The Minute Hand Phenomenon in
the Clock Test of Patients With
Early Alzheimer Disease
Journal of Geriatric Psychiatry
and Neurology
Volume 22 Number 2
June 2009 119-129
# 2009 Sage Publications
10.1177/0891988709332941
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Thomas Leyhe, MD, Monika Milian, MSc, Stephan Müller, MSc,
Gerhard W. Eschweiler, MD, and Ralf Saur, MSc
Common scoring systems for the Clock Test do not
sufficiently emphasize the correct time representation
by the clock hands. We compared Clock Drawing, Clock
Setting, and Clock Reading in healthy control persons,
patients with mild cognitive impairment, early Alzheimer
disease and progressed Alzheimer disease particularly
analyzing clock time representation. We found that
healthy control persons and participants with mild cognitive impairment did not show any impairment in Clock
Test performance. Patients with early Alzheimer disease
could be discriminated from healthy control persons and
participants with mild cognitive impairment solely by
misplacement of the minute hand in Clock Drawing and
Clock Setting. The progressed Alzheimer disease group
showed significantly more impairments in all Clock Test
variants. It is assumed that early stage Alzheimer disease
patient deficits in Clock Tests are mainly determined by a
reduced access to semantic memory about the appearance and functionality of a clock.
T
perception and constructional skills,6-8 but several
studies also found relations to other cognitive skills,
such as executive functioning,9-11 verbal abilities,12
and semantic memory.13,14 Thus, it is presumed that
the performance on the CDT depends on multiple
cognitive domains.15
There are a number of versions and scoring
systems of the CDT.6,7,16,17 In most versions, the participants are asked to place the digits of a clock face in a
predrawn circle and to draw the hour and minute
hands in the appropriate positions for a given time.16,17
Related to the CDT are Clock Setting Tests and
Clock Reading Tests.14,18,19 For the Clock Setting
Tests, participants are asked to place the clock hands
for given times into circles with marks indicating the
number locations. In Clock Reading Tests, participants must read the times represented by the clock
hands in the clock faces. In advanced stages of AD,
a sensitivity of approximately 90% for Clock Setting
and Clock Reading Tests was assessed.18,19
Several methods of quantitative and qualitative
analysis for test performance have been proposed
for the CDT. Quantitative scoring systems evaluate
the integrity of the clock face: the presence and
he Clock Drawing Test (CDT) is a well-known
and convenient screening tool for the assessment of cognitive disorders in psychiatric and
neurological diseases. It allows differentiation
between patients with Alzheimer disease (AD) and
healthy elderly people.1,2 Yamamoto et al found that
the CDT is a reliable screening method to detect
patients with mild cognitive impairment (MCI).3
However, other investigators found only a small
sensitivity for detecting very mild AD.4,5
Originally, the CDT has been used to identify
impairment of visuospatial abilities, including space
Received February 17, 2008. Received revised April 27, 2008.
Accepted for publication June 18, 2008.
From the Department of Psychiatry and Psychotherapy,
University of Tübingen (TL, MM, SM, GWE, RS); Geriatric
Center at the University Hospital of Tübingen (TL, GWE); and
Section of Experimental Magnetic Resonance of CNS,
Department of Neuroradiology, University of Tübingen (RS),
Tübingen, Germany.
Address correspondence to: Thomas Leyhe, Department of
Psychiatry and Psychotherapy, University of Tübingen,
Osianderstraße 24, 72076 Tübingen, Germany; e-mail: thomas. [email protected].
Keywords: clock reading; clock setting; clock drawing; cognitive impairment; dementia
119
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120 Journal of Geriatric Psychiatry and Neurology / Vol. 22, No. 2, June 2009
sequencing of digits, the presence and placement of
the hands, or summarize the correctness and completeness of the clock face.1,16 In some studies,
drawing difficulties have been taken into account
as well as the size of the clock, stimulus-bound
responses, conceptual deficits, spatial and/or planning deficits, omissions, perseverations, additions,
and substitutions.14,20 Feedman et al15 pointed to a
greater difficulty in adjusting the minute hand than
the hour hand in the CDT in normal participants
as well as patients with AD and Parkinson’s disease
with dementia. So far, a detailed analysis of the
errors in placing the clock hands has not been performed. Similarly, clock setting and clock reading
performance have only been evaluated by means of
registration of both correct and false answers.14,18,19
In the present explorative study, we investigated
elderly patients with MCI and AD with a test battery
including a Clock Drawing, Clock Setting, and Clock
Reading Test. For detailed analysis, we applied both
a quantitative registration of the clock hand errors
and a qualitative error analysis in the Clock Drawing
and Clock Setting task.
Methods
Participants
A total of 58 participants (36 women, 22 men) with a
mean age of 74.1 + 8.0 years (range: 61-92 years)
participated in this study, representing 4 groups:
healthy control participants (HC), patients with
MCI, patients with early Alzheimer disease (EAD),
and patients with progressed Alzheimer disease
(PAD). Patients were recruited from the Memory
Clinic of the Department of Psychiatry and Psychotherapy of the University Hospital of Tübingen.
The study was approved by the local ethics committee and written informed consent was obtained from
each individual.
The HC group consisted of relatives or friends of
the patients without a history of neurological or psychiatric disease or any signs of cognitive decline, as
confirmed by clinical interview.
Patients with AD and MCI underwent physical,
neurological, and psychiatric examinations. In addition, electroencephalography and computed tomography or magnetic resonance imaging of the brain
was performed. Routine laboratory tests included
lues serology, analysis of vitamin B12, folic acid, and
thyroid-stimulating hormone levels. In all patients,
neuropsychological testing was performed using
the ‘‘The Consortium to Establish a Registry for
Alzheimer’s Disease’’ test battery.21
Mild cognitive impairment was defined using the
Mayo criteria.22 Patients with MCI had memory deficits, in some cases in combination with other cognitive
impairments, but they were able to lead an independent life with daily living activities remaining intact.
All patients with AD met the diagnostic criteria
of probable AD according to the Diagnostic and Statistical Manual of Mental Disorders, fourth edition
(DSM-4),23 the International Classification of
Diseases, Tenth Revision (ICD-10) Classification of
Mental and Behavioural Disorders (WHO),24 and
the criteria of the National Institute of Neurological
and Communicative Disorders and Stroke and the
Alzheimer’s Disease and Related Disorders Association (NINDS-ADRDA).25
According to their stage in the Global Deterioration Scale (GDS),26 patients with AD were divided
into 2 groups: patients with a GDS score of 4 were
defined as EAD and patients with a GDS score of
5 were classified as PAD.
All patients and control participants had normal
or corrected-to-normal visual acuity and sufficient
hearing ability. None of the participants had a physical handicap influencing the ability to perform the
required tasks or an indication of neurological or
psychiatric disorders not related to their diagnosis.
The demographic data and the mean MiniMental State Examination (MMSE)27 scores of the
4 groups are shown in Table 1. One-way analysis of
variance (ANOVA) of the mean age (F[3, 54] ¼
0.97, P ¼ .412) and education (F[3, 54] ¼ 1.67,
P ¼ .184) did not show any significant group differences. The 4 groups also did not differ in gender
distribution (2 [3] ¼ 7.20, P ¼ .066). As expected,
a 1-way ANOVA was highly significant for the
MMSE (F[3, 54] ¼ 71.33, P < .001).
The Clock Test—Application and Scoring
All participants were required to complete the Clock
Test in the following order: CDT, Clock Setting Test,
and Clock Reading Test.
The Clock Drawing Test
Application and quantitative error analysis. For the
CDT, the instruction and the scoring system of the
modified version of Shulman et al16 were applied.
The participants were asked to draw the numbers
in appropriate positions in a predrawn circle, and
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Minute Hand Phenomenon in the Clock Test of Patients With AD / Leyhe et al
121
Table 1. Demographic Data and Cognitive Status
Group
Number
Female
Male
Age: mean (SD)
Education: mean (SD)
MMSE: mean (SD)
HC
MCI
EAD
PAD
14
10
4
72.6 (8.7)
12.5 (4.0)
29.4 (0.7)
15
5
10
72.7 (6.9)
13.1 (3.0)
28.0 (1.1)
16
12
4
76.9 (6.6)
11.2 (3.2)
23.9 (1.4)
13
9
4
73.7 (9.7)
10.5 (3.5)
18.6 (3.9)
NOTE: HC ¼ healthy controls; MCI ¼ patients with mild cognitive impairment; EAD ¼ patients with early Alzheimer disease; PAD ¼
patients with progressed Alzheimer disease; MMSE ¼ Mini-Mental State Examination; SD ¼ standard deviation.
Qualitative error analysis of time representation. The
qualitative analysis of time representation evaluated
the placement of the hour and the minute hand.
In Table 2, the different error categories of time
representation of the clock drawings are described.
Figure 2 shows typical examples of the EAD group
with errors in hand positioning.
The Clock Setting Test
Figure 1. Characteristic errors in clock drawings made by
patients with progressed Alzheimer disease and deficits in the
spatial component (score from left to right: 4, 4, 5).16 A,
disorganized clock face; B, missing digits; C, disorganized clock
face and missing digits.
then they were asked to place the hands on the clock
to indicate ‘‘10 past 11 o’clock.’’ The results were
evaluated by scoring from 1 point (‘‘perfect‘‘) up to
6 points (‘‘not at all representation of a clock’’).
In addition to the Shulman scoring system, we
applied an evaluation method in which we focused
on the representation of the clock time. The number
of drawn hands of each participant was counted.
Missing or false placement of either the minute or
the hour hand was scored 1 failure point each. The
hands had to point straightforward at the demanded
digit, but an offset of the placement of the hour hand
on the digit ‘‘11’’ depending on the minute specification ‘‘10’’ was tolerated.
Qualitative analysis of clock faces. For the qualitative
analysis of the clock faces, we evaluated the completeness and configuration of the digits in the predrawn circle. Registered errors included omitted,
wrongly replaced, displaced, transposed, or reversed
digits as well as digits outside the clock face and post
meridiem digits. Figure 1 shows typical examples of
deformed clock representations in drawings from the
PAD group.
Application and quantitative error analysis. For the
Clock Setting Test, an authentic clock was provided,
with a clock face of 20 cm diameter and 2 hands differing in length and color (green and long ¼ minute hand;
red and short ¼ hour hand). Digits were well visibly
printed in the right order, and marks between the numbers indicated minutes. Participants were asked to
adjust the hands to represent 10 distinct clock times
verbally communicated in the 24-hour clock notation
system in the German language: (1) ten minutes past
twelve, (2) five twenty, (3) five minutes to eleven, (4)
eight forty, (5) twenty minutes past fourteen, (6) eighteen twenty, (7) ten minutes to twenty, (8) five twenty,
(9) ten minutes past five, and (10) sixteen thirty. Prior
to the start of the test, the minute hand was placed at
the digit 12 and the hour hand at the digit 6.
Each correctly adjusted clock time was scored as
1 point, up to a maximum of 10 points. Similar to the
CDT, the errors in setting the clock hands were
counted. At maximum, a participant could receive
10 error points for the hour and the minute hand,
respectively. As in the evaluation of the CDT, the
clock hands had to point directly to the digits in
question. A missing offset of the hour hand on the
proper digit in depending on the minute specification was accepted as correct.
Qualitative error analysis of time representation. The
qualitative error analysis of time representation
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122 Journal of Geriatric Psychiatry and Neurology / Vol. 22, No. 2, June 2009
Table 2. Classification System for Qualitative
Error Analysis of Time Representation in the Clock
Drawing and Clock Setting Test
Clock Drawing Test
Hour hand
No offset: the hour hand is placed on the correct digit without
offset depending on the minute dataa
False digit: the hour hand is placed on a false digit,
instead of 11
Not drawn: the hour hand is missing
Minute hand
Stimulus bound: the minute hand is set on the
digit 10 instead of 2
Adhered to hour hand: the minute hand is clockwisely
displaced a little to the hour hand
Other: eg, the minutes are written in numbers
Not drawn: the minute hand is missing
Clock Setting Test
Hour hand
No offset: the hour hand is placed on the correct digit
without offset depending on the minute dataa
Mixed up: the minute hand is taken for the hour hand
Other: eg, the hour hand is adjusted on false digit
Minute hand
Stimulus bound: the minute hand is set on the digit with
the minute data (eg, 5 instead of 1 for the time 5 past)
Adhered to hour hand: the minute hand is clockwisely
displaced a little to the hour hand
Depending on hour hand: the minute data is counted
from the position of the hour hand
Mixed up: the hour hand is taken for the minute hand
Other: eg, minute hand is adjusted on any digit
a. Clinically not relevant.
evaluated the adjustment of the hour and the minute
hands. The different error categories of time representation in the Clock Setting Test are described in
Table 2.
The Clock Reading Test
Application and quantitative error analysis. On the
same clock used in the Clock Setting Test, 10 clock
times were adjusted by the investigator and the participants were asked to read them. To avoid learning
effects, the clock times differed from those of the
Clock Setting Test: (1) nine fifteen, (2) six forty,
(3) seven forty-five, (4) four twenty-five, (5) twelve
o’clock, (6) ten thirty-five, (7) two thirty, (8) eleven
fifty, (9) six o’clock, and (10) five minutes past one.
The participant’s performance for each item was
scored according to the system of the Clock Setting
Test. Each correctly read clock time was counted
as 1 point, up to a maximum of 10 points. Additionally, reading errors were counted separately for each
Figure 2. Characteristic clock drawings made by patients with
early Alzheimer disease without deficits in the spatial component (score 3).16 Although the presuppositions were fulfilled,
the default clock time (10 minutes past 11) is not readable. A,
adhered to hour hand; B, stimulus-bound response; C, other
solution (the time is written in numbers).
hand. Both the minute hand and the hour hand
could be read incorrectly up to 10 times.
Data Analysis
The SPSS-14 statistical package for Windows was
used for data analysis. To assess group differences for
age, education, and MMSE score, a 1-way ANOVA
was chosen. Because the data from the HC and MCI
groups in the Clock Test were not normally distributed and variances were heterogeneous, the nonparametric Kruskal-Wallis Test was applied to detect
group differences in the CDT, Clock Setting Test, and
Clock Reading Test. For post hoc comparisons, we
used the Student-Newman-Keuls test. Chi-square
tests were applied for categorical data: (1) for the
detection of differences in gender distribution; (2)
in the CDT for analyzing group differences in the
errors of hour and minute hands; and (3) in the CDT
for assessing differences between the performance in
placing the hour and minute hands for each group.
The Fisher exact test for comparisons of categorical
data between 2 groups was used where appropriate.
Sensitivities and specificities for detecting AD
patients with the modified version of the scoring system of Shulman et al16 and our scoring system for
the CDT were calculated.
Results
Quantitative Error Analysis
Overall Performance
We found highly significant differences between the
groups for each of the 3 subtasks of the Clock Test
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Minute Hand Phenomenon in the Clock Test of Patients With AD / Leyhe et al
Table 3.
123
Group Differences of Performance in Clock Drawing, Clock Setting, and Clock Reading
Group
Clock Drawing Test
Shulman Score
Number of hands
Error minute handb
Error hour handb
Clock Setting Test
Correct times
Error minute handsc
Error hour handsc
Clock Reading Test
Correct times
Error minute handsc
Error hour handsc
HC
MCI
EAD
PAD
2
P
1.0 (0.0)
2.0 (0.0)
0.0
0.0
1.0 (0.0)
2.0 (0.0)
0.0
0.0
2.4 (1.0)a
1.8 (0.7)
0.7a
0.1
3.9 (1.3)a
0.7 (0.9)a
0.9a
0.7a
40.7
31.6
39.8
28.6
<.001
<.001
<.001
<.001
10.0 (0.0)
0.0 (0.0)
0.0 (0.0)
9.8 (0.4)
0.2 (0.4)
0.1 (0.3)
7.7 (2.7)a
2.3 (3.0) a
0.8 (0.9)
2.5 (3.5)a
7.2 (3.8)a
4.5 (4.1)a
40.0
35.9
31.4
<.001
<.001
<.001
10.0 (0.0)
0.0 (0.0)
0.0 (0.0)
9.9 (0.3)
0.1 (0.3)
0.0 (0.0)
8.7 (2.9)
1.4 (2.2)
0.7 (1.2)
4.3 (3.6)a
5.4 (3.5)a
3.3 (3.0)a
35.5
35.3
28.6
<.001
<.001
<.001
NOTE: Means and standard deviations (in parenthesis) for the Shulman Score and performance in the Clock Setting Test and Clock
Reading Test as well as error probabilities for the drawing of the hour and minute hand are indicated. HC ¼ healthy controls; MCI ¼
patients with mild cognitive impairment; EAD ¼ patients with early Alzheimer disease; PAD ¼ patients with progressed Alzheimer
disease.
a. Significant difference to HC.
b. Maximum 1 error point.
c. Maximum 10 error points.
(P < .001, Table 3). No difference in any of the 3
subtests could be detected between the HC participants and the patients with MCI. In the Clock
Drawing and Clock Setting Tests, EAD patient performance was significantly worse compared with the
MCI and HC groups, whereas in the Clock Reading
Test no significant differences were found between
the HC, MCI, and EAD groups. The performance
of patients with PAD differed significantly from the
other 3 groups in all subtests.
In the PAD group, both clock hands were drawn
incorrectly an equal number of times (P ¼ .322).
Comparing our scoring system with the modified
version of the Shulman scoring system,16 we found
the same sensitivities and specificities for patients
with AD. All patients showing misplacement or lack
of the minute hand had a Shulman score 3,
whereas all patients with correct placement of the
minute hand had a Shulman score of 1 or 2. The sensitivity of both scoring systems for detecting AD was
79.3%, whereas the specificity was 100%.
Quantitative Error Analysis of Clock Hands
Clock Drawing Test. Clock hand error probabilities
in the CDT for HC and the 3 patient groups are
shown in Table 3. For both the hour hand (2 ¼
28.6, df ¼ 3, P < .001) and the minute hand (2 ¼
39.8, df ¼ 3, P < .001), Chi-square tests identified
significant differences between the 4 groups. For
hour hand placement, only the PAD group differed
significantly from the HC group (P < .001). In minute hand placement, both the EAD and PAD group
showed significantly worse performance compared
with the healthy controls (P < .001). There were no
significant differences between the HC and MCI
groups.
Both clock hands were drawn correctly an equal
number of times in the HC and MCI groups. However, EAD patients had more difficulties placing the
minute hand compared with the hour hand (P < .01).
Clock Setting Test. The mean scores and standard
deviations for the HC and the 3 patient groups for
the Clock Setting Test are shown in Table 3. Patients
with AD made more errors setting the clock hands
compared with HC participants and patients with
MCI. The minute hand was set incorrectly more
often than the hour hand. Patients with PAD made
significantly more errors compared with the HC
participants concerning placement of both hands,
and patients with EAD scored worse only in setting
the minute hand. The patients with PAD also made
significantly more errors regarding both hands
compared with the patients with EAD.
Clock Reading Test. The mean scores and standard
deviations for the HC participants and the 3 patient
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124 Journal of Geriatric Psychiatry and Neurology / Vol. 22, No. 2, June 2009
groups on the Clock Reading Test are shown in Table
3. Post hoc tests showed that only the patients with
PAD made significantly more errors in reading hands
than the HC group. Similar to the other 2 Clock Test
subtests, the minute hand was read falsely more
often than the hour hand.
13 patients (8%) could draw the minute hand correctly, 2 patients (15%) placed the minute hand
adhered to the hour hand, and 10 PAD participants
(77%) did not draw a minute hand at all. Thus,
although the patients with EAD still attempted a
solution, most of the patients with PAD did not even
reproduce the minute hand (Figure 3C).
Qualitative Error Analysis
Clock Face Drawing
All MCI and HC participants as well as 13 of the
16 patients with EAD (81%) were able to draw a
clock face allowing a correct time representation.
Some participants showed only minor conspicuous
features such as placing digits outside the clock face,
adding additional digits, or post meridiem digits.
One patient with EAD reproduced the digits in a
disorganized way, and in the drawings of the other
2 patients with EAD, some digits were missing.
In the PAD group, only 4 of the 13 patients
(31%) were able to draw the clock face properly.
Three of the PAD patients (23%) drew the digits spatially disorganized. In the drawings of 2 patients
(15%), digits were missing, and both types of
errors were found in the drawings of the remaining
4 patients (31%, Figure 3A).
Time Representation
Clock Drawing Test. A total of 7 of the 14 healthy
controls (50%), 7 of the 15 patients with MCI
(47%), and 13 of the 16 patients with EAD (81%)
placed the hour hand directly on the digit 11, neglecting the correct offset of ‘‘10 minutes past.’’ Because of
this high error percentage even in the HC group, this
offset error should not be considered clinically relevant. Thus, all the HC participants and patients with
MCI and 15 of the 16 patients with EAD (94%) were
rated as inconspicuous for hour hand placement. The
1 remaining patient with EAD (6%) and 8 of the
13 patients with PAD (62%) did not draw the hour
hand. Two patients with PAD (15%) drew the hour
hand on a false digit (Figure 3B).
Although all HC participants and all patients
with MCI were able to orient the minute hand
properly, only 5 of the 16 patients with EAD (31%)
succeeded in correctly placing the minute hand.
Three patients with EAD (19%) showed a stimulusbound response, 5 (31%) drew the minute hand
adhered to the hour hand, 2 patients (13%) did not
draw a minute hand at all, and 1 patient (6%) chose
another solution. In the PAD group, only 1 of the
Clock Setting Test. In the HC group, 93% of the solutions in placing the hour hand were completely correct, and 95% of the solutions in the MCI group were
correct. Only a few times the offset of the hour hand
was missing, and in 2% the patients with MCI mixed
up the minute and hour hand. In 39% of patients
with EAD, the solutions showed no hour hand offset,
and in 7% a confusion of the hands was noted. In the
PAD group, 43% of the solutions were incorrect: in
22% of the cases a mixing up of minute and hour
hand was noted and in 21% some other unsystematic
wrong solutions were chosen (Figure 4A).
The minute hand was nearly always placed correctly by the HC and MCI groups. In 76% of cases,
patients with EAD chose a correct solution. In 8%,
a stimulus-bound response occurred, and in 5% the
minute hand was adhered to the hour hand. In 8%,
the minute hand was mixed up with the hour hand,
and in 3% the minute hand position depended on the
hour hand. In the PAD group, the minute hand was
incorrectly set in 73% of the cases. Frequently we
observed stimulus-bound responses (19%), mixing
up with the hour hand (21%), and other unsystematic solutions (23%; Figure 4B).
Discussion
In the current investigation, we found that patients
with MCI did not show any differences in the Clock
tests compared with HC participants. However,
patients with PAD performed significantly worse in
all applied Clock subtests and the EAD group in
Clock Drawing and Clock Setting.
We found that the patients with EAD had the
greatest difficulty placing the minute hand. In the
CDT, most patients with EAD succeeded in presenting a correct clock face and 2 hands. However, only a
minority was subsequently able to draw the correct
clock time. Patients with EAD differed significantly
from the HC participants and patients with MCI in
the frequency of misplacing the minute hand,
whereas no significant difference for the hour hand
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Minute Hand Phenomenon in the Clock Test of Patients With AD / Leyhe et al
125
Figure 3. Qualitative error analysis of the Clock Drawing Test in healthy controls (HC) and patients with mild cognitive
impairment (MCI), early Alzheimer disease (EAD), and progressed Alzheimer disease (PAD). A, clock face; B, hour hand, C, minute
hand.
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126 Journal of Geriatric Psychiatry and Neurology / Vol. 22, No. 2, June 2009
Figure 4. Qualitative error analysis of the Clock Setting Test in healthy controls (HC) and patients with mild cognitive impairment
(MCI), early Alzheimer disease (EAD), and progressed Alzheimer disease (PAD). A, hour hand, B, minute hand.
score was observed. The same pattern was found in
the Clock Setting Test. The patients with EAD failed
significantly more often in setting the minute hand
compared with the HC participants and patients
with MCI, whereas no differences were found in
adjusting the hour hand. In the Clock Reading Test,
the EAD group did not differ from the HC participants with regard to the entire score and also to the
minute or hour hand errors.
The difference in performance of the EAD group
on the 3 subtests might be due to the relevance of the
tasks in everyday life. Most people rarely draw a
clock and have set a clock much more often. This
could explain the slightly better performance in the
clock setting task in the EAD group. However, in real
clocks, the minute and hour hands are connected
and are not set separately. Furthermore, clock
reading is a more common activity of everyday life.
This could be the reason why the patients with EAD
did not show difficulties in reading a presented time
and were able to transform the number ‘‘2’’ to represent ‘‘10 minutes past.’’
As expected, the patients with PAD had more
severe deficits. We found significantly poorer performances in each of the 3 Clock subtests compared
with the other 3 groups in our study. Two thirds of
the patients with PAD showed marked impairments
in drawing a correct clock face. Besides improper
digit placement, possibly caused by a deterioration
of visuospatial skills or an impairment of planning
and organization of the drawing action, digits were
often omitted or replaced by completely wrong digits.
Such errors in the reproduction of the clock face
could be also explained by an advanced loss in the
ability to retrieve semantic knowledge about the
appearance of a clock.
Furthermore, patients with PAD showed significantly poorer performance in the Clock Setting and
Clock Reading Test concerning time representation
compared with HC participants and patients with
MCI and EAD. Both tasks did not demand constructional skills. Detailed qualitative analysis of the
errors in time representation in the CDT revealed
that the majority of patients with PAD drew neither
an hour nor a minute hand. In the Clock Setting
Test, they used unsystematic approaches, the clock
hands were often set lacking any concept of time
representation. These findings indicate progressed
degradation of semantic knowledge about the clock
hands concept in the PAD group.
In addition to episodic memory disorders, there
is evidence for semantic memory impairment in early
AD and probably in patients with amnesic MCI.28-32
Both aggravated access and degraded knowledge are
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Minute Hand Phenomenon in the Clock Test of Patients With AD / Leyhe et al
discussed as factors for the deterioration.33-35 In our
study, loss of semantic knowledge cannot explain all
errors in the PAD group, but most of the difficulties
observed in the patients with EAD. The wrong placement of the minute hand could be a first sign of
impaired access to semantic memory about the concept of time representation. The correct placement
of the minute hand demands a transformation of the
phrase ‘‘10 minutes past’’ to the number ‘‘2,’’ which
cannot be performed intuitively, but requires active
access to semantic conceptual knowledge about the
functionality of a clock.
Thus, in accordance with other authors,20,36 we
assume that the deficits of the patients with AD in
Clock Tests are mainly determined by impairment
of semantic memory about the appearance and functionality of a clock, especially in the early disease
stages. In the early stages, active access to clock
knowledge is aggravated, whereas in later stages,
knowledge degradation is more pronounced and
deficits of other cognitive skills, for example, visuospatial abilities and executive functions, contribute to
the deterioration.
It has to be mentioned that other authors argue
that particularly an impairment of executive functions
in addition to deteriorated semantic memory might
explain Clock Test errors of patients with AD.37
Detailed qualitative analysis of the errors in time
representation showed that the majority of the
patients with EAD drew and set the hour hand correctly and tried to find a solution for the minute hand
problem. Often they showed a stimulus-bound
response or placed the minute hand adhered to the
hour hand probably trying to find an obvious solution.
Previous studies investigating the interpretation
of proverbs showed that patients with AD have difficulties in finding figurative senses. They often chose
a concrete explanation of phrases.38,39 Similarly, we
assume that patients with AD cannot disengage their
attention from the stimulus ‘‘10’’ or ‘‘hour hand’’ and
successfully transform the time ‘‘10 minutes past’’ to
the number ‘‘2,’’ when access to semantic memory is
reduced. This hypothesis will form the basis of further investigations.
In the current investigation, misplacement or
lack of the minute hand in the CDT for the detection
of patients with AD was as sensitive and specific as
the modified version of the scoring system of
Shulman et al16 (79.3% and 100.0%, respectively).
The transition from a normal Shulman score ‘‘2’’ to
a pathological ‘‘3’’ was mostly due to incorrect placement of the minute hand.
127
We found no differences in Clock Test performance between the patients with MCI and the HC
participants. We assume that possible impairments
in this group could not be detected with the
performed Clock Tests. These results correspond to
other studies demonstrating only a small sensitivity
of the CDT for very mild AD.4,5 In contrast, Yamamoto et al found an acceptable sensitivity and
specificity of the CDT to detect patients with MCI,
but their results were mainly due to the inclusion
of nonamnesic and multiple domain MCI patients.3
Just a minority of the patients with MCI in our study
had additional cognitive domain impairment other
than memory function. Thus, the differences in our
investigation presumably reflect a different selection
of participants.
A limitation of this explorative study is the small
sample size. Our results should be confirmed in
further examinations.
In summary, the current investigation has shown
that most patients with AD failed in interpreting the
minute hand in Clock Tests at early stages of the disease. In clinical and experimental examinations of
suspected patients with AD, this subtle indicator of
impaired cognitive function should be noticed and
further evaluated. We thus propose to introduce the
term ‘‘minute hand phenomenon’’ to describe this
indicator.
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