Robyn Langdon

DRC: a dual route cascaded model of visual word recognition and reading aloud

This article describes the Dual Route Cascaded (DRC) model, a computational model of visual word recognition and reading aloud. The DRC is a computational realization of the dual-route theory of reading, and is the only computational model of reading that can perform the 2 tasks most commonly used to study reading: lexical decision and reading aloud. For both tasks, the authors show that a wide variety of variables that influence human latencies influence the DRC models latencies in exactly the same way. The DRC model simulates a number of such effects that other computational models of reading do not, but there appear to be no effects that any other current computational model of reading can simulate but that the DRC model cannot. The authors conclude that the DRC model is the most successful of the existing computational models of reading.

Monothematic Delusions: Towards a Two-Factor Account

We provide a battery of examples of delusions against which theoretical accounts can be tested. Then we identify neuropsychological anomalies that could produce the unusual experiences that may lead, in turn, to the delusions in our battery. However, we argue against Mahers view that delusions are false beliefs that arise as normal responses to anomalous experiences. We propose, instead, that a second factor is required to account for the transition from unusual experience to delusional belief. The second factor in the etiology of delusions can be described superficially as a loss of the ability to reject a candidate for belief on the grounds of its implausibility and its inconsistency with everything else that the patient knows, but we point out some problems that confront any attempt to say more about the nature of this second factor.

Mentalising, schizotypy, and schizophrenia

Despite accumulating evidence that patients with schizophrenia perform poorly in mentalising tasks, doubts remain about the primacy of the role played by defective mentalising in schizophrenia. This study investigated the relationship between mentalising ability and self-reported schizotypal traits in non-clinical adults who reported no history of psychiatric illness in order to test two counter-proposals: (1) defective mentalising is a primary cause of psychotic symptoms in schizophrenia; and (2) defective mentalising in schizophrenia is a secondary consequence of the chronic asociality that is typical of general psychiatric illness. Mentalising ability was tested using a false-belief picture sequencing task that has been used elsewhere to demonstrate poor mentalising in patients with schizophrenia. Evidence of selective mentalising deficits in high schizotypal non-clinical subjects discounted the view that defective mentalising is restricted to psychiatric illness and strengthened the case for continuity models of psychosis-proneness. Furthermore, evidence that poor mentalisers in the normal population are more likely to self-report psychotic-like traits, as well as asocial or idiosyncratic behaviours, refuted suggestions that defective mentalising is linked solely to asocial symptomatology and supported the view that defective mentalising may have a fundamental role to play in the explanation of psychotic symptoms. In order to specify what that role might be, alternative theoretical accounts of defective mentalising were tested. Neither executive planning deficits nor failure to inhibit cognitively salient inappropriate information could adequately explain the pattern of selective mentalising deficits found in high schizotypal non-clinical subjects. Our findings suggest that there exists a domain-specific cognitive module that is dedicated to inferring and representing mental states which, when dysfunctional, causes defective mentalising that manifests phenomenologically in psychotic-like traits and impoverished social awareness of variable expression and ranging severity.

The Cognitive Neuropsychology of Delusions

After reviewing factors implicated in the generation of delusional beliefs, we conclude that whilst a perceptual aberration coupled with a particular type of attri-butional bias may be necessary to explain the specific thematic content of a bizarre delusion, neither of these factors, whether in isolation or in combination, is sufficient to explain the presence of delusional beliefs. In contrast to bias models (theories which explain delusion formation in terms of extremes of normal reasoning biases), we advocate a deficit model of delusion formation–that is, delusions arise when the normal cognitive system which people use to generate, evaluate, and then adopt beliefs is damaged. Mere bias we think inadequate to explain bizarre delusions which defy commonsense and persist despite overwhelming rational counter-argument. In particular, we propose that two deficits must be present in the normal cognitive system to explain bizarre delusions: (1) there must be some damage to sensory and/or attentional-orient-ing mechanisms which causes an aberrant perception–this explains the bizarre content of the causal hypothesis generated to explain what is happening; and (2) there must also be a failure of normal belief evaluation–this explains why a hypothesis, implausible in the light of general commonsense, is adopted as belief. This latter deficit occurs, we suggest, when an individual is incapable of suspending the natural favoured status of direct first-person evidence in order to critically evaluate hypotheses, given equal pri-ority whether based on direct or indirect sources of information. In contrast, delusions with ‘ordinary’ content may arise when a single deficit of normal belief evaluation occurs in the context of an extreme (but normal) attentional bias, thus causing failure to critically evaluate hypotheses based on misperceptions and misintrepretations of ambiguous (but ordinary) first-person experience.

The neuropsychological basis of hypersociability in Williams and Down syndrome

People with Williams syndrome (WS) display indiscriminate approach toward strangers in everyday life. People with Down syndrome (DS) can also do so, but to a lesser degree. Inappropriate approach behavior is also characteristic of people with acquired amygdala damage and people with acquired frontal lobe impairment; given this, the developmental disorder of social approach seen in WS and perhaps also DS might be due to poor emotion recognition (due to abnormal amygdala functioning) or poor control of behavior (due to frontal lobe abnormality). A third account of this developmental disorder of social cognition can be couched in terms of heightened salience for social stimuli. We explored these three hypotheses by testing emotion recognition, social approach and frontal lobe functioning in people with WS and DS. Overall, our results were inconsistent with predictions from the amygdala and social salience hypotheses. In contrast, results from a battery of neuropsychological tasks suggested that abnormal social approach in WS and DS in everyday life is best explained by frontal lobe impairment, in particular, poor response inhibition.

Recognition of metaphor and irony in young adults: the impact of schizotypal personality traits.

Patients with schizophrenia demonstrate two dissociable impairments of pragmatic language comprehension: (1) an insensitivity to irony, which is associated with poor theory-of-mind (i.e. a difficulty with inferring other peoples thoughts); and (2) poor recognition of metaphors, which may reflect degraded semantics. This study investigated whether non-clinical high-schizotypal adults show similar impairments of pragmatic language. Thirty-six university students completed the Raine Schizotypal Personality Questionnaire, the Wechsler Memory Scale Logical-Memories subtest, Ravens Progressive Matrices and a story comprehension task that tested the ability to discriminate between incongruous statements and appropriate uses of ironical, metaphorical or literal speech. Counter to the pattern found for patients, high-schizotypal adults were just as capable as low-schizotypal adults of identifying appropriate metaphors, suggesting a discontinuity between schizophrenia and schizotypy for the metaphor-recognition problem. This studys finding of intact metaphor recognition in high-schizotypal adults contrasts with previous findings of poor proverb comprehension in these individuals and is interpreted in terms of different semantic processes required for recognizing and interpreting metaphors. Consistent with the pattern found for patients, high-schizotypal adults were significantly impaired in their ability to appreciate when a literally contradictory utterance could be interpreted as ironical, suggesting continuity between schizophrenia and schizotypy for the irony-appreciation problem.

Mentalising, executive planning and disengagement in schizophrenia

Introduction: Poor mentalising has been linked to particular psychotic symptoms (e.g., paranoia) and attributed to selective disruption of a mentalising module. Mentalising, executive planning, and disengagement were tested in patients with schizophrenia and healthy controls in order to evaluate this view against nonmodular accounts that attribute poor mentalising to generalised difficulty entertaining any hypothetical state of affairs and/or difficulty inhibiting salient misleading information. Method. Mentalising and disengagement were tested in a picture-sequencing task using false-belief and capture stories - the former require inferences of mental states; the latter test ability to inhibit salient misleading cues. Executive planning was tested using the Tower of London task. Results. Whereas patients as a whole showed impairments of mentalising, executive planning and disengagement, false-belief picture sequencing ability significantly predicted the odds of being a patient, after adjusting for all other task measures. No evidence was found linking poor mentalising to positive symptoms. Conclusions. Our findings support the existence of a mentalising module, which is selectively disrupted in some patients with schizophrenia. Null results concerning the links between poor mentalising and positive symptoms are discussed in relation to current views on whether poor mentalising is best conceptualised as a state or trait marker of psychosis.

Visual perspective-taking and schizotypy: evidence for a simulation-based account of mentalizing in normal adults

Modular theory-of-mind accounts attribute poor mentalizing to disruption of a cognitive module dedicated to computing higher-order representations of primary representations (metarepresentations). Since metarepresentational capacity is needed to mentalize about other peoples beliefs but is not needed to judge visual perspectives (which can be done by mentally rotating primary representations of seen objects), this view predicts that visual perspective-taking will be intact in individuals with selective mentalizing impairments. Counter to that prediction, this study found evidence of disturbed visual perspective-taking in normal adults who score higher on the personality variable of schizotypy and who are known to be relatively poor mentalizers (despite intact ability to inhibit salient inappropriate information in order to reason consequentially on the basis of hypothetical states, other than mental states). Whereas high-schizotypal adults and low-schizotypal adults did not differ in their ability to judge item questions (asking the relative location of array features), high-schizotypal adults performed more poorly than low-schizotypal adults in judging appearance questions (asking how an array would appear from another perspective) under viewer-rotation instructions (asking subjects to imagine moving themselves relative to a fixed array) and performed better than low-schizotypal adults in judging appearance questions under array-rotation instructions (asking subjects to imagine rotating an array relative to their own fixed viewer position). Based on these and other findings we conclude that poor mentalizing in normal adults is better understood as an impairment of perspective-taking (visual and/or cognitive) and introduce the concept of allocentric simulation to explain the functional basis of this perspective-taking impairment.

Schizophrenia, theory of mind, and persecutory delusions.

Introduction. There is already a substantial body of evidence supporting Friths (1992) theory that theory of mind (ToM) is impaired in people with schizophrenia. However, a specific relationship between impaired ToM and paranoid delusions, while intuitively reasonable, has only been demonstrated in two studies to date. Correspondence should be addressed to Richard J. Siegert, Rehabilitation Teaching and Research Unit, Department of Medicine, Wellington School of Medicine & Health Sciences, University of Otago, PO Box 7343, Wellington South, New Zealand; e‐mail: rsiegert@wnmeds.ac.nz This research was supported by a Victoria University Science Faculty research grant. Thanks to Max Coltheart and other members of the Macquarie Centre for Cognitive Science who provided valuable feedback and support in the early stages of this research. Preliminary results were presented at the Australian Conference of Cognitive Neuropsychology and Neuropsychiatry, Deakin University, 2001. Methods. A total of 25 participants with schizophrenia were classified as paranoid or nonparanoid and compared with 38 healthy controls on a variety of ToM tasks. These tasks included verbal and nonverbal, and first and second order ToM tasks. Results. Participants with schizophrenia performed significantly more poorly than healthy controls on both the first and second order verbal ToM tasks but not on the nonverbal ToM tasks. However, the ToM deficit was only observed for those participants with schizophrenia who had persecutory delusions. There was also a strong relationship observed between the severity of persecutory delusions and length of illness. Conclusions. This study represents only the third demonstration of a specific link between paranoid delusions and ToM impairment. Reasons why previous findings on this issue have been so inconsistent are considered. Further research is needed to explore the relationships among paranoia, ToM, and length of illness.

Understanding Minds and Understanding Communicated Meanings in Schizophrenia

The work reported in this paper investigated the putative functional dependence of pragmatic language skills on general mind-reading capacity by testing theory-of-mind abilities and understanding of non-literal speech in patients with schizophrenia and in healthy controls. Patients showed difficulties with inferring mental states on a false-belief picture-sequencing task and with understanding metaphors and irony on a story-comprehension task. These difficulties were independent of low verbal IQ and a more generalised problem inhibiting prepotent information. Understanding of metaphors and understanding of irony made significant and independent contributions to discriminating patients from controls, suggesting that metaphor and irony make distinct pragmatic demands.