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CROSS-SECTIONAL AND LONGITUDINAL ANALYSES

OF THE EFFECTS OF AGING ON MEMORY IN HEALTHY YOUNG, MIDDLE-AGED, AND OLDEST-OLD ADULTS

A thesis presented in partial fulfillment of the requirements for the degree of

Doctor of Philosophy in Psychology

at Massey University, Palmerston North, New Zealand

ALLISON LAMONT

2006

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To my mother, Jeanie Paton, now 90 years of age, an indomitable Scotswoman whose remarkable memory ignited

my curiosity in just what does happen to memory during the aging process

iv

v

Abstract

While a growing body of research indicates that older adults typically perform more

poorly on many types of memory tasks than do younger adults, relatively little research

has addressed the question of whether this trend continues unchanged into the late

ninth and tenth decades of life. Such decrements in memory have been reported as

linear declines from early adulthood up until about 80 years of age. Questions arise as

to whether such memory declines slow or accelerate in very advanced aging, and to

what extent differences are due to aging, per se, or variables that intervene between

age and memory.

To address these two questions, six memory types – verbal recall, nonverbal recall,

short-term memory, working memory, face recognition, and prospective memory –

were examined using both cross-sectional and longitudinal methodologies. The six

types of memory and the influence of verbal processing speed, nonverbal processing

speed, and intelligence were examined in mixed-gender groups of 20 - 40 (n = 40, M =

30.7, SD = 5.52), 50 - 70 (n = 44, M = 59.2, SD = 4.94), and 85+ year olds (n = 42, M =

87.8, SD = 2.43), at two points, the second occurring two years after the first. Each

participant completed tests of word recall, geometric shapes recall, short-term memory

(digit span), working memory (letter-number sequencing), face recognition, and

prospective memory. Additionally, there were two processing speed tasks (Identical

Pictures and Finding As), and the National Adult Reading Test of verbal fluency was

used to estimate intelligence. The Mini-Mental State Examination and the Beck

Depression Inventory (BDI-II) were used to screen for dementia and depression,

respectively.

At Time 1 testing the 85+ participants showed declines in all memory types (compared

to the 20 - 40 year olds). Nonverbal recall (66.2% lower than the young group), working

memory (46.2%), verbal recall (45%), and prospective memory (38.2%) produced the

largest differences, short-term memory (12.3%) and face recognition (14.7%) the least.

Two years later, the 85+ years old participants had shown further declines, relative to

the 20 - 40 years group. Nonverbal recall (72.3% lower than the young group),

prospective memory (63.2%), working memory (55.3%), and verbal recall (54.7%)

continued to produce the largest decrements, with short-term memory (18.9%) and

face recognition (19.8%) the least. The results for the young and middle participants

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did not change appreciably between Time 1 and Time 2. The difference between

unadjusted scores and scores adjusted for intelligence, verbal processing speed, and

nonverbal processing speed, increased markedly between Time 1 and Time 2 testing

for the oldest-old participants.

These findings support the view that while memory declines may be approximately

linear from age 20 to 80 years, there is a sharp decline in most types of memory after

the age of 85 years, recall and working memory suffering the most. Intelligence and

processing speed have an effect on some types of memory, but age is by far the

largest contributor to memory decline. Furthermore, as expected, all memory types

declined over the two-year period, with prospective memory, verbal recall, nonverbal

recall, and working memory showing the greatest declines. Short-term memory and

face recognition declined at a noticeably slower rate.

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Acknowledgements

First and foremost, I wish to express my thanks to my supervisors, Associate-Professor

John Podd, Dr. Stephen Hill, and Dr. Julie Bunnell. From the moment I contacted Dr.

Podd asking him to supervise my research, he was instrumental in gathering the team

who would be enthusiastic and supportive throughout the research process. I am

deeply grateful for the generous sharing of knowledge, expertise, and encouragement I

have received. Thank you, especially, Dr. Podd for your unique combination of exacting

academic standards, statistical ‘know-how’, academic curiosity, and a sense of humour

which has lightened the journey for me many a time.

Special acknowledgement must be made to the participants, who bought this piece of

work to life. It was a delight to work with people who were fully supportive of what I was

doing. I was grateful to participants who gave of themselves amidst busy schedules of

work and study. It was a particular pleasure to spend time with many of our oldest

citizens. I appreciated their generosity in sharing their time, stories, and numerous cups

of tea! I was touched by their willingness in allowing me to investigate what was often a

source of worry to them – their memory. I especially appreciated the oft-expressed

belief of the older volunteers that together we were making a contribution to

understanding the process of aging. Thank you.

Thank you to Malcolm Loudon of Massey University who took my ideas and diagrams

and turned them into a splendid computer-based geometric shapes test, and likewise

built other test materials into computer software programmes. Thank you, too, to Hung

Ton of Massey University for his willing assistance in all matters relating to the

compilation and provision of the test battery. You are both much appreciated.

Thank you to my mother, Jeanie Paton, for her constant support. My mother was

invaluable to me in her capacity of proof-reader for this research, and in her

unwavering belief in me. I am grateful, too, to my children and grandchildren as they

have understood and accommodated my absorption in the research process.

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Table of Contents

Dedication ……………………………………………………………………………… iii

Abstract ………………………………………………………………………………… v

Acknowledgements …………………………………………………………………… vii

Table of Contents …………………………………………………………………….. ix

Appendices ......................................................................................................... xiii

List of Tables ………………………………………………………………………….. xv

List of Figures …………………………………………………………………………. xviii

Preface …………………………………………………………………………………

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Chapter One A BRIEF HISTORICAL SURVEY OF MEMORY AND MEMORY RESEARCH

1

The Influence of Ebbinghaus ................................................................ 3

Other Early Research ............................................................................ 5

Influential Landmarks in Recent Memory Research ............................. 6

The Computer Revolution ....................................................... 6

Multi-System Models ............................................................... 9

The Atkinson-Shiffrin Model .................................................... 10

Levels-of-Processing ............................................................... 12

The Baddeley and Hitch Model ............................................... 14

Schacter and Tulving ............................................................... 17

The Need for Clarification of Terminology ...............................

19

Chapter Two MEMORY AND AGING IN HEALTHY ADULTS

25

Inter-Individual and Intra-Individual Change .......................................... 26

General Decline versus Task Specific Decrements .............................. 28

Are Age-Associated Declines in Memory Inevitable? ........................... 29

Sensory Memory ................................................................................... 31

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Short-Term Memory .............................................................................. 31

Long-Term Memory ............................................................................... 32

Differing Rates of Change .....................................................................

34

Chapter Three

MEMORY AND THE OLDEST-OLD

37

Who are the Oldest-Old? ...................................................................... 38

The Scarcity of Memory Research Investigating the Oldest-Old .......... 38

Advanced Age as a Variable in Memory Research ............................... 39

Longitudinal Aging Studies ................................................................... 44

The Seattle Longitudinal Study ............................................... 45

The Duke Longitudinal Study ................................................. 45

The Canadian Victoria Longitudinal Study and the Swedish

Kingsholmen Project ............................................................... 47

The Berlin Aging Study ........................................................... 48

The Relationship Between Cognitive Decline and Mortality in the Oldest-Old ............................................................................................

50

Chapter Four

EXPLANATIONS FOR AGE DIFFERENCES IN MEMORY

59

Cognitive Explanations 60

Reduced Processing Resources ............................................ 60

Speed of Processing .............................................................. 61

Working Memory and the Role of the Central Executive ........ 67

The Role of Attention .............................................................. 69

The Neurobiological Substrates of Memory ......................................... 70

The Aging Brain ...................................................................... 71

PET and fMRI Studies ............................................................ 71

Working Memory ..................................................................... 73

Episodic Memory Encoding .................................................... 74

Episodic Memory Retrieval ..................................................... 75

The Role of the Hippocampus ................................................ 75

Demyelination ......................................................................... 78

Neurochemical Studies ...........................................................

78

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Chapter Five THE PRESENT STUDY 81

Verbal Recall ........................................................................................ 81

Nonverbal Recall .................................................................................. 85

Short-Term Memory ............................................................................. 88

Working Memory .................................................................................. 89

Face Recognition .................................................................................. 91

Typical face recognition studies............................................. 93

Age differences in face recognition research......................... 93

The age of stimulus faces...................................................... 95

Prospective Memory ............................................................................. 96

Methodological Issue ............................................................................ 101

Cross-sectional Versus Longitudinal Research ...................... 101

The Present Study ............................................................................... 103

The Expectations of the Present Study.................................................

105

Chapter Six METHOD 107

Participants.................................... ...................................................... 107

Experimental Design and Analyses...................................................... 108

ANCOVA Analyses................................................................. 110

Standard Multiple Regression Analyses................................. 110

Procedure ............................................................................................ 111

General Procedure ................................................................. 111

Measures .............................................................................................

113

Health and Demographic Data

Structured Screening Interview .............................................. 113

Mini-Mental State Examination (MMSE) ................................ 113

Beck Depression Inventory – Second Edition (BDI-II)............ 116

SF-36 Health Survey .............................................................. 117

National Adult Reading Test – Second Edition (NART) .........

119

Memory Tasks

Recall – Verbal ....................................................................... 120

Recall – Nonverbal ................................................................. 121

Delay in Verbal and Nonverbal Recall .................................... 123

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Forward Digit Span ................................................................. 124

Letter-Number Sequencing Task ............................................ 124

Face Recognition ................................................................... 125

Prospective Memory Tasks ....................................................

127

Processing Speed Measures 128

Identical Pictures ................................................................... 129

Finding A’s .............................................................................

130

Chapter Seven

RESULTS 133

Cross-sectional Analyses

Memory Types Time 1 Testing................................................ 133

Memory Types Time 2 Testing................................................ 137

Covariates at Time 1 Testing ............................................................... 140

Multiple Regression Analysis at Time 1................................. 145

Covariates at Time 2 Testing................................................................ 147

Multiple Regression Analysis at Time 2................................ 153

Longitudinal Analyses .......................................................................... 156

Subsidiary Analyses

Delay in Verbal and Nonverbal Recall Tasks.......................... 160

Chapter Eight

DISCUSSION 165

Cross-sectional Analyses at Time 1 and Time 2 Testing...................... 166

Longitudinal Analyses at Time 1 and Time 2 Testing .......................... 174

Cross-sectional Analyses of Covariates .............................................. 177

Effects of the Retained Covariates on Memory

Verbal Recall .......................................................................... 179

Nonverbal Recall .................................................................... 181

Short-Term Memory ............................................................... 184

Working Memory .................................................................... 184

Face Recognition ................................................................... 185

Prospective Memory .............................................................. 189

Overall Effects of the Covariates ......................................................... 190

The Longitudinal Effects of the Covariates........................................... 191

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The Effect of Age ................................................................................. 192

Delay .................................................................................................... 194

Towards a Theory of Aging and Memory in Normal, Healthy Adults ... 195

Limitations and Future Directions......................................................... 203

Attrition Rate ........................................................................................ 207

Summary and Conclusions...................................................................

208

REFERENCES ........................................................................................

211

APPENDICES

Appendix A: Information sheet ..................................................................... 263

Appendix B: Consent form ........................................................................... 267

Appendix C: Structured screen interview ..................................................... 269

Appendix D: Mini Mental State Examination ................................................ 271

Appendix E: Beck Depression Inventory – Second Edition ......................... 275

Appendix F: SF-36 Health Survey ............................................................... 279

Appendix G: The National Adult Reading Test ............................................. 285

Appendix H: Words used in the verbal recall task ........................................ 287

Appendix I: The Shapes Test – stimuli, development, and scoring criteria 289

Appendix J: The Digit Span subtest from the WAIS-III ................................ 301

Appendix K: The Letter-Number Sequencing Task from the WAIS-III ........ 303

Appendix L: Sample Stimulus Face from the Face Recognition Task ......... 305

Appendix M: ANOVA for all memory types at Time 1 testing ....................... 307

Appendix N: ANOVA for all memory types at Time 2 testing ....................... 311

Appendix O: Mixed design ANOVA with Time as the within groups factor,

and Age as the between groups factor ....................... 315

Appendix P: ANCOVA for all memory types at Time 1 testing .................... 319

Appendix Q: ANCOVA for all memory types at Time 2 testing .................... 323

Appendix R: Raw Data for all memory types, covariates, and screening tests for all age groups ............................................................ 327

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List of Tables

Table 1.1 A glossary of terms commonly used to describe memory types.............................................................................................

20

Table 1.2 A glossary of terms commonly used in memory research............ 21

Table 6.1 Means (SD) for the demographic characteristics of participants at Time 1 testing ..........................................................................

108

Table 6.2 Experimental tasks (in order of presentation) and associated functions

112

Table 7.1 Mean raw scores (and SDs) and possible score for all memory tasks at Time 1 testing as a function of age ................................

134

Table 7.2 The percentage decline in the middle and oldest-old groups relative to the young group in all memory tasks at Time 1.........

135

Table 7.3 The mean difference for all memory tasks for young (=1), middle (=2), and oldest-old (=3) participants at Time 1 testing ...

136

Table 7.4 Mean raw scores (and SDs) and possible score for all memory tasks at Time 2 testing as a function of age ................................

137

Table 7.5 The percentage change in the middle and oldest-old groups relative to the young group in all memory tasks at Time 2 ..........

138

Table 7.6 The mean difference for all memory tasks for young (=1), middle (=2), and oldest-old (=3) participants at Time 2 testing ...

139

Table 7.7 Pearson correlations between the potential covariates collapsed across age, at Time 1 testing (n = 126).......................................

140

Table 7.8 Pearson correlations between all potential covariates and all memory tasks collapsed across age at Time 1 testing (n = 126).

141

Table 7.9 F test, significance, partial eta squared, and power statistics for the covariates of intelligence, and verbal and nonverbal processing speed for all memory types at Time 1 .......................

142

Table 7.10 Adjusted mean scores and standard error for all memory tasks across young, middle, and oldest-old participants at Time 1 .......

143

Table 7.11 The percentage change between unadjusted and adjusted scores at Time 1 for all memory tasks as a function of age ........

144

Table 7.12 The adjusted R2, percentage of variance accounted for by the model, significance, and unique variance accounted for by the covariates, at Time 1....................................................................

146

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Table 7.13 Pearson correlations between the potential covariates collapsed across age, at Time 2 testing (n = 126) .......................................

147

Table 7.14 Correlations between all potential covariates and all memory types collapsed across age at Time 2 testing (n = 126) ..............

148

Table 7.15 F test, significance, partial eta squared, and power statistics for the covariates of intelligence, and verbal and nonverbal processing speed, and age, for all memory types at Time 2.......

150

Table 7.16 Adjusted mean scores and standard error for all memory tasks across young, middle, and oldest-old participants at Time 2 .......

151

Table 7.17 The percentage change between unadjusted and adjusted scores at Time 2 for all memory tasks as a function of age ........

151

Table 7.18 The difference between Time 1 and Time 2 for the percentage of change between unadjusted and adjusted scores on all memory tasks for the oldest-old group ........................................

152

Table 7.19 The adjusted R2, percentage of variance accounted for by the model, significance, and unique variance accounted for by the covariates, at Time 2 ...................................................................

154

Table 7.20 Comparison of the percentage of significant unique variance contributed to the six memory types by the covariates at Time 1 and Time 2 ...................................................................................

154

Table 7.21 Raw mean scores for all memory tasks (and SDs) at Time 1 and Time 2 as a function of age ..................................................

156

Table 7.22 The percentage change between the mean raw scores at Time 1 and Time 2 testing for all memory types as a function of age ..

157

Table 7.23 The raw score means (and SDs) for the verbal recall task for all groups immediately after study, and at 10-minutes and 7-day delay ............................................................................................

161

Table 7.24 The number of participants in the oldest-old group scoring 0 in the verbal recall task at Time 1 and Time 2 .................................

162

Table 7.25 Means (and SDs) for the nonverbal recall task for all groups immediately after study, and at 10-minutes and 7-day delay ......

162

Table 7.26 The number of participants in the oldest-old group (n = 42) scoring 0 in the nonverbal recall task at Time 1 and Time 2 .......

163

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Appendices Tables Table H.1 Words and frequency of words used in the verbal recall task .....

288

Table I.1 The results of pilot testing of the shapes test for the young and old groups, for recall immediately after study, and at 10-minute delay and 7-day delay periods .....................................................

292

Table R.1 Key to test titles used in all raw data tables .................................

328

Table R.2 Raw data for the Young group (20 – 40 years) for all tests at Time 1 and Time 2 testing ...........................................................

329

Table R.3 Raw data for the Middle Group (50 – 70 years) for all tests at Time 1 and Time 2 testing ...........................................................

333

Table R.4 Raw data for the Oldest-old group (85+ years of age) for all tests at Time 1 and Time 2 testing ..............................................

341

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List of Figures

Figure 7.1 Standardised z-scores for all types of memory tasks for all groups at Time 1 ......................................................................

134

Figure 7.2 Standardised z-scores for all types of memory tasks for all groups at Time 2 ......................................................................

138

Figure 7.3 The mean test scores at Time 1 after correcting for the covariates against uncorrected scores for all memory tasks and all age groups ...................................................................

145

Figure 7.4 Standardised z-scores for intelligence, nonverbal processing speed, and verbal processing speed at Time 1 and Time 2 ...

149

Figure 7.5 The mean test scores at Time 2 after correcting for the covariates against uncorrected scores for all memory tasks and all age groups ...................................................................

153

Figure 7.6 Time 1 and Time 2 z-scores for all memory tasks as a function of age .........................................................................

158

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PREFACE

There may be no more pressing intellectual need in our culture

than for people to become sophisticated about the function of memory.

Hampl (1996, p. 211)

Memory is at the very core of human existence. Everything from daily activities to the

smallest perception, thought, or reflection involves the memory. Our every action,

speaking, writing, opening a door, driving a car – all mobilise and depend on memory.

One of the most remarkable and far-reaching demographic development in the last

century has been the ‘greying’ of populations. By 2051, it is anticipated there will be

1.18 million people aged 65 years and over in New Zealand, representing an increase

of 165% since the year 2000. Within this demographic group, the number of people

aged 85+ years is expected to rise to 320,000 by 2051 (Statistics New Zealand, 2004).

While there has been an explosion of research on memory over the past two decades,

there has been little investigation of the changes in memory of healthy, community-

dwelling individuals, particularly those over 85 years of age.

The automatic linking of age and forgetting may well play a significant role in shaping

the stereotypes of aging. Writing in 1793 (Partington, 1996, p. 376), Samuel Johnson

has said:

There is a wicked inclination in most people to suppose an old man decayed in

his intellects. If a young or middle-aged man, when leaving a company, does

not recollect where he laid his hat, it is nothing; but if the same inattention is

discovered in an old man, people will shrug up their shoulders, and say, ‘His

memory is going’.

However, existing alongside the biased expectations, clearly memory deficits do occur

with advanced aging. To clarify how memory is affected by aging, it is imperative

intensive research effort is carried out. Nevertheless, despite the urgency of the need

the bias against older people has existed even within experimental endeavour,

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including leaving them out altogether. Although a large body of research literature now

exists on all aspects of memory, few studies have included individuals in their late ninth

and tenth decades of life. Of the studies which have included the oldest-old, many of

them are directed toward memory deficits which are a result of pathologies such as

Alzheimer’s disease, Parkinson’s disease, and so on. Few studies have been carried

out on healthy people who have reached these advanced ages.

The main purpose of the present research is to examine six specific types of memory

across the adult life span, with a particular focus on adults who have reached 85 years

of age and over. The choice of the memory types to be studied was a difficult one.

There are a plethora of memory aspects which could have been chosen. The final

decision – verbal recall, nonverbal recall, short-term memory, working memory, face

recognition, and prospective memory – was made because these memory types are

integral to the continued independence and to efficient cognitive functioning in

advanced old age.

The choice to incorporate both cross-sectional and longitudinal methodology in the

research design was made in order to access a balanced picture of memory ability

during advanced aging. Hartley, Harker, and Walsh (1980) note that a reliance on

cross-sectional methods has resulted in research findings that describe age differences

rather then age changes, and Schaie (1980) suggests that the role of cohort effects are

likely to influence results when reliance is placed only on cross-sectional data, although

cross-sectional investigation remains the most common method of investigating

memory to date. To the present time, little investigation which incorporates cross-

sectional and longitudinal data on the oldest-old has been carried out.

The inclusion of a longitudinal design brings its own difficulties when investigating

individuals who are in their late 80s and 90s. An inter-test interval of two years was

chosen. While this may be viewed as a short time for a longitudinal study, when life

expectancy is reduced to single digits a balance needs to be drawn between an

expected attrition rate due to declining health or death, and capturing memory change

over time.

The mixed design of the current study, while allowing for a comprehensive observation

of both differences and changes in memory across the life span, presented difficulties

in the choice of statistical analyses. Analysis of covariance (ANCOVA), widely used in

memory research, was chosen so that the main effects and interactions of the

independent variables could be assessed after dependent variable scores were

xxi

adjusted for differences associated with the covariates (Tabachnik & Fidell, 2001).

However, while this provided the necessary adjusted scores for the six types of

memory, it did not answer the question of how much unique variance was associated

with each of the chosen covariates. Thus, the decision was made to run a second

analysis, multiple regression. These two analytical methods nicely complement one

another, and together allowed for an in depth examination of certain memory changes

across ages and across time.

xxii