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Meehl�s (1962, 1989, 1990b) schizotypy and Tsuang et al.�s (1999b, 2000a, 2000b) schizotaxia are fundamentally different notions of the schizophrenia precursor. Both represent a categorical precursor but differ in the nature of their relationships to schizophrenia. Specifically, schizotypy is dimensional, unchanging despite the presence or remission of schizophrenia. In contrast, schizotaxia is a transitional precursor; the presence of schizophrenia signals the end of schizotaxia. There are also differences in the way in which risk is determined. Schizotypy is reflected in a variety of information processing and experiential aberrations, is typically assessed using self-report measures, and is best identified using taxometric analyses. In contrast, schizotaxia is characterised by negative symptoms of schizophrenia and neurocognitive impairment, can be assessed using standardised clinical measures, and is diagnosed at the individual case level. The aim of Phase 1 of this study was to investigate the manifest structure of Meehl�s schizotypy in a sample of psychiatric patients. The aims of Phase 2 were to determine if schizotypy group membership was associated with poorer functioning and to determine the nature of the relationship between Meehl�s (1962, 1989, 1990b) schizotypy and Tsuang et al.�s (1999b, 2000a, 2000b) schizotaxia. Participants in Phase 1 were 109 psychiatric patients and all completed a self-report measure of schizotypy, the Thinking and Perceptual Style Questionnaire (TPSQ; Linscott & Knight, 2004). Multivariate taxometric analyses of TPSQ subscales yielded evidence of a manifest group structure within the sample. The prevalence of the latent group, presumed to reflect schizotypy, was estimated to be 32% (SD = 8%), as yielded by MAXCOV analyses. MAXCOV analyses also yielded a mean indicator validity of 1.02; variance of 7; base rate estimates of .08; and a goodness of fit index of .98. MAMBAC analyses yielded a mean base rate of 56% (SD = 18%). Twenty-nine participants from Phase 1 took part in Phase 2. Fourteen were from the schizotypy group (had a p value of .85 or higher of schizotypy group membership) and 15 from the nonschizotypy group (had a p value of .03 or lower of schizotypy group membership). Participants completed tests of attention, verbal memory, and executive functioning. Negative symptoms of schizophrenia were also rated and diagnosis was determined using a diagnostic interview. The schizotypy group was significantly impaired relative to the nonschizotypy group on neuropsychological test scores spanning domains of attention, verbal memory, and executive functioning. A current DSM-IV diagnosis was made for 71% of the schizotypy group and 43% of the nonschizotypy group. Individuals were classified as having met criteria for schizotaxia if they had a negative symptom impairment and a neuropsychological impairment in two domains. A total of 7 people of 29 met criteria for schizotaxia, 6 of these people were from the schizotypy group. There was statistical evidence that Meehl�s (1962, 1989, 1990b) schizotypy and Tsuang et al.�s (1999b, 2000a, 2000b) schizotaxia are not independent. The proposed precursors for schizophrenia may reflect the same construct, not separate entities. Limitations and implications of these results are considered.

Meehl�s (1962, 1989, 1990b) schizotypy and Tsuang et al.�s (1999b, 2000a, 2000b) schizotaxia are fundamentally different notions of the schizophrenia precursor. Both represent a categorical precursor but differ in the nature of their relationships to schizophrenia. Specifically, schizotypy is dimensional, unchanging despite the presence or remission of schizophrenia. In contrast, schizotaxia is a transitional precursor; the presence of schizophrenia signals the end of schizotaxia. There are also differences in the way in which risk is determined. Schizotypy is reflected in a variety of information processing and experiential aberrations, is typically assessed using self-report measures, and is best identified using taxometric analyses. In contrast, schizotaxia is characterised by negative symptoms of schizophrenia and neurocognitive impairment, can be assessed using standardised clinical measures, and is diagnosed at the individual case level. The aim of Phase 1 of this study was to investigate the manifest structure of Meehl�s schizotypy in a sample of psychiatric patients. The aims of Phase 2 were to determine if schizotypy group membership was associated with poorer functioning and to determine the nature of the relationship between Meehl�s (1962, 1989, 1990b) schizotypy and Tsuang et al.�s (1999b, 2000a, 2000b) schizotaxia. Participants in Phase 1 were 109 psychiatric patients and all completed a self-report measure of schizotypy, the Thinking and Perceptual Style Questionnaire (TPSQ; Linscott & Knight, 2004). Multivariate taxometric analyses of TPSQ subscales yielded evidence of a manifest group structure within the sample. The prevalence of the latent group, presumed to reflect schizotypy, was estimated to be 32% (SD = 8%), as yielded by MAXCOV analyses. MAXCOV analyses also yielded a mean indicator validity of 1.02; variance of 7; base rate estimates of .08; and a goodness of fit index of .98. MAMBAC analyses yielded a mean base rate of 56% (SD = 18%). Twenty-nine participants from Phase 1 took part in Phase 2. Fourteen were from the schizotypy group (had a p value of .85 or higher of schizotypy group membership) and 15 from the nonschizotypy group (had a p value of .03 or lower of schizotypy group membership). Participants completed tests of attention, verbal memory, and executive functioning. Negative symptoms of schizophrenia were also rated and diagnosis was determined using a diagnostic interview. The schizotypy group was significantly impaired relative to the nonschizotypy group on neuropsychological test scores spanning domains of attention, verbal memory, and executive functioning. A current DSM-IV diagnosis was made for 71% of the schizotypy group and 43% of the nonschizotypy group. Individuals were classified as having met criteria for schizotaxia if they had a negative symptom impairment and a neuropsychological impairment in two domains. A total of 7 people of 29 met criteria for schizotaxia, 6 of these people were from the schizotypy group. There was statistical evidence that Meehl�s (1962, 1989, 1990b) schizotypy and Tsuang et al.�s (1999b, 2000a, 2000b) schizotaxia are not independent. The proposed precursors for schizophrenia may reflect the same construct, not separate entities. Limitations and implications of these results are considered.

Thesis (Ph. D.)--University of North Carolina at Greensboro, 2007. / Title from PDF t.p. (viewed Feb. 29, 2008). Directed by Thomas R. Kwapil; submitted to the Dept. of Psychology. Includes bibliographical references (p. 79-111).

Previous research suggests there are a number of variables that are associated with the expression of schizotypal personality disorder (SPD) symptoms. Such variables include childhood trauma, depression and anxiety, substance use, normal-range personality traits, ethnicity, and gender. However, research to date has not examined all of these variables in a single study to determine how they may be interrelated or differentially related to SPD symptom domains. Of particular interest is the association of these variables as explained by the diathesis-stress model. This study utilized a convenience sample of 298 undergraduate students to examine a continuous range of scores for symptoms of SPD and how the interrelation of biological factors such as gender and ethnicity and psychosocial factors and stressors such as childhood trauma and personality traits, specifically neuroticism and extroversion, influence the expression of SPD symptoms. It was predicted that anxiety, depression, stress, and childhood trauma would positively correlate to SPD symptoms. It was also hypothesized that neuroticism and substance use would positively correlate to schizotypal traits and extroversion would be negatively correlated to schizotypal traits as measured by the Schizotypal Personality Questionnaire-Brief. It was further hypothesized that psychosocial stressors would be moderated by the aforementioned biological factors.

Although they share a number of clinical features, autism and schizophrenia are usually distinguished by their different ages of onset and certain discriminating features such as major impairments to communication in the former and positive psychotic symptoms in the latter. However, the recognition that these conditions are part of broader spectrums of impairment has led to the definition of disorders which do not show such marked and discriminating features, such as autism spectrum disorders (ASD) and schizotypal personality disorder (SPD). Reviewing the historical development of these concepts and areas of potential overlap or difference between them revealed that they have both shared and discriminating features, but no study to date has directly compared them. Three experiments were therefore conducted to compare ASD and SPD using clinical, neuropsychological and functional magnetic resonance imaging (fMRI) techniques. In the clinical experiment, standardised measures were used to determine if it was possible to distinguish between the groups, and to allow their quantitative comparison. It was possible to distinguish between ASD and SPD in most cases, although 17% of the population tested met criteria for both conditions. This ‘comorbid’ (CM) group were therefore considered separately. When a single diagnosis could be allocated, there were clear overlaps of clinical features between the conditions and each condition showed more traits of the other than were seen in controls. The overlaps were most prominent for negative schizotypal traits which did not differ between the groups. The CM group were more affected than either the ASD or SPD groups across multiple domains. All groups had high levels of previously undiagnosed psychopathology. In the neuropsychological experiment, tests of social cognition, executive function and central coherence / local-global processing bias were employed. The similarities between the ASD and SPD groups were striking. Both showed similar evidence of impairment in social cognition and executive function, although there was some evidence of greater impairment in working memory in the ASD group. Differences were seen using a test of local-global processing bias, although these were potentially confounded by differences in general intellectual ability. Two fMRI tasks were conducted: a working memory task (a letter based n-back task) and a social judgment task (where individuals made judgements of either gender or approachability from a picture of a face). The former did not distinguish between the ASD and SPD groups. In the latter, individuals with SPD showed significantly greater activation than the ASD group in several brain regions known to be associated with social cognition, with the controls scoring in-between the two. Although they show marked clinical and brain functional overlaps, the results of the fMRI task of social judgement suggest that it is correct to consider ASD and SPD as separate diagnostic entities. The findings are consistent with the idea that, although both conditions are associated with impairments in understanding the mental states of others (mentalising), the mechanism which underlies these differs between the groups, with ASD associated with hypo-mentalising and SPD associated with hyper-mentalising.

Thesis (Ph. D.)--Miami University, Dept. of Psychology, 2008. / Title from second page of PDF document. Includes bibliographical references (p.45-55).

Thesis (Ph. D.)--University of North Carolina at Greensboro, 2006. / Title from PDF title page screen. Advisor: Thomas R. Kwapil; submitted to the Dept. of Psychology. Includes bibliographical references (p. 39-55).

Schizotypy as a research framework for schizophrenia emphasizes a link between the symptoms of the disorder and schizotypal traits in the non-clinical population, and argues for a symptom orientated approach to the field. One such symptom area concerns that of unusual experiences, such as hallucinations and delusions that occur in both schizophrenia and in the normal population, but differ in intensity and frequency. Hallucinations and delusions are affected by the environment in which they occur, such as a perceptually ambiguous environment. However, given that both hallucinations and delusions are misinterpretations of the current environment, the content of both could also be influenced by previous experiences, where properties of previous experiences interact with the current environment to produce such experiences. One factor that could influence hallucinations and delusions in this way is time. That is, it could be that those individuals more prone to hallucinations and delusions have stronger temporal links with the properties of previous experiences that facilitate hallucinatory and delusional experiences. The current thesis explores the relationship between the influence of environmental properties on hallucinatory reports and the possibility of differences in timing between individuals scoring high or low in schizotypy through tasks that incorporate temporal elements for optimum performance, such as time based schedules of reinforcement, or measure timing more directly, such as temporal bisection tasks. Findings from the thesis show that high schizotypy scorers make more hallucinatory-like reports than low scorers and that those reports are linked to properties of the environment in which they occur. In addition, there is some evidence that high scorers differ in timing across both schedule and temporal bisection tasks, but only under very specific circumstances.

Sensory gating helps prevent incoming irrelevant sensory information from entering into the higher cortex and ensures normal information processing. Sensory gating is seen as the ability of the nervous system to modulate its sensitivity to incoming stimuli (Braff & Geyer, 1990; Adler, Olincy, Waldo, Harris & Griffith, et al., 1998). Smoking tobacco can facilitate early sensory gating in schizophrenics, and enhance prepulse inhibition asymmetry (right greater than left) in individuals with schizotypal personality. The purpose of this study was to test the following hypotheses: 1) Individuals with schizotypal personalities have poorer sensory gating than those without them. 2) Among individuals with schizotypy (high schizotypy), those who smoke have better sensory gating than those who do not smoke; among those without schizotypy (low schizotypy), smokers will demonstrate better sensory gating. 3) After abstaining, schizotypal smokers will show increased sensory gating due to smoking. 4) Individuals with schizotypy will show greater P50 deficits in the left hemisphere, and smoking can enhance this asymmetry (left greater than right). From 613 online-surveyed participants, 39 (18 men) right-handed undergraduates (Mean age = 18.87) were selected to represent four groups: High and Low Schizotypy, half of which were smokers, and half were non-smokers. Smokers were tested while abstaining and after smoking. Non-smokers were tested twice in the same manner without smoking. P50 sensory gating, P50 amplitude and P50 latency were analyzed separately at frontal (F3, F4, Fz), fronto-central (FC3, FC4, FCz), central (C3, C4, Cz), centro-parietal (CP3, CP4, Cpz) and parietal (P3, P4, Pz) regions. With respect to the hypotheses of the study, it was found that: 1) Sensory gating, as assessed by S2 (P50-N40)/S1 (P50-N40), was greater at frontal-central and central regions in comparison to mid-frontal and parietal regions. 2) Furthermore, sensory gating was significantly greater at midline than left or right hemispheres. 3) Condition 1 showed better sensory gating than Condition 2. 4) The High Schizotypy group showed poorer sensory gating than the Low Schizotypy group among non-smokers. 5) Smokers showed poorer sensory gating than non-smokers in the Low Schizotypy group. In terms of P50 amplitude, it was found that: 1) FCz and Cz showed the highest P50 amplitude, greater than all other sites. 2) S1 had higher P50 amplitude than S2. 3) The low schizotypy individuals had significantly greater P50 amplitude in the left than in the right fronto-central region, but the high schizotypy individuals showed more P50 amplitude in the right hemisphere than did the low schizotypy individuals. 4) Smokers showed a greater left than right P50 amplitude in centro-parietal region, whereas the non-smokers showed the opposite asymmetry with a greater right than left P50 amplitude in central, centro-parietal and parietal regions. In terms of P50 latency, it was found that: 1) The P50 latency became significantly slower from posterior to anterior sites. 2) In HiS/S and LoS/NS groups, Condition1 was faster than Condition 2. In LoS/S and HiS/NS groups, Condition1 was slower than Condition 2. 3) Among smokers, left hemisphere latency was shorter than right hemisphere for S1, but for S2, left hemisphere was slower than right hemisphere. Among non-smokers, left and right hemisphere latencies were almost the same for S1 and S2. / Master of Science