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456 July/August 2008, Volume 62, Number 4 Effects of Task Instructions and Target Location on Reaching Kinematics in People With and Without Cerebrovascular Accident: A Study of the Less-Affected Limb KEY WORDS • environment • movement • stroke • task performance and analysis Keh-chung Lin, ScD, OTR, is Associate Professor and Chair, School of Occupational Therapy, College of Medicine, and Neurobiology and Cognitive Science Center, National Taiwan University, and Director, Division of Occupational Therapy, Department of Physical Medicine and Rehabilitation, National Taiwan University Hospital, Taipei. Ching-yi Wu, ScD, OTR, is Associate Professor, Department of Occupational Therapy and Graduate Institute of Clinical Behavioral Science, Chang Gung University, 259 Wen-hwa 1st Road, Kwei-shan, Taoyuan, Taiwan 33302; [email protected] Kwan-hwa Lin, PT, PhD, is Professor, Department of Physical Therapy, College of Medicine, National Taiwan University, Taipei. Chein-wei Chang, MD, is Professor, Department of Physical Medicine and Rehabilitation, National Taiwan University Hospital, Taipei. OBJECTIVE. We investigated how verbal instructions and target location interacted to influence reaching movement of the less-affected limb in participants with and without unilateral cerebrovascular accidents (CVAs). METHOD. Using a counterbalanced repeated-measures design, 26 people with CVA and 24 age-matched healthy people performed the reaching tasks under 4 conditions formed by the crossing of verbal instructions (speed and accuracy emphasis) and target locations (ipsilateral and contralateral to the performing hand). RESULTS. In the control groups, speeded instructions and ipsilateral reaches elicited significantly more preprogrammed movements than did accuracy instruction and contralateral reaches, respectively. Similar patterns of performance in response to task constraints were found in the CVA groups except for movement initiation in the right CVA group. CONCLUSION. Instruction and locations interacted to constrain reaching movements in both control and CVA groups. The combination of speeded instruction and ipsilateral reach may optimize movement performance of the less-affected limb in stroke patients. Lin, K.-C., Wu, C.-Y., Lin, K.-H., & Chang, C.-W. (2008). Effects of task instructions and target location on reaching kine- matics in people with and without cerebrovascular accident: A study of the less-affected limb. American Journal of Occupational Therapy, 62, 456–465. Keh-chung Lin, Ching-yi Wu, Kwan-hwa Lin, Chein-wei Chang O ccupationaltherapistsincorporatedifferenttypesoftaskconstraintsintoprac- ticescheduleswhendesigningtreatmentprogramsforpeoplewithcerebrovas- cularaccident(CVA;Mathiowetz&Bass-Haugen,2008;Pendleton&Schultz- Krohn,2006). Task constraintsrefertolimitationsimposedonpurposefulmovement (TromblyLatham,2008),whichmayfacilitatedesiredmovementorganizationin people with CVA (Newell, 1998; Shumway-Cook & Woollacott, 2007). Two generalsourcesoftaskconstraintsinthecontextofstrokerehabilitationhavebeen identified:augmentedinformation(e.g.,verbalinstructionsformovementprepara- tionandexecution)andphysicaldemandssuchastargetlocationandrelevanceof targettobereached(Lin,Wu,&Trombly,1998;Ma&Trombly,2004;Newell, 1998; Trombly & Wu, 1999; Wu, Trombly, Tickle-Degnen, & Lin, 2000). Appropriateintegrationofverbalinstructionandtargetlocationmaybeusedto optimize movement performance by people with CVA. This assumption awaits experimentalstudytoimproveknowledgeabouttheeffectsoftaskconstraintson movementorganizationduringgoal-directedreaching.Wedesignedthisstudyto investigate how verbal instruction and target location may interact to influence movementperformancebypeoplewithandwithoutCVA. Downloaded From: http://ajot.aota.org/pdfaccess.ashx?url=/data/journals/ajot/930098/ on 07/07/2018 Terms of Use: http://AOTA.org/terms

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456� July/August 2008, Volume 62, Number 4

Effects of Task Instructions and Target Location on Reaching Kinematics in People With and Without Cerebrovascular Accident: A Study of the Less-Affected Limb

KEY WORDS• environment• movement• stroke• task performance and analysis

Keh-chung Lin, ScD, OTR, is Associate Professor and Chair, School of Occupational Therapy, College of Medicine, and Neurobiology and Cognitive Science Center, National Taiwan University, and Director, Division of Occupational Therapy, Department of Physical Medicine and Rehabilitation, National Taiwan University Hospital, Taipei.

Ching-yi Wu, ScD, OTR, is Associate Professor, Department of Occupational Therapy and Graduate Institute of Clinical Behavioral Science, Chang Gung University, 259 Wen-hwa 1st Road, Kwei-shan, Taoyuan, Taiwan 33302; [email protected]

Kwan-hwa Lin, PT, PhD, is Professor, Department of Physical Therapy, College of Medicine, National Taiwan University, Taipei.

Chein-wei Chang, MD, is Professor, Department of Physical Medicine and Rehabilitation, National Taiwan University Hospital, Taipei.

OBJECTIVE. We investigated how verbal instructions and target location interacted to influence reaching movement of the less-affected limb in participants with and without unilateral cerebrovascular accidents (CVAs).

METHOD. Using a counterbalanced repeated-measures design, 26 people with CVA and 24 age-matched healthy people performed the reaching tasks under 4 conditions formed by the crossing of verbal instructions (speed and accuracy emphasis) and target locations (ipsilateral and contralateral to the performing hand).

RESULTS. In the control groups, speeded instructions and ipsilateral reaches elicited significantly more preprogrammed movements than did accuracy instruction and contralateral reaches, respectively. Similar patterns of performance in response to task constraints were found in the CVA groups except for movement initiation in the right CVA group.

CONCLUSION. Instruction and locations interacted to constrain reaching movements in both control and CVA groups. The combination of speeded instruction and ipsilateral reach may optimize movement performance of the less-affected limb in stroke patients.

Lin, K.-C., Wu, C.-Y., Lin, K.-H., & Chang, C.-W. (2008). Effects of task instructions and target location on reaching kine-matics in people with and without cerebrovascular accident: A study of the less-affected limb. American Journal of Occupational Therapy, 62, 456–465.

Keh-chung Lin, Ching-yi Wu, Kwan-hwa Lin, Chein-wei Chang

Occupational�therapists�incorporate�different�types�of�task�constraints�into�prac-tice�schedules�when�designing�treatment�programs�for�people�with�cerebrovas-

cular�accident�(CVA;�Mathiowetz�&�Bass-Haugen,�2008;�Pendleton�&�Schultz-Krohn,�2006).�Task constraints�refer�to�limitations�imposed�on�purposeful�movement�(Trombly�Latham,�2008),�which�may�facilitate�desired�movement�organization�in�people�with�CVA� (Newell,� 1998;�Shumway-Cook�&�Woollacott,� 2007).�Two�general�sources�of�task�constraints�in�the�context�of�stroke�rehabilitation�have�been�identified:�augmented�information�(e.g.,�verbal�instructions�for�movement�prepara-tion�and�execution)�and�physical�demands�such�as�target�location�and�relevance�of�target�to�be�reached�(Lin,�Wu,�&�Trombly,�1998;�Ma�&�Trombly,�2004;�Newell,�1998;� Trombly� &� Wu,� 1999;� Wu,� Trombly,� Tickle-Degnen,� &� Lin,� 2000).�Appropriate�integration�of�verbal�instruction�and�target�location�may�be�used�to�optimize�movement�performance�by�people�with�CVA.�This�assumption�awaits�experimental�study�to�improve�knowledge�about�the�effects�of�task�constraints�on�movement�organization�during�goal-directed�reaching.�We�designed�this�study�to�investigate�how�verbal� instruction�and� target� location�may� interact� to� influence�movement�performance�by�people�with�and�without�CVA.

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The American Journal of Occupational Therapy� 457

Task Instructions and Reaching Kinematics

One�of�the�noted�examples�of�task�constraints�in�biomechani-cal� analysis�of�movements�would�be� the� trade-off�between�speed� and� accuracy� in� goal-directed� reaching� (Duarte� &�Freitas,�2005;�Fitts,�1954).�On�the�basis�of�the�speed–accuracy�paradigm,�previous�studies�of�the�effects�of�instruction�involved�healthy�people�(e.g.,�Rival,�Olivier,�&�Ceyte,�2003)�and�clini-cal�populations�such�as�people�with�Parkinson’s�disease�(Rand,�Stelmach,�&�Bloedel,�2000).�Research�on�people�with�CVA�is�needed�to�determine�the�effects�of�task�instructions�on�reach-ing�performance�during�motor�tasks.�Such�research�will�pro-vide�information�relevant�for�task-specific�practice�of�motor�actions�important�for�daily�occupations.

One� theme� of� the� speed–accuracy� research� (Adam,�1992;�Fisk�&�Goodale,�1984;�Rival�et�al.,�2003)�is�the�use�of� temporal� and� spatial� instructions� to� study� the� speed–�accuracy�trade-off�of�reaching� in�pointing�movements.�In�this�situation,�target�characteristics�(e.g.,�target�size,�distance)�and�the�environment�remain�constant,�and�the�emphasis�on�speed�and�accuracy�is�varied�by�changing�the�verbal�instruc-tions�to�the�task�performer.�These�instructions�involve�reach-ing�for�a�target�as�quickly�as�possible�or�as�accurately�as�pos-sible.�Several�studies�involving�healthy�adults�(Adam,�1992;�Fisk�&�Goodale,�1984;�Rival�et�al.,�2003)�and�people�with�Parkinson’s�disease�(Rand�et�al.,�2000)�have�indicated�that�with�speed�instructions,�participants�initiated�faster�and�pro-duced�more�efficient�reaching�movements�with�greater�force.�These�findings�suggest�that�the�speed–accuracy�information�provided�by�verbal�instructions�can�direct�a�person’s�atten-tion�toward�the�temporal�or�spatial�aspect�of�the�reaching�movement.�The�speed–accuracy�instructions�thus�influence�the�motor�planning�and�strategies�used�to�perform�the�task�(Fasoli,� Trombly,� Tickle-Degnen,� &� Verfaellie,� 2002;�Hermsdorfer� et� al.,� 1996;� Ma,� Trombly,� Wagenaar,� &�Tickle-Degnen,�2004).�

Speed-emphasized�tasks�demand�more�efficient�perfor-mance�of�the�task�in�the�temporal�domain�than�do�accuracy-emphasized�tasks,�and�they�demand�a�shorter�time�to�com-plete� the� task� and� require� more� ballistic-like� or� more�continuous�movements.�The�more�ballistic�reaching�move-ments�depend�more�on�advanced�motor�programming�(i.e.,�more�preplanning�of�the�reaching�movement)�and�less�on�direct�sensory�feedback,�as�reflected�by�less�time�for�move-ment� initiation� (shorter� reaction� time� [RT]),�higher� effi-ciency�of�movement�execution�(less�movement�time�[MT]),�and�greater�smoothness�during�performance�(fewer�move-ment�units� [MUs];�Haaland,�Prestopnik,�Knight,�&�Lee,�2004;�Milner,�1992;�Trombly,�1992).�To�complete�the�task�more�quickly,�the�performer�needs�greater�force�or�impulse�

at�movement�initiation�to�quickly�bring�the�hand�to�the�tar-get.�The�greater�force�or�impulse�at�movement�initiation�can�be�reflected�by�a�higher�amplitude�of�peak�velocity�(PV;�Ma�et�al.,�2004).

Location ConstraintsThe� dimension� of� movements� studied� in� the� literature�related�to�the�speed–accuracy�instruction�is�limited�to�the�sagittal�plane.�It�remains�unclear�whether�those�effects�hold�true�in�other�spatial�planes.�In�addition,�target�location�is�another� important� constraint� to� consider� in�people�with�unilateral�CVA.�Previous�research�has�described�the�effects�of�the�laterality�of�the�target�position�on�movement�kine-matics�in�healthy�adults�(Fisk�&�Goodale,�1984;�Ghozlan,�1998;�Wu,�Lin,�Lin,�Chang,�&�Chen,�2005)�and�in�people�with�neurological� impairment� (Beer,�Dewald,�&�Rymer,�2000;� Castiello,� Bennett,� Bonfiglioli,� Lim,� &� Peppard,�1999;�Roy,�Kalbfleisch,�Bryden,�Barbour,�&�Black,�2000;�Trombly,�1993).�The�general�findings�suggest�that�ipsilat-eral reaches�(i.e.,�the�target�position�and�the�hand�used�to�reach�for�the�target�are�on�the�same�side)�were�more�efficient�in� movement� planning� and� execution� than� contralateral reaches (i.e.,�target�position�on�the�opposite�side�from�the�performing�limb).�Planning�and�execution�efficiency�were�reflected�by�RT�and�MT,�respectively.�Ipsilateral�reaches�are�also�more�preprogrammed�with�less�error�correction�(fewer�MUs),�more�forceful�(higher�PV),�and�more�accurate�than�contralateral�reaches.�The�information�on�targets�located�on�the�same�side�of�the�body�as�the�reaching�limb�is�processed�initially�in�the�same�hemisphere�that�controls�the�reaching�limb�(Barthelemy�&�Boulinguez,�2002).�The�advantage�for�reaches�made� into� the� ipsilateral� space�could�be�a�conse-quence� of� more� efficient� within-hemisphere� visuomotor�transmission�of�target�information�and�visual�feedback�from�the�reaching�limb�(Fisk�&�Goodale,�1984).�

One�alternative�explanation�for�the�ipsilateral�reaching�advantage�lies�in�biomechanical�factors.�Differences�between�ipsilateral�and�contralateral�reaches�could�be�accounted�for�by�differences�in�the�inertial�forces�operating�on�the�hand�for�movements�in�different�directions.�When�a�person�performs�abductive�movement�into�the�ipsilateral�space,�the�hand�path�direction�is�parallel�to�the�long�axis�of�the�upper�arm.�Such�ipsilateral�reaches�require�lower�inertial�loads�or�less�strength,�which�results�in�shorter�MT�and�higher�PV�than�contralat-eral�reaches,�in�which�the�hand�path�is�more�perpendicular�to�the�axis�of�the�upper�arm�(Carey,�Hargreaves,�&�Goodale,�1996;�Carey�&�Otto-de�Haart,�2001;�Trombly,�1993;�Wu�et�al.,�2005).�It�remains�unclear�whether�and�how�the�effect�of� location� constraint�may� interact�with� the� instructional�

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458� July/August 2008, Volume 62, Number 4

demand�to�constrain�targeted�movements�of�the�less-affected�limb�after�stroke.�

Study of the Less-Affected LimbAlthough�deficits�in�the�affected�limb�after�stroke�are�pro-nounced,�motor�deficits�may�also�appear�in�the�less-affected�limb� (Haaland� et� al.,� 2004;�Wetter,�Poole,�&�Haaland,�2005).�Reaching�movements�by�the�less-affected�limb�have�been�of� growing� interest� to� researchers� and�practitioners��(e.g.,� Hermsdorfer,� Blankenfeld,� &� Goldenberg,� 2003).�Therapists�working�with�people�with�stroke�often�teach�com-pensatory� strategies� using� the� less-affected� limb� for� fine�motor�activities�(Shumway-Cook�&�Woollacott,�2007).�In�addition,�recent�stroke�rehabilitation�literature�has�suggested�that�repetitive�training�involving�paired�movements�of�the�affected�and�less-affected�limbs�results�in�a�facilitation�effect�from�the�less-affected�limb�to�the�affected�limb�(Goble,�2006;�Whitall,�Waller,�Silver,�&�Macko,�2000).�Understanding�the�reaching�performance�of�the�less-affected�limb�in�response�to� task� constraints�may�provide� relevant� information� for�stroke�rehabilitation�that�involves�compensatory�training�of�the�less-affected�limb�or�practice�of�bilateral�movements.

Research Questions and HypothesesTo�clarify�the�effects�of�task�constraints�on�reaching�perfor-mance�of�the�less-affected�limb,�we�investigated�the�effect�of�task�instructions�and�target�location�on�reaching�in�people�with�left�and�right�CVA�(LCVA�and�RCVA,�respectively)�and�healthy�control�participants.�Specifically,�we�looked�at�reaching�kinematics�when�people�with�and�without�stroke�reached�for�an�ipsilateral�target�(i.e.,�the�target�ipsilateral�to�the�less-affected�hand�used�for�performance)�and�a�contra-lateral�target�(i.e.,�the�target�contralateral�to�the�responding�hand)�under�speed�and�accuracy�instructions.�Healthy�people�were�studied�to�provide�a�basis�on�which�to�establish�normal�patterns�in�task�performance�under�different�task�constraints�(Wu,�Trombly,�Lin,�&�Tickle-Degnen,�1998;�Wu�et� al.,�2000).�Studying�people�with�LCVA�and�RCVA�would�reveal�specific�movement�responses�to�task�constraints�and�provide�insights�into�the�role�each�hemisphere�plays�in�movement�organization�(Elliott�&�Carson,�2000;�Wu,�Wong,�Lin,�&�Chen,�2001).

The�four�experimental�conditions,�formed�by�the�cross-ing�of�task�instructions�(speed�and�accuracy�emphasis)�and�target� locations� (ipsilateral� and� contralateral� to� the� less-affected�hand�used�for�performance),�are�(1)�speed-empha-sized� reaching� for� an� ipsilateral� target� (SI),� (2)� accuracy-emphasized� reaching� for� an� ipsilateral� target� (AI),� (3)�speed-emphasized�reaching�for�a�contralateral�target�(SC),�

and� (4)� accuracy-emphasized� reaching� for� a� contralateral�target�(AC).�Participants�with�stroke�performed�the�reaching�tasks�with�their�less-affected�limbs.�

We�hypothesized� that,� for� people�with� and�without�stroke,�the�movement�would�be�more�programmed�(shorter�RT� and�MT,� fewer�MUs),�with�higher� force� generation�(higher�PV)�for�speed-emphasized�tasks�than�for�accuracy-emphasized�tasks�and�for�ipsilateral�reaches�than�for�contra-lateral�reaches.�Instruction�effects�were�further�proposed�to�override� location�effects,�based� in�part�on� the�findings�of�Adam�(1992)�and�Fasoli�et�al.�(2002)�that�speed–accuracy�or�instruction�effects�remain�robust�when�the�target�location�is�changed�or�when�different�task�conditions�are�performed.�That�is,�the�more�programmed�movements�with�higher�force�generation�would�be�elicited�by�the�testing�conditions�in�the�following�order:�SI,�SC,�AI,�and�AC.�We�also�predicted�that�differential� responses� to� task�manipulations�may� arise� in�accord�with�laterality�of�stroke�lesion.

Method

Participants

The�participants�with�stroke�were�recruited�from�two�medi-cal�centers,�and�stroke�location�was�identified�by�computed�tomography�or�magnetic�resonance�images�of�the�brain.�The�patients�were�able�to�understand�or�respond�to�directions�given�by�the�experimenter�and�had�no�clinical�signs�of�motor�apraxia�and�visuospatial�neglect.�They�had�no�history�of�prior�CVA�or�visual�deficit�that�would�prevent�participation.�The�participants� in� the� control� group�had�no�prior�history�of�neurological�or�psychiatric�disease,�determined�by�self-report.�All�participants�signed�informed�consent�forms�approved�by�the�Institutional�Review�Board�of�National�Taiwan�University�Hospital.�The�participants�with�CVA�used�the�less-affected�limb,�and�the�matched�control�participants�used�the�same�limb�as�did�the�participants�with�CVA.�

Materials and Instrumentation

The�target�object�was�a�desk�bell�with�a�diameter�of�9.65�cm�and�a�height�of�4.75�cm.�The�start�and�the�end�of�the�reach�event�were�determined�through�the�use�of�a�hand�switch�and�the�desk�bell.�Before�movement�initiation,�the�participant’s�hand�rested�on�a�switch.�The�beginning�of�movement�was�recorded�when�the�hand�moved�off�the�switch.�The�end�of�movement�was�obtained�when�the�participant�pressed�the�desk�bell.

A�six-camera�motion�analysis�system�(VICON�370�3–D;�Oxford�Metrics�Inc.,�Oxford,�England)�was�used�in�conjunc-tion�with�one�personal�computer�(IBM�clone)�to�capture�the�movement�of�the�marker�attached�to�the�styloid�process�of�

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The American Journal of Occupational Therapy� 459

the�ulna�during�reaching�to�press�the�bell�and�to�collect�two�channels�of�analog�signals�simultaneously.�The�analog�sig-nals,�connected�with�the�hand�switch�and�the�desk�bell,�were�used�to�determine�the�start�and�the�end�of�the�reach.�The�VICON�system�was�shown�to�accurately�and�reliably�mea-sure�distances� ranging� from�25�mm�to�500�mm�between�markers�statically�and�the�motion�of�markers�up�to�speeds�of�approximately�15�m�per�second.�This�precision�is�more�than�sufficient�when�measuring�motions�during�reaching�or�gait�(Bhimji,�Deroy,�Baskin,�&�Hillstrom,�2000).�This�system�was�calibrated�to�have�averaged�residual�errors�not�exceeding�3�mm�for�each�camera�before�data�acquisition.�As�the�par-ticipant�moved,�the�instantaneous�position�of�the�marker�was�digitized�at�a�sampling�rate�of�60�Hz.�After�data�acquisition,�we�used�the�VICON�system�analysis� software�to�save�the�three-dimensional�location�of�the�marker�together�with�ana-log�data�in�binary�format.�The�obtained�positional�data�were�digitally� low-pass� filtered� at� 5� Hz� using� a� second-order�Butterworth�filter�with�forward�and�backward�pass.

Design and Procedures

We�used�a�counterbalanced�repeated-measures�design.�Each�incoming�participant�was�randomly�assigned�to�one�of�four�sequences�for�executing�the�reaching�task:�SI–AI–SC–AC,�AI–SC–AC–SI,� SC–AC–SI–AI,� or� AC–SI–AI–SC� (see�Table�1).

During�the�experiment,�each�participant�sat�on�a�chair�40.00�cm�high�in�front�of�a�table�adjusted�to�5.00�cm�above�the�elbow.�The�participant’s�performing�hand�rested�on�a�pressure-sensitive�switch�that�was�located�on�the�edge�of�the�table�in�line�with�the�participant’s�midsagittal�plane.�Two�target� locations� were� used:� the� left� and� right� hemispace�located�on�a�meridian�45°�relative�to�the�start�position.�The�target�object�was�placed�38.00�cm�from�the�starting�position�for�each�task�location.�The�verbal� instruction�involved�an�emphasis�on�rapid�(i.e.,�as�quickly�as�possible)�or�accurate�(i.e.,�as�accurately�as�possible)�execution�of�the�experimental�task.�The�start�of�a�trial�was�prompted�by�a�randomly�timed�verbal�instruction,�“go,”�to�prevent�participants�from�expect-

ing�when�to�initiate�the�movement.�Under�the�speeded�con-ditions�(i.e.,�SI,�SC),�the�participants�missed�the�targets�in�some�trials,�and�these�were�not�included�for�analysis.�Each�participant�performed�three�successful�trials�for�each�condi-tion.�One�practice�trial�was�performed�before�the�participant�executed�the�task�for�each�condition.�

Data Analysis

We�used�an�analysis�program�coded�by�LabVIEW�(National�Instruments,� Inc.,�Austin,�TX)� to�process� collected�data.�Information�on�reaching�performance�including�RT,�MT,�MU,� and�PV�was� obtained.�We� conducted� the� analyses�separately�for�the�participants�with�LCVA�and�RCVA�and�for�the�healthy�control�participants.�To�test�the�effects�of�both� constraints,�we�used� contrast� analyses� (i.e.,� focused�analyses�of�variance�[ANOVAs])�in�which�specific�predic-tions�were�tested�by�contrasting�them�with�the�obtained�data�(Rosenthal�&�Rosnow,�1985).�We�first�performed�4��4�mixed�ANOVAs�for�each�dependent�variable�to�obtain�the�omnibus�F of�the�Sequence��Order�interaction.�There�was�one�between-subjects�factor,�sequence,�and�one�repeated�or�within-subjects�factor,�order,�in�this�mixed�ANOVA.�The�effects� of� the� task� constraints� (i.e.,� the�omnibus�F)�were�embedded�in�the�Sequence��Order�interaction�(Rosenthal�&�Rosnow,�1991).�This�practice�is�more�powerful�than�the�commonly�used�two-way�ANOVAs�with�repeated�factors�because�it�removes�the�confounding�effects�of�sequence�and�order�from�the�error�term.

We�then�obtained�the�focused�F�for�our�contrast�analysis�from�the�omnibus�F�as�follows:�Fcontrast�=�(r2)�(omnibus�Ftreatment�×�dfnumerator),�where� r2� is� the� square�of� the�correlation�between�the�contrast�weights�and�the�residualized�means�(Rosenthal�&�Rosnow,�1991).�For�the�present�study,�we� assigned� contrast� weights� numerically� reflecting� the�hypothesis.�For�example,�in�this�study’s�SI,�SC,�AI,�and�AC�conditions,�the�contrast�weights�for�predicting�the�trend�of�MT�were�–3,�–1,�1,� and�3,� respectively.�To� indicate� the�magnitude�of�the�effect�of�interest,�we�calculated�the�effect�size�r�for�each�dependent�variable�for�each�group�(Rosenthal�&�Rosnow,�1985).

ResultsThe�participants�in�this�study�included�26�people�with�uni-lateral�CVA�(18�men�and�8�women,�42–83�years�old,�mean�age�63.4�years)�and�24�age-matched�healthy�people�(7�men�and�17�women,�42–80�years�old,�mean�age�62.3�years),�who�were� right�handed�by� self-report.�Average� time� following�stroke�onset�was�2.62�months�(SD�=�3.12;�range�=�0.13−12.90�months).�Eleven�participants�with�RCVA�and�12�control�participants�used�their�right�limbs�to�perform�the�tasks;�15�

Table 1. A Counterbalanced Repeated-Measures Design

Sequence

Order

1 2 3 4

1 SI AI SC AC

2 AI SC AC SI

3 SC AC SI AI

4 AC SI AI SC

Note. Order refers to the order of administration of the treatment. SI = speed-emphasized reaching for an ipsilateral target; AI = accuracy-emphasized reaching for an ipsilateral target; SC = speed-emphasized reaching for a con-tralateral target; AC = accuracy-emphasized reaching for a contralateral target.

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460� July/August 2008, Volume 62, Number 4

participants�with�LCVA�and�12�control�participants�used�their�left�limbs.

Figures�1� through�4�present� the�means� and� standard�deviation�bars�associated�with�RT,�MT,�MU,�and�PV�under�each�experimental�condition�for�the�four�groups.�Table�2�shows�the�results�of�the�contrast�analyses.�For�both�control�groups�(one�group�using�the�left�hand�and�the�other�using�the�right�hand),�speeded�instructions�and�ipsilateral�reaches�elicited�more�preprogrammed�movements�than�did�accuracy�instruction�and�contralateral�reaches,�respectively.�Both�con-trol�groups�initiated�the�movement�faster�(shorter�RT)�and�performed�the�movement�more�efficiently�(shorter�MT)�and�smoothly�(fewer�MUs)�for�speed-emphasized�versus�accuracy-emphasized�tasks�and�for�ipsilateral�versus�contralateral�ones.�The�instructional�effects�overrode�the�target�location�effects�for�these�three�variables,�which�is�consistent�with�the�a�priori�hypotheses.�However,�a�scrutiny�of�the�raw�data�showed�that�the�direction�of�constraint�effects�on�force�generation�(PV)�was�not� fully� consistent�with� the�a�priori�hypothesis.�We�performed�a�post�hoc�analysis,�which� showed� that�higher�force�was�generated�for�speed-emphasized�versus�accuracy-emphasized�movements�and�for�ipsilateral�versus�contralat-eral�reaches.�Inconsistent�with�the�a�priori�hypotheses,�the�location�effects�overrode�the�instructional�effects�(Table�3).

Results� for� the� CVA� groups� using� the� less-affected�limb�showed�significant�and�large�effects�of�the�task�con-straints�for�all�variables�(RT,�MT,�MU,�PV)�for�the�LCVA�group�and�for�three�of�the�four�variables�(MT,�MU,�PV)�for� the� RCVA� group.� Nonsignificant� and� modest� task-constraint�effects�were�found�in�RT�for�the�RCVA�group.�Both� groups� showed� more� efficient� (shorter� MT)� and�smoother�(fewer�MUs)�performance�for�speed-emphasized�versus�accuracy-emphasized�movements�and�for�ipsilateral�

Figure 1. Performance by the healthy control group using the left hand as a function of task conditions. Mean and standard deviation bars are displayed.

RT = reaction time; MT = movement time; MU = movement unit; PV = peak velocity; SI = speed-emphasized reaching for an ipsilateral target; SC = speed-emphasized reaching for a contralateral target; AI = accuracy-emphasized reaching for an ipsilateral target; AC = accuracy-emphasized reaching for a contralateral target.

Figure 2. Performance by the healthy control group using the right hand as a function of task conditions. Mean and standard deviation bars are displayed.

RT = reaction time; MT = movement time; MU = movement unit; PV = peak velocity; SI = speed-emphasized reaching for an ipsilateral target; SC = speed-emphasized reaching for a contralateral target; AI = accuracy-emphasized reaching for an ipsilateral target; AC = accuracy-emphasized reaching for a contralateral target.

Figure 3. Performance by the LCVA group as a function of task condition. Mean and standard deviation bars are displayed.

RT = reaction time; MT = movement time; MU = movement unit; PV = peak velocity; SI = speed-emphasized reaching for an ipsilateral target; SC = speed-emphasized reaching for a contralateral target; AI = accuracy-emphasized reaching for an ipsilateral target; AC = accuracy-emphasized reaching for a contralateral target.

Figure 4. Performance by the RCVA group as a function of task condition. Mean and standard deviation bars are displayed.

RT = reaction time; MT = movement time; MU = movement unit; PV = peak velocity; SI = speed-emphasized reaching for an ipsilateral target; SC = speed-emphasized reaching for a contralateral target; AI = accuracy-emphasized reaching for an ipsilateral target; AC = accuracy-emphasized reaching for a contralateral target.

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The American Journal of Occupational Therapy� 461

versus�contralateral�movements.�Moreover,�the�instructional�effects�overrode�the�location�effects,�which�is�consistent�with�the�a�priori�prediction.

However,�the�raw�data�showed�that�the�effects�on�move-ment� initiation� (RT)� for� the�LCVA�group� and�on� force�generation�(PV)�for�both�groups�were�not�fully�consistent�with�the�a�priori�hypotheses.�We�conducted�post�hoc�analy-ses� of� the�data� for� the� stroke� groups.�Large� effects�were�obtained�in�favor�of�the�post�hoc�hypotheses�for�movement�initiation�in�the�LCVA�group�and�for�force�generation�in�both� groups� (Table� 3).� Speed-emphasized� conditions�required�less�time�to�initiate�the�movement�for�the�LCVA�group�than�did�the�accuracy-emphasized�conditions.�Target�location�did�not�affect�the�time�to�initiate�movement�in�this�group�under�either�type�of�task�instruction�(i.e.,�SI–SC;�AI–AC).�On�the�other�hand,�constraint�effects�on�force�genera-tion�were�found�for�the�RCVA�and�the�LCVA�groups.�Target�location�effects�overrode�the�instructional�effects,�in�which�ipsilateral�reaches�generated�higher�force�than�contralateral�reaches.�Speed�requirements�generated�higher�force,�relative�to�accuracy�demands,�for�either�type�of�reach.

Discussion

The�results�of�the�study�are�partially�consistent�with�the�a�priori� hypotheses� and� support� the�notion� that� task� con-straints� modulate� movement� preparation� and� execution�(Newell,� 1998;� Shumway-Cook� &� Woollacott,� 2007).�Healthy� people� used� more� programmed� movements� (as�suggested�by�RT,�MT,�and�MU)�with�higher�force�genera-tion� (higher� PV)� for� speed-emphasized� versus� accuracy-�emphasized� tasks� and� for� ipsilateral� versus� contralateral�movements.�The�instructional�effects�significantly�overrode�the� target� location� effects� on�movement� initiation� (RT),�efficiency� (MT),�and�smoothness� (MU)�but�not�on� force�generation�(PV).�We�found�similar�patterns�of�performance�in�response�to�task�constraints�in�the�CVA�groups�except�for�movement� initiation� in� the�RCVA�group.�Therefore,�we�concluded�that�the�integration�of�speeded�instruction�and�ipsilateral�reach�(SI�condition)�optimized�movement�execu-tion�for�healthy�adults�and�people�with�CVA.�A�major�deficit�of�people�with�CVA�in�response�to�task�constraints�lies�in�movement� initiation�because�we� found�no�differential� or�gradient�differences�in�RT�among�various�task�conditions.�However,�the�consistent�effects�of�task�constraints�on�move-ment� efficiency,� smoothness,� and� force� generation� in� the�healthy�participants�and�those�with�CVA�suggest�that�some�aspects�of�movement�kinematics�may�be�relatively�unaffected�by�stroke.

Findings�for�both�control�groups�were�consistent�with�those�of�previous�studies�on�speed–accuracy�instruction�con-straints�(Adam,�1992;�Fasoli�et�al.,�2002;�Fisk�&�Goodale,�1984;�Rival�et�al.,�2003).�Speeded�instructions�and�ipsilateral�reaches� elicited�more�preprogrammed�movements� (faster�initiation� and�more� efficiency� and� smoothness)� than� the�accuracy�instruction�and�contralateral�reaches,�respectively.�This�study�extended�previous�research�by�showing�the�ben-efit�of�speeded�instruction�in�a�simple,�functionally�relevant�task.�The�instructional�effect�may�arise�because�the�demand�for� speed�can�direct� the�performer’s� attention� toward� the�temporal�organization�of�movement�and�activate�predomi-nantly� the� preprogrammed� strategies� (i.e.,� the� ballistic�

Table 2. Results of Contrast Analyses for the Study Groups

Dependent Variable

NL NR LCVA RCVA

FocusedF(1, 24) p

EffectSize r

FocusedF(1, 24) p

EffectSize r

FocusedF(1, 33) p

EffectSize r

FocusedF(1, 21) p

EffectSize r

RT 5.44 .015 .64 9.60 .025 .74 17.33 <.001 .78 1.87 .093 .45

MT 110.21 <.001 .97 65.10 <.001 .94 36.76 <.001 .88 46.95 <.001 .93

MU 9.91 .002 .74 14.07 <.001 .80 6.03 <.001 .60 8.46 <.001 .74

PV 9.80 .002 .74 7.82 .005 .70 13.31 <.001 .74 19.18 <.001 .86

Note. NL = controls using the left hand; NR = controls using the right hand; LCVA = participants with left cerebrovascular accidents; RCVA = participants with right cerebrovascular accidents; RT = reaction time; MT = movement time; MU = movement units; PV = peak velocity.

Table 3. Results of Post Hoc Contrast Analysis

Study Group andDependent Variable Post Hoc Hypotheses Effect Size r

NL

PV SI > AI >SC > AC 0.78

NR

PV SI > AI > SC > AC 0.85

LCVA

RT SI = SC < AI = AC 0.81

PV SI > AI > SC > AC 0.82

RCVA

PV SI > AI > SC > AC 0.94

Note. NL = controls using the left hand; NR = controls using the right hand; LCVA = participants with left cerebrovascular accidents; RCVA = participants with right cerebrovascular accidents; PV = peak velocity; RT = reaction time; SI = speed-emphasized reaching for an ipsilateral target; SC = speed-empha-sized reaching for a contralateral target; AI = accuracy-emphasized reaching for an ipsilateral target; AC = accuracy-emphasized reaching for a contralat-eral target.

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462� July/August 2008, Volume 62, Number 4

movements;� Hermsdorfer� et� al.,� 1996;� Ma� et� al.,� 2004).�Another�possibility�is�that�instructions�for�speed�versus�accu-racy�indicate�different�goals�to�be�accomplished.�Task�goal�has�been�shown�to�be�a�powerful�organizing�factor�in�simple�motor�tasks�(Lin�et�al.,�1998;�Shumway-Cook�&�Woollacott,�2007;�Trombly�&�Wu,�1999;�Wu�et�al.,�2000,�2001).�The�goal�of�reaching�quickly�may�organize�the�motor�system�to�perform�faster�and�more� smoothly� to�achieve� the� task�requirement,�whereas�the�goal�of�reaching�with�accuracy�possibly�directs�the�performer’s�attention�toward�endpoint�precision,�which�may�compromise�movement�efficiency�and�smoothness.

The�results�of�location�effects�on�movement�initiation,�efficiency,�and�smoothness�in�both�control�groups�agree�with�those�of�previous�research�(Fisk�&�Goodale,�1984;�Ghozlan,�1998;�Wu�et� al.,� 2005)�demonstrating� the� advantages�of�ipsilateral�reaches.�Such�advantages�possibly�lie�in�the�effi-ciency�of�intrahemispheric�processing�for�visuomotor�infor-mation�on�target�or�visual�feedback�from�the�reaching�limb�(Barthelemy�&�Boulinguez,�2002;�Fisk�&�Goodale,�1984).�Some�positron�emission�tomography�studies�(Carey,�Abbott,�Egan,�Tochon-Danguy,�&�Donnan,�2000;�van�Mier,�Tempel,�Perlmutter,�Raichle, & Petersen,�1998)�have�shown�greater�brain�activations�in�the�hemisphere�contralateral�to�the�hand�used�than�in�the�other�hemisphere�for�ipsilateral�reaches.�By�contrast,�comparable�brain�areas�were�activated�in�both�hemi-spheres�for�contralateral�reaches.�These�findings�further�sup-port�the�notion�of�the�advantage�of�intrahemispheric�process-ing�for�ipsilateral�reaches.�The�results�might�also�be�accounted�for�by�the�biomechanical�characteristics�of�the�movement.�As�mentioned�earlier,� inertial� force�operating�at� the�hand� for�ipsilateral� reaches�was� lower�than�for�contralateral� reaches.�Ipsilateral�reaches�may�engender�faster�movement�initiation�and�higher�movement�efficiency�than�contralateral�reaches�(Carey�et�al.,�1996;�Carey�&�Otto-de�Haart,�2001).

In�agreement�with�the�findings�of�Adam�(1992)�and�Fasoli�et�al.�(2002),�speed–accuracy�effects�overrode�location�effects.�This� study� extended� the� robust� effects�of� speed–accuracy�from�reciprocal�movements�to�simple�aiming�movements�and�from�the�sagittal�plane� to� the�spatial�planes� ipsilateral�and�contralateral�to�stroke�lesion.�This�may�be�because�the�nature�of�the�auditory�information�from�the�verbal�instruction�pro-vided�strong�constraints�that�captured�the�intrinsic�dynamics�of�the�performer’s�movement�system�and�overrode�the�effects�of�target�location�(Kail�&�Salthouse,�1994).

The�effects�of�task�constraints�on�force�generation�were�not�fully�consistent�with�the�a�priori�hypotheses.�The�control�participants� exerted�more� force� for� executing� the� task�of�speeded�and�ipsilateral�reaches�than�for�accurate�and�contra-lateral�reaches,�respectively,�supporting�the�notion�that�tasks�with�speeded�emphasis�and�ipsilateral�reaches�require�greater�inertial�force�or�impulse�at�movement�initiation�for�efficient�

movement�(Beer�et�al.,�2000;�Ma�et�al.,�2004;�Rand�et�al.,�2000;� Roy� et� al.,� 2000).� Inconsistent� with� the� a� priori�hypothesis,�location�effects�overrode�speed–accuracy�effects.�The�dominant�effects�of�target� location�suggest�that�force�generation�may�be�more�sensitive�to�within-hemisphere�pro-cessing�and�biomechanical�control�than�to�preprogrammed�strategies.

The�results� for�the�CVA�groups�were�consistent�with�those�for�the�control�groups�in�movement�efficiency,�smooth-ness,�and�force�generation,�suggesting�that�these�aspects�of�movement�kinematics�of�the�less-affected�limb�may�be�rela-tively�unaffected�by�stroke.�Moreover,�the�findings�on�move-ment�efficiency�and�smoothness�are�consistent�with�those�of�the�previous�studies�(Beer�et�al.,�2000;�Castiello�et�al.,�1999;�Roy� et� al.,� 2000).� The� deficits� of� people� with� CVA� in�response� to� task�constraints� (verbal� instruction�and� target�location)�occur�primarily�in�movement�planning.�The�LCVA�group� exhibited� shorter� time� for�movement�planning�or�preparation�under�speeded�instructions�than�under�accuracy�instructions�for�reaching�to�either�location.�By�contrast,�the�RCVA�group�did�not�demonstrate�significant�effects�of�task�constraints�on�movement�initiation.�A�possible�reason�for�differences�in�effects�of�task�constraints�between�the�LCVA�and�RCVA�groups�might�be� that� the� right�hemisphere� is�dominant�for�processing�visuospatial�or�positional�aspects�of�goal-directed�movements,�whereas�the�left�hemisphere�sub-serves�nonspatial� or�nonpositional� aspects�of�preplanning�(Haaland�et�al.,�2004;�Winstein�&�Pohl,�1995).�The�task�used� in� this� study� required�position� control� to� accurately�press�the�bell�under�either�type�of�instruction�and�scale�the�spatial� relationship�between� the� target� and� the�performer�(Heath,�Hodges,�Chua,�&�Elliott,�1998).�Accordingly,�once�the�right�hemisphere� is� lesioned,� the�ability� to�preplan�or�program�the�motor�act�for�a�visual�target�such�as�that�used�in�the�present�study�is�decreased,�and�the�pattern�of�RT�in�response� to� instructional� or� location� constraints� is�impaired.

A�scrutiny�of�the�kinematic�performance�between�the�control�and�the�CVA�groups�showed�that�the�participants�with�CVA�generally�produced� fewer�programmed�move-ments�(slower�movement�initiation,�less�movement�efficiency�and�smoothness)�with�lower�force�generation�than�the�con-trol�participants.�These�findings�suggest�that�occupational�therapy�for�stroke�should�consider�motor�deficits�of�the�less-affected� limb� (Haaland� et� al.,� 2004;�Kim,�Pohl,�Luchies,�Stylianou,� &� Won,� 2003;� Quaney,� Perera,� Maletsky,�Luchies,�&�Nudo,�2005; Wetter�et�al.,�2005).�This�consid-eration� is�necessary�because�compensatory�use�of� the� less-affected�limb�after�stroke�is�common�for�precision�tasks�in�daily�life�situations.�To�facilitate�enhanced�movement�per-formance,� occupational� therapists� may� incorporate� task�

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The American Journal of Occupational Therapy� 463

�constraints�(e.g.,�verbal�instructions�and�target�location)�into�practice�of�goal-directed�actions�by�people�with�CVA.

This� study’s�findings�may�have� implications� for� task-specific�practice�of�compensatory�use�of�the�less-affected�limb�after� stroke.�Task�demands� for� speeded�movement�or� for�ipsilateral� reach� might� facilitate� movement� efficiency,�smoothness,� and� force� generation.� The� combination� of�speeded�instruction�and�ipsilateral�reach�may�elicit�the�most�preprogrammed�movements�and�optimize�movement�per-formance�when�the�less-affected�limb�is�used�for�target�reach-ing.�The�speeded�instruction�might�have�greater�benefit�than�ipsilateral�reaches�for�enhancing�movement�efficiency�and�smoothness.�By�contrast,�if�generation�of�greater�force�is�the�goal,�use�of�the�less-affected�limb�for�practice�of�ipsilateral�reaches�might�be�more�advantageous�than�speeded�instruc-tions.�If�fast�response�to�the�task�demand�is�the�goal,�speeded�demands�may�be�helpful�for�people�with�LCVA�but�not�for�those�with�RCVA.

One�limitation�of�this�study�is�that�the�effect�of�stroke�severity�was�not�studied�and�warrants�future�research.�Future�research�may�also� investigate� the� response�patterns�of� the�more-affected�hand�in�response�to�the�constraints�to�update�motor�control�rehabilitation�interventions�for�clients�with�hemiplegia.�Additional� constraint� factors� are� relevant� for�study�to�elucidate�the�dynamic�interplay�between�task�con-straints�and�people�with�CVA.�Examples�are�task�difficulty�and� complexity� (e.g.,� target� size� and� task� distance;�Hermsdorfer�et�al.,�2003;�Kim�et�al.,�2003;�Ma�&�Trombly,�2004),�position�of�the�hand�relative�to�target�location,�pres-ence�of�distracting�objects,�and�motivational�relevance�of�the�motor�act�for�individual�performers.�Further�study�that�elu-cidates�these�issues�will�improve�understanding�of�the�orga-nization� of� aiming� movements� and� inform� task-specific�approaches�to�stroke�rehabilitation.

ConclusionsOur�findings� reveal� the� confluence�of� instructional� con-straints�of�speed–accuracy�and�target�location�during�reach-ing�movements�by�people�with�and�without�CVA.�The�study�demonstrated�that�instructions�for�speeded�reaching�for�an�ipsilateral� target� elicited� the�most�preprogrammed�move-ment.�Moreover,�some�aspects�of�movement�performance—such�as�movement�efficiency,�smoothness,�and�force�genera-tion� of� the� less-affected� limb� in� response� to� the� task�constraints—may� be� relatively� unaffected� by� unilateral�stroke.�The�RCVA�group,�but�not�the�LCVA�group,�failed�to� respond� to� the� instruction� and� location� constraints� in�movement�preparation�during�the�desk�bell�task.�The�dif-ferential� responses� to� task� constraints� in� the�hemispheric�groups�suggest�that�the�right�hemisphere�may�be�responsible�

for�the�programming�and�planning�of�motor�acts�involving�space�coding.�Such�information�might�facilitate�rehabilitative�treatment�planning�for�the�less-affected�limb�that�incorpo-rates�constraint�factors�into�compensatory�strategy�practice.�Therapeutic�activities�that�involve�instructional�demands�for�fast�movement�and�ipsilateral�reaches�may�be�used�to�facili-tate�movement�efficiency,�smoothness,�and�force�generation�of� the� less-affected� limb.�Further� research�may�also� study�whether�practice� on� these� activities�may� enhance�perfor-mance� of� the� affected� limb� during� bilateral� movements�involving�both�upper�limbs�(e.g.,�opening�a�drawer�with�the�affected�hand�and�retrieving�a� target�object�with� the� less-affected�hand;�Wu,�Lin,�Chen,�Chen,�&�Hong,�2007).� s

AcknowledgmentsWe� thank� the� research� therapists� at� National� Taiwan�University�Hospital�for�their�assistance�and�the�anonymous�reviewers�for�their�insightful�comments�on�this�article.�This�project� was� supported� by� the� National� Science� Council�(NSC�91-2314-B-002-080�and�NSC�92-2314-B-002-139)�and�the�National�Health�Research�Institutes�(NHRI-EX93-9103EC�and�NHRI-EX94-9103EC)�in�Taiwan.

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Adults With Stroke (AOTA Practice Guidelines) By Joyce Sabari, PhD, OTR, FAOTA; Series Editor: Deborah Lieberman, MHSA, OTR/L, FAOTA �

Each�year,�as�many�as�700,000�people�in�the�United�States�

experience�a�new�or�recurrent�stroke,�and�more�than�500,000�survive.�

Over�a�million�of�those�survivors,�however,�report�diffi�culties�related�to�the�

functional�limitations�that�can�result�from�this�life-changing�experience.�

The�new,�evidence-based�Adults With Stroke (AOTA Practice Guidelines)�

details�the�signifi�cant�contribution�of�occupational�therapy�in�treating�adults�

dealing�with�these�limitations.�Appendixes�include�other�valuable�resources�such�as�

CPT(TM)�codes�related�to�occupational�therapy�for�stroke�survivors.�

Order #2211 Member Price: $39.00 Non-Member Price: $55.00 ISBN: 978-1-56900-263-6

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