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EXECUTIVE FUNCTIONS IN CHILDREN WITH READING DISABILITY
SARAH J. MCCANN
A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE
UNIVERSITY OF FLORIDA
O 2007 Sarah J. McCann
I thank Shelley C. Heaton, Ph.D. for her invaluable mentorship throughout this project. I
also thank Tim Conway, Ph.D., for his guidance and expertise, and Richard Frye, M.D., Ph.D.
for his help during the conceptualization of this proj ect. Finally, I thank my parents, Martha and
Joseph, for their encouragement and unconditional support.
TABLE OF CONTENTS
ACKNOWLEDGMENT S .............. ...............3.....
LI ST OF T ABLE S ................. ...............6................
LI ST OF FIGURE S .............. ...............7.....
AB S TRAC T ......_ ................. ............_........8
1 INTRODUCTION ................. ...............10.......... ......
Reading Disability .................. ........... ...............1
Neurological Underpinnings of Reading Disability ................. ........... ... ... ........... ......13
Frontal Lobe Systems, the Inferior Frontal Gyrus, and Executive Functions ........................14
Working Memory .............. ...............15....
Inhibiti on ................. ...............16........... ....
Shifting ................. .. .. .............. ........1
Attentional Control and Set-Shifting ................. .. ......... ...............17.....
Parent-rating Behavioral Measures of Executive Functions ................. ................. .... 18
Aims of the Current Study ................. ...............18.......... ....
2 METHODS .............. ...............21....
Participants .............. ...............21....
Proc edure s ................ ...............22........... ....
3 RE SULT S .............. ...............25....
Reading Ability Measures .............. ...............25....
Executive Function Measures ................. ...............26........... ....
Parent-Report Behavioral Measure ................. ...............27........... ....
4 DI SCUS SSION ................. ...............3.. 0......... ....
Working Memory .............. ...............30....
Inhibiti on ................. ...............31........... ....
Shifting ................. .. .. ... ....... .........3
Attentional Control and Switching ................. ...............33.......... ....
Parent-Rating of Executive Functions ................. ...............34................
Limitations and Strengths of Current Study .............. ...............35....
Future Directions .............. ...............37....
LI ST OF REFERENCE S ................. ...............3.. 9......... ....
BIOGRAPHICAL SKETCH .............. ...............44....
LIST OF TABLES
3-1 Group means and standard deviations for age and IQ .............. ...............28....
3-2 Means (and standard deviations) on reading measures: RD vs. control ............................28
3-3 Means (and standard deviations) on executive functions measures: RD vs. control........29
3-4 Means (and standard deviations) on three scales of the Behavioral Rating Index of
Executive Functions (BRIEF) Parent-report............... .............2
LIST OF FIGURES
1-1 Neurological underpinnings of reading ................ ........................ ..............20
Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science
EXECUTIVE FUNCTIONS INT CHILDREN WITH READING DISABILITY
Sarah J. McCann
Chair: Shelley C. Heaton
Reading disability is a neurologically-based developmental disorder characterized by a
deficit in processing phonological information in language. Linguistic models suggest that
deficits in lower-level processes, such as phonological processing, may greatly tax upper-level
domains of executive function. Additionally, functional neuroimaging conducted during reading
tasks suggest that children with reading disability have underactivation in posterior brain regions
and a relative overactivation in anterior brain regions, specifically in the inferior frontal gyrus. In
addition to phonological processing, the inferior frontal gyrus has been implicated in executive
functions such as inhibition and set-shifting. However, few studies have specifically examined
these executive functions in children with reading disability. Characterization of the executive
functions in children with reading disability is an important first step in identifying potential
subgroups of children who may require different intervention strategies to improve their reading
The current pilot study examined executive functioning of children with reading disability
(RD, n=1 1) and a control group of normal readers (control; n=8) using a battery of tests
measuring different aspect of executive functions: inhibition (Color-Word Interference subtest
from the D-KEFS), inhibition and shifting (WCST-64), attentional control and shifting (Creature
Counting and Opposite Worlds subtests from the TEA-Ch), verbal working memory (Numbers
subtest from the CMS), and parent-reported behavioral inhibition, set shifting, and working
memory (Inhibition, Shift, and Working Memory Indices from the BRIEF). The performance
profile ofRD group was qualitatively examined using norm-based standardized performance
scores and quantitative group differences were explored between the RD and normal control
Qualitative evaluation of the RD norm-referenced performance profile revealed
impairment in the inhibition and attentional control and shifting domain, but performance was
within normal limits across the other domains of executive functioning. They were rated in the
clinically significant range on the working memory index on the parent-report measure ofEF.
Quantitative group comparisons indicated that the RD sample performed worse than the control
group in four of the five domains of executive functioning and were rated worse than controls on
the shift index on the parent-report of EF. Implications and plans for continued data collection
Executive functions, broadly defined, make up a cognitive domain comprised of related,
yet distinct, abilities that enable intentional, goal-oriented, problem-solving. Executive
functioning is thought to be an over-arching construct that consists of supervisory or self-
regulatory functions, which direct and organize cognition, emotional response, and overt
behavior (Gioia, Isquith, Kenworthy, & Barton, 2002; Denckla & Reader, 1993). The commonly
agreed upon subdomains of executive functions include the ability to initiate and sustain
behavior, inhibit competing stimuli, select relevant task goals, plan and organize problem-
solving strategies, shift cognitive strategies when necessary, and monitor and evaluate one's
behavior (Pennington & Ozonoff, 1996; Hayes, Gifford, & Ruckstuhl, 1996). Additionally,
working memory and attention are commonly referred to as subdomains of executive functioning
(Pennington, Bennet, McAteer, & Roberts, 1996). The current study focuses on three aspects of
executive functions most relevant to the reading disability population under the proposed model:
the ability to inhibit irrelevant stimuli or responses, hold and manipulate verbal information in
working memory, and flexibly shift cognitive set when necessary.
Reading Disability is a developmental disorder with neurological underpinnings, and is
characterized by reading achievement (reading accuracy, speed, or comprehension) that falls
substantially below that expected given the individual's chronological age, measured
intelligence, and age-appropriate education (American Psychological Association, 1994). The
term "reading disability" and "developmental dyslexia" are synonymous, as dyslexia is not a
diagnosable disorder according to the Diagnostic Statistical Manual 4th Edition (DSM-IV), but
is the colloquial term for reading disability. Reading disabilities affect up to 5-10% of school-
age children (American Psychological Association, 1994; Shaywitz et al., 2003), often causing
significant disturbances in the child's school performance, or even leading to school failure
(Shaywitz et al., 1998). Reading disabilities can negatively impact the child's self concept and
self-esteem (Cooley, 2002). In spite of recent advances in the diagnosis and treatment of reading
disabilities, many children with reading disability fail to receive the necessary academic support.
One of the maj or difficulties with allocating appropriate services is the significant variability in
treatment efficacy at the individual level. Although commonly co-occurring conditions such as
attention deficit/hyperactivity disorder, anxiety, depression, and oppositional defiant disorder
could account for some of this variability in outcomes continues to be unexplained even when
these factors are controlled (Shaywitz & Shaywitz, 2005; Torgesen, 2004). To identify effective
intervention and paths to prevention, the underlying cognitive mechanisms must be identified
Several theories of reading disability have been proposed, such as the rapid auditory
processing theory (Tallal, Allard, Miller, & Curtiss, 1997), the cerebellar theory (Nicolson and
Fawcett, 1990), and the phonological theory (Liberman, Shankweiler, & Liberman, 1998;
Torgesen, 2004). The phonological theory is the most supported and widely accepted theory. The
phonological theory posits that, in order to learn to read and utilize language effectively, one
must recognize that that spoken words can be broken up into elemental units of sound
(phonemes) and that the letters of the written word represent these sounds (Bruck, 1992;
Shaywitz et al., 2003). This basic awareness is deficient in children and adults with reading
disability. Several studies of young school aged-children have confirmed that a deficit in
phonological awareness represents the best individual correlate of reading disability (Fletcher et
al., 1994; Morris et al., 1998; Helland & Asbjornsen, 2000). These findings are also the basis
for the most successful interventions designed to improve reading skills. These interventions
most often include training in phonemic awareness, phonics, fluency, vocabulary, and
comprehension (Report of the National Reading Panel, 2000; Torgesen et al., 1999).
A model based upon the phonological theory (Alexander & Slinger-Constant, 2004)
indicates that reading is a multi-level process. According to this model, attention and arousal are
necessary for consistent and accurate sensory input, and serves as the base level for this model.
There are five processors, which create differing forms of sensory input. These processors
include: orthographic, articulatory, phonologic, prosodic, and morphosyntactic. It is believed that
children with reading disability are impaired in the orthographic, articulatory, and phonological
processors, and therefore the output from these processors is less distinct than output from
processors functioning at the normal level. The sensory input created by these lower-level
processors is held briefly in short term memory and when processing must occur, working
memory must become available. These holding systems of working memory have been found to
serve as "slaves" for the central executive system, which is thought to develop strategies when
there are roadblocks, organize information and plan action, and are responsible for self-
monitoring and controlling intention and holding back from responding too quickly. Executive
functions depend of sensory input and cortical representations being held in working memory
long enough for processing. Increasing the burden on working memory resources may result in
an increased difficulty in controlling inhibition (Bitan at al., 2005; Pennington, Bennet,
McAteer, & Roberts, 1996). Therefore, attention, working memory, and executive functions are
integral to each other for the accurate perception, processing, and production of language.
Additionally, using a top-down perspective, the central executive system plays an important role
in mediating the language processing system, so that if these functions are impaired, a child may
have a harder time holding on to and processing linguistic information. Therefore, the child's
impairment may be further manifested in phonological processing because of a deficit in the
central executive system that is used for the management of lower-level processes.
Neurological Underpinnings of Reading Disability
Converging evidence from a number of studies using several different brain imaging
techniques [functional magnetic resonance imaging (fMLRI), positron emission topography
(PET), and magnetoencephalography (MEG)] indicates that successful reading involves a left
hemisphere posterior reading system that consists of both ventral and dorsal components and
frontal regions (e.g., the inferior frontal gyrus) (Pugh et al., 2001; Hickok & Poeppel, 2004). See
Findings from several studies suggest these circuits to be dysfunctional in children with
reading disability (Shaywitz et al., 1998; Frackowiak, Friston, Frith, Dolan, & Mazziotta, 1997;
Pugh et al., 2000). For instance, Shaywitz et al. (2003) found significant differences in brain
activation during phonological analysis compared to normal readers. Specifically, nonimpaired
readers demonstrated significantly greater activation compared to impaired readers in left
hemisphere sites including the inferior frontal, superior temporal, parieto-temporal and middle
temporal gyri. These findings further support the report from many researchers using
neuroimaging indicating children with reading disability exhibit a failure of left hemisphere brain
systems to function properly while processing linguistic information (Brunswick, 1999; Temple
et al., 2000) as well as during non-reading visual processing tasks (Demb, Boynton, & Heeger,
Several studies (Shaywitz et al., 1998; Shaywitz & Shaywitz, 2005; Pugh et al., 2000)
posit that children with reading disability utilize compensatory systems located in bilateral
anterior sites, specifically in the inferior frontal gyrus (IFG) in response to left hemisphere
weakness. For instance, nonimpaired readers showed increased bihemispheric inferior frontal
gyrus and prefrontal dorsolateral activation during non-word reading compared to non-impaired
readers (Shaywitz et al., 1998). The IFG is typically known as Broca's area, and is involved in
phonological processing. Therefore, researchers have hypothesized that the increased activity in
the IFG in children with reading disability reflects an increased reliance on this region to
phonological processing in an attempt to cope with the demands of phonological analysis (Pugh
et al., 2000; Shaywitz & Shaywitz, 2005).
Frontal Lobe Systems, the Inferior Frontal Gyrus, and Executive Functions
The phrase "frontal lobe system" refers to the actual prefrontal cortex in conjunction with
the areas of the thalamus and basal ganglia and those parts of the limbic system that are relevant
to the affective aspects of executive functions. The current study utilizes neuropsychological
assessments to measure performance on tasks that have been shown, via neuroimaging, to
activate the IFG located within the frontal lobe region. The cognitive domains of working
memory, inhibition, and set-shifting have been identified as three domains of executive functions
that have been linked to prefrontal activation, specifically the IFG (Roberts, 1994). For instance,
in a study by Buchsbaum et al., (2005), 30 normal participants completed the Wisconsin Card
Sorting Task (WCST) while in a functional MRI (fMLRI). The Wisconsin Card Sorting Task is a
common measure of executive functions, and involves the ability to form abstract concepts, to
sustain attention, and to shift cognitive sets flexibly in response to varying conceptual rules,
while simultaneously inhibiting incorrect responses (Tsuchiya, Oki, Yahara, & Fujieda, 2004;
Aron, Robbins, & Poldrack, 2004). Buchsbaum et al. (2005) found strong bilateral IFG
activation temporally related to set-shifting and set maintenance within the task. Additionally,
Aron et al., (2004) found bilateral IFG activation using fMLRI while participants completed a
stop-signal task, as task traditionally used to assess inhibitory ability. Furthermore, increasingly
taxing the working memory resources leads to an increased difficulty in controlling inhibition
(Bitan et al., 2005; Pennington, Bennet, McAteer, & Roberts, 1996). Thus, working memory,
inhibition, and set-shifting have been identified as three dimensions critical for understanding the
breadth of executive function tasks.
The sections that follow summarize the existing literature regarding the executive
functioning performances of children with reading disabilities across components of verbal
working memory, inhibition, set-shifting, and parent ratings of behavior. The current study is the
first study of reading disability to examine an attentional control/shifting subdomain as a
component of executive functions.
Working memory allows for a Einite amount of information to be actively maintained and
manipulated (Baddeley, 1986, 1992), and may serve as a mechanism for higher cognitive
processes, such as problem-solving, reasoning, decision-making, and language comprehension
(Jonides, 1995). Baddeley's tripartite model of working memory posits that it is not a unitary
system, and instead proposes two separate "slave systems" for the short-term maintenance of
information (one for verbal information and one for visual information) and one central
executive system for the supervision and information integration of the other systems (Baddeley,
1992, 1996). The articulatory loop is one of the "slave systems" that uses primarily phonological
information (verbal) and prevents its decay by refreshing its contents through articulatory
rehearsal (subvocal repetition). The visuo-spatial sketchpad is the second "slave system". Its
purpose is to store visual and spatial information.
It is posited that children with reading disability have impairment in the articulatory loop
component of working memory, and therefore show deficit in verbal working memory tasks
(Kibby, Marks, & Morgan, 2004). Verbal working memory appears important in the ability to
hold sounds and words in mind as well as content while reading a passage. Digit Span Tasks are
commonly used to assess verbal working memory. These tasks provide a measure of immediate
recall, particularly attention and short-term memory with the digits forward component; however
the digit span backward task is more of a working memory test because it requires manipulation,
or reorganization, of the information (Lezak, 1995; Sattler, 1988). In general, marked deficits
have been found in children with reading disability in verbal working memory (Wilcutt, et al.,
2002; Lezak, 1995; Reiter, Tucha, Lange, 2005; Jeffries & Everatt, 2004; and Kibby, Marks, &
Inhibition is a subdomain of executive functions that involves the ability to inhibit
prepotent (or natural) responses and stop ongoing responses. Inhibition fundamentally
contributes to the functioning of other executive functions, such as working memory (Barkley,
1992; Aron, Robbins, & Poldrack, 2004). Inhibitory processes are also important for the
development of cognitive abilities such as learning, memory, and motor activity (Johnston &
Blue, 2006). The domain of inhibition is most often assessed using a go/no-go paradigm or
Stroop color-word task, which measures the ability of a participant to inhibit a well-learned
response. Helland et al. (2000) and Wilcutt et al. (2005) found marked deficits in a group of
children with reading disability on the Stroop Color/Word task and a Stop Signal task. However,
several studies have failed to replicate these findings (Reiter, Tucha, & Lange, 2005).
This suddomain of executive functions is commonly referred to as "set-shifting", because
this subdomain requires the ability to shift attention or shift between strategies or response sets
(Baddeley, 1996; Monsell, 2003). Successful set-shifting involves the disengagement of an
irrelevant task set or strategy and the consequent activation of a more appropriate one (van der
Sluis, de Jong, & van der Leij, 2004). Task-switching is subserved by other executive functions,
particularly inhibition and working memory (Baddeley, 1996; Aron, Robbins, & Poldrack,
2004), and has been shown to have overlapping neural activation pathways utilized by working
memory and inhibition (Aron, Robbins, & Poldrack, 2004; Bushbaum, Greer, Chang, & Berman,
2005; Demakis, 2003). Task-switching paradigms focus on the switching process by providing
cues that inform the subj ect when to shift tasks, such as in the Wisconsin Card Sorting Task
(Bushbaum, Greer, Chang, & Berman, 2005). Lazar (1998) and Zhang et al. (2004) found that a
reading disability group performed significantly worse than controls on this task. However,
several studies have failed to find deficits in this sub-domain in children with reading disability.
However, these findings have not been consistently demonstrated on several scoring variables of
the WCST-64 (Wilcutt, Pennington, Olsen, Chhabildas, & Hulslander, 2005; Narhi, Rasanen,
Mesapelto, & Ahonen, 1997; Sengstock, 2001). There remain equivocal findings within this
population as to whether impairments exist in this domain. Perhaps the difficulty lies in the
failure to separate out the underlying deficit that may be causing the impairment because of the
overlap in task specificity.
Attentional Control and Set-Shifting
Attentional control (which is also sometimes referred to as attentional shift or attentional
flexibility) is defined as the ability to shift attention adaptively and flexibly (Manly, Robertson,
Anderson, & Nimmo-Smith, 1999). Attentional control is therefore closely related to set-shifting
and inhibition as outlined above. Much like its construct, tasks used to measure executive
function (and therefore stated to measure attentional control) apply multiple cognitive
components. Factor loading of subtests from the Test of Everyday Attention for Children (TEA-
Ch; Manly, Robertson, Anderson, & Nimmo-Smith, 1999), suggest two subtests represent the
domain of attentional control and switching, and are most likely also supported by the inhibition
and verbal working memory domains.
Parent-rating Behavioral Measures of Executive Functions
Performance-based neuropsychological measures may yield a limited, incomplete
assessment (Gioia & Isquith, 2002). While performance tests attempt to tap executive functions
in explicit and specific ways, many confounds limit their ecological validity and generalizability
(Gioia & Isquith, 2002). The Behavior Rating Inventory of Executive Function (BRIEF) -
Parent-report is a measure of executive functions that yields two index scores, Behavioral
Regulation and Metacognition, and eight subscale scores: Inhibit, Shift, Emotional Control,
Initiate, Working Memory, Plan/Organize, Organization of Materials, and Monitor. Past research
using the BRIEF Parent-report has found children with dyslexia to receive significantly higher
(reaching more clinical levels) scores than matched controls on the BRIEF Working Memory,
Plan/Organize, and Monitor Scales. The reading disability group did not endorse more problem
levels of the Inhibit, Shift, and Emotional Control Scales compared to normal controls (Gioia,
Isquith, Kenworthy, & Barton, 2002). Thus, the proposed study also incorporates a parent-report
measure of executive function in order to more completely assess executive function profiles in
reading disability. Specifically, the current study will be examining the Inhibit, Shift, and
Working Memory Indices from this measure.
Aims of the Current Study
The primary goals of the current study are to use a clinical assessment battery to learn
more about the specificity of executive functions impairment in children with reading disability
and to compare this profile of executive functions performance to a normal control group.
Characterization of the executive functions in children with reading disability is an important
first step in identifying potential subgroups of children who may require different intervention
strategies to improve their reading skills.
Based on the literature and anecdotal observations, we hypothesized that the reading
disability group would perform worse than controls in the domains of verbal working memory,
inhibition, shifting, and attentional control and switching.
Rule based analysis,
posterior Inferior Frontal
Gvrus/dorsal Pre-Motor (left)
Figure 1-1. Neurological Underpinnings of Reading
Inferior Frontal Gvrus
inhibition & executive
A total of 19 children between the ages of 8 and 14-years-old participated in this study: 11
diagnosed with reading disability (RD) and 8 with no diagnosis of a RD (normal control group).
The maj ority of participants were Caucasian. Within the RD group, 8 (72.2%) were Caucasian
and 3 (27.3%) were African American. Similarly, within the control group, 6 (75%) were
Caucasian, 1 (12.5%) was Hispanic, and 1 (12.5%) was African American. Participants were
excluded if their intellectual functioning was suggestive of mental retardation (FSIQ scores less
than 70 on the Wechsler Intelligence Scale for Children Third Edition, WISC-III, or the
Wechsler Abbreviated Scale of Intelligence, WASI), if they had a prior head injury, or history of
neurological condition (e.g. seizure disorder).
The RD group was recruited through flyers that were posted within the institution or at
several local elementary schools. Additionally, children with RD were referred from ongoing
studies within the University of Florida' s Clinical and Health Psychology Program, Pediatric
Neurology Department, and the Multi-Disciplinary Diagnostic and Training Program at the
University of Florida. All children had previously been diagnosed with RD by a licensed
psychologist using the discrepancy method (1 SD difference between IQ and achievement).
Diagnosis was confirmed using the child's Individual Education Program (IEP) and
psychoeducational testing reports that were obtained by the Principal Investigator. Three children
were excluded because of comorbid learning disabilities or auditory processing impairments.
Children were not excluded from the study if they had ever received a diagnosis of Attention
Deficit/Hyperactivity Disorder from a psychologist or pediatrician, as long they were currently
taking psychostimulant medication in order to treat this disorder. Given the high rates of
comorbidity of RD and ADHD (15% to 40%) it would have been extremely difficult to obtain an
adequate sample size using these exclusion criteria. Furthermore, the inclusion of ADHD as a
comorbidity enhances the generalizability of this sample (Gilger, Pennington, & DeFries,1992;
Shaywitz, Fletcher, & Shaywitz, 1995; Willcutt & Pennington, 2000).
Children within the control group were recruited via flyers posted within the institution,
local grocery stores, and at local elementary schools. The absence of diagnosis of RD and
ADHD was confirmed by parent-report via a telephone screen prior to the testing session.
Children were excluded if they were unable to complete any of the neuropsychological test
measures (no children were excluded).
Several domains of reading and reading comprehension were evaluated in the current
study. All study participants completed the Word Attack, Letter Word Identification, and
Passage Comprehension subtests from the Woodcock Johnson Tests of Achievement-Third
Edition (WJ-III; Woodcock, McGrew, and Mather, 2001). Additionally, the Gray Oral Reading
Tests-Fourth Edition (GORT-IV; Weiderhold & Bryant, 2001) was used to assess the rate,
accuracy, fluency, and comprehension of reading ability. Raw scores from the WJ-III subtests
and the GORT-IV were transformed into age-and gender-adjusted standardized scores.
WJ-III subtests yield standardized scores, with a scale mean of 100 and a standard
deviation of+ 15, such that scores below 85 reflect reading im airment. The Word Attack
subtest is a measure of pseudo-word reading that assesses phonological awareness. The Letter
Word Identification subtest measures the ability to decode relatively high frequency real words.
The Passage Comprehension subtest is a measure of covert reading comprehension.
The GORT-IV yields four scaled scores: Rate, Accuracy, Fluency, and Comprehension,
and one standardized score: Oral Reading Quotient. These scaled scores have a scale mean of 10
and a standard deviation of +3, such that scores below 7 reflect reading impairment, and the
standardized score has a mean of 100 and a standard deviation of+ 15. The Rate score represents
the amount of time taken by a participant to read a story. The Accuracy score represents the
ability to pronounce each word in the story correctly. The Fluency score is the participant' s Rate
and Accuracy combined, and the Comprehension score measure the appropriateness of the
participant' s responses to questions about the content of each story read. Finally, the Oral
Reading Quotient score is a combination the Fluency and Comprehension scores.
The current study assessed several domains of executive functions include: verbal working
memory, inhibition, shifting, and attentional control/switching. Working memory was assessed
using the Numbers subtest from the Children' s Memory Scale (CMS; Cohen, 1997), which is
essentially a Digit Span task with a forward and backward component. These scores were
combined to yield a Numbers Total Scaled score with a mean of 10 and a standard deviation of+
3. Additionally, the Numbers Forward and Numbers Backward raw scores were transformed
into Scaled scores, as the Numbers Forward task is a more of a measure of attention and short-
term memory, and the Numbers Backward is more taxing on the executive control aspects of
verbal working memory ability as there is the component of manipulation that must be utilized in
order to successfully complete the task (Lezak, 1995).
The ability to inhibit prepotent responses was assessed using the Inhibit Scaled score Delis
Kaplan Executive Function System (D-KEFS; Delis, Kramer, & Kaplan, 2001) Color-Word
Interference subtest. This subtest is similar to the traditional Stroop Color-word test, but involves
an additional task of switching between the classic stroop paradigm and normal word reading.
Therefore, the domain of shifting was also assessed using the Switching score. All scores
yielded from this subtest are scaled scores, with a mean of 10 and a standard deviation of + 3.
The ability to shift set was also assessed using the Wisconsin Card Sorting Task-64
computerized version (WCST-64; Heaton, 1981). Although this measure yields several scores,
only the Perseverative error score was used in the current study, and this score is most correlated
with the ability to shift set. The scores yielded are T-scores with a mean of 50 and a standard
deviation of + 10.
Two subtests from the Test of Everyday Attention for Children (TEA-Ch; Manly,
Robertson, Anderson, & Nimmo-Smith, 1999) were used to assess attentional control and
switching. The Creature Counting and Opposite Worlds subtests scaled scores were combined to
create a composite score to represent the ability to switch cognitive set and inhibit incorrect
responses. Specifically, for each participant, scaled scores from the two attentional control and
switching tasks were summed and divided by two, yielding a single composite attentional control
and switching Scaled score. The creation of a composite score for this domain was performed in
order to accomplish data reduction and thus reduce the number of variables to protect statistical
Cut-off scores of one or more standard deviation below the mean were used to qualitatively
determine impairment in a domain. For instance, for Scaled Scores with a mean of 10 and a
standard deviation of 3, a score of 7 or below represents impairment in that domain (Lezak,
Table 1 presents means (and standard deviations) for each group of participants for
chronological age, Full Scale IQ (FSIQ), Performance IQ (PIQ), and Verbal IQ (VIQ). A t-test
revealed that the groups were comparable in terms of age at the time of assessment (t(2) = -.234,
p = .817). Chi square analysis similarly revealed that the two groups were comparable in terms
of ethnicity, with approximately 75% Caucasian in both groups (X2 (2, N = 19) = 43.50, p =
0.00). T-tests were also conducted on the IQ scales (FSIQ, PIQ, VIQ). Groups were comparable
across all measures (FSIQ (t(2) = 1.03, p = .319), PIQ (t(2) = -.551, p = .589, and VIQ (t(2) =
1.78, p2 = .095). See Table 3-1.
Reading Ability Measures
In order to better characterize our samples, we used a MANOVA to compare groups on the
dependent measures for each of the reading domains. The dependent measures (DVs) were the
Standard Scores for real and pseudo-word reading, covert passage comprehension, and the rate,
accuracy, and comprehension for passage reading. Additionally, a standard score was used to
represent overall oral reading ability. Table 2 illustrates group means and standard deviations for
the reading measures. The overall multiple analysis of variance found significant main effects
for group (F[7,10] = 7.87, p < .01, r12=.846). This effect size suggests a large effect of group
(Field, 2005). Follow-up univariate ANOVAs were conducted to examine the location of the
significant effect. Significant effects of pseudo-word reading (F[1,17] = 5.64, p < .05, r12=.261),
rate of passage reading (F[1,17] = 15.11i, p < .01, r12=.486), accuracy of passage reading (F[1,17]
= 26.82, p I .001, r12=.626), fluency of passage reading (F[1,17] = 20.30, p < .001, r12=.559),
comprehension of passage reading (F[1,17] = 8.56, p < .05, r12=.349), and overall oral reading
ability (F[1,17] = 17.40, p < .01, r12=.521) were found between groups, with the RD group
performing worse on all tasks with significant differences. Although the RD group performed
worse on most of the reading ability measures compared to the control group, the group was in
the impaired range (-1 SD) for only rate, accuracy, fluency, and overall oral reading ability
measures. See Table 3-2.
Executive Function Measures
Initial evaluations of the data suggested that all measures were univariate normal (i.e., all
dependent variables had skewness and kurtosis between -1 and 1.) The Box-M~test for the
homogeneity of variance-covariance matrices across design cells produced a non-significant
result and the Levene' s test found that the assumption of homogeneity of variance could be
supported for the main effect of group. Residual correlations between the DVs were only
reaching relatively high levels for the two D-KEFS variables (.832), suggesting possible non-
independence of these DVs. Otherwise, it can be assumed that the DVs represent unique
information relative to one another.
We used a MANOVA to compare groups on the dependent measures for each factor of
executive functions. Scaled scores were considered to be the dependent measure for the domains
of verbal working memory, inhibition, and shifting; and a T-Score was used as the dependent
measure of set-shifting. A composite of two Scaled scores was used as the dependent measure
for the domain of attentional control and switching. Table 2 illustrates group means and standard
deviations for the executive functions tasks. The overall multiple analysis of variance found a
significant main effect for group (F[1,17] = 17.40, p < .01, r12=.521). We conducted follow-up
univariate ANOVAs, separately for each DV, to examine the location of the significant effect.
Significant effects of verbal working memory (F[1,17] = 1 1.32, p < .01, r12=.400), inhibition
(F[1,17] = 7.17, p < .05, r12=.297), shifting for the D-KEFS Switching variable (F[1,17] = 10.15,
p < .01, r12=.374), and attentional control and switching (F[1,17] = 7.56, p < .05, r12=.308) were
found between groups, with the RD group performing worse on all significant variables. There
was no significant difference between groups for the domain of shifting as measured by the
WCST-64. Additionally, in order to control for inflated family-wise error, the alpha level of
p<.05 was adjusted to reflect the number o DVs used in the MANOVA, yielding an alpha level
of p<.025. All variables of significance remain at the significant level when adjusting for family-
wise error. In order to determine if group differences in the Numbers Forward and Numbers
Backwards tasks existed, an independent samples T-test was conducted. The RD group
performed worse for both Forward and Backward (t(17) = 2.22, p = .041; t(17) = 3.31, p = .004).
Qualitatively, the RD group performed in the impaired range (- SD) in the domains of inhibition
and attentional control and switching. See Table 3-3.
Parent-Report Behavioral Measure
A MONOVA of the three BRIEF scales of interest (Inhibit, Shift, and Working Memory)
indicated that the overall model is significant (F[1,17] = 3.28, p < .05, r12=.396). Follow-up
univariate analyses of variances indicated that children with RD were rated as having
significantly higher scale elevations (indicative of higher problem levels) on the Shift scale
(F[1,17] = 7.78, p < .05, r12=.314). Qualitatively (using recommended clinical cut-off values),
children with RD were noted to have been rated within the clinical range only on the Working
Memory scale. Table 4 presents the group means for the BRIEF scales. See Table 3-4.
RD Control p-value
(N = 1 1) (N = 8)
on Reading Measures:
Table 3-1 Group Means and Standard Deviations for Age and IQ
Chronological Age (CA) 1
Full Scale IQ (FSIQ) 1
Performance IQ (PIQ) 1
Verbal IQ (VIQ) 9
Table 3-2 Means (and Standard Deviations)
Reading Task Domain
WJ-III Tests of Achievement
(Word Attack Scaled score)
Real Word Reading
WJ-III Tests of Achievement
(Word Identification Scaled score)
Covert Passage Comprehension
WJ-III Tests of Achievement
GORT-IV Rate Scaled score
Reading A accuracy
GORT-IV Accuracy Scaled score
GORT-IV Fluency Scaled score
GORT-IV Comprehension Scaled
Overall Oral Reading Ability
GORT-IV Oral Reading Quotient
RD vs. Control
(N = 1)
Table 3-3 Means (and Standard Deviations)
on Executive Functions Measures: RD vs. Control
Executive Function Domain RD Control
p-au Effect siz
(N =I 1 l=S 1)v (N = 8
Verbal Working Memoly
Numbers Scaled score from CMS 8.27 11.25
Numbers Forward Scaled score 8.13 10.13
Numbers Backward Scaled score 7.60 11.38
D-KEFS Interference subtest 6.64 9.38
(Inhibition Scaled score) (2.66) (1.30)
D-KEFS Interference subtest 7.35 11.00
(Switching Scaled score) (3.04) (1.20)
WCST-64 Perseverations T-Score 55.91 56.63
A ttentional Control and Switching
TEA-Ch Attentional Control 4.95 8.89 .014 .308
composite Scaled score (3.45) (2.42)
Table 3-4 Means (and Standard Deviations) on three scales of the Behavioral Rating Index of
Executive Functions (BRIEF) Parent-report
Index Scale RD Control
p-value Effect size
(N = 1) (N =8)
Inhibit 58.82 (11.05) 49.5 (12.90) .109 .144
Shift 60.00 (13.44) 44.5 (9.47) .013 .314
Working M~emoly 65.00 (12.11) 59.13 (16.39) .380 .046
The primary goals of the current study were to characterize the profie of executive
functions (EF) performance in children with Reading Disability (RD) and to investigate if this
childhood neurodevelopmental disorder could be differentiated from a normal control group. The
results suggest that the executive functions profie for this population reflect impairment as
hypothesized. Consistent with our predictions, the RD group exhibited deficits on the both the
neuropsychological measures of EF and on parent ratings of EF behaviors. Qualitative
examination of the RD group's neuropsychological profie revealed impaired performance (1 SD
below the mean) in the domains of inhibition and attentional control/switching. The RD group
also was rated in the clinically significant range in the domain of working memory. Moreover,
the RD group performed significantly worse than the control group in the domains of verbal
working memory, inhibition, shifting, and attentional control and switching. Furthermore, the
RD was rated has having more behavioral elevations than the control group in the shifting
It was hypothesized that the domain of verbal working memory would be a critical
component of executive functions in distinguishing RD from the control group. This prediction
was based on prior studies, as well as the proposed role that verbal working memory plays in the
mediation of lower-level processors (e.g., phonological processing) in a model of the linguistic
system (Alexander & Slinger, 2004). Specifically, digit span forward is frequently used as a
measure of the phonological loop of Baddeley's (1992) model for working memory, as this task
relies on the phonological loop with little reliance on the central executive system. The
'backward' component of this task requires resources of the central executive system as the
manipulation of information is needed (Lezak, 2004). Thus, current study results indicated that
the RD group performed significantly worse than controls in the attentional aspects of this task
as well as the executive control component. These Eindings are consistent with past research
(Wilcutt, et al., 2001; Lezak, 1995; Reiter, Tucha, & Lange, 2005; Jeffries & Everatt, 2004;
Kibby, Marks, & Morgan, 2004; Swanson, 2003; Poblano, 2000; Jong, 1998) and support the
notion that the neural substrates underlying both verbal working memory and phonological
processing appear to be located in overlapping brain regions in the left hemisphere (Shaywitz,
2005). However, this notion would need to be confirmed with functional neuroimaging.
As hypothesized, the RD group performed significantly worse on a neuropsychological
measures of inhibition compared to the control group. The ability to inhibit prepotent responses
was assessed using the score from the Interference trial from the D-KEFS Color-Word
Interference test. Of note, the RD group did not differ from the control group in the total time
taken to read the words for the Word trial, nor did they differ in their ability to rapidly name
colors. Therefore, the RD group's difficulty on the Interference trial cannot be attributed to
differences in reading rate or in color naming, and the statistical difference between groups is
attributed to the inability to adequately inhibit the natural response of word reading.
Several studies using factor analyses and regression models have demonstrated that
response inhibition tasks are implicitly involved in measures of the central executive system
(Rucklidge and Tannock, 2002; Purvis and Tanock, 2000). These Eindings support the notion
that inhibition and working memory are closely related, as proposed by Baddeley's model of
working memory (Baddeley, 2002). For instance, working memory maintenance of task-set and
items and the selection and manipulation of information in working memory requires cognitive
inhibition (Aron, Robbins, & Poldrack, 2004; Duncan & Owen, 2000). Furthermore, a close
link has been found between reading and speeded inhibition measures, (Purvis and Tanock,
2000). These findings are also supported by the common neural substrates shared by both
inhibition and phonological processing, distinctively in the inferior frontal gyrus (Aron, Robbins,
& Poldrack, 2004; Shaywitz & Shaywitz, 2005). Taken together, these findings suggest that
inhibition is a necessary component for successful reading.
Two measures were used to assess the shifting domain of executive functioning in this
study. The Switching score from the D-KEFS Color-Word Interference test was found to
significantly differentiate the groups, with the RD group performing worse. However, the
WCST-64 failed to detect group differences. There are several potential explanations for these
divergent findings. First, the Switching score from the D-KEFS Color-Word Interference test
requires one to not only inhibit their prepotent response (as described above), but also to shift
sets and, at times, read the word regardless of the ink color it is printed in. Specifically, when a
word on the page has a box surrounding it, the correct response is to read the word and not name
the ink color, but when there is no box surrounding the text, the correct response is to name the
color of ink, not read the word. Successful completion of this task not only requires inhibition,
but also the ability to shift between rules. There have been no studies that have used this scoring
component of the D-KEFS Color-Word Interference subtest in the RD population. Given the
reported deficits in inhibition and the role that inhibition plays in set-shifting in this task, it
follows that children with RD would perform poorly (Asbjornsen & Bryden, 1998; Keshner &
The WCST-64 was also used to assess set-shifting. Statistically significant differences
were not found between groups for both perseverative and non-perseverative errors. First, this
task does not have a time demand, and the participant may take as long as necessary to decide
which card is the most appropriate match. The literature suggests that children with RD may
have a marked deficit in tasks that require speeded processing (van der Sluis, de Jong, & van der
Leij, 2004; Tallal, Allard, Miller, & Curtiss, 1997). Therefore, time demands for a task may be
necessary in order for potential impairment in the domain to be observable. Furthermore, the
WCST-64 may not be a specific enough task in detecting frontal lobe pathology explicitly in the
shifting domain. For instance, there is a lack of association between WCST-64 errors and
specific cognitive and neural processes (Barcelo & Knight, 2002).
Attentional Control and Switching
In support of our hypothesis, there was a significant group difference found in the domain
of attentional control and switching, with the RD group performing significantly worse than the
control group. One way to conceptualize the attentional control and switching subtests of the
TEA-Ch is as tasks that combine the executive function components of inhibition and set-
shifting. Although this limits our ability to draw definitive conclusions regarding the specific
components of EF that differ between RD and controls, we can infer that both aspects of this
domain are impaired when considered relative to the findings in the current study. This suggests
that children with RD do have a generalized impairment in set-shifting when this skill is used in
conjunction with other cognitive skills such as inhibition and attentional control.
Many studies have investigated components of attention in children with RD and yielded
equivocal results (Helland & Asbjornsen, 2000; Pennington, 2006; Willcutt & Pennington, 2000;
Wilcutt, Pennington Olsen, Chabildas, & Hulslander, 2005), in part because the rate of
comorbidity between RD and Attention Deficit/Hyperactivity Disorder (ADHD) has been
reported to be as high as 45% (Purvis & Tannock, 2000; Wilcutt, Pennington Olsen, Chhabildas,
& Hulslander, 2005). The conventional methods of separating RD caused by deficits in
decoding skills from poor reading caused by attention problems associated with ADHD have
yielded equivocal results (Aron, Robbins, Poldrack, 2004). There are several hypotheses
proposed to explain the high comorbidity rates, including phenotypic sources, in which the
observable characteristics are similar (Wilcutt et al., 2001), genetic causes (Pennington, Bennet,
McAteer, & Roberts, 1996; Wilcutt et al., 2002); and hereditary causes (Wilcutt et al., 2002). In
particular, an extensive twin study found that approximately 95% of the phenotypic covariance
between RD and symptoms of inattention was attributable to common genetic influences.
Furthermore, 21% of the phenotypic overlap between RD and hyperactive and impulsive
behaviors was due to common genetic factors (Wilcutt et al., 2002). These findings suggest that
RD and ADHD do, in fact, share potential genetic overlap (Pennington, 2006).
The investigation of reading problems and EF impairment associated with both RD and
ADHD remains an important avenue of research because of the potential implications in the
ability differentially diagnosis and treat RD and ADHD. It is imperative to understand the
underlying deficits in order to better conceptualize and treat a disorder.
Parent-Rating of Executive Functions
Neuropsychological testing alone may not fully capture the EF profile in this population.
Therefore, three scales from the BRIEF Parent-report (Inhibit, Shift, and Working Memory)
were compared between groups. Contrary to our hypothesis of group differences across these
scales, only the Shift scale was significantly different between groups, with the RD group being
rated as having more significant problems. Furthermore, only the Working Memory scale for the
RD group was reported in the clinically significant range (T>65). All other scales were within
'normal limits' for both groups, suggesting that as a group, the RD group is not being reported
by their parents to be displaying EF difficulties. These findings are somewhat contradictory to
previous findings, in which group differences were found between RD and controls on the
Working Memory scale, but not on the Inhibit or Shift scales (Gioia, Isquith, Kenworthy, &
Barton, 2002). However, Gioia et al. (2002) failed to find the RD in the clinically significant
range for the three scales of interest in this study, which is consistent with our findings.
Sample characteristics and limited power may help explain our failure to detect significant
group differences for all three scales as hypothesized. If behavioral observations reflect
executive function impairment as detected by neuropsychological measures, the RD group would
be expected to have been rated has having more problems in these domains than our sample
exhibited. The performance of the RD group in the current study suggests that these children
may represent the milder end of the disorder' s spectrum.
Additionally, the relatively small sample size of the current study may have impacted our
ability to detect statistically significant group differences. Although the RD group received
higher (more problematic) ratings than the control group, a larger sample may potentially
demonstrate significant group differences on these scales, although the current study's effect
sizes are small. Few studies of this population have included parent-ratings in addition to a
neuropsychological battery, and it is difficult to determine the overall pattern of behaviorally
manifested executive function problems.
Limitations and Strengths of Current Study
The implications of our findings are tempered by the limitations of the current study. Due
to the nature of a pilot study our sample size, and therefore power, was relatively small.
It is important to note, however, that the significant differences found between groups on
the neuropsychological measures of executive functions yielded medium effect sizes (Field,
2004), suggesting that the group differences found in the current study would be replicable with
a larger sample. Also, neuropsychological measures inherently assess multiple domains of EF,
creating difficulty in determining impairment in specific domains of EF. This limitation
highlights the need for future test development to improve the utility of neuropsychological
measures that focus on one component of EF.
Additionally, children with RD were compared with a group of controls that were not age-
or reading age-matched. Snowling (1987) has emphasized that the value of considering studies
without reading age-matched controls is limited, as conclusion drawn with regard to reading
ability and executive functioning should be taken conservatively. The lack of phonological
measures that specifically assess lower-level phonological processing limit our ability to more
fully relate the proposed model of linguistic impairment in this population and executive
functions. In order to explore the relationship between lower-level processes, such as
phonological awareness, and the role executive functions may play in the mediation of reading
ability, a range of assessment measures must be employed. Furthermore, the IFG is specifically
involved in the phonological awareness and articulatory recoding aspects of reading, and
therefore, it is difficult to draw conclusions regarding these abilities and the executive functions
associated with activation of the brain region without more sensitive reading measures, and
ultimately, without functional neuroimaging.
Finally, the RD group included children with comorbid ADHD (n=5, 45% of RD sample).
All participants with comorbid ADHD and RD were being treated pharmacologically, which has
been shown to alleviate EF impairment in ADHD. However, this could pose a potential
limitation to the current study. Although it is not feasible for post-hoc examination of the RD
group's performance because of sample size limitations, qualitative performance for the Hyve
participants with only RD (i.e., no comorbid ADHD) was examined, revealing impairment for
three participants in the working memory domain, four participants demonstrated impairment in
the inhibition domain, four participants demonstrated impairment in the switching domain, and
four participants demonstrated impairment in the attentional control domain. Additionally, on
the parent-report measure of EF, two participants were rated in the clinically significant range for
the Inhibit index, three participants were rated in the clinically significant range for the Shift
index, and 3 participants were rated in the clinically significant range for the Working Memory
index. This impairment profile suggests that children with RD without ADHD exhibit EF
impairment and the comorbidity of ADHD is not a necessary condition for EF impairment to
exist in this population.
There are a number of strengths to the study. For instance, few studies of children with
RD have utilized a comprehensive neuropsychological test battery that focuses on the related
domains of executive functions. Inhibition, working memory, and set-shifting have similar
underlying cognitive and neural substrates, and few studies of this population have
simultaneously investigated these domains in comparison to normal controls. In order to tease
apart the specific fundamental executive function impairments within this population, systematic
examinations of this nature must be performed. Executive functioning may affect not only the
present cognitive functioning, but also the integrity of future cognitive functions and the
effectiveness of remediation (Reiter, Tucha, & Lange, 2005).
Using a multidimensional model of executive functions and parent ratings of behavior, the
current pilot study successfully describes an expected executive function profile for RD, as well
as illustrates how the pattern of RD performance differs from a control group consisting of non-
impaired readers. The next step is to examine a pure sample of children with RD only, and then
look at a sample with comorbid ADHD, as clinical group comparisons (i.e., RD, RD+ADHD,
and control) are warranted given the similar executive dysfunction pattern found in the ADHD
population (Wilcutt et al., 2002; Wilcutt, Pennington, Olsen, Chhabildas, & Hulslander, 2005).
Furthermore, the inclusion of more sensitive reading measures to the test battery would also be a
beneficial addition. The relationship between the fundamental aspects of reading ability and
executive functions could be addressed. Moreover, the utilization of functional neuroimaging
(e.g., fMRI) would enable researchers to definitively investigate the relationships between EF
and RD. Finally, the role that executive dysfunction plays in response to remediation is an
important subj ect for further research. Previous research suggests that the possible differences in
executive function may differentiate between children who will be more likely to respond to
intervention and those who do not respond as well (Shaywitz et al., 2003). If such deficits could
be detected early, potentially at the elementary school level, remedial treatment could be tailored
to specific subgroups of reading impaired individuals.
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Sarah McCann was born in Corvallis, OR, the younger of two children of Martha and
Joseph McCann. She earned a Bachelor of Science degree in psychology with a concentration in
biology at the University of Tampa. Sarah entered the Clinical and Health Psychology program
at the University of Florida in 2005. During her study at UF, she has worked as a research
assistant in a pediatric neuropsychology lab and a stroke rehabilitation center. Sarah's mentor is
Shelley C. Heaton, Ph.D., and her interests include childhood neurodevelopmental disorders such
as learning disabilities and attention deficit hyperactivity disorder. She plans to work in a
clinical research setting after earning her doctoral degree in clinical psychology.