Original Paper
Psychopathology 1992:25:100-108
Monique de Bonis Catherine Epelbaum André Féline Service Hospitalo-Universitaire de Psychiatrie, Hôpital de Bicêtre. Université Paris Xl-CNRS. Paris. France
Cognitive Processing of Contradictory Statements: An Experimental Study of Reasoning on Proverbs in Schizophrenia
Abstract
The vast majority of studies on formal logic in schizophrenia over the past 50 years, following von Domarus’ well-known hypothe sis [1] and Arieti's revision [2], were focussed on one feature of deductive reasoning: the principle of identity and one of its underlying process, the inclusion relationship [3], Be cause the syllogism, in Aristotelian logic, was considered to be the prototype of deduction, most experiments have relied on this type of paradigm. Despite the use of ingenious tasks where the syllogism is either in the target
stimulus or in the response, comparison of schizophrenics and controls matched for ver bal IQ yields inconclusive evidence [4-6], This finding led Williams [4] to conclude that 'deductive reasoning plays a small part in the thinking of schizophrenia. Even normal sub jects do not seem to rely upon it excessively’. Similar difficulties in detecting illogical modes of reasoning have emerged in more natural settings, based on spontaneous verbal material, collected during clinical interviews. When logicians are asked to evaluate a schizo-
M. de Bonis. MO CNRS UFR Krcm lin-Bicctrc Université Paris XI 63, rue Gabriel-Péri F-94276 Le Kremlin-Bicêtre (France)
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Twenty schizophrenic patients and 20 normal subjects matched for age. sex and verbal level were asked to identify, from a list of alternatives, the statement that was the most contradictory to each of 8 proverbs. Schizophrenics (whether severely disturbed or not) were found to be less accurate in detecting the contradictions [F( 1.18) = 29.21 : p < 0.0001]. No significant differences between undifferentiated and disorgan ized DSM-III subtypes were observed. The greatest tolerance of contradictory statements was interpreted in terms of viola tion of the ‘no contradiction principle’ and examined in the light of a deficit in logical abilities.
versus neutral content, the tolerance to con tradiction is not explicitly scrutinized. Thus, the present study is aimed at analyz ing how schizophrenic patients use the logical rules related to the ‘no contradiction'. As we are specifically interested in real life and clini cal situations, we decided to consider their use in language, with all the complications they entail, using verbal stimuli (proverbs) instead of other symbolic material such as geometrical figures or mathematical tests as, for example, in a study by Blein et al. [ 13]. The few previous studies devoted to the analysis of how contradictions are processed by schizophrenics have been restricted to one aspect of contradiction: the grammatical transformation of affirmative into negative sentences. For instance, Irigaray [14] asked schizophrenic patients to generate the con trary of sentences such as i hate apples’, and she found that the patients tended to reply ‘I hate pears' instead of ‘I do not hate apples'. In a more sophisticated study, Consoli [15] gave young schizophrenic subjects specific target sentences and asked them to choose the most contradictory of five possible alter natives. For example, one target sentence was ‘I feel hungry’, ‘I do not feel hungry’, and the available responses included: ‘I feel that I am not hungry any more’, ‘I feel full’. These stud ies report a tendency for schizophrenic pa tients to have difficulties in transforming an affirmative clause or its subordinate into a negative sentence. These findings are consid ered by these authors in terms of language deficit and interpreted by both of them within the frame of reference of psychoana lytic theories. It is suggested that the processing of con tradictory statements is not only a question of grammar, but that it is related to cognitive skills which, among other functions, require the filtering of information, categorization of semantic knowledge, exclusion of irrelevant
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phrenic discourse as rational or irrational [7] most consider reasoning to be intrusive or idiosyncratic but not really illogical in itself [ 8 ], These discrepancies have led some re searchers to argue that von Domarus’ princi ple should be discarded. The fact that ‘most logicians consider the syllogism to be no more than a historical curiosity’ [9] has contributed to the decline in interest in this area of research. For several reasons, this conclusion may be premature. Firstly, before jettisoning the study of deductive reasoning in schizo phrenia, it is worth inquiring whether all three laws of formal logic: identity, no contradic tion and excluded middle, have received sa tisfactory attention. Secondly, despite the in conclusive experimental data, clinical evi dence brought up by ratings still emphasizes logical bias as critical symptoms in subtyping schizophrenic patients. Andreasen [10], for example, indicates that high ratings on items such as illogicality, incoherence or derailment are the necessary prerequisite symptoms to differentiate negative versus positive schizo phrenia. As far as we know, schizophrenics sometimes produce apparently contradictory statements (surface contradictions) in sponta neous utterances and discourse [see Bonis et al.. Il, 12, for an experimental analysis on a single case design]. If this is the case, it will be interesting to know if they also understand or process contradictory statements in a differ ent way as compared to normal subjects. Therefore, the discrepancy between clinical and experimental evidence warrants further research on logical reasoning in schizophre nia. As regards the experimental data, it seem that the 'no contradiction principle' has not received enough attention. Even in William's [4] sophisticated design, in which several cog nitive factors were carefully controlled for ab stract versus concrete meaning and personal
Table 1. Epidemiological data on the schizophrenic group
meanings and formation of disjunctive classes of elements. The question addressed in the present study evolves from a larger definition of con tradiction and relies on the study of logical abilities and reasoning on proverbs. Proverbs, being common-place expressions, are nicely suited for a study of natural logic, i.e. every day way of thinking [ 16, 17],
Onset o f illness (age)
< 15 years 16-19 years 20-29 years
4 8 8
Ispisode duration < 1 month
6 8 6
2-6 months > 7 months Course o f illness
Method
Slow Acute episodes Acute episodes with pathological states
Rationale fo r Materia! and Method
The task consists in detecting the sentence which best contradicts the stimulus statement. All the target sentences are proverbs which have been used fre quently in verbal problem-solving tasks in the study of schizophrenic thinking [18. 19]. The basic format for each item was a target proverb and five multiplechoice alternative sentences. Such a format has been frequently used, the main originality of the present task consists in the construction of the alternative choices.
None One Many
2 5 13
Marital status
Single Married
17 3
Psychiatric illness in fam ily
Absent Present
13
Negative wording in the targets and in the re sponses was counterbalanced across the items. Correct contradictory statements could be either affirmative or negative. Example
Target: 'Strike while the iron is hot.' Alternatives: T h e heat strikes th e m etal (nonsense).
Heat dilates iron (correct but unrelated). It is often useful to let opportunity go by (moderate contradiction). You need to be brave to pick up a hot iron (correct but unrelated). Do not take opportunities as soon as they arise (high contradiction). (See Appendix for translation of the whole list of proverbs which are, of course, only rough approxima tions. especially in cases where an equivalent was not found in source books.)
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11
Previous psychiatric admissions
Construction o f the Multiple-Choice Alternatives
The response alternatives were constructed as fol lows. Two contradictory sentences, one of them was highly contradictory and the other was moderately contradictory and employed modal wordings (e.g. 'it is often’, 'most people’, 'some people’). These two de grees were introduced in order to evaluate the sensitiv ity to contradiction. Two semantically and syntactically correct sen tences which were unrelated to the abstract semantic meaning of the target, but which referred to the same words or pieces of meaning. They were introduced in order to know if the subjects understand or not the rules of contradiction. One nonsense sentence which contained some of the words of the target sentence, but ordered in such a way that the meaning of the sentence neither contra dicted nor resembled the target. The nonsensical char acter of this alternative made it possible to measure a low level of comprehension and to assess incoherence. A previous study in our laboratory using a nonsense task detection (same format as in the present task) with schizophrenics and normals had shown that schizo phrenics do not perform significantly worse on such a task [20],
7 2
Pretesting the Item Pool
A pool of 40 items was tested on a sample of 66 normal subjects. Eight items were retained out of the 40 tested. They were at least answered correctly (given the proper contradictory sentence) by 50% of the total sample. In this preliminary study, the subjects were also given a verbal IQ test (Binois-Pichot’s vocabulary test [21 ]) and a task detection of nonsense sentences. The correlation (Pearson product-moment coeffi cient) between the final 8-itcm version used in the present study and the raw score on vocabulary was moderately high (r = 0.29; p < 0.05), indicating that competence on word comprehension accounted for less than 9% of the total variance of the performance. In addition, the performance on the nonsense detec tion task was neither significantly related to the contra diction (r = 0.23) nor to the vocabulary scores (r = 0.14). Scoring
On the basis of pretesting results, subjects were scored 2 points if they detected the highly contradic tory sentence, 1 point for the moderately contradictory sentence and 0 point for the other alternatives. The ‘no response’, that is, no contradiction at all, was also attributed a 0 score. This numerical scoring allows a statistical parametric variance analysis to be done. In addition, each kind of response being recorded, a qual itative analysis of errors was also made possible.
Table 2. BPRS ratings (means and standard devia
tions) Item
Ratings
Somatic concern Anxiety Emotional withdrawal Conceptual disorganisation Guilt Tension Mannerism Grandiosity Depressive mood Hostility Suspiciousness Hallucinations Motor retardation Uncooperativeness Unusual thoughts Blunted affect Excitement Disorientation Elevated mood Manipulativeness Inappropriate affect Dramatization Emotional lability
3.30 ±2.18 4.75± 1.52 4.30 ±1.84 3.60 ± 1.90 1.50 ± 0.69 3.90± 1.94 2.95 ± 1.64 1.80± 1.32 3.40± 1.82 2.35+1.60 3.60± 1.82 2.95 ±1.99 3.10 ± 1.62 2.10 ± 1.68 4.80± 1.88 4.45± 1.47 2.40 ±1.76 1.30 ± 0.80 1.50 ± 0.89 2.20± 1.61 3.35 ± 1.87 1.70 ± 1.53 2.45 ± 1.61
Twenty schizophrenic inpatients (10 males and 10 females) fulfilling DSM-III criteria for schizophrenia were matched with 20 normal controls for age, sex and educational level. A strict matching between normals and schizophrenics on the vocabulary test score (each schizophrenic having its own control) made a pairedsample variance analysis possible. Mean raw scores on the verbal test were 27.2 (SD 7.28) and 19.9 (SD 9.0) for male and female schizophrenics, and 28.4 (SD 6.2) and 24.5 (SD 5.4) for male and female normal subjects, respectively. The differences are not statistically signif icant. Age means were 29.75 (SD 6.88) for patients and 23.85 (SD 6.9) for normals. The educational level was similar among both groups. Ten patients and 10 nor mals had completed the general Certificate of Educa tion (French ‘Baccalauréat’), which corresponds to 12year studies at school, and 9 patients and 11 normals had attended school only during 9 years. Epidemiolog ical data, based on an abridged French version of the Brief Psychiatric History of Previous Illness Form (BPHF), by Pichot and Overall [22], are presented in table I. Eight schizophrenic patients (2 females and 6
males) were subtyped ‘disorganized’ and 8 ‘undifferen tiated’ according to the DSM-III criteria, the remain ing were paranoid. In order to measure the symptomatic profile at the time of testing, each patient was assessed by a psychia trist on the Brief Psychiatric Rating Scale (BPRS). by Pichot. Overall and Gorham [22], The 23-item version used in this study has been described at length by Bonis et al. [23], The BPRS mean scores are given in table 2. A brief examination of this table shows that the most characteristic symptoms of schizophrenic disor ders are present in our sample. Testing took place in the second or third week after admission. All the patients were under neuroleptic medication, some of them also received other psycho tropic drugs (such as anxiolytics or antidepressive drugs). For all subjects, the contradiction detection task followed the vocabulary test. Each testing session lasted 30-45 min.
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Subjects
Detection o f Contradictions: Comparison o f Normals versus Schizophrenics Mean scores for correct answers (either high or moderate contradictions) on each of the 8 items are presented in table 3. The per formance of the schizophrenic patients was poorer than that of normal controls. An ANOVA was performed with groups (schizo phrenics vs. normals, males vs. females) as bctween-subject factors; items, as a withinsubject factor. This analysis indicated a highly significant difference between patients and normals [F(l,18) = 29.21; p < 0.0001]. No other main effects nor main interactions were observed.
Table 3. Correct responses (means and standard
deviations) Item
Schizophrenics (n =20)
Normals (n - 20)
1 2 3 4 5 6 7 8
1.15 ±0.93 1.00 ±0.91 0.70±0.86 1.00 ±0.85 0.95 ±0.88 0.75 ±0.96 0.65 ±0.87 0.85 ±0.81
1.80 ±0.61 1.75 ±0.63 1.40 ±0.82 1.50 ±0.82 1.40 ± 0.88 1.05 ±0.99 0.95 ±0.76 0.95 ±0.60
Table 4. Error patterns
Errors
Correct sentence but unrelated Nonsense sentence No contradiction at all
Schizophrenics Normals (n = 20) (n - 20)
32 28 11
Figures are percentages on 8 items.
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14 16 6
Qualitative A nalysis o f Erroneous Response Choices It must be recalled that the three alterna tive erroneous responses are constructed in the same way for all items: two sentences that are semantically meaningful but unrelated (contradictory) to the target and one nonsense sentence. Under the hypothesis of incoher ence thinking in schizophrenia, one would expect a higher proportion of nonsense sen tence choices. Percentages of each kind of errors are given in table 4. Inspection of this table shows that patients gave twice as many nonsense choices than normals. However, this comparison is misleading. It is worth reminding that the multiple-choice format of the task makes the comparison of erroneous responses between normals and patients diffi cult. As the number of correct responses is not the same for both groups, the distributions of errors are not equivalent. On the other hand, multiple statistical tests, one for each kind of error, could also introduce other bias. Thus, an overall y} = 0.38 (d.f. = 4) was done. This is not statistically significant. Schizophrenics and normals did not show any preference for one type of alternative or the other. Additional Results: Response Patterns for Schizophrenic Subgroups Subgroups as a Function o f the Severity o f the Clinical Symptomatology as Assessed through the BPRS. According to Andersen et al. [24], some BPRS items "have an additive relationship implying that their sum is a suffi cient statistic for the measurement of the severity of the schizophrenic states’. A sever ity score was computed on the basis of the sum of the following ten critical items selected by these authors: emotional withdrawal, con ceptual disorganization, retardation, gran diosity, hostility, suspiciousness, hallucina tions, uncooperativeness, unusual thought content, blunted or inappropriated affect.
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Results
Discussion and Conclusion
A difficulty inherent in the comparison of schizophrenic patients and normal controls is that there arc a number of factors intermin gled with the psychiatric disorder itself. In the
present study, although the patients have been matched for the most critical factors that can influence the performances, all the schizo phrenics were on drugs, and it cannot be dis carded that the effect of medication had played some role on the deficit observed. In addition, as pointed out by Chapman and Chapman [26], the matching itself on the ver bal test, when not controlled for the difficulty of the tasks (which was the case in our study), can also introduce some bias and inflate the statistical differences on the subsequent task. Nevertheless, schizophrenic patients and nor mal controls appeared to differ markedly in their level of tolerance to contradiction. It does not seem that these differences are due to a lack of comprehension of the meaning of the target proverbs or to that of the choice sen tences. If it were the case, the two groups would have presented different patterns of errors, which is not the case. This bias of pro cessing contradictory statements seems to be common to different levels of severity as well as to different subtypes. However, this latter finding needs to be confirmed with larger samples of subjects. The DSM-III disorgan ized subtype, in which the incoherence of thought is considered to be higher than in the other types, did not perform worse on contra dictions. This quite unexpected result needs further consideration, and performances of paranoids need to be explored. On the other hand, one can argue that patients were exam ined after their acute phase, but the BPRS profiles clearly show that most of them arc still severely disturbed. Further investigations on the interpretations or explanations that schizophrenic patients would give, in order to justify why they do not consider most state ments less contradictory, as normal controls do, would bring some light on the underlying cognitive processes at work. They are re quired in order to attribute generality and specificity to the deficit observed.
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The total-score distribution pattern on these ten items made it possible to dichoto mize the 20 subject samples on the basis of a cutoff point (sum = 37). into two extreme groups: an extremely severe group (n = 7; 5 males. 2 females) and a less severe group (n = 6; 4 males. 2 females). These two groups do not differ markedly on age. educational level and verbal scores. The results show no significant differences, both arc unable to detect contradictory state ments with sufficient accuracy [F( 1.11) = 1.25]. Subgroups as a Function o f Negative Symp tomatology as Assessed through the BPRS and DSM-III Schizophrenic Subtypes. Previous findings have shown that the BPRS could be a useful instrument to detect negative symp tomatology [21, 25], Blunted affect, emo tional withdrawal and retardation are thought to be good indicators of a negative symptom atology. Accordingly, patients with high total scores on these three critical items, n = 8 (4 males and 4 females), were compared with the remaining patients (n = 12). Negative symptomatology did not differentiate these ‘negative’ patients from the others in terms of ability to detect contradictory sentences [F( 1,18)= 1.72]. In addition, the comparison between the disorganized DSM-III. n = 8 (2 females and 6 males), and the undifferentiated subtypes, n = 8 (3 males and 7 females), led to the same neg ative results. The mean scores of correct re sponses were exactly the same (M = 0.84) for both groups.
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the clinical symptom of ambivalence. If two meanings are not opposites for them, it fol lows that the choice between them is made more difficult. However, one can also remind that too tight structures can sometimes gener ate a lack of flexibility in thinking. Another complementary interpretation is that the tol erance of contradictory statement can be seen as a case of overinclusion and a typical exam ple of loose construing [28], which has been shown within the frame of reference of per sonal construct theories. It is likely that the conclusions drawn from this field of research can also be true for the cognitive processing of contradictions in natural language.
Acknowledgments The present study was supported by a grant of the Institut National de la Recherche Médicale (IN SERM). Thanks to Connie Grvnbaum for helpful comment on the translation and to Maria Somogvi for statistical data processing. Data were collected from patients of Hôpital de Bicêtre, Serv ice du professeur André Fé line.
Appendix List o f the 8 hem s
1 Strike while the iron is hot. NS Heat strikes metal. CU Heat dilates iron (or: makes iron expand). MC It is often useful to let an opportunity go by. CU You have to be brave to pick up a hot iron. HC You must not take opportunities as soon as they arise. 2 Union is strength. CU Strength is foremost over right. MC Division sometimes leads to success. HC You can be strong by staying alone. CU Harmony of the spirits makes union. NS Cooperation creates division.
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Nevertheless, concerning the cognitive processing of the sentences, it is likely that the poor detection of contradictions cannot be solely accounted fora lack of ability to process negations (most of the items did not involve a negative wording), however patients failed on these items, nor to an inability to understand the transformation of affirmative sentences into negative ones. With this respect, our results are open to alternative explanations to that given bv both Irigaray [14] and Consoli [15]. Though additional data are still required, two interpretations can be suggested. On the one hand, the inability to detect the contra diction can be explained by a softer belief in the meaning of the target proverb. As White [27] pointed out. ‘proverbs are generally re garded as depository of folk wisdom, as sty lized saying that presume to represent com mon sensical everyday life’. It is likely that schizophrenics do not share the same belief as normals in the symbolic meaning of proverbs. As a consequence, they are unable to find the proper contradictory meaning among the al ternative responses. Such an interpretation underlines the importance of semantic as pects in studying contradictions. It empha sizes the fact that schizophrenics do not share the same interpretations, and this fact is con gruent with the hypothesis of idiosyncratic thinking suggested by Marengo et al. [8], On the other hand, the inability to detect contradictions can be interpreted in terms of the architecture of knowledge structure. Schizophrenics seem to organize their knowl edge in a way less tightly contrasted in com parison with controls. The fact that opposite meanings are not perceived to be as exclusive as they are for normal subjects shows that they do not delineate the same boundaries between what is and what is not culturally val id. and between what is and what is not true. This cognitive interpretation nicely fits with
3 Little strokes fell great oaks. NS The waterfall only flows once. CU One drop can make the barrel overflow. MC A bird can build its nest in a day. CU Water seeps into everything. HC Building must be done all at once. 5 To accomplish great things, live as though you were immortal, (transliteration) NS To accomplish great things, you must destroy them. MC Great men must live by thinking at times about their deaths. HC To accomplish great things, you must live by thinking about the coming of death. CU Accomplishing great things calls for superhu man efforts. CU Great things outlive their makers. 7 Most men spend the first part of their lives making the second part miserable. NS Everyone treats the start of their lives as they would an object. CU People make many plans when they are young but only accomplish a few. HC Most people use their childhood to provide for prosperity in their old age. MC Some people provide for prosperity in their old age at the start of their lives. CU Uncertain fate makes men unconcerned about their futures.
8 We are all strong enough to bear the sufferings of others, (transliteration) HC We cannot bear the sufferings of others. MC Our friends' problems sometimes touch us more than our own problems. NS We only suffer through the suffering of oth ers. CU Strength of character enables people to bear their sufferings. CU We are always strong enough to bear our own problems. 9 Great worth in a shy man may long go unnoticed. (transliteration) CU The wise man is indifferent to praise from the crowd. MC Being worthy of merit and remaining silent can help make someone famous. CU You must do your duty without paying atten tion to what other people think. NS Lack of modesty is a sign of intelligence. HC Wisdom cannot be hidden even when the wise man is shy. 10 Virtue is praised by all but practiced by few. NS What is rare always occurs often. MC Good deeds always move us whereas we are not very' sensitive to rare events. CU We quickly get used to things that we see often. HC We are rarely struck by uncommon things and yet we are struck by virtue. CU Is virtue as rare as is commonly believed? NS = Nonsense; CU = correct but unrelated; MC = moderate contradiction; HC = high contradiction.
References 5 Gottesman L. Chapman L: Syllogis tic reasoning errors in schizophre nia. J Consult Clin Psychol 1960:24: 250-255. 6 Epclbaum C: Troubles du raisonne ment el schizophrénie: Une revue critique. Psychiatr Psychobiol 1990: 5:241-248. 7 Harrow M. Prosen M: Intermingling and disordered logical influence on schizophrenic ‘thought disorders'. Arch Gen Psychiatr 1978:35:1213— 1219.
8 Marengo JT. Harrow M. Lanin-Keltering I. Wilson A: Evaluating bi zarre idiosyncratic thinking: A comprehension index of positive thought disorder. Schizophr Bull 1986:12:489-511. 9 Rips U : Reasoning. Anna Rev Psy chol 1990:41:321-353. 10 Andreasen NC: Negative vs positive schizophrenia: Definition and vali dation. Arch Gen Psychiatry 1982; 39:789-794.
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1 von Domarus E ( 1944): The specific laws of logic in schizophrenia; in Kazanin K.S (ed): Language and thought in Schizophrenia. Berkeley. University of California Press. 1964. pp i 0 4 - 114. 2 Arieli S: Interpretation of schizo phrenia. New York. Brunner. 1955. 3 Chapman LJ. Chapman JP: Disor dered Thought in Schizophrenia. New York. Appleton. 1973. 4 Williams EB: Deductive reasoning in schizophrenia. .1 Abnorm Soc Psychol 1964;69:47-61.
16 Grize J B: Logique et Langage. Paris. Ophrys. 1990. 17 Grize JB. Pierrault de Bonniec G: La contradiction: Essai sur les Opér ations de la Pensée. Paris, Presses Universitaires de France. 1974. 18 Gorham DR: Use of the proverbs test for differentiating schizophren ics from normals. J Consult Psychia try 1956:20:435-440. 19 Gorham DR: Additional norms and scoring suggestions for the proverb test: Psychol Rep 1963:13:487-492. 20 Epelbaum C: Troubles cognitifs et schizophrénie: Raisonnement, tolé rance à la contradiction et à l’inco hérence. UnpubI manuscript. 1989. 21 Test de Vocabulaire de Binois-Pichot. Paris. Centre de Psychologie Appliquée. 1958. 22 Brief Psychiatrie Rating Scale (BPRS) I-rench version and BPHE. Paris, Centre de Psychologie Appli quée. 1971. 23 de Bonis M. de Boeck P. Lebeaux MO: Problèmes méthodologiques posés par la classification des formes de schizophrénie. Recherche de cor rélation ou de relations d'apparte nance. Psychiatr Psychobiol 1987:2: 174-187.’
24 Andersen J, Larsen JK, Schultz V. et al: The Brief Psychiatric Rating Seale, dimension of schizophrenia. Reliability and construct validity. Psychopathology 1989:22:162-176. 25 Thiemans S. Csernansky J. Berger BA: Rating scale in research: The case of negative symptoms. Psychia try Res 1987;20:47-55. 26 Chapman LJ. Chapman JP: The measurement of differential deficit. J Psychiatr Res 1978:14:303-311. 27 White GM: Proverbs and cultural models: in Holland D. Quinn N (eds): Cultural models in language and thought. Cambridge. Cam bridge University Press. 1985. 28 Van den Berg O. Boeck P. Claeys W: Schizophrenia: What is loose in schizophrenic construing; in Button E (ed): Personal Construct Theory and Mental Health Beckenham. Croom Helm. 1985. pp 59-81.
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11 de Bonis M, Epelbaum C, Féline A. Grize JB, Hardy P, Somogyi M: Pensée formelle, opérations logicodiscursivcs et schizophrénie: Etude expérimentale d’un cas clinique. Rev Can Psychialr 1990:35:64-70. 12 de Bonis M. Grize JB. de Boeck P: Modèles psychopathologiqucs de raisonnements irrationnels dans la schizophrénie. ConflNSERM - Les empêcheurs de penser en rond. La boratoires Delagrange. Roneotyped 1990. vol 4 .30 p. 13 Blein G, Azorin JM. Dufour H, Tis sot R: Quelques aspects des activités cognitives du schizophrène. IV. Dé séquilibre des affirmations et des né gations. Ann Méd-Psychol 1990: 149:841-856. 14 Irigaray L: Négation et transforma tion négative dans le langage des schizophrènes. Langage I967:5(special issue). 15 Consoli S: Utilisation et fonction de la négation chez le jeune schizophrè ne. Neuropsychiatr Enfant 1981:29: 223-229.
Psychopathology 1992:25:100-108
Monique de Bonis Catherine Epelbaum André Féline Service Hospitalo-Universitaire de Psychiatrie, Hôpital de Bicêtre. Université Paris Xl-CNRS. Paris. France
Cognitive Processing of Contradictory Statements: An Experimental Study of Reasoning on Proverbs in Schizophrenia
Abstract
The vast majority of studies on formal logic in schizophrenia over the past 50 years, following von Domarus’ well-known hypothe sis [1] and Arieti's revision [2], were focussed on one feature of deductive reasoning: the principle of identity and one of its underlying process, the inclusion relationship [3], Be cause the syllogism, in Aristotelian logic, was considered to be the prototype of deduction, most experiments have relied on this type of paradigm. Despite the use of ingenious tasks where the syllogism is either in the target
stimulus or in the response, comparison of schizophrenics and controls matched for ver bal IQ yields inconclusive evidence [4-6], This finding led Williams [4] to conclude that 'deductive reasoning plays a small part in the thinking of schizophrenia. Even normal sub jects do not seem to rely upon it excessively’. Similar difficulties in detecting illogical modes of reasoning have emerged in more natural settings, based on spontaneous verbal material, collected during clinical interviews. When logicians are asked to evaluate a schizo-
M. de Bonis. MO CNRS UFR Krcm lin-Bicctrc Université Paris XI 63, rue Gabriel-Péri F-94276 Le Kremlin-Bicêtre (France)
© 1992 S. Karger AG. Basel 0254-4962/92/ 0252-0100$2.75/0
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Twenty schizophrenic patients and 20 normal subjects matched for age. sex and verbal level were asked to identify, from a list of alternatives, the statement that was the most contradictory to each of 8 proverbs. Schizophrenics (whether severely disturbed or not) were found to be less accurate in detecting the contradictions [F( 1.18) = 29.21 : p < 0.0001]. No significant differences between undifferentiated and disorgan ized DSM-III subtypes were observed. The greatest tolerance of contradictory statements was interpreted in terms of viola tion of the ‘no contradiction principle’ and examined in the light of a deficit in logical abilities.
versus neutral content, the tolerance to con tradiction is not explicitly scrutinized. Thus, the present study is aimed at analyz ing how schizophrenic patients use the logical rules related to the ‘no contradiction'. As we are specifically interested in real life and clini cal situations, we decided to consider their use in language, with all the complications they entail, using verbal stimuli (proverbs) instead of other symbolic material such as geometrical figures or mathematical tests as, for example, in a study by Blein et al. [ 13]. The few previous studies devoted to the analysis of how contradictions are processed by schizophrenics have been restricted to one aspect of contradiction: the grammatical transformation of affirmative into negative sentences. For instance, Irigaray [14] asked schizophrenic patients to generate the con trary of sentences such as i hate apples’, and she found that the patients tended to reply ‘I hate pears' instead of ‘I do not hate apples'. In a more sophisticated study, Consoli [15] gave young schizophrenic subjects specific target sentences and asked them to choose the most contradictory of five possible alter natives. For example, one target sentence was ‘I feel hungry’, ‘I do not feel hungry’, and the available responses included: ‘I feel that I am not hungry any more’, ‘I feel full’. These stud ies report a tendency for schizophrenic pa tients to have difficulties in transforming an affirmative clause or its subordinate into a negative sentence. These findings are consid ered by these authors in terms of language deficit and interpreted by both of them within the frame of reference of psychoana lytic theories. It is suggested that the processing of con tradictory statements is not only a question of grammar, but that it is related to cognitive skills which, among other functions, require the filtering of information, categorization of semantic knowledge, exclusion of irrelevant
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phrenic discourse as rational or irrational [7] most consider reasoning to be intrusive or idiosyncratic but not really illogical in itself [ 8 ], These discrepancies have led some re searchers to argue that von Domarus’ princi ple should be discarded. The fact that ‘most logicians consider the syllogism to be no more than a historical curiosity’ [9] has contributed to the decline in interest in this area of research. For several reasons, this conclusion may be premature. Firstly, before jettisoning the study of deductive reasoning in schizo phrenia, it is worth inquiring whether all three laws of formal logic: identity, no contradic tion and excluded middle, have received sa tisfactory attention. Secondly, despite the in conclusive experimental data, clinical evi dence brought up by ratings still emphasizes logical bias as critical symptoms in subtyping schizophrenic patients. Andreasen [10], for example, indicates that high ratings on items such as illogicality, incoherence or derailment are the necessary prerequisite symptoms to differentiate negative versus positive schizo phrenia. As far as we know, schizophrenics sometimes produce apparently contradictory statements (surface contradictions) in sponta neous utterances and discourse [see Bonis et al.. Il, 12, for an experimental analysis on a single case design]. If this is the case, it will be interesting to know if they also understand or process contradictory statements in a differ ent way as compared to normal subjects. Therefore, the discrepancy between clinical and experimental evidence warrants further research on logical reasoning in schizophre nia. As regards the experimental data, it seem that the 'no contradiction principle' has not received enough attention. Even in William's [4] sophisticated design, in which several cog nitive factors were carefully controlled for ab stract versus concrete meaning and personal
Table 1. Epidemiological data on the schizophrenic group
meanings and formation of disjunctive classes of elements. The question addressed in the present study evolves from a larger definition of con tradiction and relies on the study of logical abilities and reasoning on proverbs. Proverbs, being common-place expressions, are nicely suited for a study of natural logic, i.e. every day way of thinking [ 16, 17],
Onset o f illness (age)
< 15 years 16-19 years 20-29 years
4 8 8
Ispisode duration < 1 month
6 8 6
2-6 months > 7 months Course o f illness
Method
Slow Acute episodes Acute episodes with pathological states
Rationale fo r Materia! and Method
The task consists in detecting the sentence which best contradicts the stimulus statement. All the target sentences are proverbs which have been used fre quently in verbal problem-solving tasks in the study of schizophrenic thinking [18. 19]. The basic format for each item was a target proverb and five multiplechoice alternative sentences. Such a format has been frequently used, the main originality of the present task consists in the construction of the alternative choices.
None One Many
2 5 13
Marital status
Single Married
17 3
Psychiatric illness in fam ily
Absent Present
13
Negative wording in the targets and in the re sponses was counterbalanced across the items. Correct contradictory statements could be either affirmative or negative. Example
Target: 'Strike while the iron is hot.' Alternatives: T h e heat strikes th e m etal (nonsense).
Heat dilates iron (correct but unrelated). It is often useful to let opportunity go by (moderate contradiction). You need to be brave to pick up a hot iron (correct but unrelated). Do not take opportunities as soon as they arise (high contradiction). (See Appendix for translation of the whole list of proverbs which are, of course, only rough approxima tions. especially in cases where an equivalent was not found in source books.)
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11
Previous psychiatric admissions
Construction o f the Multiple-Choice Alternatives
The response alternatives were constructed as fol lows. Two contradictory sentences, one of them was highly contradictory and the other was moderately contradictory and employed modal wordings (e.g. 'it is often’, 'most people’, 'some people’). These two de grees were introduced in order to evaluate the sensitiv ity to contradiction. Two semantically and syntactically correct sen tences which were unrelated to the abstract semantic meaning of the target, but which referred to the same words or pieces of meaning. They were introduced in order to know if the subjects understand or not the rules of contradiction. One nonsense sentence which contained some of the words of the target sentence, but ordered in such a way that the meaning of the sentence neither contra dicted nor resembled the target. The nonsensical char acter of this alternative made it possible to measure a low level of comprehension and to assess incoherence. A previous study in our laboratory using a nonsense task detection (same format as in the present task) with schizophrenics and normals had shown that schizo phrenics do not perform significantly worse on such a task [20],
7 2
Pretesting the Item Pool
A pool of 40 items was tested on a sample of 66 normal subjects. Eight items were retained out of the 40 tested. They were at least answered correctly (given the proper contradictory sentence) by 50% of the total sample. In this preliminary study, the subjects were also given a verbal IQ test (Binois-Pichot’s vocabulary test [21 ]) and a task detection of nonsense sentences. The correlation (Pearson product-moment coeffi cient) between the final 8-itcm version used in the present study and the raw score on vocabulary was moderately high (r = 0.29; p < 0.05), indicating that competence on word comprehension accounted for less than 9% of the total variance of the performance. In addition, the performance on the nonsense detec tion task was neither significantly related to the contra diction (r = 0.23) nor to the vocabulary scores (r = 0.14). Scoring
On the basis of pretesting results, subjects were scored 2 points if they detected the highly contradic tory sentence, 1 point for the moderately contradictory sentence and 0 point for the other alternatives. The ‘no response’, that is, no contradiction at all, was also attributed a 0 score. This numerical scoring allows a statistical parametric variance analysis to be done. In addition, each kind of response being recorded, a qual itative analysis of errors was also made possible.
Table 2. BPRS ratings (means and standard devia
tions) Item
Ratings
Somatic concern Anxiety Emotional withdrawal Conceptual disorganisation Guilt Tension Mannerism Grandiosity Depressive mood Hostility Suspiciousness Hallucinations Motor retardation Uncooperativeness Unusual thoughts Blunted affect Excitement Disorientation Elevated mood Manipulativeness Inappropriate affect Dramatization Emotional lability
3.30 ±2.18 4.75± 1.52 4.30 ±1.84 3.60 ± 1.90 1.50 ± 0.69 3.90± 1.94 2.95 ± 1.64 1.80± 1.32 3.40± 1.82 2.35+1.60 3.60± 1.82 2.95 ±1.99 3.10 ± 1.62 2.10 ± 1.68 4.80± 1.88 4.45± 1.47 2.40 ±1.76 1.30 ± 0.80 1.50 ± 0.89 2.20± 1.61 3.35 ± 1.87 1.70 ± 1.53 2.45 ± 1.61
Twenty schizophrenic inpatients (10 males and 10 females) fulfilling DSM-III criteria for schizophrenia were matched with 20 normal controls for age, sex and educational level. A strict matching between normals and schizophrenics on the vocabulary test score (each schizophrenic having its own control) made a pairedsample variance analysis possible. Mean raw scores on the verbal test were 27.2 (SD 7.28) and 19.9 (SD 9.0) for male and female schizophrenics, and 28.4 (SD 6.2) and 24.5 (SD 5.4) for male and female normal subjects, respectively. The differences are not statistically signif icant. Age means were 29.75 (SD 6.88) for patients and 23.85 (SD 6.9) for normals. The educational level was similar among both groups. Ten patients and 10 nor mals had completed the general Certificate of Educa tion (French ‘Baccalauréat’), which corresponds to 12year studies at school, and 9 patients and 11 normals had attended school only during 9 years. Epidemiolog ical data, based on an abridged French version of the Brief Psychiatric History of Previous Illness Form (BPHF), by Pichot and Overall [22], are presented in table I. Eight schizophrenic patients (2 females and 6
males) were subtyped ‘disorganized’ and 8 ‘undifferen tiated’ according to the DSM-III criteria, the remain ing were paranoid. In order to measure the symptomatic profile at the time of testing, each patient was assessed by a psychia trist on the Brief Psychiatric Rating Scale (BPRS). by Pichot. Overall and Gorham [22], The 23-item version used in this study has been described at length by Bonis et al. [23], The BPRS mean scores are given in table 2. A brief examination of this table shows that the most characteristic symptoms of schizophrenic disor ders are present in our sample. Testing took place in the second or third week after admission. All the patients were under neuroleptic medication, some of them also received other psycho tropic drugs (such as anxiolytics or antidepressive drugs). For all subjects, the contradiction detection task followed the vocabulary test. Each testing session lasted 30-45 min.
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Subjects
Detection o f Contradictions: Comparison o f Normals versus Schizophrenics Mean scores for correct answers (either high or moderate contradictions) on each of the 8 items are presented in table 3. The per formance of the schizophrenic patients was poorer than that of normal controls. An ANOVA was performed with groups (schizo phrenics vs. normals, males vs. females) as bctween-subject factors; items, as a withinsubject factor. This analysis indicated a highly significant difference between patients and normals [F(l,18) = 29.21; p < 0.0001]. No other main effects nor main interactions were observed.
Table 3. Correct responses (means and standard
deviations) Item
Schizophrenics (n =20)
Normals (n - 20)
1 2 3 4 5 6 7 8
1.15 ±0.93 1.00 ±0.91 0.70±0.86 1.00 ±0.85 0.95 ±0.88 0.75 ±0.96 0.65 ±0.87 0.85 ±0.81
1.80 ±0.61 1.75 ±0.63 1.40 ±0.82 1.50 ±0.82 1.40 ± 0.88 1.05 ±0.99 0.95 ±0.76 0.95 ±0.60
Table 4. Error patterns
Errors
Correct sentence but unrelated Nonsense sentence No contradiction at all
Schizophrenics Normals (n = 20) (n - 20)
32 28 11
Figures are percentages on 8 items.
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14 16 6
Qualitative A nalysis o f Erroneous Response Choices It must be recalled that the three alterna tive erroneous responses are constructed in the same way for all items: two sentences that are semantically meaningful but unrelated (contradictory) to the target and one nonsense sentence. Under the hypothesis of incoher ence thinking in schizophrenia, one would expect a higher proportion of nonsense sen tence choices. Percentages of each kind of errors are given in table 4. Inspection of this table shows that patients gave twice as many nonsense choices than normals. However, this comparison is misleading. It is worth reminding that the multiple-choice format of the task makes the comparison of erroneous responses between normals and patients diffi cult. As the number of correct responses is not the same for both groups, the distributions of errors are not equivalent. On the other hand, multiple statistical tests, one for each kind of error, could also introduce other bias. Thus, an overall y} = 0.38 (d.f. = 4) was done. This is not statistically significant. Schizophrenics and normals did not show any preference for one type of alternative or the other. Additional Results: Response Patterns for Schizophrenic Subgroups Subgroups as a Function o f the Severity o f the Clinical Symptomatology as Assessed through the BPRS. According to Andersen et al. [24], some BPRS items "have an additive relationship implying that their sum is a suffi cient statistic for the measurement of the severity of the schizophrenic states’. A sever ity score was computed on the basis of the sum of the following ten critical items selected by these authors: emotional withdrawal, con ceptual disorganization, retardation, gran diosity, hostility, suspiciousness, hallucina tions, uncooperativeness, unusual thought content, blunted or inappropriated affect.
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Results
Discussion and Conclusion
A difficulty inherent in the comparison of schizophrenic patients and normal controls is that there arc a number of factors intermin gled with the psychiatric disorder itself. In the
present study, although the patients have been matched for the most critical factors that can influence the performances, all the schizo phrenics were on drugs, and it cannot be dis carded that the effect of medication had played some role on the deficit observed. In addition, as pointed out by Chapman and Chapman [26], the matching itself on the ver bal test, when not controlled for the difficulty of the tasks (which was the case in our study), can also introduce some bias and inflate the statistical differences on the subsequent task. Nevertheless, schizophrenic patients and nor mal controls appeared to differ markedly in their level of tolerance to contradiction. It does not seem that these differences are due to a lack of comprehension of the meaning of the target proverbs or to that of the choice sen tences. If it were the case, the two groups would have presented different patterns of errors, which is not the case. This bias of pro cessing contradictory statements seems to be common to different levels of severity as well as to different subtypes. However, this latter finding needs to be confirmed with larger samples of subjects. The DSM-III disorgan ized subtype, in which the incoherence of thought is considered to be higher than in the other types, did not perform worse on contra dictions. This quite unexpected result needs further consideration, and performances of paranoids need to be explored. On the other hand, one can argue that patients were exam ined after their acute phase, but the BPRS profiles clearly show that most of them arc still severely disturbed. Further investigations on the interpretations or explanations that schizophrenic patients would give, in order to justify why they do not consider most state ments less contradictory, as normal controls do, would bring some light on the underlying cognitive processes at work. They are re quired in order to attribute generality and specificity to the deficit observed.
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The total-score distribution pattern on these ten items made it possible to dichoto mize the 20 subject samples on the basis of a cutoff point (sum = 37). into two extreme groups: an extremely severe group (n = 7; 5 males. 2 females) and a less severe group (n = 6; 4 males. 2 females). These two groups do not differ markedly on age. educational level and verbal scores. The results show no significant differences, both arc unable to detect contradictory state ments with sufficient accuracy [F( 1.11) = 1.25]. Subgroups as a Function o f Negative Symp tomatology as Assessed through the BPRS and DSM-III Schizophrenic Subtypes. Previous findings have shown that the BPRS could be a useful instrument to detect negative symp tomatology [21, 25], Blunted affect, emo tional withdrawal and retardation are thought to be good indicators of a negative symptom atology. Accordingly, patients with high total scores on these three critical items, n = 8 (4 males and 4 females), were compared with the remaining patients (n = 12). Negative symptomatology did not differentiate these ‘negative’ patients from the others in terms of ability to detect contradictory sentences [F( 1,18)= 1.72]. In addition, the comparison between the disorganized DSM-III. n = 8 (2 females and 6 males), and the undifferentiated subtypes, n = 8 (3 males and 7 females), led to the same neg ative results. The mean scores of correct re sponses were exactly the same (M = 0.84) for both groups.
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the clinical symptom of ambivalence. If two meanings are not opposites for them, it fol lows that the choice between them is made more difficult. However, one can also remind that too tight structures can sometimes gener ate a lack of flexibility in thinking. Another complementary interpretation is that the tol erance of contradictory statement can be seen as a case of overinclusion and a typical exam ple of loose construing [28], which has been shown within the frame of reference of per sonal construct theories. It is likely that the conclusions drawn from this field of research can also be true for the cognitive processing of contradictions in natural language.
Acknowledgments The present study was supported by a grant of the Institut National de la Recherche Médicale (IN SERM). Thanks to Connie Grvnbaum for helpful comment on the translation and to Maria Somogvi for statistical data processing. Data were collected from patients of Hôpital de Bicêtre, Serv ice du professeur André Fé line.
Appendix List o f the 8 hem s
1 Strike while the iron is hot. NS Heat strikes metal. CU Heat dilates iron (or: makes iron expand). MC It is often useful to let an opportunity go by. CU You have to be brave to pick up a hot iron. HC You must not take opportunities as soon as they arise. 2 Union is strength. CU Strength is foremost over right. MC Division sometimes leads to success. HC You can be strong by staying alone. CU Harmony of the spirits makes union. NS Cooperation creates division.
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Nevertheless, concerning the cognitive processing of the sentences, it is likely that the poor detection of contradictions cannot be solely accounted fora lack of ability to process negations (most of the items did not involve a negative wording), however patients failed on these items, nor to an inability to understand the transformation of affirmative sentences into negative ones. With this respect, our results are open to alternative explanations to that given bv both Irigaray [14] and Consoli [15]. Though additional data are still required, two interpretations can be suggested. On the one hand, the inability to detect the contra diction can be explained by a softer belief in the meaning of the target proverb. As White [27] pointed out. ‘proverbs are generally re garded as depository of folk wisdom, as sty lized saying that presume to represent com mon sensical everyday life’. It is likely that schizophrenics do not share the same belief as normals in the symbolic meaning of proverbs. As a consequence, they are unable to find the proper contradictory meaning among the al ternative responses. Such an interpretation underlines the importance of semantic as pects in studying contradictions. It empha sizes the fact that schizophrenics do not share the same interpretations, and this fact is con gruent with the hypothesis of idiosyncratic thinking suggested by Marengo et al. [8], On the other hand, the inability to detect contradictions can be interpreted in terms of the architecture of knowledge structure. Schizophrenics seem to organize their knowl edge in a way less tightly contrasted in com parison with controls. The fact that opposite meanings are not perceived to be as exclusive as they are for normal subjects shows that they do not delineate the same boundaries between what is and what is not culturally val id. and between what is and what is not true. This cognitive interpretation nicely fits with
3 Little strokes fell great oaks. NS The waterfall only flows once. CU One drop can make the barrel overflow. MC A bird can build its nest in a day. CU Water seeps into everything. HC Building must be done all at once. 5 To accomplish great things, live as though you were immortal, (transliteration) NS To accomplish great things, you must destroy them. MC Great men must live by thinking at times about their deaths. HC To accomplish great things, you must live by thinking about the coming of death. CU Accomplishing great things calls for superhu man efforts. CU Great things outlive their makers. 7 Most men spend the first part of their lives making the second part miserable. NS Everyone treats the start of their lives as they would an object. CU People make many plans when they are young but only accomplish a few. HC Most people use their childhood to provide for prosperity in their old age. MC Some people provide for prosperity in their old age at the start of their lives. CU Uncertain fate makes men unconcerned about their futures.
8 We are all strong enough to bear the sufferings of others, (transliteration) HC We cannot bear the sufferings of others. MC Our friends' problems sometimes touch us more than our own problems. NS We only suffer through the suffering of oth ers. CU Strength of character enables people to bear their sufferings. CU We are always strong enough to bear our own problems. 9 Great worth in a shy man may long go unnoticed. (transliteration) CU The wise man is indifferent to praise from the crowd. MC Being worthy of merit and remaining silent can help make someone famous. CU You must do your duty without paying atten tion to what other people think. NS Lack of modesty is a sign of intelligence. HC Wisdom cannot be hidden even when the wise man is shy. 10 Virtue is praised by all but practiced by few. NS What is rare always occurs often. MC Good deeds always move us whereas we are not very' sensitive to rare events. CU We quickly get used to things that we see often. HC We are rarely struck by uncommon things and yet we are struck by virtue. CU Is virtue as rare as is commonly believed? NS = Nonsense; CU = correct but unrelated; MC = moderate contradiction; HC = high contradiction.
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1 von Domarus E ( 1944): The specific laws of logic in schizophrenia; in Kazanin K.S (ed): Language and thought in Schizophrenia. Berkeley. University of California Press. 1964. pp i 0 4 - 114. 2 Arieli S: Interpretation of schizo phrenia. New York. Brunner. 1955. 3 Chapman LJ. Chapman JP: Disor dered Thought in Schizophrenia. New York. Appleton. 1973. 4 Williams EB: Deductive reasoning in schizophrenia. .1 Abnorm Soc Psychol 1964;69:47-61.
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11 de Bonis M, Epelbaum C, Féline A. Grize JB, Hardy P, Somogyi M: Pensée formelle, opérations logicodiscursivcs et schizophrénie: Etude expérimentale d’un cas clinique. Rev Can Psychialr 1990:35:64-70. 12 de Bonis M. Grize JB. de Boeck P: Modèles psychopathologiqucs de raisonnements irrationnels dans la schizophrénie. ConflNSERM - Les empêcheurs de penser en rond. La boratoires Delagrange. Roneotyped 1990. vol 4 .30 p. 13 Blein G, Azorin JM. Dufour H, Tis sot R: Quelques aspects des activités cognitives du schizophrène. IV. Dé séquilibre des affirmations et des né gations. Ann Méd-Psychol 1990: 149:841-856. 14 Irigaray L: Négation et transforma tion négative dans le langage des schizophrènes. Langage I967:5(special issue). 15 Consoli S: Utilisation et fonction de la négation chez le jeune schizophrè ne. Neuropsychiatr Enfant 1981:29: 223-229.
