Quantitative and qualitative analyses of clock drawings in Alzheimer's and Huntington's disease

BRAIN AND COGNITION 18, 70-87 (1992)

Quantitative and Qualitative Analyses of Clock Drawings in Alzheimer’s and Huntington’s Disease

ISABELLE ROULEAU

Department of Psychiatry, University of California, San Diego

DAVID P. SALMON

Department of Neurosciences, University of California, San Diego

AND

NELSON BUTTERS, COLLEEN KENNEDY, AND KATHERYN MCGUIRE

Department of Psychiatry, University of California, San Diego, and Psychology Service, Department of Veterans Affairs Medical Center, San Diego

Although visuoconstructive impairment has been reported in both Alzheimer’s (DAT) and Huntington’s (HD) disease, there is little knowledge concerning how this cognitive deficit differs quantitatively and qualitatively in these two progressive dementias. To address this issue, the present study compared performances on the Clock Drawing Test (CDT: command and copy) of 25 DAT patients, 25 equally demented HD patients, and 25 elderly normal controls (NC). In the command condition, both patient groups were significantly impaired compared to the NC group. Although there was no significant difference between DAT and HD patients’ total quantitative scores, a qualitative error analysis revealed a number of dissociations between the two patient groups. Graphic difficulties, very common in HD patients, were virtually absent in DAT patients; in contrast, conceptual errors were almost exclusively seen in DAT patients and were related to the severity of their dementia. Perseveration and “stimulus-bound” responses were also more frequent in DAT patients, and both groups made visuospatial errors. In the copy condition, the DAT, but not the HD, patients evidenced a

This study was supported by funds from the Medical Research Service of the Department of Veterans Affairs, by NIA Grants AG-05131 and AG-08204 to the University of California at San Diego, and by FRSQ (Fonds de la recherche en Sante du Quebec) Postdoctoral Fellowship to Dr. Rouleau. All correspondence and reprint requests should be addressed to Dr. Nelson Butters, Psychology Service (116B), Dept. of Veterans Affairs Medical Center, 3350 La Jolla Village Drive, La Jolla, CA 92161.

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0278-2626192 $3.00 Copyright 0 1992 by Academic Press, Inc. All rights of reproduction in any form reserved.

VISUOCONSTRUCTIVE IMPAIRMENT 71

marked improvement in performance. These results indicate that while both DAT and HD patients have significant visuoconstructive difficulties even in the early stages of their disorders, the specific cognitive processes underlying their quantitative impairments are quite different. It is possible that the DAT patients’ conceptual errors are yet another indicator of the deterioration of their semantic knowledge. (2‘ 1992 Academic Preu. Inc

INTRODUCTION

Studies comparing the neuropsychological profiles of Alzheimer’s (DAT) and Huntington’s disease (HD) patients have demonstrated that various forms of dementia may differ in terms of the quantitative and qualitative features of their language, attention, and memory impairments (for review, see Butters, Salmon, & Heindel, 1990b). Alzheimer’s patients, even in the early stages of their disorder, make frequent seman- tically based naming errors and are more impaired on category than on letter fluency tasks (Bayles & Tomoeda, 1983; Butters, Granholm, Salmon, Grant, & Wolfe, 1987; Hodges, Salmon & Butters, 1991; Huff, Corkin & Growdon, 1986). This pattern of deficits has been viewed as an indicator of a deterioration in the structure of these patients’ semantic knowledge (Chertkow & Bub, 1990; Martin, 1987; Martin & Fedio, 1983). In contrast, patients with HD make relatively few naming errors, most of which represent perceptual (rather than semantic) confusions, and are equally impaired on both category and letter fluency tasks (Butters, Salmon, Heindel, & Granholm, 1988b; Hodges et al., 1991). This profile of impairments has been interpreted as representing HD patients’ deficiencies in initiating retrieval strategies and in processing visuoperceptual materials (Butters et al., 1990b; Hodges et al., 1991). Studies that have compared DAT and HD patients’ attentional abilities have noted greater deficits in HD than in DAT patients (Brandt, Folstein, & Folstein, 1988; Folstein, Brandt, & Folstein, 1990; Starkstein et al., 1988; Troster, Jacobs, Butters, Cullum, & Salmon, 1989).

Differences between DAT and HD patients are apparent on both explicit and implicit memory tasks. Patients with DAT seem unable to store new information (Moss & Albert, 1988), evidence rapid rates of forgetting (Butters et al., 1988a; Hart, Kwentus, Taylor, & Harkins, 1987; Moss, Albert, Butters, & Payne, 1986; Welsh, Butters, Hughes, Mohs, & Hey- man, 1991), are very prone to intrusion errors (Butters et al., 1987; Jacobs, Salmon, Troster, & Butters, 1990), and have severe retrograde amnesias even in the early stages of the disease (Beatty, Salmon, Butters, Heindel, & Granholm, 1988; Sagar, Cohen, Sullivan, Corkin & Growdon, 1988). On implicit memory tasks DAT patients have been reported to be impaired on lexical, semantic, and perceptual priming tasks but to perform normally in the acquisition of motor skills (for review, see Butters, Heindel & Salmon, 1990a). On the other hand, HD patients’ explicit memory

72 ROULEAU ET AL.

deficits have been characterized by retrieval rather than storage problems (Butters, Wolfe, Granholm, & Martone, 1986; Butters, Wolfe, Martone, Granholm, & Cermak, 1985; Delis et al., 1991), relatively normal rates of forgetting (Butters 1988a; Delis et al., 1991; Moss et al., 1986), and only mildly elevated tendencies to make intrusion errors (Butters et al., 1987; Delis et al., 1991; Jacobs et al., 1990). On tests of remote memory, HD patients are less impaired than DAT patients (Beatty et al., 1988). When administered tests of implicit memory HD patients demonstrate a pattern of deficiencies contrary to that reported for DAT patients. That is, HD patients are impaired in the acquisition of motor skills but evidence normal performance on lexical, semantic, and perceptual priming tasks (Butters, Heindel, & Salmon, 1990a; Heindel, Salmon, & Butters, 1990). These striking differences in memory have been attributed to the dysfunction of the mesial and lateral temporal lobes and of the corticostriatal structures associated with DAT and HD, respectively (Butters et al., 1990a; Heindel, Salmon, Shultz, Walicke, & Butters, 1989).

Despite these consistent findings for memory, language, and attentional deficits, there have been relatively few studies of DAT and HD patients’ visuoperceptual and constructional impairments. Deficits in visuoperceptual processes have been reported in both DAT (Brouwers, Cox, Martin, Chase, & Fedio, 1984; Huff et al., 1986) and HD patients (Fedio, Cox, Neophytides, Canal-Frederick, & Chase, 1979; Portegal, 1971), but it is not clear whether the deficits involve the same underlying mechanisms (Brown and Marsden, 1988). Similarly, visuoconstructive impairments also have been noted in both HD (Brandt & Butters, 1986; Butters, Sax, Montgomery, & Tarlow, 1978; Fedio et al., 1979) and DAT patients (Ajuriaguerra, Muller & Tissot, 1960; Brantjes & Bouma, 1991; Brouwers et al., 1984; Gainotti, Caltagirone, Masullo, & Miceli 1980; Henderson, Mack, & Williams, 1989; Kirk & Kertez, 1991; Martin, Cox, Brouwers, & Fedio, 1985; Sunderland et al., 1989) on various tasks (e.g., drawings of geometric patterns, objects, clocks; Block Design and Object Assembly subtests of the WAIS-R), but again there is little knowledge as to how these patients’ deficits differ in quantitative and qualitative terms.

In order to provide some initial comparisons of DAT and HD patients’ constructional and visuoperceptual impairments, the present study focuses upon their performances on clock drawing tasks. Since it is possible to identify the graphic, conceptual, perceptual, and spatial deficiencies that underlie failures on such drawings (Henderson et al., 1989; Kaplan & Delis, in press; Sunderland et al., 1989; Wolf-Klein, Silverstone, Levy, Brod, & Breuer, 1989), clock drawing tasks seem most suitable for as- sessing quantitative and qualitative differences between these patient groups. Several detailed descriptions of the clock drawings of DAT patients have already appeared, but none of these reports have attempted to compare these constructional deficiencies with those of another pro-


TABLE 1 AGE, EDUCATION, AND DEMENTIA RATING SCALE SCORE (DRS) (MEAN -+ SD) for the

DAT, HD, AND NC SUBJECTS

Age Education DRS

DAT HD NC

71.00 (6.70) 49.84 (12.78) 70.88 (6.65) 14.20 (2.79) 13.74 (2.32) 13.68 (2.75)

114.68 (20.07) 110.08 (27.08) 138.96 (3.20)

gressive dementia (Henderson et al., 1989; Kirk & Kertez, 1991; Sun- derland et al., 1989). More specifically, DAT and HD patients, as well as age-matched intact control subjects, are asked to draw a clock to command and to set the hands to a specified time. To compare drawing- to-command with copying ability, the patients and control subjects are also asked to copy the drawing of a clock with the hands already set to a specified time. A modified version of Sunderland et al.3 (1989) scoring criteria and error categories are used in the analyses of all drawings.

METHOD

Subjects A total of 75 subjects participated in this study. They were equally divided into three

groups: 25 patients with DAT, 25 HD patients, and 25 elderly neurologically intact normal control subjects. The DAT and HD patients were matched for overall level of dementia with the Dementia Rating Scale (DRS) (Mattis, 1976). All subjects were participants in the research activities of the Alzheimer’s Disease Research Center (ADRC) at the University of California at San Diego. As part of this program, all patients received a yearly comprehensive neurological and neuropsychological assessment.

The diagnosis of probable DAT was made by two senior staff neurologists using the criteria developed by the National Institute of Neurological and Communication Disorders and Strokes (NINCDS) and the Alzheimer’s Disease and Related Disorders Association (ADRDA) (McKhann et al., 1984). Laboratory tests (e.g., CT scan, urinalysis, SMA-12, T4, folate levels) were performed to rule out various viral, metabolic, or traumatic causes of dementia. To reduce the possibility of including multi-infarct dementias, patients with a score of 5 or greater on the Hachinski ischemia scale (Hachinski et al., 1975) were excluded from the DAT group.

The diagnosis of HD was made by a staff neurologist on the basis of positive family history for the disease, the presence of involuntary choreiform movements and dementia. The functional capacities were assessed with Shoulson and Fahn’s disability scale (1979). Nine of the patients were judged to be at stage II, 12 at stage III, and 4 at stage IV. In addition to being matched on the DRS, and DAT and HD patients were equated for years of education.

The normal elderly control subjects (NC) were selected to match DAT patients for age and for education. Any subject with a history of alcoholism, drug abuse, or serious neurological or psychiatric condition was excluded from the study.

The demographic data for the three groups are shown in Table 1. A one-way analysis of variance (ANOVA) of the mean age showed a highly significant group difference [F(2, 72) = 44.07, p < .OOl]; post hoc analysis revealed that HD patients were significantly younger than both DAT patients [t(48) = 7.33, p < .OOl] and NC subjects [t(48) = 7.30,

74 ROULEAU ET AL.

p < .OOl]. There was no significant difference in age between DAT and NC subjects [t(48) < 11. A one-way ANOVA showed no significant difference in the mean education levels of the three groups [F(2, 70) < 11. There was no significant difference between DAT and HD patients in the severity of dementia, as assessed by the DRS [t(47) < 11, and both patient groups were significantly impaired compared to NC subjects (p < .OOl).

Material and Procedures The Clock Drawing Test (CDT) adopted from the Boston Parietal Lobe Battery (Good-

glass & Kaplan, 1972) was administered as part of the yearly comprehensive neuropsychological evaluation. The subjects were presented with an 8.5 x 11-in. blank sheet of paper and a pencil, and the following instructions were given: “I would like you to draw a clock, put in all the numbers, and set the hands for 10 after 11.” Following this drawing-to- command condition, the patients were instructed to copy, as accurately as possible, a clock from a model. The model which contained all the numbers on the clock, was 3 in. in diameter and located on the upper part of an 8.5 x 11-in. sheet of paper. The hands on the model were set for 10 after 11. The subject was instructed to copy the model on the lower part of the same sheet of paper.

The resulting drawings were analyzed by three independent judges who were unaware of the patients’ diagnostic group. Drawings under copy and command conditions were scored separately in a different random order for each judge. Quantitative analyses using rating scales were initially performed, followed by a qualitative error analysis.

Rating Scale The clocks were first scored using Sunderland et al.‘s lo-point rating scale from worst

(score = 1) to best (score = 10) representation of a clock (Sunderland et al., 1989). However, this scale proved difficult to apply according to the criteria provided since it assumes that the representation of the hands is first and solely affected (score 6 to lo), and additional errors in the representation of numbers and the clockface occur later (score 1 to 5). Con- sequently, some drawings received very low scores on this scale because of minor errors in the representation of numbers (added or missing numbers) even though the hands were adequately set. To circumvent this scoring problem, the clocks were reevaluated with a new lo-point scale (see Table 2) designed to independently assess the accuracy of the representation of the clockface (maximum, 2 points), the layout of numbers (maximum, 4 points), and the position of the hands (maximum, 4 points).

Qualitative Error Analysis In order to study the underlying mechanisms leading to deficits in clock drawing, a

qualitative error analysis was performed on the command and copy drawings. The following dimensions were assessed:

1. Size of rhe clock. A clock was considered small if it measured less than 1.5 in. and large if it measured more than 5 in.

2. Graphic difficulties. The lines were not precise, resulting either in distortions of the clockface or in making the numbers difficult to read. The hands were not straight and sometimes failed to connect in the middle. The overall performance appeared inaccurate and clumsy. The graphic difficulties were rated according to their severity:

Mild: some distortions in tracing the clockface and/or the hands and/or the numbers were present, but the overall performance remained adequate.

Moderate: distortions were evident, but the overall performance remained interpretable (see Fig. la).

Severe: distortions were evident and precluded, in some cases, the unequivocal interpre- tation of the overall performance (see Fig. lb).

VISUOCONSTRUCTIVE IMPAIRMENT

TABLE 2 REVISED SCALE USED FOR SCORING THE CLOCK DRAWINGS

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1. Integrity of the clockface (maximum: 2 points) 2: Present without gross distortion 1: Incomplete or some distortion 0: Absent or totally inappropriate

2. Presence and sequencing of the numbers (maximum: 4 points) 4: All present in the right order and at most minimal error in the spatial arrangement 3: All present but errors in spatial arrangement 2: Numbers missing or added but no gross distortions of the remaining numbers Numbers placed in counterclockwise direction Numbers all present but gross distortion in spatial layout (i.e., hemineglect, numbers outside the clock) 1: Missing or added numbers and gross spatial distortions 0: Absence or poor representation of numbers

3. Presence and placement of the hands (maximum: 4 points) 4: Hands are in correct position and the size difference is respected. 3: Slight errors in the placement of the hands or no representation of size difference between the hands. 2: Major errors in the placement of the hands (significantly out of course including 10 to 11) 1: Only one hand or poor representation of two hands 0: No hands or perseveration on hands

3. Srimulus-bound response. The tendency of the drawing to be dominated or guided by a single stimulus. Two types of such boundedness were apparent:

(A) The hands are set for 10 to 11 instead of 10 after 11. That is, the patient fails to recode the “10” in “10 after 11” as a “2” in order to set the minute hand. He is thus “attracted” to the strong stimulus source (i.e., “10”) rather than giving the appropriate response that involves a more complex operation (i.e., setting the minute hand at “2”). This type of error only occurs in the command condition since no recoding of the stimulus is required in the copy condition (see Fig. lc).

(B) The time is written (in letters and/or numbers) besides the “11” or between “10 and 11” on the clock; hands are either absent (see Fig. 3a) or pointed toward “10” and/or “11” (see Fig. lb). This second type of stimulus-bound response was also rated as a conceptual error.

4. Conceptual deficit. In general, conceptual errors reflect a loss, or a deficit in accessing knowledge of the attributes, features, and meaning of a clock. This category encompasses a wide variety of errors:

(A) Misrepresentation of the clock itself (only a clockface without numbers or inappropriate use of numbers), suggesting the unavailability of a correct graphic representation of a clock (see Figs. 2a-2c).

(B) Misrepresentation of the time on the clock: the hands are either absent or inadequately represented (see Figs. 2c and 3e). The time is written on the clock (see Figs. 2b and 3a). These errors suggest a deficit in the knowledge of the feature (the hands) that confer most of the meaning of a clock, namely, communicating the time.

5. Spatial and/or planning deficit Deficit in the layout of numbers on the clock: (A) Neglect of the left hemispace (see Fig. 3a). (B) Deficit in planning, with gap before 12 or 3, 6, or 9 depending on the strategy used

in drawing (see Figs. 3b and 3~).

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a) pt.2188: HD (command) b) pt 2038:HD (copy)

c) pt 2095: DAT (command) d) pt 2145: DAT (command) FIG. 1. Samples of errors observed. Graphic difficulties: (a) moderate, (b) severe. Stim-

ulus-bound response: (c) associated with visuospatial deficit, (d) associated with a conceptual deficit in representing the time on the clock.

(C) Deficit in spatial layout of numbers, without any specific pattern in spatial disorga- nization (see Fig. 3d).

(D) Numbers written outside the clockface (see Figs. 3a and 3e). (E) Numbers written counterclockwise (see Fig. 3f). 6. Perseverufion. In general, perseveration is defined as the continuation or the recurrence

of activity without an appropriate stimulus. In clock drawing, different types of perseverative responses could be observed:

(A) Perseveration of hands: presence of more than two hands reflecting a failure to terminate, when appropriate, the ongoing set of tracing the hands (see Figs. 4a and 4b).

(B) Perseveration of numbers: abnormal prolongation of numbers, such as writing beyond “12” (See Fig. 4c) or inappropriate recurrence of the same numbers (see Fig. 4d).

The same three judges reviewed each clock independently, and an error was considered present only if there was agreement between two of the judges.

RESULTS

The scores obtained for the clock drawings using both Sunderland et al.% and the revised scale are presented in Table 3. The overall correlation between the total scores (three judges) obtained with Sunderland et al.% scale and with the revised scale was .89. The interrater reliability was high in all conditions (i.e., all subjects pooled vs. separated by diagnostic groups) varying from .86 to .97 with Sunderland et al.‘s scale and from


a) pt 2119: DAT (command)

c) pt 2179: DAT (command)

b) pt 2232: DAT (command)

d) pt 2179: DAT (copy)

FIG. 2. Samples of errors observed. (a-c) Conceptual deficit in the command condition; (c,d) comparison of the command and copy conditions in the same patient.

.92 to .97 using the revised scale. The scores obtained with the revised scale were retained for further analysis.

A two-way ANOVA (Group [DAT, HD, NC] x Condition [Command, Copy]) with repeated measures across conditions yielded significant main effects of Group [F(2, 69) = 9.52, p < .OOl] and Condition [F(l, 69) = 10.44, p < .005] and a significant Group x Condition interaction [F(2, 69) = 5.85, p < .005]. The results are presented in Fig. 5.

Post hoc comparisons revealed a significant difference between NC subjects and DAT patients for both command [t(48) = 4.54, p < .OOl] and copy [t(46) = 2.43, p < .05] conditions. The difference between NC and HD subjects was also significant in both conditions [command: t(48) = 4.54, p < .OOl; copy : t(46) = 4.37, p < .OOl]. Although there was no significant difference between DAT and HD patients in the command [t(48) = < l] and in the copy conditions [t(46) < 11, further comparisons (paired sample t test) between command and copy performances revealed a significant effect for DAT patients [t(23) = 3.27, p < .005] but not for

78 ROULEAU ET AL.

c

0 B

doq& a) pt 2176: DAT (command)

d)pt 2216: DAT (command)

b) pt 2075 HD (command)

e) pt 2151: DAT (command)

c)pt 612: HD (command)

f) pt 612: HD (command)

FIG. 3. Samples of various visuospatial errors observed. (a) Neglect of the left hemispace; (b.c) planning deficit; (d) deficit in the spatial layout of numbers; (e) numbers written outside the clockface; (f) numbers written in counterclockwise direction.

HD patients [t(23) < l] or for NC subjects [t(23) < 11. That is, the DAT patients performed significantly better under copy conditions than under command conditions, whereas the NC and HD subjects showed no differences between these drawing conditions.

Qualitative Error Analysis

1. Size of the clock. A total of 11 subjects drew on command a clock that was relatively small (< 1.5 in.) compared to what is usually observed in normal subjects (2.5 to 4 in.): 7 patients with HD, 3 with DAT, and 1 NC. A relatively large clock (> 5 in.) was produced by a total of 9 subjects: 2 patients with HD, 7 with DAT, and no NC subjects (see Fig. 6). A x2 test of independence between Group (HD-DAT) x Size (small- large) was significant [x*(l) = 4.33, p < .05], suggesting an opposite tendency of DAT and HD patients to produce large (DAT) and small (HD) clocks on command, respectively. In the copy condition, no subject drew either a relatively small or large clock.

2. Graphic difJiculties. Although mild graphic difficulties were observed in all subjects groups in both command and copy conditions, HD patients


a) pt 2222: DAT (copy)

C) pt 92: DAT (command)

b) pt 2232: DAT (COPY)

d) pt 2018: HD (command)

FIG. 4. Samples of perseverative errors observed. (a.b) Perseveration on hands; (c,d) perseveration on numbers.

were more likely than DAT and NC subjects to have moderate (see Fig. la) and severe (see Fig. lb) graphic difficulties (see Table 4). A x2 test of independence between Group (HD-DAT-NC) and Graphic difficulties (present-absent) was highly significant for both command [x2(2 df> = 27.49, p < .OOl] and copy [x2(2 @) = 16.32, p < .OOl] conditions.

An attempt was made to determine whether the HD patients’ graphic difficulties were related to their overall disability and motor dysfunction. When HD patients with no or mild graphic difficulties were compared with those patients who evidenced moderate or severe deficits, no significant differences were noted on the Shoulson and Fahn (1979) disability

TABLE 3 SCORNS OBTAINED (MEAN -t SD) FOR THE DAT. HD, AND NC SUBJECTS FOR CLOCK

DRAWINGS USING SUNDERLAND ET AI..‘S AND REVISED SCALES

DAT HD NC

Sunderland et al.‘s scale Command 6.07 (2.X’)) 6.83 (2.83) 8.96 (1.52)

Revised scale Command 6.30 (2.74) 6.X8 (2.14) 8.94 (1.12) COPY 7.88 (2.10) 7.11 (1.92) 0.01 (0.02)

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‘0 r

u g- 0 0

‘5

i:: +

6 -

M NC

5 O-0 DA1

0-O HO

Command COPY Condition

FIG. 5. Scores obtained in the command and copy conditions as a function of diagnostic groups (NC, DAT, and HD).

scale [t(23) = 1.65, n.s.] and on measures of chorea [t(9) < l] and motor impairment [t(9) < l] derived from the Chorea and Motor Impairment scale (Folstein, Jensen, Leigh, & Folstein, 1983).

FIG. 6. Distribution of error types in HD and DAT patient groups in the command condition.


TABLE 4 NUMBER OF DAT, HD, AND NC SUBJECTS PRESENTING WITH GRAPHIC DIFFICULTIES IN THE

COMMAND AND COPY CONDITIONS

DAT

Command

HD NC DAT

COPY

HD NC

Mild 6 8 3 6 5 7 Moderate 0 I 0 3 11 0 Severe 0 5 0 0 4 0

3. Stimulus-bound response. Among the 75 subjects tested, 8 set the hands at 10 to 11 in the command condition. In our sample, this behavior was more common in DAT patients (5 cases) than in HD patients (2 cases; see Fig. 6) and NC subjects (1 case, aware of his error). This type of performance may reflect, besides a stimulus-bound response, a mis- understanding of the time setting (grammatical error) or a transient lapse in attention (with subsequent awareness of the error). Although this performance could be seen in isolation, it was often associated with other deficits (Figs. lc, Id, and 4~). This error was never observed in the copy condition.

4. Conceptual deficit. If patients in whom graphic deficits were too severe to assess this dimension are excluded (3 cases with HD), a conceptual deficit (see Figs. 2a-2c) was suggested in 16 of 46 demented patients: 13 DAT and 3 HD patients [x2(1 df, = 8.31, p < .Ol]. The frequent oc- currence of this deficit in DAT patients might explain why, unlike the HD patients, their performance significantly improved in the copy condition (see Figs. 2c and 2d). This, however, was not the case for 3 DAT patients who exhibited, in both the command and the copy conditions, severe misrepresentation of the clock.

A comparison of the DAT patients’ DRS scores according to the presence (N = 13) or absence (N = 12) of a conceptual deficit (see Table 5) revealed significant differences in the total score [t(23) = 2.95, p < .Ol], and in the Initiation/Perseveration [t(23) = 2.55, p < .05] and Conceptualization [t(23) = 3.16, p < .Ol] scores. Attention, Construction, and Memory scores did not differ significantly between patients with and without conceptual deficit.

5. Spatial/planning de&it. A total of 23 patients committed visuospatial errors (DAT, 10; HD, 13) in the command condition. Some errors were observed equally often in both patients groups: this was the case for neglect of the left hemispace (HD = 1, DAT = 1; see Figs. 3a-3f), deficit in the spatial layout of numbers, without specific pattern in spatial disor- ganization (HD = 3, DAT = 4; see Figs. lc, Id, and 3d) and numbers written in counterclockwise direction (HD = 1, DAT = 1; see Fig. 3f).

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TABLE 5 DEMENTIA RATING SCALE SCORES (MEAN, SD) IN DAT PATIENTS AS A FUNCTION OF THE

PRESENCE OR ABSENCE OF CONCEPTUAL ERRORS

Presence of conceptual errors

N = 13

Total DRS score 104.77 (23.42) Attention 33.46 (4.01) Initiation/Perseveration 23.46 (8.45) Construction 4.77 (1.30) Conceptualization 29.38 (7.95) Memory 13.69 (5.30)

Absence of conceptual errors

N = 12

125.42 (6.27)** 35.42 (1.31) 30.17 (2.55)* 5.42 (0.79)

36.83 (l.SS)** 17.58 (4.78)

Note. Significant statistical differences between groups (**p < .Ol, *p < .05).

By contrast, some deficits were more frequent in a specific patient group: deficits in planning (HD = 8, DAT = 1; see Figs. 3b and 3c) were observed almost exclusively in HD patients, whereas the tendency to write numbers outside the clock (see Figs. 2b and 3e) was more frequent in DAT patients (HD = 1, DAT = 4; see Fig. 6). In the copy condition, visuospatial errors were also common in both patients groups. However, contrary to what was observed in the command condition, planning deficits occurred almost as often in DAT (6 cases) as in HD patients (8 cases). Neglect of the left hemispace and numbers written outside the clock, respectively, were observed only once, both in DAT patients. No patient wrote the numbers in a counterclockwise direction in the copy condition.

6. Perseveration. If the cases in which only one number was repeated are excluded, three patients exhibited number perseverations (2 DAT, 1 HD; see Figs. 4c and 4d) and one DAT patient drew an additional hand in the command condition. In the copy condition, perseveration of hands was observed in two DAT patients (see Figs. 4a and 4b), but no subjects exhibited perseveration of numbers.

DISCUSSION

Although both DAT and HD patients are impaired in their drawings of clocks, it is quite evident that the processes underlying their low quantitative scores are quite distinct. The DAT patients’ tendency to commit conceptual errors contributed greatly to their especially poor performance on the drawing-to-command condition. When they lacked a model to guide their drawings, the DAT patients appeared unable to retrieve the specific attributes that define a clock and consequently were very impaired in their attempts to draw an accurate representation. Their marked improvement under the copy condition further emphasizes that their drawing deficiencies are not due primarily to graphic, motor, or even visuoper-


ceptual difficulties; rather, their deficit is likely due to a loss of the semantic associations usually evoked by the word “clock.” The finding of an association between the production of conceptual errors and lower scores on the Initiation/Perseveration and Conceptualization sections of the DRS also suggests that semantic impairments play a major role in DAT patients’ poor clock drawings. Thus, DAT patients’ well-documented impairments on language tasks involving confrontation naming and fluency (Bayles & Tomoeda, 1983; Butters et al., 1987; Chertkow & Bub, 1990; Hodges et al., 1991; Huff et al., 1986; Martin & Fedio, 1983), on memory tests requiring semantic encoding (Corkin, 1982; Granholm & Butters, 1988; Salmon, Shimamura, Butters & Smith, 1988), and on construction tasks involving the graphic representation of common objects may all reflect a deterioration of the hierarchical structure of these patients’ semantic knowledge. At the very least, the significant tendency of DAT patients to manifest conceptual errors on a drawing-to-command task suggests that such semantic deficits are ubiquitous even in the early and middle stages of this disorder and may be evident on many neuropsychological tests.

Unlike the DAT patients, HD patients’ performance was characterized by the presence of moderate and severe graphic deficits, a tendency to draw small clocks, and planning deficits in the spatial layout of numbers. The graphic deficits and small drawings are consistent with their marked difficulties on tests of motor functions such as the Motor Steadiness Test (Josiassen, Curry, and Mancall, 1983) and their low scores on most of the WAIS-R Performance scale subtests (Butters et al., 1978; Fedio et al., 1979; Folstein et al., 1990; Josiassen, Curry, Roemer, Debease, & Mancall, 1982). Their planning deficits may be related to the frontostriatal dysfunction commonly associated with HD (Brandt & Butters, 1986) and are apparent on tasks such as the Wisconsin Card Sorting Test (Josiassen et al., 1983) and the Picture Arrangement subtest of the WAIS-R (Butters et al., 1978). As suggested by Kaplan and Delis (in press) a planning deficit may also result from an inability to execute simultaneously two sequential tasks (i.e., producing and writing the numbers in the right order and spacing them equally around the clock), and may explain why the HD patients often self-corrected their production.

Although visuospatial errors were noted in both patient groups, the type of error differed: DAT patients tended to draw very large clocks, to write the numbers outside the outline of the clock, and to commit errors in the spatial layout of the numbers, whereas HD patients drew small clocks and made a variety of visuospatial errors that could be attributed to their inability to sequence or plan their motor responses. Some evidence of spatial neglect was noted, albeit infrequently, in both patient groups. However, the tendency to write all the numbers on the right side of the clock could be an indication of a planning deficit rather than a true neglect of the left hemispace.

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Perseveration of numbers or hands and stimulus-bound responses, though not totally absent in HD, were more frequent in DAT. This finding is consistent with the observation that even in the early stages of the disease, DAT patients often manifest numerous perseverations and stimulus-bound behaviors on their cognitive evaluations (Moss & Albert, 1988). Although perseverative tendencies are commonly associated with a frontal dysfunction (Lhermitte, Derouesne, & Signoret, 1972; Luria, 1965; Stuss & Benson, 1986), a number of studies have shown that HD patients make fewer perseverative errors than do DAT patients on various tasks such as verbal fluency, tactile reversal learning, and other episodic memory tasks (Butters et al., 1983, 1988b; Freedman & Oscar-Berman, 1987). Why a patient group with frontostriatal damage (HD) should gen- erate fewer perseverations than a group with primarily temporal deterioration (DAT in the early stages) has not yet been adequately explained.

Besides the obvious clinical implications of these results for the diagnosis and understanding of DAT and HD, the present findings, like those from studies of memory and language, demonstrate the heterogeneity of the cognitive deficits associated with various forms of dementia. Since our patient groups were matched for overall level of dementia, the noted qualitative differences cannot be attributed to differences in severity of cognitive loss. Rather, it appears that dementia involving primarily limbic- cortical regions are characterized by a pattern of losses which is clearly distinct from those associated with dementias due to basal ganglia and corticostriatal dysfunction. While it has not been established whether the differences noted in the present study would also be found on a close scrutiny of other constructional tasks and whether different types of basal ganglia dementias would perform similarly, the results of this investigation suggest that such comparisons are likely to yield valuable clinical and theoretical insights.

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Quantitative and qualitative analyses of clock drawings in Alzheimer's and Huntington's disease