Inhibition, unusual perceptual experiences and psychoticism

Person. indiuid.01% Vol. 8, No. 5, pp. 6X7-691, 1987 Printed

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0191-8869/X7 $3.00 + 0.00 Q 1987 Pergamon Journals Ltd

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INHIBITION, UNUSUAL PERCEPTUAL EXPERIENCES AND PSYCHOTICISM J. G. BULLEN,‘* ‘University

College

London

D.

R.

HEMSLEY’

and %stitute of Psychiatry, London, England

and N. F. DIXON’ De Crespigny

Park,

Denmark

Hill,

(Received 23 October 1986) Summary-The dimensional approach to psychosis suggests that research should focus on the performance of psychiatrically normal individuals on measures derived from the study of psychosis. Recent theories of schizophrenia postulate a defect at the interface of preconscious/conscious processes. Such a defect could occur as a result of some disturbance in inhibitory attentional mechanisms. A group of normal S’s were assessed on three measures; (a) a priming task measuring inhibition, (b) a perceptual task, the verbal transformation effect, and (c) a number of questionnaires of relevance to the psychoticism dimension. As predicted low inhibition was correlated with unusual experiences on the perceptual task. Each of these measures correlated with a questionnaire measure of predisposition to hallucinations, but not with the other measures of psychoticism. No correlations with other personality variables as assessed by the EPQ were found.

INTRODUCTION

The traditional view of psychotic disorders is that they represent a state of being and behaviour that is wholly distinct from normality. This view, although pervasive, is becoming the subject of increasing controversy as a number of authors present an alternative dimensional model of psychotic phenomena (Eysenck and Eysenck 1975; Zubin and Spring, 1977; Claridge, 1985). Claridge, for instance, suggests that “. . . psychotic characteristics are not the perogative of the classically psychotic patient”. He argues that there is rather “. . . a continuity of behaviour blending into a spectrum of illness” at the extreme of which some degree of discontinuity may become apparent. Support for this view is provided by genetic research which observes a spectrum of disorder in the relatives of schizophrenics and which offers a polygenic model of inheritance for schizophrenia (Heston, 1966; Gottesman and Shields, 1982). Diagnostic research also supports the existence of borderline categories to the main psychotic categories and these are formally recognised in the American system (DSM III, 1980). The dimensional model suggests that research should focus on the performance of psychiatrically normal individuals in relation to measures derived from the study of, or models of, psychosis. This strategy is adopted in the present study. The proposition of a primary attentional dysfunction has been central to much research on schizophrenia (for review see Hemsley, 1975, 1982). The more recent models propose some dysfunction at the interface of automatic/preconscious processes and controlled/conscious processes resulting in intrusions and discontinuities in conscious experience (Dixon, 1971; Frith, 1979; Callaway and Naghdi, 1982). Such a condition could occur as a result of deficiencies in inhibitory mechanisms, for instance Johnson (1985) suggests that “input activation can normally be inhibited . . such inhibition.. . [may be]. . . diminished in schizophrenics”. In the present study a measure of inhibitory attentional mechanisms was employed (Posner and Snyder, 1975) and it was predicted that S’s high on ‘psychoticism’ would show reduced inhibition. Concerning the measurement of ‘psychoticism’ a variety of questionnaires have been developed. These have often taken form within widely differing perspectives and although they may overlap there may also be areas of divergence. That the latter is the case is suggested by Muntaner and Garcia-Sevilla (1985) who found three main factors in a correlational study of a number of these questionnaires. As it is not yet clear which factor is of primary importance in defining this dimension we chose to employ a number of relevant questionnaires. In addition to questionnaires a laboratory analogue procedure was employed. One aspect of *Present

address:

Dept. of Experimental

Psychology,

University 687

of Oxford,

South

Parks

Road,

Oxford,

England.

J. G. BULLEN

688

psychotic experience covered by some of the questionnaires concerns abnormal perceptual experience. Hence a perceptual task was adopted as an analogue measure. The perceptual procedure used was that which produces the verbal transformation effect, VTE (Warren and Gregory, 1958). This involves the repetition of a single word at a rapid rate over a period of a few minutes during which time subjects commonly report hearing changes in the word to other words or sounds. Slade (1976) found that hallucinating schizophrenics heard significantly more words with only a weak phonetic connection to the presented stimulus than non-hallucinating schizophrenics and normals. He proposed that the “VTE may be tapping a function basic to an hallucinatory predisposition”. It was predicted therefore that Ss experiencing more unusual transformations on the VTE would show less inhibition as assessed by the attentional task and high ‘psychoticism’ on the questionnaires. METHOD

Subjects

The subject group consisted of undergraduates and employees of University College London. The age range was from 18-53 years, with a mean of 21.3 years (SD 5.3 years). There were 52 subjects in all, 25 women and 27 men. Not all subjects completed all tests, when this is so it is indicated in the appropriate section. Most of the Ss were not trained in psychology. Ss were not informed of the purpose of the study until they had completed all the tests. Design

A within subjects design was employed, each S providing data on three sets of measures; (a) attentional, (b) perceptual and (c) questionnaires. Each measure and its associated procedure is described in detail below. Attentional measure. Subjects: N = 45; 50 Ss tested, data lost as a result of technical faults. Design: A within S design employed. Ss were required to perform a matching task. They were presented with two letters (‘AA’ or ‘AB’) and asked to indicate whether these were the same or not. The number of presentations of each of these two stimuli was equal. The target letters were preceded by priming stimuli; on half the trials this was a ‘+‘, on the other half it was either ‘A’ or ‘B’. The probability of either ‘AA’ or ‘AB’ following each prime was varied as shown in Fig. 1. Considering the ‘Yes’ responses only, this arrangement creates three conditions; (i) Neutral, N, in which ‘AA’ is preceded by ‘+ ‘, (ii) Expected, E, in which ‘AA’ is preceded by ‘A’ and (iii) Unexpected, U, in which ‘AA’ is preceded by ‘B’. The measure taken was the RT for correct response in each of these conditions. From these data a measure of facilitation was derived from the difference between N and E, and of inhibition from the difference between N and U. Ss were presented with 400 trials. Order of presentation was randomised. A check on compliance was made by asking Ss to indicate which stimulus had been the prime on the immediately preceding trial. This question was asked eight times at randomised points during the sequence of trials, number of correct responses being the measure taken. Temporal parameters. A warning stimulus ‘*’ was displayed for 500 ms, followed immediately by the prime. The prime was displayed for 500 ms followed immediately by the letter pair. The letter pair was response terminated, but was terminated after 1 set if a response had not occurred within this time. Apparatus and materials. The stimuli were presented using a BBC microcomputer connected to two response keys. The letters were 6mm high. The prime was centred above the paired letters which were in adjacent horizontal positions ie ‘A’ AA Procedure. Ss were instructed by written instructions displayed on the screen. They were informed of their task and all of the six possible conditions. The instructions in relation to the Prime Target

:

A

+. :

Fig. 1. Diagram

/\

AA( .5)

showing

AB( .5)

the probability

B

/\

AA( .4)

of either

/\

ABC.11

AA( . 1)

‘AA’ or ‘AB’ following

ABC.4)

each of the primes.

Psychotism

689

priming stimuli were as follows: “Do not respond to these letters but do take note of them as they may act as a clue to what follows.” They were asked to respond as quickly as possible and were warned of the length of the task. Perceptual

measure

Subjects. N = 51 ,l S did not attend. Design. Ss were presented with the word

‘TRESS’ repeatedly for three 3 minute sessions, each session being separated by a 1 min silence. The Ss task was to shadow their auditory experience during the session. The number of different words was noted and a qualitative measure derived by categorising the words obtained as follows; O-words with no syllables in common with Tress, l-words with one syllable in common, similarly for 2, 3 and 4. Phrases and double words were scored separately. Apparatus and materials. The word ‘TRESS’ was taped into a PDPI 10 computer and replicated continuously, 140 times per minute. A cassette tape was constructed with periods of Tress and silence as specified in the design. The tape was played to each individual S via headphones. Ss were seated in a comfortable chair in a semi-soundproofed room. The E completed a response sheet as S performed the task. Procedure. Ss were tested individually. First, an estimate of the Ss threshold was obtained and the volume set at a fixed level above this. The following instructions were then read to the S. “When the tape begins you will hear the word Tress repeated over and over again. After a while you may begin to hear changes to different words or sounds. Whenever it changes to a different word or sound please say out loud what you can hear. If you hear two words or sounds alternating rapidly just say the two together. So, every time it changes, either to something new or to something you have already heard, please say it out loud. I am interested in what you experience. Finally don’t worry about whether what you hear makes sense or not, it may do, but on occasions it may not. Any questions?” Ss were then given a one minute practice trial followed by the main trials as specified in the design. Questionnaires Ss were asked to complete the following questionnaires chosen to be of relevance to the psychoticism dimension. (i) Launay-Slade predisposition to hallucinations scale, LS. (Launay and Slade, l!#l). (ii) Eysenck Personality Questionnaire, EPQ. (Eysenck and Eysenck, 1975). ’ (iii) Personality Inventory, PI. (Eysenck and Eysenck, 1969). (iv) Claridge’s STQ, consisting of the STA and the STB. (Claridge and Broks, 1984). (v) Magical Ideation Scale, MIS. (Eckblad and Chapman, 1985). (vi) Perceptual Aberration Scale, PAb. (Chapman, Chapman and Raulin, 1978). Ss were also required to complete the Mill Hill vocabulatory test as an estimate of verbal intelligence (1977 revision). Finally Ss were fully debriefed on completion of all tests.

RESULTS Analysis of the attentional paradigm

The RT data for the three priming conditions; neutral, expected and unexpected were compared using ANOVA. The RT data are shown in Table 1. The overall priming effect was significant (F = 42.25, P < 0.0001). There was a significant inhibition effect (F = 25.58, P < 0.0001) and a significant facilitation effect (F = 44.04, P < 0.0001). There were no gender differences (F = 0.01, P < 0.9). Spearman

Rank Correlations

Since the total number of correlations made was 1024, 51 would be expected to be significant by chance at the 5% level. The number of significant correlations actually obtained was 87

J. G. BULLEN

690 Table

I.

times and standard attentional test Neutral

WOIXll MelI

Expected

deviatmns

the

Unexpected

R SD

482.9 56.4

458.5 60.2

516.3 65.5

K

488.X 62.8

459.x 61.4

513.6 70.5

SD

for

including correlations of the questionnaires with other questionnaires and measures within the VTE and within the attentional test. These within measure correlations are not reported. Correlations with Inhibition. The size of the inhibition effect correlated as predicted with the number of qualitatively unusual words experienced on the VTE; (a) for words with one syllable in common with ‘tress’ (r = 0.309, df = 42, P < 0.025, l-tailed) and (b) for a combination measure, words with 0 or 1 syllables in common plus double words and phrases (r = 0.285, df = 42, P < 0.05, l-tailed). There were no other significant correlations between these two measures. The size of the inhibition effect also correlated significantly in the predicted direction with items of the Launay-Slade questionnaire (Y = 0.346, df = 43, P < 0.01, l-tailed). There were no significant correlations with the other questionnaire measures of psychoticism (P, r = 0.02; STA, r = 0.104; STB, r = 0.031; MIS, r = 0.083; PAb, r = 0.065). The inhibition effect was not related to the Mill Hill (r = 0.127), nor to the check on compliance (r = 0.002). There were also no significant correlations with Extraversion (r = -O.OSl), Neuroticism (r = -0.085) and the Lie scale (r = 0.028) of the EPQ. Correlations of the perceptual measure with the questionnaires. The total number of different words experienced in the ‘tress’ test correlated significantly with items of the LaunayySlade (r = 0.25 1, df = 48, p < 0.05, 1-tailed). The number of qualitatively unusual words (0, 1 plus double words and phrases) correlated significantly with the Magical Ideation Scale (r = 0.256, df = 46, P < 0.05, l-tailed). There were no other significant correlations with measures of psychoticism. The number of qualitatively unusual words also correlated with the Mill Hill vocabulary test (r = 0.413, df = 48, P < 0.01, 2-tailed). There was a significant negative correlation between number of words with only one syllable in common with ‘tress’ and the Lie scale of the EPQ (r = -0.336, df = 48, P < 0.02, 2-tailed). There were no significant correlations with Extraversion and Neuroticism (E with no. words r = 0.198, with unusual words r = 0.106; N with no. words r = 0.101, with unusual words r = 0.058).

DISCUSSION facilitation and inhibition effects, the The Posner attentional paradigm yielded significant magnitudes of which were not affected by the level of compliance obtained in this sample. The prediction that subjects high on scales measuring traits related to psychosis would show reduced inhibition was confirmed with the LaunayySlade scale. Similarly subjects experiencing unusual words in the perceptual task, VTE showed reduced inhibition as predicted. The number of words experienced in the perceptual task correlated as predicted with the LaunayySlade. The experience of unusual words correlated with the Magical Ideation Scale. There were no other significant correlations with the other questionnaires, nor with other aspects of personality as assessed by the Extraversion and Neuroticism scales of the EPQ. The most noteworthy aspect of these findings is that two different measures, inhibition and the VTE, correlated with each other and each independently with similar questionnaires relating to unusual experiences. These findings support the proposal that attentional mechanisms are of relevance to understanding perceptual anomalies which may lie on a continuum with psychotic phenomena. There are, however, some problems with this study. The perceptual task used, the VTE, may not be as pure a measure of ‘hallucinatory predisposition’ as hoped. The experience of unusual transformations correlated significantly with the Mill Hill vocabulary test and negatively with the lie scale of the EPQ. This suggests that the quality of the experience may depend in part on the

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691

vocabulary available to the subject and on a certain ‘openness’. Perceptual measures without a verbal component should be used in future work. Furthermore, the failure of both the inhibition measure and the VTE to correlate with the other measures of psychoticism is of importance. It may be attributable to the possibly multifactorial nature of the ‘psychoticism’ dimension (Muntaner and Garcia-Sevilla, 1985). Hence the Eysenckian scales and the STB may relate to unconventional/antisocial aspects which may be, to some extent, independent of those pertaining to the perceptual/attentional anomalies. This, however, would not account for the failure to find correlations with the Perceptual Abberations Scale nor the STA. The PAb scale consists of extremely abnormal items which few people endorse. This could make it an inappropriate scale to use with a normal sample. Future research may be able to explain the failure to find a correlation with the STA scale but it remains an anomaly at present. More work is required on the relation between these different scales to clarify what each is measuring and their correlates. To conclude, the findings of this exploratory study suggest that it would be fruitful to explore the links between attentional mechanisms and experiential/perceptual phenomena in relation to the proposed ‘psychoticism’ dimension. Acknowledgemenfs-We shoud like to thank generous help with the analysis. The project University of London.

Niko Preston was financed

for invaluable technical assistance and Anne McBride for her by the MRC with assistance from the Tregaskis Fund of the

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