Doctor of Philosophy (Clinical Psychology)
School of Psychology
Schizotypy is regarded as a trait vulnerability marker for psychosis. The study of this personality trait in otherwise healthy samples affords opportunities to research potential co-occurring risk factors for psychosis, without the confounds inherent to psychiatric diagnosis. The current thesis is focused on the expression of schizotypy alongside neurodevelopmental, language and affective risk factors for psychosis. The specific risk factors investigated were neurological soft signs (NSS), semantic processing, affective temperament, and psychological distress. Additionally, this thesis investigated whether propensity to hallucinate had an effect on these factors when combined with psychometric schizotypy. Language abnormalities have also been extensively researched in schizotypy and along the psychosis continuum. Given the overlap between the psychosis continuum and language abnormalities such as those seen in dyslexia, this thesis also sought to determine whether risk factors for psychosis are also present in a dyslexia sample.
This thesis is made up of a combination of five studies, some of which are published and submitted manuscripts, with the remainder being manuscripts in preparation for publication. Study One investigated the relationship between schizotypy and distress. Affective temperament was found to mediate this relationship. Contrary to predictions hallucination predisposition was not found to exert significant effects on either the direct or indirect relationship between schizotypy and distress. Study Two explored whether NSS are expressed differently in those with high and low levels of schizotypy and additionally, whether hallucination predisposition interacts with this effect. Results indicated that those with high overall schizotypy express significantly more NSS, and that hallucination predisposition has additive effects on this association. Study Three looked at the expression of NSS in a dyslexia sample. It was found that individuals with dyslexia expressed a significantly greater amount of NSS compared to controls. Individuals with dyslexia also had significantly higher rates of schizotypy, which was found to contribute to the higher level of distress found in those with dyslexia compared to controls. Study Four investigated semantic processing capabilities of those with high and low positive schizotypy, as well as high and low hallucination predisposition. High levels of positive schizotypy resulted in slower reaction times compared to low positive schizotypy, whilst high hallucination predisposition resulted in faster reaction times compared to low hallucination predisposition. Study Five investigated semantic processing in a dyslexia sample. There was some evidence that the dyslexia group responded slower than controls. The dyslexia group also had difficulty discriminating degree of relatedness between semantic pairs, and schizotypy was found to contribute to this effect.
This thesis concludes with a synthesis of the findings across the five studies. Theoretical and clinical implications are also considered, alongside limitations of the research and possible avenues for further enquiry. Overall, the results of this thesis indicate that individuals with high levels of schizotypy have associations with distress through affective temperament, as well as an increased expression of NSS, and abnormal semantic processing. Hallucination predisposition is not synonymous with schizotypy in its effects on these risk factors, suggesting schizotypy and propensity to hallucinate may have different mechanisms of effect. Dyslexia was associated with an increased expression of NSS, as well as semantic processing abnormalities that were contributed to by schizotypy. These findings are indicative of schizotypy and dyslexia having overlapping features, which may be suggestive of possible shared aetiologies.
de Leede-Smith, Saskia, Schizotypy: Consideration of neurological soft signs, language and affective factors, Doctor of Philosophy (Clinical Psychology) thesis, School of Psychology, University of Wollongong, 2017. https://ro.uow.edu.au/theses1/222