Commissions and Omissions Are Dissociable Aspects of Everyday Action Impairment in Schizophrenia

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1 Journal of the International Neuropsychological Society (2014), 20, Copyright INS. Published by Cambridge University Press, doi: /s Commissions and Omissions Are Dissociable Aspects of Everyday Action Impairment in Schizophrenia Kathryn N. Devlin, Tania Giovannetti, Rachel K. Kessler, AND Molly J. Fanning Department of Psychology, Temple University, Philadelphia, Pennsylvania (RECEIVED July 3, 2013; FINAL REVISION June 15, 2014; ACCEPTED June 23, 2014; FIRST PUBLISHED ONLINE July 30, 2014) Abstract Prior research using performance-based assessment of functional impairment has informed a novel neuropsychological model of everyday action impairment in dementia in which omission errors (i.e., failure to complete task steps) dissociate from commission errors (i.e., inaccurate performance of task steps) and have unique neuropsychological correlates. However, this model has not been tested in other populations. The present study examined whether this model extends to schizophrenia. Fifty-four individuals with schizophrenia or schizoaffective disorder were administered a neuropsychological protocol and the Naturalistic Action Test (NAT), a performance-based measure of everyday action. A principal component analysis (PCA) was performed to examine the construct(s) comprising everyday action impairment, and correlations between the resultant component(s) and neuropsychological tests were examined. Results showed that omissions and a subset of commissions were distinct components of everyday action. However, results did not support unique associations between these components and specific neuropsychological measures. These findings extend the omission-commission model to schizophrenia and may have important implications for efficient assessment and effective rehabilitation of functional impairment, such as the potential efficacy of targeted interventions for the rehabilitation of omission and commission deficits in everyday functioning. Larger studies with prospective designs are needed to replicate the present preliminary findings. (JINS, 2014, 20, ) Keywords: Naturalistic action, Principal component analysis, Neuropsychology, Functional capacity, Disability, Psychotic disorders INTRODUCTION Diverse clinical populations ranging from dementia to schizophrenia exhibit functional impairments that are associated with considerable public health burden (Wu et al., 2005; Zhu et al., 2006). Functional impairment has often been examined via self- or caregiver-report questionnaires (Green, Kern, Braff, & Mintz, 2000), which provide only coarse and potentially biased assessments (Atkinson, Zibin, & Chuang, 1997; Zanetti, Geroldi, Frisoni, Bianchetti, & Trabucchi, 1999). These drawbacks limit the depth of our understanding of functional impairment and its treatment. By comparison, performance-based measures of everyday action provide detailed, objective assessment of functional errors, allowing for the conceptualization of impairment within a neuropsychological framework that may inform targeted interventions for specific functional disabilities. Correspondence and reprint requests to: Tania Giovannetti, Department of Psychology, Temple University, Weiss Hall, 1701 North 13th Street, Philadelphia, Pennsylvania tgio@temple.edu. The Naturalistic Action Test (NAT), a validated measure that examines an array of error types, including omissions and various commissions (Schwartz, Buxbaum, Ferraro, Veramonti, & Segal, 2003), has informed two neuropsychological theories of everyday action impairment: resource theory and the omission-commission model. According to the latter model, omission errors (i.e., failure to complete task steps) and commission errors (i.e., inaccurate performance of task steps) represent dissociable components of everyday functioning resulting from distinct underlying processes. Resource theory, by contrast, proposes that seemingly disparate errors arise from a unitary deficit in overall cognitive resources (Schwartz, 2006; Schwartz et al., 1998). Giovannetti et al. (2008) examined these theories in dementia using a principal component analysis (PCA) aimed at reducing various error types to their essential components. Results showed that omissions and a subset of commissions (sequence errors, perseverations, substitutions) comprised two separate, uncorrelated (r =.08) components of functional impairment. These components were associated with distinct neuropsychological domains, namely, commissions with executive 812

2 Everyday action impairment in schizophrenia 813 functioning and omissions with episodic memory and global cognition (Giovannetti et al., 2008, see also Giovannetti et al., 2012), and with distinct brain regions (Bailey, Kurby, Giovannetti, & Zacks, 2013; Seidel et al., 2013), suggesting that these error components are the result of separate underlying processes. In addition to their theoretical contributions, findings supporting the omission-commission model in dementia have important practical implications. Reducing numerous error types to two primary components may allow for efficient and optimal assessment and treatment of functional impairments. Evidence from the treatment of aphasia and other complex neuropsychological disorders suggests interventions may be most effective when matched to the specific demonstrated problem (Riddoch & Humphreys, 1994; Sohlberg & Mateer, 2001; Wilson, 1999). Because certain types of commissions (i.e., sequence errors, perseverations, and substitutions) appear to share a common underlying process in dementia, they are most efficiently examined and rehabilitated together rather than separately in this population. On the other hand, because omissions and commissions reflect distinct components of action impairment in dementia, they should continue to be assessed separately in this population and may benefit from distinct targeted interventions. Specifically, omissions may be prevented by interventions promoting recall and access of task goals (Bickerton, Humphreys, & Riddoch, 2006; Brennan, Giovannetti, Libon, Bettcher, & Duey, 2009), whereas commissions may be prevented with interventions that facilitate task organization by imposing environmental structure (Bickerton et al., 2006; Giovannetti et al., 2010) or promoting task monitoring (Bettcher et al., 2011; Levine et al., 2000, 2007; Robertson, 1996). However, the omission-commission model has thus far only been tested in dementia; therefore, it is unclear whether this model generalizes to other populations. Given the heterogeneity of functional and neuropsychological impairments across disorders, testing this model in other populations is crucial. The unique cognitive and functional profile of schizophrenia makes it a prime population in which to test the generalizability of the omission-commission model. Individuals with schizophrenia have demonstrated a higher proportion of NAT commissions (81% of total errors) and fewer omissions (19%), despite comparable total errors as individuals with dementia (Kessler, Giovannette, & MacMullen, 2007). This commissive pattern differed from that observed not only in dementia (41% omissions) but also in a range of diverse neurological populations, including brain injury and right and left hemisphere stroke (38%, 47%, and 44% omissions, respectively; Buxbaum, Schwartz, & Montgomery, 1998; Schwartz et al., 1998, 1999). This unique pattern of impairment may be attributable to schizophrenia s distinct neuropsychological profile, which differs from the amnestic profile that characterizes AD (Bilder et al., 2000). Among studies examining neuropsychological correlates of everyday action impairments in schizophrenia (Iampietro, Giovannetti, Drabick, & Kessler, 2012; Kessler et al., 2007; Rempfer, Hamera, Brown, & Cromwell, 2003; Semkovska, Bédard, Godbout, Limoge, & Stip, 2004; Zayat, Rempfer, Gajewski, & Brown, 2011), all have highlighted the role of executive function. For example, Kessler et al. (2007) showed that the commission errors characteristic of individuals with schizophrenia were associated with executive dysfunction. Semkovska et al. (2004) observed that various types of everyday action errors were more strongly related to executive dysfunction than to episodic memory impairment. This dysexecutive, commissive pattern of everyday action impairment in schizophrenia has lent support to an executive account of functional impairment in schizophrenia (Kessler et al., 2007), which posits that a unitary deficit in executive dysfunction underlies everyday action impairments. An examination of everyday action components in schizophrenia has the potential both to assess the validity of the omission-commission model and to deepen our understanding of the nature and causes of functional impairment in this population. If the omission-commission model generalizes, then functional impairment in schizophrenia may be best explained by this model or a variant thereof. Alternatively, everyday action impairment in schizophrenia might be better explained by resource theory, an executive account, or another model. Although several studies have examined functional impairment in schizophrenia with performance-based measures (Harvey, Velligan, & Bellack, 2007; Harvey et al., 2009, 2013; Kessler et al., 2007; Klapow et al., 1997; Rempfer et al., 2003; Semkovska et al., 2004; Seter, Giovannetti, Kessler, & Worth, 2011; Zayat et al., 2011), to our knowledge none have examined empirically-defined components of everyday action impairment using data reduction techniques (e.g., PCA). Several studies have used gross measures that do not capture the nuances of functional impairment (e.g., Harvey et al., 2007, 2009; Klapow et al., 1997). Others have used a large number of detailed error measures (e.g., Kessler et al., 2007; Semkovska et al., 2004), which may be inefficient. Previous publications using the NAT in schizophrenia (Iampietro et al., 2012; Kessler et al., 2007) have analyzed omissions and commissions separately and have analyzed action-additions, perseverations, substitutions, and sequence errors together as a unitary category of commissions without empirical support for these error groupings in this population. Reducing a wide range of action errors to their empirically-defined components is, therefore, essential for efficient and accurate assessment of everyday action in schizophrenia. Thus far, there is mixed evidence regarding whether specific aspects of everyday action impairments in schizophrenia have unique neuropsychological correlates. Although Kessler et al. (2007) reported a predominantly commissive error pattern in schizophrenia, which was associated with a characteristic executive impairment, omissions nonetheless occurred in this sample in association with global cognitive impairment, providing preliminary support for the omission-commission model. Analyses examining relations between a priori-defined components of everyday action performance (i.e., accuracy and efficiency) and neuropsychological measures have broadly supported associations between accuracy and processing

3 814 K.N. Devlin et al. speed/working memory, and between efficiency and executive functions (e.g., planning, set-shifting; Rempfer et al., 2003; Zayat et al., 2011), further supporting the existence of distinct components of action impairment in schizophrenia. Nevertheless, these components neuropsychological correlates also overlap substantially, with roughly as many shared correlates (including memory and executive function) as unique predictors (Rempfer et al., 2003; Zayat et al., 2011). Similarly, in another study (Semkovska et al., 2004), specific error types had both distinct and overlapping neuropsychological correlates. Given these discrepancies, it is necessary to clarify whether empirically identified everyday action error components show unique or common neuropsychological correlates in schizophrenia. The purpose of this study was to examine the component structure of everyday action errors in schizophrenia to enhance our understanding of the nature and causes of functional impairment in this population, enable meaningful and efficient assessment, and inform intervention strategies. We evaluated whether the omission-commission model, developed in dementia, could be extended to understand functional impairments in schizophrenia. We examined a range of errors made by individuals with schizophrenia on a performance-based test of everyday action, used PCA to reduce these errors to their principal components, and correlated resultant components with measures of global cognition and executive function. Given prior findings (Giovannetti et al., 2008, 2012; Iampietro et al., 2012; Kessler et al., 2007; Rempfer et al., 2003; Zayat et al., 2011), we hypothesized the PCA would yield at least two components reflecting the omission-commission distinction. We predicted these components would be associated with distinct neuropsychological functions, with commissions relating to executive function and omissions relating to global cognition. METHODS Participants Participants (N = 54) were recruited from inpatient units at two local hospitals for a study of environmental adaptations (n = 38) or a study of goal management therapy (n = 16). All individuals met Diagnostic and Statistical Manual of Mental Disorders Fourth Edition, Text Revision (American Psychiatric Association, 2000) criteria for schizophrenia or schizoaffective disorder, determined through chart review and structured diagnostic interview. When disagreement arose between charts and structured interview (n = 3), diagnoses were determined from the structured interview. Participants also met the following inclusion criteria: no substance abuse in the past month; no history of traumatic brain injury or neurological disorder (e.g., stroke, epilepsy); and no mental retardation, defined as verbal and nonverbal IQ scores < 70 on the Kaufman Brief Intelligence Test Second Edition (Kaufman and Kaufman, 2004). All participants spoke English and were taking antipsychotic medication. Procedures Research was conducted in accordance with Temple University s Institutional Review Board and the Declaration of Helsinki. Participants signed approved consent forms and received financial compensation for participation. Measures were administered in two to three sessions over 1 to 4 weeks to minimize fatigue. NAT Procedures The NAT requires participants to perform three everyday tasks with little guidance from the examiner: (1) prepare toast with butter and jelly and coffee with cream and sugar; (2) wrap a gift while distractor objects (e.g., gardening clippers for scissors) are available on the table; and (3) pack a lunch box with a sandwich, snack, and drink and pack a school bag with supplies for school, while several necessary objects are stored out of view in a drawer with potentially distracting objects. Instructions, object placement, cueing procedures, and scoring are standardized and described in the test manual (Schwartz et al., 2003). The NAT was developed for use with inpatient rehabilitation populations (i.e., brain injury and stroke) and has sound psychometric properties in these populations (Buxbaum, Schwartz, & Montgomery, 1998; Schwartz et al., 1998, 1999, 2003; Schwartz, Segal, Veramonti, Ferraro, & Buxbaum, 2002) and in schizophrenia (Kessler et al., 2007). Prior studies have shown NAT scores are not affected by education, gender, or motor difficulties (Schwartz et al., 2002, 2003). A previous study of a heterogeneous dementia sample (n = 51) has demonstrated significant correlations between NAT variables and caregiver-reported activities of daily living (Giovannetti, 2006; Giovannetti, Libon, Buxbaum, & Schwartz, 2002). NAT Scoring Procedures Performance was videotaped for subsequent scoring. The following scores were obtained according to the procedures outlined in the test manual and prior publications (Buxbaum et al., 1998; Giovannetti et al., 2002, 2008; Schwartz et al., 1998, 1999, 2003): Accomplishment Score: Percentage of task steps completed with or without error (range = 0 100). NAT Score: Accomplishment Score combined with a sum of key errors that reliably distinguish patient from healthy populations. A score ranging from 0 (Accomplishment Score <50% and 0 errors) to 6 (Accomplishment Score = 100% and <2 errors) is assigned to each NAT item and summed to equal the NAT Score (range = 0 18). According to older adult norms, a NAT Score <14 indicates impairment (Sestito, Schmidt, Gallo, Giovannetti, & Libon, 2005). Comprehensive Error Score (CES): Total number of errors, including omissions and commissions. Table 1 describes all error categories. Neuropsychological Assessment Participants completed neuropsychological tests (described in Table 2) selected for their relation to everyday action errors

4 Everyday action impairment in schizophrenia 815 Table 1. NAT Comprehensive error score categories Error category Definition Examples Omission A step or subtask is not performed Does not add sugar to coffee Commission a Substitution Semantically related or perceptually similar alternate object Spreads butter on toast with spoon instead of knife used in place of target object Sequence Anticipation of a step which entails a subsequent omission (anticipation-omission), steps or subtasks are performed in Applies butter on bread, without first toasting bread; applies jelly on bread, then applies butter reverse order (reversal) Perseveration A step or subtask is performed more than once; an action is Toasts multiple slices of bread performed repetitively or for an excessive amount of time Action-addition Performance of an action not readily interpreted as a task step Adds butter, jelly, and coffee grinds to toast Quality Task performance is grossly inadequate Pours too much cream into coffee so that the cup overflows Gesture substitution Correct object is used, but with an inappropriate gesture Grasps knife incorrectly Spatial misorientation Object is misoriented relative to the participant s hand or Misorients wrapping paper with respect to the gift another object Spatial misestimation The spatial relationship between objects is incorrect Cuts too small a piece of wrapping paper Tool omission A task step is performed without the appropriate object or tool Rips wrapping paper (i.e., does not use scissors); stirs coffee with finger instead of spoon Note. Reprinted with permission from Kessler, R.K., Giovannetti, T., & MacMullen, L.R. (2007). Everyday action in schizophrenia: performance patterns and underlying cognitive mechanisms. Neuropsychology, American Psychological Association, 21(4), a Commission errors entail instances when a task step is inaccurately preformed or an extra, off-task step is performed. and sensitivity to executive dysfunction in schizophrenia (Giovannetti et al., 2008; Iampietro et al., 2012; Kessler et al., 2007; Rempfer et al., 2003; Semkovska et al., 2004; Zayat et al., 2011). Design and Statistical Analyses This study used a single-group, cross-sectional, retrospective design with data from two different studies. First, correlations and exploratory PCA were performed to examine relations among NAT error types. Spearman Rank Order Correlations (r s ) were performed because most NAT variables were not normally distributed. Alpha for all comparisons was set at.05 (two-tailed). PCA was performed with eigenvalue criterion >1 to determine the number of components and with varimax rotation to simplify interpretation. Second, correlations between NAT component(s) and neuropsychological tests were examined. Approximately one-third of the sample (n = 20) had missing neuropsychological data; the 16 participants in the goal management study did not complete the neuropsychological tests examined here, and four participants in the environmental adaptations study were unable to complete either the Trail Making Test (n = 1), Zoo Map Test (n = 2), or Digit Span Test (n = 1) due to inability to understand task requirements. RESULTS Sample Characteristics On average, participants were 42 years old (SD = 11.3; range = years) and had completed 12 years of education (SD = 2.2; range = 7 18 years). Women comprised approximately half the sample (48%; n = 26). Average IQ was (SD = 10.72). Participants recruited for the two studies did not differ in age, gender, education, IQ, or overall NAT errors (all p >.05). Mean MMSE score was 25.8 (SD = 2.1; range = 20 30), suggesting normal to mildly impaired global cognition. Neuropsychological performance is reported in Table 3. NAT Performance NAT performance is shown in Table 4. Mean NAT score fell within the impaired range relative to published norms, with 53% of the sample demonstrating impaired performance (i.e., > 2 SD below norms; Kessler et al., 2007). As described previously, Accomplishment Scores were high, and the distribution of error types differed from that observed in other clinical populations (Kessler et al., 2007). Participants made very few quality, gesture substitution, spatial misorientation and misestimation, and tool omission errors. As in prior studies (Giovannetti et al., 2008; Kessler et al., 2007), we combined these errors into a category called other but did not include this category in subsequent analyses because of its infrequency and heterogeneity. Correlations and PCA of NAT Error Types Correlations among NAT error variables revealed a significant association between action-additions and sequence errors, both types of commissions (see Table 5). The appropriateness of PCA was supported by the Kaiser-Meyer-Olkin measure of sampling adequacy (0.58) and Bartlett s test of

5 816 K.N. Devlin et al. Table 2. Neuropsychological protocol Targeted function Test Description Reference Global function Mini-Mental State Examination (MMSE) Dependent variable is a summary score on 11 items in the domains of orientation, attention/calculation, recall, language, and visuoconstruction. Possible range: Language D-KEFS Category Fluency Dependent variable is the number of animals produced in 60 seconds. Initiation D-KEFS Letter Fluency Dependent variable is the total number of words produced in 60 seconds beginning with F, A, or S, excluding proper nouns. Cognitive D-KEFS Trail Making Test, Participants switch between connecting numbers and letters in Flexibility Switching Condition sequential order. Dependent variable is time to completion (seconds). Inhibition D-KEFS Color-Word Participants name the dissonant ink color of written color words. Interference Test Dependent variable is time to completion (seconds). Planning BADS Zoo Map Test Participants indicate how they would visit a series of designated locations on a map of a zoo while abiding by a set of specified rules. Dependent variable reflects planning accuracy and rule violations. Possible range: 0-4. Working Memory WAIS-III Digit Span Backwards Repetition of orally presented numbers backward. Dependent variable is the scaled score for the number of correct trials. Possible range: Folstein, Folstein, & McHugh, 1975 Delis, Kaplan, & Kramer, 2001 Delis et al., 2001 Delis et al., 2001 Delis et al., 2001 Wilson, Alderman, Burgess, Emslie, & Evans, 1996 Wechsler, 1997 Note. BADS = Behavioural Assessment of the Dysexecutive Syndrome; D-KEFS = Delis Kaplan Executive Function System; WAIS III = Wechsler Adult Intelligence Scale Third Edition. Sphericity, χ 2 (10) = 29.69, p <.001. The ratio of cases to variables (10.8:1) was appropriately high. The PCA yielded a two-component solution accounting for 60% of the variance (Table 6). Sequence errors, perseverations, and actionadditions loaded on the first component and omissions on the second; substitutions loaded weakly (rotated loadings <.6) on both components, although somewhat more strongly on the second. Substitutions consistently fell between omissions and commissions in component plots (Figure 1). When performed without substitutions, the PCA yielded a two-component solution accounting for 71% of the variance. Sequence errors, perseverations, and additions loaded on the first component (rotated loadings =.80,.59, and.86, respectively) and omissions on the second (rotated loading =.93). A PCA with only participants who had complete neuropsychological data (n = 34) yielded similar results, a twocomponent solution accounting for 63% of the variance. Table 3. Mean neuropsychological test scores Test M (SD) MMSE (n = 38) (2.12) Category Fluency (n = 38) 6.02 (3.46) Letter Fluency (F, A, S) (n = 38) (9.89) Trail Making Test Switching (n = 37) (55.98) Color-Word Interference (n = 38) (37.00) Zoo Map Test (n = 36) 0.41 (1.29) Digit Span Backwards (n = 37) 4.16 (1.75) Note. MMSE = Mini-Mental State Examination. Sequence errors, perseverations, and additions loaded on the first component (rotated loadings =.83,.54, and.80, respectively) and omissions on the second (rotated loading =.89). Substitutions loaded weakly on both components, although somewhat more strongly on the first than on the second (rotated loadings =.51 and.35, respectively). Finally, because of the skewed distribution of NAT errors, a PCA was performed with log-transformed error variables and yielded similar results. A two-component solution accounting for 55% of the variance resulted. Sequence errors, perseverations, and additions loaded on the first component (rotated loadings =.70,.68, and.70, respectively) and Table 4. Mean naturalistic action test scores and distribution of error types (N = 54) M SD Minimum Maximum % of total errors a Accomplishment Score NAT Score Total CES Omissions Sequence Perseverations Substitutions Action-additions Other Note. NAT = Naturalistic Action Test; CES = Comprehensive Error Score. a Proportions calculated from the total sum of errors.

6 Everyday action impairment in schizophrenia 817 Table 5. Spearman rank order correlation coefficients among NAT error types (N = 54) Omissions Sequence Perseverations Substitutions Action-additions Sequence.02 Perseverations Substitutions Action-additions * Other Note. NAT = Naturalistic Action Test. *p <.05. omissions on the second (rotated loading =.80). Substitutions also loaded strongly on the second component (rotated loading =.70). After considering the results, we reasoned that substitutions should be analyzed separately from omissions and commissions. PCA results were interpreted as suggesting two primary components underlying NAT performance: commissions and omissions. The weak loading of substitutions on both components suggests substitutions may represent an additional component. Furthermore, correlations among these error types showed substitutions were not significantly correlated with either commissions (i.e., sequence, perseverations, and action-additions combined; r s =.09; p =.51) or omissions (r s =.11; p =.41). The correlation between omissions and commissions was also nonsignificant (r s =.14; p =.31). Thus, in subsequent analyses, sequence, perseveration, and action-addition errors were summed to form a single commission category. Omissions and substitutions were analyzed as separate categories. Relations among NAT Variables and Neuropsychological Test Scores Correlations among neuropsychological measures and NAT omissions, commissions, and substitutions are shown in Table 7. Commissions were associated with poorer performance on the Trail Making Test Switching Condition (p =.033). Omissions and substitutions were associated with poorer Zoo Map Test performance (p =.044 and p =.048, respectively). After Bonferroni correction for multiple comparisons, no correlations reached the significance threshold. Table 6. Rotated component matrix (N = 54) Component 1 Component 2 Omissions Sequence Perseverations Action-additions Substitutions Note. Boldface indicates values >.60. DISCUSSION The present study investigated the components of everyday action impairment in schizophrenia and their associated neuropsychological functions with the aims of furthering our understanding of functional impairment in this population and determining the generalizability of the omission-commission model, a neuropsychological model of functional impairment developed in dementia (Giovannetti et al., 2008). PCA yielded a two-component solution; perseverations, sequence errors, and action-additions (i.e., commissions) comprised the first, omissions comprised the second, and these components were not correlated with each other. These results are generally consistent with our findings with dementia patients (Giovannetti et al., 2008) and support the omissioncommission model; namely, omissions and commissions represent two dissociable components of everyday action errors. These findings are inconsistent with the resource theory, which predicts that everyday action errors would be reduced to a single component. The present study is notable in being the first to test the omission-commission model in a population other than dementia. Given the neuropsychological and functional dissimilarities between dementia and schizophrenia, the current findings lend support for the generalizability of the omissioncommission model across diverse clinical populations. One major difference between prior findings in dementia and the present findings is the emergence of substitutions as a separate error type, uncorrelated with either omissions or commissions but with a somewhat stronger loading on the omission component. By comparison, an analogous result was observed for action-additions in dementia. This difference may be attributable to these populations distinct neuropsychological profiles and suggests that although the omission-commission model is generally supported across populations, slight differences may emerge in the composition of the commission component, with sequence and perseverative errors consistently co-occurring across populations. This divergence emphasizes the importance of empirically defining action error components in different populations. The present findings are generally consistent with results from another performance-based measure of everyday action, the Test of Grocery Shopping Skills (TOGSS), in schizophrenia. This task yields separate, uncorrelated scores for accuracy and efficiency (Rempfer et al., 2003; Zayat et al., 2011). Although

7 818 K.N. Devlin et al. Fig. 1. Component loading plots obtained from the rotated (top) and unrotated (bottom) Principal Component Analyses of NAT Error Types. Both plots show perseverations, sequence, and additions (i.e., commissions) were closely clustered and distinct from omissions, with substitutions falling between commissions and omissions. scoring differences between the NAT and the TOGSS prevent direct comparisons, omissions and substitutions would generally be reflected in TOGSS accuracy scores, whereas perseverations, action-additions, and sequence errors would be reflected in efficiency scores. Therefore, prior studies support the notion that substitutions occur independently of other types of commissions and may have more underlying similarities with omissions in individuals with schizophrenia. By examining the neuropsychological correlates of everyday action components, we identified potential underlying cognitive origins of functional impairments. Commissions were significantly associated with impairments on the Trail Making Test Switching Condition, a measure of cognitive flexibility, whereas omissions and substitutions were significantly associated with impairments on the Zoo Map Test, a measure of planning. The association between commissions and executive dysfunction, specifically cognitive inflexibility, is consistent with prior findings in schizophrenia (Iampietro et al., 2012; Kessler et al., 2007; Semkovska et al., 2004) and other populations (e.g., Giovannetti et al., 2002, 2008), suggesting the ability to perform everyday tasks in the right sequence and to inhibit incorrect or repetitive actions is consistently related to executive control. The link between omissions and planning deficits is in contrast with earlier studies in populations such as dementia and stroke that have supported global cognition and episodic memory as the primary neuropsychological correlates of omissions (Buxbaum et al., 1998; Giovannetti et al., 2002, 2008; Kessler et al., 2007; Schwartz et al., 1998). On the other hand, this finding is consistent with prior evidence linking executive function with omissions in schizophrenia (Rempfer et al., 2003; Semkovska et al., 2004; Zayat et al., 2011). Furthermore, although global functioning was not significantly associated with any error component, the effect size was larger for commissions (r =.29) than omissions (r =.11), suggesting increased statistical power might have yielded a significant association between global functioning and commissions, not omissions. Together with existing literature, results suggest that relations between action errors and neuropsychological functions in schizophrenia differ from those observed in other populations and may reflect a greater contribution of executive function. Alternatively, omissions may be related to episodic memory in schizophrenia as observed previously in other populations, but our limited neuropsychological protocol precluded such a finding. Another key objective in examining the neuropsychological correlates of action components was to elucidate whether Table 7. Spearman rank order correlation coefficients among NAT error types and neuropsychological test scores Commissions Substitutions Omissions MMSE (n = 38) Category Fluency (n = 38) Letter Fluency (F, A, S) (n = 38) Trail Making Test Switching (n = 37).35* Color-Word Interference (n = 38) Zoo Map Test (n = 36).26.33*.34* Digit Span Backwards (n = 37) Note. NAT = Naturalistic Action Test; MMSE = Mini-Mental State Examination. *p <.05.

8 Everyday action impairment in schizophrenia 819 each component is associated with distinct cognitive functions. Although omissions and commissions were associated with different neuropsychological measures, there was insufficient evidence to support a dissociation. First, the Zoo Map Test and the Trail Making Test, which were significantly associated with omissions and commissions, respectively, are both complex executive function measures. Second, several small correlations failed to reach significance, possibly because of limited statistical power. Notably, the Zoo Map Test was associated with commissions (r =.26; p =.12) and the Trail Making Test with omissions (r =.26; p =.12), and these correlations did not differ meaningfully from those that did reach statistical significance (e.g., Zoo Map Test with omissions, r =.34, and substitutions, r =.33; Trail Making Test with commissions, r =.35), suggesting these action components may actually be associated with shared neuropsychological functions. Finally, correction for multiple comparisons suggests a lack of distinct neuropsychological correlates, an interpretation consistent with other studies of schizophrenia (Iampietro et al., 2012; Zayat et al., 2011). In fact, support for unique neuropsychological correlates of specific action components in schizophrenia has been mixed (Rempfer et al., 2003; Semkovska et al., 2004; Zayat et al., 2011), with distinct and overlapping neuropsychological correlates reported with roughly equal frequency. The present findings may be interpreted to suggest that neuropsychological measures are not sufficiently sensitive to discriminate the different types of functional impairment in schizophrenia. Another aim in identifying components of functional impairment in schizophrenia was to inform efficient and optimal assessment and treatment of functional deficits in this population. To our knowledge, this study is the first to use data reduction to identify components of action errors in schizophrenia. Present findings suggest that sequence errors, perseverations, and action-additions appear to share a common underlying process and may, therefore, be most efficiently examined and treated altogether in schizophrenia. Omissions, a subset of commissions, and substitutions, on the other hand, should be assessed separately and targeted with separate intervention strategies in this population. This matching of intervention strategies to specific deficits has been proven most effective for other complex neuropsychological disorders (Riddoch & Humphreys, 1994; Sohlberg & Mateer, 2001; Wilson, 1999). Although further research is needed to examine the efficacy of targeted intervention strategies in schizophrenia, evidence from other populations suggests omissions may be reduced by interventions promoting recall and access of task goals (Brennan et al., 2009), commissions by interventions promoting task monitoring (Bickerton et al., 2006; Giovannetti et al., 2006, 2007), and substitutions by removing non-essential objects that are semantically related to task objects (Giovannetti et al., 2010). Another intervention approach may involve cognitive remediation, which has shown significant and lasting effects on cognition and functioning in this population (McGurk et al., 2007). Associations between action errors and executive dysfunction in the present sample suggest cognitive remediation of executive function may be an effective broad strategy for schizophrenia. However, the lack of discrete neuropsychological correlates of action errors in this sample suggests that intervention strategies based solely on neuropsychological deficits may not target the impairment of interest as effectively as intervention strategies matched to the specific profile of functional deficits. Detailed, performance-based measures of everyday action, with attention to omissive, commissive, and substitution profiles, may be more useful in identifying effective interventions that reduce functional impairment, caregiver burden, and public health costs. We acknowledge several limitations of the present study. First, analyses were retrospective and used data from two different prior studies, which may increase the possibility of spurious results. Still, the two subsamples were comparable in demographic, cognitive, and functional characteristics, and PCA results were analogous when excluding participants from the smaller study. The study s retrospective nature limited the neuropsychological protocol, which was originally selected to assess executive deficits central to schizophrenia; episodic and semantic memory, which are relevant to the omissioncommission model, were not assessed. The protocol may have restricted our ability to determine whether components of everyday action in schizophrenia have unique neuropsychological correlates. Nonetheless, we did include measures of global cognition and executive functioning, the neuropsychological functions most strongly associated with omission and commission components in dementia. Still, future studies should include a comprehensive protocol to better examine neuropsychological correlates of error components. Additionally, because of differing neuropsychological protocols of the parent studies, a third of participants were missing neuropsychological data, which further limited statistical power. Because these analyses were sufficiently powered to detect only moderate-to-large effects, and only large effects when controlling for multiple comparisons, they should be considered preliminary. In addition, although our data met the basic assumptions required for a PCA and maintained an appropriately high ratio of cases to variables, caution is nonetheless advisable when interpreting PCA results with n < 100. Thus, future studies with larger samples and prospective designs should look to replicate these preliminary findings. Finally, participants were inpatients with few real world functional demands; this precluded the possibility of examining whether error components have distinct real world functional correlates and may limit the generalizability of the present results to community-dwelling populations. Despite these limitations, a major strength of the present study is the use of the NAT, a well-researched, validated measure allowing for detailed analysis of errors in everyday action. In comparison with self- or caregiver-report questionnaires that may be prone to bias, the performance-based NAT provides a more objective, standardized measure of everyday action. In comparison with questionnaires and broader performance-based measures that provide only a gross assessment of functioning, the NAT assesses a wide range of error types that may be reduced to empirically-defined

9 820 K.N. Devlin et al. components, allowing for a more thorough understanding of the nature of everyday action impairment. In summary, our results support a model for everyday action impairment in schizophrenia comparable to that observed in dementia, in which omissions and commissions reflect distinct components of everyday action errors. Thus, the omission-commission model may apply to everyday action impairment across diverse clinical populations, although the specific error types comprising the commission component and the neuropsychological correlates of these components may differ across populations. These findings have important implications in schizophrenia and beyond for our understanding of the nature and causes of functional impairment, the meaningful and efficient assessment of everyday action, and the development of effective interventions, namely the use of separate intervention strategies for the treatment of omissive and commissive errors. 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