Visual controlled information processing resources and formal thought disorder in schizophrenia and mania

Schizophrenia

Research,

TJ 1993 Elsevier

SCHRES

9 (1993)

59

59-66

B.V. All rights

Science Publishers

reserved

0920.9964/93/$06.00

0028 1

Visual controlled information processing resources and formal thought disorder in schizophrenia and mania

NOW York University (Received

Mark

R. Serper

Medical

Center, Ne\v York, NY 10016, USA

30 June 1992; revision received 21 September

1992; accepted

4 October

1992)

Visual selective attentional performance under low and high processing load conditions was examined in patients with schizophrenia (n = 20) or bipolar affective disorder-manic type (n = 21) and a group of normal control subjects (n = 18). Although schizophrenic patients demonstrated significantly more impaired cognitive performance than normal controls, bipolar patients were found to be as deviant as the schizophrenic patients on almost all of the performance variables. Positive thought disorder under high processing load demands was moderately correlated with schizophrenic patients’ response processing ability. In contrast, negative thought disorder ratings were found to be moderately associated with reaction time performance during high processing demands for both patient groups. These findings are discussed with regard to the visual-motor controlled information processing deficits, and relationship between selective attention, thought disorder in psychosis. Key words:

Visual selective attention;

Processing

load; Thought

INTRODUCTION

Attentional impairment has traditionally been included as a defining feature of schizophrenia (e.g., Bleuler, 1911; Kraepelin, 1919). More recent theorists postulate that the allocation of effortful, capacity demanding, controlled information processing resources (as defined by Schiffrin and Schneider, 1977) is one of the most significant schizophrenic cognitive deficits (Neale and Oltmanns, 1980; Callaway and Naghdi, 1982; Nuechterlein and Dawson, 1984). A widely accepted theory accounting for the pervasive cognitive deficits exhibited by schizophrenics is that these individuals have an abnormal reduction in the availability of processing resources compared to normals (Gjerde, 1983; Knight and Russell, 1978; Nuechterlein and Dawson, 1984). Correspondence to: M.R. Serper, NYU Medical Center, Department of Psychiatry, HN 323, 550 First Avenue. New York, NY 10016. USA.

disorder;

(Schizophrenia)

The relevance of a lowered controlled processing threshold to the formation and maintenance of formal thought disorder is great. For example, both Maher (1983) and Rochester (1979) have proposed that schizophrenics’ reduced processing resources lead to information overload and cause discourse failures. Studies using auditory selective attention tasks designed to vary processing load conditions (e.g., distraction vs. nondistraction) have generally found positive, but not negative, thought disorder to be associated with distraction in schizophrenia but not in mania (Oltmanns et al., 1979; Harvey and Serper, 1990). In contrast, studies examining the relationship between psychosis and attention using visual-motor tasks have generally found these tasks to be associated with negative symptoms and negative thought disorder, but not positive symptoms or positive thought disorder (e.g., Nuechterlein et al., 1986; Walker and Green, 1982). The relationship between schizophrenic deficits and negative symptoms have been attributed to sustained attentional difficulties

60

(Nuechterlein et al., 1986) as well as to visualmotor abnormalities in both affective disorder and schizophrenia (Walker and Green, 1982). There is a lack of studies to date that have examined either visual-motor selective attention or auditory sustained attention in schizophrenia and mania. It remains unclear, as a result, whether schizophrenic positive thought disorder is related to deficits in their effortful selective attention processing ability and/or due to auditory modality processing failures. Similarly, it remains uncertain whether schizophrenic negative thought disorder is related to sustained attentional difficulties and/or due to visual-motor task requirements. The present study attempted to clarify one of these issues by assessing schizophrenic, manic, and normal subjects on a visual-motor selective attention task. This task has been demonstrated to require effortful processing (Hanson et al., 1981) and contains both low and high processing demand conditions. Processing demand conditions are a reflection of task complexity and determines how much processing resource must be allocated to successfully complete a task (Kahneman, 1973). In this study, performance variables were correlated with positive and negative thought disorder ratings to determine if processing demand was related to thought disorder. Based on the current knowledge in these areas it was hypothesized that (1) only schizophrenic subjects cognitive performance would be related to their thought disorder ratings; and (2) high processing load demands would be more strongly associated with schizophrenic patients positive and negative thought disorder ratings than low processing load demands.

METHODS Subjects Subjects were 20 schizophrenic patients, 21 manictype bipolar patients, and a control sample of 18 normal subjects. The psychiatric patients were recruited from consecutive admissions at a state psychiatric hospital and were evaluated within ten days of their admission to an acute treatment unit. They were assessed with the Schedule for Affective Disorders and Schizophrenia (SADS; Spitzer et al., 1978) and diagnoses utilized DSM-III criteria. Diagnoses were generated independently by a

group of clinical psychology graduate students and a Ph.D. level clinical psychologist. Diagnostic reliability between the students and the Ph.D. level psychologist was high: 0.88 (kappa), for all cases; and diagnostic disagreements were settled by discussion. Patients with a history of substance abuse, neurological disorder or any disorder of the central nervous system were excluded from participation. Normal control subjects were solicited from a local community and from the student population at a major state university. Community populations and undergraduates were approached and their participation was solicited. No subject with a personal or familial history of psychiatric treatment, hospitalizations, or any neurologic or behavioral disorders was assessed. Demographic information for all subjects is presented in Table I. There were no statistically significant betweengroup differences in subjects’ age (p > 0.05) level of education (p > 0.05) and number of previous hospitalizations for the patients (p > 0.05).

TABLE

1

Demographic Variable

data on .suhjccts Group Schixphrenic in=ZO) (mean) SD)

Munic (II=211 (mean f SD)

Normd in = 18) imraniSD)

Age

30.3 k6.6

33.1 k6.4

29.4k11.3

(% Female)

40

42

50

Years of education

11.6+2.0

12.1 F 1.6

13.212.2

Prior hospitalizations

7.6* 1.8

x.3*

Medication neuroleptic (% of group)

100

52”

Medication lithium (% of group)

-

86h

1.5

“8 manics were receiving neuroleptic in addition to lithium, and 3 manics were receiving only neuroleptic. bPercentage based on the 18 manics receiving lithium alone or in combination with neuroleptic.

61

Clinical thought disorder ratings Clinical thought disorder ratings were generated with the Scale for the Assessment of Thought, Language and Communication (TLC; Andreasen 1979). The source of the ratings was the tape recorded clinical interview (SADS). In this taperecorded interview subjects were asked a series of open-ended questions, with the interviewer using prompts as necessary and talking as little as possible. Two trained raters listened to all of the interviews, with 20% of the interviews overlapped for reliability. They rated the interviews using a five point (O-4) scale for five positive signs of thought disorder (pressure of speech, derailment, tangenand illogicality) and two incoherence, tiality, negative signs of thought disorder (poverty of speech and poverty of content of speech) according to the definitions and instructions from the Scale for Assessment of Thought, Language and Communication (TLC; Andreasen, 1979). All ratings were conducted blind to subject identity, diagnosis, or any other information. These raters made 183 ratings, from which the present sample is a subset. Reliabilities (kappas) were: pressure of speech: 0.92; derailment: 0.91; tangentiality: 0.79; incoherence: 0.30; illogicality: 0.24; poverty of speech: 0.88; poverty of content of speech: 0.60. Composite positive and negative thought disorder scores were created by summing the ratings of the signs within each category after excluding incoherence and illogicality because of low reliability. Incoherent and illogical speech occurred infrequently and may have accounted for the low reliability in these ratings. Means and standard deviations for the composite positive and negative thought disorder ratings for both patient groups are presented in Table 2. Manic and schizophrenic patients manifested equally severe positive thought disorder F( 1,39) = 0.62, p > 0.44, but the schizophrenic patients had a higher level of severity in negative thought disorder F( 1,39) = 6.67, p < 0.01. For both manic and schizophrenic groups, positive and negative thought disorder scores did not intercorrelate (manic: r = 0.15, p > 0.5 15; schizophrenic: r= 0.24, p > 0.14). Task description Subjects were asked to monitor either 4 (low load) or 8 (high load) line stimuli in the form of moving

TABLE Meun

2 TLC

posilivr

und negutive

composite

thouxht

disorder

wrings Group

PTD” NTDb PTD, positive disorder. *pco.o5.

Manic

Schizophrenic

(meun & SD)

imeun i_ SD)

3.51+3.12 0.X5 & I .26

2.85+2.14 2.00 f I .77*

thought

disorder.

NTD,

negative

thought

histograms and asked to track them as they moved horizontally from the center of a computer display, originating from a vertical line of 15 cm length that bisected the computer screen. The vertical line extended to 1.25 cm from the edges of the computer screen. The histograms moved in a single direction toward a vertical line barrier (also 15 cm in length) on the same side of the visual display from which the lines originated. This movement was in the form of histogram extension-originating from the center vertical line (the stimulus origin) and extending to the vertical line barrier at the side of the screen. Fig. 1 depicts the task configuration. The histograms moved at a constant rate toward this barrier. The barrier extended to 1.25 cm from the edges of the computer screen. Subjects were asked to push a single response key with their preferred hand whenever any of the histograms contacted the barrier. Only one histogram would contact the barrier for a given trial but the subject was required to monitor all the histograms. The

Response

Origin Fig. 1. Representation

of high load condition. display and screen.

Barrier 1.25 cm between

62

histograms that did not turn out to be the target served as distracters. Once one of the histograms contacted the barrier, the subject had three seconds to respond (i.e., push the response key) after which time the histogram was removed and then reset with the histogram originating in various randomly determined lengths with the center most end of the histogram touching the stimulus origin. When any histogram contacted the barrier the display remained stable until either a response was made or three seconds expired. There were six blocks in total, with the blocks successively alternating between four and eight histograms. Within a block, the histograms always moved in the same direction toward the barrier (i.e., starting on the left and moving toward the barrier located on the left, or starting on the right and moving toward the barrier located on the right). Direction of histogram movement alternated at random, but the stimulus display was not changed in number until the subject completed a minimum of 10 responses without a 10 ms decrease in reaction time from the average reaction time of the ten previous trials. The number of trials was selfdetermined by reaction time performance. The inter-block interval was 1 s. The rate of histogram movement required a response at an average of once every three seconds. Performance was continuously monitored and collected by the computer. Dependent variables collected by the computer were the response latency, the number of three second intervals per block where no response took place after a histogram reached the barrier (errors of omission) and the number of times a response was made when no histograms were in contact with the barrier (total errors of commission). Errors of commission did not affect the latency timer. As a warm-up, all subjects completed a brief version of the task. In this practice version, after five histograms reached the border, regardless of whether a response was made, or a failure to respond occurred, the block was ended and a new block was initiated (with total of 6 blocks in all). Procrdure

Subjects were seated 12 display screen of an Apple were familiarized with the Subjects were instructed

inches in front of the IIe microcomputer and response key apparatus. to respond immediately

by pushing the response key whenever a histogram touched the outer border of the display. The computer collected reaction time and all error data. Eight patient subjects did not complete the assessment and testing sessions.

RESULTS

The means and standard deviations for reaction time performance for all subjects are presented in and Fig. 2. Subjects’ age, level of education number of prior admissions were uncorrelated with their reaction time and error frequencies (p > 0.05). A 3 (Diagnosis) x 2 (Condition) x3 (Block) repeated measures ANOVA for reaction time found a significant Diagnosis x Condition interaction, F(2,56) = 3.26, p < 0.046. Simple effects tests (Winer, 1962) were computed, finding significant effects of diagnosis in the low load condition, F(2,56)= 10.82, p
time were

63

MEAN

MILLISECONDS

Manics

Schizophrenics

Fig. 2. Reaction

TABLE

3

Means

and

standard

deviations

,for

errw.s

of

omission

and

commission Variuhle

Manic

Schkophrenic

Normal

in=Zl)

(n=ZO)

in=

18)

Errors of omission: low load trials

0.90 k

I .56

I .45 + 2.06

0.1

Errors of omission: high load trials

1.46i

1.85

I .93 k 2.48

0.32kO.48

Errors of commission

50.74+41.39

48.05i_38.40

I kO.42

Normals

time performance.

subjects errors of omission during low load trials (r = 0.47, p < 0.05). In contrast, almost all reaction time correlates of thought disorder were significant and are presented in Table 4. For the bipolar subjects, reaction time performance during low load correlated significantly with positive thought disorder. Negative thought disorder was not significantly associated with the bipolar patients reaction time performance under low load, but was strongly associated with their high load performance. For schizophrenic subjects, reaction time perfor-

19.17+19.25 TABLE

4

Correlutions

commissions committed F(2,56) = 4.62, p < 0.01. Newman-Keuls analysis revealed that the normal control group made significantly fewer errors of commission than manics and schizophrenics, who again did not differ. Correlational unalyses To examine the association between clinically rated thought disorder and reaction time performance and error scores, Pearson product-moment correlations were calculated for each patient group. No correlations between thought disorder and error scores were significant, except for schizophrenic

lwrween

reaciion

rime prrfiwmanw

and

thought

disorder Variable

Manic

Schkophrenic

(n=21/

(n = 20)

PTD

NTD

PTD

NTD

Reaction time low demand

0.44*

0.32

0.16

0.29

Reaction time high demand

0.09

0.5s**

0.41*

0.39*

PTD, positive disorder. *p
thought

disorder.

NTD,

negative

thought

64

mance was not significantly correlated with either positive or negative thought disorder under low processing load. However, both positive and negative thought disorder scores were significantly associated with schizophrenics’ reaction time performance during high load processing.

DISCUSSION

Crucial to the interpretation of the results is the issue of the type and amount of processing required by the task. Several pieces of evidence support the view that this is a controlled processing selective attention task. Normal subjects were load responsive, in that their reaction times were longer and their error scores higher in the high load condition. This suggests that more processing capacity was tapped by high load requirements. In addition, no decreases in response latency or error rates occurred across the successive blocks of trials, suggesting that performance was not improving over time. Also, the current task demands were constantly shifted in order to prevent practice effects from occurring, and subjects were required to monitor distractor histograms while selectively responding to the targets. Finally, the task used in the present investigation has been utilized in a previous study in a dual task paradigm, with a secondary auditory reaction time task (Hanson et al., 1981). When the two tasks were performed concurrently, performance on both tasks decreased, suggesting that performance on the task used in the present study required effortful and resource-limited cognitive capacity. The results of this study found schizophrenic patients to manifest low and high load controlled processing deficits compared to normals. Comparing the patient groups, schizophrenic subjects manifested a poorer performance in the low load condition compared to manics, but equally poor performance during high load conditions. These findings are consistent with the notion that for schizophrenic patients, the actual pool of resources may be more limited than other patient groups (Nuechterlein and Dawson, 1984). Schizophrenic patients poor performance across a wide variety of cognitive tests, often referred to as a ‘generalized

deficit’, may reflect these patients processing resource limitations. In contrast to expectations and to previous reports (e.g., Oltmanns, 1978) that suggested that manic patients may not manifest controlled processing deficits, the bipolar sample in the present study were as impaired as the schizophrenic patients on this task, performing as deviant as the schizophrenic sample on almost all performance measures. The manic sample also manifested similar demographic and clinical profiles as the schizophrenic sample, including equal severity of positive thought disorder, and nonsignificantly different numbers of past psychiatric hospitalizations. Recent research has suggested that manics may present with formal thought disorder as severely and frequently as schizophrenic patients (e.g., Harvey, Earle-Boyer and Wielgus, 1984) and, in some cases as chronic and treatment refractory (Harrow et al., 1990; Coryell, Endicott, Keller, 1990). The present results further suggest that chronic manic patients’ impairment may also extend into the cognitive realm. Similarly, contrary to expectations, the correlational analyses revealed that both patient groups demonstrated a moderate relationship between components of their clinically rated formal thought disorder and their task performance. Speculatively, the pattern of the correlations support the suggestion that there are at least two components of cognitive dysfunction that produce thought disorder: an effortful, high resource demanding visualmotor response processing component that may be related to both manic and schizophrenic negative thought disorder; and a selective attentional processing component that may underlie schizophrenic positive thought disorder. Each type of deficit may independently contribute to or mediate thought disorder in psychotic patients. For example, significant correlations were found between negative thought disorder and high processing task demands in both patient groups. Past studies have reported an association between psychotic patients’ performance on visual-motor tasks and their negative symptomatology (Walker and Green, 1982; Green and Walker, 1984; Hemsley, 1977, 1978). If these conclusions can be generalized to the present investigation, it may be the case that the high load visual-motor component

65

of the present task mediated the association with patients’ negative thought disorder ratings. schizophrenic patients positive In contrast, thought disorder was significantly correlated with their reaction time performance under high load demands and manic patients positive thought disorder was significantly correlated with task performance under low-load demands. These findings suggest that positive thought disorder may be mediated by selective attention processing overload conditions in schizophrenia, but not mania. Additionally, it may be the case that the component of the task requiring effortful selective attentional processing mediated the significant relationship between patients’ positive thought disorder and their task performance. Past investigations haSe found auditory selective attentional tasks to be highly associated with schizophrenic positive thought disorder and unassociated with negative thought disorder (e.g., Harvey and Serper, 1990; Wielgus and Harvey, 1988). Also, a recent study (Harvey and Pedely, 1989) found an association between visual selective attention performance and positive, but not negative thought disorder using serial recall as a dependent measure instead of a motor response. These findings along with the present results support the notion that deficits in selective attention ability, regardless of response and stimulus modality, may mediate or contribute to positive thought disorder in psychosis. Cognitive theories of thought disorder that postulate selective attention overload as a mediating factor in discourse failure include deficits in controlled processes that enable one to plan speech while monitoring ongoing conversation (Rochester, 1978); and increased distractibility that prevents patients from inhibiting associative intrusions during discourse (Maher, 1983). Several important limitations, however, in the present study qualify this discussion. Firstly, it is, of course, very possible that positive thought disorder, negative thought disorder, and task performance are all highly associated because of their joint association with some generalized deficit or other underlying factor. This possibility is undermined by the fact that the two types of thought disorder did not correlate with each other (a finding that has been consistently reproduced in other samples, (e.g., Walker et al., 1988). This suggests that differential aspects of the laboratory

task may have independently contributed to the significant associations between performance variables and positive and negative thought disorder ratings. A second limitation concerns the patients medication status. All patients were tested while receiving antipsychotic medication and/or lithium. Past investigations of cognitive performance in schizophrenia indicate that medication alters schizophrenic patients’ cognitive performance (e.g., Spohn et al., 1985; Serper et al., 1990) as well as alter its association with clinical symptoms (Harvey and Pedley, 1989). However, reaction time performance has been reported to be unaffected by administration of neuroleptic medication (Oltmanns et al., 1978; Medalia et al., 1988; Wykes et al., 1992). A recent study (Earle-Boyer et al., 1991) that directly compared medicated and unmedicated schizophrenic subjects’ attentional and motor tasks performance and found no adverse affects of medication on motor competency or cognition. As a result, the extent of medication status as a confounding variable in terms of its influence on cognitive performance or in mediating the relationship between symptoms and attentional performance in the study remains unclear, but suggests that administration of neuroleptic medication did not impair cognitive performance. Another limitation in the discussion concerns the use of a single controlled processing task. The use of multiple controlled processing tasks in both auditory and visual modalities, validated to assess independent aspects of task performance (e.g., information overload; selective attention) will help elucidate the relationship between response modality, type of attentional functioning and their relation to positive and negative thought disorder. The results of this study supports the utility of reaction time performance as a correlate of symptoms in psychiatric patients. Longitudinal studies examining patients’ response processing performance on both selective and sustained attentional tasks in auditory and visual modalities may help resolve these remaining issues. Such manipulations could begin to provide better understanding about the role of controlled information processing failures in psychosis and how they contribute to the development and maintenance of positive and negative thought disorder.

66

ACKNOWLEDGEMENTS

The author would like to thank Philip D. Harvey for his thoughtful comments on an early draft of this paper.

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