Br. J. med. Psychol. (1976). 49, 161-166 Printed in Great Britain

161

Preconscious processing in schizophrenics: an exploratory investigation B Y S. H. A. H E N L E Y

AND

N. F. DIXON*

Recent research on dichotic listening (Corteen & Wood, 1972; Henley & Dixon, 1974; Lewis, 1970; Mackay, 1973), on dichoptic viewing, i.e. the simultaneous presentation of a different input to each eye (SomCkh & Wilding, 1973), and on the effects of subliminal auditory stimuli upon responses to a supraliminal visual stimulus (Henley, 1973, has provided evidence for the view (Dixon, 1971) that the major part of perceptual processing in selective attention occurs prior to awareness. In view of this fact, and in view of the suggestion (e.g. McGhie & Chapman, 1961) that a breakdown in the selective and inhibitory functions of selective attention is the fundamental deficit in schizophrenia, it becomes of some interest to determine the e.xtent to which the same preconscious mechanisms, which have been shown to operate in normals, also operate in schizophrenics. In a preliminary attempt to investigate this question, the present study examined changes in threshold for a spot of light, presented to one eye, as a function of emotional or neutral stimuli presented, below threshold, to the other eye. The changes in threshold were measured by the method of closed loop control wherein the subject himself adjusts the intensity of the light spot so as to make it alternately appear and disappear. In the light of results from previous studies which have employed this method to examine perceptual defence in normal subjects CDixon, 1960;Dixon & Haider, 1961; Henley, 1974), it was predicted that schizophrenic patients would show raised thresholds for an emotional word (CANCER or BREAST)relative to their thresholds for a neutral word (RECANT). A second hypothesis was based upon the repeated finding (e.g. Chapman, 1961; Davis & Harrington, 1957; Dunn, 1954; Moriarty & Kates, 1962; Turbiner, 1961; Whiteman, 1954) that schizophrenics show greatest deficit, relative to normals, on tasks involving social stimuli. On the assumption that social stimuli have a threatening quality for schizophrenics, it was predicted that these patients would show raised thresholds for stimuli depicting mother-child interactions relative to their thresholds for an impersonal stimulus. METHOD

Design The method (following Dixon, 1958) involved taking a continuous measure of the subject's awareness threshold for light presented to the right eye, while emotional and neutral stimuli were presented, below threshold, to the left eye. Apparatus and materials The closed loop apparatus was constructed round two S.E.I. photometers. Each consisted of a simple telescope through which the eyes were trained onto a diffusely lit screen of brightness level sufficient for stable adaptation of the eye, under the control of the experimenter, and calibrated in log foot-lamberts (1 log unit = 10 foot-lamberts). Onto the rear of the screen two projectors were aimed, one for either eye. These projectors held interchangeable 2x2 slides. The brightness level of the two images could be manipulated via two knobs,

* Department of 6

Psychology, University College, London M P S 49

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calibrated in log ft It, under the control of the experimenter, and by neutral density filters (density 3.0, transmission 10 per cent). Each photometer, in addition to giving a picture of the screen, also had in its centre of view a small spot (approximately %r" wide). The brightness of the spot could be ( a ) pre-set by the experimenter and switched onloff, and (b) raised and lowered by the subject via a box with a 'joystick'. The range of brightness could be varied between 0.01 and IOOOO ft It. Arrangements were made for altering the interocular distance, focusing, etc., and bellows prevented extraneous light from reaching the eyes. The observation and control of various functions by the experimenter were made possible by a main control box which consisted of two meters for brightness in log f t It, two integrators giving an integration of spot brightness being varied by the subject against time, and switches for projectors, integration start, spots, and left or right spot motor drive power. Outputs from the two spot meters were taken to a two-channel Washington pen recorder for a permanent record of the rise and fall of spot brightness during the experiment. The stimulus material consisted of the words CANCER, BREASTand RECANT. The pictorial stimuli were ones used previously by Dunn (1954) in a study involving schizophrenic patients. Three of these depicted mother-child interactions (a whipping scene, a scolding scene, and a feeding scene); the fourth, a 'neutral' stimulus, was a picture of a house and a tree.

Subjects Seventeen hospitalized male schizophrenics took part in the experiment. Of these, two were unable to complete the task because of eyesight deficiencies (confirmed by the charge nurse), and a further two because of a total inability (or unwillingness) to cooperate (refusal to look into the apparatus, etc.). The mean age of the 13 subjects whose results were considered in the analysis was 46.4 years (standard deviation 5.8 years; range 35-53 years), and the mean duration of illness (i.e. time elapsed since first admission to a mental hospital) was 19.7 years (s.D.5 years; range 11-27 years). Five of the group were diagnosed as paranoid, and eight as non-paranoid chronic schizophrenics. All of these patients, except two who were on placebo, were on doses of chlorpromazine which ranged from 150 to 800 mg daily. (These dosages remained unknown to the experimenter until after the experiment.) The subjects were randomly assigned to one of two groups, A or B, according to which of the emotional verbal stimuli, BREAST or CANCER, was to be presented. By chance, each group consisted of four non-paranoid and two paranoid patients. (The fifth paranoid subject was presented with only the pictorial stimuli.) There were no significant differences between groups A and B, either in terms of age or in terms of length of illness.

Procedure The subjects in this investigation were led to believe that the experiment was essentially a test of visual acuity. They were told that the experimenter was interested in examining 'how bright a spot of light must be in order for most people to be able to see it, and how dim it must become in order for it to disappear'. An attempt was made to ensure that the visual fields overlapped by asking the subject to look into the apparatus and report whether he could see one circle of grey light or two. Adjustments were made accordingly. Background illumination was subsequently set at a brightness level of log I ft It, and the word CANTER presented in the right eye field at a supraliminal intensity. The subject was then instructed, 'First of all, I'm going to show you a word. Can you tell me what the word is?. . .Good. Now, when I turn this knob, you will see that the word gets dimmer and dimmer. Will you tell me when it disappears?. . .Is it still there?. . .' This procedure for determining threshold by the descending method of limits was repeated using a neutral pictorial stimulus (two rectangles). The threshold was always the same for both stimuli. Brightness intensity was subsequently adjusted to give an image brightness to the right eye 0.3 log unit below the level at which the subject reported that the stimulus had disappeared. The subject was then shown the control box and told, 'If, while you're looking into the apparatus, you push the lever up like this (given demonstration), you will see a small spot of light start to appear. Can you see it?. . .Good. Now, if you push the lever down again, the spot will start to disappear. Is it doing that?. . .' The subject was allowed to practice making the spot come and go until he seemed reasonably competent at the task. He was then instructed: 'Your task during this experiment is to keep making the spot appear

Preconscious processing in schizophrenics

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Fig. I. Mean spot brightness values recorded for Group A ( n = 6) at 1 sec intervals during subliminal stimulation with emotional and neutral words. and disappear. When I say 'Go', raise the lever until you can see the spot, then lower it until the spot disappears, then make it reappear again just as you have been doing. Keep making the spot come and go until I tell you to stop.' The slides were subsequently presented to the subject, in random order, for a duration of 30 seconds each. Left spot brightness (pre-set at log 1 ft It before each stimulus presentation) was continuously recorded throughout this time. The procedure was identical for all subjects except that, in addition to the four pictorial stimuli and the neutral verbal stimulus RECANT,subjects in group A were presented with the (emotional) word BREAST,while those in group B were presented with the (emotional) word CANCER.One subject, who misread the word CANTERwhen this was presented supraliminally, but who was able to identify the two rectangles (state which was the larger, etc.) without difficulty, was presented with only the pictorial stimuli. The order in which the slides were presented was different for each subject, and remained unknown to the experimenter until the end of the trial. (Luminous dots on one corner of each slide made it possible for them to be shuffled, and placed in the apparatus the correct way up without the experimenter ever having to be aware of their content .) RESULTS

Efects of verbal stimuli Fig. 1 shows the mean left spot brightness values, given by subjects in group A, at intervals of 1 second from 10 to 29 seconds after onset of the emotional stimulus, BREAST,and the neutral stimulus, RECANT.(Values for the thirtieth second after stimulus onset are not given since, due to mis-timing, these data were not available for all subjects.) The overall mean spot brightness values obtained during the 29-second interval following onset of the stimulus words BREASTand RECANTwere 1.52 log units and 1.098 log units respectively. Five of the six subjects in group A gave higher left spot brightness values during presentation in the right eye field, of the emotional word than during presentation of the neutral word. A 6-2

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Table 1. Mean spot brightness value (log unit)* during the 29-second interval following stimulus onset ( n = 13)

scene

Scolding scene

Feeding scene

Neutral scene

1.42

1.82

1.93

1 *I5

Whipping

*

1 log unit = 10 foot-larnberts.

Wilcoxon matched-pairs signed-ranks test showed that his difference was significant ( T = I , 2 = 1-99, P= 0.023, one-tail). It might be added that the negative difference score (i.e. mean spot brightness during presentation of the word BREASTminus mean spot brightness during presentation of the word RECANT) of the sixth subject in this group was so small (0.003 log unit) as to have been most probably attributable to random error in the apparatus. Contrary to expectations, four of the six subjects in group B gave lowerspot brightness values during presentation of the word CANCER than during presentation of the word RECANT.The overall mean brightness values given by this group during the 29-second interval following onset of the emotional and neutral stimuli were 1.52 log units and 1.82 log units respectively.

Effects of pictorial stimuli Table 1 gives the overall mean spot brightness value given during the 29-second interval following onset of each of the four pictorial stimuli. It can be seen from this table that awareness thresholds (spot brightness values) tended, as predicted, to be higher during presentation of the scolding and feeding scenes than during presentation of the neutral (impersonal) scene. In the case of the feeding scene, this difference approached significance at the 5 per cent level of confidence ( T = 23.5, Z = 1-53, P=O.O63, one-tail). However, spot brightness values given during presentation of the whipping scene tended to be lower than those given during presentation of the impersonal stimulus. This (non-significant) trend was opposite to the one predicted. On the assumption that the feeding scene is tapping oral dependency, it seems reasonable to suggest that both the feeding scene and the scolding scene represent human interactions of a ‘psychological’ nature, unlike the whipping scene in which the interaction is clearly physical. In the light of evidence which suggests that schizophrenics tend to make little use of psychological constructs when describing people in photographs, but do not differ from normals in their use of physical constructs (Dixon, 1967),it seems possible that interactions of a ‘psychological’ nature are more threatening to schizophrenics than ones of a ‘physical’ nature. To test this possibility, it was decided - bearing in mind evidence (e.g. Dixon, 1958) that the effects of ‘emotional ’ stimulus items upon recognition threshold vary from individual to individual - to examine the consistency shown in threshold responses to the two ‘psychologically’ threatening pictures. This investigation revealed that if the threshold (i.e. spot brightness)recorded during the subliminal presentation of the scolding scene was higher than that recorded during presentation of the neutral stimulus, then so also was the threshold recorded during presentation of the feeding scene. In the same way, if a low threshold was recorded for the scolding scene relative to that recorded for the neutral scene, then a low threshold also tended to be found for the feeding scene. Of the 13 subjects who took part in this study, 11 showed threshold consistency across these two stimuli. This tendency, which is significant by a sign test (P = 0.022, two-tail),

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supports the view that these subjects were responding to the emotional connotations of the stimuli which were the same for both the scolding and feeding scenes.

Effects of subject variables (i) Drugs. That the trends found in the present results were not attributable to the effects of chlorpromazine is suggested by the fact that a negative correlation obtained between the extent of perceptual defence shown for each of the ‘social’ stimuli and daily drug dosage, i.e. subjects on low doses of chlorpromazine obtained higher ‘difference scores ’ (mean spot brightness subliminal stimulation with ‘ social ’ stimulus minus mean spot brightness during subliminal stimulation with neutral stimulus) than subjects on higher doses of chlorpromazine. The extent of this correlation was very small in the case of the whipping scene (rs = -0-15), but considerably larger in the case of the feeding scene (rs = -0.41) and the scolding scene (rs = -0.62). The latter correlation was significant ( f =2.6, d.f. = 11, P

Preconscious processing in schizophrenics: an exploratory investigation.

Br. J. med. Psychol. (1976). 49, 161-166 Printed in Great Britain 161 Preconscious processing in schizophrenics: an exploratory investigation B Y S...
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