehension, processing speed, and working memory as well as other tests of executive function and episodic memory. The groups showed an equivalent pattern of performance on all WAIS subtests except digit symbol processing speed, on which the patients were significantly worse. Patients were also worse on measures where performance correlated with digit symbol score, namely working and verbal memory tasks. Standardized residual scores for each subtest were calculated for each patient using the difference between their actual subtest score and a predicted subtest score based on their full-scale IQ and the performance of controls. Scaled scores and residual scores were examined for relationships with clinical measures. Digit symbol-scaled score was significantly correlated with concurrent negative syndrome score at baseline, and digit symbol residual score significantly predicted residual negative symptoms at 1-year follow-up. In summary, our comparison of patients and controls precisely matched for IQ revealed that processing speed was attenuated in recent-onset schizophrenia, contributed significantly to working and episodic memory deficits, and was a prognostic factor for poor outcome at 1 year.
Leeson VC, Robbins TW, Franklin C, et al., 2009, Dissociation of long-term verbal memory and fronto-executive impairment in first-episode psychosis, PSYCHOLOGICAL MEDICINE, Vol: 39, Pages: 1799-1808, ISSN: 0033-2917
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- Citations: 31
Leeson VC, Joyce EM, 2009, Cognitive Impairment in Schizophrenia, Research Progress in Alzheimer's Disease and Dementia, Editors: Sun, ISBN: 9781608761524
Leeson VC, Robbins TW, Matheson E, et al., 2009, Discrimination Learning, Reversal, and Set-Shifting in First-Episode Schizophrenia: Stability Over Six Years and Specific Associations with Medication Type and Disorganization Syndrome, BIOLOGICAL PSYCHIATRY, Vol: 66, Pages: 586-593, ISSN: 0006-3223
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- Citations: 166
Gutierrez L, Wheeler-Kingshott C, Altmann D, et al., 2009, CHARACTERISTICS OF FRONTAL AND TEMPORAL CORTEX IN RELATION TO COGNITIVE DYSFUNCTION IN PATIENTS WITH FIRST-EPISODE PSYCHOSIS, 12th International Congress on Schizophrenia Research, Publisher: OXFORD UNIV PRESS, Pages: 208-208, ISSN: 0586-7614
Leeson VC, Robbins TW, Barnes TR, et al., 2009, ATTENTIONAL SET-SHIFTING ABILITY AND REVERSAL LEARNING OVER THE FIRST THREE YEARS OF PSYCHOTIC ILLNESS: CHANGES OVER TIME AND RELATIONSHIP WITH IQ AND CLINICAL MEASURES, 12th International Congress on Schizophrenia Research, Publisher: OXFORD UNIV PRESS, Pages: 277-277, ISSN: 0586-7614
Harrison I, Barnes TR, Leeson V, et al., 2009, THE IMPACT OF CANNABIS USE ON ILLNESS COURSE IN FIRST EPISODE PSYCHOSIS, 12th International Congress on Schizophrenia Research, Publisher: OXFORD UNIV PRESS, Pages: 319-320, ISSN: 0586-7614
Joyce EM, Leeson VC, Sharma P, et al., 2009, COMPARISON OF CURRENT AND ESTIMATED PREMORBID IQ AT FIRST-EPISODE: UTILITY IN PREDICTING CLINICAL AND COGNITIVE FUNCTIONING DURING THE FIRST THREE YEARS OF PSYCHOTIC ILLNESS, 12th International Congress on Schizophrenia Research, Publisher: OXFORD UNIV PRESS, Pages: 288-288, ISSN: 0586-7614
Leeson VC, Barnes TRE, Hutton SB, et al., 2009, IQ as a predictor of functional outcome in schizophrenia: A longitudinal, four-year study of first-episode psychosis, SCHIZOPHRENIA RESEARCH, Vol: 107, Pages: 55-60, ISSN: 0920-9964
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- Citations: 96
Barnes TRE, Leeson VC, Mutsatsa SH, et al., 2008, Duration of untreated psychosis and social function: 1-year follow-up study of first-episode schizophrenia, BRITISH JOURNAL OF PSYCHIATRY, Vol: 193, Pages: 203-209, ISSN: 0007-1250
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- Citations: 105
Joyce EM, Leeson VC, Mutsatsa SH, et al., 2007, Is the effect of dup on social function mediated via negative symptoms? A one-year follow-up study of first-episode psychosis, 11th International Congress on Schizophrenia Research/8th Biennial Mt Sinai Conference on Cognition in Schizophrenia, Publisher: OXFORD UNIV PRESS, Pages: 592-593, ISSN: 0586-7614
Leeson V, Barnes TR, Kapasi M, et al., 2007, Verbal memory in first episode psychosis: Relationship to IQ, executive function and one year outcome, 10th International Congress on Schizophrenia Research, Publisher: OXFORD UNIV PRESS, Pages: 566-566, ISSN: 0586-7614
Leeson VC, Laws KR, McKenna PJ, 2006, Formal thought disorder is characterised by impaired lexical access, SCHIZOPHRENIA RESEARCH, Vol: 88, Pages: 161-168, ISSN: 0920-9964
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- Citations: 14
Laws KR, Leeson VC, McKenna PJ, 2006, Domain-specific deficits in schizophrenia., Cogn Neuropsychiatry, Vol: 11, Pages: 537-556, ISSN: 1354-6805
INTRODUCTION: Object recognition deficits are well documented in certain neurological disorders (e.g., Alzheimer's disease, herpes simplex encephalitis). Although agnosic problems have been documented in some patients with schizophrenia (Gabrovska et al., 2003), no study has investigated whether such deficits differentially affect specific categories of information (as they sometimes do in neurological cases). METHOD: In Part I of this study, we compared object recognition in 55 patients with chronic schizophrenia and 22 age- and NART IQ-matched healthy controls. In Part II, we present a detailed case study of one patient with schizophrenia (DH) who displays a severe category specific semantic knowledge for living things. RESULTS: Of the patients with schizophrenia, 75% had object recognition below the 5th percentile, and in 11% of cases, a highly specific classical category dissociation emerged (5 cases with nonliving deficit and 1 with living deficit); and two other patients showed strong dissociation for living things. These findings provide convincing evidence of a classical double dissociation across the two categories. In Part II, the in-depth case study of one schizophrenic patient (DH), documented a profound agnosia for living things. While DH displayed intact low level perceptual and spatial ability and could copy drawings, he was severely impaired at naming, picture-name matching, semantic fluency, and could not describe or draw items from memory. CONCLUSIONS: The presence of impaired object recognition in most schizophrenic patients, along with highly selective category specific deficits in a minority, is discussed with reference to similar findings in neurological patients.
Barnes TRE, Leeson VC, Mutsatsa SM, et al., 2006, Duration of untreated psychosis as a predictor of initial treatment response in first episode schizophrenia, 5th International Conference on Early Psychosis, Publisher: ELSEVIER SCIENCE BV, Pages: S115-S115, ISSN: 0920-9964
Leeson VC, McKenna PJ, Laws KR, 2005, Storage and access procedures in schizophrenia: evidence for a two phase model of lexical impairment., J Clin Exp Neuropsychol, Vol: 27, Pages: 700-710, ISSN: 1380-3395
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.
Laws KR, Gale TM, Leeson VC, et al., 2005, When is category specific in Alzheimer's disease?, Cortex, Vol: 41, Pages: 452-463, ISSN: 0010-9452
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.
Leeson VC, Simpson A, McKenna PJ, et al., 2005, Executive inhibition and semantic association in schizophrenia., Schizophr Res, Vol: 74, Pages: 61-67, ISSN: 0920-9964
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.
Leeson VC, McKenna PJ, Murray G, et al., 2005, What happens to semantic memory when formal thought disorder remits? Revisiting a case study., Cogn Neuropsychiatry, Vol: 10, Pages: 57-71, ISSN: 1354-6805
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.
Murray GK, Leeson V, McKenna PJ, 2004, Spontaneous improvement in severe, chronic schizophrenia and its neuropsychological correlates., Br J Psychiatry, Vol: 184, Pages: 357-358, ISSN: 0007-1250
Cognitive impairment is well established in schizophrenia but its relationship to the course of the illness remains incompletely understood. Here we document two patients with schizophrenia who underwent neuropsychological testing while chronically unwell, and this was repeated after improvement took place. Both patients showed significant recovery of general intellectual function, accompanied by improvements in some but not all areas of neuropsychological function: executive function remained particularly impaired.
Kondel TK, Mortimer AM, Leeson VC, et al., 2003, Intellectual differences between schizophrenic patients and normal controls across the adult lifespan, JOURNAL OF CLINICAL AND EXPERIMENTAL NEUROPSYCHOLOGY, Vol: 25, Pages: 1045-1056, ISSN: 1380-3395
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- Citations: 13
Gale TM, Laws KR, Frank RJ, et al., 2003, Basic-level visual similarity and category specificity., Brain Cogn, Vol: 53, Pages: 229-231, ISSN: 0278-2626
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.
Laws KR, Gale TM, Leeson VC, 2003, The influence of surface and edge-based visual similarity on object recognition., Brain Cogn, Vol: 53, Pages: 232-234, ISSN: 0278-2626
The role of 'visual similarity' has been emphasised in object recognition and in particular, for category-specific agnosias. [Laws and Gale, 2002] recently described a measure of pixel-level visual overlap for line drawings (Euclidean Overlap: EO[line]) that distinguished living and nonliving things and predicted normal naming errors and latencies ( [Laws et al., 2002]). Nevertheless, it is important to extend such analyses to stimuli other than line drawings. We therefore developed the same measure for greyscale versions of the same stimuli (EO[grey]), i.e., that contain shading and texture information. EO[grey], however, failed to differentiate living from nonliving things and failed to correlate with naming latencies to the greyscale images. By contrast, EO[line] did correlate with the naming latencies. This suggests that similarity of edge information is more influential than similarity of surface characteristics for naming and for categorically separating living and nonliving things (be they line drawings or greyscale images).
Laws KR, Leeson VC, Gale TM, 2003, Inflated and contradictory category naming deficits in Alzheimer's disease?, Brain Cogn, Vol: 53, Pages: 416-418, ISSN: 0278-2626
Although some studies have documented category-specific deficits in patients with Alzheimer's disease, others have not. One possible reason is that where control groups have been used in previous studies, they have performed at ceiling; and this may spuriously affect the incidence and type of deficit reported (especially with common statistical techniques such as z-scores). We examined this issue in 18 Alzheimer's patients and 26 elderly controls, who named two picture sets: a simple set that typically produces ceiling effects (Set 1) and one that produces a normal distribution in controls (Set 2). Sets 1 and 2 produced inconsistent and even contradictory deficits in the same patients. The results also show that ceiling effects may inflate the number of living thing deficits and hence, distort the reported ratio of living to nonliving cases.
Laws KR, Leeson VC, Gale TM, 2002, A domain-specific deficit for foodstuffs in patients with Alzheimer's disease., J Int Neuropsychol Soc, Vol: 8, Pages: 956-957, ISSN: 1355-6177
Laws KR, Leeson VC, Gale TM, 2002, The effect of 'masking' on picture naming., Cortex, Vol: 38, Pages: 137-147, ISSN: 0010-9452
It is frequently assumed that because compared to nonliving things, living things are less familiar, have lower name frequency, and are more visually complex, this makes them more difficult to name by patients and normal subjects. This has also been implicitly accepted as an explanation for the greater incidence of living thing disorders. Patient studies do not, however, typically contain any premorbid data and so, we do not know that the same variables would have necessarily predicted their 'normal' performance. To examine this issue, we measured picture-naming latencies in normal subjects presented with unmasked and masked versions of the same line drawings. In accord with other recent studies, living things were named faster than nonliving things. Furthermore, contrary to some theories of category naming, the living thing advantage persisted regardless of whether stimuli were undegraded, degraded or the density of degradation. Finally, multiple simultaneous regression analyses showed that one visual variable (Euclidean Overlap) and one linguistic variable (Age of Acquisition) predicted naming latencies across all masked and unmasked conditions. Other variables either had no predictive value (Contour Overlap; Name Frequency; Category); predicted only high masking (Visual Complexity; Familiarity), or normal and low masking (Number of Phonemes). These findings imply that the more commonly documented deficits for living things do not reflect an exaggeration of the normal profile (be it with masked or unmasked stimuli) or the influence of the same variables that affect normal naming.
Kondel TK, Hirsch SR, Leeson VC, et al., 2002, Severe anomia in elderly schizophrenics: Does retraining improve naming?, SCHIZOPHRENIA RESEARCH, Vol: 53, Pages: 150-150, ISSN: 0920-9964
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- Citations: 1
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