University of Massachusetts Boston ScholarWorks at UMass Boston Graduate Masters Theses Doctoral Dissertations and Masters Theses 12-31-2017 Examining Attentional Control and Processing Speed Deficits as Underlying Mechanisms of Neuropsychological Impairment in Schizophrenia Mayte Forte University of Massachusetts Boston Follow this and additional works at: https://scholarworks.edu/masters_theses Part of the Clinical Psychology Commons, and the Cognitive Psychology Commons Recommended Citation Forte, Mayte, "Examining Attentional Control and Processing Speed Deficits as Underlying Mechanisms of Neuropsychological Impairment in Schizophrenia" (2017). Graduate Masters Theses.edu/masters_theses/472 This Open Access Thesis is brought to you for free and open access by the Doctoral Dissertations and Masters Theses at ScholarWorks at UMass Boston. It has been accepted for inclusion in Graduate Masters Theses by an authorized administrator of ScholarWorks at UMass Boston. For more information, please contact library.
EXAMINING ATTENTIONAL CONTROL AND PROCESSING SPEED DEFICITS AS UNDERLYING MECHANISMS OF NEUROPSYCHOLOGICAL IMPAIRMENT IN SCHIZOPHRENIA A Thesis Presented by Mayte Forte Submitted to the Office of Graduate Studies, University of Massachusetts Boston, in partial fulfillment of the requirements for the degree of MASTER OF ARTS December 2017 Clinical Psychology Program © 2017 by Mayte Forte All rights reserved EXAMINING ATTENTIONAL CONTROL AND PROCESSING SPEED DEFICITS AS UNDERLYING MECHANISMS OF NEUROPSYCHOLOGICAL IMPAIRMENT IN SCHIZOPHRENIA A Thesis Presented by MAYTE FORTE Approved as to style and content by: ________________________________________________ Paul G. Nestor, Professor Chairperson of Committee ________________________________________________ Alice Carter, Professor Member ________________________________________________ Laurel Wainwright, Professor Member _________________________________________ David Pantalone, Program Director Clinical Psychology Program _________________________________________ Jane Adams, Chairperson Psychology Department ABSTRACT EXAMINING ATTENTIONAL CONTROL AND PROCESSING SPEED DEFICITS AS UNDERLYING MECHANISMS OF NEUROPSYCHOLOGICAL IMPAIRMENT IN SCHIZOPHRENIA December 2017 Mayte Forte, B. University of Massachusetts Boston Directed by Professor Paul G. Nestor Neuropsychological impairment is a key characteristic of schizophrenia (SZ), but its cognitive profile and underlying information processing mechanisms are not yet well understood.
We compare patterns of neuropsychological functioning in 85 persons with SZ and 76 healthy controls across measures of intelligence, memory, and executive function. We then test the hypothesis that neuropsychological impairment in SZ is related to dual deficits in two related but distinct information processes: processing speed and attentional control. All research participants completed Wechsler Adult Intelligence Scale-Third Edition (WAIS- III), Wechsler Memory Scale Third Edition (WMS-III), and Wisconsin Card Sorting Test (WCST), all of which provided measures of overall neuropsychological functioning. In addition, the neuropsychological battery included Trails B as a measure of attentional control and the WAIS-III Processing Speed Index (PSI).
We hypothesized that a) patients with SZ will show a distinct pattern within and across measures of intelligence, memory, and executive functioning and b) attentional control and processing speed will each uniquely account for a significant portion of the variance in neuropsychological functioning across iv these measures. Our findings showed that WAIS-III Verbal Comprehension Index performance was primarily predicted by a slower Processing Speed Index (PSI), accounting for 12.25 % of the variance, and to a lesser extent by higher perseverative errors in the WCST(PE), accounting for 6.76% of the variance in the Verbal Comprehension Index. Perceptual Organization Performance was similarly primarily predicted by WAIS-III- PSI, which uniquely accounted for 30.25% of the variance and to a lesser extent by WCST PE, uniquely accounting for 15.21% of the variance. WMS-III Immediate General Memory Index was primarily predicted by the WAIS-III (PSI), accounting for 7.29 % unique of the variance, followed by WCST PE, accounting for 5.
WMS-III Delayed General Memory performance was primarily predicted by WCST PE, uniquely accounting for 6.76% of the variance, yet PSI was not a significant predictor of the model in this domain. Overall, our study suggests that processing speed and secondarily attentional control mechanisms using the above proxy measures seem to account for unique portions of the variance in broad measures of overall intellectual functioning and declarative memory in SZ. v ACKNOWLEDGEMENTS First, I would like to thank the members of my master’s thesis committee Drs. Nestor, Alice Carter, and Laurel Wainwright, for their support and insightful feedback throughout this process.
I would like to express my deepest gratitude to my research mentor, Paul, for providing me with this valuable learning opportunity. His guidance, time, and support were much appreciated. I am also very grateful to the Nestor’s lab research team at the University of Massachusetts Boston, who previously collected the data analyzed for this project, as well as the many Veterans who participated in the larger longitudinal study. Lastly, I would like to thank my parents, Magali Forte and Jose Forte, for all their unconditional love and support, and my amazing partner, Jonathan, for his patience, and words of encouragement every step of the way.
I wouldn’t be where I am now without them cheering me on. Their endless support and infinite believe in my goals and aspirations mean the world to me. vi TABLE OF CONTENTS ABSTRACT. vi LIST OF TABLES.
viii CHAPTER Page 1. BACKGROUND AND SIGNIFICANCE. 1 Differential versus Generalized Impairment. 3 Working Memory and Schizophrenia: Underlying Mechanisms.
4 Attentional Control and Working Memory. 6 Processing Speed and Working Memory. 8 Attentional Control versus Processing Speed. 10 Relationship between Attentional Control, Processing Speed, and Outcomes Measures: Intelligence, Declarative Memory, and Executive Functions.
12 Wisconsin Card Sorting Test, Trails B Test, and Executive Functions. 16 Specific Aims & Hypotheses. RESEARCH DESIGN AND METHODS. 26 Descriptive Statistics and Preliminary Analyses.
26 Hierarchical Regressions Examining Attentional Control and Processing Speed Variables on General Intellectual Function and Memory Performance. 39 Performance on Measures of Attentional Control and Processing Speed. 40 Attentional Control, Processing Speed, and Perceptual Organization Index. 44 Declarative Memory Findings, Encoding, and Forgetting rates in Schizophrenia.
57 vii LIST OF TABLES Table Page 1.Demographics of Research Participants (N= 161) .Means and Standard Deviations of Test Performance on Neuropsychological Measures for all Participants (N=161) .Correlations of Trail Making Test and Wisconsin Card Sorting Test with Wechsler Intelligence Test subscales for Schizophrenia Group Participants (n=81) .Correlations of Trail Making Test and Wisconsin Card Sorting Test with Wechsler Memory Test subscales for Schizophrenia Group Participants (n=81). Summary of Hierarchical Regression (Model 4) Analysis for Variables Predicting Performance on Verbal Comprehension Index on SZ sample. Summary of Hierarchical Regression (Model 4) Analysis for Variables Predicting Performance on Perceptual Organization Index on SZ sample .Summary of Hierarchical Regression (Model 4) Analysis for Variables Predicting Performance on General Memory Index (Delayed) on SZ sample. Summary of Hierarchical Regression (Model 4) Analysis for Variables Predicting Performance on General Memory Index (Immediate) on SZ sample.
38 viii CHAPTER 1 BACKGROUND AND SIGNIFICANCE Introduction Cognitive impairment is a hallmark of schizophrenia. In fact, a key quantitative review consistently cited in the literature conducted by Heinrichs and Zakzanis (1998) found the largest mean effect sizes for cognitive deficits in SZ to be reflected in full scale IQ, verbal episodic memory, and executive performance. There seems to be variability in the magnitude of deficit across domains, yet deficits have been found to be long-standing and relatively stable, and do not seem to be affected by patient age or length of disease course (Li, 2004). In addition, studies have shown that deficits in declarative verbal memory are robust and stable across SZ samples, and are seen at different phases of the illness (Stone & Hsi, 2011).
Unaffected, first, and second-degree relatives of SZ have been found to perform less well than controls on multiple tests of verbal and non-verbal declarative memory (Whyte, McIntosh, Johnstone, & Lawrie, 2005) which suggests that these impairments may, in part, be genetically influenced (Ragland et al., 2009) or represent a possible endophenotype of the illness (Gottesman & Gould, 2003). Impairment in general intellectual ability in schizophrenia seems to be as severe as that observed in other neuropsychological functions, suggesting that specific impairment occurs in the context of a general intellectual impairment (Reichenberg & Harvey, 2007). Furthermore, as indicated by meta-analytic studies, the impairment in performance IQ is at least 50% larger than that observed for verbal IQ in schizophrenia. Relatedly, a study by MacCabe et al.
(2012) examining premorbid IQ and its relation to working memory, provides meaningful insights into the role of premorbid IQ in memory declines in SZ. Essentially, the results suggest that among patients with high premorbid IQ scores, working memory may be 1 a good predictor of post-onset decline, in which individuals with better working memory usually show less evidence of decline. Consequently, it is suggested that individuals with schizophrenia showing superior premorbid intellectual functioning show less decline than those with lower cognitive reserve, although a similar pattern of decline in cognition is observed in control samples, which tend to decline to a point similar to those of typical schizophrenia patients, but to a lesser extent. Relatedly, McCabe and colleagues (2012) further suggest that some of these patients seem to remain indistinguishable from healthy controls in most cognitive tests.
In contrast, Miyake et al. (2000) have argued that only the updating functions, which are encompassed by broader executive functions, predict intelligence in healthy controls. Executive function deficits are also among the most prominent cognitive impairments in SZ. Executive function deficits are seen through most stages of the disease (Orellana & Slachevsky, 2013) and include deficits in shifting mental sets, inhibition of the dominant responses, and updating working memory representations (Wongupparaj, Kumari, & Morris, 2015).
Mild to moderate impairments in executive functions has been found in patients with first-episode SZ, as well as their first-degree relatives and adolescents at risk (Orellana & Slachevsky, 2013). Executive function is mostly associated with the dorsolateral prefrontal cortex (PFC) and involved with voluntary control of behavioral responses (Orellana & Slachevsky, 2013). Declarative memory deficits have also been reported in schizophrenia. Specifically, meta-analytic findings examining the results of 110 studies found evidence of severe impairments in immediate and delayed verbal and nonverbal memory in schizophrenia (Cirillo & Seidman, 2003).
Of note, the most severe impairments have been found in episodic memory. By closely examining neuropsychological evidence of schizophrenia in their meta-analysis, Cirillo and Seidman (2003) concluded that recall deficits in schizophrenia are likely due to impaired initial acquisition of information and not due to 2 retrieval. By comparing affected and normal control subjects, this review proposed 10% to 20% less information retained by schizophrenia patients, although there is no evidence of an abnormal rate of forgetting, characteristic of frontal lobes dysfunction (Wheeler, Stuss, & Tulving, 1995). On the other hand, non-declarative memory and procedural (habit) learning have been found to be preserved in schizophrenia (Reichenberg & Harvey, 2007).
Differential versus Generalized Impairment While neuropsychological deficits are a robust characteristic of schizophrenia, the debate is ongoing regarding whether the impairment is mostly driven by selective characteristics or a generalized impairment. One of the caveats of neuropsychological schizophrenia research as mentioned in Chapman & Chapman (1973) is that it remains unclear whether differential deficit in performance translates into differential deficit in ability. Supporting this line of reasoning, research has shown that various factors such as floor and ceiling effects may impact the effect sizes that have been reported (Heinrichs & Zakzanis, 1998). Likewise, Chapman & Chapman (1973) have argued that in order to measure differential deficits in ability, tasks should be matched psychometrically.
Meta-analytic findings have shown that despite the magnitude of deficits, no specific neuropsychological impairment seems to be able to separate a schizophrenia sample from healthy controls, but rather, deficits in schizophrenia occur in the context of a general impairment continuum (Heinrichs, 2003; Heinrichs & Zakzanis, 1998). For example, meta- analytic reviews focusing on the WCST studies in schizophrenia have argued in favor of a generalized impairment, specifically refuting the hypothesis that SZ performance failure on this task reflects evidence of a differential deficit in attentional perseveration, as measured by perseverative errors. As such, these findings call for caution in interpreting poor performance on the WCST as reflecting set-shifting or inhibitory function deficits related to a specific impairment in attentional perseveration (Li, 2004).