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Schizophrenia Bulletin Advance Access originally published online on July 27, 2005
Schizophrenia Bulletin 2005 31(4):910-921; doi:10.1093/schbul/sbi035
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© The Author 2005. Published by Oxford University Press on behalf of the Maryland Psychiatric Research Center. All rights reserved. For permissions, please email: journals.permissions@oupjournals.org.

Negative Symptoms and Specific Cognitive Impairments as Combined Targets for Improved Functional Outcome Within Cognitive Remediation Therapy

Kathryn E Greenwood
Department of Psychology, Institute of Psychiatry, De Crespigny Park, London SE5 8AF

Sabine Landau
Biostatistics and Computing, Institute of Psychiatry, London

Til Wykes
Department of Psychology, Institute of Psychiatry, De Crespigny Park, London SE5 8AF


   Abstract
Top
 Abstract
Introduction
 Method
 Results
 Discussion
 References
 
Negative symptoms and poor cognition are both associated with poor functional outcome in schizophrenia. This poor functional outcome has been attributed to poor cognition rather than any independent contribution from symptoms. Identifying target cognitive processes and mechanisms that predict community function, and possible moderator effects of negative symptoms, will allow the development of cognitive remediation programs that are successful in improving functional outcome. A referred sample of 53 in- and outpatients with schizophrenia with general cognitive impairment (including 28 with severe negative symptoms) and 22 healthy controls, balanced for premorbid IQ, were compared cross sectionally on measures of community shopping skills, executive function, and working memory. Across the groups, there were direct relationships between community functioning and specific executive functions, and there were interactions between group membership and the types of associations found. Working memory was independently associated with accurate community functioning only in people with schizophrenia and negative symptoms. This association was not due to the sole presence of working memory impairment or just to negative symptoms. Poor community function is predicted both by specific cognitive impairments that are prominent in people with negative symptoms and through the moderating effect of negative symptoms on the working memory–community function relationship. This may reflect a synergistic association between symptoms and cognition: negative symptoms arise from cognitive impairment but also impact detrimentally on working memory functioning. Both cognitive processes and negative symptoms should be targeted in cognitive remediation to effect the greatest change in community functions.

Keywords: schizophrenia / cognition / mechanisms / community function / neurocognitive / interventions


   Introduction
Top
 Abstract
 Introduction
Method
 Results
 Discussion
 References
 
The association between cognition and functioning in schizophrenia has been widely reported in the last decade,1–2 yet the positive effects of remediation programs on cognition do not translate directly to improved real-life functioning.3 The cognitive mechanisms that should be targeted to achieve the best outcomes are, as yet, only loosely defined,2 and certain groups of people, such as those with negative symptoms, may respond better than others.4 Indeed both cognition and negative symptoms are associated with poor community function in schizophrenia, yet the role of negative symptoms on functioning is contentious.1, 5–15 Previous studies have considered the strong independent associations between cognition and community functioning, while symptoms have been assumed to contribute only indirectly through their link with cognition or through overlaps with definitions of functioning.1, 5 The independent contribution of symptoms to community functioning has not been fully explored, however, due to the confounding of negative symptoms with poor general cognition.16–18 The area is also complicated by the range of different cognitive measures, the use of global and questionnaire measures of functioning, and the scarcity of theoretical frameworks.1–2

Broad global domains such as IQ, executive function (Wisconsin Card Sorting Test), vigilance, memory, and more recently working memory have each been associated with poor function.1, 5–12 Indeed composite executive function scores, in particular, have been associated with daily living skills, occupation, and community function, as assessed through indirect questionnaire or global measures.1 The use of these global measures adds little, however, to our understanding of the mechanisms by which poor cognition is related to poor function.

Negative symptoms are associated with the same global cognitive impairments in IQ, executive function, vigilance, memory, and working memory that predict poor community function.17–26 Negative symptoms have, however, also been linked theoretically and empirically with specific cognitive processes. These processes have included deficits in the generation of plans and strategies, the initiation of actions, and the use of immediate working memory, which result in a restriction in spontaneous activity.27–28 Strategy, response initiation, and working memory impairments may constitute core impairments in schizophrenia with negative symptoms.29 The strong association between negative symptoms and global poor cognition has confounded investigations of specific cognition–function relationships. This confounding has rendered equivocal the independent effect of negative symptoms on community function when cognition is included. Certainly, while symptoms have been associated with poor community function in some first-episode and chronic schizophrenia studies,11–15 others have described only limited or indirect links through the association of symptoms with poor cognition.1, 5

Cognitive and neurocognitive remediation programs do improve cognition.3, 30–31 Some studies have suggested selectivity in the response to cognitive remediation therapy, with better effects, for example, for people with negative symptoms of schizophrenia than for those without these symptoms.4 Few studies have looked at real-world outcomes, and those that have report mixed results.3 Improved real-life community, occupation, and daily living skills do occur following remediation programs. The best effects are limited to comprehensive programs that incorporate a real-life element, such as neurocognitive enhancement with work therapy.32 Certainly it is apparent that improving cognition does not translate simply to improved functional outcome.

This study will elucidate the cognitive processes and mechanisms that result in poor community function in schizophrenia, particularly for people with negative symptoms. Executive functions and working memory are targeted because of their close links both to negative symptoms and to poor functioning in the community. If general cognitive functioning is the significant driver of poor community function, then people with schizophrenia matched for broad general cognition but not negative symptoms should differ from healthy controls but not from each other. If, however, the main predictor of community function is specific executive processes, then these poorer executive processes would be associated with poorer community function within each group. Finally if negative symptoms are important in the prediction of community function, then they should moderate the relationship between executive function and community function.


   Method
Top
 Abstract
 Introduction
 Method
Results
 Discussion
 References
 
Design
The study was cross sectional, with the dependent variables (community function) and the independent variables (executive function and general cognitive level) measured in participants who fell into 1 of 3 groups: these were healthy controls and 2 groups of participants with schizophrenia defined according to the presence or absence of negative symptoms.

Participants
Participants with DSM-IV schizophrenia were in- or outpatients. They were referred by mental health teams because they demonstrated some problems with cognition and/or functioning and were deemed suitable candidates for cognitive remediation therapy. Participants with schizophrenia were excluded if they demonstrated intact general memory (a score of 22 or more on the Rivermead Behavioural Memory Test)33 and intact general executive function (a score of 4 categories or more on the Wisconsin Card Sorting Test)34 or intact social behavior function (a score of 3 or less on the Social Behaviour Scale).35 This enabled the 2 schizophrenia groups to be balanced for general cognitive level. These 53 participants with DSM-IV schizophrenia and cognitive impairments were divided into 2 groups—28 participants with negative symptoms and 25 participants without negative symptoms—and were compared to 22 healthy control participants.

Participants with negative symptoms additionally fulfilled criteria of at least 2 negative symptoms (score of 3–5) on the Positive and Negative Syndrome Scale (PANSS), including at least 1 of the core psychomotor poverty symptoms of blunted affect and lack of spontaneity and flow of conversation.36 Healthy control participants comprised a nonpsychiatric volunteer sample recruited from within local employment and sheltered work centers in order to facilitate the balancing of premorbid IQ and education levels across samples. All participants gave informed consent for participation in this study, and ethical approval for the work was obtained from the South London and Maudsley National Health Service Trust Ethical Committee. All participants were aged 18–65, with premorbid IQ (National Adult Reading Test–Revised)37 above 70, English as a first language, no neurological problems or head injury, and no current substance abuse.

Measures

Executive Function Measures. Component executive process and task selection were theoretically and empirically motivated. Executive measures were selected that were specifically impaired in participants with negative symptoms in a previous study or were theoretically predicted to be specifically impaired in people with negative symptoms.27, 29

Working Memory. Verbal working memory was assessed using the Letter Number Span Task (scaled score).38–39 Working memory was defined as the ability to hold information in memory for conscious processing and manipulation.40

Response Initiation–Inhibition. Verbal response initiation–inhibition was evaluated using 2 measures. Response initiation was assessed using the Phonological Fluency Test (total number of correct words).41 Response inhibition was assessed using the Hayling task (error scaled score).42 Participants were required to complete sentences presented orally, with a single word that made no sense at all in the context of the sentence. Meaningful and related completions contributed to an error score that reflected poor inhibition.

Strategy Use. Strategy use was assessed using 3 measures. Spatial strategy use was evaluated using the Key Search Task (profile score) from the Behavioural Assessment of the Dysexecutive Syndrome.43 Participants were required to draw a spatial search route to ensure finding lost keys within a paper representation of a field. A poorer profile score reflects a less organized search strategy.

Verbal strategy use was assessed using measures derived from the phonological fluency task (percentage of words using a phonemic strategy, percentage of words using a semantic strategy, number of clusters, and mean cluster length).44–46 Phonemic cluster words included successive words that differed by 1 letter, began with the same letter sound or 2 letters, or rhymed. Semantic cluster words are successive words that are linked by a superordinate semantic category, represent 2 forms of the same word, or form a common phrase. Verbal strategy use was also assessed using a strategy assessment from the Hayling task (strategy score).42 The measure was the percentage of meaningless sentence completions that encompassed a strategy of either reporting items visible in the room or reporting successive semantically related completions.

Community Function Measures. Community function was assessed directly using a supermarket shopping task, introduced by Hamera and Brown47–48 and shown to be reliable and ecologically valid in assessing real-life community living skills in schizophrenia. The task was adapted for the United Kingdom, and measures were taken to reflect those relevant executive processes thought to underlie performance. Participants were required to select the correct item, size, and cheapest alternative for each of 10 items presented on a shopping list. All normal shopping strategies, such as requesting help from staff, were allowed:

  • Accuracy was assessed through the total number of correct items, correct sizes, and lowest-price items selected.
  • Efficiency was evaluated using the time taken.
  • Redundancy of effort was calculated using the number of aisles entered above the minimum required when using the most efficient route.
  • Strategy was measured by the number of items selected when using an ordered progression through the aisles without entering unnecessary aisles.

Supermarkets were chosen from a single chain of stores with comparable store layout and selection of items. Participants were taken to a novel store in order to provide the greatest test of executive functions. Allocation of participants to stores was such that group, gender, IQ, and age distributions were similar across stores, and confounding of these effects with store effects was avoided.

Statistical Analyses
The main objective of the statistical analyses was to identify the differential effects of group membership and specific executive functions on community function.

Demographics and Clinical Data. One-way analyses of variance and chi-squared tests (for sex, category of illness length, proportion of atypical and cholinergic medication use) were employed to investigate group differences in sociodemographic and clinical characteristics and cognitive exclusion criteria.

Executive Functions. Group differences in executive functions were investigated using analyses of variance for continuous variables and Kruskall Wallis tests for discrete noncontinuous variables (Key Search profile score and Hayling error scaled score). The Hayling task verbal strategy score was arcsine transformed to approximate normality.

Community Functions. Group differences in community functions were investigated using generalized linear models,49 with group as a between-subject factor and model distribution specified according to the predetermined nature of the data, which were a 30-trial binomial distribution with logit link for accuracy and an equivalent 10-trial distribution for the strategy measure, a Poisson distribution with log link for redundancy, and a normal distribution with identity link for efficiency.

Model Building. The associations between community functions and cognitive measures were analyzed in 3 steps using generalized linear regression analyses and the distributions described above. Corrections were made for multiple group comparisons. Premorbid IQ was included throughout the analyses in order to investigate specific cognition–function relationships.

Step 1: Determining Which Variables Should Be in the Model. Relationships were tested across the whole group between community function measures and single executive and working memory impairments identified from the analysis of group differences.
Step 2: Determining Which Executive Process–Group Interactions Should Be in the Model. To identify community functions that were differentially predicted by executive processes in particular groups, individual executive function–group interaction terms were entered into the regression analyses, in addition to the main effects of group and of executive processes from previous analyses. Potential moderator effects were thus identified.
Step 3: Final Model With All Significant Process and Process–Group Interactions Included. The full regression model was constructed for each community function measure. All individual executive functions from step 1, and all group–cognitive function interactions identified at step 2 were included. For interactions between group and executive function, the associations between community measures and executive functions were further assessed for each group separately.

Systematic Analysis of Significant Process–Group Interactions. A possible explanation of the moderating effect of the negative group could be that executive function affects community function increasingly for more severe levels of executive impairments (a threshold effect). This was investigated for accuracy and verbal working memory. The negative group was divided into 2 subgroups with different levels of impairment. This resulted in 12 participants with severe working memory impairment (at least 2 standard deviations below the average standard score) and 16 participants with moderate to intact working memory. If the level of impairment affected the association between working memory and community function, then this would suggest that the impairment factor had a moderating effect in the negative group.

Investigations of group differences in all analyses were adjusted for multiple group comparisons using Holm's Multistage Bonferroni procedure: the smallest p values were compared in series to 0.05/3, 0.05/2, or 0.05/1, depending on the number of remaining group comparisons.50 Demographic and executive functions were investigated using the Statistical Package for the Social Sciences (version 10).51 Community function and association analyses were investigated in STATA (version 7).52


   Results
Top
 Abstract
 Introduction
 Method
 Results
Discussion
 References
 
Demographics
Sociodemographic, clinical, and cognitive data are presented in table 1. By definition, the schizophrenia groups differed due to group selection on negative, general, and total psychopathology. The groups were balanced for premorbid IQ, age, sex, and years of education and did not differ clinically or statistically on any other measure. Importantly, the schizophrenia groups were also balanced for IQ and broad memory, executive, and social behavior measures.


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  		Table 1. Sociodemographic, Cognitive, and Clinical Characteristics

 
Do the Schizophrenia Groups Differ on Executive Functions?
Executive measures have been linked to negative symptoms and therefore should be specifically impaired in the negative group compared to the non-negative group and healthy controls. The groups differed in verbal working memory performance (F[2,72] = 8.67, p < .001), with the negative group being significantly impaired compared to controls (p < .001 compared to 0.05/3). The non-negative group showed a trend toward greater impairment than controls (p = .026 compared to 0.05/2) and did not differ significantly from the negative group (p = .061 compared to 0.05/1). The groups also differed in verbal response initiation (F[2,72] = 3.17, p = .048), with a trend for impairment in the negative group relative to controls (p = .022 compared to 0.05/3) and a similar level of impairment in the non-negative group relative to controls (p = .044 compared to 0.05/2). Finally, the groups differed in spatial strategy use (X2[2] = 16.3, p < .001), with greater impairment in the negative group compared to each other group (for controls, p < .001 compared to 0.05/3; for non-negative, p = .007 compared to 0.05/2) but no difference between the non-negative group and controls (p = .36; see figure 1). There were no significant group differences for the remaining executive measures.



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  		Fig. 1. Group Differences in Executive Functions. The graphs present the mean score and standard error bars for each group.

 
Are There Differences in Community Function Between the Groups?
People with negative symptoms have poor functional outcome and specific impairments in working memory, strategy, and initiation processes that may underlie this poor function. For these reasons, people with schizophrenia and negative symptoms were predicted to perform less well on community function measures than either the comparison schizophrenia group or healthy controls. Table 2 presents the group comparisons on community function measures adjusted for multiple group comparisons.


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  		Table 2. Group Differences in Outcome Measures on the Supermarket Shopping Task

 

Accuracy. The negative group was significantly less accurate in selecting items correctly than either the non-negative schizophrenia group or healthy controls (see table 2). The nonnegative group was also significantly less accurate than controls. Overall, the negative participants were less than half as likely as controls to accurately select items.

Efficiency, Redundancy, and Strategy Measures. The negative group also completed the task less efficiently and more slowly, with increased redundancy and poorer strategy use, compared to both the non-negative group and controls. The non-negative group demonstrated significantly poorer strategy use than controls but showed less redundancy, in that they entered significantly fewer aisles above the minimum. Overall, controls were 4 times more likely and non-negative participants were twice as likely to use a strategy compared to negative participants. Negative participants were likely to enter twice as many aisles above minimum as controls and nearly 3 times as many as non-negative participants (see table 2).

Hence, despite similar IQ and general cognitive function, the negative group performed more poorly than the non-negative group on all community function measures. General cognitive function cannot, therefore, account for all the differences between groups in community function. The next set of analyses therefore investigated whether specific executive functions, which are impaired in the negative group, can account for these differences.

Model Building

Step 1: Which Executive Impairments Predict Community Function Impairments? Regressions of single executive function variables on community function measures were undertaken across the whole group to identify executive processes that could account for community function impairments. These are shown in table 3. The direction of the correlations across the groups is as predicted, such that the overall odds ratios predict that higher cognitive function is associated with better performance. All individual associations between cognitive and functional measures were significant.


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  		Table 3. Model Building Steps 1 and 2—Executive and Premorbid Predictors of Community Function in Individual Analyses

 
Step 2: Which Executive Impairments Interact With Group in Predicting Community Function? In order to test whether executive function measures interact with group, individual executive function–group interaction terms were entered into the regression models in addition to significant predictors from step 1. Working memory interacted with group membership for most investigated measures (accuracy: X2[2] = 22.5, p < .001; redundancy: X2[2] = 13.0, p = .0015; strategy: X2[2] = 9.2, p =.01) and is thus a particularly strong contender for a differential group effect in predicting community function. Premorbid IQ also interacted with group membership for 2 measures (accuracy: X2[2] = 7.9, p = .02; strategy: X2[2] = 6.4, p = .04), spatial strategy for 1 measure (redundancy: X2[2] = 6.2, p = .045), and response initiation for 1 measure (redundancy: X2[2] = 32.4, p < .001). These significant interactions between cognitive measures and group are indicated by a double asterisk in table 3.
Step 3: Which Executive Functions Independently Predict Community Function Either Differentially Within a Particular Group or Within All Groups? The final model for each community function measure included both the significant predictor main effects from step 1 and the significant interaction terms from step 2. The results are presented in table 4. When a predictor effect interacted with group, this effect was assessed separately for each group.


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  		Table 4. Final Model (Step 3)—Core Independent Predictors of Community Function

 
Two cognitive processes were each predictive of community functioning across the groups: poor working memory predicted less efficient community function, and poor spatial strategy use predicted less accurate community function. These cognitive measures were predictive despite being independent from the real-life supermarket context.

In addition, numerous cognitive processes were shown to be independently predictive of community function only within particular groups. Importantly, poor working memory was a highly significant independent predictor of inaccurate community function, and low premorbid IQ was a specific independent predictor of inefficiency only in the negative group. Good working memory also significantly predicted better aisle strategy use only in controls, although the same pattern was found in the negative group. Response initiation predicted redundancy in controls, with a trend also in the negative group, but the associations were in opposite directions. In the latter association, the same underlying relationship may have operated differently in the different groups. In the negative group, whose search strategies were poorer, better response initiation may have contributed to more active searches and less redundancy, but in controls, whose search strategies were already superior, better response initiation may have reflected higher self-motivated sustained attention resulting in longer searches and greater redundancy. There were no independent cognitive predictors of community function within the non-negative group.

Are the Associations in the Negative Group due to the Greater Prevalence of Severe Executive Impairments in This Group?
The possibility of a threshold effect was investigated. Executive function may be related to community functioning only where these executive impairments are marked, as in the negative syndrome. Within the negative group, and for the selected community function measure (accuracy), the interaction between the impairment factor (marked versus moderate–intact working memory impairment group) and the working memory–community function relationship was not significant (z = 0.98, p = .33). Contrary to the case in a threshold model, the effect of working memory on community functioning was not stronger in the marked impairment subgroup compared to the moderate–intact subgroup. In fact, the odds of accurately selecting an item were estimated to increase by 22% for every unit change in working memory score in the moderate–intact group but only by 11% in the marked impairment group. Also counter to a simple threshold model, 50% of participants with marked impairment but no negative symptoms (n = 8) demonstrated good community functioning within half a standard deviation of controls and above the negative group mean. Indeed, the poorest working memory span in the absence of negative symptoms coincided with intact community functioning above the control mean. Negative symptoms alone with intact working memory (n = 6) were also associated with good community functioning above the negative group mean and within half a standard deviation of the control group mean. Hence, working memory impairment in the absence of negative symptoms did not necessarily confer poor outcome, and many of those with marked working memory impairment alone performed well on the community functioning task.


   Discussion
Top
 Abstract
 Introduction
 Method
 Results
 Discussion
References
 
This study revealed 2 distinct and important mechanisms through which cognition and/or symptoms are related to poor community function in schizophrenia. These are, first, direct associations between specific cognitive impairments and community functions and, second, a synergistic interaction between negative symptoms and cognition in predicting community function. The negative group was associated both with specific verbal working memory and executive impairments and with impairments in a direct and ecologically valid measure of real-life community function when compared to non-negative schizophrenia and healthy controls. These impairments were independent of global cognitive deficits, as, on the whole, they were not present in the non-negative group despite the equivalent IQ, general memory, and general executive function in this group. The results pave the way for a more refined consideration of the mechanism by which negative symptoms and executive processes contribute to community functioning.

In the first mechanism, specific cognitive impairments were directly associated with specific aspects of poor community function. People who had trouble in an empirical task with drawing a spatial search strategy to locate a hypothetical lost item within a designated space were also less accurate in a real-life supermarket environment in locating and selecting items correctly. In addition, people who were less accurate at holding and manipulating information in working memory were less efficient and took significantly longer to complete the community function task. While numerous studies have demonstrated links between cognition and community function1–2 and even between cognition and real-life skills such as grocery shopping,48 this study is unique in demonstrating such close links between similar underlying processes on both empirical and real-life tasks. Both working memory and strategic processes would appear to be ideal candidates for cognitive remediation therapy, in order to enhance generalization to the real world.

In terms of mechanisms derived from the literature (see figure 2), cognition and negative symptoms may contribute to community function independently (model 1).14 Cognition may contribute to community functioning directly, while symptoms are associated only indirectly through their link with cognition (model 2), or indeed the reverse may occur so that cognition only associates indirectly to community functioning through symptoms (model 3).5 The mechanism thus far is similar to that reported by previous researchers, in that a direct association is demonstrated across all groups between cognition and community function. This study extends current knowledge, however, by demonstrating that this mechanism occurs for cognitive predictors that are theoretically and empirically linked to negative symptoms. Since impairments in these processes are greater in people with negative symptoms, these people are significantly less skilled in the cognitive processes that underlie community functioning and so do less well (model 2 or 3).



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  		Fig. 2. Models of Hypothetical Relationships Among Cognitive Function, Negative Symptoms, and Community Function.

 
However, the second and perhaps more important mechanism is the previously undocumented role of negative symptoms as a moderator of the relationship between cognitive impairments (particularly working memory) and poor community functioning in schizophrenia. The moderator effect reflected the specific association between cognition and community function only in people with negative but not non-negative schizophrenia. The interaction between working memory and symptoms in the current study is not consistent with independent contributions from cognition and symptoms to community function (model 1). Neither is it consistent with indirect contributions of symptoms or cognition to community function (models 2–3).

Several mechanisms may explain the interaction between cognition and the negative symptom group. Working memory impairments may be particularly marked in schizophrenia with negative symptoms, and only these marked impairments then predict poor community function (an adaptation of model 2). This explanation seems unlikely, however, as there was no interaction between the severity of impairment (marked versus moderate–intact) and cognition on community function in the negative group. In fact, cognition was a somewhat stronger predictor of community function in the group with moderate–intact cognition. This suggests that, if anything, symptoms play a greater role where impairments are milder. So, the effect was not a simple threshold effect, since the most cognitively impaired people in the negative group did not perform the least well on community functions.

Negative symptoms may, instead, bestow some additional contribution to the relationship between cognition and function found in this group. A mechanism for this interaction is suggested by a consideration of working memory capacity and function, which are governed both by general ability and by domain-specific experience. Domain-specific experience enhances working memory capacity in experts compared to novices, across such spheres as professional chess and academic performance.54–57 Experience may increase working memory capacity by providing a broader knowledge base and so promoting enhanced "chunking" and organization of domain-specific information in working memory through the development of new cognitive schemata.58 Reduced active participation across a varied array of community, social, and occupational experiences, as a result of negative symptoms, may create exactly this division in "expertise" between negative and non-negative schizophrenia and controls. This will, in turn, lead to even poorer domain-specific working memory and community function. The significant association between good working memory and good strategy use only in the control group may reflect the opposite "expert" end of this continuum.

Hence, the current data are consistent with symptoms acting as a true moderator of the relationship between cognition and community functioning (model 4). It is proposed that a synergistic interaction between working memory and negative symptoms arrests the normal development of working memory mechanisms within particular domains, through the curtailing of appropriate domain-specific experiences. This synergy between symptoms and working memory impairment produces the poorest community functioning. It may also have the greatest impact where the core impairment is milder and where environmental effects can have a greater effect.

This second mechanism provides further significant clinical implications. The interaction of negative symptoms with poor working memory may gradually expand the divide between novice and expert working memory, leading to a progressive disruption of community and other functional domains and a more chronic disorder. According to this mechanism, programs that address poor functional outcome should target both cognition and negative symptoms early in the disorder. A wider and more immersed experience of community function may break the synergistic link between negative symptoms and cognition to promote a more adaptive functional outcome.

There are several limitations to the current study. Supermarket shopping is a narrow domain of community function, and the target processes for remediation may not generalize to other aspects of community living. Furthermore, the current cognitive processes predict baseline function. It is unclear whether change in these cognitive processes will predict change in functioning. Both cognitive processes and mechanisms are identified, however, which are specific to a particular target group and which can be investigated further. The dynamic nature of the interaction model, in particular, provides both a process and a mechanism by which change may occur. The study controlled for multiple group comparisons but not for multiple correlations between cognition and community function. This was deliberate in order to capture all valid mechanisms, but the possibility of Type I errors is thus greater. The findings require replication, but, nevertheless, many of the results including the moderating effect of negative symptoms on the working memory–community function relationship were particularly robust and were highly significant.

In conclusion, this study provides strong evidence that influencing real-world community function in schizophrenia may require a more complex approach than simple remediation of cognition in general across all people. Rather, the study supports several distinct cognitive processes and mechanisms, moderated by negative symptoms, which may be active simultaneously and which predict the exceptionally poor community function in people with schizophrenia and negative symptoms. Targeting these processes and mechanisms in conjunction with their moderating symptoms will provide the greatest opportunity for cognitive remediation therapy to improve community function in the real world.


  Footnotes
 
To whom correspondence should be addressed; tel: +44 (0) 207 919 2983, fax: +44 (0) 207 919 2473, e-mail: k.greenwood{at}iop.kcl.ac.uk.


   Acknowledgments
 
This study was supported by a grant, RFG 757, from the Department of Health. We would like to thank Dr. Pall Matthiasson, M.D., MRCPsych, Division of Psychological Medicine, Institute of Psychiatry, London, for his diagnosis and symptom assessments for people with schizophrenia. Earlier forms of this work have been presented at the Society for Research in Psychopathology, San Francisco, September 2002; the International Congress of Schizophrenia Research and Sixth Biennial Mt. Sinai Conference on Cognition in Schizophrenia, Colorado Springs, Colo., April 2003; and the Fifth International Conference on Psychological Treatments for Schizophrenia, Oxford, September 2003.


   References
Top
 Abstract
 Introduction
 Method
 Results
 Discussion
 References
 

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