D. John Done

VISUAL CROWDING AND CATEGORY SPECIFIC DEFICITS FOR PICTORIAL STIMULI : A NEURAL NETWORK MODEL

This paper describes a series of modular neural network simulations of visual object processing. In a departure from much previous work in this domain, the model described here comprises both supervised and unsupervised modules and processes real pictorial representations of items from different object categories. The unsupervised module carries out bottom-up encoding of visual stimuli, thereby developing a “perceptual” representation of each presented picture. The supervised component then classifies each perceptual representation according to a target semantic category. Model performance was assessed (1) during learning, (2) under generalisation to novel instances, and (3) after lesion damage at different stages of processing. Strong category effects were observed throughout the different experiments, with living things and musical instruments eliciting greater recognition failures relative to other categories. This pattern derives from within-category similarity effects at the level of perceptual representation and our data support the view that visual crowding can be a potentially important factor in the emergence of some category-specific impairments. The data also accord with the cascade model of object recognition, since increased competition between perceptual representations resulted in category-specific impairments even when the locus of damage was within the semantic component of the model. Some strengths and limitations of this modelling approach are discussed and the results are evaluated against some other accounts of category-specific recognition failure.

Loss of high-level perceptual knowledge of object structure in DAT.

Visual object recognition and naming deficits in patients with dementia of the Alzheimer type (DAT) have typically been attributed to deficits in semantic processing. On a visual object naming test, a group of 10 mild, early stage DAT patients (mean MMSE=23.8) were found to suffer from anomia, compared to a group of 10 age-matched control participants. DAT naming errors were typically within category (commission), associative or circumlocutory errors. Performance on tests of low level visuo-spatial ability fell within the normal range. Together these results suggested that anomia resulted from a dysfunctional semantic system with intact visual perception. However, in a naming task using visually degraded images of familiar objects, the recognition threshold in DAT patients was significantly higher, indicating the need for a more visually complete object representation, before it could be accurately recognised. In a matched task using words visually degraded in an identical manner, the recognition threshold for DAT patients was very similar to that of the control group. It is argued that these results support the idea that impaired structural descriptions of objects (i.e., pre-semantic representation of an object within the visual perceptual system) combines with degraded semantic representations to produce anomia in mild early stage DAT.

Risk of Adult Schizophrenia and Its Relationship to Childhood IQ in the 1958 British Birth Cohort

BACKGROUND An inverse relationship between risk of schizophrenia and premorbid IQ is a robust empirical finding. Cognitive impairment may be a core feature of schizophrenia in addition to the clinical symptoms that have historically defined the disorder. AIMS To evaluate whether risk of schizophrenia increases linearly or nonlinearly with the lowering of premorbid IQ after adjustment for a range of confounding factors. METHODS IQ data from the 1958 National Child Development Study, a prospective national birth cohort (n = 17 419), were linked with psychiatric admissions in England and Wales over a 20-year period. Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition diagnoses were derived from case notes. RESULTS A clear nonlinear inverse relationship between general intelligence at ages 7 and 11 and risk of adult psychosis was found even after adjustment for potential social, behavioral, or demographic confounding factors. No such relationship was found for affective disorders. CONCLUSIONS The nonlinear relationship suggests an excess risk of schizophrenia in children with premorbid IQ in the learning disabilities range. Previous reports of a linear relationship are likely to be a result of less sensitive statistical methods for detecting nonlinearity.

Elasticity and confabulation in schizophrenic delusions.

BACKGROUND This experiment examines two aspects of delusional cognition that have been reported clinically but not investigated empirically. These are the incorporation of potentially conflicting information into the recall of delusion-related scripts and the type and amount of material produced additional to that presented for recall, referred to here as confabulation. METHODS Three groups of patients--deluded schizophrenics, non-deluded schizophrenics and matched non-psychiatric controls--were asked to recall two 15-item scripts, which comprised 10 typical and five atypical components. It was hypothesized that deluded subjects whose delusion was relevant to one of the scripts would recall more of the atypical components of the script and would also be less likely to make script-atypical confabulations in the recall of this particular script. RESULTS Recall was assessed for the amount and type of content remembered and the amount and type of confabulation. The results did not support the hypothesis that atypical items would be incorporated into the recall of delusion-relevant material. However, deluded subjects did retain their schema boundaries in the recall of script items relevant to their own delusion but were less able to adhere to a script framework in the recall of material unrelated to their delusion. CONCLUSIONS These results are discussed within a schema specific account of delusions, which conceptualizes the delusion as an overused schema whose preferential use leads to a failure to develop other scripts but whose own contents remain well-defined.

A case series evaluation of a brief, psycho-education approach intended for the prevention of relapse in bipolar disorder

The development of a brief psychological intervention aimed at clinicians without high levels of bipolar disorder expertise was described, and the manual based therapy was evaluated for feasibility with 13 bipolar diagnosed clients. Outcome was assessed using inventories related to central concerns with the bipolar population including suicide risk (Beck Hopelessness Scale), perceived control over mood and other internal states (Perceived Control of Internal States Scale) and satisfaction with treatment (Client Satisfaction Questionnaire). Data from Visual Analogue Scales and research interviews were used to complement the main results. Significant improvements were observed on all measures and it is concluded that the evaluated treatment can have important effects on central aspects of the bipolar experience and that it can be a useful adjunct to pharmacological therapies. Implications for clinical practice and service provision are discussed.

Overinclusive thought and loosening of associations are not unique to schizophrenia and are produced in Alzheimer's dementia

Introduction. Bleulers concept of loosening of associations which he believed epitomised psychotic thinking can manifest as overinclusion (merging of semantic categories) on semantic categorisation tasks. Overinclusion is explained by excessive activation within the semantic memory network to subordinate features with low associative strength. Therefore patients with degradation of subordinate semantic knowledge (e.g., with Alzheimers Dementia—AD) should not produce overinclusion errors. Methods. 22 people with schizophrenia and 26 people with AD (nonpsychotic, semantic memory impairment) were compared on a semantic categorisation test, the Category Generation Test (CGT). The CGT involves free-sorting 45 cards of pictured objects from five taxonomic groups (e.g., animals). Overinclusion and underinclusion (subdivision of categories) errors were recorded and the strategies used in generating these abnormal categories were explored qualitatively. Results. Two-thirds of both groups generated abnormal categories, including frequent overinclusions. Using a semantic probes test, abnormal categorisations could not be attributed to knowledge degradation as this appeared preserved. Qualitatively, the two groups differed in their sorting strategies. Conclusions. Loosening of associations is found in nonpsychotic people, who have semantic memory impairments (e.g., AD), using semantic knowledge tasks. However there may be different explanations; atypical semantic categorisation in schizophrenia appears to result from attention to thematic rather than feature-based associations.

Pragmatic use of Language by Children who develop Schizophrenia in adult life

At eleven years of age all children in a UK national birth cohort wrote short stories about the life they expected to be leading at age 25. Using a data linkage exercise, we identified those who later developed schizophrenia, affective psychosis, or other non-psychotic psychiatric disorders in later life based on the PSE CATEGO diagnostic system. The majority of these had completed the written essays. Controls from the reference population were selected, matched for gender, IQ and social and economic status. The essays were scored using well established methods for assessing pragmatic use of language, namely narrative coherence and linguistic cohesion. We hypothesised that children pre-morbid for schizophrenia (Pre-Scz) would obtain low scores on all these measures. However this general hypothesis was largely disproved by the data, although some unpredicted gender effects were found. It is concluded that thought is organised in an unexceptional way in adolescents before they develop schizophrenia, once the data are corrected for any lowering of general cognitive ability in the Pre-Scz cases.

Recent research relevant to discharge planning from medium secure psychiatric units: re-examining the literature

Clinicians working in NHS and private medium secure units aiming to produce effective community care plans for their patients are faced with large amounts of information from studies of community care. Conflicting results from large-scale studies have been further complicated by semantic confusions. Lack of consideration of the impact of international differences in systems of delivery of health and social care may also have affected attempts to replicate research results cross-nationally. Re-examining the literature for evidence of effectiveness with these points in mind produces some useful evidence. Using a needs-based approach to consider the characteristics of the current patient population in medium secure units presents possibilities of formulating effective community care plans based on current research evidence in the absence of studies of this particular group.

A Modular Attractor Model of Semantic Access

This paper presents results from lesion experiments on a modular attractor neural network model of semantic access. Real picture data forms the basis of perceptual input to the model. An ultrametric attractor space is used to represent semantic memory and is implemented using a biologically plausible variant of the Hopfield model. Lesioned performance is observed to be in agreement with neuropsychological data. A local field analysis of the attractor states of semantic space forms a basis for interpreting these results.

Learning through experience: an emergent connectionist account of letter production behaviour

In handwriting, the drawing or copying of an individual letter involves a process of linearizing, whereby the form of the letter is broken down into a temporal sequence of strokes for production. In experienced writers, letters are produced consistently using the same production methods that are economic in terms of movement. This regularity permits a rule-based description of such production processes, which can be used in the teaching of handwriting skills. In this paper, the outstanding question from rule-based descriptions as to how consistent and stable letter production behaviour emerges as a product of practice and experience is addressed through the implementation of a connectionist model of sequential letter production. This model: (1) examines the emergence of letter production behaviour, namely the linearizing process; (2) explores how letters may be internally represented across both spatial and temporal dimensions; and (3) investigates the impact of learning certain letter production methods when generalizing to produce novel letterforms. In conclusion, the connectionist model offers an emergent account of letter production behaviour, which addresses the co-representation of spatial and temporal dimensions of letters, and the impact of learning experiences upon behaviour.