INVESTIGATING THE RELATIONSHIP BETWEEN
BLAST-RELATED TRAUMATIC BRAIN INJURY
AND EXECUTIVE FUNCTION PERFORMANCE IN
A MILITARY SAMPLE
Jacob Wisnoski
Professor: Antonio E. Puente, Ph.D.
ACKNOWLEDGEMENTS
• I would like to thank the following individuals who,
without their advice and support, this project would not
have been possible:
• My mentor, Dr. Puente
• My committee members, Dr. MacKain & Dr. Pond
• The UNCW Neuropsychology Lab
• My family and my girlfriend, Julie
PRESENTATION OVERVIEW
• Introduction
• Objective
• Methods
• Expected Results
• Discussion
PRESENTATION OVERVIEW
• Introduction
• Objective
• Methods
• Expected Results
• Discussion
WHAT IS A TRAUMATIC BRAIN INJURY (TBI)?
• There are many different examples of what falls
under the category of “TBI”
• The definition often varies depending on the
guidelines of a particular organization (e.g., ICD-9,
DVBIC)
WHAT IS A TBI? (CONT.)
INTRACRANIAL INJURY, EXCLUDING THOSE WITH SKULL FRACTURE (850-854)
•
850 Concussion
•
Includes:
• commotio cerebri
•
851 Cerebral laceration and contusion
•
852 Subarachnoid, subdural, and extradural hemorrhage, following injury
•
853 Other and unspecified intracranial hemorrhage following injury
•
854 Intracranial injury of other and unspecified nature
•
Includes:
• injury:
• brain NOS
• cavernous sinus
• Intracranial
•
(Taken from the International Classification of Diseases (ICD-9))
WHAT IS A TBI? (CONT.)
•
TBI in military operational settings is defined as an injury to the brain resulting from an
external force and/or acceleration/deceleration mechanism from an event such as a blast,
fall, direct impact, or motor vehicle accident which causes an alteration in mental status
•
Typically resulting in the temporally related onset of symptoms such as:
• headache
• nausea
• vomiting
• dizziness/balance problems
• fatigue
• insomnia/sleep disturbances
• drowsiness
• sensitivity to light/ noise
• blurred vision
• difficulty remembering
• and/or difficulty concentrating
•
(Defense and Veterans Brain Injury Center (DVBIC) , 2006)
A BRIEF HISTORY OF BLAST-RELATED
TRAUMATIC BRAIN INJURY (bTBI)
• During World War I, soldiers were exposed to more potent
explosives and, as a result of advances in medicine/protective
gear, were able to survive these injuries.
• Soldiers also began demonstrating a new host of
psychophysiological symptoms that would give rise to the term,
“shell shock”.
• “It was soon recognized that one type of case was due to the
explosion of big shells in the immediate vicinity of the patient,
who did not himself receive any detectable physical injury or
bodily wound” (Turner, 1915, p.833)
A BRIEF HISTORY OF bTBI(CONT.)
•
Turner’s description of the symptoms seen in “shell shock”:
• “In the first group, there is a definite type of mental shock in
which the symptoms are essentially of psychical character.
• In the second group there is a spinal type characterized by a
limitation of the symptoms to the extremities, and usually to the
lower limbs.
• In a third group the symptoms are referred more particularly to
the special senses.
• More specialized symptoms, such as stammering or hesitation of
speech, local palsies and tic-like movements, have been
included in a fourth group.” (Turner, 1915, p.833)
HISTORY OF bTBI (CONT.)
• By World War II, the term “postconcussion syndrome” replaced “shell
shock” as it took into account the number of blasts, the time since injury,
and reported symptoms.
• Wittenbrook (1941) describes the symptoms of this syndrome as followed:
• “The most common symptoms form a triad of headache, dizziness, and
nervousness.
• Many show a fatigability similar to that seen in neurasthenics.
• Certain of the cases with tinnitus, impairment of memory, poor
concentration…character changes, emotional instability, and antisocial
behavior belong in this syndrome.” (Wittenbrook, 1941, p.170)
BLAST-RELATED TBI TODAY
• Since 2000, the Department of Defense estimates that 294,172 new
diagnoses of TBI have occurred.
BLAST-RELATED TBI TODAY (CONT.)
• The increased use of
improvised explosive devices
and advances in medicine and
protective equipment have
contributed to this high
prevalence of TBI (McCrea et
al., 2011; Taber et al., 2007).
• While more U.S. warfighters
are surviving blast injuries,
these same individuals are
now dealing with a host of
neuropsychological problems.
MECHANISM OF bTBI DAMAGE
• “Primary blast injury results
from blast wave-induced
changes in atmospheric
pressure (barotrauma).
Organs and tissues of
different densities are
accelerated at different
relative rates, resulting in
displacement, stretching and
shearing forces.”
• (Taber, Warden, & Hurley,
2006, p. 142-143)
MECHANISM OF bTBI DAMAGE (CONT.)
• “Secondary blast injury results from objects put in motion by the
blast wind impacting a person (ballistic trauma). This category
includes both injuries due to flying debris and due to collapse of
structures.
• Tertiary blast injury results from a person being blown into solid
objects by the blast wind.”
• (Taber, Warden, & Hurley, 2006, p. 142-143)
• The secondary/tertiary injuries brought about by the primary
mechanism of injury damage the brain through a process known
as “coup/contrecoup injury”.
MECHANISM OF bTBI DAMAGE (CONT.)
• This process means that the brain will injure itself against a surface/object as a
product of the blast mechanism (coup).
• Contrecoup damage is caused when the brain bounces back against the back of
the skull in response to the impact of the coup injury.
• The damage done to the brain after being exposed to a blast is described as
follows:
• “Impact mechanisms associated with secondary injury result primarily in
cortical injury, affecting the anterior and inferolateral temporal lobes,
orbitofrontal regions, and frontal poles. Acceleration and deceleration
associated with tertiary injury lead to diffuse traumatic injury to white
matter in the brain” (Bogdanova & Verfaellie, 2012, p.6)
THE EFFECTS OF TBI ON THE FRONTAL LOBES:
A HISTORICAL EXAMPLE
• “He is fitful, irreverent,
indulging at times in the grossest
profanity…impatient of restraint
or advice when it conflicts with
his desires…devising many
plans of future operation, which
are no sooner arranged than they
are abandoned in turn for others
appearing more feasible.”
(Harlow, 1868, p.340-341)
THE FRONTAL LOBES
The orbitofrontal cortex is divided into ventromedial
(reddish) and the lateral orbitofrontal cortex (green)
Pictures presented with permission of Toth, J.
PREFRONTAL CORTEX (PFC) CONNECTIVITY IN
THE HUMAN BRAIN
Figure presented with permission of Toth, J.
NEUROANATOMY & EXECUTIVE FUNCTIONS
• Luria (1966)
• Luria’s model of frontal lobe functions is a three-stage, hierarchical
model with the first two stages being primarily focused on motor
activity
• The tertiary stage is much more closely related to the PFC and EFs
• “The higher development and perfection of the whole sphere of
voluntary, goal-directed acts was associated with the formation of
the tertiary fields of the frontal region proper…These fields,
occupying in man about one quarter of the entire surface of the
cortex, belong to the phylogenetically youngest divisions of the
neocortex” (Luria, 1962/1966, p.57).
NEUROANATOMY & EXECUTIVE FUNCTIONS
(CONT.)
• Stuss & Benson (1986)
• “The executive function represents many of the important activities
that are almost universally attributed to the frontal lobes which
become active in nonroutine, novel situations that require new
solutions” (Stuss & Benson, 1986, p. 244)
• Additionally, Stuss and Benson emphasize that, similar to Luria, “the
prefrontal cortex is the anatomical basis for the function of control”
(Stuss & Benson, 1986, p.244).
WHAT ARE EXECUTIVE FUNCTIONS?
• Baddely & Hitch (1974)
• Working memory research conducted by the team incorporated a “central
executive” component in their theory.
• “Responsible for coordinating and monitoring the many and complex
subroutines that are responsible for both acquiring new material and
retrieving old” (Baddeley & Hitch, 1974, p.47).
• Lezak (1982)
• “Those mental capacities necessary for formulating goals, planning how to
achieve them, and carrying out the plans effectively” (Lezak, 1982, p.281).
• Lezak described EFs are necessary for an individual to perform activities that
are considered creative, productive, and socially and personally fulfilling.
WHAT ARE EXECUTIVE FUNCTIONS? (CONT.)
•
Miyake et. al (2000)
• “General-purpose mechanisms that modulate the operations of various cognitive
subprocesses and thereby regulate the dynamics of human cognition” (Miyake et al.,
2000, p.50).
• Additionally, Miyake et al have placed emphasis on the “unity/diversity” of EFs
•
Alvarez & Emory (2006)
• “higher-level cognitive functions involved in the control and regulation of “lowerlevel” cognitive processes and goal-directed, future-oriented behavior.” (Alvarez &
Emory, 2006, p.17)
•
Gilbert & Burgess (2008)
•
“the high-level cognitive processes that facilitate new ways of behaving, and optimize
one’s approach to unfamiliar circumstances” (Gilbert & Burgess, 2008, p. R110).
WHAT ARE EXECUTIVE FUNCTIONS? (CONT.)
•
While there is no singularly agreed upon definition of the term ‘executive function’
(EF), it is often thought as an umbrella term which looks at the following variables:
• planning
• cognitive flexibility
• inhibition of behavior
• creating goals/goal-oriented behavior
• problem solving
• verbal fluency/reasoning
• adapting to novel situations and stimuli
• decision-making
• multitasking
• working memory
• switching between tasks
• filtering out interference
•
(Banich, 2009; Chan, Shum, Toulopoulou, & Chen, 2008; Gilbert & Burgess, 2008; Jurado &
Rosselli, 2007; Lezak, 1982)
TRAUMATIC BRAIN INJURY & EXECUTIVE
FUNCTIONS
• Among issues related to EF, TBI, and frontal lobe damage, is an ailment
known as dysexecutive syndrome.
• This syndrome is categorized by, “complex cluster of executive function
concerns (i.e., cognition, behavior, and emotion) that arose as a result of
damage to the brain” (Wilson, Evans, Emslie, Alderman, & Burgess, 1998).
• The team of Wilson et. al (1998) defined this syndrome to better capture EF
deficits rather than the term previously used describe these clusters of issues,
frontal lobe syndrome.
• Researchers have found that the following EFs have had deficits as a result of
TBI damage: working memory, attention (and divided attention aka multitasking), cognitive flexibility, rule attainment, and decision-making.
•
Fonseca, Zimmermann, Cotrena, Cardoso, Kristensen, Grassi-Oliveira, 2012; Hartikainen et. al, 2010; Serino, Ciaramelli, Santantonio,
Malagù, Servadei, & Làdavas, 2006.
ISSUES IN TBI & EF RESEARCH
• Issues in Measurement
• There have been many critiques raised against the ability for
neuropsychological tests to predict “real-world” outcomes 
this is an issue of ecological validity.
• There is a fair amount of literature that has shown that there is
poor ecological validity in EF measures with particular
emphasis on populations with both mild and severe TBI
(Douglas, 2010; Wood & Liossi, 2006)
• As the previous slides have illustrated, there is issues in the
operationalization of EF and frontal lobe functions which
creates discrepancy in what is truly being measured.
ISSUES IN TBI & EF RESEARCH (CONT.)
•
Issues in Generalizability
• While the research that has discussed the deficits of EF in varying clinical
populations has been important, there is limited generalizability of findings to
a “neurotypical” population (Busch, McBride, Curtiss, Vanderploeg, 2005;
Schieser, Delis, Filoteo, Delano-Wood, Han Jak, Drake, & Bondi, 2011)
•
Issues in Experimental Design
• Studies looking at the relationship between EFs and TBIs often have some
variation of the following issues: small n value, limited number of EF
measures, low level statistical processes.
• As will be discussed later, the issue of “unity/diversity” also presents a
problem when discussing EF testing.
ISSUES IN TBI & EF RESEARCH (CONT.)
•
Examples of TBI & EF studies with the issues discussed in the previous slide
• Brenner et al. (2010)
• N=45
• Number of EF tests: 3 (Stroop, Trail Making Test, and Wisconsin Card Sorting
Task)
• Findings show a decline in executive function performance in TBI group
• Procedures used: t-tests
• Verfaellie, Lafleche, Spiro, & Bosquet (2013)
• N=127
• Number of EF tests: 3 (Delis-Kaplan: Stroop, Trail Making Test, and Verbal
Fluency Test)
• Findings show a mild impairment of executive functioning
• Procedures used: multiple regression analyses
PRESENTATION OVERVIEW
• Introduction
• Objective
• Methods
• Expected Results
• Discussion
OBJECTIVE
• The prospective study will contribute to the present body
of literature discussing the relationship between blastrelated TBIs’ and EFs in the following ways:
• Analyze a larger sample size (N=735)
• Incorporate more EF measures (4)
• Utilize more advanced statistical techniques (e.g.,
latent variable analysis)
• Investigate the influence of the EF measures against
one another
PRESENTATION OVERVIEW
• Introduction
• Objective
• Methods
• Expected Results
• Discussion
METHODS: PARTICIPANTS
• The prospective study will utilize a large electronic data set
consisting of evaluations from Marines and sailors.
• The following exclusion criteria will be applied to these data:
• Unspecified demographic information (n=165)
• Sub-optimal performance (score of less than 45) on the Test of
Memory Malingering (n=156)
• Based on these exclusion criteria, the prospective study will
analyze data of 735 Marines and sailors
DEMOGRAPHIC INFORMATION
•
Gender
•
721 Male
•
14 Female
•
Age
•
Mean: 25.85 Years
•
SD: 5.6 Years
•
Education
•
Mean: 12.5 Years
•
SD: 1.1 Years
•
Handedness
•
Right-Hand: 498 participants
•
Left-Hand: 191 participants
•
Ambidextrous: 46 participants
METHODS: PROCEDURE
• Evaluation Procedure
• Psychodiagnostic Interview
• Neuropsychological Testing
• Follow-up Session
• Data Collection
• Jacksonville Trips
• Data Input
METHODS: MATERIALS
• The dataset collected from Camp Lejeune includes four
measures of EF that will be used for the proposed
study:
• The Hayling Sentence Completion Test & Brixton
Spatial Anticipation Test (Burgess & Shallice, 1997)
• The Controlled Oral Word Association (COWA) Test
• The Trail Making Test (Reitan & Wolfson, 1993)
• The Stroop Test (Stroop, 1935 & Golden, 1978)
THE HAYLING & BRIXTON TESTS
• The Hayling Sentence Completion Task
• Consists of two, 15 sentence completion tasks where
the final word of each sentence is missing.
• The first round of 15 sentences has participants filling
in the missing word as quickly as possible.
• The second round tasks participants with completing
the sentence with a nonsensical answer thus,
challenging them to inhibit automatic, logical
responses.
THE HAYLING AND BRIXTON TESTS (CONT.)
• The Brixton Spatial Anticipation Task
• Consists of a 56 page stimulus book where each page has ten
circles aligned in a two by five line up. Each circle is
numbered one through ten.
• On each page, one of the circles is blue and the blue coloring
will change from page to page.
• How the changes occur depends on a series of simple rules and
the participant is tasked with determining this rule and figuring
out where the blue circle will be next.
• Together, these tests are supposed to measure the following EF
variables: initiation speed, response suppression, and rule
attainment.
CONTROLLED ORAL WORD ASSOCIATION
TEST (COWAT)
• The COWA Test is a two component neuropsychological test which is intended
to measure the EF variable, verbal fluency
• Letter Fluency
• The letter fluency component of the COWA is commonly referred as the
“FAS test” since the participant is asked to produce as many unique words
beginning with the letters F, A, and S as they can in one minute (per letter).
• The participant cannot give the names of proper nouns (e.g. names) or
repeat words with a different ending (e.g., fish, fishing, fishes, etc.)
• Semantic Fluency
• The procedures for the semantic fluency task are essentially the same as the
letter fluency task except participants are now tasked with naming as many
animals, fruits, and vegetables as they can in one minute per category.
THE TRAIL MAKING TEST (TMT)
• Trail A
• Trail A contains 25 circles with numbers in them and tasks the participant
with connecting the dots in numerical order as quickly as possible.
• Trail B
• Trail B of the TMT is uses a similar form as Trail A but, instead of
numbers alone being in the circles, the 25 circles contain both numbers
and letters.
• The goal of Trail B is to have participants alternate between numbers and
letters (e.g., 1-A, 2-B, 3-C, 4-D,and so on) as quickly as possible
• Research conducted using the TMT has shown that the following EF variables
are measured with this test: cognitive flexibility, ability to maintain set, and
ability to switch between sets (in the case of Trail B) (Arbuthnott & Frank,
2000; Kortte, Horner, & Windham, 2002).
THE STROOP TEST
• The Stroop task typically consists of three sections:
• The Neutral Task: Participants are asked to read aloud various color names
printed in black ink and name as many as possible in a pre-determined
amount of time (usually 45 seconds-1 minute).
• The Color Task: Participants are then asked to read aloud color names (or
a neutral series of letters such as “xxxxx”) printed in inked whose color is
congruent to the color name being red (e.g., ‘red’ being printed in red ink).
• The Color-Word Task: Participants are then presented with color names
printed in ink incongruent to the actual word given (e.g., the word ‘green’
printed in blue ink). Participants must inhibit their natural tendency
towards language processing and name the color of the ink instead.
• The EF measures that are tapped by the Stroop task include: goal-oriented
behavior and behavior inhibition.
METHODS: PROPOSED PROCEDURE
• The proposed research project will consist of two main
studies, each focusing on a different series of research
questions.
• Study 1 will be more clinically oriented and investigate
the relationship between mechanism of injury (MOI),
number of times blasted, and EF performance.
• Study 2 will be more experimental and exploratory in
nature as it will probe deeper into the question of what
an executive function is and how to measure them.
METHODS: STUDY 1 PROCEDURE
• Study 1 will begin by comparing two different categories of
blast injured groups (single v.s. multiple) to see if there are
significant differences in EF performance between the
groups.
• Single-Blast Group (n = 136)
• Multiple-Blast Group (n = 303)
• This will be accomplished through the use of a two-tailed,
dependent samples t-test.
• This will inform whether or not a single “blast” group can
be used for statistical analyses in Study 1 or if two separate
groups must be compared.
METHODS: STUDY 1 PROCEDURE (CONT.)
• Study 1 also aims to compare EF performance using a three
(or four) factor one-way ANOVA in three different MOIs:
• A bTBI group (n = 439)
• Single-blast (n = 136)
• Multiple-blast (n = 303)
• A TBI group whose injury was not blast-related (n =
107)
• A no TBI group (n = 22)
• Post-hoc pairwise comparisons will also be conducted to
examine specific differences amongst the groups.
METHODS: STUDY 2 PROCEDURE
• Study 2 is organized into three levels of analyses which
range from low to high complexity in terms of the depth of
analysis.
• The first level is intended to examine the “unity/diversity”
issue through the use of ANOVA and regression.
• Specifically, a repeated measures ANOVA and post-hoc
analyses will be used to probe for significant differences
between EF measures (diversity).
• Multiple regression will analyze the correlation between EF
measures and how well each measure predicts values of
other EF tests (unity).
METHODS: STUDY 2 PROCEDURE (CONT.)
• The next level of analysis is intended to build off of the
regression analyses by looking at possible third variables
that may affect the statistical relationships between EF
measures.
• This will be accomplished through the use of moderation
analyses which will analyze:
• Categorical variables (e.g., gender, ethnicity, MOI, and
loss of consciousness)
• Continuous variables (e.g., age, number of blasts, time
since last injury, education, and, most importantly, EF
scores)
METHODS: STUDY 2 PROCEDURE (CONT.)
• Phase II will probe
for these interactions
between EF
measures and
additional variables
using the moderation
procedure developed
by Preacher, Curran,
& Bauer (2006)
METHODS: STUDY 2 PROCEDURE (CONT.)
• The final level of analysis will utilize the methodology
developed by Miyake et al. (2000) to study the
“unity/diversity” issue which is conducted as followed:
• “One selects multiple exemplar tasks that seem different on
the surface but still capture the target ability.
• If exemplar tasks are chosen that share little systematic nonEF variance, one can statistically extract what is common
across those tasks (using multivariate statistical techniques
such as structural equation modeling and exploratory factor
analysis).
• Use the resulting “purer” latent variable as the measure of
EF.” (Miyake et al., 2000, p 8-9)
Hayling &
Brixton
Rule
Attainment
Response
Suppression
Stroop Task
Inhibition
Trail Making
Test
Cognitive
Flexibility
COWAT
Verbal
Fluency
Common
Executive
Function
Construct
PRESENTATION OVERVIEW
• Introduction
• Objective
• Methods
• Expected Results
• Discussion
STUDY 1 PREDICTIONS
• It is hypothesized that the initial t-test will reveal that
there is no significant difference between individuals
who experienced a single blast when compared to those
who experienced multiple blasts on any of the executive
function measures.
• This hypothesis is supported by a number of studies
(Ivins, Kane, & Schwab, 2009; Luethecke, Bryan, Morrow, &
Isler, 2011; Verfaellie, Lafleche, Spiro, & Bousquet, 2013)
which have demonstrated that the number of TBIs
experienced has no significant effect on the outcomes of
neuropsychological test performance.
STUDY 1 PREDICTIONS (CONT.)
• It is predicted that the ANOVA will yield a statistically significant
F-value and thus, there will be a significant difference present
between the three MOI groups on all four EF tests.
• It is likely that this prediction will come about due to the mere
differences in the sample sizes of each MOI group rather than an
actual effect.
• A Levene’s test will be conducted to reduce the violation of
assumed heterogeneity of variance (HOV) as the size of the
dataset may be overpower findings and will produce significant
findings.
• Therefore, the subsequent pairwise comparisons will also yield
significant differences between MOI groups on each EF test.
STUDY 2 PREDICTIONS
• In regards to the first level of analyses, it is hypothesized
that each repeated measure ANOVA will produce a
statistically significant result which suggests that there are
significant differences present amongst the four EF
measures.
• Subsequent pairwise comparisons will further yield
significant results and illustrate where those differences lie
between each EF measure when compared to one another.
• The purpose of this series of analyses is to begin to examine
the diversity of EF measures as that will likely be more
apparent.
STUDY 2 PREDICTIONS (CONT.)
• Furthermore, while discussing the first level of analyses,
it is predicted that the multiple regression experiments
will yield statistically significant results.
• It is hypothesized that the relationship between each
measure of EF (when compared with one another) will
be low to moderately strong and positively directed.
• Significant findings in the regression analyses will being
to empirically support the notion that there is a unity
amongst the EF measures.
STUDY 2 PREDICTIONS (CONT.)
• In regards to the second round of analyses in Study 2, there
has been little information published that looks at
moderators of interest.
• However, there are previous studies that have demonstrated
differences in EF measures based on the following
categorical variables:
• gender (Niemeier, Marwitz, Lesher, Walker, & Bushnik,
2007)
• ethnicity (Proctor & Zhang, 2008)
• loss of consciousness
• mechanism of injury
STUDY 2 PREDICTIONS (CONT.)
• There also a number of continuous variables which have
previously shown demonstrated differences that will also be
probed:
• time since last injury (Belanger, Curtiss, Demery, Lebowitz, &
Vanderploeg, 2005)
• age (Bryan & Luszcz, 2000)
• number of blasts
• education
• scores on the four measures of EF
• As little research has been done looking at moderation on this type
of sample with these variables (both continuous and categorical), it
is predicted that interactions between each EF measure to one
another will be dependent on each of these variables.
STUDY 2 PREDICTIONS (CONT.)
• In regards to the third level of analysis, the
individual EF measures appear to be quite diverse in
terms of the constructs being measured.
• A latent variable analysis needs to be conducted in
order to determine if there is an underlying all of the
tests.
• It is likely that since all of the measures in this
study are considered EF measures, there should be a
minor portion of the variance that can be explained
by this underlying EF component.
Hayling &
Brixton
Rule
Attainment
Response
Suppression
Stroop Task
Inhibition
Trail Making
Test
Cognitive
Flexibility
COWAT
Verbal
Fluency
Common
Executive
Function
Construct
PRESENTATION OVERVIEW
• Introduction
• Objective
• Methods
• Expected Results
• Discussion
STUDY 1 DISCUSSION
• In Study 1, the intended goal was to begin evaluating the relationship
between certain variables (e.g., # of blasts, MOI) that may affect EF
performance within the sample.
• If the expected results of study one are found to be as predicted, then
this will add support to the literature that states that factor such as
MOI (Belanger et al. 2009) and number of blasts (Ivins et al., 2009;
Luethecke, et al., 2011; Verfaellie et al., 2013) may not be the most
salient when evaluating a client.
• That is not to imply that these variable do not have an important role
to play in the evaluation of the client but, perhaps, that other variables
such as the presence of depression or PTSD may have greater impact
on neuropsychological performance.
STUDY 2 DISCUSSION
•
The findings of the first level of analysis of Study 2 will demonstrate whether or
not it is possible to statistically illustrate the unity/diversity framework using
lower level mathematical functions.
• The findings of the post-hoc tests will be very important in determining what
conclusions can be drawn from these statistical procedures as there must also
be a way to compensate for overpowered data due to the large sample size.
•
The second level of analysis is an investigation into whether or not there are
additional variables that may be impacting the regression analyses from the prior
analyses.
• This level will operate as a screening for third variable moderators that may
not have been considered by previous research or considered at all.
• The majority of these variables may also, to some small degree, act as
manifest variables and thus, the variance attributed to these variables needs to
be explained before probing the possible latent variable(s) within the dataset.
STUDY 2 DISCUSSION (CONT.)
• The third level of analysis is the major portion of Study 2 as it is the
most statistically sophisticated and has the most implications
associated with its findings.
• If it is indeed found that there is unity underlying all of the EF
measures in this project, then it would mean that it may be necessary
to re-evaluate the tests themselves to ensure that future forms of these
measures accommodate the effects of other EF measures on each
individual test.
• Additionally, a latent variable analysis demonstrating unity within the
model will also prove that the methods discussed by Miyake et al
(2000) can be completed with more dissimilar tests and with fewer
tests.
GENERAL DISCUSSION
• As this study utilizes data from a military sample (which has often
been considered to have different cultural habits/attitudes than
civilian populations) and this sample has been exposed to bTBIs,
this project may also inform how this sort of sample differs from
civilian samples.
• Further, it may be possible to start learning how bTBIs affect the
common EF construct as well as the individual EF constructs
captured by each test.
• As this is a military sample being measured, the findings of this
research may even be able to modify EF measures to better reflect
the conditions and conditioning that a military sample would be
exposed to while in training, in combat and as a veteran sample.
LIMITATIONS
• This is a retrospective analysis rather than a prospective
analysis.
• Testing procedure relied on the subjective knowledge and
opinion of a clinician, additional error may have been factored
in without report or inter-rater reliability procedures being
carried out.
• Alvarez & Emory (2006) found in their review of EF and
frontal lobe studies that, contradictory to what they considered
the historical neuropsychological approach of localization, that
“both frontal and non-frontal brain regions are necessary for
intact executive functions” (Alvarez & Emory, 2006, p.33).
FUTURE DIRECTIONS
• Utilize a broader range of EF measures to better capture key functions such as
decision-making and working memory and developer a more powerful
argument in the “unity/diversity” framework.
• It is important to note that the proposed study is, arguably, only investigating
half of what may be considered an executive function.
• In Ardila’s (2008) discussion on the possible evolutionary origins of EFs,
two types of EF are brought up: metacognitive and emotional. Ardila
describes a second type of EF, emotional (or “hot” cognition), which is
supposed to deal with motivation as well as the frontal lobe serving as an
emotional impulse control for limbic system activity.
• To further enhance this procedure, the inclusion of neuroimaging would be an
important addition to provide clear structural/functional relationships between
EFs and their neuroanatomical correlates.
QUESTIONS?
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