Healthy schizotypy

Personality and Individual Differences 32 (2002) 141±154

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Healthy schizotypy: the case of out-of-the-body experiences Charles McCreery *, Gordon Claridge Department of Experimental Psychology, University of Oxford, South Parks Road, Oxford, UK Received 27 July 2000; received in revised form 14 November 2000; accepted 29 December 2000

Abstract The present study tested the hypothesis that a group of normal subjects reporting at least one hallucinatory experience (an `out-of-the-body' experience or OBE) could score highly on one of the factors of schizotypy without scoring highly on the rest. A total of 684 subjects were recruited, of whom 450 reported at least one OBE and 234 did not. They completed the Combined Schizotypal Traits Questionnaire of Bentall, Claridge, and Slade [Bentall, R. P., Claridge, G., & Slade, P. D. (1989). The multi-dimensional nature of schizotypal traits: a factor analytic study with normal subjects. British Journal of Clinical Psychology, 28, 363±375]. A number of discriminant analyses were carried out to compare di€erent sub-groups of the OBErs with suitable controls, using the factor scores on four factors as predictors of group membership (OBErs versus non-OBErs). It was found that OBErs scored signi®cantly higher than non-OBErs only on the ®rst of the four factors, aberrant perceptions and beliefs, but not on the other three: cognitive disorganisation with social anxiety, introvertive anhedonia, and asocial schizotypy. The results are interpreted as supporting the idea of `healthy schizotypes' who are functional in spite of, and even in part because of, their anomalous perceptual and other experiences. It is argued that this idea ®ts best with a fully dimensional model of schizotypy, independent of, although causally related to, the disease process of schizophrenia itself. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: Hallucination; Schizotypy; Factor analysis; Discriminant analysis; Schizophrenia

1. Introduction One of the main strands of schizotypy research in recent years has consisted of the factor analysis of schizotypy scales, or in some cases individual items from such scales. At least three * Corresponding author. Present address: Institute of Psychophysical Research, 118 Banbury Road, Oxford OX2 6JU, UK. Tel.: +44-1865-558787; fax: +44-1865-558064. E-mail address: [email protected] (C. McCreery). 0191-8869/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S0191-8869(01)00013-7

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distinct theoretical questions have been addressed by such studies: (1) the number and nature of the di€erent factors required to encompass the content of the schizotypy construct (Claridge, 1994; Rosenberger & Miller, 1989; Venables & Bailes, 1994; Vollema & van den Bosch, 1995); (2) the degree of independence or orthogonality of these factors (Mason, Claridge, & Jackson, 1995; Mason, Claridge, & Williams, 1997); and (3) the relationship of the factors uncovered in the schizotypy domain to the possible subdivisions within the diagnosis of schizophrenia itself (Gruzelier, Burgess, Stygall, Irving, & Raine, 1995; Venables & Bailes, 1994). With regard to the ®rst of the three questions, a consensus seems to be emerging that there are at least three, and possibly four, separate factors within the schizotypy construct. The work of Claridge and his collaborators has tended to support a four-factor model. These factors may be characterised as Aberrant Perceptions and Beliefs, Cognitive Disorganisation with Anxiety, Introvertive Anhedonia, and Asocial Behaviour. (1) Factor 1, Aberrant Perceptions and Beliefs, appears to be tapping subclinical forms of positive symptomatology; i.e. anomalous perceptual experiences, such as hallucinations, and the unusual beliefs which may be a consequence of them. Questionnaire scales with high loadings on this factor include the STA of Claridge and Broks (1984), the Chapmans' `PerMag' combination, i.e. Perceptual Aberration and Magical Ideation (Chapman, Chapman, & Raulin, 1978; Eckblad & Chapman, 1983); and, perhaps most interestingly, the Hypomania scale of Eckblad and Chapman (1986). The possible theoretical signi®cance of this last ®nding will be discussed below (Section 4). (2) The second factor is Cognitive Disorganisation with Anxiety. This concerns subclinical forms of such cognitive failures as thoughtblocking, along with the trait of heightened social anxiety, for example in unfamiliar social surroundings. The factor again has a high loading from the STA, but also from Eysenck's Neuroticism scale (Eysenck & Eysenck, 1975) and the Schizophrenism scale of Nielsen and Petersen (1976). (3) The third factor, Introvertive Anhedonia, is largely de®ned by the Physical and Social Anhedonia scales of Chapman, Chapman and Raulin (1976), positively, and by Eysenck's Extraversion scale, negatively. The factor may be thought of as tapping subclinical forms of the negative symptomatology of schizophrenia, in contrast to the positive forms mentioned above. (4) The ®nal factor, Asocial Behaviour, seems to be tapping social nonconformity and impulsiveness, along with disinhibition of mood, in both a positive and a negative direction. It has high loadings from Eysenck's Psychoticism scale, the Chapmans' Hypomania scale, and to a lesser extent the STB of Claridge and Broks (1984). This four-factor structure ®rst emerged in a study by Bentall, Claridge, and Slade (1989), involving 180 participants, and has since been replicated in a much larger study by Claridge et al. (1996), involving 1095 subjects. This population of subjects included both the original 180 participants of the Bentall et al. (1989) study and the 684 subjects of the present enquiry, so it is this four-factor structure which will be the main focus of the present paper. This choice of factors receives some support from a recent development in the use of factor analytical methods in this area, which is the application of the model-testing technique of con®rmatory factor analysis to the data derived from schizotypy scales. Mason (1995), using the full range of scales comprising the Combined Schizotypal Traits Questionnaire (CSTQ) of Bentall et al. (1989), and the large body of subjects incorporated into the Claridge et al. (1996) study, found that the four factors described above provided the model with the best ®t to the data. Raine, Reynolds, Lencz, Scerbo, Triphon, and Kim (1994) found that three factors gave the best ®t to their data, which was derived from the SPQ of Raine (1991; see also Raine & Benishay, 1995).

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Their ®rst factor, cognitive-perceptual, was made up of unusual perceptual experiences, magical thinking, paranoid ideation and ideas of reference, and so corresponds very closely to Factor 1 above. Their second, interpersonal factor, which taps de®cits in interpersonal functioning, can be related to introvertive anhedonia. And their third, disorganised factor, which taps odd behaviour and odd speech, may be seen as corresponding to the cognitive disorganisation with anxiety factor, with the di€erence that social anxiety loads on their second, interpersonal factor. The major difference between the Raine et al. (1994) three-factor model and the Claridge et al. (1996) fourfactor one is clearly the absence of the fourth, asocial schizotypy factor from the Raine model. However, this is scarcely suprising in light of the fact that Eysenck's P-scale, with its somewhat distinctive content, was not used in their analysis. The precursor to the present study was an analysis by McCreery and Claridge (1995) of the individual CSTQ scales scores of a large group of normal subjects (n=450) reporting at least one spontaneous experience of hallucination, who were compared with a group (n=214) reporting no such experiences. The particular variety of hallucination involved was the so-called `out-of-thebody' experience (OBE), or perceptual anomaly in which subjects seem to believe themselves to be located in a di€erent position from that of their physical body. An interesting pattern of results emerged from this analysis, with OBErs scoring higher than non-OBErs only on certain scales and not on others. In particular, while the putatively more schizotypal group, the OBErs, scored higher on such scales as the Hallucination Scale of Launay and Slade (1981) and the Hypomania scale of Eckblad and Chapman (1986), they did not score higher on scales with a relatively large component of questions tapping social anxiety, such as the Nielsen and Petersen (1976) Schizophrenism scale and Eysenck's N. OBErs also tended to score lower than non-OBErs on the Physical Anhedonia scale of Chapman et al. (1976), as if in some ways, far from being anhedonic, they were particularly enjoying life. In view of the continuing development of the factorial analysis of schizotypy, and bearing in mind the highly selective way in which the individual scales discriminated between the OBErs and controls, it was considered of interest to investigate which of the four factors, if any, would discriminate between the two groups, and how successfully. The results from the individual scales suggested that Factor 1 should be an e€ective discriminant, but not necessarily any of the others, and particularly not Anhedonia, given the result mentioned above concerning the Chapman's Physical Anhedonia scale. On the empirical level, therefore, the purpose of the present analysis was to test this hypothesis, using the multivariate technique of discriminant analysis. On the theoretical level, the purpose of the present paper will be to shed light on an underlying theoretical preoccupation in all schizotypy research, namely the question of the dimensionality of schizotypy/psychosis-proneness. Here three distinct views may be distinguished. First, there is the quasi-dimensional model of Rado (1953) and Meehl (1962), for example, according to which schizotypal symptoms merely represent less explicitly expressed manifestations of the underlying disease process which is schizophrenia. Secondly, there is the more personality-based model of Eysenck (1960), according to which a person exhibiting the full-blown manifestations of psychosis is simply someone occupying the extreme upper end of his `psychoticism' dimension. Finally, there is the fully dimensional model of Claridge (1997, 1999). This may be seen on the one hand as an extension of the Eysenck model, inasmuch it represents schizotypy itself as a continuously distributed trait throughout the population, associated with normal functioning for most of its extent, and playing a causal role in the aetiology of psychosis only at the upper

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extreme. On the other hand, this view also incorporates the quasi-dimensional, disease model in its upper reaches, since the spectrum of schizophreniform disorders from schizotypal personality disorder to schizophrenic psychosis proper features as a second, graded `continuum', quite separate from the continuously distributed personality trait of schizotypy, albeit causally related to it. This compound model obviates at least one objection to the simple Eysenckian model, namely that it treats normals and patient groups as qualitatively indistinguishable. The Claridge view, by contrast, recognises the utility of the disease model when applied to the latter groups. In the light of the data to be presented in the present paper, taken together with other empirical observations, we will be arguing for the concept of healthy schizotypy, that is to say, for the uncoupling of the concept of schizotypy from the concept of disease. We believe this is best done within the context of the fully dimensional model, and that the present data, along with other recent studies, are best interpreted as lending support to this model, rather than that of the schizoid taxon. Among the other studies we have in mind are those of Jackson (1997), who proposed the concept of benign schizotypy in the context of religious experiences, some classes of which he suggested could be regarded as a form of problem-solving and therefore of adaptive value. 2. Method 2.1. Participants A three-fold approach was adopted to the problem of comparing hallucinators with non-hallucinators: 1. The `Postal OBErs': a group of volunteers reporting at least one OBE was recruited by means of media appeals, mainly in newspapers and magazines (n=408). To compare with them, a group of 77 people was recruited through the Oxford Subject Panel, matched for age, gender and social class (as de®ned by HMSO, 1980). 2. To obtain a comparison group of OBErs who could not be characterised as self-selected a question devised by Palmer (1979) to tap the occurrence of OBEs in a normal population was put to a sample of 203 people. The question is worded as follows: Have you ever had an experience in which you felt that `you' were located `outside of' or `away from' your physical body; that is the feeling that your consciousness, mind or centre of awareness was in a di€erent place from your physical body? Endorsement of this question was adopted as the operational criterion of having had an OBE as it has been used in a number of previous studies (Blackmore, 1984, 1986; Irwin, 1985; Kohr, 1980; Myers, Austrin, Grisso, & Nickeson, 1983; Palmer, 1979; Tobacyk & Mitchell, 1987). A total of 42 out of the 203 subjects endorsed it in the present context. This endorsement rate of 21% is comparable with results obtained in earlier studies. 3. The Postal OBErs were subdivided according to whether they reported only one, two to ®ve or more than ®ve OBEs in response to the Palmer question, and the factor scores of the three

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sub-groups so generated were compared with one another. Since the members of all three groups had been recruited by the same method, namely media appeal, any di€erence between their scores on the four factors could be reasonably attributed to their di€erential proneness to hallucination, rather than to any peculiarities arising from the method of recruitment. 2.2. The questionnaire The questionnaire used in the present study was the CSTQ as devised by Bentall et al. (1989), and the subscales considered in the present analysis consisted of the following: The four subscales (E, N, P and L) of the Eysenck Personality Questionnaire (Eysenck & Eysenck, 1975) The two subscales of the Claridge and Broks's (1984) STQ (STA and STB) Five Chapman scales: Magical Ideation (Mgl) (Eckblad & Chapman, 1983); Hypomania (Hypo; Eckblad & Chapman, 1986); Social and Physical Anhedonia (SoAn and PhAn; Chapman et al., 1976); Perceptual Aberration (Pab; Chapman et al., 1978). Launay and Slade's (1981) Hallucination Scale (LSHS) Nielsen and Petersen's (1976) Schizophrenism Scale (N/P) Golden and Meehl's (1979) Schizoidia Scale (MMPI) Factors were extracted by principal components analysis, and the Kaiser criterion of an eigenvalue greater than one was used to determine the number of factors. Varimax was the method of rotation employed. As the factor structure was found to be essentially similar in the two groups, OBErs and non-OBErs, factor scores were computed from an analysis carried out on the combined group (n=684). The following question was also included in the questionnaire with a view to elucidating the subjects' psychiatric history if any: Have you ever taken or received medical treatment or advice for any form of psychological problem or mental illness?

3. Results The rotated factor matrix generated from the scales of the CSTQ is shown in Table 1. Four factors were extracted, with eigenvalues of 5.30, 2.28, 1.23 and 1.11, accounting for 37.9, 16.3, 8.8 and 7.9% of the variance, respectively (total=70.9 percent of the variance). The ®rst and second factors correspond to the ®rst and second factors discussed in Section 1, i.e. Aberrant Perceptions and Beliefs and Cognitive Disorganisation with Anxiety, respectively. The third and fourth factors are Asocial Schizotypy and Introvertive Anhedonia; i.e. they are in reverse order to that discussed above, as Asocial Schizotypy has accounted for slightly more of the variance than Introvertive Anhedonia in this analysis.

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3.1. Discriminant analyses of the group means In the ®rst two disciminant analyses, group membership (OBErs versus Non-OBErs) was the dependent variable and the four factors were the independent or predictor variables. In both comparisons the groups were ®rst equalised by applying the Sample procedure within SPSS. For example, 77 members of the Postal OBE group were selected at random to compare with the 77 matched members of the Oxford Subject Panel. As these were both two-group comparisons, only one discriminant function was computed in each case. Both comparisons were highly signi®cant (P<0.001), but the ®rst even more so than the second. In the ®rst comparison, that between the Postal OBErs and the matched Subject Panel Controls, the eigenvalue associated with the discriminant function was 0.66 and the canonical correlation (the Pearson correlation coecient between the discriminant score and the grouping variable) was 0.63. The square of this latter value represents the proportion of the variance in the discriminant function accounted for by group membership Ð in this case 40%. The classi®cation rate was 79.22%. In the second comparison, that between the Palmer OBErs and their respective controls, the eigenvalue was 0.32, the canonical correlation 0.49 and the classi®cation rate 69.05%. The relative contribution of the di€erent factors to discriminating between the various groups was investigated by examining univariate F-tests on the di€erent group means. In the case of the comparison between the Palmer OBErs and Palmer Controls, the means were ®rst adjusted for age as a covariate. Table 2 shows the group means for the four factor scores. In this table the means shown are for all the members of each group, rather than for the random selections used for the discriminant analyses. It will be seen that in both comparisons the di€erence between OBErs and controls is concentrated on Factor 1, Positive Schizotypy, for which the univariate F-test is highly signi®cant. In the case of the comparison between the Palmer OBErs and their respective controls, OBErs score less than Controls on Factor 4, Introvertive Anhedonia, to an extent that almost reaches signi®cance at the 0.05 level. Table 1 Rotated (varimax) factor matrix Scale STA STB E N P L SoAn PhAn Hypo PAb MgI LSHS N/P MMPI

Factor 1

Factor 2

Factor 3

Factor 4

0.76 0.44 0.32 0.27 0.23 0.10 0.13 0.25 0.74 0.79 0.87 0.85 0.19 0.23

0.48 0.54 0.53 0.80 0.04 0.26 0.26 0.08 0.05 0.16 0.07 0.21 0.83 0.48

0.15 0.54 0.32 0.20 0.80 0.61 0.02 0.10 0.46 0.12 0.16 0.05 0.04 0.37

0.01 0.02 0.43 0.00 0.19 0.47 0.72 0.81 0.08 0.07 0.03 0.02 0.19 0.24

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3.2. Intra-group e€ects in the postal OBE population Table 3 shows the mean factor scores and S.D.s of the three sub-groups within the Postal OBErs, namely those reporting one, two to ®ve or more than ®ve OBEs. It will be seen that on Factor 1 the mean score increases with increasing numbers of OBEs reported. A three-way discriminant function analysis was carried out on these data. There were signi®cant age-di€erences between the three sub-groups: somewhat counter-intuitively the more Table 2 Group means, S.D.s and associated univariate F-tests for di€erent subject groups Comparison

Group

Predictor

Postal OBErs vs. Matched Controls

Postal OBErs (n=408)

Factor Factor Factor Factor

1 2 3 4

0.319 0.040 0.081 0.064

0.99 0.97 1.01 0.98

Matched Controls (n=77)

Factor Factor Factor Factor

1 2 3 4

0.631 0.110 0.022 0.058

0.61 0.88 1.00 0.99

Palmer OBErs (n=42)

Factor Factor Factor Factor Factor Factor Factor Factor

1 2 3 4 1 2 3 4

0.311 0.106 0.100 0.490 0.744 0.048 0.084 0.132

0.86 1.05 0.79 0.89 0.67 1.00 1.01 1.01

Palmer OBErs vs. Palmer Controls

Palmer Controls (n=161)

Mean

S.D.

F

d.f.

P

7.21 0.33 0.73 0.00

1,483

0.007 0.565 0.393 0.958

12.59 0.90 0.47 3.30

1,200

0.000 0.342 0.490 0.071

Table 3 Group means and S.D.s for the three sub-groups of the Postal OBErs No. of OBEs

Predictor

1 (n=200)

Factor Factor Factor Factor Factor Factor Factor Factor Factor Factor Factor Factor

2±5 (n=117)

>5 or `At Will' (n=87)

1 2 3 4 1 2 3 4 1 2 3 4

Mean 0.075 0.058 0.117 0.107 0.465 0.116 0.042 0.091 0.623 0.197 0.071 0.070

SD 0.95 0.94 0.97 0.96 0.99 0.92 1.02 1.02 0.90 1.09 1.09 0.96

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OBEs a subject reported the lower his/her age was likely to be. (The theoretical signi®cance of this ®nding is discussed in McCreery, 1997.) Age was therefore entered in addition to the four factor scores as a predictor in the discriminant analysis. At the start of the analysis the three groups were equalized (n=87 in each case) using the SAMPLE procedure. As there were three groups, two discriminant functions were derived. When all ®ve predictors were entered simultanously, the ®rst function accounted for 84% of the total discriminating power of the two functions, and the second accounted for the remaining 16%. The ®rst function was signi®cant at the 0.01 level (Wilks' lambda=0.904, chi-square(10)=25.86, P=0.004). The canonical correlation between the discriminant function and the grouping variable was 0.285. The second discriminant function was not signi®cant. The overall classi®cation rate for this discriminant analysis was 47.5% of cases correctly classi®ed (chance=33.33%). To investigate the relative importance of the individual variables in predicting group membership, including the degree to which the age di€erence between the groups might be responsible for the overall signi®cance of the ®rst discriminant function in distinguishing between them, a stepwise analysis was performed in which change in Rao's V was the criterion of entry. The ®rst predictor to enter the equation on this basis was Factor 1, which was highly signi®cant [Rao's V(2)=13.10, P=0.001]. At step 2 age was entered, which was also signi®cant, but not at the level of Factor 1 [Change in V(4)=6.71, P=0.035]. No other predictors produced a signi®cant change in Rao's V. This suggests that, as in the earlier analyses, Factor 1 is the most potent predictor of group membership, and the signi®cant separation of the three groups by the ®rst discriminant function is not solely due to the age di€erential between them. 3.3. Psychiatric history With regard to the question concerning subjects' psychiatric history, if any, 25% of the OBErs endorsed it, compared with 21% of the controls. This di€erence is not statistically signi®cant [corrected 2 (1)= 1.39, n.s.]. The commonest reason given by both groups for seeking or receiving advice or treatment was depression, which supports the validity of the question, since this is generally considered the commonest form of psychological dysfunction in the population at large (Davison & Neale, 1998). 4. Discussion The present study produced a result that was both clear-cut and consistent. As expected, Factor 1, Aberrant Perceptions and Beliefs, successfully disciminated between the two groups, OBErs and Controls; and, perhaps just as signi®cantly from a theoretical point of view, the other three factors, Cognitive Disorganisation with Anxiety, Introvertive Anhedonia and Asocial Behaviour, did not. Moreover, this two-fold result was consistent across several di€erent comparisons, and using two distinct methods of subject-selection, which implies a certain robustness to the ®nding. The only exception to this pattern of results was the suggestion in one of the comparisons that OBErs might be scoring lower than non-OBErs on the Introvertive Anhedonia factor. Vollema and van den Bosch (1995) have put forward the proposal that subjects high on Social Anhedonia and/or Social Anxiety scales may be under-represented in volunteer subject populations,

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as socially anhedonic or anxious subjects may be less willing to volunteer than subjects scoring high on positive schizotypy. This idea is of interest in the context of the present study, where the largest sub-set of subjects, the Postal OBErs, were also self-selected. However, the failure of the anhedonia factor to discriminate between OBErs and non-OBErs was apparent not only in the comparisons involving the volunteer Postal OBErs, but also in those involving the Palmer OBErs, who were not self-selected. Indeed it was in this comparison that the tendency of OBErs to score lower on anhedonia than non-OBErs was most apparent, suggesting that it was not just a general depression of anhedonia scoring among volunteer subjects that was responsible for the failure of the anhedonia factor to operate as a discriminant. The endorsement rate for the question concerning psychiatric history may appear high at ®rst sight, in both the OBErs and controls, but it was framed in an inclusive way, and was clearly taken in that spirit; subjects included such things as consulting their GP at times of stress due to life-events. As mentioned in Section 1, factor analytic studies of schizotypy in normal subjects suggest that the trait is not a unitary one, but rather consists of several Ð possibly as many as four Ð relatively independent components. The present data clearly suggest that it is possible for fully functional schizotypes to rate highly on one of these components while not displaying any unusual evidence of the others. Moreover, it is clear from the present data that this one factor can on occasion be the one that appears most closely related to the phenomenology of psychosis itself. One of the aims of schizotypy research has been to identify questionnaire scales, or combinations of scales, which may act as `markers' for the subsequent development of clinical psychosis in normal subjects (Chapman & Chapman, 1987). The present result, in a large group of non-clinical schizotypes, would appear to suggest that Factor 1 on its own is not that marker Ð a result which is prima facie somewhat surprising, given that this is the factor which most closely captures the essence of psychosis: anomalous experiences and beliefs. Moreover, it is the factor which consistently, across studies with various di€erent instruments, accounts for the largest proportion of the variance in individual scores It would appear that something more than the mere presence of an elevated score on the ®rst factor is required to produce an increased risk for psychotic breakdown. One possibility is that only certain combinations of sub-factors within the schizotypy complex determined an unfavourable outcome. Rado (1953) and Meehl (1962) put forward anhedonia as the basic `neurointegrative defect' in schizophrenia, and perhaps, in light of this, we ®nd various writers, among them Kelley and Coursey (1992) and Chapman, Chapman, Kwapil, Eckblad, and Zinser (1994), suggesting that anhedonia may be a potentiating factor in predisposing to psychosis a person with other schizotypal traits. This particular suggestion might ®t with the present data, in which a slight tendency to decreased anhedonia may have been present in a population of subjects with elevated schizotypy scores in other respects. Such a combination Ð a tendency to anomalous perceptual experiences combined with a protective capacity for hedonic enjoyment Ð might well be compatible with complete functionality in professional and other capacities. In the present connection, it is interesting to note that Maier, Falkai, and Wagner (2001), following a detailed review of the literature on schizohrenia-spectrum disorders, conclude that: consistent evidence has been compiled during nearly a century of research that not the productive [i.e. positive] signs of schizotype but more the negative signs of schizotype (as social

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and emotional behaviour and basic cognitive dysfunctions) are pointing to a relationship with the etiology of schizophrenia. On the other hand, since his 1962 paper Meehl (1990) has put forward two di€erent candidates for the role of crucial factor, namely associative loosening and aversive drift. If correct, these features would point more towards Factor 2, with its emphasis on cognitive failures and social dysfunction. It is also possible that elevated scores on more than two elements of schizotypy are a necessary condition of overt psychosis (Claridge, 1988). Mason (1995) has discussed the possible aetiological relevance of all four of the factors used in the present study to the occurrence of psychotic breakdown. In this context it is worth drawing attention to the disparity between the various factors with regard to their respective levels of description. The scales which load on Factor 1, Positive Schizotypy, are for the most part directly tapping transient states or experiences, and it is an inference that these transient states or experiences are causally related to some latent, underlying trait. Factors 3 and 4, Anhedonia and Impulsive Nonconformity, are more evidently and directly dealing with long-term traits, by virtue of questions dealing more with attitudes and stable patterns of behaviour. The second factor, Cognitive Disorganisation/Social Anxiety, is perhaps a mixture of these two kinds of descriptor, some of the questions which load on this factor dealing with transient cognitive failures, such as thought-blocking, while others tap more trait-like tendencies, such as being easily hurt by criticism. The distinction between traits and states in the schizotypy sphere is relevant to a theoretical issue discussed by Venables and Bailes (1994), for example, concerning the causal priority of the various factors in both schizotypy and schizophrenia itself. They suggest that `an interpretation of the existence of social impairment shown by some schizophrenics, as a reaction to increasing ``oddness'' as positive symptoms develop, may be incorrect as social impairment exists in the schizotypic state.' The present data might also be seen as running counter to the view that anhedonia is merely a secondary reaction to the anomalous experiences tapped by Factor 1, since there was no sign that the elevated Factor 1 scores of the OBErs was associated with social impairment; if anything the reverse. To turn to the question of how the present results bear on the main theoretical question posed in Section 1, namely is schizotypy fully- or only quasi-dimensional? We believe the present data tend to support a fully dimensional model. On the quasi-dimensional, `schizoid taxon'' model, schizotypy is by de®nition pathological; it is something intrinsically negative which has to be prevented from decompensating into psychosis by positive factors such as physical vigour, high intelligence or even economic factors. On the fully dimensional model, on the other hand, schizotypy is something essentially neutral: a dimension which is, to be sure, correlated with psychosis-proneness, inasmuch as the higher one is on this dimension the more likely one is to display symptoms such as hallucinations and delusions in a maladaptive or disabling form, but which has no necessary connection with psychosis, inasmuch as one can be high on the dimension and not decompensate even in the absence of protective factors. On the present view, we may draw an analogy between schizotypy and trait anxiety. The latter is in itself neutral with regard to pathology. It is possible to have a high level of trait anxiety and never develop any of the anxiety disorders. Indeed, a high level of trait anxiety may even be adaptive in certain walks of life. Clearly something more than a tonically high level of anxiety is

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necessary for someone to develop phasic anxiety episodes of the pathological sort we call anxiety disorders. Situational factors such as life stress may play a part, as may more physical factors such as drugs, diurnal ¯uctuations of arousal, and so on. In a similar way, we suggest, schizotypy as a trait is in itself strictly neutral with respect to pathology, indeed, may even have its adaptive aspects, particularly in certain walks of life. In this context we may mention the links that have long been thought to exist between psychosis-proneness and creativity (e.g. Claridge, Prior, & Watkins, 1990, for a discussion of such links in the literary ®eld). If certain aspects of schizotypy/psychosis-proneness are indeed related to creativity and hence of adaptive value, this would help to explain the occurrence of apparently adaptive forms of anomalous perceptual experiences in normal populations such as those considered in the present study. The present data in fact suggest a way in which a disjunction between schizotypy and pathology might be possible. It may be that the real distinction is not so much between healthy and unhealthy schizotypy on the trait level as between healthy and unhealthy schizotypal `symptoms' Ð i.e. discontinuous, or phasic, events to which the underlying trait is but one contributory cause. In the case of the present subjects, a distinction between healthy and unhealthy manifestations or `symptoms' certainly suggests itself. It is noteworthy that, in contrast to schizophrenic subjects, who often ®nd their hallucinatory experiences aversive and wish to stop them, the subjects of out-of-the-body experiences may report that they ®nd them highly reinforcing, so that they wish to repeat them. A small minority even develop techniques for inducing them at will (Green, 1968). It is possible that certain types of anomalous perceptual experience may even have adaptive value. Those who are in post-operative pain, for example, prior to an OBE may report feeling diminished pain, or at any rate less emotional disturbance as a result of the pain, following the experience. Similarly, Green and McCreery (1975) identi®ed a class of hallucinations of the human ®gure, which they termed `reassuring apparitions', which seemed to have the e€ect of calming the person at a time of particular life stress. On this view, the distinction between healthy and unhealthy schizotypy might depend on the distinction between aversive and reinforcing (and hence adaptive and maladaptive) forms of the same experience. The question for research would become one of uncovering what determined the hedonic tone of hallucinatory experiences in di€erent subjects, for example; a question which could be pursued on a variety of di€erent levels, such as the biographical (do speci®c sorts of life experience predispose to aversive hallucinations?) and the electrophysiological. McCreery (1997) has put forward a model in which lability of arousal, and in particular a tendency to episodes of hyperarousal due to relative weakness of inhibitory mechanisms, is the basic characteristic of the schizotypal nervous system. The model has the incidental merit of providing a rationale for why the Chapmans' Hypomania scale should load highly on Factor 1, and in particular, why there should be such high correlations between this scale and hallucination scales such as PAb and LSHS. The proposal is that hyperarousal triggers brief episodes of Stage 1 sleep, with its attendant phenomena of hallucinations and delusions, while the subject is still in the waking state. Whether correct or not, this model may serve to illustrate how schizotypy as a trait might be intrinsically neutral, but capable of giving rise to both adaptive and maladaptive forms of the same type of experience, such as hallucination. The same trait of liability to hyperarousal might give rise to very di€erent forms of experience, dependent on other individual

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di€erences of nervous organisation. Such a model would be in contradistinction to the schizoid taxon view, according to which schizotypy is almost to be conceived as a milder, or less fully expressed, form of schizophrenia itself. The present view of schizotypy has the incidental merit of obviating the criticism that is liable to occur to those who hold a dualistic view of out-of-the body experiences, that by relating them, albeit indirectly, to schizophrenia, one is pathologising an experience that is clearly highly valued by many people, and given by many an almost religious signi®cance. Further clari®cation of what distinguishes the healthy from the unhealthy schizotype promises both practical and theoretical advantages. On the practical level, it has implications, not only for prophylaxis but even for treatment. For example, in the case of hallucinations, it is possible that a better understanding of what distinguishes hedonic from aversive hallucinatory experiences might lead to treatments for the hearing-voices experiences su€ered by many schizophrenics. On the theoretical level, the exploration of the distinction between the healthy and unhealthy schizotype might aid our understanding of the nature of the psychotic breakdown process itself. References Bentall, R. P., Claridge, G., & Slade, P. D. (1989). The multi-dimensional nature of schizotypal traits: a factor analytic study with normal subjects. British Journal of Clinical Psychology, 28, 363±375. Blackmore, S. J. (1984). A postal survey of OBEs and other experiences. Journal of the Society for Psychical Research, 52, 225±244. Blackmore, S. J. (1986). Out-of-body experiences in schizophrenia: a questionnaire survey. Journal of Nervous and Mental Disease, 174, 615±619. Chapman, L. J., & Chapman, J. P. (1987). The search for symptoms predictive of schizophrenia. Schizophrenia Bulletin, 13, 497±504. Chapman, L. J., Chapman, J. P., Kwapil, T. R., Eckblad, M., & Zinser, M. C. (1994). Putatively psychosis-prone subjects 10 years later. Journal of Abnormal Psychology, 103, 171±183. Chapman, L. J., Chapman, J. P., & Raulin, M. L. (1976). Scales for physical and social anhedonia. Journal of Abnormal Psychology, 85, 374±382. Chapman, L. J., Chapman, J. P., & Raulin, M. L. (1978). Body-image aberration in schizophrenia. Journal of Abnormal Psychology, 87, 399±407. Claridge, G. S. (1988). Schizotypy and schizophrenia. In P. Bebbington, & P. McGun, Schizophrenia: the major issues. Heinemann. Claridge, G. (1994). Single indicator of risk for schizophrenia: probable fact or likely myth? Schizophrenia Bulletin, 20, 151±168. Claridge, G. (1997). Theoretical background and issues. In G. Claridge, Schizotypy, implications for illness and health (pp. 3±18). Oxford: Oxford University Press. Claridge, G. (1999). Esquizotipia: teoria y medicon. Revista Argentina de Clinica Psicologia, 8, 36±51. Claridge, G. S., & Broks, P. (1984). Schizotypy and hemisphere function Ð I. Theoretical considerations and the measurement of schizotypy. Personality & Individual Di€erences, 5, 633±648. Claridge, G., McCreery, C., Mason, O., Bentall, R., Boyle, G., Slade, P., & Popplewell, D. (1996). The factor structure of `schizotypal' traits: a large replication study. British Journal of Clinical Psychology, 35, 103±115. Claridge, G. S., Prior, R., & Watkins, G. (1990). Sounds from the bell jar: ten psychotic authors. Houndmills, Basingstoke, Hampshire: The Macmillan Press Ltd. Davison, G. C., & Neale, J. M. (1998). Abnormal psychology: an experimental clinical approach. New York: John Wiley. Eckblad, M., & Chapman, L. J. (1983). Magical ideation as an indicator of schizotypy. Journal of Consulting and Clinical Psychology, 51, 215±225.

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