THE EFFECTS OF PRESENTATION AND PROCESSING ON EXPLICIT MEMORY
IN OLDER ADULTS
A Thesis
Presented to the faculty of the Department of Psychology
California State University, Sacramento
Submitted in partial satisfaction of
the requirements for the degree of
MASTER OF ARTS
in
Psychology
by
Felicia Elena Luz Oropeza
SPRING
2012
THE EFFECTS OF PRESENTATION AND PROCESSING ON EXPLICIT MEMORY
IN OLDER ADULTS
A Thesis
by
Felicia Elena Luz Oropeza
Approved by:
__________________________________, Committee Chair
Kelly Cotter, Ph.D.
__________________________________, Second Reader
John Schaeuble, Ph.D.
__________________________________, Third Reader
Emily Wickelgren, Ph.D.
____________________________
Date
ii
Student: Felicia Elena Luz Oropeza
I certify that this student has met the requirements for format contained in the University
format manual, and that this thesis is suitable for shelving in the Library and credit is to
be awarded for the thesis.
__________________________, Graduate Coordinator
Jianjian Qin, Ph. D.
Department of Psychology
iii
___________________
Date
Abstract
of
THE EFFECTS OF PRESENTATION AND PROCESSING ON EXPLICIT MEMORY
IN OLDER ADULTS
by
Felicia Elena Luz Oropeza
Forty eight older adults, sampled from two senior communities, watched a series of
words on a computer monitor and then took a written exam that tested their explicit word
recall. Results revealed a main effect for presentation, such that participants correctly
recalled more words when those words were presented for 2 seconds than when those
words were presented for .04 seconds. Results also revealed an interaction between
presentation and processing, where the supraliminal presentation yielded more correctly
recalled words in thematic conditions than in non-thematic conditions. These results
suggest that older adults exhibit higher explicit memory performance when words
belonging to a theme or category are presented within conscious awareness than outside
awareness, likely because they are able to process the information more deeply.
_______________________, Committee Chair
Kelly Cotter, Ph.D.
_______________________
Date
iv
DEDICATION
I would like to dedicate this thesis to my deceased maternal grandparents, Maria
de la Luz Razo and Salvador Gomez who raised me and served as the inspiration for my
topic on cognition and aging.
v
ACKNOWLEDGMENTS
First and foremost, I would like to thank my parents for everything they have
done for me. Since preschool, my parents have impressed upon me the value of education
and importance of using one’s intellect to make a significant impact on the world;
however small or big that may be. They gave me the greatest gift that any parent could
bestow on their child, individuation, by giving me the freedom to explore my academic
pursuits. My thesis topic availed me this golden opportunity to spread my wings and fly.
Special thanks to my mother’s extended family for their undying support of my
educational endeavors and contributions to my personal development throughout
graduate school. During graduate school, my grandmother passed away which was a
major setback for our family, for she was the anchor that held our family together.
Amidst those trying times, my mom’s family taught me to rise above hardships and to
find my inner strength within to finish my degree. I would like to thank Dr. Kelly Cotter
for her patience, immense wisdom, alacrity, and generosity of time and effort towards
helping me finish my thesis. I would also like to thank Dr. John Schaeuble for helping me
arrive at my thesis topic and for assisting me with narrowing my thesis topic down to two
variables. I would like to thank Dr. Wickelgren for helping me with the Latin Square
Experimental Design of my video presentations to eliminate bias. I would like to thank
Debbie Kircher for pacing me through the program and helping me see my own beauty
within.
vi
TABLE OF CONTENTS
Dedication ............................................................................................................................v
Acknowledgements ............................................................................................................ vi
List of Tables ..................................................................................................................... ix
List of Figures ......................................................................................................................x
Chapter
1. INTRODUCTION ........................................................................................................1
Memory ....................................................................................................................1
Supraliminal and Subliminal Memory Processes ....................................................3
Levels of Processing ................................................................................................4
Interaction of Levels of Processing and Timing of Presentation .............................5
The Present Study ....................................................................................................6
2. METHOD .....................................................................................................................8
Materials ................................................................................................................10
Participants .............................................................................................................13
Procedure ...............................................................................................................13
3. RESULTS ...................................................................................................................16
Hits .........................................................................................................................17
False Alarms ..........................................................................................................19
4. DISCUSSION ............................................................................................................20
Strengths and Limitations ......................................................................................23
vii
Future Directions ...................................................................................................28
Conclusion .............................................................................................................29
Appendix
Final List of Forty Words Used in the Four Video Conditions ...................30
References ........................................................................................................................31
viii
LIST OF TABLES
Tables
Page
1. Descriptive Statistics for Hits and False Alarms ....................................................... 16
ix
LIST OF FIGURES
Figures
Page
1. The Interaction of Presentation and Relatedness for Hits ..............................................18
2. The Main Effect of Presentation for False Alarms ........................................................19
x
1
Chapter 1
INTRODUCTION
Dementia is a degenerative disease of the aging brain that impairs cognitive
functioning by attacking the central nervous system at the vascular and cellular levels
(Whitehouse, Price, Strubie, Clark, Coyle, & Delon, 1982). A reputable occupational
health and medical disability advisory website, MDGuidelines, provides the article
“Dementia definition” (2009) stating that although dementia impairs cognitive
functioning in many ways, profound and irreversible memory loss is its primary effect.
Because dementia is an increasingly prevalent age-related neural disease within senior
populations, developing cognitive strategies for preventing memory loss is necessary for
maintenance of quality of life and positive life orientations (Santacruz & Swagerty,
2001). I focus on two potential memory-enhancing strategies in the present study:
presentation of information and processing of information. I examine these strategies as
employed by older adults who do not suffer from cognitive impairment, in hopes that
what is learned in normal aging populations can be beneficial for those at risk of
developing dementia.
Memory
Memory, as defined in The American Heritage Dictionary (1985), is the act of
encoding, storing, and recalling a past event or item of factual knowledge. Memory can
be divided into two forms: implicit and explicit (Graf & Schacter, 1985), both of which
are affected by the aging process (Light & Singh, 1987). Implicit memory depends on
2
cognitive processes occurring outside of one’s conscious awareness (Schacter, 1987).
These automatic processes can include stimuli-associate conditioning, social modeling,
relearning and practice effects, and priming (Schacter, 1987). Roediger and McDermott
(1993) and Schacter (1987) described implicit memory tasks as indirect, where there was
no reference to past exposure to information.
In contrast, explicit memory tasks require the conscious recollection of an item
directly referenced by past experience (Graf & Schacter, 1985). When one performs well
on an explicit memory test, he or she has brought factual knowledge into awareness
(Challis, 1996; Joyce, Paller, McIsaac, & Kutas, 1998). Roediger and McDermott (1993)
and Schacter (1987) characterized explicit memory tests as tasks performed with
intention, where participants are instructed to recall or recognize stimuli they had
previously seen.
I chose to analyze free recall test performance as a measure of explicit memory
processes in the current study. Performance on a free recall exam is a direct measurement
of the conscious recollection of previously presented stimuli. This type of memory task
relies on processing capacity, revealing the influence of working memory and processing
speed on retrieval (Craik, Govoni, Naveh-Benjamin, & Anderson, 1996; Whiting &
Smith, 1997). Free recall tests typically depend on effortful cognitive control and bottom
up retrieval processes.
In cross-sectional and longitudinal studies examining age-related memory, older
participants tend to score lower than younger participants on explicit memory tasks
(Anooshian, 1997; Carroll, Byrne, & Kirsner, 1985; Ellis, Ellis, & Hosey, 1993;
3
Greenbaum & Graf, 1989; Lorsbach & Morris, 1991; Lorsbach & Worman, 1990; Naito,
1990; Parkin & Streete, 1988). However, older cohorts show equal performance to young
adults on perceptual implicit tasks (Light & Singh, 1987) shedding light on potential
compensatory mechanisms used by older adults to preserve explicit memory. To
investigate the older cohorts’ adaptive use of cognitive tools further, I analyzed the
influence of two associative memory processes on explicit memory test performance in
older adults: level of processing (shallow versus deep) and awareness of presentation
(subliminal versus supraliminal), described in detail below.
Supraliminal and Subliminal Memory Processes
As described above, explicit memory tests often involve asking participants to
recall or recognize information presented to them in a laboratory setting. The information
can be presented supraliminally (within one's conscious awareness) or subliminally
(outside one's ability to consciously perceive presented stimuli) in the study/encoding
session. Supraliminal memory processes are driven by strong feelings of event
recollection that enhance one’s ability to visualize the scene (Aggleton & Brown, 1999;
Gardiner, 1988; Gardiner & Java, 1990; Gardiner & Java, 1991; Gardiner, Java &
Richardson-Klavehn, 1996; Jacoby, 1991; Rajaram, 1993; Tulving, 1985; Wagner,
Verfaeille, & Gabrieli, 1997; Yonelinas, 2002). Subliminal processes depend upon
feelings of familiarity that lack a concrete experience of an actual event (Khilstrom,
1990; Khilstrom, Barnhardt, & Tataryn, 1992a; Khilstrom, Shames, & Dorfman, 1996;
Roediger & McDermott, 1993; Szymanski & MacLeod, 1996; Toth, 1996). The priming
4
task is a classic methodology for studying subliminal processes (Kiefer, 2007). Age has
little effect on priming (Light & Singh, 1987).
Levels of Processing
Ritchey, Bessette-Symons, Hayes, and Cabeza (2011) showed that semantic
elaboration can enhance neural processing in the medial prefrontal cortices of the human
brain. Deep encoding requires the utilization of meaning-based encoding to activate
associative memory network connections, while shallow processing refers to the
presentation of stimuli encoded at a rudimentary or physical level without the use of
semantic-level memory access (Craik & Lockhart, 1972). For example, deep processing
is applied during exposure to a word list consisting of items belonging to the same
category, such as Zoo Animals, because people form associations between the words. On
the other hand, shallow processing is utilized during exposure to randomly chosen words
because there is no categorical link between the words. Craik and Lockhart (1972)
showed that deep or semantically-processed stimuli had a higher chance of being recalled
than shallow or physically-processed stimuli. This effect was found even when
participants did not expect subsequent recall or recognition tests.
Bradshaw and Anderson (1982) also showed the effect of elaboration and
thematic-relatedness on memory processes: Participants in their study demonstrated
higher memory performance in the thematic conditions, which required the elaborate
integration of memory traces, and lower memory performance in the conditions with
minimal thematic-relatedness. Similarly, levels of processing theory stipulates that
performance is facilitated by elaborately encoded or “deeply” processed stimuli and
5
degraded by low-level encoding or “shallow” processing of stimuli (Craik & Lockhart,
1972). Hence, Bradshaw and Anderson’s (1982) study draws parallels between thematicrelatedness and levels of processing theory, shedding light on the role of neural networks
in the creation of interconnected explicit memory traces. In the current study, I adapted
the methodology that used thematic-relatedness in order to operationally define levels of
processing.
Interaction of Levels of Processing and Timing of Presentation
Effortful processing may enhance memory performance in older cohorts on
priming tests. Englekamp and Wippich (1995) demonstrate an age effect for conceptual
priming, such that younger cohorts generally show higher memory on implicit tests than
older cohorts when presented with atypical stimuli at study. Englekamp and Wippich
showed that younger cohorts tend to perform better than older cohorts in random stimuli
and subliminal presentation conditions while performing worse in moderate-relatedness
conditions.
The distinction between the cognitive resources that drive explicit and implicit
memory processes begin to blur (Srinivas & Roediger, 1990) as category exemplar tasks
capture both conceptual subliminal processes and perceptual subliminal processes. While
unraveling the effects of conscious and unconscious processes on memory, Monti et al.
(1996) investigated how category exemplar tasks rely on relatedness to create meaningbased or deeply processed memory traces. Although category exemplar tasks are
classically referred to as “implicit” memory tasks, their conceptual properties are
sensitive to different levels of processing at the supraliminal level (Monti et al., 1996).
6
Hence, category exemplar tests may have more conceptually-driven effects on memory if
coupled with deep levels of processing conditions. Therefore, among the memory tasks
available to researchers, the category exemplar test is one of the most effective priming
tools for studying the interaction of levels of processing and exposure to subliminal and
supraliminal stimuli (Mitchell & Bruss, 2003). Thus, in the present study I applied the
category exemplar test by presenting target exemplars from taxonomic groups of animals
and vegetables to the participants and by asking participants to recall those targets later.
Despite the potential interaction between processing and presentation, there
remains a paucity of research that examines the moderated effects of semantically
processed stimuli on category exemplar task performance in older adults. Thus, in
contrast to recent studies examining the relationship between relatedness, elaboration,
and explicit memory (Bradshaw & Anderson, 1982), I analyzed the effect of presentation
timing and thematic-relatedness on the explicit memory of older adults in the current
study.
The Present Study
In the present study, I examined how levels of processing (deep versus shallow)
affects explicit memory task performance when moderated by presentation timing
(subliminal versus supraliminal). I operationally defined deep processing as the
presentation of thematically-related words from two thematic categories (Zoo Animals
and Vegetables). I defined shallow processing as the presentation of randomly generated,
non-thematically-related words. I defined supraliminal presentation as seeing a series of
7
words for 2 seconds each. Subliminal presentation was defined as seeing a series of
words for .04 seconds each.
I expected to find main effects for both presentation and processing of stimuli. For
the main effect of presentation, I expected to see a higher number of supraliminallypresented words recalled than subliminally-presented words. For the main effect of
relatedness, I proposed that memory for thematically-related words would be higher than
memory for non-thematically-related words. Specifically, I expected that thematicallyrelated words would provide a semantic (deep) form of processing that would facilitate
memory performance across both supraliminal and subliminal presentation conditions.
I also hypothesized that participants would have higher memory performance in
supraliminal-deep levels of processing conditions and lower performance in supraliminalshallow, subliminal-deep, and subliminal-shallow conditions. I expected to see this
interaction because meaningful, related words shown for a longer amount of time on a
computer screen tend to produce more durable memory traces than random words or
words presented for a shorter amount of time. The focusing of one’s mind on semantic
content should yield a compound effect on explicit memory performance because
supraliminal processes require the effortful application of cognitive resources that spark
neural network activation and parallel processing stream distribution.
8
Chapter 2
METHOD
With a 2x2x4 mixed repeated-measures factorial design, described in detail
below, I examined the nature of semantic facilitation on explicit memory for words
presented at the conscious and the unconscious perceptual level. I showed each
participant a series of forty words flashed on a computer screen and later asked
participants to recall the words. The two within-subjects independent variables were
thematic association of words and presentation of stimuli. The between-groups
independent variable was order of presentation. Explicit memory recall test performance
was my dependent variable.
The first within-subjects independent variable was thematic association/level of
processing. Thematic association referred to how easily participants could form
associations with presented words (thus affecting their memory for those words), and was
comprised of two levels: a thematically-related word condition (deep processing) and a
non-thematic word condition (shallow processing). The thematically-related word
condition was a list of ten words related to the same category, either Zoo Animals (e.g.,
zebra, kangaroo) or Vegetables (e.g., broccoli, potato). The non-thematic word condition
was a list of ten randomly generated words that had no relation to each other (e.g., skirt,
motorcycle).
The second within-subjects independent variable, presentation of stimuli, referred
to how long participants saw words flashed on the computer screen. This variable had
9
two levels: the supraliminal condition and the subliminal condition. In the supraliminal
condition, participants were exposed to words for 2 seconds each. This presentation time
was long enough for participants to read and understand the word, thus processing it
completely (Moore, 1982; Whiting, 1997). Words were presented for .04 seconds each in
the subliminal condition. This presentation time was long enough for participants to
detect a word, but not long enough to consciously process the word (Khilstrom, 1987;
Moore, 1982).
Video presentation, consisting of four levels, was the only between-subjects
variable used in this study. It was used in order to control for potential order effects. I
used a partial Latin-Square to counterbalance the sequence of phases within each video
presentation. This method of counterbalancing ensured that the thematic and nonthematic words were presented in every possible order (first, second, third, fourth). For
example, order one consisted of supraliminal thematic words presented in phase 1,
subliminal non-thematic words presented in phase 2, supraliminal non-thematic words
presented in phase 3, and subliminal thematic words presented in phase 4. In order two,
by contrast, supraliminal non-thematic words appeared in phase 1, subliminal thematic
words appeared in phase 2, supraliminal thematic words appeared in phase 3, and
subliminal non-thematic words appeared in phase 4. (Each video started with a
supraliminal phase in order to prevent the participant from thinking that there were no
words presented in the video.) Thus, the presentation conditions were counterbalanced
across the four different videos. A total of forty words were presented in each video.
10
Materials
Word Generation
To create the vegetable word list I randomly selected 41 Vegetable words from
the following website: http://www.gardenology.org/wiki/List_of_vegetables. To create
the zoo animal word list I randomly selected 26 Zoo Animal words from the following
website: http://www.catalandictionary.org/wordnets/eng/ZooAnimalList.htm. To create
the non-thematic word list I randomly generated 24 words from the following website:
http://coyotecult.com/tools/randomwordgenerator.php. Next, I trimmed each list to 10
words following the procedures described below.
Inter-rater Reliability
The relatedness of a word to a category could affect the speed and accuracy by
which a participant could retrieve the word from memory, thus assisting in the formation
of cognitive associations (Anderson, 1980). Therefore, I wanted to make sure that one
word list did not contain words that were more related to their respective theme than the
other words to that list’s respective theme. To check the equivalence of thematicrelatedness of the words in the two thematic word lists, I collected inter-rater reliability
data on the degree of relatedness of each word to its specific category.
Ten friends and family members below the age of 55 participated as raters. They
were asked to rate how much each word from the vegetable list was related to the theme
of vegetables, and how much each word from the zoo animals list was related to the
theme of zoo animals. Relatedness ratings were collected only for thematic words.
11
I also collected inter-rater reliability data on the commonness of each word in
everyday usage because the commonness of a word could also increase the accuracy of
recall (Deese, 1960; Gregg, Montgomery, & Castano, 1980; Hall, 1954; Matthews, 1966;
May, Cuddy, & Norton, 1979; May & Tryk, 1970; Postman, 1970; Sumby, 1963; Tulving
& Patkau, 1962; Whiting & Smith, 1997). The commonness inter-rater questionnaire
asked raters to rate how commonly words are used in everyday speech. Commonness
ratings were collected for thematic and non-thematic words. Upon completion of the
word rating procedure, I rewarded the raters with $5.00 Target gift cards.
Final Word List Creation
To create lists of equivalent length (10 words) for each processing condition
(thematically-related and non-thematically-related), I entered the participants’ ratings into
a spreadsheet. Next, I eliminated some words from the original lists by sorting the word
lists (Zoo Animals, Vegetables, non-thematic) from the highest to lowest mean
commonness rating. Then I chose every other two words descending from the highest to
lowest mean commonness rating until I obtained 20 words for each thematic list (Zoo
Animals, Vegetables) and 20 words for the non-thematic word lists. The final list of 40
words was divided into four lists of ten words each using the ABBA sorting sequence.
Refer to Appendix for the list of words used in the video conditions.
After the final word lists were created, I calculated the variability between the two
thematic word lists on relatedness and the variability between the two thematic and the
two non-thematic lists on commonness. T-tests revealed no significant differences
between Zoo Animal words (M = 4.09, SD = .54) and Vegetable words (M = 3.71, SD =
12
.76) on relatedness to their respective thematic category; t (38) = 1.73, p = .09. In other
words, Zoo Animal words and Vegetable words had the same degree of relatedness to
their respective theme. T-tests also showed no significant differences between thematic
(M = 3.49, SD = .63) and non-thematic words (M = 3.34, SD = 1.03) on commonness; t
(38) = .70, p = .48. Thus, both thematic and non-thematic words were considered
equivalent on commonness.
Upon completion of the word list generation procedure I had four lists of 10
words. These lists were capped at 10 words each because the average older adult has a
working memory capacity of 4 (+/- 2) items (Bo, Borza & Seidler, 2009). I chose to
increase the size of the word list from four words to ten words because I wanted to avoid
any potential ceiling effects (Miller, 1956).
Finally, to randomly sort the words within the four lists for the video presentation
conditions, I used the following website: http://textmechanic.com/Sort-Text-Lines.html,
which generated random orders for each 10-word list.
Computer
Words were presented to participants on an ASUS gaming laptop computer
running Windows Live Movie Maker for Windows 7 Home Premium operating system.
Demographic Questionnaire
Before administering the computerized portion of the procedure I collected the
following demographic information: Gender, Highest Education Achieved, Occupation,
Ethnicity, and Religion. Age information was not collected because my entire participant
13
pool consisted of older adults and I did not want the sensitivity of the age question to
deter potential subjects from participating in my study.
Participants
I sent letters to fourteen different agencies within the Sacramento Valley region
and called ten agencies. I recruited forty-eight older adults over the age of 55 from the
following agencies: Senior Center at Elk Grove, Mission Oaks/Swanston Community
Center in Carmichael, and Ethel Hart Senior Center. Of the twelve participants who
answered the question on “Gender,” 3 participants were “Male” and 9 participants were
“Female.” Four out of 48 participants “Completed High School,” 11 “Went to college but
did not finish,” 12 participants “Finished some graduate school or higher,” and 2 “Earned
a doctorate degree.” (The questionnaire did not include an option for those who
completed college but did not attend graduate school.) Almost half of the participants
were “Caucasian” (n = 23), 4 were “Hispanic,” 1 participant was of “Asian American”
descent, 2 were “African American,” and 18 did not indicate their ethnicity. Out of 45
participants who responded to the Religion question, 12 were “Catholic,” 13 were
“Christian,” 5 were “Spiritual,” 1 was “Mormon,” 1 was “Episcopalian,” 3 participants
were “Atheist,” 3 were “New Age,” 2 were “Baptist,” and 5 participants reported “Other”
to signify that they were of a religious affiliation other than what was asked on the
questionnaire. Three participants out of 48 did not respond to the religion question.
Procedure
I received approval at minimal risk to recruit participants from the Human
Subjects Committee in the Department of Psychology in Spring 2011. Next, I pilot-tested
14
the procedure with four individuals who did not meet the study’s criteria for participation
to make sure the testing protocols ran smoothly. There were no problems with the
procedure.
To prepare for the experiment, I made arrangements with the activity coordinators
from each agency listed above to secure a room and a specific time to run my study.
Before the day of the experiment, I randomly assigned the participants to one of four
video conditions. On test day, I greeted each participant individually, showed the
participant to his or her seat in front of the laptop, and led the participant through the
informed consent procedure. Next, I handed the participant a consent form to sign and
return back to me. I then provided the participant with a demographic questionnaire that
asked the participant to reveal his or her gender, education status, occupation, religion,
and ethnicity.
Before starting the video presentation, I instructed the participant to not touch any
key on the keyboard or touchpad because the screen ran by itself. Next, I started the video
assigned to the participant. Within each video, the supraliminal condition had one
thematic phase and one non-thematic phase. The subliminal condition also had one
thematic phase and one non-thematic phase. The order was counterbalanced, as described
above.
The video presentation lasted for 3.99 minutes. In the supraliminal condition, a
blank screen appeared first for 1 second. The orienting stimulus, "_ _ _ _ _ _ _ _ _ _ ",
flashed for .5 seconds before each word appeared on the screen. The masking stimulus,
"XXXXXXXXXX", followed each word and remained on the screen for .5 seconds. A
15
blank screen appeared for 1 second before the orienting stimulus for the next word. In the
subliminal condition the blank screen was shown for 2 seconds before the appearance of
the next word. The orienting stimulus, "_ _ _ _ _ _ _ _ _ _", flashed for .5 seconds before
each word and the masking stimulus, "XXXXXXXXXX", appeared on the screen for a
duration of .5 seconds after the flashing of each word. A blank screen appeared for 2
seconds before the orienting stimulus for the next word. The difference in timing of the
presentation of blank screens was potentially problematic but unequal durations for the
four videos would have compromised the internal validity of my repeated measures
design. To ensure that each video condition lasted for an equivalent amount of time, I
prioritized consistency of video presentation length across my video conditions over
equal time spacing between orienting stimuli, test words, and masking stimuli.
After the video was complete, I administered the free recall exam by giving the
participant a pen and piece of lined 8.5 x11 white printer paper with the following
instructions at the top of the page: “Please write as many words as you can remember from
the presentation you just saw. You have as much time as you want to complete this form.”
Next, I told the participant that he or she could take as much time as needed to complete
the test. After I read the instructions to the participant, I quietly left the room. After the
exam was complete, I debriefed the participant and gave the participant a $5 gift card to
Walmart.
16
Chapter 3
RESULTS
Using two mixed repeated measures ANOVAs, I examined differences between
the thematic and presentation conditions on word recall (see Table 1).
Table 1
Descriptive Statistics for Hits and False Alarms (N = 48)
Hits
Source
M
SD
Relatedness
False Alarms
F(1, 44)
p
100.37
< .001
M
SD
Thematic
2.13
0.13
0.10
0.04
Non-thematic
0.57
0.11
0.13
0.05
Presentation
220.90
< .001
Supraliminal
2.63
0.17
0.22
0.06
Subliminal
0.07
0.05
0.01
0.01
Relatedness x Presentation
109.13
< .001
Thematic Supraliminal
4.10
0.23
0.21
0.07
Thematic Subliminal
0.15
0.09
0.00
0.00
Nonthematic Supraliminal
1.15
0.21
0.23
0.09
Nonthematic Subliminal
0.00
0.00
0.02
0.02
F(1, 44)
p
.19
.67
10.05
.003
0.00
1.00
The first dependent variable, the number of “hits,” represented the number of
words the participant wrote down on the recall task that were presented in the video
presentation (i.e., correctly-recalled words). The second dependent variable, number of
17
false alarms, was the number of words that the participant wrote down on the recall task
that were not presented in the video presentation. I associated each false alarm with the
condition that contained a structurally similar word. For example, if one condition
contained the word ”torchlight” and the participant wrote the word “headlight,” I placed
the false alarm score in the condition that contained “torchlight.”
Hits
The between subjects variable, presentation order, did not show a significant main
effect for hits, F (3, 44) = 2.18, p = .10, indicating that order of presentation had no effect
on correct recall for presented words. Additionally, there were no significant two-way or
three-way interactions with presentation order for hits. The first within-subjects variable,
timing of presentation, showed a significant main effect for hits, F (1, 44) = 220.90, p <
.001, semi-partial η2 = .46, such that supraliminal presentation conditions yielded a higher
number of hits than subliminal presentation conditions, as predicted (see Table 1).
However, the presence of an interaction modified the nature of this main effect. The
second independent variable, thematic-relatedness, also showed a significant main effect
for hits, F (1, 44) = 100.37, p < .001, semi-partial η2 = .17, such that thematic conditions
produced significantly more hits than non-thematic conditions. However, the interaction
showed that this effect did not exist for the subliminal condition.
Both main effects had to be viewed in the context of a significant interaction, F
(1, 44) = 109.13, p < .001, semi-partial η2 = .14. Pairwise comparisons were used to test
for simple effects of the thematic conditions. For supraliminal presentation conditions
there was a significant mean difference between thematic and non-thematic conditions
18
such that the number of hits in thematic conditions was significantly higher than the
number of hits in non-thematic conditions, Mean difference = 2.96, p < .001. However,
there was no difference between the two thematic conditions in the subliminal condition,
Mean difference = .15, p =.11.
6.00
Performance
5.00
4.10
4.00
Presentation
3.00
Supraliminal
2.00
Subliminal
1.15
1.00
0.15
0.00
0.00
Thematic
Non Thematic
Relatedness
Figure 1. The interaction of presentation and relatedness for hits.
19
False Alarms
The between subjects variable, presentation order, did not show a significant main
effect for false alarms, F (3, 44) = .60, p = .62, revealing no effect of video order on the
number of written responses that were not on the word list but resembled words on the
list. Moreover, there were no significant two-way or three way interactions with
presentation order for false alarms. Presentation showed a significant main effect for
false alarms, F (1, 44) = 10.05, p < .001, semi-partial η2 = .10, such that there were
more false alarms produced in supraliminal presentation conditions than in subliminal
presentation conditions (see Table 1). However, thematic-relatedness did not show a
main effect for false alarms, F (1, 44) = .19, p = .67. Similarly, there was no interaction
of presentation and thematic-relatedness, F (1, 44) = .00, p = 1.00, for false alarms. See
Figure 2 for the main effect of presentation time on false alarms.
Performance
0.30
0.25
0.23
0.20
Presentation
0.21
0.15
Supraliminal
0.10
Subliminal
0.05
0.00
0.02
0
Thematic
Non Thematic
Relatedness
Figure 2. The main effect of presentation for false alarms.
20
Chapter 4
DISCUSSION
The results of the present study confirmed my hypothesis that older adults would
exhibit higher explicit memory performance when words were presented to conscious
awareness than when words were not presented within conscious awareness, but this
difference was much larger for words belonging to a theme or category than for words
not related to each other in any obvious way. Furthermore, the results supported my
prediction that words belonging to a theme or category would be more easily
remembered than words that were not related to each other in any obvious way, but this
was true only when words were presented within conscious awareness.
As I mentioned above, performance on the recall test was higher in supraliminal
conditions than in subliminal conditions. This result is consistent with research on the
facilitation of visual recall through the engagement of conscious processes (Aggleton &
Brown, 1999; Gardiner, 1988; Gardiner & Java, 1990; Gardiner & Java, 1991; Gardiner,
Java & Richardson-Klavehn, 1996; Jacoby, 1991; Rajaram, 1993; Tulving, 1985;
Wagner, Verfaeille, & Gabrieli, 1997; Yonelinas, 2002).
The deep processing phenomenon is evidenced in my study, which shows higher
explicit memory performance on the free recall exam in thematic conditions than in nonthematic conditions. This finding resembled the results of Craik and Lockhart (1972),
showing the positive effect of deep processing on explicit memory.
21
Past research indicates that older adults are more likely to use semantic
associations than younger adults when performing serial recall tasks (Golomb, Peele,
Addis, Kahana, & Wingfield, 2008). Moreover, Englekamp and Wippich (1995) found
that, for older adults, word-relatedness enhances memory of subliminally presented
words. Conversely, younger adults remember more words that are not related to each
other in priming tasks than do older adults (Englekamp & Wippich, 1995). Younger
adults may not use categories to facilitate memory performance during the completion of
implicit memory tasks such as priming.
In contrast, older adults’ dependence on semantic content for memory
consolidation amplifies the effects of consciously perceived stimuli on explicit memory
test performance. By depicting the relationship between presentation and levels of
processing, my study demonstrated the importance of supraliminal effortful processes on
semantic facilitation of explicit memory. This claim is further supported by evidence
from Monti et al. (1996), who showed how meaning-based encoding processes through
the engagement of supraliminal memory processes enhance conceptually-driven aspects
of memory tasks. Additionally, Bradshaw and Anderson (1982) made advances in
conceptual priming and processing research by revealing the compound effect of
supraliminally-presented stimuli and thematic relatedness on category exemplar test
performance. Conclusively, the results from my study and previous research exemplified
the pivotal role that semantic associations play on conscious processes during explicit
memory tasks.
22
Notably, older adults falsely-remembered more words in the video presentation of
supraliminal stimuli than of subliminal stimuli. In other words, there were more false
alarms in the supraliminal than in the subliminal conditions. Supraliminality and the
application of cognitive effort seemed to have a stronger effect on incorrect guessing than
the effect of meaning-based memory processes, such as levels of processing, on memory.
Possibly, deep processing produces more accurate automatic memory trace formations in
older cohorts as a result of more efficient neural activation (Hinojosa, Martin-Loeches,
Munoz, Casado, & Pozo, 2004; Karni et al., 1995) whereas increased exertion of
resources help younger cohorts with situations that require the generation of novel ideas,
such as college or graduate school (Cabeza, Anderson, Houle, Mangels, & Nyberg,
1997).
Older adults who experience age-related memory declines due to the natural
degradation of interdependent cognitive systems could benefit from research findings on
how linguistic, semantic, and presentation tools might enhance memory (Luczsz &
Bryan, 1999). Researchers have relied on two principal theories to identify the sources of
aging phenomenon: Slowed central nervous system processing speed (Salthouse, 1980;
Salthouse, 1982; Salthouse, 1985; Salthouse, 1996) and diminished use of working
memory executive processes (Dempster, 1992; Parkin & Walter, 1992; Parkin, 1997;
Woodruff-Pak, 1997). By identifying the possible sources of age-related cognitive
declines, one can apply the findings from the present study to develop memory
preservation techniques for the aging mind, thus attempting to prevent the onset of the
debilitating disease of dementia.
23
Although the term “dementia” encompasses a variety of cognitive deficits, the
patient with dementia undergoes a series of phases before reaching the stage of clinical
diagnosis. Mild cognitive impairment diagnoses are given to individuals who experience
more serious cognitive decline than is expected for their age group or education level;
however, this class of impairment does not affect daily functioning (Gauthier et al.,
2006). The diagnoses of mild cognitive impairments and early onset of dementia-related
disorders tend to overlap (Santacruz & Swagerty, 2001). Preventative medicine could
provide memory-enhancing strategies to individuals with a genetic history of dementia.
The dual cognitive effects of meaningful, persistent stimuli could help reduce the risk of
the onset of dementia in that population.
Strengths and Limitations
The study’s design strengths bolstered its internal validity. For example, the recall
test was administered immediately after the study condition to reduce the time gap
between study and test. This measure increased the accuracy of word recall because
visual persistence of stimuli declines as the time gap increases between study and test
(Coltheart, 1980). Furthermore, by including two thematic word categories, I ensured that
the test measurement protocol was truly assessing the effect of relatedness on memory:
Using two thematic categories instead of one eliminated the possibility that recall could
be affected by category type instead of the intended independent variable, relatedness.
Equal variances among the two thematic word categories also protected the
internal validity of the study by ensuring that one category did not contain words of
higher relatedness than the other category. In other words, the equal variances among the
24
words within each thematic category buffered the study against possible biases of two
videos showing words from the same category with differing degrees of relatedness.
To accomplish the task of using two different categories, I used the partial
counterbalancing measure to present the four relatedness conditions in every possible
order, thus eliminating the possible confounding effect of a previous phase influencing
memory for words presented in a subsequent phase. However, the Latin-Square partial
counterbalancing measure did not eliminate all bias because the supraliminal condition
was always the first phase of each video. While a complete counterbalancing measure
would have removed this bias, it would have required that half of the videos present the
subliminal condition as the first phase, thus creating confusion for half of the participants
who saw the first set of words outside of their conscious awareness. In sum, I used a
partial counterbalancing measure to minimize this potential anxiety during the test phase.
Additionally, my decision to study individuals over 55 years of age was based on
aging literature revealing that 55 heralds a 16 year cognitive decline affecting list and text
recall in older adults. This cutoff is one of few widely accepted norms for investigating
age related decline in memory (Powell & Whitla, 1994). Using this age bracket to
conduct a longitudinal study, Zelinski and Burnight (1997) investigated normative
changes in memory and compared performance on intelligence tests of younger and older
adult cohorts. In their study, all age cohorts over 55 showed reliable decreases in
cognitive ability. Their findings confirm that normative age-related change in cognition
typically starts to appear at age 55, thus providing a solid age baseline for my study of
cognitive aging.
25
Furthermore, if I were to replicate this experiment, I would use the same time
limit methodology I used in the current study and not set a time limit for the testing
condition because older adults have slower processing speed than younger adults (Bryan
& Luszcz, 1996; Bryan & Luszcz, 2001). The rate of cognitive processes, such as
memory performance, varies widely from one participant to another and setting a time
limit would favor those with faster rates of cognitive processes. Thus, a time limit would
create a disadvantage for those with slower processing speeds.
In contrast to these strengths, various methodological limitations surfaced during
the development of my study’s experimental design. The small sample size of forty-eight
participants increased the risk of Type II error, which is the tendency to accept the null
hypothesis when it is false. My null hypothesis was that there was no difference in recall
between conditions. The small sample size may have underestimated the number of
significant memory score differences between the levels of the two independent
variables: relatedness and presentation. Although the heightened risk of committing a
Type II error was potentially problematic for my study, my hypotheses were still
supported by the results.
A small sample size also hindered my ability to draw generalizeable conclusions
about the entire senior population. Because I collected data from a convenience sample in
the community, the personalities and motivations of those who decided to volunteer for
my study could have differed from those who did not volunteer for my study. This
disparity could have biased my results to reflect positive attitudes toward academia or
community service. Furthermore, taking a convenience sample from a select group of
26
senior communities may not have adequately captured the true population mean with a
high degree of confidence. If I were to conduct this study again, I would allot more time
to participant recruitment in hopes of increasing my sample size to at least 100
participants.
My decision to draw a convenience sample instead of a random sample limited
the representativeness of my subject pool. Because I did not collect a random sample, the
economic, educational, and health characteristics unique to the senior communities
sampled may have biased the results in favor of individuals with high levels of selfesteem and active lifestyles. Because I used a convenience sampling method for my data
collection, my distribution of mean scores may have deviated from the normal
distribution of population test scores. To adequately capture the complete constellation of
characteristics within my target senior population I should have used a random sample
because it would have fairly represented each characteristic without bias, effects of
outliers, and confounding covariates.
In addition, my method for recording false alarms exposed my study to
experimenter bias because it included a degree of subjectivity. I decided that an answer
was a false alarm if it shared structural similarity to the words in the video phases. The
subjectivity I used to determine whether the word was a false alarm may have positively
skewed the distribution of false alarm scores in my study. Furthermore, testing after each
phase would have been a better approach than testing after the video ended because
exposure to words from previous phases could have rendered ambiguous false alarm
assignments.
27
The sample also consisted of a disproportionate number of females compared to
males. Research shows that females in general have higher rates of depression than males
(Kessler et al., 1994; Regier et al., 1988; Robins et al., 1984). Royall, Palmer, Chiodo,
and Polk (2011) show that depression attenuates executive motor functions. Bo, Borza
and Seidler (2009) show that diminishing executive processes are related to cognitive
declines during aging. Therefore, depression could hasten the onset of dementia. Because
depression, a disease more prevalent in women than in men, is likely to produce
deleterious effects on aging memory, the disproportionate number of women in my
sample may have created negatively biased memory performance results.
Additionally, some participants experienced mild to moderate degrees of
frustration while watching the video, which escalated when they realized that a memory
test would immediately follow the video. My overreliance on the proctoring script and
the participants' uneasiness about taking a memory exam may have increased the
ambiguity in some of their responses and reduced the accuracy of scoring their answers.
Their anxiety may have hindered their ability to remember the exact structure of certain
words, producing a somewhat higher number of false alarms in supraliminal conditions.
Finally, to obtain a more accurate picture of the baseline cognitive functioning
status of the participant pool, I would use the Telephone Interview Questionnaire for
Cognitive Status, a cognitive assessment tool developed by Brandt, Spencer, and Folstein
(1988). An assessment of cognitive status could help me to screen individuals and
remove those who have stages of mild cognitive impairment or physical disabilities such
as blindness that would prevent them from participating in my study. Although my study
28
did not include individuals with these types of impairments, this screening tool would
ensure that I capture only individuals with high cognitive functioning.
Future Directions
Assisting cognitive aging through modern technology and educational media
creates a dynamic transmission of knowledge throughout younger and older generations.
To further analyze the relationship between relatedness and presentation, one might want
to incorporate elements from human-computer interface psychology literature to produce
websites that will facilitate the engagement of older adults. Websites designed with agerelevant meaning-based contextual cues can assist older adults’ recall by activating
associative frameworks within their cognitive substrates. The results of such a study may
have important applications in the design of educational curricula in senior centers. For
example, teachers could use computers to present seniors with supraliminally-timed
reading exercises that consist of related material sparking consolidation of short-term
memories and association formations within cognitive networks.
My study of cognitive aging offers many benefits from a holistic health
perspective paving the way for further analysis of the interaction of many sociodemographic variables that affect memory. Future studies analyzing the relationship
between age, cognitive functioning, risk for dementia, and test performance would create
a portrait of the dynamic relationship between these four variables and their significant
implications for gerontological health science research. These studies would chronicle the
progression of dementia and age-related cognitive impairments. Advances from this line
29
of research would not only impact science at an epidemiological level but also at an ionic
and cellular level.
The results from my study may assist those older adults with a genetic history of
Alzheimer’s disease because knowing how to facilitate recall could provide older adults
with a buffer against memory loss. My research findings that processing and timing of
presentation affect explicit memory in senior populations could mobilize future research
endeavors to study consciousness and its correlates with memory. Creative uses of deep
processing and semantic memory enhancing strategies could apply not only to senior
citizens but to other populations who would benefit from effortful retrieval and controlled
allocation of cognitive resources such as dyslexic or autistic children who might use
semantic networks for reading comprehension. Comparing healthy cognitive aging to
anomalous cognitive aging in later studies would impact neuropathological research
along the lines of preventative gerontological medicine and gerontological education.
Conclusion
Gerontology research throughout the past decade has chronicled the debilitating
effects of the gradual breakdown of cognitive systems in older adult populations. Despite
cognitive decline’s deleterious impact on memory capacity, compensatory memory
systems such as semantic associations and processing time can enhance memory
consolidation within complex neural networks. The activation of these networks unveils
the profound effect of meaning and consciousness on human experience and our reliance
on memory for survival.
30
Appendix
Final List of Forty Words Used in the Four Video Conditions
Video 1
Video 2
Them-Zoo
Non-them (A)
Non-them (B)
Them-Veg
Non-them (B)
Them-Zoo
Veg
Non-them (A)
Phase I
Phase II
Phase III
Phase IV
Phase I
Phase II
Phase III
Phase IV
Sup.
Sub.
Sup.
Sub.
Sup.
Sub.
Sup.
Sub.
elephant
grandchild
unfasten
cauliflower
bandanna
rhino
onion
test
hippo
torchlight
bandanna
broccoli
exhilarate
tiger
cucumber
torchlight
leopard
compactor
incongruity
lettuce
unfasten
panther
pepper
thumbprint
lion
test
rottweiler
potato
rottweiler
chimp
carrot
notion
orangutan
thumbprint
skirt
pea
drive
panda
celery
bankruptcy
crocodile
notion
buddy
spinach
skirt
penguin
corn
middlebrow
gorilla
middlebrow
motorcycle
peanut
motorcycle
kangaroo
asparagus
grandchild
giraffe
groin
exhilarate
avocado
baron
snake
garlic
groin
bear
technician
drive
pumpkin
buddy
zebra
cactus
technician
alligator
bankruptcy
baron
squash
incongruity
gazelle
beet
compactor
Video 3
Them-Veg Non-Them (A)
Phase I
Phase II
Video 4
Non-Them (B)
Them-Zoo
Non-Them (B)
Them-Veg
Them-Zoo
Non-Them (A)
Phase III
Phase IV
Phase I
Phase II
Phase III
Phase IV
Sup.
Sub.
Sup.
Sub.
Sup.
Sub.
Sup.
Sub.
corn
groin
buddy
chimp
buddy
cauliflower
elephant
notion
pepper
notion
exhilarate
penguin
incongruity
broccoli
leopard
middlebrow
onion
test
motorcycle
kangaroo
bandanna
spinach
giraffe
technician
asparagus
technician
unfasten
snake
skirt
potato
lion
compactor
beet
bankruptcy
bandanna
panther
exhilarate
lettuce
crocodile
torchlight
celery
thumbprint
skirt
tiger
unfasten
avocado
orangutan
bankruptcy
cucumber
torchlight
rottweiler
panda
motorcycle
pumpkin
bear
test
carrot
grandchild
drive
rhino
drive
peanut
alligator
groin
garlic
middlebrow
baron
zebra
rottweiler
squash
gorilla
thumbprint
cactus
compactor
incongruity
gazelle
baron
pea
hippo
grandchild
31
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