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Journal article in Cortex
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1
Preserved Conceptual Priming in Alzheimer’s Disease
Carla A. R. Martins and Toby J. Lloyd-Jones
University of Kent, UK
Correspondence to: Carla Alexandra Rodrigues Martins, 5, Vivienne Court, Peat Moors,
Headington, Oxford, OX3 7HG, Tel. 07743379194, Email: [email protected].
Running page heading: Conceptual priming in Alzheimer’s disease.
2
Abstract
We assess Alzheimer’s disease (AD) and healthy older adult control (HC) group
performance on: (1) a conceptual priming task, in which participants had to make a
semantic decision as to whether a degraded picture of an object encountered previously
belonged to the category of living or non-living things; and (2) a recognition memory
task. The AD group showed a dissociation between impaired performance on the
recognition task and preserved priming for semantic decisions to degraded pictures. We
argue that it is not whether priming is conceptual or perceptual that is important for the
observation of priming in AD, rather it is the nature of the response that is required (cf.,
Gabrieli, et al., 1999).
3
Introduction
Explicit memory, as measured by tests of conscious recollection of a previous
episode (e.g., recognition or recall tasks) deteriorates as a function of age (e.g. Mitchell
& Brown, 1988) and is dramatically impaired in individuals with Alzheimer’s disease
(AD; e.g. Fleischman, et al., 1995; Keane, Gabrieli, Growdon & Corkin, 1994; Keane
et al., 1991; Koivisto, Portin & Rinne, 1996). In contrast implicit memory, the
unconscious or unintentional retrieval of memories measured usually through ‘repetition
priming’ (i.e., the facilitation of performance for studied compared with unstudied
stimulus) can be preserved in AD.
Patients with AD can show normal priming on a range of implicit tasks, for
instance: mirror reading (e.g., Deweer, et al., 1994); word and pseudoword
identification (e.g., Fleischman et al., 1995; Keane et al., 1994; Keane et al., 1991;
Koivisto et al., 1996); picture naming (e.g., Gabrieli, Francis, Grosse & Wilson, 1991;
Park & Gabrieli, 1995; Gabrieli et al., 1999); and picture-fragment identification (e.g.,
Gabrieli, Keane, Stager, Kjelgaard, et al., 1994). Nevertheless, impaired priming has
been also observed in tasks such as category-exemplar generation (e.g. Monti et al.,
1996; Vaidya et al., 1999) and word-association (e.g. Salmon, Shimamura, Butters &
Smith, 1988; Carlesimo, Fadda, Marfia & Caltagirone, 1995)
This diversity of preserved and impaired priming in AD has led to the suggestion
that the dissociation reflects a distinction between perceptual and conceptual implicit
memory processes (Keane et al., 1991; Gabrieli et al., 1994; Fleischman & Gabrieli,
1998). That is, AD patients may display intact priming in perceptually driven-tasks,
which draw on processes concerned with the visual, auditory or tactual form of a target
stimulus. However, impaired or no priming will be found in conceptually-driven tasks
4
which draw on processes concerned with the content or meaning of a target stimulus
(Keane et al., 1991; Fleischman & Gabrieli, 1998).
This functional distinction between perceptual and conceptual priming in AD is
supported by converging evidence from normal participants (e.g. Blaxton, 1989), and
evidence of a corresponding anatomical separation between neural systems that may
mediate the two kinds of implicit memory (e.g., Blaxton, 1999). However, the picture is
complicated by the fact that AD patients also exhibit dissociations between perceptual
priming tasks. For instance, priming can be intact in tests such as word-identification
and picture naming, but impaired in word-stem completion and degraded picture and
word naming (see Fleischman & Gabrieli, 1998, for a review). Furthermore,
dissociations between conceptual priming tasks have also been reported for AD
patients. For instance, a dissociation between intact category-exemplar verification and
impaired category-exemplar production (Vaidya et al., 1997; 1999; Gabrieli et al.,
1999).
These results suggest that a distinction between perceptual and conceptual
priming alone is insufficient to account for all AD implicit memory deficits.
Identification versus production
Accordingly, Gabrieli et al. (1999) have suggested a distinction in the cognitive
and neural organization of implicit memory which is based on the dissociation between
identification and production forms of knowledge retrieval. Gabrieli et al. (1999) found
intact priming in AD patients for perceptual (i.e., picture-naming) and conceptual (i.e.
category-exemplar identification) tasks that required an identification response, while
performance was impaired on perceptual (i.e., word-stem completion) and conceptual
(i.e., category-exemplar production) tasks which required the generation or production
5
of a response. More precisely, a distinction is made between identification tasks which
instruct participants to identify presented stimuli, and production tasks which instruct
participants to use a presented cue to guide retrieval of a response. This distinction is
related to the different attentional demands of each task, which can be affected by AD
whereby the division of attention may have a selective effect on response production but
not on identification. It is suggested that production is more demanding on study phase
attentional resources than identification, due to response competition at test (Vaydia et
al., 1997): the identification task, by definition, lacks response competition because the
stimulus is provided at test, while in most production tasks response competition
involves multiple legitimate responses. It is possible that effects of Alzheimer’s disease
do not impair conceptual implicit memory processes in general, but rather selectively
impair word production processes that are called upon in many of these tests (Lazzara,
Yonelinas & Ober, 2001).
The Present Study
The present study examined AD performance on explicit and implicit tests of
memory which involved the manipulation of nonverbal material, namely intact and
fragmented pictures of common objects. Explicit memory was measured using a picture
recognition test, and implicit memory was measured via priming of a semantic decision
task. In the semantic decision task, complete pictures were presented during a study
phase, and fragmented pictures were presented during the test phase. Participants were
required to identify whether the fragmented picture was a living or nonliving thing,
without being required to produce the name of the object (for details of picture
fragmentation stimuli, see Snodgrass, Smith, Feenan & Corwin, 1987, and Snodgrass &
Corwin, 1988).
6
Very few studies examining implicit memory performance in AD have used
fragmented pictures as stimuli. Some of these studies used identical fragmented pictures
at both study and test (e.g., Bondi & Kaszniak, 1991; Gabrieli et al., 1994), whereas
other studies have used complete pictures at study and fragmented pictures at test (e.g.
Heindel, Salmon, Schults, Walicke & Butters, 1989). The evidence arising from these
studies is mixed: some investigations show impaired priming of fragmented picture
naming (e.g. Bondi & Kaszniak, 1991) while others show preserved priming of
fragmented picture naming. For instance, Gabrieli et al. (1994) examined the repetition
priming performance of AD patients on the Gollin Incomplete-Pictures task and found
intact priming in AD on incomplete picture identification.
One contributing factor to these contrasting findings may be the nature of
‘perceptual closure’; the process whereby an observer fills in missing portions of a
stimulus so as to complete an image and produce an identifiable object (Snodgrass &
Kinjo, 1998). Perceptual closure is an important process influencing priming effects in
picture fragment identification. Snodgrass and Feenan (1990) propose that optimal
priming arises from a situation that produces the closure experience and contains the
minimum amount of information necessary to support the closure. Supporting this idea,
they found that a moderately fragmented study picture produced more priming than
either a very fragmented or an intact picture.
On the basis of previous findings we predict that the AD group will show
impaired performance on the recognition memory test relative to a healthy older adult
control (HC) group. In contrast, the AD group will show intact priming, within the
normal range, on the semantic decision task. The logic is that although the semantic
decision task is conceptual, it requires an identification rather than a production
response, and it is this dimension rather than the perceptual-conceptual dimension that
7
is most important for priming to be observed in AD (Fleischman, Gabrieli et al., 1995;
Koivisto et al., 1996; Fleischman & Gabrieli 1998; Park & Gabrieli et al., 1998; Vaidya
et al., 1999). To maximise the possibility of finding priming, we used stimuli that were
moderately fragmented at test (Snodgrass & Feenan, 1990). Alternatively, if the AD
group show no or impaired priming in the semantic decision task, it will suggest that
perceptual-conceptual dimension of the task is more important than the nature of the
response.
As a subsidiary issue we examined whether altering the nature of the study task
would influence priming. If priming occurs only when the tasks at study and test are
identical, that is when both are semantic decisions, such priming may be the result of
task-specific encoding processes. Alternatively, if equivalent priming effects on
semantic decisions at test are obtained for both semantic decision and naming tasks at
study, then we can be assured that such priming effects are the result of retrieval rather
than encoding-based processes or an identical match between encoding and retrieval
processes (cf., Maki & Knopman, 1996).
Experiment
Method
Participants
An AD and HC group participated in this experiment (see Table 1). The AD
group consisted of 16 participants in all, 9 males and 7 females ranging in age from 67
to 85 years (M = 75.6; SD = 5.86) and in years of education from 0 to 17 years (M =
6.1; SD = 4.18). The AD participants were recruited from the Psychiatric Hospital of
Magalhães Lemos and from the Clinic of Neurology of Dr. Manuel Laranjeira at Porto
8
in Portugal. All patients were evaluated by a neurologist, psychiatrist and psychologist
who gathered information concerning patients’ medical history, neuropsychological
testing (i.e., the mini-mental state exam; MMSE, Folstein et al., 1975) and
neuroimaging examinations. Patients met the clinical criteria of the NINCDS-ADRDA
(McKhann, Folstein, Katzman, Price & Stadlan, 1984) and DSM-IV (1994) for a
diagnosis of AD. Camcog scores (Roth, Huppert, Mountijoy & Tym, 1998) ranged from
30 to 68 (M = 51.4; SD = 10.31) and the MMSE scores ranged from 10 to 20 (M =
16.2; SD = 3.14) suggesting that patients were within the mildly to severely cognitive
impairment.
The HC group consisted of 16 participants in all, 7 males and 9 females, raging
in age from 64 to 85 years (M = 73.5; SD = 6.26) and years of education ranging from 0
to 17 years (M = 4.8; SD = 4.13). These controls were recruited from a nursing home at
Porto (Portugal) – Lar do Comércio – and from an elderly voluntary group in the
Lordelo do Ouro Church, at Porto (Portugal). The inclusion criteria for normal
participants were that the MMSE scores be within the cut-off scores for no cognitive
impairment according to the level of education of participants for the Portuguese
population (Guerreiro et al, 1993): no education ≥ 15; 1 to 11 years of education ≥ 22
and more than 11 years of education ≥ 27. The MMSE Scores ranged from 22 to 29 (M
= 25.6; SD = 2.68).
The two groups did not differ significantly on age (t (30) = 0.99; p = n.s.) or
education (t (30) = 0.85; p = n.s.) but differed significantly on MMSE scores (t
(28.424) = – 8.643) (see Table 1).
9
----------------------
Table 1 about here
-----------------------
Material
The material consisted 60 pictures of common objects selected from the
Snodgrass and Vanderwart (1980) norms. Half were living things and half were non-
living things. The pictures were fragmented according to the algorithm developed by
Snodgrass et al. (1987). Briefly, fragmented pictures were created on the Apple
Macintosh Computer and original drawings from the 260 pictures in Snodgrass and
Vanderwart (1980) were reduced so as to fit within a 246 x 246 pixel square (8.3 x 8.3
cm) on the computer screen. These pictures were then digitised using the Thunderscan
digitiser and saved as a MacPaint File. Through a set of procedures written in Microsoft
Basic, pictures were subject to fragmentation. In order to delete cumulatively, and to
ensure that each successive fragmentation level has fewer fragments than the next lower
level 16 x 16 blocks were identified that contained information. The fragmentation
program lays out a grid of 16 x 16 blocks, determines which blocks contain black
pixels, and stores the locations of these critical blocks. The program then randomly
selects increasing proportions of critical blocks to be erased according to an exponential
function (number of remaining blocks (level) = number of total blocks [1 – aEXP (8-
level)]), to produce eight levels of fragmented images per stimulus. The level of
fragmentation selected for this study was level 3; a medium level that would not prove
too difficult for patients and controls. All items were presented one at the time on single
cards (10 cm x 7.5 cm) with the picture centred on the card.
10
Design
The experiment consisted of 4 phases, sequentially presented to each participant:
(1) a study phase which was either a semantic decision task or a naming task; (2)
neuropsychological evaluation (i.e. Camcog and MMSE); (3) a semantic decision task
(in which priming was measured); and (4) a recognition memory test.
The pictures presented in the study phase of the semantic decision task were
intact, and those presented in semantic decision test phase were fragmented. Similarly,
for recognition test the pictures presented in the recognition phase were fragmented.
The original list of 60 objects was divided into 3 lists each of 20 pictures. Participants
would encounter one of these lists as the study list, then the same list again plus a new
list as the unprimed items in the semantic decision test phase. For the recognition task,
the unprimed items in the semantic decision task served as the study list (and thus as
‘old’ items in the recognition test), and another new list acted as the unstudied ‘new’
items for the recognition test. To ensure that the study phases of both the implicit
semantic decision task and the recognition task were similar, participants were also
asked to name an intact version of each picture following their semantic decision to the
fragmented picture. This was to enable recognition performance to be as efficient as
possible and to provide the maximum possibility of successful recognition performance
for the AD group, who we had predicted would find recognition particularly difficult.
The lists of objects were rotated across participants, and within participant
groups, so that no object was encountered more than once for each participant and both
implicit and explicit tasks were carried out by each participant. This design yields the
following variables: (1) for the study phase, Group (AD vs. HC participants) and Study
Task (semantic decision task vs naming task), which are between-subject measures; (2)
for the semantic decision test phase, Group (AD vs. HC), Study Task (semantic decision
11
vs. naming) and Priming (Unprimed vs. Primed), where priming is a repeated measure;
and finally (3) for the recognition test phase, the main variable was Group (AD vs. HC).
Note, we also included Study Task (semantic decision task vs naming task) as a variable
for the recognition test phase to ensure there was no influence on recognition
performance of having carried out either of these tasks in particular during the initial
study phase prior to the semantic decision test phase.
Due to a procedural error in operationalization of the design, the full stimulus
rotation procedure was carried out for only half the participants within each group,
whereas for the remaining half all the participants in that group received the same three
lists (i.e., study list A, semantic decision lists A and B, recognition lists B and C). To
assess whether this influenced the results we added this group difference as a within AD
and HC group variable to the statistical analyses.
The dependent variable for the naming and semantic decision tasks was
percentage correct. For the recognition test, the measures were hits, false alarms, and a
corrected recognition score (calculated as hits minus false alarms).
Procedure
Each participant was tested individually in a single experimental session that
was scheduled to last approximately 45 minutes. In the initial study phase participants
were presented with intact pictures displayed one at the time on separate cards which
participants were asked either to categorize as living or non-living, or to name. There
was no time limit for the answer to be provided, but participants were instructed to
answer as quickly and accurately as possible. After a short delay of 15 minutes during
which the neuropsychological test was conducted, the semantic decision test phase
began. As in the study phase, pictures were presented one at the time on separate cards,
12
and participants were asked to categorize the fragmented picture as living or non-living.
After each response, participants were shown the corresponding intact picture and asked
to name it. There was no time limit for the answer to be provided, but participants were
instructed to answer as quickly as possible. Finally, the recognition task was
administered 10 minutes after the semantic decision task. In this task participants were
asked to perform a yes or no recognition judgement to fragmented pictures. Participants
were instructed to respond “yes” to a picture if they had previously encountered the
object and “no” if they had not.
Results
Recognition
The average hits and false alarms for the AD group were 14.9 (SD = 4) and 13.6
(SD = 4.6) respectively, compared with 15.7 (SD = 3.5) and 3.4 (SD = 3.4) respectively,
for the HC group.
AD patients and HC participants did not differ significantly in terms of hits,
t(30) = -6.10, p = n.s., but there was a significant difference for false alarms between the
two groups with more false alarms for the AD group, t(30) = 7.10, p ≤ 0.001 (see Table
2).
Corrected recognition scores (i.e., hits minus false alarms) were also computed
for each participant. The mean corrected recognition score was 0.6 (SD = 0.15) for AD
patients, and 0.43 (SD = 0.35) for HC participants (see Table 2). AD patients exhibited
a significant recognition memory impairment in comparison to the HC group. A two
factor analysis of variance (ANOVA) computed on corrected recognition scores with
group (AD vs HC) and study task (semantic decision vs naming) as a between-subject
13
variables reveals a main effect of group with AD patients significantly less accurate at
recognizing previously seen pictures, F(1,28) = 15.5, p < 0.001. However, there was no
effect of study task, F (1,28) = 0.48; p = n.s., and no interaction between group and
study task, F(1,28) = 2.02, p = n.s..
To examine whether there were any differences between the groups for the
initial study phase, t-tests were also carried out on corrected recognition scores. There
was no significant difference between: (1) AD patients that performed a semantic
decision task at study (M = 0.03, SD = 0.13) and AD patients that performed a naming
task at study (M = 0.09, SD = 0.18), t(14) = -0.09, p = ns; and (2) NC participants that
performed a semantic decision task at study (M = 0.5, SD = 0.3) and NC participants
that performed a naming task at study (M = 0.3, SD = 0.4), t(14) = 1.16, p = ns.
----------------------
Table 2 about here
-----------------------
Semantic decision task
Study phase
The mean percentage correct responses were analysed in a two factor ANOVA
with group and study task as between-subject variables. There was a main effect of
group, with fewer correct for the AD than the HC group, F(1,28) = 62.76, p ≤ 0.001.
AD and HC group means were 77.5 (SD = 2.4) and 100 (SD = 2.41), respectively.
However, there was no effect of study task, F(1,28) = 7.031, p = 0.700, and no
interaction between group and study task, F(1,28) = 2.04, p = 0.164 (see Table 3).
14
----------------------
Table 3 about here
----------------------
Test phase
The data was analysed using a mixed ANOVA, with group (AD vs HC) and
study task (semantic decision vs naming) as between-subjects variables and priming
(primed vs. unprimed) as the within-subjects variable. There was a main effect of
Group, with AD less accurate than NC, F(1,28) = 20.03, p ≤ 0.001. There was also a
main effect of priming, with greater accuracy for primed as compared with unprimed
conditions, F(1,28) = 140.23, p ≤ 0.001, Finally, there was also a marginal group x
priming interaction, revealing a trend towards a greater priming for the AD patients
relative to NC participant, F(1,28) = 3.76, p ≤ 0.1, (see Table 4). There was no effect of
study task, F(1,28) = 0.92, p = 0.35.
When we add a grouping variable to account for different groups of participants
receiving either rotated or unrotated lists of items (see Design section) the findings are
unchanged. There was no main effect of rotation, F(1,24) = 0.09, p = n.s.; and there was
no interaction between rotation condition and subject group F(1,24) = 0.04, p = n.s. The
main effect of Group remained, F(1, 24) = 17.8, p < 0.01, as did the main effect of
priming, F(1,24) = 131.5, p < 0.005. The group x priming interaction approached
significance, F(1,24) = 3.52, p = 0.07.
15
----------------------
Table 4 about here
----------------------
Discussion
Although severely impaired in recognition, AD patients exhibited normal
priming with fragmented pictures in a semantic decision task. This is consistent with
intact conceptual priming in AD patients, when an identification response is required
(e.g., Gabrieli et al., 1999). It is also consistent with normal priming in AD of
fragmented picture processing, which has only been observed previously in picture
naming (e.g., Ergis, Van der Linden & Deweer, 1995; Gabrieli et al., 1994). Thus,
perceptual closure, the process whereby an observer fills in missing portions of a
stimulus so as to complete an image and produce an identifiable object, is preserved in
AD.
Nevertheless, the present results are inconsistent with two previous studies in
particular. First, Verfaellie et al. (1996) found preserved priming for undegraded
pictures, but impaired priming for degraded pictures for AD patients in a naming task.
They argue that impaired priming of naming degraded pictures arises because
processing such pictures requires explicit memorial retrieval strategies which are
impaired in AD. In the Verfaille and colleagues study priming was impaired when
degraded pictures were presented in both study and test phases of the experiment. It is
possible therefore that preserved priming is observed here because pictures were only
degraded at test. However, this is unlikely to be the case as Heindel et al. (1989) found
impaired priming of picture naming with undegraded pictures presented at study and
16
degraded pictures presented at test. Rather, we suggest that explicit retrieval strategies
may contaminate implicit picture processing performance when a naming rather than a
forced two-choice categorization response is required. Naming is more difficult than
forced two-choice categorization as in the former case a single unique label has to be
attached to the stimulus, and in the latter a more general label is applied. This added
difficulty for naming may lead to explicit retrieval strategies normally being used to
benefit performance.
Second, Lazzara, Yonelinas and Ober (2001) assessed conceptual priming in AD
with a semantic decision task in which participants were required to make judgements
about the size of the objects (e.g., ‘Does the word basket represent an item that can be
larger or smaller than a shoebox?’). Conceptual priming was impaired in AD patients
relative to the control group. The reason for the disparity between the Lazarra et al.,
study and the data presented here may be either: (1) the degree of semantic impairment
in the AD groups; or (2) the extent to which the tasks used in each study require
semantic processing.
AD patients can have degraded semantic processes. For instance, recently
Giffard et al. (2002) have suggested that from the onset of Alzheimer’s dementia
semantic representations deteriorate progressively with specific features affected first
(e.g., for tiger – stripes). Differentiating between concepts becomes more difficult as
distinguishing features are lost. In a similar vein, AD patients (and other brain-damaged
groups) have been shown to have category-specific semantic memory deficits, whereby
they perform worse on living as compared with non-living things (see e.g., Whatmough
& Chertkow, 2002, for a recent review). One possible reason for the living things deficit
is that AD patients may have lost perceptual features of objects which are particularly
important for processing living things, while the functional features (such as how an
17
object is used) which are more salient for non-living things remain intact. There may
also be longitudinal changes where a larger number of intercorrelated perceptual
attributes contributing to the conceptual representation of living things make them less
vulnerable in the early stages of AD, but the collapse of this correlational structure
exaggerates deficits for living things with advanced disease (Gonnerman et al., 1997,
although see Garrard, Patterson, Watson & Hodges, 1998). Returning to the present
study, it may be that the present AD group was less impaired semantically, or
alternatively that the decision as to whether an object is living or non-living is not as
sensitive to semantic processing as a comparative judgement as to an object’s size.
One final point to make is that although priming was essentially normal, the AD
group showed a trend towards a greater priming than the HC group. This is most likely
due to poorer initial baselines, as prior research suggests that the magnitude of priming
increases as a function of absolute baseline performance (e.g., Ostergaard, 1994).
However, following Park et al. (1998) who found a similar result (although for naming),
it may be that because AD patients have difficulty in semantically processing pictures,
prior processing may have disproportionately enhanced the retrieval of semantic
knowledge of those items that are usually difficult or indeed unable to be retrieved by
patients. This suggestion is also supported by studies of ‘hyperpriming’ (i.e., greater
priming for patients relative to controls) in semantic priming tasks where such priming
is observed for items for which semantic processing is impaired (e.g., Chertknow, Bub
& Seidenberg, 1989; although see e.g., Bell, Chenery & Ingram, 2001, and Giffard et
al., 2001, for alternative accounts of hyperpriming).
In sum, a dissociation between perceptual and conceptual implicit memory
processes alone is not sufficient to explain implicit memorial performance in AD
patients observed here. Rather, the nature of the response that is required (i.e., an
18
identification or production response) is likely to be important as well (e.g., Gabrieli et
al., 1999). An alternative suggestion is that impaired priming in AD is a consequence of
the ‘hyperspecificity’ in their processing abilities (Maki & Knopman, 1996). According
to this view, AD patients exhibit normal priming only when processing operations are
identical between study and test phases of the experiment. The reason for this is that as
they are unable to convert information between different operations involved in the
different phases of the study. However were this the situation here, we would have
expected greater priming for the semantic decision-semantic decision group, as
compared to the naming-semantic decision group. This was not the case. Rather, in line
with Gabrieli et al. (1999), we suggest that impaired attentional resources in AD can
have important consequences for the unconscious or unintentional retrieval of long-term
memories.
19
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Table 1
Descriptive Characteristics for Alzheimer’s Disease (AD) and Healthy Older Adult
Control (HC) Participants.
Group Age Years of education Neuropsychological test
AD (n = 16)
Mean
S D
HC (n = 16)
Mean
SD
75.6
5.86
73.5
6.26
6.1
4.8
4.8
4.13
CAMCOG & MMSE
51.4/16.2
10.30/3.41
MMSE
25.5
2.68
27
Table 2
Percentages of Hits and False Alarms, and Corrected Recognition Scores for
Recognition
Hits False Alarms Corrected Recognition Scores
AD
Mean
SD
14.9
4
13.6
4.6
0.6
0.15
HC
Mean
SD
15.7
3.5
3.4
3.4
0.43
0.35
28
Table 3
Mean Percentage Correct for Semantic Decision and Naming as Study Tasks
Groups Task
Semantic Decision Naming
AD
Mean
SD
77.5
2.4
81.9
2.41
HC
Mean
SD
100
2.41
97.5
2.41
29
Table 4
Mean Primed and Unprimed Scores for AD and HC Groups for Semantic Decision
as the Test Task With Naming and Semantic Decision as Study Tasks
Naming at Study Semantic decision at Study
Primed Unprimed Primed Unprimed
AD
Mean
SD
89.4
6.23
69.4
6.23
90.6
4.17
70.6
4.17
HC
Mean
SD
95.6
4.17
79.4
14.5
96.2
3.54
83.7
5.18