learning of grasp control in children with hemiplegic cerebral palsy

Learning of graspcontrol in childrenwith hemiplegiccerebral palsy

Susan V Duff* EdD PT OT CHT;Andrew M Gordon PhD, Department of BiobehavioralSciences, Teachers College, Columbia University, New York, USA.

*Correspondence to first author at Shriners Hospitals for Children, 3551 N Broad Street, Philadelphia, PA 19140, USA.E-mail: [email protected]

This study examined whether children with hemiplegiccerebral palsy (CP) have anticipatory control of fingertipforces during lifts of familiar objects, and what type ofpractice (blocked or random) best enhances the retention ofanticipatory control during lifts of novel objects. Eighteenchildren with hemiplegic CP (7 females, 11 males; 7 to 14years of age, mean age 10 years, SD 1.8) and 18 age-matchedtypically developing children (8 males, 10 females; mean age10.4 years, SD 1.7) participated in the study. In the firstexperiment the children lifted familiar objects of variousweights and sizes five times each, while the vertical lifting(load) force was measured. Most participants demonstratedhigher rates of load force increase for heavier (and larger)objects already during the first lift, indicating anticipatorycontrol. Furthermore, the load force rates generally weresimilar across the five lifts for each object, suggesting thatthey had stable representations of the objects’ properties. Inthe second experiment children lifted three novel objectsvarying in weight (but identical in volume) 27 times each, ineither a blocked or a random order, followed by nineimmediate and nine delayed (24 hours) retention trials.Blocked practice resulted in greater differentiation of theforce rates between objects during acquisition than didrandom practice. Both practice schedules resulted in similarretention. These findings suggest that children withhemiplegic CP have a priori internal representations used foranticipatory force scaling with familiar objects. Furthermore,the results indicate that these children can form and retaininternal representations of novel objects for anticipatorycontrol, irrespective of the type of practice scheduleemployed. Thus, clinically based practice sessions thatincorporate lifts with novel objects may enhance anticipatoryforce scaling and related prehensile function in children withhemiplegic CP.

Children with hemiplegic cerebral palsy (CP) have unilateralprehensile dysfunction as a consequence of lesions in thesensorimotor cortex and corticospinal tract (Brown et al.1987, Uvebrant 1988, Yokochi et al. 1992). These childrenoften have irregular prehension patterns, weakness, spasticity,incomplete finger fractionation, and sensory disturbances(Lesny et al. 1993, Yekutiel et al. 1994, Gordon and Duff1999b; Krumlinde-Sundholm and Eliasson 2002). Childrenwith CP also have impairments in fingertip force control andtiming during object manipulation (Eliasson et al. 1991, 1992,1995; Gordon and Duff 1999a; Eliasson and Gordon 2000).Among these impairments, they exhibit a deficit in anticipato-ry control, which is used to scale the grip (normal) and load(tangential) forces based on internal representations of anobject’s physical properties (Johansson and Westling 1984,1987, 1988; Gordon et al. 1993). Unlike typically developingchildren (Gordon 2001), children with hemiplegic CP oftenuse a default rate of force increase regardless of an object’sproperties (Eliasson et al. 1992, 1995; Gordon and Duff1999a). This lack of anticipatory control can contribute totheir prehensile difficulties. Given extended practice, thesechildren can develop anticipatory control during the manipu-lation of novel objects (Eliasson et al. 1995, Gordon and Duff1999a), but it is not known whether such behavior can beretained and what type of practice is most beneficial.

Children and adults encounter a range of practice condi-tions by engaging in playful or purposeful motor acts. Classiclearning studies on healthy adults have revealed a dichotomybetween random and blocked practice schedules (e.g. Sheaand Morgan 1979) whereby, during training, blocked prac-tice leads to better performance, but random practice resultsin better retention (Lee and Magill 1983, Gabriele et al. 1987;see Wulf and Shea 2002 for review). In typically developingchildren, blocked or mixed practice may be better for sometasks (Del Rey et al. 1983, Pigott and Shapiro 1984) and agegroups (see Wulf and Shea 2002), whereas random practicemay be better for others (Pollock and Lee 1997).

Anticipatory control of fingertip forces does not requirethe learning of a new task structure; rather, it requires theforces to be parameterized. Parameter learning (Magill andHall 1990, Tsutsui et al. 1998) is achieved by varying specificfeatures, such as movement time or force, to match con-straints without altering the basic task structure. The type ofpractice most beneficial for parameter learning may differfrom task learning. Magill and Hall (1990) proposed thatrandom practice would not be advantageous for parameterlearning, although recent evidence does not support thisproposal (Sekiya et al. 1994, 1996; Wright and Shea 2001).

Few studies have examined parameter learning in chil-dren with CP. Neilson and McCaughey (1982) found thatadults with CP improved their suppression of involuntarymuscle activity during passive movement and increased vol-untary contractions after practice. They could also reduceextraneous muscle activity without altering their force pro-duction (Neilson et al. 1990). Valvano and Newell (1998)found that, after a blocked practice schedule over several ses-sions, children with CP retained the ability to grade isometricgrip force (using on-line visual feedback) after a five-daydelay. We (Gordon and Duff 1999a) also found that within asingle session of extended blocked practice, children withhemiplegic CP improved their ability to scale fingertip forcesto the weight and texture of novel objects, although we did

746 Developmental Medicine & Child Neurology 2003, 45: 746–757

Grasp Control in Children with Hemiplegic Cerebral Palsy Susan V Duff and Andrew M Gordon 747

not test the effect of random practice or measure retention.Although individuals with CP can learn to parameterizemovements, it is not known whether they retain fingertipforce scaling for novel objects after extended practice andwhich practice conditions best promote learning. Also, it isnot known whether they can use anticipatory force scalingfor lifts of familiar objects based on previous experience.

The present study examined learning of fingertip forcescaling during the grasping and lifting of both familiar andnovel objects. The first experiment examined whether chil-dren with hemiplegic CP have anticipatory control for famil-iar objects of different weights and whether they can use sizecues to estimate weight for anticipatory control. We hypothe-sized that after years of contact with familiar objects, theywould display appropriate anticipatory control. In the sec-ond experiment, we examined whether these children couldacquire anticipatory control for novel objects of variousweights given extended practice with the involved hand, andwe also investigated which type of practice (blocked or ran-dom) best facilitated learning (as measured by retention). Itwas hypothesized that random practice would enhancelearning of anticipatory control better than blocked practice.

MethodPARTICIPANTS

Eighteen children with hemiplegic CP (7 females, 11 males;7 to 14 years; mean 10 years, SD 1.8; Table I) and 18 age-matched typically developing children (controls; 8 males, 10females; mean 10.4 years, SD 1.7) participated in Experiments Iand II. This age group was selected because typically devel-oping children approximate the grasping behavior of adultsby 6 to 8 years of age (Forssberg et al. 1991, 1992, 1995;

Gordon et al. 1992). The children were recruited from pri-vate and public schools in the area. Before participation,each child was screened individually for eligibility. All partici-pants could grasp and lift a 600g object using a precision gripor lateral pinch pattern, follow task directions, and scoredwithin 2SD on the Kaufman Brief Intelligence Test duringthe initial screening (Kaufman and Kaufman 1990). Childrenwere excluded if they had any upper-extremity anomalies,uncontrolled seizures, or significant visual deficits. Informedconsent was obtained from all participating children andtheir parents. The study was approved by the Teachers College,Columbia University Institutional Review Board.

APPARATUS

Multi-axial force transducers (ATI Industrial Automation, Apex,NC, USA) were used in both Experiments I and II. Each transduc-er measured two orthogonal force components, normal (grip)and tangential (load; 0.025N resolution). For Experiment I,familiar objects were lifted off a plastic plate that covered a sin-gle force transducer resting horizontally on its side on the table(resembling a scale; Fig. 1a). The load force was measuredfrom the force transducer as the vertical lift of the object wasinitiated. For Experiment II, objects of three different shapeswere attached separately to a grip device (Fig. 1b), equippedwith two parallel force transducers located under two grip sur-faces (4.5cm diameter, 4.4cm apart), covered with 200-gritsandpaper. The grip and load forces were measured from theparallel force transducers. In both experiments an electromag-netic position–angle sensor (Polhemus Fastrack, Colchester,VT, USA), secured to each object, measured the object’s verticalposition (about 0.08cm accuracy) and roll (0.15° accuracy).The force and position signals were sampled at 400Hz and

Table I: Description of participants

Group Age (y:m) Sex Non-dominant Practice Spasticity Pinch Pressure Two-point Stereognosis Manual

or involved schedule (0–4)a strength sensitivity discrimin. (nr correct/8)b dexterity(s)b

hand (kg)b (log10

F, mg)b (mm)b

CP 7:7 F Left Random 1 1.5 2.44 3 3 73CP 7:9 M Right Random 1 3.0 2.83 14 0 547CP 8:2 M Right Random 1 1.5 3.61 3 6 231CP 9:0 M Left Random 1 3.0 2.83 3 2 217CP 9:11 M Left Random 2 2.0 2.36 7 0 457CP 9:11 F Right Random 1.5 2.5 1.65 2 7 125CP 11:7 F Right Random 1 3.5 2.36 2 5 48CP 12:6 M Left Random 1 0.5 3.61 5 1 151CP 12:9 F Left Random 1.5 2.0 2.83 4 8 103CP 7:11 M Right Blocked 1 1.0 3.61 6 1 433CP 8:7 F Right Blocked 1 1.5 3.61 10 0 201CP 9:4 M Left Blocked 0 2.5 2.44 3 8 105CP 9:7 M Left Blocked 1 3.0 2.83 6 4 91CP 10:3 F Right Blocked 1 3.0 4.08 6 1 272CP 10:3 M Left Blocked 2 1.5 3.61 15 0 42CP 11:4 M Right Blocked 1 1.5 2.44 3 6 135CP 11:11 F Left Blocked 2 3.5 4.17 15 0 379CP 13:2 M Left Blocked 1 3.5 2.83 4 3 97Control 10:5 4F, 5M Left Random 0 4.0 2.36 2 8 44Control 10:3 6F, 3M Left Blocked 0 3.6 2.44 2 7 39

a Elbow flexor spasticity measured using the Modified Ashworth Scale (Bohannon and Smith 1987) ranging from zero points as normal to 4 points as severe spasticity. bNormative values for clinical tests are available: Pinch strength (Mathiowetz et al. 1986); Pressure sensitivity (Bell-Krotoski et al. 1995); Two-point discrimination (Louis et al. 1984); Stereognosis (Ayres 1989); Dexterity (Taylor et al. 1973).

120Hz, respectively, with a flexible data acquisition and analy-sis system (SC/ZOOM; Umeå University, Sweden).

PROCEDURE

Each child was tested with standard clinical assessments(Table I), which included sensibility (pressure sensitivity, two-

point discrimination), stereognosis, pinch strength, manualdexterity, and spasticity (see Gordon and Duff 1999b). Thesewere performed on the non-dominant hand of the controlsand the involved hand of the children with hemiplegic CP.

Each participant washed his or her hands before participa-tion. They sat in a chair with a firm back support in front of atable adjusted to allow the forearm to be parallel to the tablesurface (elbow flexed to 90°) and aligned with the shoulder.After an auditory cue, participants reached forward and lift-ed, at a preferred pace, familiar (Experiment I) and novel(Experiment II) objects placed directly in front of their hand(50% of arm’s length) 6cm off the table in alignment with anadjacent vertical marker. Each object was held in the air forseveral seconds and then replaced on the support surface.

The children with hemiplegic CP lifted the objects withtheir involved hand and controls with their non-dominanthand, because each are typically used less frequently. To min-imize fatigue all participants were given a 1-minute rest every25 lifts, or on request.

Experiment I: familiar objects

The aim of the first part of the experiment was to determinewhether children with hemiplegic CP have anticipatory con-trol of the required load forces based on the weight of famil-iar objects. The four objects were: a chalkboard eraser (25g),a videotape within a cardboard holder (210g), a 355ml can ofsoda (390g), and a 473ml lemonade bottle (720g; Fig. 1a).The aim of the second part of the experiment was to deter-mine whether these children could use object size to esti-mate weight for anticipatory control. To examine this, thethree glue bottles lifted were small (36ml, 50g), medium(118ml, 145g), and large in size (226ml, 275g; Fig. 1a). Allobjects were chosen on the basis of observations of typicalclassroom tasks and interviews with school-aged childrenand their parents, as well as pilot data.

Before starting the experiment, all children rated the fre-quency with which each object had been previously lifted(with each hand) on a scale of 1 to 4 (1=never, 2=rarely,3=sometimes, 4=frequently) to verify that they had priorexperience lifting each object and to compare the lift fre-quencies with the force scaling data as appropriate. On aver-age, all of the objects scored 3 to 4 for all children.

After a demonstration, participants grasped each objectwith a preferred prehension pattern and lifted it off the forcetransducer five times (the order was counterbalanced acrossparticipants).

Experiment II: novel objects

The aim of Experiment II was to examine the acquisition andretention of anticipatory control in children with hemiplegicCP during lifts of novel objects (Fig. 1b). Three novel objectsof various weights and shapes (200g cylinder, 400g pyramid,and 600g cube) were constructed and separately attached tothe grip device (acting as a handle). These shapes were cho-sen to give the participants tangible geometric properties toidentify the objects and to assist in the formation of aninternal representation for each of them. The objects weredesigned to be of the same volume (300ml) and color (red)to avoid size–weight illusions (Charpentier 1891; Gordon etal. 1991a,b) or color–weight illusions (Pinkerton andHumphrey 1975, Shick and Plack 1975), which can influenceperformance.


Figure 1: Experimental set-up and force/position signals.(a) Familiar objects employed in Experiment I included

chalkboard eraser (25g), videotape (210g), 355ml soda can

(390g), 473ml lemonade bottle (720g), and three sizes of glue

bottles (small 36ml, medium 118ml, and large 226ml).

These objects were lifted off a force transducer placed on its

side. (b) Three novel objects from Experiment II attached to a

grip device equipped with two parallel force transducers (as

seen attached to pyramid). Bottom of this grip instrument

slid into a slot on top of each object. Objects included a

cylinder (200g), pyramid (400g), and cube (600g). Position

sensor was secured to each familiar and novel object before

lifts. (c) Traces from a control represent, from top to bottom:

grip force from thumb (th) and index (ind) and load force

and their derivatives; position of object; and acceleration of

object during lift. Traces are aligned at onset of load force,

and grip and load force rates are shown with use of a +20-

point numerical differentiation. Anticipatory scaling

parameters: (i) peak grip force rate; (ii) peak load force rate;

(iii) peak acceleration after lift-off.

c

a b

i

ii

iii

Glu

e

Soda

Lemonade

Videotape

Eraser

4N

4N

15N/s

3N

20N/s

200cm/s2

3cm

250ms

Grip Force (th)

Grip Force (ind)

Grip Force Rate

Load Force

Load Force Rate

Position

Acceleration

The participants were randomly assigned to the blockedor random practice group; there were nine children with CPand nine controls in each group. The children lifted eachobject with the grip device attached by using a precisiongrip, a three-jaw chuck (three-fingered pinch) or a lateral(thumb to lateral index) pinch, because grip pattern does notsignificantly influence anticipatory control (Gordon and Duff1999a). However, each child used a consistent prehensionpattern throughout the study. During the acquisition phase,each shape (cylinder, pyramid, or cube) was lifted 27 times in

either a blocked or random order (81 total lifts). The order ofblocked practice was counterbalanced for object shape. Forthe random practice schedule, each of the three shapes waslifted three times in a random order within each block ofnine lifts. An immediate retention test of nine lifts (three foreach shape) was conducted 5 minutes after acquisition. Adelayed retention test of nine lifts (three for each shape) wasconducted 24 hours later. All retention lifts were performedin a random order because random practice closely approxi-mates natural variable environments.


Figure 3: Mean ± standard

error of the mean (SEM) load

force rates and acceleration

after lift-off employed for

eraser (circles), videotape

(triangles), soda can

(squares), and lemonade

bottle (diamonds) during

each of five trials across all

control children (left) and

children with hemiplegic

CP (right).

Figure 2: Load force, load

force rate, position, and

acceleration after lift-off

from a representative control

participant (left) and child

with hemiplegic CP (right)

during first lift of each

familiar object (weight

group): eraser, videotape,

soda can, and lemonade

bottle. Traces are aligned at

onset of load force.

Controls CP

Load Force

Load Force Rate

Position

Acceleration

4N

10N/s

6cm

150cm/s2

250ms

Load

For

ce R

ate

(N/s

)A

ccel

erat

ion

(cm

/s2 )

Controls CP

Trial Trial

80

60

40

20

0250

200

150

100

50

01 2 3 4 5 1 2 3 4 5

Lemonade - 720gSoda - 390gVideo - 210gEraser - 25g

DATA ANALYSIS

The data were analyzed with SC/ZOOM. Because higher ratesof force increase are typically used to lift heavier (larger)objects than lighter (smaller) ones, the rates of force increase(see peak labeled [ii] in Fig. 1c) were measured by determin-ing the maximum or the first peak after a steady increase inload force above a 0.1N threshold. The acceleration after lift-off (peak labeled [iii] in Fig. 1c) was used as an outcome mea-sure of anticipatory control to determine whether theperformance remained similar across consecutive lifts. Theuse of transducers as contact surfaces in Experiment IIallowed the additional measurement of grip force and gripforce rate (peak labeled [i] in Fig. 1c). In Experiments I and II,trials were excluded if a lift was attempted but contact was lostor if values exceeded 3SD from the mean. This resulted in theexclusion of 1% of individual trials from Experiments I and II.

In Experiment I each dependent variable was evaluated byanalysis of variance (ANOVA) using two designs with repeat-ed measures on the last two factors: (a) a 2 (group: CP versuscontrols) × 4 (object weight: eraser, video tape, soda can,lemonade bottle) × 5 (trials); and (b) a 2 (group) × 3 (objectsize: small, medium, large) × 5 (trials). For Experiment II,dependent variables during acquisition and retention phas-es were evaluated by using a 2 (groups) × 2 (practice sched-ule: random versus blocked) × 3 (object weight) ANOVA withrepeated measures on the last factor. The additional repeat-ed-measures factor for acquisition data was nine blocks ofthree trials, and for retention data it was immediate versusdelayed tests (blocks of three trials). Retention of anticipa-tory control was also analyzed by using only the first trial(instead of the block of three trials). Statistical evaluationsused a 0.05 probability level. Newman–Keuls post-hoc

comparisons were performed as appropriate.

ResultsEXPERIMENT I: FAMILIAR OBJECTS

The findings indicated that all participants had anticipatorycontrol of load forces when lifting familiar objects. Figure 2shows the superimposed load force, load force rate, posi-tion, and acceleration during the first lift of the four familiarobjects (25g eraser, 210g videotape, 390g soda can, 720glemonade bottle) for a control and a child with hemiplegicCP. The load force rates were highest for the heaviest object(lemonade bottle) and lowest for the lightest object (eraser).

Figure 3 shows that these participants were representa-tive of all participants (p<0.01 in both participant groups).The force scaling displayed during the initial lifts suggeststhat all participants have a priori internal representationsfor the familiar objects. Yet the load force rates for the fourobjects were slightly higher and more differentiated forcontrols than the children with CP (but p>0.05). The loadforce rates remained similar (p>0.05) across the five trialsfor all objects except the lemonade bottle, which showed anincrease in rate with practice (p<0.05 for both groups).Interestingly, this object reportedly had been lifted the leastby all participants before this experiment.

Unlike in adults (Gordon et al. 1993), peak accelerationvaried according to the object weight (p<0.01) and was high-er for the children with CP than for controls (p<0.05), espe-cially for lifts of the soda can.

Figure 4 displays the mean load force rates for lifts of thethree glue bottles (small 50g, medium 145g, large 275g). Thecontrols exhibited higher force rates for all sizes of gluebottle (p<0.01) and greater differentiation between them


Figure 4: Mean ±

standard error of the

mean (SEM) load force

rates and acceleration

after lift-off employed for

small (circles), medium

(triangles), and large

(squares) glue bottles

during each of five trials

across all control children

(left) and children with

hemiplegic CP (right).

50

40

30

20

10

0

Load

For

ce R

ate

(N/s

)

1 2 3 4 5 1 2 3 4 5

Trial Trial

200

150

100

50

0

Acc

eler

atio

n (c

m/s

2 )

Controls CP

across all trials (p<0.01) than the children with CP. Loadforce rates remained stable across all five lifts for both partici-pant groups (p>0.05).

The accelerations after lift-off (Fig. 4) were similar acrossall three sizes of glue bottles (p>0.05), yet they were general-ly higher for the children with CP (p<0.05). The accelera-tions remained relatively consistent across all five trials forboth groups (p>0.05).

In summary, all participants exhibited anticipatory controlduring the first lifts of familiar objects. The general stabilityacross practice suggests that both groups of children have sta-ble internal representations of the weight of the familiarobjects lifted that they used for anticipatory force scaling, andthat they could use size cues to estimate weight for anticipatorycontrol.

EXPERIMENT II: NOVEL OBJECTS

Acquisition

With extended practice, the participants improved anticipa-tory force scaling for novel objects of various weights, partic-

ularly under blocked practice. Figure 5 shows superimposedtraces from lifts of the three novel objects (200g cylinder,400g pyramid, 600g cube) for the first and ninth acquisitionblocks for a control and for a child with hemiplegic CP fromeach practice group. The force rates from the representativeparticipants were not well scaled in the first block of trials foreither practice group, as seen by the similar amplitudes ingrip and load force rate between objects. However, by theninth block both practice groups displayed greater differen-tiation in force rates; the highest rates were exhibited for theheaviest object (cube) and the lowest rates for the lightestobject (cylinder).

Figures 6 and 7 show the force rates for each block ofthree trials for each object across acquisition. Grip forcerate differed for object weight between the practice groupsacross acquisition, as indicated by an object weight×prac-tice interaction (p<0.001) and a block×practice interaction(p<0.01). With extended practice the difference in rate forobject weight increased, as shown by a weight×block inter-action (p<0.01 in all cases). Post-hoc tests on grip force


Figure 5: Grip force (averaged from thumb and index finger), grip force rate, load force, load force rate, position, and

acceleration from a representative control participant and child with hemiplegic CP during one lift with the cylinder (dashed

lines), pyramid (dotted lines), and cube (solid lines), from block one, block nine, and delayed retention for random practice

group (top), and blocked practice group (bottom). Traces are aligned at onset of load force.

Control CP

Block 1 Block 9 Block 1 Block 9Delayedretention

Delayedretention

RANDOM

BLOCKED

6N

15N/s

5N

15N/s

5cm

100cm/s2

6N

15N/s

5N

15N/s

5cm

100cm/s2

300ms

Grip Force

Grip Force Rate

Load Force

Load Force Rate

Position

Acceleration

Grip Force

Grip Force Rate

Load Force

Load Force Rate

Position

Acceleration

rate revealed that for both groups differentiation wasgreater in the ninth block than in the first block (p<0.01)and greater by the ninth block for those who underwentblocked versus random practice (p<0.05). For load forcerate, an object weight×block×practice interaction and aweight×group×practice interaction (both p<0.01) werefound. Post-hoc analyses of load force rate revealed thatalthough the differentiation between objects was present inboth practice groups by the ninth block (p<0.05), it wasgreater for participants who underwent blocked practice(p<0.001) and was greatest for controls (p<0.001). Resultssuggest that blocked practice led to better anticipatory con-trol during acquisition than random practice for both partici-pant groups.

Figure 8 shows that the peak acceleration after lift-off dif-fered between novel objects of various weights (p<0.01).Post-hoc analyses revealed that accelerations were greaterduring the initial block of acquisition for those who under-went random versus blocked practice (p<0.01), especiallyfor lifts with the cylinder. Controls who underwent randompractice displayed greater similarity in acceleration after lift-off between objects by the ninth block (p>0.05), whereas thechildren with CP continued to display differences (p<0.01),

particularly between the lightest object (cylinder) and thetwo heavier objects. Thus, the control group demonstratedan improvement in control of object acceleration after lift-offwith extended random practice, whereas the children withCP did not. Despite an improvement in control, the accelera-tions between the different objects were more similar(p>0.05) during acquisition for all children in the blockedpractice group than in the random practice group.

Retention

At the end of acquisition the blocked practice group dis-played greater differentiation in grip and load force ratebetween objects than the random practice group. However,as illustrated by the representative participants in Figure 5,all participants exhibited similar (reduced) differentiation inforce rate on the delayed retention test. Figures 6 and 7 fur-ther illustrate that the large differentiation in grip and loadforce rate found in the ninth block for the blocked practicegroup was not maintained at immediate or delayed retention(similar rates at retention).

Figures 6 and 7 retention blocks (main graph depictingmean of three trials) indicate that significant differences forobject weight were found for grip (p<0.01) and load



error of the mean (SEM)

grip force rate across nine

blocks of acquisition,

immediate retention (IR),

and delayed retention (DR)

during lifts with cylinder

(circle), pyramid (triangle),

and cube (square) for


children with hemiplegic

CP (right). Insets are mean

(SEM) single trials from

first trial at immediate

retention and first trial at

delayed retention.

Controls CP

Random

Blocked

Grip

For

ce R

ate

(N/s

)

50

40

30

20

10

0

50

40

30

20

10

01 2 3 4 5 6 7 8 9 IR DR 1 2 3 4 5 6 7 8 9 IR DR

Blocks Blocks

Grip

For

ce R

ate

(N/s

)

40

20

0Grip

For

ce R

ate

(N/s

)

40

20

0

40

20

0

40

20

0

Grip

For

ce R

ate

(N/s

)

Grip

For

ce R

ate

(N/s

)

First Trial First Trial

IR DRFirst Trial

IR DRFirst Trial

IR DRFirst Trial

IR DRFirst Trial

Grip

For

ce R

ate

(N/s

)

(p<0.01) force rates. The retention inset graphs (represent-ing first trials only) show that the significant differencesbetween object weight were found already on the first trialfor grip (p<0.01) and load force rate (p<0.01) at immediateand delayed retention. Post-hoc tests reveal that there was agreater differentiation in grip force rate at delayed retentionfor both types of practice across both participant groups(p<0.001). This suggests that the force scaling was learnedby both participant groups to a similar extent regardless ofthe type of practice employed during acquisition, and to agreater extent at delayed retention. For load force rate aweight×group×practice interaction was found (p<0.05).Post-hoc tests revealed that there was greater differentiationin load force rate at delayed retention among controls forthose who underwent blocked practice and at immediateretention for children with CP who underwent random prac-tice (p<0.05).

To determine whether the perception of object size influ-enced performance at retention, a random subset of partici-pants (five controls and five children with hemiplegic CP)was interviewed after the experiments. Most children withCP perceived the pyramid (400g) to be the largest, followedby the cube (600g) and the cylinder (200g). Most controls

perceived the objects to be the same size. Interestingly, thegrip force rates at immediate retention (Fig. 6, inset graphs)seemed to be scaled in accordance with these perceptions.The children with CP tended to use similar force rates for thepyramid and the cube (i.e. the size perception might havebiased their performance) whereas the controls typicallyscaled the forces appropriately.

Figure 8 shows peak acceleration after lift-off for theretention blocks (main graph) and the first trial (insetgraphs). For the retention block, an object weight×block(p<0.01) interaction was found. Post-hoc tests revealedincreases in acceleration from immediate to delayed reten-tion for lifts of the cube for controls (p<0.05) and childrenwith CP (p<0.05). For the first trials, an object weight× trial(p<0.01) interaction was found. Although post-hoc analysesrevealed that the accelerations generally became more simi-lar between trials (p<0.05) from immediate to delayedretention for both participant groups, this trend was not con-sistent across practice groups. There was not a main effect forpractice or a significant interaction involving practice sched-ule for either retention block or first trial. These findingsindicate that all children learned anticipatory force scalingregardless of the practice schedule followed.




load force rate across nine

blocks of acquisition,

immediate retention (IR),

and delayed retention (DR)

during lifts with cylinder

(circle), pyramid (triangle),

and cube (square) for


children with hemiplegic CP

(right). Insets show mean

(SEM) single trials from first

trial at immediate


delayed retention.

Blocked

Random

Controls CP

Load

For

ce R

ate

(N/s

)Lo

ad F

orce

Rat

e (N

/s)

Load

For

ce R

ate

(N/s

)Lo

ad F

orce

Rat

e (N

/s)

Load

For

ce R

ate

(N/s

)

50

40

30

20

10

0

50

40

30

20

10

01 2 3 4 5 6 7 8 9 IR DR 1 2 3 4 5 6 7 8 9 IR DR



Blocks Blocks

50

25

0

50

25

0

50

25

0IR DRFirst Trial

IR DRFirst Trial

IR DRFirst Trial

IR DRFirst Trial

50

25

0

Load

For

ce R

ate

(N/s

)

Clinical assessments and anticipatory control

The sensibility, strength, and dexterity tests were significant-ly different between the typically developing children andthe children with CP (all p<0.05). There was no significantdifference between children with CP in the blocked versusrandom practice groups (p>0.05), indicating that the lack ofdifferences between practice groups was not due to differ-ences in severity of CP.

DiscussionThe present results indicate that children with hemiplegicCP have a priori internal representations for the weight offamiliar objects and can use size cues to estimate weight foranticipatory control of grasping. Given extended practicethey can also acquire and retain internal representations ofnovel objects for anticipatory control, regardless of the typeof practice used. This suggests that it is the amount ratherthan the type of practice that is important.

INTERNAL REPRESENTATIONS OF FAMILIAR OBJECTS

The results from Experiment I support our hypothesis that,after years of manipulating objects, children with hemiplegic

CP acquire internal representations of familiar objects asobserved in healthy adults (Gordon et al. 1993). Internal repre-sentations of an object’s texture, shape, weight, and center ofmass are formed and updated through the somatosensory andvisual input gained during object manipulation (Johanssonand Westling 1984, 1988; Jenmalm and Johansson 1997; Salimiet al. 2000). Visual and haptic cues can also be used to retrievethese representations from memory for anticipatory control(Gordon et al. 1993, Jenmalm et al. 2000). Most of the expe-rience that participants had with the objects had been gainedwith the non-involved or non-dominant hand. Because antic-ipatory control was displayed during initial lifts with theinvolved/non-dominant hand and the performance was sta-ble for all trials, the internal representations had to be gener-alized across the hands, as found previously for healthyindividuals (Gordon et al. 1994, 1999) and children withhemiplegic CP (Gordon et al. 1999).

Although the children with CP had anticipatory control,their load force rates were not as well differentiated forobjects of various weights. The children with CP had betteranticipatory control during lifts of the one object varying insize, suggesting that the visual size cues might have been




acceleration after lift-off across

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more easily transformed into information used to scale theload force than the combination of size and density cues(Gordon et al. 1991a–c).

ACQUISITION OF ANTICIPATORY FORCE SCALING

Task complexity, learner attributes, and the amount of prac-tice are variables that can influence eventual learning (DelRey 1982, Shea et al. 1990, Van der Weel et al. 1991, Proteauet al. 1994). The task in Experiment II did not require partici-pants to learn how to grasp and lift objects. Rather, it involvedparameter learning, whereby participants learned to scale fin-gertip forces during lifts, making an association between thenovel objects’ shapes and weights. Although force control hasbeen examined in children with CP (Neilson and McCaughey1982; Neilson et al. 1990; Eliasson et al. 1991, 1992, 1995;Valvano and Newell 1998; Gordon et al. 1999; Gordon andDuff 1999a,b), the effect of practice schedules on parameterlearning has not been reported. Consistent with most studiesof motor learning (e.g. Shea and Morgan 1979, Hanlon 1996,Pollock and Lee 1997) we found that blocked practice wasadvantageous during acquisition, as indicated by greater dif-ferentiation in force rates between objects and more similaraccelerations after lift-off.

RETENTION OF ANTICIPATORY FORCE SCALING

In contrast to our hypothesis that random practice wouldbetter enhance the learning of anticipatory force scaling(Sekiya et al. 1996, Lai et al. 2000), we found that both prac-tice groups retained anticipatory control. Thus, the type ofpractice did not differentially affect learning. These findingssupport the original hypothesis put forth by Magill and Hall(1990) that random practice would not have an advantageover blocked practice for parameter learning.

Despite the amount of practice provided (27 trials witheach object), the children with CP did not show the same levelof anticipatory control for novel objects as they did for familiarobjects. There are a few possible explanations for the incom-plete anticipatory control. First, the internal representationsof familiar objects for the children with CP were formed pri-marily from lifts with the non-involved hand, whereas lifts withnovel objects were performed only with the involved hand,which has mild sensibility impairments. The sensibility deficitsmight have led to incomplete internal representations of thenovel objects, as suggested by the strong relationship betweentwo-point discrimination and anticipatory control reportedpreviously (Gordon and Duff 1999b). However, even the con-trols (with intact sensibility) lacked good anticipatory con-trol during Experiment II. Thus, impaired sensibility mightnot completely account for our findings. The influence of visu-al perception on force scaling might be another possibleexplanation for the reduced force rate differentiation atimmediate retention for either group (Gordon et al. 1993). InExperiment II the objects all had the same color and volume.The lack of tangible object features other than shape mighthave restricted the ease with which participants associated agiven object with a weight (see Salimi et al. 2003). Even theshape cues might have been misleading because most of thechildren with CP interviewed, perceived the pyramid (whichwas taller) to be larger than the cube. Thus, size perceptionsmight have influenced their force output (see Gordon et al.1991a–c) during retention. Varying object density and sizemight have provided more meaningful clues to form stronger

internal representations of the objects.Finally, because number of trials (Shea et al. 1990) and level

of experience (see Wulf and Shea 2002) influence learning, itis conceivable that the 27 trials in Experiment II were insuffi-cient to allow the participants to form strong internal repre-sentations for these novel objects and for one type of practiceto have an advantage over the other. Additional trials or ses-sions might, therefore, be required to better enhance learning(retention) of anticipatory force scaling for novel objects withthe involved hand through a particular practice schedule.

The time (24 hours) and sleep between training and reten-tion testing might have aided memory consolidation (Karni etal. 1994, Shadmehr and Holcomb 1997), leading to greaterretention. Using positron emission tomography, Shadmehrand Holcomb (1997) confirmed that memory consolidationin participants who attempted to learn a novel internal modelfor an anticipatory reaching task was greater after a rest periodof at least 6 hours. The 24-hour delayed retention test mayhave allowed for a greater consolidation of anticipatory forcescaling acquired during practice.

CLINICAL IMPLICATIONS

Despite their prehensile limitations, the results of this studysuggest that extended practice lifting familiar objects in every-day life or novel objects, using either a blocked or a randompractice schedule, may promote anticipatory control with theinvolved hand in children with hemiplegic CP. However, toenhance learning of anticipatory control, the amount of prac-tice time should be much longer than used in this study. Withgreater anticipatory force scaling, prehensile skill, and thusefficient function, may be promoted. Such structured prac-tice forms the basis for intervention strategies such as con-straint-induced therapy (Taub and Crago 1995), whereby thenon-involved extremity is restrained and the involvedextremity is engaged in extensive practice (Charles et al.2001, Gordon and Charles 2003, Eliasson et al. 2003).

DOI: 10.1017/S0012162203001397

Accepted for publication 23rd July 2003.

Acknowledgements

This project was supported by a Dean’s grant from TeachersCollege, Columbia University, to SVD. The project was performed inpartial fulfillment for the requirements of a Doctor of Education atTeachers College, Columbia University, by the first author under theguidance of the second author. We wish to extend our gratitude toJeanne Charles, Ellen Godwin, Maria LaMadrid, Amy Shrank, andthe Physical and Occupational Therapists of the New York CityBoard of Education for assistance with recruiting participants, andto the parents and children who made this project possible. We alsothank Ann Gentile PhD, Terry Kaminski EdD, PT, and SteveSilverman PhD for helpful comments.

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XIV. IFTA World Family Therapy Congress organized by The International FamilyTherapy Association (IFTA) and theTurkish Association of Marital andFamily Therapy (AETD)

Istanbul, Turkey, on 24�27 March, 2004

The theme of the congress is 'Families in a time of GlobalCrisis'. Other themes include theory, clinical intervention andresearch on prevention, impact, healing and resilience offamilies.

The XIV. IFTA World Congress will ask questions about whathappens to families, children, parents and communities oncethe immediate crisis has passed. How do families cope withthe loss of loved ones, of country and community? Can healingpractices make a difference? What role does therapeutic helphave in providing an integrated approach which will effectregeneration and rebirth for the many millions affected bysuch events?

This congress will attempt to tackle this global themethrough a series of plenaries, sub-plenaries and workshops,which will involve participants in dialogues about theseuniversal themes.

FIRST DAY – model for understanding the impact of naturaland man made disastrous events on families and family life

SECOND DAY – effective intervention in family andcommunity life in a time of global crisis

THIRD DAY – helping families and communities developresilience, hope and empowerment

The deadline for the submission of abstracts is 1 November 2003.

For more information on how to submit an abstract, please visitwww.ifta2004.org/scientific/absSubmission.asp

Please visit the congress website by clicking to www.ifta2004.orgwhich is a source of information on the congress, the scientific andsocial program and of course your host city Istanbul.

We look forward to welcoming you!

Murat Dokur, MD (President, AETD; President of the Local Organizing Committee) Arnon Bentovim, MD, FRC Psych (President IFTA) Chana Winer, Ph.D (Past - President IFTA)

7th Annual Meeting of the Infantile Seizure Society

Announcement and Call for Papers

International Symposium on Neuronal Migration Disordersand Childhood Epilepsies – Clinical Manifestations,Pathomechanisms and Epileptogenesis

Date: April 16th (Fri) and 17th (Sat), 2004Venue: Conference Hall, Tokyo Women's MedicalUniversity, Tokyo, JapanAbstract deadline: January 15, 2004Contact: Dr Yukio FukuyamaChild Neurology Institute6-12-17-201 Minami-Shinagawa, Shinagawa-ku, Tokyo 140-0004, JapanTel: +81-3-5781-7680 Fax: +81-3-3740-0874e-mail: [email protected]: http://www.field.gr.jp/ISS (valid after October 1st)

learning of grasp control in children with hemiplegic cerebral palsy

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