The Role of the Dynamic Body Schema in Praxis: Evidence from Primary Progressive Apraxia

Brain and Cognition 44, 166–191 (2000) doi:10.1006/brcg.2000.1227, available online at http://www.idealibrary.com on

The Role of the Dynamic Body Schema in Praxis: Evidence from Primary Progressive Apraxia Laurel J. Buxbaum,*,† Tania Giovannetti,* and David Libon‡ *Moss Rehabilitation Research Institute, Philadelphia, Pennsylvania; †Temple University Medical Center, Philadelphia, Pennsylvania; and ‡Crozer-Chester Medical Center, Upland, Pennsylvania Published online August 15, 2000 On an influential model of limb praxis, ideomotor apraxia results from damage to stored gesture representations or disconnection of representations from sensory input or motor output (Heilman & Gonzalez Rothi, 1993; Gonzalez Rothi et al., 1991). We report data from a patient with progressive ideomotor limb apraxia which cannot be readily accommodated by this model. The patient, BG, is profoundly impaired in gesturing to command, to sight of object, and to imitation, but gestures nearly normally with tool in hand and recognizes gestures relatively well. In addition, performance is profoundly impaired on imitation of meaningless gestures and on tasks requiring spatiomotor transformations of body-position information. We provide evidence that BG’s apraxia is largely attributable to impairments external to the stored gesture system in procedures coding the dynamic positions of the body parts of self and others; that is, the body schema. We propose a model of a dynamic, interactive praxis system subserved by posterior parietal cortex in which stored representational elements, when present, provide ‘‘top-down’’ support to spatiomotor procedures computed on-line. In addition to accounting for BG’s performance, this model accommodates a common pattern of ideomotor apraxia more readily than competing accounts.  2000 Academic Press Key Words: body schema; body representation; body-centered coding; praxis; apraxia; ideomotor apraxia; gesture.

Ideomotor apraxia (IM) is a disorder of complex movement characterized by spatiotemporal errors in tool use, gesture pantomime, and/or gesture imitation (Heilman & Gonzalez Rothi, 1993). There are numerous subtypes of This research is supported by a grant to the first author from the National Institute for Neurological Disorders and Stroke (No. R29-DC03179-01). Address correspondence and reprint requests to Laurel J. Buxbaum, Moss Rehabilitation Research Institute, 1200 West Tabor Rd., Philadelphia, PA 19141. E-mail: LBuxbaum@aehn2. einstein.edu. 166 0278-2626/00 $35.00

Copyright  2000 by Academic Press All rights of reproduction in any form reserved.

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the disorder. Some IM patients can recognize gestures but not produce them in any context (Piccirilli, D’Alessandro, & Ferroni, 1990; Rapcsak, Ochipa, Anderson, & Poizner, 1995), while others are able to gesture to command but not imitate or recognize gesture (Gonzalez Rothi, Ochipa, & Heilman, 1991). Some patients show input-modality-specific deficits (e.g., inability to pantomime or imitate to visual input). At least one patient has been reported with intact gesture recognition in the context of moderately impaired gesture to command and severely impaired imitation (Ochipa, Rothi, & Heilman, 1990). The presence of these and other patterns has proven challenging to investigators attempting to model the subcomponents of the praxis production and recognition system(s). An influential contemporary model of the praxis system accounts for various patterns of apraxia in terms of two routes to praxis production, recognition, and imitation (Gonzalez Rothi, Ochipa, & Heilman, 1991). The model includes a lexical route to gesture comprehension and production involving stored gesture representations at two loci (the input and output praxicons, respectively). Each praxicon contains stored spatiomotor gesture representations which provide the ‘‘time-space-form picture of the movement’’ (Liepmann & Maas, 1907) and confer a processing advantage for skilled gestures. The two-route model also contains a direct or nonlexical route which can be used in gesture imitation. Figure 1 is a simplified schematic of this model. On this model, different patterns of ideomotor apraxia are viewed as having parallels in aphasic disorders and are attributed to deficits in stored gesture representation, access, or egress. For example, impairments in gesture comprehension with spared gesture to command is viewed as akin to ‘‘word deafness’’ in Wernicke’s aphasia: Sensory signals fail to gain access to the input praxicon. Intact gesture comprehension with impaired gesture production, like Broca’s aphasia, is proposed to result from impairments in the output praxicon. Impairments of gesture imitation in the context of intact gesture comprehension, similar to relatively severe repetition deficits in conduction aphasia, are posited to result from lesions between the input and output praxicons. Reliance on the direct route from vision to action explains the performance of IM patients who, akin to transcortical sensory aphasics, are able to imitate (‘‘repeat’’) gestures they cannot comprehend. Although the two-route model successfully accounts for numerous subtypes of apraxia, it does not appear to explain a common pattern of the disorder. Many patients with IM as assessed by gesture pantomime, object use, and/or meaningful imitation tasks exhibit relatively greater difficulty in imitating meaningless movements (Kimura & Archibald, 1974; De Renzi, Motti, & Nichelli, 1980; Pieczuro & Vignolo, 1967). On the two-route account, this is suggestive of dual lesions to the lexical and direct routes, with the lesion to the direct route the relatively more severe. In this study, we

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FIG. 1. A schematic of the model of the praxis system proposed by Gonzalez Rothi, Ochipa, and Heilman (1991).

explore a more parsimonious possibility: that this pattern reflects damage to a unitary set of procedures or representations common to both lexical and direct routes. Consider that both skilled and novel movements are likely to require spatial coding of the dynamic locations of body parts relative to one another (what we will term intrinsic spatial coding of body part positions, to be distinguished from extrinsic egocentric coding of object locations with respect to body parts). Several lines of evidence suggests that such information is computed by the brain. Physiologic data indicate that computation of spatial coordinates for action includes calculation of the positions of the fingers with respect to one another (e.g., Gallese, Fadiga, Fogazzi, & Rizzolatti, 1996), of the eye with respect to the head, and of the head with respect to the torso (e.g., Snyder, Grieve, Brotchie, & Andersen, 1998). In addition, there is evidence that neurons in the superior parietal lobe (area PE in monkeys) integrate inputs from primary somatosensory cortex to construct complex representations of body postures. For instance, coding of a posture in which the

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left hand contacts the right shoulder may occur at the level of the single neuron (Sakata, Takaoka, Kawarasaki, & Shibutani, 1973; see also Gurfinkel & Levick, 1998). It has been suggested that such coding may be the basis for a mental model of the body (Bonda, Frey, & Petrides, 1996). According to Jeannerod and colleagues (Jeannerod, Arbib, Rizzolatti, & Sakata, 1995), schemas for coding the positions and movements of body parts relative to one another may form a basic vocabulary from which many skilled movements can be constructed. There is also evidence that the same spatiomotor body representations may be invoked in production, recognition, and imitation tasks. For example, there are data suggesting that the perception and representation of others’ bodies, and of action, is constrained by implicit knowledge of the movements the system is able to produce. Parsons (1987, 1994) elegantly demonstrated that left/right decisions about hands are made by mentally rotating ones’ own motor hand image into congruence with the view depicted; response latencies indicated that the mental rotations took into account the starting position of subjects’ arms and hands and the mechanical (joint) constraints of rotation in one or another direction. Subsequent PET studies have indicated that such judgments are accompanied by activation in superior parietal and intraparietal cortex (Bonda et al., 1996). Reed and Farah (1995) presented data from whole-body-position judgment tasks similarly consistent with involvement of a dynamic spatiomotor body representation: Subjects’ response latencies to perform same/different judgments about others’ body positions was affected by the subjects’ own position during the judgment. That judgment and matching of body-part positions differs qualitatively from matching of visual stimuli was confirmed by a recent PET study demonstrating that comparison of the positions of hand stimuli, but not abstract branching shapes, activates regions of premotor and motor cortex (Kosslyn, Digirolamo, Thompson, & Alpert, 1998). Finally, several physiologic studies indicate the presence of ‘‘mirror’’ neurons in the superior temporal sulcus and frontal lobe which discharge both during monkeys’ active movements and observation of the same movements by others. Rizzolatti and co-workers (1988) have proposed that such observation/execution mechanisms play a role in comprehension of action. Similarly, Jeannerod has suggested that an observed action can be understood and imitated whenever it becomes the source of a representation of the same action within the brain of the observer (Jeannerod, 1999). In sum, then, there is evidence that the representations and procedures providing for ‘‘intrinsic’’ spatial coding of the dynamic positions of body parts may be used both for planning one’s own actions as well as in recognizing the actions in others. In cognitive neuropsychological terms, there is historical precedent for characterizing dynamic body-part location coding as one of the functions of the so-called ‘‘body schema’’ or ‘‘plastic schema’’ (Head & Holmes, 1911/ 1912), an ‘‘on-line’’ map of the position of the body parts in space over

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time which enables measurement of postural changes and appreciation of passive movement. As noted by Mussa Ivaldi, Morasso, and Zaccaria (1988), ‘‘the concept of an internal model (of the body) is a way to deal at the same time with many frames of reference and to emphasize one with respect to the others during the planning process according to specific task needs; it can be considered as a revisitation of the old neurological concept of the body schema’’ (p. 53). It is of note that in discussing the left/right hand discrimination findings just described, Parsons (1994) suggested, ‘‘Because the kinematic configuration of the body that is represented and transformed in mental simulations of action matches the actual current kinematic configuration of one’s body, the representation underlying performance is likely what has been termed ‘body schema’ ’’ (p. 726). Several investigators have noted that gesture pantomime and imitation may rely on the body schema or something akin to it (e.g., Heilman, Gonzalez Rothi, Mack, Feinberg, & Watson, 1986; Kimura, 1977; Russell, 1976). For example, Heilman et al. (1986) reported a patient with superior parietal (area 5) damage whose apraxia they attributed to deficits in a proprioceptive comparator system which transcodes visual information into somatesthetic spatial coordinates. They postulated that the superior parietal lobe is critical for transcoding praxicons into a somatesthetic spatial code. Kimura (1977) discussed the dependence of praxis upon internal spatial functions responsible for encoding changes in the position of one body part relative to the rest. Generally, however, such intuitions have not been tested with measures designed to assess body schema integrity, nor explicitly incorporated into models of the praxis system.1 We present data from a primary progressive apraxic woman which cannot be accommodated by the two-route model without augmentation. The data are consistent with a revised model of the praxis system which explicitly incorporates the role of intrinsic spatial coding of body-part positions in both lexical and direct gesture processing. In this manuscript, we use the term ‘‘body schema’’ as a shorthand for the procedures and representations involved in the on-line coding of the position of body parts with respect to one another over time and resulting in an internal dynamic model of the body; note that this usage appears similar to those intended by other contemporary investigators mentioned above (Mussa Ivaldi et al., 1988; Parsons, 1994). We demonstrate that a revised model of the praxis system explicitly

1 There is some controversy about the degree to which the body schema may be impaired in other parietal syndromes. While there is evidence that the schema for the left hand may be impaired in personal neglect (Coslett, 1998), it is not as clear whether autotopagnosia (Ogden, 1985) and Gerstmann’s syndrome (Benton & Sivan, 1993) should be considered body schema impairments as well. There is evidence suggesting that the impairment in autotopagnosia is rather in a system of body-specific visual structural descriptions (Sirigu et al., 1991; Buxbaum & Coslett, 1998a; in press).

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FIG. 2. A saggital view of a T1-weighted MRI demonstrating prominent atrophy of posterior parietal and frontal cortex, with relative preservation of prefrontal and occipital cortex.

incorporating the role of the body schema can accommodate the performance of a common IM subtype more readily than the original two-route account. Patient Description BG was a 67-year-old left-handed woman with a 12th-grade education who complained of the slow onset of articulatory speech problems 2 years prior to the present investigations. She denied memory or concentration problems, but suspected that her thinking was ‘‘not as sharp’’ as it had been several years previously. She also admitted to becoming confused when attempting to navigate in unfamiliar environments. Repeated neurological evaluations over the course of a 2-year period corroborated BG’s subjective impression of ‘‘slowed speech’’ as well as hypophonia, but revealed normal limb strength, proprioception, and sensation bilaterally, intact cranial nerves, and the absence of pathologic reflexes. Diagnoses under consideration included Pick’s Disease, corticobasal degeneration, and Alzheimer’s Disease. An MRI revealed moderate cortical and cerebellar atrophy (see Fig. 2). A SPECT scan was remarkable for decreased activity in the mesial temporal lobes as well as in the superior posterior parietal lobes, left greater than right. BG exhibited a WAIS-R IQ of 90 (25th percentile), reflecting probable mild decline from premorbid levels given a NART IQ score of 100.6 (Nelson & O’Connell, 1978). Language testing revealed dysarthria and articula-

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tory deficits affecting repetition and fluency, but no evidence of aphasia. As can be seen in Table 1, motor functioning was normal with the left hand and just below normal with the right. BG made substitution errors in pointing to named body parts on the left, right, and midline (total 19/35 correct), but performed relatively accurately in body-part pointing upon imitation (33/ 35 correct; both errors on the right). There were mild deficits in right–left discrimination. There were also severe deficits on tests of finger gnosis and graphisthesis (recognition of numbers written on fingertips), bilaterally. Finally, BG performed poorly with arithmetic calculations (12/20 correct on one-step addition, subtraction, multiplication, and division). Thus, she exhibited three of four components of Gerstmann’s syndrome (right–left confusion, finger agnosia, and acalculia, but not agraphia) as well as evidence of a more general parietal syndrome. Table 1 provides a summary of the results of these and other background tests. BG’s performance was rapid and accurate bilaterally on tests of reaching to targets in peripheral vision while fixating on the examiner’s face; i.e., she did not exhibit optic ataxia. She was likewise unimpaired in reaching to the remembered locations of coins that were placed on a large (36″ ⫻ 48″) sheet of paper and then removed. Comparatively severe deficits were evident on clinical tests of limb praxis. When asked to pantomime the use of common objects (e.g., hammer, scissors) with either hand, BG frequently performed a small, circular ‘‘rubbing’’ gesture upon her thigh or a tabletop. She appeared to improve only slightly with vision of the target objects. Thus, apraxia was by far the most prominent feature of the progressive degenerative process, consistent with the syndrome of primary progressive apraxia. These observations prompted a more thorough investigation of the deficits underlying BG’s limb praxis, informed by a working model of the praxis system. In the first several studies, we provide evidence that BG has severe IM and that her gesture representations are largely intact and accessible. In the second set of studies, we demonstrate that BG’s gesture impairment is likely to be attributable to deficits in procedures and representations used to code the intrinsic positions of the body in space over time. EXPERIMENTAL STUDIES

Study 1: Gesture Production Methods. BG was asked to produce common gestures in three conditions. In the Command condition, she was asked to produce 18 transitive gestures (e.g., ‘‘show me how to use a hammer’’), imagining that she was holding and using the specified tool. Tools were not in sight. In the Use condition, she was permitted to actually hold and use the same set of 18 tools. Finally, in the Imitation condition, she viewed a videotaped model performing 10 transitive gestures performed without tools and 5 intransitive gestures (e.g., waving, beckoning ‘‘come here,’’ signaling ‘‘stop’’) and performed the same gestures; she was permitted to begin while watching the model. Gestures in all conditions were performed with both left and right hands; hand was blocked in an ABBA order.

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TABLE 1 BG’s Performance on Neuropsychological Tests Neuropsychological test Motor Function Finger Tapping Grooved Pegboard Grip Strength Sensory Function Finger gnosis Tactile double simult. stimulation (hands) Visual double simult. stimulation Language Real object naming (sight) Boston Diag. Aphasia Exam (BDAE) b Complex ideational material Word reading Spell to dictation High-probability repetition Low-probability repetition Visual/Spatial Processing Rey–Osterrieth Complex Fig— Copy Letter Cancellation d Memory Nine-Item California Verbal Learning Test e Trials 1–5 Delay free recall Delay cued recall Recognition discriminability Rey–Osterrieth Complex Figure— Immediate recall Rey–Osterrieth Complex Figure— Delay recall Executive Function Automized mntl ctrl (count backwds., alphabet, months) Nonautom. mntl ctrl (count 3’s, months backward, rhymes, letter imagery) Trail Making Testa —Part A Trail Making Test—Part B a

Score 45 L, 20 R 105″ L, 139″ R 25 L, 24 R

T scores: L ⫽ 55, R ⫽ 25 a T scores: L ⫽ 35, R ⫽ 30 a T scores: L ⫽ 49, R ⫽ 55 a

50%L, 38%R 100%L, 100%R

Bilateral impairment Normal

28% (all R misses)

R extinction

21/22

Normal

9/12 9/10 12/12 1/8 1/8

Cntl. Cntl. Cntl. Cntl. Cntl.

25/36

⬍10th percentile c

Errors: 3L, 8R

Impaired

30/45 3/9 4/9 94% 25/36

Cntl. M ⫽ 37.1, SD ⫽ 4.3 Cntl. M ⫽ 7.1, SD ⫽ 1.7 Cntl. M ⫽ 7.4, SD ⫽ 1.5 Cntl. M ⫽ 95.5, SD ⫽ 4.8 ⬍10th percentile c

16.5/36

⬍10th percentile c

M ⫽ 100%

Cntl. M ⫽ 98.7, SD ⫽ 2.3 f

M ⫽ 93%

Cntl. M ⫽ 91.1%, SD ⫽ 10.6 f

58″, O errors 148″, O errors

T Score ⫽ 40 T Score ⫽ 35

Norms from Heaton, Grant, and Matthews (1991). Goodglass and Kaplan (1983). c Lezak (1995). d Mesulam (1985). e Libon et al. (1996). f Cloud et al. (1994). b

Comments

M M M M M

⫽ ⫽ ⫽ ⫽ ⫽

11.2, SD ⫽ 1.0 8.0, SD ⫽ 0.2 8.4, SD ⫽ 1.4 7.9, SD ⫽ 0.4 7.7, SD ⫽ 0.5

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TABLE 2 BG’s Performance on Tests of Praxis (Percent Correct) Hand

Grasp

Right Left

84 84

Right Left

33 39

Right Left

33 40

Traject.

Amplit.

Tool Use 89 84 95 95 Gesture to Command 61 67 72 78 Gesture Imitation 53 73 60 73

Timing

Total

83 83

86 90

72 61

57 63

67 87

57 65

Each gesture was initially rated for content: substitutions of recognizable gestures (e.g., ‘‘sawing’’ → ‘‘hammering’’) received ‘‘incorrect content’’ scores and were not further coded. Gestures with correct content were scored for the spatial/temporal components grasp, trajectory, amplitude, and timing (4 points maximum for each gesture) by two independent coders according to detailed criteria (see Appendix 1). Interrater agreement for content was 100%. Mean interrater agreement across all spatial/temporal gesture components was 84% (grasp 84%, trajectory 85%, amplitude 87%, timing 80%). Scores for which there was disagreement were reconciled by additional review of videotapes.

Results. BG’s errors were all spatial and/or temporal; there were no recognizable gesture substitutions. For example, when asked to pantomime the use of a hammer with her right hand, she produced a rapid oscillating movement of the hand and forearm of low amplitude (approximately 6 inches) with a vertical trajectory and an open, flat palm. Data are shown in Table 2. A Kruskal–Wallis test performed on the 0- to 4-point scores for gestures in the three conditions revealed a significant effect of condition (Right hand: H ⫽ 12.2, p ⬍ .01; Left hand: H ⫽ 12.6, p ⬍ .005). Multiple comparisons testing (see Siegal & Castellan, 1988) demonstrated that for both hands, the Use condition was superior to both Imitation and Command conditions (differences in mean rank exceed critical value of 12.99); the latter two conditions did not differ from one another. As Table 2 indicates, performance was generally superior in the Use condition across all spatial/temporal gesture components (grasp, trajectory, amplitude, timing), with the exception of relatively superior left-hand timing scores in the Imitation condition. Perhaps not surprisingly, the greatest relative improvement in the Use condition occurred in the grasp component, but other improvements were substantial as well. Discussion. BG’s deficits in both the Command and Imitation conditions confirm the clinical impression of a severe IM characterized by spatial and temporal errors. Her parallel performance in both conditions indicate that errors in the Command condition are not attributable to language-comprehension deficits. If one adopts the two-route model’s assumption that IM results from deficits in gesture representation access or egress, or damage

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to representations themselves, at least two questions arise from these data. First, what is the basis for the relative integrity of BG’s tool use? Second, why does she fail to use the direct route upon provision of a model to be imitated? In the next set of studies, we explore the first question; later, we turn to the second. Improved gesture production with actual tool use is a common feature of IM, though the underlying reasons for this finding remain unclear. One possibility is that tool shape, size, and weight may assist selection from a pool of potential gestures by excluding gestures that would be difficult to perform with that tool. A second possibility is that the visual and tactile (structural) characteristics of tools may directly activate otherwise inaccessible gesture representations; i.e., structural information may trigger stored gestures in a ‘‘bottom-up’’ fashion (Pilgrim & Humphreys, 1991). Finally, deficient spatiotemporal positioning of the body (e.g., due to partially degraded engrams or impairments in intrinsic spatial coding) may benefit from the cues to posture/joint angles/trajectory that a tangible object provides. In BG’s case, the substantial improvement in the grasp component of the gesture seen in the Use condition is suggestive of this possibility.2 In the case of each of these scenarios, the tool-use augments deficient (but not obliterated) gesture-related procedure or representations. In other words, adequate gesturing with tool in hand suggests that gesture information is at least partially intact. However, there is another possible explanation for relatively intact tool use in apraxia. On some accounts, plausible actions upon objects may be triggered directly from objects’ perceptible attributes without invoking stored gestures; i.e., the action may be driven by affordances of the object for certain actions (e.g., the handle of a hammer for grasping and swinging, the openings of a scissors for inserting fingers and opening/closing; see Gibson, 1977; but see also Sirigu, Duhamel, & Poncet, 1991; and Buxbaum, Schwartz, & Carew, 1997, for discussion of the limitations of affordances). If BG’s actions with objects are triggered solely by such affordances, then she should perform similar, affordance-driven gestures with objects that have in common a set of affordances. To pursue this possibility, we analyzed BG’s production of gestures with sets of objects matched for affordances. Study 2: Gesturing with Objects Matched for Affordances Methods. BG was asked to demonstrate gestures with eight pairs of affordance-matched objects with objects in her dominant (left) hand. The matched object pairs were rubber band– hair elastic, pencil (unsharpened)–chopstick, foundation makeup (label removed)–mouthwash 2 Sirigu, Cohen, Duhamel, Pillon, Dubois, and Agid (1995) reported a patient with isolated impairments in positioning of the hand with respect to objects; when the hand posture was corrected by the examiner, other aspects of the gesture improved to normal. Unlike that subject, BG’s gesture trajectories and timing were impaired on some trials even when her hand posture was correct.

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(label removed), hairbrush–scrub-brush, birthday candle–cigarette, baseball–orange, decorative hair comb–regular comb, magic marker–lipstick, and aftershave (label removed)–nailpolish remover (label removed).

Results. BG performed perfectly with 15/16 (94%) of the objects, demonstrating the correct grasp, use, and placement of each. She erred with the candle, whose wick she pinched repeatedly while saying, ‘‘you light this.’’ Discussion. BG’s nearly perfect performance with objects matched for affordances indicates that she does not rely solely on information given by object weight, shape, and texture in producing gesture. Instead, the data suggest that the motor system is able to access the specific stored gesture information relevant to distinct objects. These data do not speak to whether tools ‘‘cue’’ gesture selection by narrowing the range of candidate gesture representations, directly trigger activation of otherwise inaccessible representations via structural object properties (Pilgrim & Humphreys, 1991), or guide spatiotemporal positioning of the body, but we provide additional evidence relevant to this question below. On the two-route model of praxis, relatively intact tool use in the context of severely deficient imitation suggests severe degradation of the input praxicon or disconnection of praxicons from visual input. In either case, BG should be severely deficient in gesture recognition. If, on the other hand, the deficit is external to the stored gesture representation system, gesture recognition should be relatively intact. We assessed these competing possibilities next. Study 3: Gesture Recognition Methods. In the Tool Match condition, BG performed a modified version of the Gesture to Object Matching task from the Florida Apraxia Battery (Gonzalez Rothi, Raymer, Ochipa, Maher, Greenwald, & Heilman, 1991). She was asked to view 17 pantomimed gestures on videotape and to match the gesture with a drawing of an appropriate tool from an array of four tools. One of the three tool ‘‘foils’’ in the array was visually and semantically similar to the target (e.g., target: paintbrush; foil: hairbrush), the second was functionally associated with the target (e.g., target: paintbrush; foil: paint can), and the third was associated with a visually similar gesture (e.g., target: paintbrush; foil: hammer). In the Tool-Use Decision Condition, BG was asked to make ‘‘correct’’ vs ‘‘incorrect’’ decisions for 30 videotaped gestures performed with tools, 20 of which were incorrect. Incorrect gestures were performed with errors of grasp, trajectory, amplitude, and/or timing. Objects were not named by the examiner in this or the preceding condition. In the Pantomime Decision condition, she similarly made ‘‘incorrect’’ vs ‘‘correct’’ decisions for videotaped gestures; in this condition, however, the gestures were pantomimed without tools. There were 50 pantomimes, 20 of which were performed incorrectly. Incorrect gestures were spatial in nature and were qualitatively similar to those of the Tool-Use Decision condition.

Results. In the Tool Match condition, BG matched 15/17 (88%) of gestures to tools. In the Tool-Use Decision condition, she appropriately made 25/ 30 (83%) ‘‘correct’’ vs ‘‘incorrect’’ decisions about gestures with tools. In contrast, she performed poorly in the Pantomime Decision condition, making only 21/50 (42%) accurate decisions. Nineteen of her 29 errors were failures

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to recognize correct gestures and the remaining 10 errors were failures to detect incorrect gestures. Her performance in this condition was at chance and significantly more impaired than in the other two conditions (Tool Match vs Pantomime Decision: χ 2 ⫽ 10.9, Fisher’s Exact p ⫽ .0015; Tool-Use Decision vs Pantomime Decision: χ 2 ⫽ 13.1, Fisher’s Exact p ⫽ .0004). Discussion. Results of the Tool Match and Tool-Use Decision conditions indicate that BG can recognize gestures when they are performed with tools or can be associated with tools through a matching procedure. On the tworoute model, these data indicate that BG’s input praxicon, while perhaps not perfectly normal, is largely intact and accessible to visual input. Recall that the results of Studies 1 and 2 suggest that the praxicon(s) can access motor systems (at least when tools are used). Taken together, these data raise questions about the reasons for BG’s failures in gesture pantomime and imitation and in gesture recognition without tool context information. There are at least two explanations for the pattern of BG’s performance. One possibility is that degradation of the gesture praxicon(s) is sufficiently mild or moderate that it solely affects tasks in which tool context information is not provided. On this account, one would have to accept the possibility that the presence of tool context information explains the striking disparity between BG’s severely impaired gesture pantomime and her very mildly impaired gesture with tool in hand. Another possibility is that the impairment is external to the stored gesture representation system. On the latter account, it might be suggested that BG imperfectly codes dynamic body part positions and that this deficit affects all tasks relevant to the ability to position body parts in space over time or to appreciate such positioning in others. We may speculate that when tools are used with the gesture to be recognized or imitated, knowledge of the characteristic trajectory and amplitude of tool movement (e.g., hammers swing up and down in an arc) may provide a form of ‘‘top-down’’ feedback to processes encoding the dynamic body positions of the actor. Fortunately, the two accounts make differential predictions about the performance expected in meaningful as compared to meaningless gesture tasks. If impairments are due to deficits within the lexical route, performance should be superior with meaningless movements, as these are performed via the direct route and do not engage the putatively damaged system. If impairments are external to the lexical system, performance should be superior with meaningful gesture tasks, as these take advantage of the relative integrity of stored gesture representations. We assessed these competing possibilities in Study 4. Study 4: Imitation of Meaningless Gesture Analogs Methods. Fifteen meaningless gesturelike movements were created with reference to the gestures assessed in the Imitation condition of Study 1. For each meaningful gesture, the plane of movement (vertical/horizontal), joints moved (shoulder/elbow/wrist/fingers), grip type

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(hand open/clenched/partially open), and oscillations (present/absent) were tabulated. As can be seen in Appendix 1, meaningless analogs preserved the characteristics of the meaningful gesture with respect to these attributes. For example, the ‘‘hitchhiking’’ gesture assessed in Study 1 is a vertical motion with greatest movement at the elbow, the hand is partially open (the thumb is extended), and there are oscillations. The meaningless analog of the hitchhiking gesture similarly entailed a vertical motion with greatest movement at the elbow, the hand was partially open (the fifth finger was extended), and there were oscillations. BG viewed a videotape of a model performing each movement with her right hand and was required to reproduce the movement as precisely as possible. She was permitted to perform during her observation of the model; there was thus no memory requirement. Right- and left-hand performance was blocked by ABBA design. A healthy 62-year-old female control subject was also assessed with this procedure as well as with the procedure used in the Imitation condition of Study 1 above (meaningful gesture imitation). BG’s productions were scored individually by two coders with the 4-point scale used in Study 1 (see Appendix 2). Percentage agreement averaged across all spatial/temporal gesture components was 76% (grasp ⫽ 84%, trajectory ⫽ 79%, amplitude ⫽ 73%, timing ⫽ 68%). Gestures about which there was disagreement were reconciled through review of videotapes. The control data were scored by a single coder.

Results. The control subject was near ceiling in both Meaningful and Meaningless Imitation conditions [Meaningful: R ⫽ 96% (58/60), L ⫽ 94% (56/60); Meaningless: R ⫽ 94% (56/60), L ⫽ 95%(57/60)]. BG was profoundly impaired in imitating meaningless analogs (R ⫽ 42%, L ⫽ 30%) and performed even more poorly than in imitating the meaningful gestures of Study 1 (Meaningless imitation R hand: grasp ⫽ 53%, trajectory ⫽ 20%, amplitude ⫽ 47%, timing ⫽ 47%; Meaningless imitation L hand: grasp ⫽ 40%, trajectory ⫽ 33%, amplitude ⫽ 33%, timing ⫽ 13%). An ANOVA with the factors Hand (left, right) and Imitation Condition (Meaningful, Meaningless) revealed a significant effect of condition such that meaningful gestures were performed better than meaningless gestures [F(1, 56) ⫽ 9.9, p ⬍ .005], no effect of hand (p ⫽ .8), and no condition by hand interaction (p ⫽ .21). Discussion. When gesture information is absent, BG is particularly deficient in positioning both her left and right hands and arms in space over time to match the positioning of another person’s body. For BG, but not for a control subject, stored gesture information confers a processing advantage in on-line imitation. The relative superiority of meaningful gestures is more subtle with the right than left hand, but as judged by the absence of an interaction in the ANOVA, is present for both hands. This pattern is entirely inconsistent with a deficit within the praxicon system, as such a deficit should result in relatively greater impairment for learned gestures dependent upon a stored representation. Instead, the findings support the predictions of a model positing that the deficit(s) causing BG’s apraxia are largely external to the stored gesture system. In this context, it is noteworthy that a recent investigation by Goldenberg (1995) demonstrated that nearly half of the left-hemisphere aphasic patients assessed were impaired on meaningless posture-imitation tasks. Impaired subjects also performed deficiently when asked to pose a mannequin to match

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a given hand posture. Based on this, as well as on subsequent studies (e.g., 1997), Goldenberg has suggested that subjects were deficient in apprehending the movement and configuration of body parts in general, based on deficient ‘‘conceptual knowledge’’ of the human body. A different account is suggested by investigators studying childhood autism, who have proposed that impairments in novel gesture imitation may reflect difficulty in spatially transforming the child’s view of another’s action into a matching action on the self (Barresi & Moore, 1996; Smith, 1998). The present account appears to be closely aligned with the latter perspective. However, it remains possible that the deficient representation is conceptual (i.e., semantic), as Goldenberg (1995) has suggested. Deficits in a semantic or propositional representation of the relationship of body parts to one another should not be affected by the spatial attributes of movements that subjects are required to recognize or imitate. Thus, for example, the ability to encode the fact that the hand rests ‘‘above’’ the eye in a ‘‘saluting’’ gesture should not be affected by whether a salute to be recognized or imitated is viewed from a head-on or side view. Conversely, if the difficulty lies in encoding the precise spatial relationships of body parts, then spatial characteristics of the stimuli, such as viewing angle, should affect performance. We assessed this in the next study, in which BG was asked to make same/different decisions about gestures when viewed from differing angles. It should be noted that this task bears resemblance to the body-position matching task used by Reed and Farah (1995) to assess the body schema. Study 5: Gesture Matching—Effect of Viewing Angle Methods. BG was asked to decide whether pairs of pantomimed movements presented on videotape were the ‘‘same’’ or a ‘‘different’’ gesture. In half the trials, the two movements were the same meaningful or meaningless gesture; in the remaining trials the second movement of each pair differed in its spatial characteristics (amplitude or trajectory, e.g., key-use pantomimed with a large vertical rather than circular trajectory of the wrist). There were two conditions with 40 pairs each. In the Same View condition, movement pairs were filmed from identical viewing angles. In the Rotated View condition, the second movement of each pair was filmed at an angle 90° from the first. Half the movements in each condition were meaningful gestures, and half were the same meaningless gesture analogs assessed in Study 4. Each gesture was performed for approximately 5 s; there was approximately a 1-second delay between gestures in a pair. For both meaningful and meaningless gestures, Same View and Rotated View Conditions were blocked and presented in ABBA order. A 62-year-old female control subject was assessed on the meaningful conditions only.

Results. BG’s performance in the Same View condition was significantly better than in the Rotated View condition (35/40 vs 28/40; χ 2 ⫽ 3.6, p ⫽ .05). This pattern of results was present for both meaningful gestures (Same View: 18/20, 90%; Rotated View 14/20, 70%) and meaningless gestures (Same View: 17/20, 85%; Rotated View:14/20, 70%). Several errors in the Rotated View condition were incorrect rejections of ‘‘same’’ movements,

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while others were failure to detect ‘‘different’’ movements. For example, BG failed to detect that pantomimed cutting with scissors in a single linear trajectory differed from cutting in multiple radial trajectories. The control subject performed perfectly in both conditions. Discussion. BG’s performance in the Same View conditions indicates that she was able to comply with the demands of the task, including the requirement to hold body positions in memory. Her imperfect performance in this condition may be suggestive of some degree of difficulty in coding or maintaining body position information. Stronger evidence, however, comes from BG’s relatively impaired performance in the Rotated View condition, in which she had to match gestures across a shift in perspective. The fact that BG performs particularly poorly when a spatial transformation of the body is required suggests that the representation underlying her deficient appreciation of others’ bodies is spatial rather than conceptual (semantic) in nature. Below, in Study 7, we provide further evidence supporting this conclusion. Although the data to this point are consistent with deficits in a spatiomotor body representation, an additional possibility is that BG suffers a general deficit in spatial rotation or transformation which affects numerous classes of objects, bodies included. We assessed this possibility next. Study 6: Object Matching—Effect of Viewing Angle Methods. BG was given our laboratory’s Matching Across View Shifts Test. She was required to match a reference photograph of a familiar object in a standard view to a target photograph. The target was presented in an array with two distractors. In 1/3 of the 72 trials the reference photo is an object in a standard view, in 1/3 an atypical view, and in 1/3 an odd view. The latter two conditions require a mental rotation. Normal controls perform this task at ceiling.

Results. BG performed correctly on 24/24 (100%) of standard view, 23/ 24 (96%) of atypical view, and 22/24 (92%) of odd view trials. Her performance in the object-matching condition not requiring rotation (standard view) was equivalent to her performance in the Same View condition of the gesture-matching study reported above (χ 2 ⫽ 2.2, p ⫽ .2), indicating that these baseline matching tasks were approximately equally difficult for BG. In contrast, her performance in the conditions of the object-matching study requiring rotation (atypical and odd views) is superior to the Rotated View condition of the gesture-matching study reported above (χ 2 ⬎ 6.9, p ⬍ .01 for both comparisons). These data provide support for the hypothesis that BG has a specific deficit in spatially transforming body (but not object) information. It remains possible that BG’s specific deficits in transformation of body information reflect problems in rotating and manipulating a visual, rather than spatiomotor, image of the body. In that case, it would be inaccurate to characterize the deficient representation as spatiomotor in the sense implied by accounts of the body schema. To assess this, we asked BG to perform a

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FIG. 3.

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BG’s performance on the mental hand rotation task of Study 7.

variant of the task developed by Persons and colleagues (1994) mentioned earlier, which demonstrated that decisions about hand laterality are made by mentally rotating one’s own motor hand image. The investigators asked control subjects to make decisions about whether drawings depicted left or right hands while they maintained their own hands, out of sight, in prespecified positions. Subjects’ responses were fastest when there was congruence between their own hand positions and those depicted. Furthermore, the pattern of response latencies suggested that subjects were rotating a ‘‘motor image’’ of their own hands through the same trajectory that would be used in a real movement: Systematic discontinuities in latency occurred when subjects would have had to rotate their own hand-image in a biomechanically impossible manner. BG performed an easier variant of this task, assessing accuracy (but not latency) of left/right decisions to hand-stimuli that were congruent or incongruent with her own hand positions. Study 7: Mental Body Rotation (Motor Imagery) Methods. BG and a 62-year-old female control were asked to identify whether a photograph depicted a left or right hand. Ninety-six photos of hands were presented, half in palm-up and half in palm-down views. All stimuli were in canonical position with fingers pointing away from the subject. The subjects’ own hands, covered with a dark cloth, were positioned palmup on 48 trials and palm-down on 48 trials. Thus, subjects’ hand positions were congruent with stimuli on half the trials. Subjects were not permitted to move their hands. Subjects’ hand position was blocked, and blocks were performed in ABBA order (see Coslett, 1998, for details of the task).

Results. As shown in Fig. 3, with her own hands positioned palms down, BG was correct on 20/24 (83%) of palm-down and only 7/24 (29%) of palmup pictures; with her own hands positioned palms up, she was correct on 23/24 (95%) of palm-up and only 17/24 (70%) of palm-down pictures (Total

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on ‘‘congruent’’ trials ⫽ 89%; Total on ‘‘incongruent’’ trials ⫽ 50%; χ 2 ⫽ 17.8, p ⬍ .0001). She also tended to be less accurate in discriminating pictures of right hands (30/48; 62%) than left hands (37/48; 77%), though the difference did not reach significance (p ⫽ .12). The control subject performed equally accurately in congruent and incongruent trials [Total on ‘‘congruent’’ trials ⫽ 46/48 (96%); Total on ‘‘incongruent’’ trials ⫽ 45/48 (94%)]. Discussion. BG, but not a control subject, is significantly more accurate in making left/right decisions about hands in ‘‘congruent’’ trials in which she does not have to perform a mental rotation to align her own internal hand-image with the stimuli. Data from the behavioral studies of Parsons et al. (1987, 1994) and the PET study of Kosslyn et al. (1998), described above, suggest that the present task is performed by rotating a motor image of the hand. BG’s inability to perform motor rotations supports the findings of Study 6 in suggesting that she is deficient in the dynamic spatiomotor representation of the body supporting such motor imagery; i.e., the body schema. There is one final question relevant to the nature of the procedures and/ or representations disrupted in BG. Several accounts of the body schema propose that as it represents information about the position and extent of the human body, it underlies the ability to position the body in space to interact with objects in the environment; that is, to perform so called ‘‘extrinsic’’ egocentric spatial coding. Inconsistent with this, clinical observations of BG were not suggestive of optic ataxia (misreaching under visual guidance). We further explored BG’s ability to position her hand with respect to objects in a final study. Study 8: Hand-in-Slot Test Methods. BG was assessed with a variant of a task described by Goodale, Milner, and colleagues (Goodale, Milner, Jacobson, & Carey, 1991; Milner et al., 1991) in which she was required to position her hand with respect to a large slot displayed in a number of different orientations. A 12 ⫻ 4-cm slot in a round disk 56 cm in diameter was presented 40 cm from the chest wall. On each trial, the slot was oriented horizontally, vertically, 45° left, or 45° right. BG was required to begin each trial with her hand palm-down on a tabletop and, upon a ‘‘go’’ signal, to reach her hand through the slot as accurately as possible. There were five trials with each hand in each of the four slot orientations presented in random order. Hand position relative to the slot was videotaped with a head-on camera and later coded from the videotape. Any contact of the edges of the slot by the hand was coded as an error.

Results. BG performed perfectly accurately with both hands. There were no trials on which the hand contacted the edge of the slot. Discussion. The hand-in-slot task requires coding of an object in the environment with respect to the body, a form of spatial coding usually referred to as ‘‘egocentric.’’ There is evidence that patients with optic ataxia, a parietal disorder of misreaching, are impaired in the forms of egocentric coding needed to direct the hand to object locations (see Buxbaum & Coslett, 1997, 1998b). But BG exhibits optic ataxia neither on clinical testing nor in the

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present study. This suggests that extrinsic egocentric spatial coding is intact, at least for spatial positions near midline.3 The evidence for impaired intrinsic spatial coding of dynamic body position presented above is of particular interest in this context, as it suggests that while both intrinsic body-part position coding and egocentric coding of object location may rely (to a greater or lesser degree) on an implicit internal model of the body, they are nevertheless dissociable. GENERAL DISCUSSION

We have presented data from a primary progressive apraxic woman which cannot be accommodated by the ‘‘two-route’’ account of IM (Gonzalez Rothi et al., 1991) without additional assumptions. BG is unable to gesture to command or imitation, but performs relatively well with tool in hand. Study 2 indicated that her relatively accurate performance with tools can not be attributed to object affordances, suggesting that gesture representations are largely intact and accessible to motor output. Study 3 demonstrated that she recognizes gestures well when contextual tool information is provided, indicating that (at least under these circumstances) gesture representations can be accessed by visual input. Study 4 indicated that BG is more deficient in imitating meaningless gesturelike movements than spatially matched meaningful gesture analogs, supporting the conclusion that gesture representations are relatively intact and may provide a form of ‘‘top-down’’ support to deficient processes external to the stored gesture system. Studies 5–7 attempted to elucidate the nature of the deficient representations and/or processes and showed that BG has difficulty in matching gestures (but not objects), particularly when a spatial transformation is required, and in performing mental motor transformations to assess the positions of body-part stimuli. These suggest that the deficient processes are not conceptual or visual, but spatiomotor in nature. Proponents of the dual-route model might attempt to suggest that BG (and other similar patients) suffer deficits in both lexical and direct gesture routes. The deficits in gesture pantomime, meaningful imitation, and some recognition tasks, it might be argued, are attributable to some combination of damage to input and output gesture representations. The severe deficits in meaningless imitation, as well as the other difficulties with body-position encoding demonstrated in Studies 4–7, are due to an additional severe deficit in the procedures and representations of the direct route. However, this argument fails to satisfactorily explain the significant disparity between BG’s severely impaired gesture pantomime and near-normal performance on gestures with tool in hand, the integrity of her performance on recognition tasks with tools, 3 Note that on some accounts BG’s mild right neglect is attributable to a deficit in egocentric coding for positions in the right hemispace (see, e.g., Buxbaum & Coslett, 1994).

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FIG. 4. A schematic of the praxis system explicitly incorporating a dynamic body schema which participates in both meaningful and meaningless gesture processing.

or the superiority of her meaningful as compared to meaningless imitation. Alternatively, it might be suggested that BG suffers deficits at the level of the ‘‘innervatory patterns’’ that form the final common pathway for both the direct and lexical routes. However, a deficit at this level would not explain BG’s impaired recognition of gestures pantomimed without tools or the relative superiority of meaningful as compared to meaningless gestures. The data from BG, then, suggest that the dual-route account requires modification or augmentation. Taken together, the evidence suggests that BG’s deficits in gesture pantomime, recognition, and imitation result primarily not from gesture representation integrity, access, or egress, but from deficits in dynamic coding of the intrinsic positions of the body parts of self and others. Figure 4 provides a schematic of a model of the praxis system incorporating this dynamic representation. Note that this representation, which we have termed the ‘‘body schema’’ in agreement with other contemporary investigators (e.g., Parsons, 1994) is the substrate for both the ‘‘lexical’’ and ‘‘direct’’ routes in that it instantiates the procedures used to calculate and update the dynamic positions of the body parts relative to one another in all contexts; the ‘‘lexical’’ route differs only in the availability of augmentative support from stored representations. We might speculate that the stored portion of the gesture representation contains only the information critical in distinguishing one particular learned movement from another, whereas procedures computed on-line add information about particular joint angles, hand aperture, and orientation, i.e., the features that render a given gesture precisely appropriate for a particular context. For example, the stored portion of a ‘‘hammering’’ gesture might

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include a broad oscillating movement at the elbow joint and a hand grip in the ‘‘clench’’ position, whereas the ‘‘flexible’’ features derived on-line in response to the environment might include shoulder angle (appropriate for hammering on a vertical vs horizontal surface), oscillation amplitude and frequency (appropriate for driving a large vs small nail), and clench size (appropriate for holding a large vs small hammer). The on-line computations may constitute the procedures and routines (‘‘schemas’’) that form the building blocks of learned gesture. Note that dynamic information about the position of body parts relative to one another remains the substrate for both the stored (‘‘lexical’’) and on-line (‘‘nonlexical’’) features of the gesture. In other words, the critical assumption is that output to the motor system is embedded in intrinsic spatial coordinates defined by the body schema. In this model, then, the procedures involved in intrinsic spatial coding of the body positions of self and others should not be viewed merely as an elaboration of the direct route. In gesture-imitation and -comprehension tasks, specification of the actions of self and others in a common system of body-centered coordinates decreases the computational demand on spatial transformation procedures (Mussa Ivaldi, Morasso, & Zaccaria, 1988; Morasso & Sanguineti, 1995). In movement production tasks, accurate specification of the dynamic relative positions of body parts is essential when extrinsic egocentric coding (i.e., coding of positions of body parts with respect to objects in the environment) cannot be used, as is the case in gesture pantomime tasks performed without objects. Thus, BG’s deficits in intrinsic spatial coding affect all tasks requiring the relative positioning of body parts in space over time or recognizing the body positions of others. Because the system is interactive, support from stored tool and/or gestural information may augment the deficient body position coding, explaining BG’s relatively good performance on production, recognition, and imitation tasks in which such information is available. The language-based model of two distinct routes to praxis, while clearly explaining many forms of IM, cannot readily accommodate the pattern exhibited by BG because it does not consider the strong intrinsic relationship of ‘‘lexical’’ and ‘‘nonlexical’’ gesture representations. Contrary to the predictions of an account positing that deficits in IM necessarily stem from the integrity or accessibility of input and/or output gesture representations, the model clearly predicts that at least one subtype of IM patients will perform better in gesture production and in recognizing others’ gestures with tools than without and better in imitating meaningful as compared to meaningless gestures.4 Because the relationship of meaningful and meaningless gesture 4 We believe that there are indeed IM patients for whom gesture representation integrity or accessibility is deficient. For such patients, however, there should be diminished evidence of ‘‘top-down’’ support from stored representations, such that meaningful gestures are as impaired as meaningful gestures.

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imitation distinguishes apraxia attributable to a deficit in stored gesture access or integrity from that attributable to impairment in the ‘‘body schema’’ as we have used the term here, meaningless gesture imitation is an important component of the apraxia evaluation. Finally, given the SPECT scan evidence that the superior posterior parietal lobes are involved in patient BG, it is of note that according to Morasso and Sanguineti (1995), a likely site for the body schema is the posterior parietal cortex (PPC), and in particular, the superior PPC area 5. Area 5 is an area of confluence between somatosensory cortex (areas 1, 2, and 3), motor cortex (areas 4 and 6), and other areas of the PPC (area 7) involved in integrating external (egocentric) space and subcortical and spinal circuits; thus, it processes a number of peripheral and centrally generated inputs and is potentially able to synthesize these various inputs in active movements. Area 5 is also activated in anticipation of movement (Crammond & Kalaska, 1989) and is insensitive to load variations (Kalaska, Cohen, Prud’homme, & Hyde, 1990), suggesting that it codes the kinematic aspects of movement. These features of area 5 have been characterized as ‘‘ideal’’ for a motor planning subsystem that relies on a continually updated internal body schema (Morasso & Sanguineti, 1995). Notably, patients with corticobasal degeneration and Pick’s disease, two diagnoses under consideration for BG, have frequent involvement of the superior parietal lobes (e.g., Dick, Snowden, Northen, Goulding, & Neary, 1989; Fukui, Sugita, Kawamura, Shiota, & Nakano, 1996; Piccirilli, D’Alessandro, & Ferroni, 1990). This predicts that IM patients with superior parietal involvement should exhibit patterns of performance on meaningful and meaningless gesture tasks consistent with impairment of the body schema as we have outlined it here, and thus similar to the pattern demonstrated by BG.

Salute Wave bye Hitchhike Stop Come here

1. 2. 3. 4. 5.

Hand in ‘‘c’’, arm waved back ⫹ forth in front of head Hand clawed, rotate wrist side to side in front of face Pinkey up, hand back and forth beside head Palm down, fingers pointing to left (‘‘L’’), move L Fingers fanned, wrist shakes side to side, hand in front of face

Meaningless analogs 1. Arm up, hand clawed, up/down by head 2. Hand flip side/side, move arm forward 3. Fingers fanned, arm move forward/back 4. Fingers together, flat; thumb up, flip wrist 5. First clenched, ‘knock’ progressively rightward 6. Arm up, hand in ‘‘o’’, up and down near head 7. Tap thumb and forefinger together repeatedly 8. Hand in claw, shake elbow ⫹ wrist in front of face 9. Hand in ‘‘o’’, forefinger rapidly out then in once 10. Fingers fanned, hand up and down, wrist flips

1. 2. 3. 4. 5.

Meaningful gestures 1. Hammer 2. Scissors 3. Saw 4. Screwdriver 5. Pencil 6. Comb 7. Wind watch 8. Toothbrush 9. Flip coin 10. Fork

Vertical Vertical Vertical Vertical Vertical

Vertical Radial Radial Vertical Horizontal Vertic (head) Horizontal Vertical Horizontal Vertical

Vertical Vertical Vertical Vertical Vertical

Vertical Radial Radial Vertical Horizontal Vertic (head) Horizontal Vertical Horizontal Vertical

Plane

Elbow Wrist Elbow Elbow ⫹ wrist Wrist

Elbow Shoulder ⫹ elbow Shoulder ⫹ elbow Wrist Shoulder ⫹ elbow Shoulder ⫹ elbow Fingers Elbow ⫹ wrist Thumb Elbow ⫹ wrist

Elbow Wrist Elbow Elbow ⫹ wrist Wrist

Elbow Shoulder ⫹ elbow Shoulder ⫹ elbow Wrist Shoulder ⫹ elbow Shoulder ⫹ elbow Fingers Elbow ⫹ wrist Thumb Elbow ⫹ wrist

Joints

APPENDIX 1 Details of Spatiotemporal Characteristics of Meaningful and Meaningless Gestures

(arm ⫹ hand)

(arm) (hand) (arm) (hand) (hand) (hand) (fingers) (hand)

(arm ⫹ hand)

(arm) (hand) (arm) (hand) (hand) (hand) (fingers) (hand)

No Yes (hand) Yes (elbow) No Yes (hand)

Yes Yes Yes Yes Yes Yes Yes Yes No Yes

No Yes (hand) Yes (elbow) No Yes (hand)

Yes Yes Yes Yes Yes Yes Yes Yes No Yes

Oscillations

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APPENDIX 2 Praxis Scoring Guidelines

Gestures are scored dichotomously (correct/incorrect) in five categories: 1. Content Score as ‘‘0’’ only if another recognizable gesture is substituted for target gesture (e.g., substitution of hammer for saw). If content is scored ‘‘0,’’ remaining four categories are not scored. If subject receives ‘‘1’’ for content, score on the following. 2. Hand Posture Score as ‘‘0’’ if hand posture/grasp is unrecognizable, flagrantly incorrect, or only transiently correct (small fragment of total gesture with correct posture or grasp). Score ‘‘0’’ for ‘‘body part as object’’ (BPO) errors. Score as ‘‘1’’ if posture is correct or subtly incorrect (e.g., hand aperture slightly too big or small; wrist angle slightly incorrect). 3. Arm Posture/Trajectory Score as ‘‘0’’ if arm posture and/or trajectory [e.g., joint angles, plane of movement relative to body/environment (e.g., side to side instead of back and forth)], shape of movement (e.g., circular instead of linear) are flagrantly incorrect or only transiently correct (small fragment of total gesture with correct posture). Score as ‘‘1’’ if both arm posture and trajectory are correct or if arm posture and/or trajectory are subtly incorrect (e.g., elbow slightly too bent; trajectory at slight angle relative to what is appropriate; shape of movement slightly distorted. 4. Amplitude Score as ‘‘0’’ if size of movement is clearly too large or too small (e.g., ‘‘sawing’’ with small ‘‘scratching’’ movement) or if size is only transiently correct (e.g., small fragment of total gesture with correct amplitude). Score as ‘‘1’’ if size is correct or subtly too large or too small (e.g., slight ‘‘overshoot’’ or ‘‘undershoot’’ in movement amplitude). 5. Timing/Frequency Score as ‘‘0’’ if speed of movement is flagrantly too fast or slow and/ or if number of cycles of movement is flagrantly too few or many (e.g., ‘‘flipping’’ coin four times in succession; ‘‘scissoring’’ only once). Score as ‘‘1’’ if speed of movement is subtly too fast or slow and/or if frequency is subtly inappropriate (e.g., flipping coin twice; scissoring only twice).

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