University of British Columbia, Vancouver, Canada
Hammersmith Hospital, London, UK
Correspondence: Professor P.F. Liddle, Division of Psychiatry, A Floor, South Block, Queen's Medical Centre, Nottingham NG7 2UH, UK
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Aims To assess the interrater reliability, sensitivity and factor structure of a new assessment instrument, the Thought and Language Index (TLI), and to determine if minor aberrations detectable in the speech of healthy individuals are related to the more severe formal thought disorders characteristic of schizophrenia.
Method Interrater reliability was evaluated by determining the intraclass correlation for the ratings by five assessors. Factor analysis of the TLI scores of 87 patients was performed, and TLI scores in matched patients and controls were compared.
Results The intraclass correlation was good for individual TLI items, and excellent for sub-scale scores. Factor analysis identified three groups of approximately orthogonal disorders. Mild speech aberrations were observed in healthy participants and in patients with schizophrenia. The prevalence of mild aberrations was correlated with the prevalence of definite formal thought disorders.
Conclusions The TLI is reliable and capable of detecting subtle disorders. Some mild aberrations occurring in the speech of healthy individuals appear to be attenuated forms of the florid disorders characteristic of schizophrenia.
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
In recent decades one of the most widely used instruments for assessing formal thought disorder has been the Thought, Language and Communication (TLC) scale, devised by Andreasen (1979). Subsets of TLC items are incorporated in the positive thought disorder sub-scale of the Scale for the Assessment of Positive Symptoms (SAPS) and in the alogia sub-scale of the Scale for the Assessment of Negative Symptoms (SANS) (Andreasen, 1987). The TLC scale provides concise definitions of many aspects of thought disorder. However, in a comprehensive review, Straube & Oades (1992) concluded that the TLC scale is not sensitive to subtle anomalies such as those that occur in relatives of patients. In contrast, the Thought Disorder Index (TDI) devised by Johnston & Holzman (1979) was designed to measure a wide range of disorders, including quite subtle anomalies. The TDI entails assessment of speech during two standardised procedures: responding to Rorschach ink-blots, and completing the Wechsler Adult Intelligence Scale. The use of a procedure that is standardised, yet gives the patient substantial executive responsibility for speech generation, is likely to provide sensitivity and reliability without sacrificing validity. However, the TDI is too time-consuming for routine clinical use, and the scoring of disorders requires extensive training (Johnston & Holzman, 1979).
Wynne & Singer (1963) employed Rorschach ink-blots to elicit communication deviance in the families of patients with schizophrenia. They described a variety of aspects of communication deviance, including responses that are confused, vague, incomplete, or involve odd usage of words, that could be detected in the parents of patients with schizophrenia. Employing these researchers' concept of communication deviance in a prospective longitudinal study, Goldstein (1985) observed communication disturbances in families that were detectable before the onset of schizophrenia in the identified patient.
![]() |
METHOD |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The study reported here was designed to test the reliability and factor structure of the TLI items, and the prevalence of these abnormalities in patients with schizophrenia and in healthy control individuals. Whether or not the overt disorganisation of thought that occurs in schizophrenia is on a continuum that embraces the mild oddities of speech and thought discernible in healthy individuals has been a subject of debate. This is a part of the larger debate regarding the prevalence of psychotic symptoms, perhaps attenuated in severity, in a healthy population (van Os et al, 2000). In the TLI, individual instances of disordered thought or language are assigned a score of 0.25, 0.50, 0.75 or 1.0, depending on severity. A score of 0.25 indicates that the abnormality of the phenomenon is questionable. For example, in scoring peculiar word use, the use of a rare word when a more common word would convey the meaning more clearly would be rated 0.25. A score of 0.25 for looseness would be assigned for intrusion of loosely related or unrelated ideas, after which the subject immediately returns to the original train of thought. If the disorganisation of thought characteristic of schizophrenia lies on a continuum that embraces the mild aberrations of speech and thought discernible in healthy individuals, it would be predicted that disorganisation item scores of 0.25 would be observed in healthy participants and in those with schizophrenia. Furthermore, a positive correlation between the prevalence of items scored at 0.25 and the prevalence of items scored at 0.50 or above would be expected.
Participants
Two samples of patients satisfying ICD10 criteria for schizophrenia
(World Health Organization,
1992) were recruited: 49 patients from Ealing Hospital, London,
UK, and 38 patients from Vancouver Hospital, Canada. The Ealing patients were
predominantly people with severe, chronic illness undergoing rehabilitation,
either in hospital or in the community. Their mean age was 43.6 years and 41
were male. The participants from Vancouver were mainly in the resolving phase
of an acute psychotic episode. They were assessed a mean of 24 days after
admission to an acute psychiatric ward. Their mean age was 35.0 years and 21
were male. All patients in both samples were receiving treatment with
antipsychotic medication. In addition, 24 healthy participants with a mean age
of 32.4 years, 13 of whom were male, were recruited by advertisement in
Vancouver and matched in age and gender to 24 of the Vancouver patients. The
healthy participants had no current psychiatric illness, no personal history
of psychotic illness and no history of psychotic illness in a first-degree
relative. The procedure was approved by the ethics review committees of Ealing
Health Authority and the University of British Columbia.
Assessment procedure
The TLI was administered to each participant and scored according to the
TLI manual (details available from the author upon request). Eight pictures
from the Thematic Apperception Test were presented sequentially for 1 min
each, and the participant was asked to talk about each picture. If the person
stopped speaking before the minute was over, a non-directive prompt (e.g.
Can you say more?) was given. At the end of the minute, the
interviewer asked the person tested to explain any odd or unusual utterances
that had been made during the minute. After this enquiry phase, the next
picture was presented. The entire procedure lasted approximately 15 min. The
interview was recorded on audiotape and subsequently transcribed. The SANS and
the SAPS were administered to the Vancouver group.
Interrater reliability
For the purpose of assessing interrater reliability of the TLI, the
transcripts of 25 interviews from the Vancouver study group were scored
independently by five assessors (four psychology graduate students and a
psychiatrist) who had participated in six training sessions each of
approximately 1-h duration, conducted by the author of the scale (P.F.L.).
Interrater reliability was quantified using intraclass correlation
coefficients (ICCs) (Bartko &
Carpenter, 1976).
Factor analysis
Scores for TLI items for the entire sample of 87 participants were
subjected to factor analysis using the Statistical Package for the Social
Sciences (SPSS, 1999). Initial
factors were extracted using the method of principal factors, and subjected to
oblique rotation using the oblimin procedure.
Comparison with healthy controls
For the purpose of comparing TLI item prevalence in patients with that in
healthy participants, the transcripts of the interviews with the 24 healthy
people and 24 matched patients from the Vancouver sample were scored by an
assessor who was blind to diagnostic status. The severity of TLI item scores
in each group were compared using the MannWhitney test. To test the
hypothesis that thought disorders typical of schizophrenia occur in attenuated
form in healthy individuals, the prevalence of item scores at level 0.25 for
the four disorganisation phenomena was compared in healthy participants, in
patients without definite disorganisation (i.e. without any disorganisation
phenomena scored at level 0.5 or above) and in patients with definite
disorganisation phenomena. The significance of differences in prevalence
between the three groups was assessed according to the KruskalWallis
test, using SPSS for Windows Release 10.0.05
(SPSS, 1999). In addition, the
Spearman correlation between prevalence of disorganisation phenomena scored at
level 0.25 and the prevalence of disorganisation phenomena scored at level 0.5
or greater was computed.
Relationship of TLI sub-scales to SANS and SAPS sub-scales
The Spearman correlation between the TLI disorganised thought/language
sub-scale score (sum of scores for looseness, peculiar word use, peculiar
sentence construction, peculiar logic) and the SAPS positive thought disorder
global score was computed for the Vancouver sample. Similarly, the correlation
between TLI impoverished thought/language sub-scale score (sum of scores for
poverty of speech and weakening of goal) and the SANS alogia global score was
computed.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
Factor analysis
The factor analysis revealed three factors with eigenvalues greater than
1.0, which together accounted for 71% of the shared variance. The factor
loadings, after oblique rotation, are shown in
Table 2. The four
disorganisation items loaded heavily on the first factor; the two
impoverishment items loaded heavily on the second factor; and perseveration
and distractibility loaded on the third factor. The first factor reflected the
existence of significant mutual correlations, ranging from 0.29 to 0.60,
between the four disorganisation items. The second factor reflected a strong
correlation of 0.76 (P0.001) between poverty of speech and
weakening of goal. The third factor reflected the existence of a moderate
correlation between perseveration and distractibility (r=0.41,
P<0.001). All pair-wise correlations between factors were
trivially small (less than 0.15 in absolute magnitude).
|
Comparison of patients with controls
The mean severity of TLI items (and the sub-scale scores) in the Ealing
patient sample, and in the 24 matched patients and controls from Vancouver,
are shown in Fig. 1. Although
the mean severity of TLI items was substantially less in healthy control
individuals than in the matched Vancouver patients, the scores in the healthy
control group were not negligible. However, apart from one instance of
looseness and one peculiar sentence (each scored at level 0.5) in one healthy
individual, and one peculiar sentence scored at level 0.5 in another, the
scores in healthy participants were accumulated from items scored at level
0.25, which denotes phenomena of questionable abnormality.
|
The mean number of disorganisation phenomena scored at level 0.25 was 1.8
per person for healthy control participants. From the matched sample of 24
patients, 12 had no definite evidence of disorganised thought/language (i.e.
no individual disorganisation phenomenon scored at the level 0.5 or above).
For these 12 patients the number of disorganisation phenomena scored at level
0.25 was 3.6 per person, whereas for the 12 patients with definite evidence of
disorganised thoght/language the number was 9.0 per person. The difference
between these three groups in the prevalence of phenomena scored at level 0.25
was significant (KruskalWallis test, 2=16.0, d.f.=2,
P<0.001). Comparison of pairs of groups demonstrated that patients
with definite disorganisation exhibited significantly more phenomena scored at
level 0.25 than both the healthy control group (MannWhitney
U=26.5, P<0.001) and the patients without definite
disorganisation (U=27, P=0.009). However, the patients
without definite evidence of disorganisation did not differ significantly from
the healthy control individuals in the number of phenomena scored at level
0.25 (U=118.8, P=0.38). The Spearman correlation between the
prevalence of disorganisation phenomena scored at level 0.25 and the
prevalence of disorganisation phenomena scored at level 0.5 or above was 0.615
(P<0.001).
Correlations with SANS and SAPS scores
The correlation between the TLI disorganisation sub-scale score and the
SAPS positive thought disorder global score was 0.49 (P=0.001), and
the correlation between the TLI poverty of thought sub-scale and the SANS
alogia global score was 0.40 (P=0.001).
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Item severity scores
In the Ealing patient group, predominantly people with severe chronic
illness, poverty of speech was the item with greatest mean severity. It is
noteworthy that all aspects of disorganised thought/language were relatively
common, despite the fact that the amount of speech produced by these patients
was low. In the Vancouver patient group, who were predominantly in the
resolving phase of an acute psychotic episode, peculiar sentence construction
had the highest mean severity. Poverty of speech was appreciable, but less
severe than in the more chronic sample from Ealing.
The severity of TLI item scores in the healthy participants was much lower than in the matched Vancouver patients, but not negligible. The order of items when ranked according to mean severity was similar in the healthy control group to that in the Vancouver patients. Distractibility was rare or absent in all groups assessed in this study. However, this item has been retained in the TLI because distractible speech is relatively common in patients acutely ill with psychosis, especially in those with mania.
The continuum of severity of disorganisation
The finding that mild aberrations of thought and language occur in healthy
individuals but are more prevalent in people with schizophrenia and,
furthermore, that the prevalence of these mild aberrations is correlated with
the prevalence of more severe, clearly abnormal disorders, suggests that there
might be a continuum of severity of disorganised thought in the human
population. The occurrence of such a continuum would have important
implications for the nature of psychotic thought disorder, suggesting that
this disorder might arise from one or more causal factors that exert an
influence widely in the population. However, it should be noted that on
account of the small sample size in this study, further investigation is
warranted to confirm the existence of a continuum of severity of formal
thought disorder in the population at large.
Relationship to SANS and SAPS sub-scales
The significant correlation between TLI sub-scale scores and SANS and SAPS
thought disorder sub-scale scores confirms that the phenomena elicited by the
TLI overlap with the phenomena scored using SANS and SAPS. However, the modest
magnitude of the correlations demonstrates that the phenomena revealed by the
TLI are not identical to those assessed by SANS and SAPS. The question of
which scales provide the most valid measurement of thought disorder in
schizophrenia is unlikely to be answered until the intrinsic nature and
pathological mechanism of formal thought disorder have been established.
TLI scores and the pathophysiology of thought disorder
An additional feature of the TLI is its suitability for use in functional
imaging studies where it is necessary to elicit the phenomena of interest
within a standard frame-work and within a time frame of several minutes. It
has been used successfully in a positron emission tomography study by McGuire
et al (1998) and a
functional magnetic resonance imaging study by Kircher et al
(2001). Both of these studies
found that severity of positive thought disorder is correlated with decreased
activation of language areas in the left superior temporal gyrus, and with
abnormal function of the anterior cingulate cortex, a brain region engaged in
the executive control of behaviour and speech. The consistency of these
findings suggests that the TLI is a valid measure of language disorder in
schizophrenia. This conclusion receives further support from the finding by
Kuperberg et al (1998)
that positive thought disorder assessed by the TLI was associated with reduced
sensitivity to linguistic violations during a word monitoring task.
The TLI is a reliable measure of thought and language disorders that is sensitive to subtle disorders which are prevalent in schizophrenia and discernible in healthy individuals. The existing evidence indicates that it quantifies phenomena related to specific deficits in linguistic performance and to specific patterns of aberrant brain activity. Studies of the relationships between TLI scores, abnormalities of cognition assessed by the techniques of cognitive psychology and regional cerebral activity assessed by neuroimaging, offer the prospect of further delineation of the mechanism of formal thought disorder in both psychological and neurological terms.
![]() |
Clinical Implications and Limitations |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
LIMITATIONS
![]() |
APPENDIX |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Andreasen, N. C. (1987) Comprehensive Assessment of Symptoms and History. Iowa City, IA: University of Iowa.
Bartko, J.J. & Carpenter, W.J. (1976) On the methods and theory of reliability. Journal of Nervous and Mental Disease, 163, 307-317.[Medline]
Goldstein, M. J. (1985) Family factors that antedate the onset of schizophrenia and related disorders: the results of a fifteen year prospective longitudinal study. Acta Psychiatrica Scandinavica Supplementum, 319, 7-18.[Medline]
Johnston, M. H. & Holzman, P. S. (1979) Assessing Schizophrenic Thinking. San Francisco, CA: Jossey-Bass.
Kircher, T.T.J., Liddle, P. F., Brammer, M. J., et al
(2001) Neural correlates to formal thought disorder in
schizophrenia: an fMRI study. Archives of General
Psychiatry, 58,
769-774.
Kuperberg, G. R., McGuire, P. K. & David, A. S. (1998) Reduced sensitivity to linguistic context in schizophrenic thought disorder: evidence from on-line monitoring for words in linguistically anomalous sentences. Journal of Abnormal Psychology, 107, 423-434.[CrossRef][Medline]
McGrath, J. (1991) Ordering thoughts on thought disorder. British Journal of Psychiatry, 158, 307-316.[Abstract]
McGuire, P. K., Quested, D. J., Spence, S. A., et al (1998) Pathophysiology of positive thought disorder in schizophrenia. British Journal of Psychiatry, 173, 231-235.[Abstract]
Murray, H. A. (1943) The Thematic Apperception Test Manual. Cambridge, MA: Harvard University Press.
Norman, R. M., Malla, A. K., Cortese, L., et al
(1999) Symptoms and cognition as predictors of community
functioning: a prospective analysis. American Journal of
Psychiatry, 156,
400-405.
Rorschach, H. (1942) Psychodiagnostik. Bern:Hans Huber.
Spohn, H. E., Coyne, L., Larson, J., et al (1986) Episodic and residual thought pathology in chronic schizophrenics: effects of neuroleptics. Schizophrenia Bulletin, 12, 394-407.[CrossRef][Medline]
SPSS (1999) Statistical Package for the Social Sciences, Version 10.0.5. Chicago, IL: SPSS Inc.
Straube, E. R. & Oades, R. D. (1992) Schizophrenia: Empirical Research and Findings, pp. 30-31. New York: Academic Press.
Van Os, J., Hanssen, M., Bijl, R. V., et al (2000) Strauss (1969) revisited: a psychosis continuum in the general population? Schizophrenia Research, 45, 11-20.[CrossRef][Medline]
World Health Organization (1992) The ICD10 Classification of Mental and Behavioural Disorders. Geneva: WHO.
Wynne, L. C. & Singer, M. (1963) Thought disorder and family relations of schizophrenics. II: A classification of forms of thinking. Archives of General Psychiatry, 9, 199-206.
Received for publication January 8, 2002. Revision received June 20, 2002. Accepted for publication June 24, 2002.
Related articles in BJP: