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.However, Claridge (1972; later revised in 1987),proposed a model of schizophrenia/schizotypy that incorporates both the viewof schizophrenia as illness and as a psychological dimension (see Chapter 6, thisvolume).The notion of continuity in mental illness has since been interpreted in differingways.Claridge (1994) labels the two viewpoints as ‘quasi’ and ‘fully’ dimensional.The former takes the abnormal state as its reference point, and construes thecontinuity as varying degrees of expression of the clinical signs and symptoms.Incontrast, the latter view emphasises dimensionality at the dispositional level,conceptualising schizotypy as a personality trait – albeit deviant – analogous toother individual differences, such as the extroversion–introversion dimension(Eysenck, 1992).A crucial difference is the notion that ‘deviant’ traits are seen inthe fully dimensional model as being represented in personality as healthy diversity,whereas the quasi-dimensional viewpoint conceptualises schizotypy as attenuatedpsychotic symptoms.The presence of schizotypal traits in the normal population can now be measuredpsychometrically from both the ‘fully’ (Claridge and Broks, 1984; Raine, 1991), and‘quasi’ (Chapman et al., 1978; Peters, Joseph and Garety, 1999) dimensionalviewpoints.Individuals scoring highly on such indices have been shown to resembleschizophrenics on a number of experimental correlates (Peters et al., 1994; Linneyet al., 1998), which provides some evidence for the validity of the concept.Inaddition, the structure of schizotypy has been found to parallel the multidimen-sionality of schizophrenia, with three schizotypal dimensions being identifiedwhich are comparable to Liddle (1987) three-factor model of schizophrenia: apositive, a negative, and a disorganisation factor (Bentall et al., 1989; Claridge et al., 1996).Positive Symptoms in the General PopulationMuch of the work on schizotypy has been concerned with positive symptomatology.For instance, it has been found that certain identifiable groups of people haveelevated scores on positive symptom measures, such as those who believe in theparanormal (Thalbourne, 1994); those who have out-of-body experiences (McCreeryand Claridge, 1995); members of certain ‘cults’1 or New Religious Movements1 The word ‘cult’, as it is used by the media and in popular parlance, tends to be a pejorative term for religious (or ‘pseudo-religious’) groups (Richardson, 1993a).The term commonly used by sociologists of religions is ‘new religious movement’ (or NRM; Barker, 1996), and will therefore be the term used in this chapter.Are Delusions on a Continuum?129(NRMs) (Day and Peters, 1999); and those who have profound religious experiences(Jackson, 1997).Others have taken actual positive symptoms as their starting point,and investigated their incidence in non-psychiatric or “normal” populations.Rommeand Escher (1989), in their influential book ‘Accepting Voices’, were some of the firstauthors to point out that many individuals have auditory hallucinations outside thecontext of a psychiatric illness, which can be construed as beneficial life experiences,rather than as symptoms of an illness.More recent, large-scale population surveys have confirmed the high incidence ofseemingly benign positive symptoms in the general population.At least two studieshave found that 10–15% of the normal population has had some kind of halluci-natory experience in their lives (Tien, 1991; Poulton et al., 2000), whereas approx-imately 20% report delusions (Poulton et al., 2000).In all, approximately one in fourof the Dunedin Study cohort (approximately 1000 people) reported having had atleast one delusional or hallucinatory experience that was unrelated to drug use orphysical illness (Poulton et al., 2000).Similarly, van Os et al.(2000) found that 17.5%of the Netherlands Mental Health Survey and Incidence Study (NEMESIS) sample(over 7000 people) were rated on at least one symptom of psychosis using theComposite International Diagnostic Interview (CIDI; World Health Organisation,1990), whereas only 0.4% qualified for a formal diagnosis of psychosis.This suggeststhat psychotic-like phenomenology is 50 times more prevalent than the narrower,medical concept of schizophrenia.In addition, strong associations existed betweenall types of symptom ratings on the CIDI and all types of lifetime diagnoses, furthersuggesting that the boundaries of the ‘psychosis phenotype’ do not concur withtraditional diagnostic labels.Psychiatric Definitions of DelusionsJaspers (1913) originally ascribed three defining characteristics to delusions: themesstill reflected in modern psychiatric definitions of delusions, such as in the Diag-nostic and Statistical Manual of Mental Disorders-IV (DSM-IV, 1994):A false belief based on incorrect inference about external reality (falsity) that isfirmly sustained (certainty) despite what almost everyone else believes and despitewhat constitutes incontrovertible proof or evidence to the contrary (incorrigibility).The belief is not one ordinarily accepted by other members of the person’s culture orsubculture (my additions in italics) [ Pobierz całość w formacie PDF ]

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