Categorisation in High and Low Schizotypes

Categorisation in High and Low Schizotypes Aaron C. Roberts (A.Roberts.10@unimail.winchester.ac.uk) Department of Psychology, University of Winchester, Winchester, SO22 4NR, UK Nick Braisby (Nick.Braisby@winchester.ac.uk) Department of Psychology, University of Winchester, Winchester, SO22 4NR, UK along a continuum from such psychologically healthy individuals to those diagnosed with schizophrenia (Claridge, 1985). Those high in schizotypy are described as psychosis- prone, and may experience oddities of belief, behaviour, eccentricities, idiosyncratic speech, peculiar ideas, and social awkwardness or aversion at a subclinical level (Siever, Kalus & Keefe, 1993). High schizotypes have been studied in order to gain understanding of vulnerabilities to schizophrenia (Peters, Pickering & Hemsley, 1994). Indeed, in the presence of sufficient environmental stressors, the contention is that high schizotypes may develop schizophrenia, and present with appropriate clinical symptoms. High schizotypes therefore provide the researcher with a compelling opportunity to examine ‘disordered’ cognition in an otherwise healthy population. However, there have been relatively few studies of categorisation in high and low schizotypes, and what data there are appear inconsistent. Abstract Disorders provide an important source of information in developing theories of normal categorisation. Disruption in categorisation in individuals diagnosed with schizophrenia has been widely evidenced. However, findings are often contradictory and subject to significant confounds. In the present study 35 high schizotypes and 35 low scorers completed a semantic categorisation task and a borderline categorisation task, with measures of category membership judgment, similarity and response time being taken. Results revealed that high schizotypes made significantly fewer positive category membership judgments than low schizotypes (p = .003) and suggest that different theoretical explanations may be required to explain the categorisation of high and low schizotypes. Explanations in terms of theories of normal categorisation are developed. Keywords: Concepts; Categorisation; Essentialism; Semantic Processing. Schizotypy; Introduction Disorders of categorisation are an important source of information in developing theories of normal categorisation. Work on category-specific impairment, for example, has led to the proposal that functional and appearance attributes are represented in concepts in different ways (cf. Strnad, Anzellotti & Caramazza, 2011). Categorisation is known to be disrupted in other disorders, most notably dementia (Doughty et al., 2009), autism (Church et al., 2010), and schizophrenia (Doughty & Done, 2009), as well as in neuropsychological cases (Cohen, Johnston & Plunkett, 2000). Schizophrenia has long been associated with the suggestion that categorisation is subject to over-inclusion, that category boundaries are shifted outward, incorporating into the category items that would normally be regarded as non-members (Lawrence, Doughty, Al-Mousawi, Clegg & Done, 2007). However, disorders also present difficulties for experimental investigations of categorisation. In the case of schizophrenia, for example, significant confounds are often present, such as hospitalisation, medication, psychosis, and attentional dysfunction. Perhaps unsurprisingly, and in spite of the prominence the suggestion of over-inclusion has received, relatively little is actually known of categorisation in schizophrenia. Moreover, the sparse evidence is often inconsistent or contradictory. However, schizophrenia has been linked theoretically to schizotypy, a multidimensional construct that assumes healthy individuals may manifest subclinical presentations of schizophrenic symptoms. Schizotypy varies in degree Semantic Processing in Schizophrenia Abnormalities in semantic processing are thought to be central to cognitive abnormalities in schizophrenia, with deficits reported on a wide variety of semantic processing tasks (Chen, Wilkins & McKenna, 1994). Further, semantic deficits are suggested to underlie disturbances in thought and language in schizophrenia, which might not only explain deficits observed in other cognitive domains, but also provide a cognitive explanation for common symptoms in schizophrenia, such as delusions (Rossell, Rabe-Hesketh, Shapleske & David, 1999) and thought disorder (Gouzoulis- Mayfrank et al., 2003). Semantic Processing in Schizotypy Although impairments in attention (Lenzenweger, Cornblatt & Putnick, 1991) and executive functioning (Suhr, 1997; Tallent & Gooding, 1999) have been found in schizotypy, few studies have addressed the relationship between schizotypy and semantic processing. Those that have done so have used semantic priming tasks (Beech, McManus, Bayliss, Tipper & Agar, 1991; Morgan, Bedford & Rossell, 2006) and revealed differences between high and low schizotypes (Morgan et al., 2006). However, there has been little research on other areas of semantic processing in schizotypy, Morgan, Bedford, O’Reagan & Rossell (2009) being a notable exception. Very few studies of schizotypy have included categorisation tasks and none have made categorisation a primary focus.