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This is to certify that the

thesis entitled

INHIBITION AND AGING: A CLINICAL APPLICATION

presented by

Carol C. Persad

has been accepted towards fulﬁllment
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MSU le An Afﬁrmative Action/Equal Opportunlty Inetltutlon
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INHIBITION AND AGING: A CLINICAL APPLICATION
By

Carol Catherine Persad

A THESIS
Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of

MASTER OF ARTS

Department of Psychology

1996

ABSTRACT
INHIBITION AND AGING: A CLINICAL APPLICATION
By

Carol C. Persad

One hundred comnmnity dwelling older adults (half female, Mean age 73 years)
were administered the Wisconsin Card Sort test, the Trail Making test, a verbal ﬂuency
measure and a reading with distraction measure in order to study age differences in
inhibition. Factor analysis indicated that these measures all loaded on a single factor
supporting the view that inhibition partly underlies performance on these
neuropsychological tasks. In addition, hierarchical regressions were used to examine the
role of inhibition in memory and attention. The relationship of age and inhibition was also
examined. Implications of these ﬁndings were discussed in relationship to diagnosis and

rehabilitation.

TABLE OF CONTENTS

INTRODUCTION
Evidence for reduced inhibitory functioning
Suppression of no longer relevant information
Reading with distraction
Directed Forgetting
Clinical Applications

METHODS
Participants
Measures

RESULTS

DISCUSSION

APPENDD(

LIST OF REFERENCES

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19

20

28

34

47

56

LIST OF TABLES

Table 1. Means and Standard Deviations for the
Neuropsychological Tests Administered to 100 Older Individuals

Table 2. Means and Standard Deviations for the Reading with
Distraction Test Administered to 92 Older Individuals

Table 3. Correlations between Age and the Neuropsychological Measures

Table 4. Interconelations between the clinical measures and the
Reading with Distraction task (11 = 100)

Table 5. Results from the hierarchical regression analyses

47

48

49

51

52

LIST OF FIGURES

Figure 1. Interaction of Age and Trails B-A in predicting Intrusions

Figure 2. Interaction of Age and Perseverative Responses in
predicting False Positives

53

54

INTRODUCTION

Declines in cognitive functioning with age have been extensively reported in the
literature and encompass many realms of cognition including memory, attention and
problem solving (Albert, 1984; Hochandel & Kaplan, 1984; Lezak, 1995). Currently,
many theorists have invoked the concept of working memory to understand many of these
deﬁcits. Since working memory has been extensively reviewed elsewhere (Baddeley,
1995), for the purposes of this paper only a brief description will be provided. Working
memory, as currently conceptualized by Baddeley, consists of three components: the
phonological loop, the visuo-spatial Sketchpad and the central executive. The ﬁrst two
components, often referred to as the slave systems, temporarily hold and maintain verbal
and visual/spatial information respectively. The central executive, on the other hand, is
viewed as an attentional control system, one that integrates and processes information
ﬁ'om both long term memory and the two slave systems, and subsequently acts upon this
information, being responsible for planning and response selection.

It has been argued that working memory has a limited capacity; performance on a
particular task will depend upon the amount of resources available at a given time (Light,
1991). In addition, these resources are theorized to diminish with advancing age.

Therefore, as older adults have less resources available to them, performance on tasks that

2

rely on working memory capacity will be decreased as compared to younger adults (Craik
& Byrd, 1982; Moscovitch, 1994). Although this point of view has been very ﬁ'uitﬁrl for
generating research, a number of issues have been recently highlighted (Hasher & Zacks,
1988; Light, 1991; Navon, 1984; Stoltzﬁis, Hasher & Zacks, 1994). One such problem
deals with the resources of working memory. There is no consensus concerning the
properties of this resource. For example, is it a general pool that is tapped in working
memory tasks, or are there diﬂ‘erent available resources that are speciﬁc to certain
cognitive domains? Although a number of measures have been developed that are
purported to be good indicators of working memory capacity, often these measures do not
strongly correlate with each other (Light & Anderson, 1985), leading some investigators
to propose the presence of multiple domain-speciﬁc working memories (Light, 1991).
Given this diﬁculty, to date there has not been a single agreed upon clinical or
emerimental measure devised that can be said to reﬂect the capacity of working memory
and also predict behavior on other tasks that may be dependent on the availability of these
resources. In addition, given that there is only a limited amount of capacity available to a
person at any given time, performance on a dual task paradigm should be predictable.
Performance on a single task is theorized to reﬂect a certain amount of capacity. Given
the amount of resources or capacity a task is theorized to need when performed singly,
and that overall capacity is limited, then when two tasks are performed simultaneously
predictions concerning performance patterns can be made. Ifthe proposed capacity
necessary for both tasks when performed together exceeds total available capacity, then
decrements in performance on at least one of the tasks should be evidenced. Research

ﬁndings are contradictory on this point, with a number of studies not conforming to these

3
predictions (Allport, 1989; Light, 1991; Navon, 1984; Salthouse, 1990).

One alternative to limited capacity in working memory as an explanation for age
effects is generalized cognitive slowing (Salthouse, 1994, 1995). Salthouse argues that
most of the performance decrements in older adults as compared to younger adults on a
wide variety of tasks can be accounted for by an overall slowing of information processing
abilities. It is not that older adults cannot perform tasks due to speciﬁc changes related to
the cognitive domain that is being assessed, but that older adults are just slower at the
tasks which can lead to poorer performance when compared to younger individuals.
Although there is considerable research to support this claim, there are some age related
changes on various tasks that cannot be ﬁrlly explained by this account. For example, age
related changes are reliably shown on various measures of executive ﬁrnctioning
measuring the ability to eﬂecﬁvely plan, execute and shift strategy sets as well as on
certain tasks of problem solving, even though there are no time demands required of the
tasks (Cronin-Golomb, 1990; Leuk, 1995). In addition, when partialling out response
speed on tasks that show an age decrement, a generalized slowing of response only
accounts for some of the variance suggesting the presence of other variables that are
important to age diﬂ‘erences (see Hartley 1992; Light, 1991 for reviews).

Alternatively, Hasher and lacks (1988; Zacks & Hasher, 1994) proposed a view
that centers on the contents of working memory rather than its capacity to help account
for deﬁcits seen due to aging. They argue that working memory eﬂiciency is dependent
on aspects of the selective attentional ability of an individual Selective attention refers to
the ability to focus or allocate eﬂon to a speciﬁc stimulus in order to process and respond

to it (Kausler, 1991; Sheer & Schrock, 1986). Some researchers have theorized that this

4

ability is a reﬂection of two processes: activation and inhibition (Hasher & Zacks, 1988;
Tipper, 1985; Tipper, Weaver & Houghton, 1994). Most theories of attention focus on
the activational aspect of attention, which is intimately connected to the initiation and
execution of the focusing mechanisms. Inhibitory processes, on the other hand, are
central to Hasher & Zacks concept, and refer to the active 'ignoring' or suppressing of
irrelevant stimuli It is this second mechanism that inhibits the allocation of attention to
irrelevant information in the internal or external environment, as well as disengages
attention from what was previously important but now is no longer the target of
processing (Hasher & Zacks, 1988; Zacks & Hasher, 1994). The process of inhibition
suppresses access of irrelevant information to working memory and allows for eﬂicient
processing of the target information. It is thought that "inhibition helps maintain attention
to selected information to enable the development of a coherent thought stream" (Zacks &
Hasher, 1994, p.242). Hasher and lacks (1988) have theorized that inhibition plays a
central role in many aspects of cognition, including memory, language comprehension and
speech production, and problem solving.

Given this framework for working memory, Hasher and lacks have theorized that
it is this inhibitory mechanism that becomes deﬁcient with age. Instead of a reduced
capacity in older adults that results in less information having access to working memory,
this viewpoint states that in older adults, too much information may have access to
working memory. Some of this additional information then may add an element of
distraction. Ineﬁcient inhibitory processes can lead to the increased access of irrelevant
information into working memory or can maintain activation of information, originally

relevant, but now no longer important to the task at hand (Hasher & Zacks, 1988;

5

Stoltzﬁrs, Hasher & Zacks, 1994; Zacks & Hasher, 1994). The presence of irrelevant or
distractor information in working memory can result in lowered performance due to

interference eﬂects and response competition.

EVIDENCE FOR REDUCED INHIBIT ORY FUN CTIONING

Based on this ﬁamework, a number of studies have been conducted that support
the idea of reduced inhibitory functioning in older adults. Negative priming has been a
classic paradigm used to study inhibitory processes in young adults. This procedure
generally involves presenting two stimuli simultaneously with the instruction to respond to
one stimulus (target) while ignoring the other (distractor). Then on the next trial, either
two new stimuli are presented, or the distractor stimulus now becomes the target stimulus.
Results clearly show that response time to the target is slower if it was a distractor on the
previous trial, this eﬂect being referred to as negative priming (May, Kane, & Hasher,
1995; Tipper, 1985). Negative priming is a fairly robust eﬂ‘ect and has been shown to
occur for a number of diﬂerent stinnrli (letters, words, pictures etc.) and across diﬂ‘erent
response sets (May, et aL, 1995). Currently two mechanisms have been proposed to
account for negative priming; inhibition and episodic retrieval (May, et al., 1995; Neil],
Valdes, Terry & Gorfein, 1992). These diﬂ‘erent mechanisms may be evoked under
certain conditions. For the purposes of this paper, the role of inhibition in negative
priming will be discussed. In the inhibition view, it has been theorized that one initially
inhibits the distractor in order to more eﬁciently attend to the target stimulus. When on

the next trial, the previously inhibited stimulus now becomes the target, the individual

6
responds more slowly to this target because it is still being temporarily inhibited (May, et
a1, 1995; Tipper, 1985).

Hasher and colleagues (Hasher, Stoltzﬁrs, Zacks & Rypma, 1991), among others,
have employed this same paradigm to investigate inhibitory processing in older adults. If
older individuals have deﬁcient inhibitory processes, as suggested by Hasher and Zacks's
theory (1988), then this age group should not exhibit negative priming. The ﬁndings ﬁom
their study supported this hypothesis. Their group of young adults did show negative
priming, replicating the many previous ﬁndings reported in the literature. However, the
older age group failed to exhibit negative priming. Even when conditions were made
optimal for the older adults (longer target presentation time, as well as longer inter-trial
intervals; Kane, Hasher, Stoltzfus, lacks & Connelly, 1994 ) negative priming was still
not evidenced by the older age group, suggesting that the older adults did not inhibit
distractors, as did young adults. Although there is evidence that older adults do not show
negative priming, age diﬂ‘erences can be attenuated if not eliminated when task demands
are altered. For instance, if the negative priming task requires the individual to make a
response based on the location of the stimulus rather than its identity, then older adults
will show the same amount of negative priming as younger adults (Connelly & Hasher,
1992; Sullivan & Faust, 1993). In addition, not all results have shown an age decrement
in identity negative priming tasks (Sullivan & Faust, 1993)

Distracting information does not have to be introduced from the environment but
can also be thoughts and associations that are generated by the subject to the material
being presented. One paradigm that has been used to examine this is the fan eﬂ‘ect

(Gerard, Zacks, Hasher, & Radvansky, 1991). Participants are presented sentences to

7

learn (for example, the doctor cut the apple into six pieces), followed by a timed
recognition test. The individual must choose the studied sentences from amongst other
sentences that consist of new combinations of the concepts from the original sentences.

In general, in young adults, the more sentences that are learned about a certain concept
(for example, the doctor) the longer the recognition response time and the higher the error
rate on the recognition task. This ﬁnding is referred to as the fan eﬂ'ect. Gerard and
colleagues (1991) used this procedure to assess both young and old individuals. It was
theorized that the older adults, due to a reduction in inhibitory processing, would not only
exhibit interference as the number of sentences to be learned about a speciﬁc concept
would increase, but would experience interference as a result of their own personal
associations that would be generated to the sentences themselves. For example, not only
would the older individual recall that the doctor cut the apple, but also perhaps that their
own doctor works down the street, and is very nice, and owns a dog. Because of these
increased associations it was hypothesized that the older adults would show a larger fan
eﬂect than the younger adults. Results supported this expectation. Both young and old
individuals evidenced the fan eﬂect, however, the older subjects did show a greater
decrement in performance when the number of sentences learned about a particular

concept increased.

SUPPRESSION OF NO LONGER RELEVANT INFORMATION

Another implication of reduced inhibitory functioning centers aromrd the

suppression of information in working memory that was once important but due to

8

changing goals is no longer relevant to the task at hand. Once task demands change, in
order to respond eﬂiciently, one has to inhibit the original response and process the new
information that has entered working memory in order to choose a more appropriate
response. Ifolder adults have difﬁculty suppressing the previously relevant information,
then they should experience interference on tasks that require a change in response.
Hartman and Hasher ( 1991; also see Zacks & Hasher, 1994), conducted an experiment
using garden path sentences to test this hypothesis. Participants were asked to read
sentences that had the last word missing. The sentences were constructed so that the
individual would generate a speciﬁc ending with a high probability. Once the ending was
generated, then either the consistent ending word or another, less likely ending was
provided to the subjects with the instructions to remember only the word provided by the
experimenter. After all of the sentences had been presented, the participants completed a
priming task for the ending words. The task consisted of the presentation of additional
new sentences with the ending word missing. These sentences were chosen so that there
was an equal probability of the subject completing the sentence with either the provided
word or the originally generated word. Priming in this task is exhibited when the subject
completes the sentences with the target words more often than if (s)he were completing
the task not having previously completed the experimental task. In this study, young
adults only exhibited priming for the words provided by the experimenter. Older adults,
however, showed priming for both the provided as well as the initial generated word. This
study supported the idea that older adults maintained information in working memory that
was not relevant to the task at hand. The same results have been found using garden path

stories (Hamm & Hasher, 1992). Subjects are instructed to read various passages and

9

then were asked to remember the stories. The wording of the text would lead the subject
to interpret the story one way, but as the story progressed and additional information was
provided, the correct interpretation becomes clear. Sometimes the original interpretation
is conﬁrmed (erqiected condition) and other times the original interpretation is invalidated
with the additional information (unexpected condition). Results indicated that older adults
remembered less of the correct interpretations on a cued recall task than younger subjects,
but only in the unexpected condition. Cued recall performance was equivalent for the
expected condition. In another condition, a speeded judgement task was administered at
diﬂ‘erent points in the story. Either half way through a story when the subject had the
original interpretation in mind or at the end of the passage when the correct interpretation
had been attained, a word was presented and the subject had to respond yes or no if to
indicate whether it was consistent with their interpretation of the story. When the word
was consistent with the correct interpretation, there were no age diﬂerences in the number
of yes responses. However, when the word was consistent with the original interpretation,
older adults responded positively more oﬂen than did younger adults, suggesting that the
older adults maintained both versions, whereas the young were more likely to forget or
discard the original interpretation. The researchers were able to show that older adults

held the incorrect interpretation longer in working memory than the young adults.

READING WITH DISTRACTION

Another paradigm that has been used to study the inhibitory processes in older

adults is reading with distraction (Connelly, Hasher & Zacks, 1991). Subjects are

10

presented with a passage to read in italic print and reading time is recorded. In some
conditions, interspersed within the passage are short phrases and words that are presented
in normal type. The subjects are instructed to ignore this distracting text and to read only
the passage in italic print. After controlling for vocabulary levels, ﬁndings showed that
although both young and old subjects were signiﬁcantly slower to read the story when
distractors were present, older adults exhibited a greater slowing in this condition. The
type of distractor present was then varied. In one condition, the distractor consisted of
words and phrases that were not related to the text (irrelevant), whereas in another
condition the distractors were meaningfully related (relevant) to the passage being read. A
third condition employed x's as the distractor. In the two distraction conditions with text,
both groups exhibited slowing but the older group showed a diﬂ‘erential increase in
reading time. Of interest in this study was the diﬂerence in performance between the age
groups with text distractors. The young subjects showed a signiﬁcant but equal increase
in reading time for both relevant and irrelevant conditions. The old however showed a
diﬂerent pattern. Distractors that were relevant to the passage slowed reading times more
than irrelevant distractors. Once again, as compared to young adults, this study suggests
that older individuals are more distractable and have diﬁculty ignoring irrelevant material,

especially when that information is related in some way to the target material

DIRECTED FORGETTING

One last area of research to be reviewed deals with a study that looked at the

performance of older adults on tasks of directed forgetting. In a typical directed

ll

forgetting paradigm a list of words is presented to the subject. Either after each word or
aﬂer a block of words has been presented, a cue is given that lets the subject know if the
word(s) are to be remembered or forgotten. As the cues are presented after the word has
been presented and the subject does not know if he/ she will have to remember the
particular item, it is assumed that the person must attend to each word and process it.
Once the entire list has been presented, subjects are asked to recall all of the to-be
remembered words. Young adults have little difﬁculty recalling the appropriate words and
give few intrusions of the to-be forgotten words (Bjork, 1989; Geiselman & Bagheri,
1985). Also, if asked to recall the to-be forgotten words, young subjects' recall for these
items is poor . A number of experiments have been conducted to examine performance in
older adults (lacks, Radvansky & Hasher, 1996). Ifolder adults have less eﬂicient
inhibitory processes, and if inhibition is important to directed forgetting tasks, then they
should have more difﬁculty ignoring those words that were cued as to-be forgotten.
Results from these studies bore out the predictions. Regardless of the type of list
presented (categorized or uncategorized), the timing of the cues (aﬂer each word or
blocks of words), or the type of memory task employed (ﬂee recall or recognition or a
speeded response task), the diﬂerence between the number of words recalled from the to-
be remembered list and the to-be forgotten list was smaller for the older adults as
compared to younger adults (Zacks, et al, 1996). This study lends additional support to
the idea that older individuals have more diﬁculty inhibiting material that is no longer
relevant to a goal

In summary, research ﬁndings generally support the idea that inhibition processes

are ineﬂicient in older adults, although under certain circumstances older adults exhibit

12

comparable performance to younger adults. Reduced inhibitory functioning can lead to an
increase of irrelevant or extraneous information in working memory, thereby causing

interference and increasing the risk of incorrect responses on a variety of tasks.

CLINICAL APPLICATIONS

Given the premise that older adults have reduced inhibition processes, to what
extent do they underlie the deﬁcits seen on a variety of clinical measures of cognitive
ﬁrnctioning? Selective attention has been theorized to be very important for a variety of
cognitive tasks (Kausler, 1991). As inhibition processes are important for eﬁcient
selective attentional ability, it follows that decrements in inhibitory processing may lead to
poorer performance on these cognitive measures. The presence of irrelevant or distracting
material, due to decreased inhibitory ﬁmctioning can lead to deﬁcient task performance.
Therefore, these older adults who have less efﬁcient inhibitory processing will be more
likely to experience greater diﬂiculty on these measures.

Little research however, has been done to examine the relationship of inhibition
and aging within the clinical setting. This extension into the clinical reahn can be useﬁrl to
help elucidate the generalizability of the inhibitory viewpoint and make it more accessible
to clinical applications. Oﬂen many of the experimental tasks that have been developed
to assess a speciﬁc theory of attention are not feasible within a clinical setting, due to such
things as time and monetary costs as well as lack of standardization procedures and
normative data, factors that are invaluable in a clinical setting. Since experimental

research is often focused on diﬂerences between two age groups (young versus old) , the

13

experimental design may not be conducive to the study of individual diﬂerences within an
age range. In addition, individual variables that can have an impact on task performance
such as affective disorders, health status and physical ability often are not accounted for in
experimental research. This last point is especially important to the study of older
individuals as these and other factors can become more problematic with increasing age.
Therefore an approach to the study of inhibition that takes into account some of these
issues can assist in the further understanding of the role of inhibitory functioning in an
older adult's performance on various cognitive tasks.

Many older adults do complain of difﬁculties with memory and selective attention
as assessed by self-report measures (Crook & Larrabee, 1992). These types of diﬁculties
also are evidenced on a variety of clinical neuropsychological measures; older adults show
poorer performance than younger adults on a number of these tasks. Older adults have
been shown to be more susceptible to distraction by irrelevant stimuli (Kausler, 1991) and
have more diﬁculty with visual search tasks when distracting stimuli are present (Fisk &
Rogers, 1991). This age group also experiences more diﬂiculty switching response set
(Cronin-Golomb, 1990) and can show increased perseverative behavior on tasks (Lezak,
1995) as well as increased verbosity (Arbuckle & Gold, 1993) even when there are no
time demands on performance. Performance on divided attention tasks can also show
declines with advancing age (Kausler, 1991). In addition research has demonstrated that
older adults exhibit decrements on various tasks designed to measure selective attention
(Hochandel & Kaplan, 1984; Kausler, 1991).

Working within the framework of reduced inhibition in older adults, Arbuckle and

Gold (1993) examined the relationship of verbosity to various neuropsychological

14

measures in older adults. The authors speculated that oﬂltarget verbosity reﬂected an
inability to maintain focus; the person would originally respond appropriately to a
question/statement but then would begin to talk about other loosely associated or non-
related topics. Verbosity was hypothesized to be a reﬂection of the inability to inhibit
irrelevant information or associations to the questions. In this study, a variety of
neuropsychological measures were chosen to be administered to a large group of older
adults, along with a measure of verbosity. Since research studies have shown (for reviews
see Cronin-Golomb, 1990; Stuss & Benson, 1984) that patients with ﬁontal lobe
dysfunction oﬂen show deﬁcits in inhibition (perseveration and inability to maintain set), a
number of "ﬁontal lobe" tests were included (WC ST, verbal ﬂuency and Trail Making as
well as release from proactive interference), as well as measures of memory (logical
passages) and simple attention (digit span). The authors found that the frontal lobe
measures correlated highly with the measure of verbosity (the higher the verbosity, the
lower the scores on the neuropsychological measures) whereas verbosity did not correlate
with the memory or simple attention measures. The results of a factor analysis showed
that these three neuropsychological measures (W CST, verbal ﬂuency and Trails) fell out
on one factor that was also highly correlated with verbosity. The authors hypothesized
that this factor reﬂected inhibitory ftmctioning in their sample.

The results ﬁ'om this study are intriguing as the authors apply the theory of
inhibition to the clinical realm Although previously the three neuropsychological tasks
have been linked together as measures of executive functioning that is generally thought to
be subserved by the frontal lobes (Cronin-Golomb, 1990; Stuss & Benson, 1984), the

theoretical application of the role of inhibitory processes in verbosity and the

15

neuropsychological measures can be seen as an advance in theoretical understanding of
performance on these tasks.

Theoretically an argument can be made for the role of inhibition on performance of
these standardized measures. All of the measures appear to require suppression of
irrelevant or non- goal directed information in order to make an appropriate response. The
Wisconsin Card Surﬁng Task (Heaton, Chelune, Tally, Kay & Curtis, 1993) requires the
participant to sort cards according to one strategy and then aﬂer a predetermined number
of responses the sorting principle changes unbeknownst to the subject who then nnrst alter
his strategy and attempt to discover the new sorting rule. For accurate performance, the
participant must suppress the initial sorting rule and switch response sets as the demands
of the test change. The Trail Making test (Reitan & Wolfson, 1993) also involves the
alternating of response sets. On Trails B of this test, one is required to connect letters and
numbers sequentially, alternating between the two sets (i.e. 1, A, 2, B etc. ). Once the
participant connects a number, then he/she must inhibit the number set in order to make
the next response (to connect a letter). Both of these measures require the participant to
suppress a response that was originally necessary for obtaining accurate performance but
is no longer appropriate to the task goal The additional measure, Verbal ﬂuency requires
the individual to generate as many words as possible that begin with a presented letter
within a time limit (Lezak, 1995). The person must not only inhibit items previously
generated but also associations to the generated items. Generated items may also activate
other related items that are meaningfully associated in some way but are not appropriate to
the task (i. e. do not begin with the target letter). Persons who have less eﬁcient inhibitory

processes may experience greater response competition due to these activated

16

associations, much like the results seen in the fan eﬂ‘ect paradigm

The intent of the present study was to replicate and extend the ﬁndings of the role
of inhibition in performance on the neuropsychological measures in a group of healthy
older individuals. The initial aim of this study was to replicate the factor analytic results of
Arbuckle and Gold (1993). For this study an experimental task was chosen, in lieu of the
verbosity measure, that has been used previously to demonstrate inhibition processes in
young and old participants, speciﬁcally the reading with distraction task as described
above. The three neuropsychological tasks as employed in their study also were
administered. As argued above, performance on these neuropsychological measures may
be partially subserved by inhibitory functioning. Ifinhibitory processes imderlie
performance on all of these measures, then a strong relationship between all of the tasks
should be evidenced.

The second purpose of this study was to examine the relationship between
inhibition and additional neurop sychological measures, to determine the extent that
inhibition plays a role in successful performance on these tasks. Generally the ability to
shiﬂ set, alternate responses or suppress irrelevant information is evaluated with measures
thought to reﬂect frontal lobe functioning (cf Cronin-Golomb, 1990). However, as
inhibition is theorized to serve the general ﬁmction of suppressing distracting or irrelevant
information in working memory, then it could be expected that inhibitory processes are
important for response selection in many other types of cognitive tasks. Therefore, the
role of inhibitory functioning in the present study was explored in two additional
neuropsychological tasks: a measure of memory and learning (California Verbal Learning

Test; CVLT, Delis, D., Kramer, J. H, Kaplan, E. & Ober, B. A., 1987) and a measure of

17

attentional capacity (Paced Auditory Serial Addition Test; PASAT, Gronwall, 197 7 ).
Both of these measures incorporate features that are similar to the directed forgetting
procedures described above. In both tasks, information that was relevant becomes
irrelevant to the task, and must be suppressed for good performance on the tests. The
CVLT requires the learning of a categorized list over trials followed by another
categorized list to learn. The participant must then recall the ﬁrst list after a short delay as
well as after a long delay. On this measure, memory and learning is assessed by free recall,
cued recall (the category names are used as cues) and recognition. If inhibition is
important for eﬁcient performance on this measure then it was hypothesized that a
decrease in inhibitory functioning would be reﬂected in a higher rate of intrusions and
perseverations on both recall and recognition on the CVLT, as well as an overall decrease
in learning. Reduced inhibition processes could lead to increased response competition
from the second list that was presented as well as additional associations to the categories,
resulting in increased intrusions and perseverations.

Poorer performance would also be expected on the PASAT. On this test, a list of
numbers is presented one at a time, and the task is to add each number presented only to
the preceding number and say out loud the total (but not keep a running total of all
numbers presented). Once a sum has been presented, it must be “forgotten" so that the
person can now complete the next response. It is a very demanding measure of attention
requiring a continual suppression of responses. Reduced inhibitory ﬁmctioning would be
expected to be evidenced in a reduced ability to perform this task, as one would have
diﬁculty suppressing the previous response in order to add the next two numbers. If

performance on the memory and attention measures are inﬂuenced by inhibitory factors

18

then a relationship should be evidenced between these two measures and the inhibition
measure used in this study, as well as the three clinical measures. Speciﬁcally, as one
exhibits more diﬂiculty on the measures thought to reﬂect inhibitory functioning
(speciﬁcally WCST, Trails B, Verbal Fluency and Reading with Distraction), then
increased diﬂiculty would be evidenced on the memory and attention measures to the
extent that inhibition also partly underlies performance on these measures (i e. higher rates
of intrusions and perseverations and decreased rates of learning on the CVLT and more
errors on PASAT). If this relationship is obtained then one can utilize these standardized
measures in the clinical setting to examine inhibitory functioning in a wide population of
patients.

The next aim of this study was to assess the relationship of age and inhibitory
functioning. Although there are experimental studies comparing younger and older
subjects on inhibition measures, with older individuals showing decreased inhibitory
ﬁmctioning, there is no data that has looked at the relationship of inhibition within an older
population. There is an increasing body of literature that demonstrates that there are
declines in cognitive functioning across the decades and normative data has been collected
to reﬂect this (for an example see Heston, Grant & McSweeny, 1991; Lezak, 1995) and it
is possible that performance on measures thought to reﬂect inhibition may show the same
pattern of results. A sample of community dwelling individuals between the ages of sixty
and eighty-ﬁve were assessed in this study so that these age comparisons could be made.
Therefore, the hypothesis stated, although more tentative, that as age of the individual
increased inhibitory functioning as measured by the clinical tasks becomes less eﬁcient. In

addition, the possible diﬂerenﬁal role of inhibition and cognition with advancing age was

l9
assessed.

Just as age may account for some of the variance that may be evidenced in
inhibitory ﬁrnctioning, so may other factors that are relatively independent of age.
Depression is a growing concern in the older population and has been shown to impair
performance on many neuropsychological measures (Austin et al, 1992; Sweet, Newman,
& Bell, 1992). The ﬁnal aim of the study was to examine the possible relationship
between depression and performance on the measures thought to reﬂect inhibitory

ﬁmctioning.

METHODS

PARTICIPANTS

One hundred older volunteers were recruited from the greater Lansing, Michigan
area. The participants were recruited ﬁom three local churches and the Foster
Grandparents Association. A donation of 10 dollars was made to the church for every
person who vohmteered for this project. As an additional incentive, for every 20
vohmteers that were recruited from the same church, an additional 50 dollars was
donated. Vohmteers ﬁ'om the Foster Grandparents Association were paid twelve dollars
for their participation.

Mean age ofthe entire sample was 73.07 ( S_D = 7.16 ; range 60-85) with a mean
education of 13.47 (SD = 2.51; range 8-20). Fiﬂy males and 50 females were assessed.
None of the participants were excluded on the basis of the presence of dementia as

measured by the Mini Mental State Examination (F olstein, Folstein, & McHugh, 1975; M

20

= 27.9, SD = 1.67; range 24-30). In order to study the eﬂ‘ects of age on inhibitory
functioning, approximately equal numbers of individuals were recruited from ﬁve age
ranges. Nineteen participants between the ages of 60 and 65 were assessed (M = 62.42,
SD = 1.64), 19 in the 66-70 range (M = 68.58, SD = 1.39), 22 in the 71-75 range (M =
72.91, SD = 1.57), 21 in the 76-80 range (M = 78.19, SD = 1.44) and 19 in the 81-85 age
range (M = 83.74, SD = 1.37). Education levels for the respective groups were 14.63
(SD = 3.3), 13.58 (SD = 2.17), 13.32 (SD = 2.15), 13.24 (SD = 2.70), 12.63 (SD = 1.80).
Education levels were found not to diﬂer signiﬁcantly across age groups on a one-way
analysis ofvariance, F(4, 95) = 1.66, MSE = 6.15.

Administration of the measures was performed by three graduate students from the
clinical psychology program at Michigan State University. Consent was obtained from
each vohmteer prior to testing. The testing session took approximately three and a half
hours to complete. Approval for this study was obtained from the Human Subjects

Review Committee at Michigan State University.

MEASURES

Trail Making Test (Reitan & Wolfson, 1993). The Trail Making Test is one of the
measures of the Halstead Reitan Neurop sychological Battery. This measure is thought to
reﬂect one's ability to shiﬂ attention and sequence between two alternate response sets
(LaRue, 1992). It is necessary to suppress one response set temporarily in order to shiﬂ
to the alternate set. There are two components to this test. Trails A requires the
participant to draw a line connecting 25 numbers, in order. Trails B, in contrast, presents

a page of numbers and letters and the individuals task is to alternate between the numbers

21

and letters in order. Time to complete both parts is recorded as well as the number of
errors.

This test also requires visual conceptual and visual-motor tracking abilities, and
deﬁcits in these processes can lead to poor performance on this test, as can motor slowing,
and poor motivation (Lezak, 1995). Older adults do show a general slowing on Trails A
and B as compared to younger adults (Lezak, 1995; van Zomeren & Brouwer, 1994), and
normal motoric slowing with age needs to be taken into account on this measure. As a
result, Trails B - Trails A was calculated in an attempt to control for motoric differences in
this older sample, and used in the subsequent analyses. A higher score represents more
diﬂiculty on this task.

Test-retest reliability coefﬁcients vary across diﬂerent studies but are generally fair
ranging from at least .60 to as high as in the .90's (Lezak, 1995). Normative data for the
older age ranges are available in the literature (Heaton et a1. 1991), as age does eﬂ‘ect
performance. Education also has been found to be a factor in performance on this test
(Lezak, 1995). Trails A and B can be very sensitive to brain damage, but taken alone one

cannot indicate the source of the problems (Lezak, 1995).

Wisconsin Card Sorting Test (WCST; Heaton, Chehrne, Tally, Kay & Curtis, 1993).
Decision making and the ability to ﬂexibly change response sets was measured by counting
the number of perseverative responses ﬁ'om the WCST, with higher scores representing
greater impairment. The participant was given a set of 128 cards on which are printed
one to four symbols of either stars, crosses, triangles or circles in one of four diﬂ‘erent

colors. The task was to place each of the cards under one of four stimulus key cards

22

according to a principle that the person must deduce from the pattern of the examiner’s
responses to the person's placement of the cards ('1 e. color, form or number). Aﬂer a am
often correct placements in a row, the examiner shifted the to-be sorted principle,
indicating the shift to the subject only in the changed pattern of his "ri t" and "wrong"
statements. This was continued until six category shiﬂs were achieved or all cards were
used. Although many measures can be obtained from this test, it was felt that the
Perseverative Response score was the best to reﬂect diﬂiculties with set shifting.
Perseverative Responses reﬂects the individual's inability to suppress the original set,
perseverating on matching the cards by the category that is no longer correct.

The WCST has been shown to have a high interrater reliability of .93 for
perseverative responses and an intrascorer reliability (deﬁned as the consistency of scoring
multiple tests of one rater) of .96 (Heaton et al, 1991). As reported in the manual, studies
of concurrent validity have supported the idea of the WC ST as a measure of executive
fimction

Normative data has been collected on a wide range of ages ( 6-90 years; Axelrod,
Jiron, Henry, 1993; Heston et al, 1993). As reported in one normative study, Mean
perseverative responses for 70-79 year olds is 14.8 (SD = 5.4) and 20.4 (SD =13.2) for
80-89 year olds (Axelrod et al, 1993). In addition this test has been used diagnostically
with a variety of samples such as patients with Parkinson's Disease, Multiple Sclerosis,
Seizure disorders, Brain Damage, and psychiatric samples like Schizophrenia (Heaton et

al,1993)

23

Controlled Orgl Word As_se£°ation or Verbal Flueng (Lezak, 1995). Participants are
asked to generate as many words as possible that begin with a certain letter in one minute.
Three separate letters are administered, C,F,L and the total number of words generated for
all three words are summed. Lower scores on this task represent greater diﬂiculty. If an
individual has less efﬁcient inhibitory processes, as already discussed above, then one
would expect that there would be diﬂiculty suppressing items once they have been
generated as well as associations to the generated items. Since these items are still active
in working memory, then there may be increased response competition, which could be
reﬂected in a lower number of valid generated items on this task.

Overall, performance is related to level of education. If education level is
restricted to 13 years and above, then age is not correlated with performance, Imtil over
the age of 75 (Spreen & Strauss, 1991). Concurrent validity has been demonstrated
(Spreen & Strauss, 1991). Using a diﬂ"erent set of letters (FAS), inter-rater reliability has
been shown to be very high with the re-test reliability being .70 (Spreen & Strauss, 1991).

Normative data is available for a range of ages (Lezak, 1995; Spreen & Strauss,
1991). Verbal ﬂuency also has been administered diagnostically to a wide variety of
populations such as patients with Alzheimer‘s Disease, Parkinson's Disease and various

types of brain damage.

Reading with Distraction (Connelly, Hasher & lacks, 1991). As described in the
introduction, a reading with distraction task was administered to the participants. This
task has been shown to be a good measure of inhibitory processes, though normative data

is not available.

24

Stories were presented in italic print with the distracting material in upright print.
Font was large (14 point) to compensate for visual problems commonly experienced by
older individuals. Subjects were instructed to read each story accurately and carefully out
loud, starting with the title, and told that they will have to answer four multiple choice
questions about the passage just read. After an initial practice story, nine stories and
multiple choice tests were administered. Time to read each story was recorded. Three of
the passages had distracting text that was related to the story being read. Three of the
passages had unrelated text as distractors and the remaining three stories did not have any
distracting information embedded within the text. Across subjects, each story was used
across the three reading conditions equally often and two order presentations were
determined. This resulted in six versions that were randomly assigned to subjects. Each
subject received all three distracting conditions. Passages were chosen to be
approximately equal length and each story was spaced to be the same length regardless of
the condition, to control for eye scanning speed. This task took approximately ﬁﬂeen
minutes to administer. The recognition test consisted of four multiple choice questions,
each having six choices consisting of the correct response, the related response that was
embedded in the relevant text condition, and four additional plausible words. The
recognition test was scored for number of correct responses as well as the percentage of
false alarms that were made to the related word. The speciﬁc measure to be used in the
regression analyses was calculated by subtracting baseline reading times from the no
distraction condition ﬁom the two distraction conditions to control for individual reading

speed.

25
California Verbal Learning Test (CVLT; Delis, D., Kramer, J. H., Kaplan, E. & Ober, B.
A, 1987). The CVLT was designed to examine categorized list learning over a series of
trials. Short and long term recall are assessed using both ﬂee and cued recall as well as a
recognition test. The use of categorized lists also allows for the examination of a person's
learning and recall strategy.

The procedure consists of presenting a 16 item categorized list for learning (i e.
Monday‘s shopping list; consisting of four words ﬂom four diﬂerent categories:
vegetables, clothing, tools and spices and herbs). The list was read out loud ﬁve times and
the subject was instructed to recall as many words as (s)he can ﬂom the list after each
presentation. After the ﬁfth trial, the subject was then given another 16 item categorized
shopping list for recall (Tuesday's list). Two of the categories in this list were the same as
Monday's list and two were new. Once recall of Tuesday's list was attempted, the subject
was that instructed to recall all of the words ﬁom Monday's list once more. This was then
followed by a cued recall trial, with the category names serving as cues. Aﬂer a 20 minute
delay, the subject was asked to recall Mondays list once more and was again given a cued
recall trial This was lastly followed by a recognition trial of words ﬂom Monday's list.
The distractors in the recognition test consist of words ﬂom Tuesday's list that were ﬂom
the shared categories, new words that also belong to one of the categories, new items that
are phonemically similar to target items, and new unrelated words.

Various measures of learning and recall can be obtained. A number of the scores
are of interest in this study. Total recall over the ﬁve trials, as well as short and long
delayed recall was calculated. In addition the total number of intrusions and

perseverations was measured. An intrusion is deﬁned as a word recalled that was not part

26

of the list to be remembered. A response is scored as a perseveration when the individual
recalls the same word as if it is the ﬁrst time that he/she has recalled it. On the
recognition component, the number of hits and false positives were recorded. The false
positives can be further analyzed to see the type of error made, be it an item ﬂom the
Tuesday's list, or semantically or phonetically related.

Results ﬂom reliability and validity studies have been reported in the CVLT
manual and will be summarized here (Delis et al, 1987). Internal Consistency has been
measured three diﬂ‘erent ways obtaining values ranging ﬂom .70 to .92. Split half
reliability coeﬂicients of .77 and .86 have been reported. Test-retest reliability has also
been calculated, and 13 of the 18 scores that were looked at were signiﬁcantly correlated.
As described by the authors, test-retest reliability will not be very high due to practice
eﬂects on this measure. Total recall over the ﬁve trials has been shown to be higher
(averaging two words more) on second testing, and higher scores are also found with the
short and long delay recall and the recognition tests.

Studies have conﬁrmed the construct validity of the CVLT. Factor analytic studies
have consistently found 6 factors: general verbal learning, response discrimination,
learning strategy, proactive eﬂ‘ect, serial position eﬂect and acquisition rate. The authors
suggest that "the results of the factor analyses indicate that the nnrltiple indices assessed
by the CVLT cluster into theoretically meaningﬁrl factors consonant with the experimental
constructs they were designed to measure" (p. 43). The various measures also
signiﬁcantly correlate .60 with the Wechsler Memory Scale (WMS), another test designed
to measure memory ﬁrnctions.

Normative data are available across a wide range of ages. The manual provides

27

norms that are stratiﬁed by age and gender. Lezak (1995) has reported that education is
also correlated .36 with test performance. This test has also been used with a variety of
populations including patients with Parkinson's Disease, Alzheimer’s Disease, Multiple

Sclerosis, Head Injury patients and healthy job applicants.

heed Auditory SeriA Addition Test (PASAT, Gronwall, 1977) This test has been
considered to be sensitive to information processing speed and concentrations skills
(Gronwall & Wrightson, 1981; Roman, Edwall, Buchanan & Patton, 1991). A string a
numbers was presented at predetermined intervals, and the task is to add each number to
the number that was presented just before it, and say the total out loud. (Gronwall, 1977;
Lezak, 1995). Presentation times of the digits range ﬂom 1.2 sec to 2.4 sec. Once a
response has been given, the individual must in a sense "forget" or suppress the total
he/she has just said out loud, in order to generate the next response (which is to and add
the new number to the previous number presented). Total number correct was recorded
Although all age groups have diﬂiculty with this task, older adults perform worse on this
test as compared to younger adults (Roman, Edwall, Buchanan & Patton, 1991). In
addition intelligence scores and educational level correlate with performance (Roman,

Edwall, Buchanan & Patton, 1991; van Zomeren & Brouwer, 1994).

Vocabul_a_ry Subtest (Wechsler, 1981). The Vocabulary subtest ﬂom the Wechsler Adult
Intelligence Scale- Revised (WAIS-R) was also administered. Subjects were asked to
deﬁne a list of words. This test has been shown to be a good measure of vocabulary

ability and is highly correlated with the verbal intelligence score ﬂom the WAIS-R (Lezak,

28

1995). As vocabulary level is signiﬁcantly correlated with a number of the clinical
measures and can also impact on the reading with distraction task, this test was

administered to all subjects so that vocabulary ability could be statistically controlled.

RESULTS

All statistical analyses were done using the SPSS for Windows statistical package,
Release 6.0 ( 1993 ). Unless otherwise speciﬁed, an alpha level of .05 was used for all the
statistical tests.

Descriptive characteristics of the measures are presented in Tables 1,2 and 3. For
this sample, the mean vocabulary score was 47.56 (S_D = 10.69, range 17-65) out of a
possible 70 points. Results of the remaining neuropsychological measures are reported in
Table 1. Eight individuals were not administered the reading with distraction task. Two
of the individuals were unable to visually discriminate the diﬂerent fonts due to poor
eyesight, one individuals reading comprehension was too poor to read the text, another
discontinued testing during administration ﬁnding the task too diﬁcult, and the remaining
four participants were not administered the test due to time considerations. For the
remaining 92 participants, no diﬂ‘erences were found in reading times for the related and
tmrelated text conditions in the reading with distraction task, t(88) = -.64 (Table 2; M =
82.88, SD = 27.54; M = 83.97, _S_D = 28.55 respectively). Data obtained ﬂom these two
conditions were combined to derive the reading with distraction score. Reading time ﬁom
the no distraction condition was subtracted ﬂom the mean reading times for the distraction

conditions and used in all of the subsequent analyses. The relationship between age and

29

the neurop sychological measures are reported in Table 3.

As the ﬁrst aim of this study was to replicate the factor analytic results of Arbuckle
and Gold (1993), a factor analysis was done using the three clinical measures and the
reading with distraction score. The correlational matrix for the three clinical measures of
interest and the reading with distraction task is shown in Table 4. The correlations are
very close to those found by Arbuckle and Gold (1993); the latter are listed in Table 4 in
parentheses for comparison. A principal component factor analysis with varirnax rotation
was performed with the three clinical measures and the reading with distractor measure.
The analysis showed that one factor had an eigenvalue greater than or equal to l,
accounting for 45.6% of the variance. The factor loadings for the individual variables were
..80, -.69, .68, .49, for Trails B-A, the verbal ﬂuency score, the perseverative response
score and the reading with distraction measure respectively.

The second goal of this study was to evaluate the role of inhibition in other
cognitive tasks. Speciﬁcally it was hypothesized that given that inhibitory functioning
partially underlies performance on many tasks, then performance on the four "inhibitory"
measures should predict performance on additional neurop sychological measures. In
order to examine this relationship between the three clinical measures and the reading with
distraction measure hierarchical regressions were performed. The three clinical measures
and the reading with distraction score were the independent measures. In order to control
for possible diﬂ‘erences in reading ability and education and their eﬂ‘ects on the clinical
measures and the reading with distraction task, vocabulary score and education level were
entered into the equations ﬁrst to control for these variables (subsequently referred to as

control variables). Then verbal ﬂuency, trails B-A, perseverative responses, reading with

30

distraction and age were entered into the equation (referred to as predictor variables).
Finally, to examine the possible eﬂects of age on inhibition, the interaction terms for each
independent variable and age were entered into the regression equations. Age was
centered around the mean to increase the interpretabilty of the beta weights.

The results ﬂom the hierarchical regression analyses are summarized in Table 5.
The hierarchical regression analysis for predicting the CVLT total recall score produced a
signiﬁcant overall R’( .38), accounting for 38% of the variance. With regard to the
individual predictor variables, entering in the control variables produced a 32 of .11.
When the individual test measures were entered, R” increased by .25. Only age was a
signiﬁcant individual negative predictor of total recall; as age increased the number of
words recalled decreased. A trend was evidenced for perseverative responses (1; < .09)
and reading with distraction (p < .06), with greater impairment ('1 e. reduced inhibitory
ﬁmctioning) being associated with a lower total recall score for the CVLT. The addition
of the interaction terms resulted in an additional .02 increase in R’. None of the
interaction terms were signiﬁcant.

The regression analysis for predicting the CVLT total intrusion score produced a
signiﬁcant overall R2 (.38) accounting for 38% of the variance. The control variables
accormted for 15% of the variance (R2 = .15). With regard to the individual predictor
variables vocabulary was found to be a signiﬁcant negative predictor of the intrusion
score. A higher vocabulary level was associated with a lower intrusion score. An increase
of .10 was obtained in 152 when the individual measures were next entered Trails B-A
was found to be a signiﬁcant positive predictor of the intrusion score. With the addition

of the interaction terms, the amount of variance accormted for increased by 13%. Age x

31

Trails B-A was a signiﬁcant positive predictor of the intrusion score. In order to
understand the interaction, simple regressions were performed with just age, trails B-A
and the interaction terms entered into the model as described in Cohen (1983 ). In order to
plot the interactions, two values of age were chosen, 2t 1 SD around the mean and using
the beta weights ﬂom the simple model, I solved for the dependent measure. The
interaction is plotted in Figure 1. Increased impairment, (i. e. reduced inhibition) as
reﬂected in trails B-A was more strongly associated with intrusions in the older ages. The
reverse association was seen for the younger age.

The regression analysis for predicting the CVLT total perseveration score
produced a nonsigniﬁcant overall F vahre ( R’ = .11, E(11,80) = .56). The failure to ﬁnd a
signiﬁcant regression analysis can partially be accounted for by the restricted range of
scores for the CVLT perseveration score.

The regression analysis for predicting the number of false positives on the CVLT
produced a signiﬁcant overall 3’ (.35) accounting for 35% of the variance. The control
variables resulted in an R’ of .03. An increase in R’ of .24 was obtained when the
individual test measures were entered into the equation. Both the perseverative response
score and the reading with distraction score were signiﬁcant positive predictors of the
false positive score ﬂom the CVLT. For each signiﬁcant individual predictor, greater
impairment (i.e. reduced inhibitory ﬁrnctioning) was associated with a higher false positive
score on the CVLT. A ﬁnal increase of .08 was obtained with the addition of the
interaction terms. Age x Perseverative Responses was a signiﬁcant positive predictor of
false positives. The interaction is plotted in Figure 2. For the younger age, perseverative

responses did not predict false positives, however increased perseverative responses did

32

predict increased false positives for the older age.

Since the CVLT has diﬂ‘erent subtypes of distractors on the recognition test, a one
factor repeated analysis of variance was done to examine the types of false positives made
in the recognition test and a signiﬁcant 15 was obtained (F(4,392) = 27.53, p < .0001).
Post hoc comparisons showed that the highest false alarms were made to words that were
ﬂom the Tuesday list that shared the same category membership as Monday's list (M =
1.03, SD = 1.05). This score was signiﬁcantly diﬂerent ﬂom the four other subtypes
(words ﬂom Tuesday's list, nonshared category membership, M = .34, SD = .73; words
not on either list but share the same category membership, M = .52, SD = .77; words on
neither list that were phonetically similar to items ﬁom Monday's list, M = .41, SD = .42;
and unrelated words, M = .13, M2 = .42). Analyses also showed that the number of false
positives to the unrelated items were signiﬁcantly lower than the other four types.
Regressions analyses could not be performed using the subtypes of the false positive
response due to restricted variability of responses.

The regression analysis for predicting the PASAT produced a signiﬁcant overall l_{’
(.44), accounting for 44% of the variance. An initial 15’ of .22 was obtained when the
control variables were ﬁrst entered into the equation. Vocabulary was found to be a
signiﬁcant positive predictor of PASAT. Higher scores on the vocabulary test were
associated with higher scores on the PASAT. An increase of . 17 resulted when the
individual scores were entered. As a group, these measures accormted for a signiﬁcant
proportion of the variance, however none of the individual measures were separately
signiﬁcant. A trend was evidenced with the perseverative response score (p < .08). The

addition of the interaction terms increased R2 by an additional .05. Age x Reading with

33

distraction was a signiﬁcant negative predictors of PASAT. As age increased,
perseverative responses and reading with distraction became less strongly associated with
PASAT. However, this interaction should be interpreted with caution. When the simple
regression analysis was done to plot the interaction, this interaction term became non
signiﬁcant.

The last aim of this study was to examine the relationship of age and inhibition.
Speciﬁcally, it was hypothesized that inhibitory ﬁrnctioning would become less emcient
with advancing age. As already discussed, to examine the possible age diﬂ‘erences in the
prediction abilities of the independent measures, interaction terms were entered into the
regression analyses to evaluate this relationship. These results are reported above in the
individual regression analyses. Also, correlations between age and the test measures were
calculated and are presented in Table 3. Age was signiﬁcantly correlated with all of the
test measures except for the number of perseverations on the CVLT. In all cases, as age
increases, performance on these tasks decreases. As vocabulary level has been formd to
eﬂ‘ect performance on the reading with distraction task, the correlation between age and
this measure was computed partialling out vocabulary. The correlation between age and
the reading with distraction measure remained signiﬁcant (r = .27, p < .01).

To examine the effect of depression on the test measures, the Geriatric Depression
Scale (GDS; Brink et al 1982) was administered. The mean GDS score for the entire
sample was 3.88 (M)_ = 3.36, range 0 - 16). Only ﬁve of the sample could be classiﬁed as
having mild depression as measured by this self-report questionnaire. Thus, for this
sample the relationship between depression and inhibition could not be examined. None of

the correlations between the GDS and the various neurop sychological measures were

34

signiﬁcant (1’s = -.08, .06, .15, and .03 for verbal ﬂuency, perseverative responses, trails

B-A and reading with distraction score respectively).

DISCUSSION

The initial aim of the study, to replicate the factor analytic results of Arbuckle and
Gold (1993) was achieved. As performance on the reading with distraction measure is
thought to partially reﬂect the eﬂ‘ects of inhibition, the ﬁnding of one factor in the analysis
with the inclusion of this measure lends further support for the role of inhibition in the
three clinical measures as theorized by Arbuckle and Gold (1993 ).

Although the factor analysis did produce one factor, the reading with distraction
task had a lower factor loading score than the other measures. This was partly due to the
low correlation between the reading with distraction task and the perseverative response
score ﬂom the WC ST. This correlation is surprising since initially, I would have thought
that these two measures would have exhibited the strongest relationship. Although it is
diﬂicult to explain the small correlation between these two measures, several explanations
are possible. First, the reading with distraction task is an experimental measure and no
studies have been conducted looking at the reliability of this measure. The eﬂ‘ects of
distraction were found as in previous studies (Connelly et al, 1991), but the diﬂ‘erence
usually evidenced between the related and unrelated distractor condition (older adults
show slower reading times in the related as opposed to the unrelated condition) was not
obtained. The inability to replicate this ﬁnding leads one to question the reliability of this

measure.

35

On the other hand, if the low correlation between reading with distraction and
perseverative responses is indeed a replicable ﬁnding then another possible reason may be
reﬂective in the diﬂ‘erent task requirements of these two measures. The reading with
distraction task requires the focusing of attention towards the relevant words based on
surface characteristics of the text, ignoring the irrelevant words. On the other hand,
performance on the WCST is dependent on the ability to suppress information that was
once important and activated in working memory but is now no longer relevant to the
goal Although speculative, these two tasks may reﬂect two diﬂ'erent types of inhibitory
mechanisms; one that promotes the ability to ignore extraneous stimuli and one that
suppresses (internal) information that is already in working memory. Based on evidence in
the literature, various researchers have in fact postulated the presence of (at least) two
distinct attentional systems that may mediate in part two types of inhibitory mechanisms.
The ﬁrst attentional system is thought to be subserved by posterior areas of the brain
(based on Posner & Peterson, 1990). This system has been hypothesized to be responsible
for the orienting or focusing towards a stimulus on the basis of its characteristics such as
location, shape, color and movement, integrating information ﬂom both of the dorsal and
ventral visual systems (Kramer, Humphrey, Larish, Logan & Strayer, 1994; Posner &
Peterson, 1990; Van Zomeren & Brouwer, 1994). By contrast the other mechanism is
thought to be mediated anteriorly by the ﬂontal lobes, and is involved in the suppression
of information in working memory (either once relevant, or irrelevant associations to the
task) allowing for the focusing of attention towards one line of thought/processing
(Hartley, 1993; Kramer et al, 1994).

The posterior system consists of the parietal cortex, pulvinar nucleus of the

36

thalarrms and the superior colliculus (Kramer, et al, 1994; Posner & Peterson, 1990). It
has been theorized that the parietal cortex disengages attention ﬂom a previous stimulus,
then the midbrairr area allocates attention to the area of the new target and the pulvinar is
said to be involved in processing the information ﬂom the target location (Posner &
Peterson, 1990). The processes of spatial selective attention seem to be mediated by this
system (Kramer, et al, 1994).

Lesion studies have lent some support to this system although the applicability of
the ﬁndings to normal adults is certainly speculative. Patients with damage to the
posterior parietal lobe exhibit a syndrome known as unilateral or hemineglect, which is
described as the tendency of decreased or absent awareness to one halfof extrapersonal
space (Lezak, 1995; Walsh, 1978). Damage to the posterior parietal lobe also eﬂects the
ability to disengage attention ﬂom one stimulus to another located on the contralateral
side of the side of the lesion (Posner & Peterson, 1990). Patients who have progressive
deterioration in the superior colliculus and/or surrounding areas show a deﬁcit in ability to
shiﬂ attention manifested in a slowing in allocating attention to a target stimulus. These
patients also return attention to already examined locations just as readily as to new
locations, suggesting that the inhibitory mechanisms of selective attention are impaired
(Posner & Peterson, 1990). In addition, patients with thalamic lesions have diﬂiculty in
focusing attention towards a stimulus on the opposite side of the lesion suggesting
problems in engaging target location in a way that allows responding to be fully selective
(Posner & Peterson, 1990). Recent PET studies have also implicated the pulvinar nucleus
of the thalamus in visual selective attention tasks (LaBerge, 1990a, 1990b).

As described above, the reading with distraction task may be partly mediated by

37

this posterior system Good performance on this task, as measured by reading times,
relies in part on the ability to selectively attend to the text based on characteristics that
discriminate the two fonts used in the task. Ineﬂicient inhibitory mechanisms in this
system would result in increased eﬂ‘ects of distraction resulting in longer reading times.
Although no diﬂerences were obtained in this study between the two distractor conditions,
as described earlier, generally results show that older individuals have more difﬁculty
inhibiting information when the irrelevant words are associated in some way to the target
text (Connelly, et al, 1991). This seems to suggest that although the posterior system may
initially be involved in the failure to inhibit attention towards irrelevant stimuli, once
processed and activated in working memory, it is still necessary to suppress this
information, perhaps involving the anterior system

Information concerning the anterior system is less well developed (Van Zomeren &
Brouwer, 1994). The anterior system involves structures located within the ﬂontal lobe,
speciﬁcally the anterior cingulate, preﬂontal and supplemental motor areas (Posner &
Peterson, 1990; Van Zomeren & Brouwer, 1994). It has been hypothesized that this
system is responsible for a number of ﬁrnctions like planning, coordinating the processing
of multiple stimuli, the initiation and cessation of thoughts and behaviors and the
processing of semantic information (Kramer et al, 1994). Although speculative, this
system may be involved in the suppression of already activated information in working
memory. Researchers have argued for the role of the frontal lobes in working memory,
although little has been focused on the role of inhibition (Goldman-Rakic, & Friedman,
1991; Moscovitch, 1994). It has been suggested that the two systems work within a

hierarchical ﬂamework; the anterior cingulate being the more dominant of the two

 

38

(Posner & Peterson 1990; Van Zomeren & Brouwer, 1994). The anterior cingulate is
particularly involved with target detection and has been shown to have increased
projections to the dorsolateral preﬂontal cortex and to the posterior parietal lobe (Posner
& Peterson, 1990; Van Zomeren & Brouwer, 1994). Given the task components of the
WSCT, performance may be partially reﬂective of ﬂontal lobe functioning, although
impaired performance can be evidenced with patients who have brain damage to other
areas (Anderson, Damasio, Jones, & Tranel, 1991; Lezak, 1995).

However, studies that have supported the idea of two inhibitory mechanisms
generally argue for the preservation of the posterior system in older adults whereas the
anterior system declines with age. The results ﬂom this study do not support this claim If
there are two inhibitory mechanisms, then the ﬁndings ﬂom the multiple regression
analyses suggest that both types of inhibitory mechanisms are aﬂected with advancing age.
Although the postulation of two attentional systems that subserve diﬂerent inhibitory
mechanisms is intriguing, if there are multiple systems it is unlikely that they will be
independent of each other. As described above, neuroanatomically there are many
interconnections between brain regions and speciﬁcally the ﬂontal cortex projects to
multiple areas including the posterior regions. In this study, the fact that both measures
did come out on the same factor supports the idea that there is one underlying process,
that I would propose is a general inhibition mechanism It is still feasible that the
diﬂerences in inhibitory frmctioning as a function of task demands is accountable in part by
the engagement of additional processes that are reﬂective of diﬂerent neuroanatomical
regions, dependent upon the nature of the task.

Once the factor analysis had been replicated, the next goal of this study was to

39

evaluate the role of inhibitory functioning in other cognitive domains. It was found that in
a sample of comnnmity dwelling older individuals that the predictor variables (verbal
ﬂuency, perseverative responses, trail making test, reading with distraction) were
predictive of performance on neuropsychological tasks measuring memory (CVLT
subscores) and attentional performance (PASAT). In particular, the predictor variables
accounted for an increase in variance (10 to 25%) on most of the memory scores (recall,
the number of intrusions, and false positives) and the attention measure. Decreased
performance on the predictor variables was related to decreased performance on the
memory and the attention measure.

Reduced performance on the predictor variables was associated with greater
numbers of errors on the CVLT. Individuals had diﬁculty suppressing semantically
related items when recalling the list. This relationship was evidenced on the recognition
task as well The highest number of false positives were made to responses that were
from the same semantic category that were presented in the second list. Although the
relationship was not statistically signiﬁcant with total recall, the alpha level reached .06
w'nh the reading with distraction task. It is quite possible that with a larger sample size,
this relationship would reach signiﬁcance.

Why the predictor variables did not predict perseverations on the CVLT is unclear.
The inhibition view would argue that decreased inhibitory processing would lead to an
impairment in the ability to suppress the response, now considered to be irrelevant to the
task goal, increasing the probability of repetition. This hypothesis was not supported in
this study. On inspection of the data, one possible reason may be due to the fact that the

range of perseverative responses for this sample was restricted, although quite similar to

40

the normative data available for this age group (Delis et al, 1987). It is possible that a
relationship would be evidenced in a population of older adults who are more impaired on
this measure. Another possible explanation, although counter-intuitive, is that
perseverations as measured by the CVLT may reﬂect a diﬂerent process than errors due to
intrusions on this test. In a factor analytic study of the CVLT, Wiens and colleagues
(Wiens, Tindall, & Crossen, 1994) found that the perseveration score loaded on the same
factor as the semantic and serial clustering scores, measures of learning strategies used in
this task. By contrast, intrusions and false positives loaded on a separate factor, termed
response discrimination. The factors obtained in their study suggested that number of
perseverations may be more related to the learning strategy used by an individual As
inhibition is thought to be necessary for response selection, the relationship between the
target variables and intrusions and false positives is understandable. By contrast, there is
no reason to theorize that inhibitory processes would be important in determining the type
of strategy used to generate the response. This may explain why there is no relationship
between the perseveration score and the predictor variables, however ﬁrture studies are
needed to explore this further.

This study found support for the role of inhibition in tasks assessing memory and
attention. On the other hand, Arbuckle and Gold (1993) did not ﬁnd a relationship
between their measure of verbosity, which was theorized to partially reﬂect inhibitory
ﬁmctioning and other measures of memory and attention. This diﬂerence in results could
be due to the types of tasks used to assess memory and attention performance. In the
Arbuckle and Gold study, the use of a paragraph learning task with a single trial

presentation and no available measure of errors, may make this task less suitable for the

 

41

assessment of inhibitory ﬂmctioning. As reported above, inhibition processes were related
to the number and certain types of errors produced on the memory test. The lack of this
measure may reduce the sensitivity of the paragraph memory task to evaluate inhibitory
functioning. Whether good performance on this memory task is not as reliant on eﬂicient
inhibitory ﬁmctioning or whether the psychometric properties of this task do not lend itself
to eﬂecﬁvely measure inhibition is unclear. The same kinds of arguments can be used for
their attention measure, digit span. The PASAT is clearly a more complex and diﬁcult
test, as opposed to digit span. The range of scores on digit span is quite limited, and again
this task may not be sensitive enough for the assessment of inhibition.

The second hypothesis that was evaluated in this study was that there would be a
signiﬁcant relationship between age and inhibition, as measured by the predictor variables.
The results show that this relationship is not a straightforward one and is at least
dependent upon the characteristics of the various tasks being measured. As predicted,
advancing age was related to reduced performance on all the individual predicted
variables. However, in predicting performance on the memory and attention measures, the
relationship between the predictor variables and the dependent measures, changed as a
function of age and test measure. The relationship between the predictor variables and the
types of errors made on the CVLT (i e. intrusions and false positives) was generally
stronger with age. This suggests that with advancing age, inhibitory functioning continues
to decline, further impairing performance on the predictor and memory measures.

However, on the attention measure, contradictory ﬁndings were evidenced
suggesting that for this study, the ﬁnding of an age interaction is unreliable for this

variable. One possible reason may be the way in which the test was scored. A score of

42

zero was entered regardless if the participant could not perform the task or if that person
reﬁrsed to do the task. These two results may not reﬂect the same processes, yet are
coded the same way. In addition, the inclusion of the zeros also skewed the distribution of
results. When these zeros were not included in the analysis, then the main eﬂ‘ects were
still found but the interaction was no longer signiﬁcant. Thus, it would have to be
tentatively concluded that there is no relationship between age and inhibition for this
measure, but ﬁrrther study is necessary with a larger sample of adults, and perhaps a
different coding system for the zero scores, before stronger conclusions can be made.

Although the results are mixed in this study, there is some evidence that the ability
to ignore and/or suppress irrelevant information changes with advancing age. This is
consistent with other ﬁndings that have formd age differences between those participants
who have been classiﬁed as "young-old" (generally between 60 and 74) and "old-old"
(generally 75 and older) on various cognitive measures. Evidence has been accumulating
in the literature showing that those individuals who are over the age of 75 exhibit lower
levels of performance on a variety of neuropsychological measures as compared to the
those individuals who are between the ages of 60 and 74 (Christensen, MacKinnon, Jorm
& Henderson, 1994; Osterweil, Mulford, Syndulko & Martin, 1994). However, the
nature of the relationship between age and inhibitory ﬁmctioning was essentially the same
across the decades.

Although this study has provided evidence that age is related to performance on
the measures, other individual variables may also play a role. The recruitment process
used in this study attempted to enlist older individuals living in the comrmmity who

normally would not vohmteer for research studies in an attempt to assess a more

43

representative sample. As a result, many of the vohmteers did not have a college
education, and exhibited average ability on the vocabulary test. This sample may be
diﬂerent ﬂom those older individuals who answer advertisements in the newspaper, on
variables such as education and vocabulary knowledge. These individual differences,
generally ignored in relation to inhibition, may partially account for the ﬁndings of reduced
eﬁciency in both inhibitory mechanisms. There is some suggestion that individual
diﬂerence variables can partially account for inhibitory ﬁmctioning even in young adults.
For example, in one study, Gemsbacher (1993) reported ﬁnding reduced suppression on

tasks of reading comprehension requiring the suppression of inappropriate meanings of

__ _ __..._.__...._- “nun-_m-Q'

ambiguous words, in adults who are classiﬁed as less skilled readers. Based on these
ﬁndings, it would be important to further study the role of individual differences in the
eﬂiciency of inhibitory functioning. One individual diﬂerence variable, the presence of
depressive symptoms, did not appear to be related to performance on the

neurop sychological and experimental measures in this study. However only ﬁve
individuals in this sample scored in the mildly depressed range on the Geriatric Depression
Scale as classiﬁed by a score of 11 or above. Incidence rates for depression have been
reported to be anywhere ﬂom 1 to 29% (Gomez & Gomez, 1993 ). Although this study
attempted to assess a more representative sample of the older population, the recruitment
procedure still relied on volunteers for the study. It is quite possible that this study was
aﬂ‘ected by self selection problems; those individuals who could be classiﬁed as depressed
probably did not vohmteer for this study. This self-selection bias has in fact recently been
reported (Thompson, Heller, & Rody, 1994). The absence of individuals with diagnosable

depression in this study limits the generalizability of the current ﬁndings. A more

44

systematic approach that attempts to measure and control for other individual variables,
such as reading skill or health status is necessary to understand the impact of individual
diﬂerence variables on inhibitory ﬁmctioning.

Although inhibitory processing was interpreted as being the underlying link
between the neurop sychological measures employed in this study, it is possible that other
factors also could explain the relationship among these measures. The most noteworthy
is that of a general slowing of information processing speed that has been hypothesized to
occur with age (Salthouse, 1994, 1995). Many of the neuropsychological measures did
have a timed component but a number of them did not have time constraints, such as the
CVLT and the WCST. However, the WCST did load on the same factor as the other
timed neuropsychological measures. In addition, if speed of processing was the most
important underlying factor to the neuropsychological tasks, then it would follow that the
reading with distraction task would have loaded higher on the factor than it actually did
(and possibly higher than the WCST perseverative response score that does not have a
speed component). In this study although none of the tasks used were optimal measures
of speed of processing, Trails A, a measure with a large speed component, did not
signiﬁcantly correlate with either verbal ﬂuency or the number of false positives on the
CVLT. Yet hierarchical regression analyses supported the hypothesis that performance on
the tasks were related, with the predictor variables accormting for a signiﬁcant proportion
of the variance of most of the memory scores and the attention measure. Although a
generalized cognitive slowing theory could still be used to account for some of the
ﬁndings of this study, it is proposed that the construct of inhibitory processing can more

thoroughly accormt for the signiﬁcant results.

45

Given that inhibition does partly subserve performance on the neuropsychological
tasks, these results demonstrate that one's ability to ignore or suppress irrelevant
information is associated withiperformance on many cognitive tasks, and can be assessed
using clinical measures. The ability to use clinical measures to assess inhibitory
ﬁrnctioning in older adults can allow for a broader test of this theory, with a wider range
of ages and patient populations with cognitive disorders such as Alzheimer's disease and
Parkinson's disease. There is some preliminary data suggesting that inhibitory ﬁmctioning
is greatly reduced in patients with Alzheimer's disease as compared to old healthy
individuals. For example, patients with Alzheimer’s disease show evidence of impaired
inhibitory functioning on tasks of identity negative priming and the Stroop eﬂ‘ect (Spieler,
Balota & Faust, 1996; Sullivan, Faust & Balota, 1995). Although to my knowledge, no
research has been speciﬁcally conducted looking at the relationship between inhibition and
Parkinson's disease, there is some evidence to suggest that these patients may also have
diﬁculties in suppressing irrelevant information. Research has shown that patients with
Parkinson's disease have difﬁculty shifting set and alternating response sets (Flowers &
Robertson, 1985; Raskin, Bored, & Tweedy, 1992) and produce an increased number of
perseverative responses on the WCST as compared to age-matched healthy older
individuals (Lees & Smith, 1983; Taylor, Sairrt-Cyr & Lang, 1986). These ﬁndings
suggest that these patients may have deﬁcient inhibitory mechanisms. Future research can
help elucidate the role of eﬁcient inhibitory functioning in these and other patient groups.
Ifinhibitory functioning is impaired in certain patient groups, it is possible that the
assessment of inhibitory functioning may become part of the diagnostic assessment battery

in dementia and other disorders.

46

Aside ﬂom diagnostic considerations, to understand the role of inhibition and
selective attention in cognition may help in the selection and development of techniques or
strategies that could be utilized by older individuals and patients to compensate for
ineﬁcient inhibitory processing. For example, if older individuals have more diﬂiculty
processing information when presented together with extraneous material, then one simple
intervention would be to present the pertinent information succinctly and relatively ﬂee of
irrelevant material to reduce the impact of distraction. In one study employing the reading
with distraction task, Carlson and colleagues (Carlson, Hasher, Connelly & Zacks, 1995)
showed that when the distracting material was placed in predictable locations in the text,
then the age diﬂ'erences usually seen on this task were greatly reduced.

In summary, although in need of replication, the ﬁndings ﬂom this study suggest
that easily available neuropsychological measures can be used to assess inhibitory
functioning in older adults. The use of clinical measures can allow for the assessment of
inhibition in a wider range of ages and patient populations to further understand the role of
inhibition and general cognitive ﬁrnctioning. This increased understanding can possibly
lead to the development of interventions that can help older individuals to ignore
distracting information so that they can selectively attend to the necessary information to
complete the task at hand. The ﬁndings of diﬂerences in inhibition with age, within a
group of older adults emphasizes the need to conduct future research on the relationship

of age and additional individual variables and inhibition.

APPENDIX

 

APPENDIX

47

APPENDIX

Table 1.

Means and Standard Deviiions for the Neuropgchological Tests Administered to

 

 

100 Older Individuals
Test Measure Mean (SD)
Vocabulary Score ﬂom the WAIS-R 47.56 ( 10.69)
Verbal Fluency Total Score 37.17 (12.08)
WCST Perseverative Responses 22.52 ( 19.06)
Trails B - Trails A 65.54 (40.68)
California Verbal Learning Test (CVLT)
Total recall over 5 trials 40.82 (10.12)
Total Perseverations 3.81 (4.02)
Total Intrusions 5.28 (5.80)
Recognition Hits 13.52 (1.84)
Recognition False Alarms 2.5 (2.68)
Paced Auditory Serial Addition Test (PASAT) 90.43 (46.03)

 

 

48

APPENDIX

Table 2.

Means and Standard Deviations for the Reading with Distraction Test Administered to

92 Older Individuals

 

 

 

- ‘zr't'l-F'

‘.
Hi i

l.

81-. P385” 11mm?

Test Measure Mean (SD)
Reading Time
Related Condition 83.03 (27.37)
Unrelated Condition 84.16 (28.43)
No Distraction 56.45 (17.80)
Correct Responses on the Recognition test (out of 4)
Related Condition 2.71 (.61)
Unrelated Condition 2.95 (.52)
No Distraction 3.03 (.55)
Percent Foils
Related Condition 53.05 (26.44)
Unrelated Condition 31.62 (26.62)

No Distraction 31.89 (25.72)

49

APPENDD(

Table 3.

Correlations between Age and the Neuropggchological Measures

 

 

 

1. Age -- :
2. Education -.25* -- g
3. Vocabulary -.17 .54* -- y
4. Verbal Fluency -.21* .33* .47* --

5. Trails B-A .45“ -.27* -.43* -.35* --

6. WCST .26* -.22* -.24"' -.31* .39* --

7. Reading with Distraction .28* -.09 -.07 -.15 .31“ .08 --

8. CVLT Total Score -.46* .30“ .30* .29* -.45* -.36* -.33* --

9. CVLT Perseverations -. 12 .18 .08 .10 -. 16 -.01 -.02 .36*

10. CVLT Intrusions .24* -. 17 -.39* -.21* .43* .23* .08 -.37*

ll.CVLTFalsePositives .33* -.09 -.17 -.22"‘ .31* .41* .29"l -.69*

12. PASAT -.37* .32* .46“ .41* -.46* -.38"‘ -.27* .48*

 

*signiﬁcant at p < .05; n=100

Table 3 (cont'd).

50

APPENDIX

 

10 ll 12

 

9. CVLT Perseverations
10. CVLT Intrusions

11. CVLT False Positives

12. PASAT

.59* --

-.31* -.39* --

 

*signiﬁcant at p < .05; n=100

mm”; :ajn‘. rum I? WW-
" b

51

APPENDIX

Table 4.

Intercorrelations between the clinical measures and the Reading with Distraction task (11 =

100)

 

 

Test Measure 1 2 3 4

1. Verbal Fluency -- -.35 (-.33") -.31 (-.29°) -.15
2. Trails B- Trails A -- .39 (.38) .31
3. Perseverative Responses -- .08

4. Reading with Distraction ' -

 

' n = 92 for this measure
b correlations in parentheses are those obtained by Arbuckle and Gold (1993)

° perseverative errors instead of perseverative responses was used by Arbuckle and Gold

(1993)

303.51." r7734?! 1' m it!”

‘1‘ Kill] 3"» i

52

APPENDD(

Table 5.

Results ﬂom the hierarchical regression anmses

 

 

Dependent variable Controlled Variable R2 Increase in R2
CVLT Total Recall

Control Measures . 1 1*

Predictor Variables .36“ .25*

Interaction Terms .38* .02
CVLT Intrusions

Control Measures . 15*

Predictor Variables .25* . 10

Interaction Terms .38* .13*
CVLT False Positives

Control Measures .03

Predictor Variables .27 * .24*

Interaction Terms .35* .08
PASAT

Control Measures .22*

Predictor Variables .39“ .17“

Interaction Terms .44* .05

 

*p<.05

53

APPENDD(

 

Intrusions

_ 0 Old - Old (+ 1 SD)
- 7:1 Young - Old (+1 SD)

 

 

 

25 (-1 SD) 106 (+ 1 SD)
TRIALS B-A

Figure ‘l
Interactions of Age and Trials B - A in Predicting Intrustions

nrg Ilnﬂfu'. “ragga; I
'n'r - ‘ r -" r’ ' ‘
I . ‘. _

54

APPENDIX

 

False Positives

 

 

 

3 (-1 SD) 42 (+ 1 SD)

Perseverative Responses

Figure 2
Interactions of Age and Perseverative Responses in Predicting
False Positives

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