This is among the first studies, to our knowledge, to investigate the relative role of several domains of neurocognition, symptoms and treatment process variables for prediction of generalization of the effects of cognitive remediation to a measure of performance-based instrumental-life skills. These results demonstrate in a longitudinal design that neurocognitive skills predicted change in functional status after a one-year course of cognitive remediation in persons with schizophrenia even when variance attributable to symptoms, treatment intensity and duration, and crystallized verbal intelligence was controlled. More specifically, analysis of individual neurocognitive measures showed that auditory sustained attention and working memory was linked to functional status after the cognitive remediation trial and this link remained a significant predictor of change in functional status even when intercorrelations with other neurocognitive domains were controlled. Measures of positive and negative symptoms, verbal learning and memory, problem-solving, treatment intensity and duration, and crystallized verbal ability were not related to change in functional status after outpatient rehabilitation. These findings are particularly salient in that they do not simply suggest a link between neurocognitive skill and functional status, but instead suggest which cognitive skills are most predictive of the ability of patients with schizophrenia to capitalize on cognitive remediation programs consisting of computer-administered, extended drill-and-practice cognitive exercises organized hierarchically from simpler to more complex neurocognitive functions. The observation that the measure of auditory sustained attention and working memory selected for the current study (Digit Span ) remained a significant predictor of functional outcome at the end of the remediation trial even after including Vocabulary scaled scores in the stepwise regression model, suggests that these findings were not an epiphenomenon of estimated individual differences in global, verbal IQ.
Studies of predictors of response to cognitive remediation interventions to date in patients with schizophrenia are very small in number and have studied outcome measures that were a component of the remediation intervention itself (Fiszdon et al., 2005
), or have used heterogeneous samples that have included people with schizophrenia along with other diagnostic groups (Choi & Medalia, 2005
; Medalia et al., 2005
). Thus, an important feature of the current findings is that they provide a window on predictors of change as a function of remediation treatment on the ability to conduct basic life-skill tasks that are distal from the site of the remediation intervention in a homogenous sample of patients with schizophrenia/schizoaffective disorder.
One interpretation of the current findings is that impairment in basic sustained auditory attention and working memory interferes with the ability to learn cognitive tasks in cognitive remediation, making acquisition of skills slower and more laborious than patients with less impaired sustained auditory attention. These findings also suggest that the integrity of simple aspects of neurocognition are crucial for acquisition of more complex, multifactorial neurocognitive skills trained in this type of comprehensive, hierarchically organized, sustained remediation intervention.
An important implication of the current results is that they suggest that individuals diagnosed with schizophrenia who receive more than 5 hours of cognitive remediation treatment per month do not show greater generalization to measures of everyday life skills than those individuals diagnosed with schizophrenia receiving less than 5 hours of treatment per month. Similarly, individuals diagnosed with schizophrenia treated with over 50 hours of cognitive remediation do not show greater benefit than those receiving less than 50 hours of treatment. We note that the failure to find effects of treatment intensity or duration on outcome of cognitive remediation in the current report is discrepant from those reported by Choi and Medalia (2005)
. Two explanations for the source of this inconsistency in findings may be advanced. First, differences in proximity of outcome measures to the cognitive intervention selected for these respective studies may have lead to differing results. In the Choi and Medalia study, intensity was linked to performance on a test of clerical skill that was more closely allied with measures of sustained visual attention. Measures of work function, considerably more distal from the site of the cognitive intervention, did not show effects of treatment intensity. Similarly, the performance-based measure of everyday life-skills selected for the present study can be considered moderately distal from the target of the remediation intervention and thus, perhaps, less sensitive to the effects of remediation. Second, variation in treatment intensity was more restricted in the current study (mean=4.7 hours/month, SD=1.7) and the vast majority of participants in the current study would have been classified as “low intensity” in that study. Effects of treatment intensity might become evident with a subsample of patients receiving higher intensity treatment.
We also note that the failure to find relationships between treatment intensity and outcome in the current study is inconsistent with findings from the literature on Integrated Psychological Therapy (IPT) for schizophrenia which includes cognitive remediation as a crucial element of treatment (e.g., Roder et al., 2006
). Again, this discrepancy may be explained by the wider range of treatment intensity evident in those studies.
Several caveats to the current findings should be noted. First, the results of this study are of a group that provides guidance on which
neurocognitive variables may be linked to change in functional status as a result of remediation, rather than how
these variables impact functional status (i.e., whether sustained auditory attention has a direct or indirect effect on change in functional status). Larger sample sizes, coupled with the inclusion of additional, potential mediating variables, would be necessary to address these questions Second, some clinical researchers argue that meaningful clinical change on an outcome variable occurs when performance is elevated to a level after treatment that is indistinguishable from healthy controls (e.g., Kendall & Grove, 1988
). The absence of data on the UPSA from a demographically-matched, healthy control group precluded measurement of task normalization. Third, the current sample size of 36 participants is modest for a multiple regression analysis, and important relationships between study variables and changes in performance-based functioning as a result of rehabilitation may have been overlooked as a consequence. Fourth, cognitive remediation was not offered as a stand-alone treatment, but was administered as part of a more generalized outpatient rehabilitation program that included group therapy and daily goal formulation, as well as vocational counseling, exercise and individual therapy. Thus, as an observational study, predictors of change in functional capacity in this treatment trial could be linked to these other interventions in addition to cognitive remediation. Lastly, measures of performance-based everyday life skills have been criticized for serving as simply more ecologically-valid measures of neurocognitive skill, and thus links between neurocognitive skill and these measures may represent an artifact of method variance. Nonetheless, we note that while performance-based measures of everyday life skills undoubtedly require a host of neurocognitive skills, including sustained attention, memory and problem-solving, we have documented a selective relationship between only one aspect of neurocognition, auditory sustained attention and working memory, and the relationship was not with absolute level of everyday life skills but rather in change in everyday life skills over the course of a specific intervention. In summary, these results emphasize the importance of baseline auditory sustained attention and working memory as a predictor of acquisition of everyday life-skills for patients with schizophrenia enrolled in sustained programs of outpatient cognitive rehabilitation.