Motor Learningand Motor Control
KellyCole,PhD,Universityof lowo
After readingthis chapter,you should be able to'
1. Definethe terms ruotorcontroland motorlearning
and explain their significanceto understanding
motor behavior.
2. Providea brief overviewof the history of the
scienceof motor control and motor learning.
3. Describeconditions that are optimal for learning
and refining skilled movements.
4. Describekey conceptsof the current understand'
i n e o f h o w s k i l l e dm o v e m e n ti s p r o d u c e d .
posturalcontrol
anticipatory
appliedmotorcontrol
physiologists
hlnnluorl
nrentiro
v l qLL' ! v
brainplasticity
centralpatterngenerator
centralrepresentation
Ie
www.mhhe.com/wilson
Explainthe careeroptions for students with training in motor control and motor learning.
6 . Identifythe various professionalscientificand
clinical organizationsthat are relevantto the
broad field of motor behaviorand their associated
certifi cation programs.
constant practice
deafferented
distributed practice
initialconditions
Law of Practice
massedpractice
motor behavior
motor control
motor learning
posture
random practice
retention test
sensoryinformation
variablepractice
Chapter Five Motor Learningand Motor Control
75
Considerthe words of Sir CharlesS. Sherrington(winn e r o f t h e N o b e l P r i z e i n P h y s i o l o g yo r M e d i c i n e ,
1932):
lElvenin vnanthecrownof lifeis an action,not a
thought. . . t0 vnlvethingsis all that rnankindcando,
whether
is rnuscle,
and thatfor suchthe soleexecutant
or in fellinga forest.(Linacre
a sqllable
in whispering
L e c t u r e ,C a m b r i d g e ,E n g l a n d 1 9 2 4 )
S h e r r i n g t o nw a s t e l l i n g u s t h a t m o t o r b e h a v i o ri s a
fundamental human function that is essentialto virt u a l l y a l l o f o u r a s p i r a t i o n si n l i f e .T h i s i s w h y c o u r s e s
i n m o t o r b e h a v i o ra r e f o u n d u n i v e r s a l l yi n e x e r c i s e
sciencecurricula.
Motor behavior can be defined as the study of
human movementror action. Motor behaviorinvolves
t w o o v e r l a p p i n gt h e m e s : m o t o r c o n t r o l a n d m o t o r
learning. Motor control focuses on the processes
that underlie the production of movement in health
and disease;motor learning focuseson how skilled
m o v e m e n t sa r e a c q u i r e d ,i n c l u d i n gt h e o p t i m a l c o n ditions for learning new motor skills.
Coursesin motor control and motor learningoften
appear as intermediate- or upper-level components
of an exercisesciencecurriculum and follow courses
in anatomy, physiology,and physics An understanding of basic physics is essentialbecausemovements
result from the interaction of our body with our environment. For example,gravity acts on the massesof
our body segments,body segmentsaffect each other
as they move, and obiects exert forces on our bodi e s ( a n d v i c e v e r s a )a s w e m a n i p u l a t et h e m . T h e p r o cessof producing coordinated,functional movements
must account for these physical properties at some
level, and so the study of motor behavior should
b e i n t e r t w i n e d w i t h t h e s t u d y o f b i o m e c h a n i c s .A
coursein generalpsychologyis helpful becauseour ev'
erydaymovementsalso depend on attention, perception, memory, motivation,and even decision making.
A BRIEFHISTORY
OF MOTORCONTROL
AND MOTORLEARNING
The origins of contemporarymotor behaviorare found
i n m e d i c i n e ,p h y s i o l o g yp, s y c h o l o g ya, n d e n g i n e e r i n g .
Our understandingof how the nervoussystemparticipates in the production of movement began within
t h e r e l a t e d d i s c i p l i n e so f m e d i c i n e a n d p h y s i o l o g y .
Severalkey eventsoccurredduring the late 1800sand
early 1900sthat propelled motor neuroscienceinto
a m o d e r n d i s c i p l i n e .L e t ' s p l a c e t h e l e v e l o f u n d e r rln this chaptermlvement
to referto
is oftenusedgenerically
actionsinvolvingthe productionof forceor motion.
of basicneuroscistanding(or lackof understanding)
Thiswasa
enceduringthe late 1800sin perspective.
debatedthe
time whenanatomistsand physiologists
existenceof the synapse,the iunctionbetweenneuin
to informationprocessing
ronsthat is fundamental
the nervoussystem.
The Riseof ElecuoPhysiologY
I n 1 8 7 0 G u s t a v T h e o d o r F r i t s c h ( 1 8 3 8 - 1 9 2 7 )a n d
J u l i u sE d u a r d H i t z i g ( 1 8 3 8 - 1 9 0 7 b) e g a n t h e s t u d y o f
They applied localized,
the brain's electrophysiology.
low-level electricalstimulation to the brains of dogs
and demonstratedthat brain areaspreviouslythought
t o b e i n v o l v e d e x c l u s i v e l yi n t h o u g h t a n d e m o t i o n
p a r t i c i p a t e dd i r e c t l y i n p r o d u c i n g m o v e m e n t J o h n
H u g h l i n g sJ a c k s o n( 1 3 3 5 - 1 9 1I ) , " t h e f a t h e r o f B r i t i s h
neurology,"wrote extensively on the neural control
of movement. He often gained insights from his observationsof patients. For example,lacksonobserved
grand mal epileptic seizuresand noticed that there
was a progressiveinvolvementof different body parts
that followed a similar pattern acrosshis patients, including his wife. This led him to deduce that seizures
resultedfrom excessiveelectricalactivitythat beganin
one area of the brain and then spread.The regularity
of the movement patterns allowed him to conclude,
beforethe work of Fritschand Hitzig,that the highest
level of the brain-the cerebral cortex-participated
in the generationof movement. He also deducedthat
the muscles of the body are representedin the cere'
bral cortex by a systematicbody map (Figure5.1).
These key observations were followed by those
of Sir David Ferrier (1843-1924),who confirmed and
elaboratedthe concept of cerebralcortical maps.
The modern era of motor neurophysiology
began with the systematicresearchof Sir Charles S.
Sherrington (1857-1952)who shared the Nobel Prize
(automatic motor rein 1932 for his study of reflexes
stimulus) and their
external
to
an
reaction
in
sponses
role in the brain's control of movement and posture.
Sherrington ushered in a highly productive era of inc r e a s i n g l ys o p h i s t i c a t e ds t u d y o f h o w t h e n e r v o u s
system participates in the production of simple and
s k i l l e d m o v e m e n t s .T h i s m o t o r n e u r o s c i e n c et r a d i tion developed at an increasinglyfast pace and was
directed mostly at discovering the neural causes of
movement with little regard to the properties of the
movementsthemselves.
EarlyContributionsFrom Psychology
At the same time a completely separatetradition of
researchin the discipline of psychology developed.
Beginningin the late 1880s,scientistsfocusedon the
studyof highlyskilledmovementsby observingand de'
scribing the properties of movements under a variety
o
SF
{ri
<-
Medial
period of researchconcerningmotor learning,optimal
t r a i n i n g m e t h o d s ,a n d t h e o p t i m a l d e s i g n o f e q u i p ment to minimize human-usererrors (now known as
e r g o n o m i c so r h u m a n f a c t o r se n g i n e e r i n g )S. e m i n a l
work duringthis time includedresearchby K. J.W. Craik
(1914-1945\and his theorythat informationprocessing
in the brain occursin bursts ratherthan continuously.
A. T. Welford(1914-199r)built on Craik'swork with his
influential theory that information processingin the
nervoussystem encountersdelays becausethe infor'
mation is processedin single channels.Paul M. Fitts
(1912-1965)continuedalong this theme of the brain as
an information processorby describingfundamental
relationsbetweenmovementduration,movementsize,
and movement accuracyin rapid, aimed movements.
Finally,FranklinHenry (1904-\993)studied motor behavior in a physical education setting. He trained a
generationof prominent scientistswho begantheir car e e r si n t h e 1 9 6 0 sa n d 1 9 7 0 s .
T h e 1 9 2 0 s 3 0 s ,a n d 4 0 s a l s o s a w t h e e m e r g e n c e
of the field of motor development. This field began
w i t h s e m i n a l p u b l i c a t i o n so f o b s e r v a t i o n a rl e s e a r c h
, yrtle
, a r y S h i r l e y( 1 9 3 1 ) M
b y A r n o l d G e s e l l( 1 9 2 8 ) M
(1936).
(1935),
and Nancy Bayley
McGraw
Merging of Physiological
end PsychologicalApProaches
5.L The somatotopic map of the primary motor
, ho
c o n d i t i o n s .R . S . W o o d w o r t h ( 1 8 6 9 - 1 9 6 2 ) w
on to servebrieflyas an assistantto Sherrington,
by studyingthe principles of rapid hand movets, includingthe interaction of speed, accuracy,
a colleague
vision.E. L. Thorndike 11874-1949),
Woodworthon the ColumbiaUniversityfaculty,
iedthe processesthat underlie skill learning.His
olEffwtwas influential in formulating early 20th
theory.Thislaw statesthat relarded
rylearning
B e g i n n i n gi n t h e 1 9 7 0 st h e r e w a s a r a p i d m e r g e r
o f t h e t r a d i t i o n s o f p s y c h o l o g ya n d m o t o r n e u r o p h y s i o l o g y .T h e w o r k o f t h e R u s s i a nn e u r o p h y s i o l o g i s t N i k o t a i B e r n s t e i n ( 1 8 9 7 - 1 9 6 6 )w a s p a r t i c u l a r l y
i n f l u e n t i a l i n t h i s m e r g i n g o f d i s c i p l i n e s .B e r n s t e i n
w o r k e d i n o b s c u r i t yi n R u s s i ad u r i n g t h e 1 9 3 0 sa n d
1 9 4 0 so n t h e f u n d a m e n t a l i s s u e o f h o w a s y s t e m
a s c o m p l e x a s t h e n e u r o m u s c u l a rs y s t e m i s c o o r d i n a t e d . H e u s e d a p p r o a c h e st o t h e s t u d y o f m o t o r
c o n t r o l t h a t m e r g e dt h e b e h a v i o r a la n d n e u r a l l e v e l s
o f i n q u i r y . I n p a r t i c u l a r h e o b s e r v e dh o w t h e b o d y ,
a s b o t h a n e u r a l a n d m e c h a n i c a ls y s t e m ,i n t e r a c t e d
w i t h t h e e n v i r o n m e n t .H e t h e o r i z e dt h a t f u n c t i o n a l
m o v e m e n ti s t h e r e s u l t o f c o n t r o l t h a t i s d i s t r i b u t e d
a c r o s sm a n y l e v e l s o f t h e n e r v o u ss y s t e m ,a n d a l s o
a m o n g t h e n e u r o m u s c u l a ra n d m e c h a n i c a ls y s t e m s
o f t h e b o d y . B e r n s t e i n ' sw o r k w a s n o t w i d e l y k n o w n
u n t i l a n E n g l i s h t r a n s l a t i o n a p p e a r e d i n 1 9 6 7 ,o n e
year after his death. This and other translations
a c c e l e r a t e dt h e c o m b i n e d n e u r a l a n d b e h a v i o r a l
a p p r o a c ht o t h e s t u d y o f m o t o r c o n t r o l , w h i c h c o n tinues today.
, h e r e a sr e s p o n s e s
t e n d t o b e r e p e a L e dw
arenot rewardedtend not to be repeated
WorldWarII sawscientistsin the UnitedStates
MOTORLEARNING
t Britain study critical questions for the war
, suchas how to selectand rapidlytrain pilots,
iers, and gunners.This researchdeveloped
that carried on into a productive postwar
om/wilsonle
T h e a c q u i s i t i o na n d r e f i n e m e n to f n e w m o t o r s k i l l s
h a v ea m a j o r i m p a c t o n o u r l i v e sa s w e t a k e u p n e w
hobbies or jobs, participatein sports, or begin to
Chapter Five Motor Learningand Motor Control
77
I
T
12
1
IJ
14
Trials
Figure5.2 Hypothetical data demonstrating a typical performance curve in which perfor'
mance lncreasesmore rapidly during the early phasesof practiceand less rapidly as the
learnergains more experiencewith the task. Learningcan be inferredfrom the retention of
performancefollowing a rest period.
engage in important activities of modern life like
driving a car or typing on a keyboard. lt is not surprising that considerableresearcheffort has been ex'
pended over the past 70 years to understand how we
learn and refine new motor skills. The results of this
research have influenced how instructors, coaches,
therapists, and others approach teaching and rehab i l i t a t i o n t o o p t i m i z e m o t o r l e a r n i n g .R e c e n t l yt h e
s t u d y o f m o t o r l e a r n i n g h a s b e e n r e e n e r g i z e db y
remarkable discoveries of rapid structural changes
t h a t o c c u r i n o u r b r a i n sa s w e l e a r n n e w m o t o r s k i l l s .
These discoveries have fueled intense study of the
neural mechanisms underlying learning and how
t h i s n e w k n o w l e d g e c a n e n h a n c e t h e r e c o v e r yo f
m o t o r f u n c t i o n f o l l o w i n g b r a i n i n j u r i e s .T h i s p a r t o f
the chapter considers the results of several decades
o f r e s e a r c ho n m o t o r s k i l l a c q u i s i t i o nb y e x a m i n i n g
the conditions that facilitate motor learning so that
o n e c a n m a x i m i z et h e e f f i c i e n c yo f t r a i n i n g a n d p r a c tice sessions.Next recent exciting discoveriesin the
area of brain plasticity and its implications for motor
learning and the recoveryof motor function follow'
i n g b r a i n i n i u r ya r e e x a m i n e d .
S c h m i d t a n d L e e ( 2 0 0 5 1d e f i n e d m o t o r l e a r n i n g s u c c i n t l y :" M o t o r l e a r n i n g i s a s e t o f p r o c e s s e s
a s s o c i a t e dw i t h p r a c t i c e o r e x p e r i e n c el e a d i n g t o
r e l a t i v e l y p e r m a n e n t c h a n g e si n t h e c a p a b i l i t y f o r
m o v e m e n t " ( p . 3 0 2 ) .I n o t h e r w o r d s , w h e n w e l e a r n
a m o t o r s k i l l , w e p e r m a n e n t l yc h a n g e o u r c a p a b i l i t y f o r p r o d u c i n ga s k i l l e d a c t i o n , a n d t h e s e c h a n g e s
o c c u r t h r o u g h n e u r a l p r o c e s s e st h a t a r e a s s o c i a t e d
. e c a u s em o t o r l e a r n i n g
w i t h p r a c t i c eo r e x p e r i e n c e B
for movement,
is defined as a change inthe capabilitU
r a t h e r t h a n i n m o v e m e n t i t s e l f , w e m u s t i n f e rt h a t
m o t o r l e a r n i n gh a s o c c u r r e df r o m a c h a n g ei n m o t o r
p e r f o r m a n c e .I t i s a c o m m o n e x p e r i e n c et o i m p r o v e
p e r f o r m a n c eo n a n e w t a s k d u r i n g t h e i n i t i a l p r a c tice session. If we plot measuresof performance
over the course of practice, we may see a curve like
t h a t i n F i g u r e5 . 2 .
The curve shown in Figure 5.2 certainly reflects
improving performance with practice, but does the
increased performance from the lst to the 1Oth
trial reflect motor learning? Our definition specifies
that only relativelypermanent changesqualify as
e v i d e n c ef o r m o t o r l e a r n i n g .O n e w a y t o d e t e r m i n e
whether the increasedperformance is relatively perm a n e n tw o u l d b e t o t e s t o u r p e r f o r m a n c eo n a n o t h e r
day or after a suitable delay or rest, which would
allow temporaryeffects(such as being warmed up
o r i n a s t a t e o f h e i g h t e n e da t t e n t i o n ) t o d i s s i p a t e .
from the
In this way we can estimate what we retained
p r e v i o u ss e s s i o n .E x a m i n i n gt h e r e s u l t so f r e t e n t i o n
tests is one approach to inferring motor learning
f r o m m e a s u r e so f p e r f o r m a n c e .l n F i g u r e 5 . 2 , t r i a l s
1 I t h r o u g h I 5 r e p r e s e n tt h e r e s u l t s o f a r e t e n t i o n
test and show that the increased performance was
maintained after a rest period. The opposite also
cafl oCCUf;that is, performance can improve after
rest from dissipationof conditions such as fatigue
that impair performance.
Schmidt and Lee'sdefinition of motor learning
also states that the processesthat underlie learning
witft practice or experience. Why not say
are associated
instead that the learning occursduringpractice or ex'
p e r i e n c e ?O n e r e a s o n i s t h a t n e u r a l p r o c e s s e st h a t
help to make the changed motor performance permanent are active for many hours after practice and
some may even require a night of sleep (BrashersKrug,Shadmehr,€-Bizzi,I 996;Cohen,Pascual-Leone,
Press,& Robertson,2005;Robertson,Pascual-Leone,
E M i a l l , 2 0 0 4 ) .C o n s o l i d a t i n gm o t o r m e m o r y i n t o a
relativelypermanentstateappearsto occurgradually
and may consistof severalstagesthat involvediffer'
ent brain areas(Luft & Buitrago,2005)This may be
anotherreasonperformanceon retentiontests can
exceedperformanceat the end of the previoustralning period.
Motor learningdoes not alwaysrequirephysical practiceor experience.One can improvemotor
in a permanentwayby imitatingsomeperformance
learning)or
(observational
one else'sperformance
description
a
verbal
by attemptinga task following
is a rich
there
oi the tait. Perhapsmore surprising,
you
that
imagining
literatureindicatingthat vividly
performance
yields
increased
areperforminga task
on retentiontests(Feltz& Landers,1983;Jeannerod'
gainsarenot as
Althoughtheseperformance
1995).
practice'they
physical
greatas those obtainedby
& Horan'
Thomas,
are substantial(Hird, Landers,
comes
learning
Onetheoryis that the motor
1991).
internally'
task
about by the brain practicingthe
as
usingthe samebrain regionsand mechanisms
inhibit'
then
and
it wouldfor performingthe task,
ing the final commandsthat would producemus2001).The factthat increased
clJ force(leannerod,
followingmental
strengthhas been demonstrated
(Yue&
mechanism
practiceindirectlysupportthis
performance
the
Cole,1992).Anotherview is that
gainsfollowingphysicalversusmentaltrainingresult from activity in differentbrain areas(Nyberg
on
E Marklund,2006),depending
Larsson,
Eriksson,
comdon't
we
the complexityof the task.Although
pletelyunderstandthe mechanismsthat underlie
motorlearningfollowingmentalpractice,there is
no doubtthat we can learn new tasks,to a polnt'
withoutphYsicalPractice.
cerebralcortex.lt had beenbelievedthat little motor
recoverycould occurafter 6 to l2 monthsfollowing
the stroke.Researchover the past decadehas now
that intense,repetitivepracticeof the
demonstrated
impairedupper limb, practicelastingseveralhours
per day overa few weeks,can substantiallyimprove
motor functionevenyearsafter a stroke.This was
true when the therapeutictechnique included
forceduse of the impairedlimb in functionaltasks
(Wolfet al., 2006)or when the impairedupper limb
was assistedor resistedroboticallyduring reaching
movements(Fasoliet al., 2004).Thesefindingshave
poweredan excitingrevolutionin the approachesto
is
therapyfollowingstroke.What is moreremarkable
repetiintense,
these
that strokerecoveryfollowing
tive practicetherapiesand motor learningin healthy
individualsfrom repetitivepracticeappearto share
involvingbrain plasticity(dis'
commonmechanisms
cussedlaterin this chaPter).
MASSED VERSUS DISTRIBUTED PRACTICE
Howshouldone schedulepracticeto maximizelearning?Studiesof practicedistributionhavefocusedon
determininghow muchtime shouldbe spentin practice versusrest duringa practicesession,as well as
the distributionof practicesessionsduringthe day'
A considerableamount of researchhas focusedon
whetheryou retain more with relativelyshort rest
intervalsduringa practicesession,termedmassed
practice,or if betterretentionoccurswith relatively
long rest intervalsduringa session,termeddistrib'
uted practice. Practicesessionsorganizedaround
will requiremoretlme
distributedpracticeschedules
if an equalnumberof repetitionsare to occurcomparedto practicebasedon a massedpracticeschedule.Thegeneralfindingis that massedpracticetends
to result in poorerperformanceduringthe practice
Learning
Optimel
for
Conditions
sessioncomparedto distributedpractice(Lee E
who practicedunder
1988).Participants
Genovese,
instructors'
THE LAW OF PRACTICE Coaches,
a distributedpracticeschedulealso showedbetter
and studentsall seek,or shouldseek,to
therapists,
retentionwhen tested either a short time after the
how one shouldpracticein orderto learn
understand
practicesession(minutes)or a long time afterprac(to achievethe most learningwith the
mostfficienthtr
months)
tice (weeks,
the numberof practicetri'
Maximizing
leastpractice).
that a practice session with
suggests
This
be
to
come
has
alsis thefirstprincipleof practiceand
adequaterest periodsyields better motor learning'
knownas the Law of Practice.lt should come as no
pracconcerning
H o w e v e rm
, u c ho f t h i s r e s e a r c h
that more practiceleadsto more learning'
surprise
motor
on
tice distributionscheduleshas focused
Thechangein performancetypicallyis rapid early
tasksthat are best describedas continuous,suchas
(see
improves
in practiceand slowsas performance
follow,or track,the motionsof someFigure5.2).Afterextensivepractice,the performance attemptingto
or climbingup anddown
thingmovingcontinuously,
gainsmay slow so much that it may be tempting to
a smallladderthat you mustbalancewhileclimbing'
concludethat learningno longeroccurs However'
Do the findingsfromthesestudieson practiceschedgainsthat continue
therearereportsof performance
ules for continuoustasks generalizeto so'called
evenaftermillionsof repetitionsof a taskovermany
discretetasksthat last less than a second,such
1959).
(Crossman,
years
as kickingor throwing?The answer,basedon much
An important application of this Law of Practice
seemsto be that massedpracticeyields
lessresearch,
the recent change in the treatment of individuals
better performanceon discretetasks comparedto
the motor areas of the
lowing a stroke affecting
le
.mhhe.com/wilson
Chapter Five Motor Learning and Motor Control
79
c o n t i n u o u st a s k s b o t h d u r i n g p r a c t i c ea n d o n r e t e n t i o n t e s t s p e r f o r m e dl a t e r . I t s e e m s f a i r t o c o n c l u d e
t h a t w h i l e a m a s s e d p r a c t i c es c h e d u l em a y b e b e s t
f o r l e a r n i n ga d i s c r e t et a s k ,c o n t i n u o u st a s k st h a t i n t r o d u c et h e p o s s i b i l i t yo f f a t i g u es h o u l d b e p r a c t i c e d
u n d e r a d i s t r i b u t e d s c h e d u l e .C l e a r l y , i n s t r u c t o r s ,
c o a c h e s ,a n d t h e r a p i s t st e a c h i n g d i s c r e t es k i l l s w i l l
favor the efficiency of a massed practice schedule,
b u t t h e y s h o u l d b e p r e p a r e dt o a l t e r t h e i r p r a c t i c e
s c h e d u l i n gf o r c o n t i n u o u s t a s k s .C o n s i d e rh o w t h i s
s t a t e m e n tw o u l d i m p a c t a p h y s i c a lt h e r a p i s tw o r k i n g
w i t h a c l i e n t a t t e m p t i n gt o r e g a i nu p p e r l i m b r e a c h i n g s k i l l s v e r s u sw a l k i n g , o r t h e p r a c t i c es c h e d u l e s
t h a t m a y f a v o r t h e s k i l l s n e e d e d i n b a s e b a l lv e r s u s
those of the musician
A n o t h e r i s s u e o f c o n s i d e r a b l ep r a c t i c a l i m p o r t a n c e i s w h e t h e ro n e s h o u l d s c h e d u l em u l t i p l e s h o r t
practices during the day or week, or if fewer, longer
p r a c t i c e s y i e l d b e t t e r p e r f o r m a n c ea n d r e t e n t i o n .
R e s u l t sf r o m a n e x p e r i m e n ti n w h i c h p o s t a l w o r k ers were taught a typing task used for a mail sorting
m a c h i n e ( B a d d e l e y& L o n g m a n , 1 9 7 8 )i n d i c a t e dt h a t
m a s s e dp r a c t i c es c h e d u l e s( e . g . t, w o l - h o u r s e s s i o n s ,
twice per day for 15 days) yielded worse performance
while practicing and poorer retention i to 9 months
l a t e r t h a n d i d m o r e d i s t r i b u t e d p r a c t i c es c h e d u l e s
( e . g . ,1 - h o u rs e s s i o n so n c e p e r d a y f o r 6 0 d a y s ) .
At this point the astute readermay begin to wonder how the Law of Practiceaffectsconclusionsabout
practice schedules.Studies on practice distribution
s c h e d u l e sa r e d e s i g n e dt o h o l d c o n s t a n tt h e n u m b e r
of task repetitionsor the actual time spent practicing
Thus, under distributed practiceschedulesit will take
l o n g e rt o a c h i e v et h e s a m ea m o u n t o f t i m e o r n u m b e r
of task repetitions compared to a massed practice
schedule. The Law of Practice states that performance and retention increasewith increasingpractice
. u t t i n gt h e s ec o n c e p t s
t i m e o r n u m b e ro f r e p e t i t i o n s P
t o g e t h e r o n e c a n a s k i f , d u r i n g p r a c t i c es e s s i o n so f
equal duration for massedversusdistributed practice,
the negativeeffectsof massedpractice (in the caseof
continuous tasks)can be offset by the increasedpractice that can be realizedduring the massed practice
sessions compared to distributed practice sessions.
While these issues require additional study, research
confirms the benefits of massed practice in stroke
recovery for upper limb skills, as noted previously
(although many of the skills were discretein nature)
PRACTICE
VARIABLE VERSUS CONSTANT
practice
play
when
designing
into
come
issues
Other
of
repetitiveness
the
involves
these
of
one
sessions;
practice.When learninga brand new skill like throwing
a curve ball in baseball,one tends to repeatthe same
m o v e m e n t sa g a i na n d a g a i nw i t h o u t i n t e r r u p t i n gt h i s
practice by throwing a different pitch, such as a fastball or change-up.This approachhelps you to achieve
80
Part Three Exploringthe Behavioral
the "feel"of the essentialmotions for throwing a curve
b a l l .O n c et h i sf i r s fp h a s eo f l e a r n i n gi s c o m p l e t ey' o u r
goal probably is to learn to throw the pitch accurately
to different locations in the strike zone (e g., close to
the batter's body versus away from the batter) and
a l s o t o t h r o w t h e c u r v e a c c u r a t e l ya f t e r j u s t h a v i n g
thrown a differenttype of pitch. How should you plan
your practicesessionswith these latter goals in mind?
S h o u l d y o u p r a c t i c et h r o w i n g a c c u r a t e l yt o a s i n g l e
t a r g e t a n d a s s u m et h a t t h i s a c c u r a c yw i l l g e n e r a l i z e
when you want to throw the ball to a different part
of the strike zone?Or should you practicepitching to
a variety of targets?Similarly, if you want to practice
, n d c h a n g e ' u p sd u r i n g a s i n g l e
c u r v eb a l l s ,f a s t b a l l s a
practice session,will you learn them more efficiently
by practicingfirst one pitch to a desiredlevel of performance before moving on to another?Theseexamples
raise the issue of two important factors in designing
a practice session:variable versus constant practtce
and blocked versusrandom practicescheduling
Variable practice refers to practicing the same
skill under varyingconditions or at different levels
o r t a r g e t s .O u r b a s e b a l lp i t c h e r c o u l d e m p l o y a c o n '
s t a n t p r a c t i c e s c h e m e b y r e p e t i t i v e l yp i t c h i n g t o
o n e l o c a t i o n ,s u c h a s t h e m i d d l e o f t h e s t r i k e z o n e .
Variable practice would involve attempting to pitch
t o a v a r i e t y o f l o c a t i o n s ( e . g . ,h i g h , l o w , I e f t c o r n e r ,
r i g h t c o r n e r ) .S t u d i e sc o m p a r i n gc o n s t a n tv e r s u sv a r i a b l e p r a c t i c e s c h e m e sg e n e r a l l yi n d i c a t e t h a t i n d i v i d u a l s w h o t r a i n u n d e r v a r i a b l ep r a c t i c ec o n d i t i o n s
perform worseduringthe training session but perform
betterduring the later retention test, from which we
infer better learning for the variable practice group.
You can imagine as a coach it could be difficult to
c o n v i n c et h e a t h l e t e t h a t h e o r s h e w i l l l e a r n m o r e
w i t h v a r i a b l ep r a c t i c ew h e n t h e a t h l e t e i s e x p e r i e n c i n g w o r s e p e r f o r m a n c ew h i l e p r a c t i c i n gc o m p a r e dt o
c o n s t a n tp r a c t i c es c h e m e s .
T h e e f f e c t so f v a r i a b l e p r a c t i c e a l s o h a v e b e e n
studied when individuals practicea variety of diff e r e n t t a r g e t l o c a t i o n sa n d t h e n a r e t e s t e d l a t e r o n
a t a r g e t u p o n w h i c h t h e y n e v e r p r a c t i c e d .T h e p e r f o r m a n c eo f t h e s e i n d i v i d u a l s i s c o m p a r e d a g a i n s t
individuals who practiced only one target location before their test on the novel target location.
S t u d i e s l i k e t h i s r e v e a lt h a t t h o s e w h o e x p e r i e n c e d
v a r i a b l e p r a c t i c ep e r f o r m e dw o r s e d u r i n g t h e t r a i n '
i n g s e s s i o nt h a n t h o s e w h o p r a c t i c e da s i n g l et a r g e t ,
b u t t h e y p e r f o r m e db e t t e r w h e n t e s t e d o n t h e n o v e l
target. Thus, it seems that variable practice also
helps us learn how to adiust our motor commands
t o n e w c l r c u m s r a n c e s .l t h a s b e e n s u g g e s t e dt h a t
v a r i a b l e p r a c t i c e i s p a r t i c u l a r l yb e n e f i c i a lt o t h o s e
w h o g e n e r a l l y a r e l e s s e x p e r i e n c e di n m o v e m e n t ,
s u c h a s c h i l d r e n( S c h m i d t& L e e ,2 0 0 5 ) .l n a n y c a s e ,
v a r i a b l ep r a c t i c eh a s n o t b e e n d e m o n s t r a t e dt o i m p e d e l e a r n i n gc o m p a r e dt o c o n s t a n t p r a c t i c e .
BLOCKED VERSUS RANDOM PRACTICE
How should one schedulepractice?In the caseof
throwingdarts accuratelyto a varietyof targetson
theboard,shouldyou practicefirstat onetargetuntil
you becomeproficient,then anothertarget,and so
on?This would be an exampleof a blocked practlce schedule.Undera random practice schedule,
you would attemptto hit a differenttargeton each
ihrow.lntuitivelyyou might think that practicingdifferenttargetsrandomlywould slow your learning
Perhapsconstantlychangingtargetswill interfere
withyourability to concentrateand get into a groove'
comparingblockedversus
Theresultsof experiments
randompracticeschedulesshowsthat blockedpracthan randompractice
ticeyieldsbetterperformance
but practiceundera random
thetrainingsessions,
dunng
scheduleyields better performance0n retentilntests
to practiceundera blockedscheduleOne
compared
explanationfor this often-reportedfinding is that
we learnbetter when we don't "get into a groove"'
we mustengagein moreelaborateand combecause
plete preparationfor each movementrather than
carryingoverthe preparationfrom repetitionto repetition.This line of reasoningwas derivedfrom the
(Battig,1979)This
theoryof contextualinterference
supportsthe approachsomebasketballcoachestake
freethrowshootingpractice
in whichtheyintersperse
in smallblocksthroughouta practicesessionrather
thanrequiringplayersto repetitivelyshootfreethrows
in largeblocksat the beginningor end of practice'
Beforewe leavethis topic,it is importantto note
also havestudiedintermediateforms
thatscientists
in whichsmallblocksof the same
ofrandompractice,
taskaremixedrandomlyamongsmall blocksof differenttasks.Under these conditions,we find that
onecanachievethe samelevel of learningwithout
practiceschedto a completelyrandomized
.resorting
the softballpitchermaythrowfour
Forexample,
and then
singpitches,followedby four change'ups,
curvesor drop balls.ln any case,the resultsof
h lead us to conclude that once an individual
performthe task in a basic way, one should avoid
ling on the task by repeating it over and over and
againwithout performingan interveningskill
is conclusionshould hold for efficientlylearning
aboutanv motor skill one can imagine,across
skills
, music,hobbies,and occupational
ICAL GUIDANCE After consideringthe
of motor learningby mentalimag'
r discussion
, and the reasoningbehind the positive effectsof
it may come as no sur'
oracticeschedules,
that we learn better when we performmoveas much as possibleunder our own power
or guidance'This
thanwithphysicalassistance
importantissuebecausephysicalassistance
or roboticdeviceis frequentlyusedin
therapist
followingnervoussysteminiuryor disrehabilitation
ease.Thereis no doubtthat guidance,eitherphysical
or verbal(talkingsomeonethroughthe task),is useful
at first. Likewise,physicalguidanceor feedbackdurduringa training a taskwill improvethe performance
At this point in the chapter,you probably
ing session.
the conditionsthat lead
areskepticalaboutaccepting
conditionsfor
gain as representing
to a performance
learning,unlessthesegainsare retainedin latersessions.Your skepticismwould be justified,as once
againwe find a conditionof practiceguidance,which
is not as effectivein producingsustainablegainsin
performanceas other techniques.Techniquesthat
iorce the performerto generatethe actionson his
or her own as muchas possibleprovidegreaterperformancegainsduring subsequenttests than when
the actionsare guided.ln particular,feedbackabout
at the end of the task,or at the end of
performance
a blockof repetitions,is more effectivein producing
motorlearningthanarephysicalguidanceor continuduringeachtrial.
ous feedback
Currenttechniquesin motor rehabilitationfollowingbrain iniuryattemptto weanthe patientfrom
physicalguidanceas quicklyas possible.ln strokereis a problem,earlystages
whenweakness
habilitation,
in producing
of therapymay involvesomeassistance
Laterstagesof this therapyinreachingmovements.
andeven
volvethe patientworkingwithoutassistance
(to increasestrength)as he or she
againstresistance
progresses.
Brein Plasticity
Brain plasticity refers to the ability of the brain
to show modification in response to experlence
(learning and memory) or injury. Researchin motor
learning has been reenergizedduring the past
20 years by exciting discoveriesthat revealed more
r a p i d a n d e x t e n s i v eb r a i n p l a s t i c i t yt h a n w a s p r e v i ously believed.
One of the remarkablefindings emergingrecently
the motor areas that are active during movethat
is
ment of a particular joint, or the sensory areas that
respond to stimulation of a particular body part, can
reorganizewithin hours while acquiring new tactile
perceptualskillsor motor skills (Xerri,Coq,Merzenich,
E lenkins, 1996;for a review see Sanes & Donoghue'
2000).In experimentssuch as these, the brain areas
that respondedto the stimulation or movement of a
particularpart of the body expand as the skill is practiced, while nearby areas representing noninvolved
body parts shrink. These findings reveal that the
basic cortical areas involved in sensing stimuli and
generating movement are not static but reorganize
dynamically in response to experience Ouite simply, the demands placed upon us by our environment
causethe brain to adaPt.
Chapter Five Motor Learning and Motor Control
81-
We now know that this adaptation includes in'
creasesand decreasesin the number and complexity
of dendrites (the portions of neurons important for
receiving information from other neurons) and their
connectionswith other neurons,along with changesin
the strength or effectivenessof these synapticcontacts'
The role of these fundamentalchangesduring the early
phases of skill acquisition is under increasedstudy
For example,drugsthat affectthe electricalexcitability
of cells in the brain can affect motor learning Drugs
that decreaseexcitabilityin the motor cortex (and act
as central nervoussystemdepressants),such as lorazepam (usedto relieveanxiety)and dextromethorphan
, pair motor learning
( u s e d i n c o u g h s u p p r e s s a n t s )i m
(Donchin,Sawaki,Ghangadar,€"Cohen,2002)
A l t h o u g h r a p i d c h a n g e si n b r a i n p l a s t i c i t y m a y
b e a d a p t i v e( h e l p f u l )t o t h e o r g a n i s m ,t h e y m a y a l s o
b e m a l a d a p t i vl te .i s b e l i e v e dt h a t p l a s t i c c h a n g e sa r e
partly to blame for a rare disorder known as focal dys'
t o n i a , w h i c h i s m a n i f e s t a s a c r a m p i n g l i k eb e h a v i o r
that impairsthe ability to producehighly practiced
l usicians
m o v e m e n t s ,s u c h a s t h o s e o f m a s t e r - l e v em
( B y l ,2 0 0 a ) .
P a r a l l e l i n go u r e x p a n d i n g k n o w l e d g e o f b r a i n
plasticity during motor learning is a researcheffort
a i m e d a t d i s c o v e r i n gt h e m e c h a n i s m st h a t u n d e r l i e
recoveryof motor function following brain injury' It
h a d l o n g b e e n b e l i e v e dt h a t t h e p r i m a t e b r a i n w a s
c a p a b l e o n l y o f l i m i t e d s t r u c t u r a lc h a n g e f o l l o w i n g
i n y u r y .T h e b r i l l i a n t a n a t o m i s t a n d N o b e l L a u r e a t e
R a m o n y C a i a l ( c o n s i d e r e db y m a n y a s a f a t h e r o f
) e l i e v e dt h a t t h e a x o n s a n d
m o d e r n n e u r o s c i e n c eb
d e n d r i t e so f m a m m a l i a n n e u r o n s i n a d u l t s w e r e i n capable of further growth and regeneration (Ramon
y C a j a l , 1 9 2 8 )W
. e now knowthat this is not true and
t h a t a f t e r i n i u r y t h e r e i s b r a i n p l a s t i c i t ya t m o l e c u l a r ,
synaptic,cellular,network,and systemslevels (Nudo,
2006).Our rapidty expanding knowledgeabout what
drives new growth and regenerationafter brain in jury
holds promise for better recoveryof function through
behavioraland pharmacologicaltherapies.
A key question is the extent to which these
a d a p t i v e p r o c e s s e sc a n b e e n h a n c e d .T h e r a p e u t i c
i n t e r v e n t i o n sh a v e b e e n e x p l o r e du s i n g d r u g s ,e l e c t r i c a l s t i m u l a t i o n ,a n d b e h a v i o r a lt h e r a p y S c i e n t i s t s
a l s o a r e i n v e s t i g a t i n gi s s u e s l i k e t h e t i m i n g o f
i n t e r v e n t i o n st o d e t e r m i n e h o w b e s t t o t a k e a d v a n t a g e o f t h e a d a p t i v e m e c h a n i s m st h a t a r e s p u r r e d
i n t o a c t i o n f o l l o w i n g i n i u r y .A n i m p o r t a n t f i n d i n g i s
t h a t p o s t i n j u r yb e h a v i o r a le x p e r i e n c ef a c i l i t a t e st h e
a d a p t i v er e w i r i n g .l t i s t h o u g h t t h a t t h e a c t i v a t i o no f
the intact areasthrough our attempts to move serves
a s s o m e s o r t o f s i g n a lt h a t , i n e f f e c t ,c a l l s o u t t o t h e
sproutingaxonsso that the area can be recognized
as a targel.
It is easyto see why there is so much interestnow
in studies focused on determining which therapeutic
practicesare most effective,how the therapy sessions
s h o u l db e s c h e d u l e da n d s t r u c t u r e d( t i m i n g ,i n t e n s i t y ,
type of movements),and how the intervention should
be modified, if at all, according to the site of lesion
and size of lesion. In addition to the effectivenessof
therapy, the fficiencqof therapy is of great concernbecause therapy time is expensive.The role of robotic
devices in stroke therapy is garnering considerable
interest for this reason.Collectivelythese issues are
rapidly reshaping the face of poststroke therapeutic
practlces.
MOTORCONTROL
The movements that we produce require vast net'
works of neurons in our central nervous system that
ultimately converge on the neurons that directly
activate our muscles. These neuronal networks that
plan and execute our movements also interact with
networks concerned with motivation (it's time for
me to go to school),attention (ignore the television program you've been watching and look for your
backpack),sensoryinformation about the state of the
environment (my backpackis 1 foot in front of me and
6 inchesto the right of my right shoulder,and it weighs
l0 pounds) and the state of your body (l'm already
standingup, my left hand is holding my jacket,and my
right hand is at my side), and emotional or strategic
factors(l'm running late,so t'd better move quickly).
Scientists don't completely understand how we
produce even simple coordinatedmovements like
reaching,so there is no single theory of motor con'
trol. This part of the chapter introduces some of the
most fundamentalobservationsthat have been made
about movement production. These observations
begin to help us understand how skilled movements
are oroducedfrom the interactionsof the nervoussystem, musculoskeletalsystem,and the environment.
Central Motor RePresentations
end the Roleof SensoryInfiormation
The central nervous system is continuously bombarded by sensory signals carrying information
important for planning and executingour movements'
Besidesvision, sensorysignals from receptorsin our
muscles,tendons, skin, vestibular system, jolnts,
and ligaments can inform our motor system about
the state of our body (particularly the musculoskeletal system) and the state of our surroundings.lt is
not surprising,therefore,that there is a long history
of researchfocusedon the problem of discoveringexactly how sensory information contributes to motor
control.An important finding of this researchwas that
individualswho were deprived of sensoryinformation
through diseaseor iniury still could producevoluntary
movements.This means that the brain must store, or
represent,motor actions in some way. ln this section
we'll focus on the movement capabilitiesof individuals deprivedof sensory information, and in the pro'
cesswe'll learn a little about how action is stored or
representedin the central nervoussystem.
An influential study by Mott and Sherrington
( 1 8 9 5 )r e p o r t e dt h a t a m o n k e y f a i l e d t o u s e i t s f o r e limb after the sensorynerve roots to that limb alone
were severedwhere they enter the spinal cord They
concluded,incorrectly,that sensorysignals were abs o l u t e l ye s s e n t i a lt o p r o d u c e m o v e m e n t . T h i s w a s
v i g o r o u s l yd i s p u t e d a f e w y e a r sl a t e r ( H e r i n g , 1 8 9 7 ) '
T h u sb e g a n a p e r i o d o f a b o u t I 5 0 y e a r so f c o n t r o versyregardingthis topic. (We now know that monk e y sw i l lu s e t h e i r s e n s a t i o n - d e p r i v e fdo r e l i m b w h e n
forcedto; for example, when the normal forelimb is
Thesecontroversieswere rerestrainedlTaub, 1976]t).
two reports were published
when
1980s
solvedin the
w
h o l o s t a l l s e n s o r ys i g n a l s
i
n
d
i
v
i
d
u
a
l
s
concerning
from an unknown disease
legs
and
arms
from their
of the arms and legs
neurons
sensory
that affected
u
n a f f e c t e d( R o t h w e l l
n
e
u
r
o
n
s
m
o
t
o
r
while leaving
D
a
l
a
k a s&
, E v a r t s ,1 9 8 5 ) '
M
a
u
r
i
t
z
,
S
a
n
e
s
,
et al.,1982;
were
individuals
(or
deafferented)
Theseinsensate
they
b
u
t
s
t
r
e
n
g
t
h
,
m
u
s
c
l
e
i
n
r e l a t i v e l yu n i m p a i r e d
w
hen
o
r
t
o
u
c
h
e
d
w
a
s
s
k
i
n
t
h
e
i
r
w
h
e
n
c o u l dn o t f e e l
r
e
f
l
e
xive
t
h
e
w
e
r
e
m
i
s
s
i
n
g
A
l
s
o
their ioints moved.
o
c
cur
n
o
r
m
a
l
l
y
t
h
a
t
m
u
s
c
l
e
s
o
f
t
h
e
i
r
contractions
(
e
.
g
.
,
t
he
w
h
e
n
s
t
r
e
t
c
h
e
d
r
a
p
i
d
l
y
a
r
e
whenmuscles
j
u
s
t
y
o
u
r
w
i
th
k
n
e
e
b
e
l
o
w
t
h
e
t
e
n
d
o
n
p h y s i c i a nt a p s
a r e f l e xh a m m e r ) .
The most revealing results were obtained when
the patientsclosed their eyes,for it was then that the
scientistscould observe the capacity of the central
n e r v o u ss y s t e mt o p r o d u c e m o v e m e n t w i L h o u ts e n soryinformation.ln the laboratorythese patientswere
ableto initiateand performsimple and complexmovements,though poorly. Clearly,Mott and Sherrington
( 1 8 9 5 )w e r e w r o n g ! L e a r n e d ,v o l u n t a r y m o v e m e n t s
could be performed without sensory information
Thismeansthat movementsare representedcentrally
in some form and, at our desire, can be reproduced
o r a s s e m b l e df r o m t h e i r e s s e n t i a le l e m e n t sb y p r o '
that continue to be the subject of considerable
cesses
research(see Shumway'Cook& Woollacott, 2007,for
a succinctreview of contemporarytheories of movementcontrol).
One important clue to the nature of these central representations of skilled movements can be
foundin the observationsof Sanesand his colleagues
(1985).They observedthat the movements that their
insensatepatients produced typically contained err o r s .W h e n v i s i o n w a s r e m o v e d , n o t o n l y d i d p r o founderrorsof movement sizeoccur in these patients
but frequently even the direction of movement was
incorrect.We must conclude that the brain does not
Ie
www.mhhe.com/wilson
store complete, well-formed actions that are simply
replayed from memory. lnstead, additional information from our sensorysystemsis needed,such as the
current state of the body and the state of our immediate surroundings,to assemblethe detailed movement
commands so that accurate movements can be produced. (This topic is addressedin the next section )
S u c h o b s e r v a t i o n ss u p p o r t t h e w i d e l y h e l d b e l i e f
today that movementsare elaboratedin their details
by a progressionof neural processes,beginning with
an abstractrepresentationof the movement,and that
sensory information is required at several steps in
this processto generateaccurateand efficient move'
m e n t s . H o w w e a c q u i r e ,m a i n t a i n , a n d a d a p t t h e s e
central representations are topics of intense study
today.
SensorySignalsend Motor control
We now come to the obvious issue: Exactly what is
the role of sensory information in producing accurate actions?ln 1941the eminent neuroembryologist
Paul Weisswrote, "Nobody in his senseswould think
of questioning the importance of sensory control
of movement. But iust what is the precise scope of
that control?" (p. 23) Scientistscontinue to address
Weiss'squestion todaY.
We can gain insight to
POSTURAL CONTROL
t h i s i s s u e b y f u r t h e r e x a m i n i n gh o w i n s e n s a t ei n d i viduals behavewhile they attempt to produce various
m o t o r a c t i o n s . F i r s t , s e n s o r yi n f o r m a t i o n i s c r u c i a l
in correcting for small errors that occur during slow
movements and while attempting to hold a steady
posture. One of the most profound behaviorsof these
i n s e n s a t ep a t i e n t s i s t h e i r l a c k o f p o s t u r a l s t a b i l i t y
When attempting to hold a steady hand position,
t h e y d o s o r e a s o n a b l yw e l l w i t h v i s i o n o f t h e h a n d ,
but without vision their hand position drifts substant i a l l y ( F i g u r e5 . 3 b ) .T h u s , o n e c r i t i c a lr o l e o f s e n s o r y
i n f o r m a t i o nf r o m t h e l i m b s i s t o s i g n a l t h e n e r v o u s
system to correct the small imbalancesthat occur in
the forces around a ioint as we contract our muscles
and attempt to maintain a steady posture Without
sensoryinformation (from our limbs or from vision of
our limbs),these small errorsin force and position
accumulate,causingthe limb to drift slowly out of the
d e s i r e dp o s i t i o n .
ERROR CORRECTION DURING MOVEMENT
The gradualaccumulationof error when sensoryinformation is absent also may explain the behaviors we
observe when an insensate individual attempts to
touch the thumb to each of his or her fingers in rapid
succession(Rothwellet al., 1982).The patient performs
the task reasonablywell with eyesclosedat the start of
the task (Figure5.4a).However,after 30 secondshad
Chapter Five Motor Learningand Motor Control
83
A ExoerimentalsetuP
ScreendisPlaY
TargetQ
.q
.. \
.'Cursor
startCj
Two-waymirror
Loudspeaker
Digitizing
tablet
B Rapidmovements
q
^d\
Figure5.3 (a) The experimental setuP for a studY that
examined the effect of removing vision of one's limb on
s l i d i n gt h e h a n d t o a t a r g e t
(b) The paths that the hand
followed when moving from
the start position {left circles)
to the target Position {right
circles),for normal subiects
and for subiectswho had
an insensatelimb due to
disease("deafferented")
Jo"tt
Normalsubiect
No visionof hand
No visionof cursor
d#%'
DeafferentedPatient
No visionof hand
No visionof cursor
DeatferentedPatient
Visionof cursor
Duringtrial
become
elapsed (Figure5.4b),the fingers and thumb
other
each
miss
they
until
misaligned
increasingly
information
sensory
that
conclusion
The
completely.
they
is used to correct small errors in movements as
evi'
of
lines
other
many
by
supported
evolve also is
such
characteristics
movement
on
denceand depends
as speed,size,and the neededaccuracy'
lt mav
lNlTlAL CONDITION INFORMATION
main
t
h
e
t
h
a
t
c
o
n
c
l
u
d
e
p
o
i
n
t
t
o
t
h
i
s
be tempting at
c
o
n
t
r
o
l are
m
o
t
o
r
f
o
r
i
n
f
o
r
m
a
t
i
o
n
roles oi ,"ntory
that
e
r
r
o
r
s
f
o
r
c
o
m
p
e
n
s
a
t
e
o
r
(l ) to help correct
both
during
movements'
and
forces
develop in our
locam o v e m e n t a n d p o s t u r e , a n d ( 2 ) t o s p e c i f yt h e
contact
to
intend
we
that
space
in
tions of obiects
yet' but
or avoid (a role that we haven'tdiscussed
Source:Kandelet al (1991).
of neuralscience
Principles
(3rded.).NewYork:Elsevier.
w h i c h s h o u l d s e e m o b v i o u s ) . S e n s o r yi n f o r m a t i o n
p l a y s a n o t h e r , c r u c i a l l yi m p o r t a n t r o l e t h a t r e v e a l s
little more about the nature of our central
io ,t
(1967)
"
r e p r e s e n t a t i o n so f m o t o r a c t i o n s B e r n s t e i n
pro'
w
i
r e c o g n i z e dt h a t t h e s a m e m o t o r c o m m a n d l l
s
t
a
r
ting
duce different results depending on the
a
p o s i t i o n o f t h e l i m b . P e r h a p ss e n s o r y s i g n a l s l s o
provide information about the beginning state of
o u r m u s c l e s ,i o i n t s ,a n d l i m b s '
lndeed, it is clear that central representatlons
to
require this initial condition sensory information
C
l
a
u
de
g e n e r a t et h e a p p r o p r i a t em o t o r c o m m a n d s .
i
n
s
e
n'
Che, and his colleagues (1995) observed
q
u
e
s
t
i
o
nI
s a t e ( d e a f f e r e n t e d )i n d i v i d u a l s w i t h t h i s
s
m
a
l
l
a
in mind. They asked participants to slide
I
d
i
f
f
e
r
e
n
t
object, similar to a computer mouse, to
I
I
I
II
AB
patientwith
Figure5.4 Photographsof the hand of a
to
instructed
in the upperlimb who was
nJ sensation
performance
(a)
Accurate
tapeachfingerto the thumb
hiseyes'
in'thesecondsfollowingthe patientclosing
hadbeen
patient
the
after
performance
1b1tnu..uru,"
the taskfor 30 seconds'
performing
B L'' Obeso'I' A '
SourceR
: o t h w e l l ,J .C ' T r a u b ,M ' M ' D a y
Manual motor perfor'
(
1
9
8
2
)
'
D
C
'
M
a
r
s
d
e
n
,
&
K
.
,
P
.
Thomas,
5' 515-542
mance in a deafferented man Brain' 10
if
viewingthe arm prior to the movement disappeared
movement
their
delayed
participants
the deifferented
colleagues
for any more than a minute Ghez and his
inforsensory
use
individuals
.onlira"a that healthy
nervous
the
provide
to
limb
mation from their upper
configuration
,frt"- with the starting position and
e s s e n t i a lt o
w
a
s
i
n
f
o
r
m
a
t
i
o
n
oi tn" limb, and this
well'planned
and
accurate
generating
the processof
informa'
movements.ln the absenceof this sensory
subpatients
deafferented
the
tion from the limb,
limb
starting
the
about
stituted visualinformation
to see their
configuration (when they were allowed
arm before movement).
proThesefindingsindicatethat our centralmotor
body
initial
about
information
cessesrequlre sensory
commands'
conditions to generate accurate motor
from
change
to
likely
are
Also, these initial conditions
limbs
and
body
our
move
we
moment-to-moment as
initial conslightly, so the sensoryinformation about
the
Presumably'
long
very
dit]ons is not stored for
s
t
ate
t
h
e
c
o
n
c
e
r
n
i
n
g
s t r e a m so f i n c o m i n gi n f o r m a t i o n
decayrapidly
our
replace
of our body continuously
This means
ing memoiies about initial conditions
thatthecentralmotorprocessespredictivelqgenerate
infor-
the needed commands as long as accurate
positionson a table using horizontalarm moveof the limb
mation about the starting configuration
computer
ments(seeFigure5.3a) A cursoron a
This type
available
are
target
and the location of the
indicatedthe positionof the
*o"iroi continuously
Sensory
call
been
feedforward
of predictive control has
obiect's
lni".t to that participantscould seethe
then
can
movement
during
information from the limb
parmovementprogress.A two-waymirror blocked
using
remain'
that
errors
small
correctfor the typically
ui"* Lt their arm,and theycouldonlv see
iicipants'
control.
light
a
feedback
illuminated
thelrarmwhenthe investigators
central motor processesalso require initial
Our
or
cursor
underthe mirror.Without vision of the
condicondition information about the ever-changing
participantswere sig'
the deafferented
to
in"i,
happens
what
Consider
tions of our surroundings
"r*, less accuratein movementdirectionand
nificantly
of
lemonpitcher
a
you
lift
your arm movement when
participants'
pitcher
extentwhen comparedto the healthy
tn", is nearly empty if you expected that
than
andtheir movementstended to curvemore
pond
com"a"
frozen
a
across
you
walk
to be full, or how
reinice
the healthyadults (Figure5 3b) This finding
patch
of
a
encountering
pared to unexpectedly
from
forcesthe importanceof sensoryinformation
p
l
a
n
n
ing
m
o
v
e
m
e
n
t
o
u
r
o n t h e s i d e w a l k .C l e a r l y ,
reachthe upperextremityin producingtargeted
estlto
memory
and
signals
processesuse sensory
participants
Oncethe deafferented
ingmovements.
mate the mechanicalconditions of the surroundings
to
riopp"amovingat the locationthat they believed
with which we interact'
demonbeihe target,theirarmbeganto drift'again
Thus far we have focused on the importance
controlstratingtie role of sensoryinformationin
for (i )
of sensory information in motor control
posture.
ling
d
evelop
t
h
a
t
-ihe
e
r
r
o
r
s
correctlng or compensating
surprisingnew findingin this studywasthat
c
o
n
dition
i
n
i
t
i
a
l
p
r
o
v
i
d
i
n
g
(
2
)
duringthe movement,
fo the no-visioncondition' the deaffercompared
w
orld'
e
x
t
e
r
n
a
l
t
h
e
a
n
d
informationabout our body
lmprovedtheir movementperforentedparticipants
t
o
c
o
n
tact
w
i
s
h
w
e
t
h
a
t
and (3) locatingsomething
simplyby viewingtheir arm just
mance'substintially
(oravoid).
startof their arm movement(but nol durpriortothe
'ing
The control of walking provides good examples
prior
to
In fact,viewingthe arm
(4)
armmovement).
o f t w o a d d i t i o n a l r o l e s f o r s e n s o r yi n f o r m a t i o n :
yielded
(butnot duringthe movement)
(5) sig'
themovement
a
n
d
m
u
s
c
l
e
s
o
u
r
o
f
setting the springiness
that
nearlyasaccurateasthe movements
movements
a point so
naling when our movement has reached
arm
whenthe patientscouldseethelr
wereproduced
started A
be
can
the nlxt phase of the movement
the positionof theirhand)
receptors
from
1orthecurso,representing
signals
continuous flow of sensory
during the movement(Figure5 3b;
continuously
n
e
u
r
o
nsin our
t
o
b
a
c
k
i n o u r m u s c l e sa n d t e n d o n s
Another
.o*pur" the rightmosttwo groupsof data)
m
uscles
o
u
r
o
f
a
c
t
i
v
a
t
i
o
n
s p i n a l c o r d i n f l u e n c et h e
from
,rrpiiringfindingwas that the improvements
Ie
www.mhhe.com/wilson
Control
ChaDterFive Motor Learningand Motor
85
Together:
(alongwith
Putting lt Att
Thesesensorysignalsto the spinalcord
Postura[Controt
on the spinalcordfrom other
commandsconverging
the
like
properties
set
to
touched
parts of the brain)
Let'sconsidera taskthat we'veonly briefly
"pp""
lengthto
lspringiness"
(resistance
that
muscles
essential
of our
uponto this point,posturalcontrol'It is
our
in
muscles
the
of
exmanv
against
walk,
while we
;;c;
we stabilizeour body,or partsof our body'
relatively
from.a
change
moveown
lo*ei'limbs rhythmically
ternal forcesand againstforcesfrom our
load of our
gravityis
siificonaition, when supportingthe
ment.Maintainlngour balancein the faceof
swinging
is
limb
the
when
external
stiff,
to
Lody,to muchless
an exampleof posturalcontrol in relation
animal
in
experiments
while
position
Extensive
forwardin the air.
forces.Maintaininga stableshoulder
of
these
patterns
basic
of
the
that
example
locomotionindicate
movingthe forearmat the elbow is an
from
result
activation
move
we
muscle
rhythmicchangesin
how posturalcontrolis requiredwhenever
that func'
forcescomein pairs(equal
networksof neuronswithin the spinalcord
a noiy segment.Because
switched
Once
generator'
pattern
of moving
tion as a central
unj oppoti,elydirected),the simpletask
central
th.e
centers'
brain
you
stabilize
on, notmutlyvia higher
on" ,"grn"nt of your limb requiresthat
rhythalternating
basic
the
movements
patterngeneratorissues
or sufferunintended
the othersegments,
and across
the fundarecognized
mic patternsof muscleactivationwithin
segl'ents.Sherrington
informatlon'
sensory
of
he elo'
"iin"t"
limbs, even in the absence
mentalimportanceof posturalcontrolwhen
individudeafferented
of
like
This is akin to the ability
qr"n,fy statedthat "posturefollowsmovement
thumb'
their
to
fingers
&
their
Liddell'
als to rhythmicallytap
its shadow"(Creed,Denny'Brown'Eccles'
at'
individuals'
deafferented
Ho*"u"t, just like the
1932,PP'147-148)'
Sherrington,
together'
i"tp1t ut'tuppingthe thumb and fingers
Maintainingour balancewhilestandingupright
activations
muscle
the
the vertiwithout sensoryinformation
solvesthe mechanicalproblemof keeping
generator
pattern
central
point
at the
the
that are issuedfrom
cal proiectionof our centerof mass(the
until
accumulate
quickly
of
base
that
containsmall errors
."ni"t of our total body mass)within our
appears
generator
pattern
supa
walkingfails.The central
support (the area of our body that contacts
assumption
to issue motor commandsunder the
pori turfr."). While standinguprightand supported
is returnareafrom
that sensoryinformationfrom the limbs
only at our feet,our baseof supportis the
inwill
signals
these
that
of the
and
ine to ti-t"spinalcord
the'lateraledgeof one foot to the lateraledge
result'
a
As
reflexes
via
of
task
creasemusclespringiness
.pp.tit" foot]2the first requirementin this
part
lower
the
like
and
gravity
some featuresof a movement'
rnuin,uiningbalanceis the needto fight
brieflyduring one part of its
collaps
of our leg accelerating
,uppou oui body load without saggingor
movement
the
because
not
forward swing, occur
ini ioward the ground To do this' we automaticall
beneckto
pt"ui""l explicitlycommandedthis featurebut
activatethe appropriatemusclesfrom our
of
interactions
complex
the
by sensorysignalsfromthose
caule it emergedout of
our ankles,reinforced
system'
musculoskeletal
the nervoussysremand
muscles.This basic activationof our antigravt
progtone'But this task
Finally,sensoryinformationalsosignalsthe
muscleshas been termed postural
of
phase
next
the
trigger
can
frictionles
ressof our actionsand
is not so easilyachievedWith nearly
information'
on eac
forces
the
in
an action,whichis a fifth rolefor sensory
imbalances
,till
i.i"rt u"ry
leg
opposite
the
(while
load
positionaldrif
Theleg bearingour body
siO"of a ioint will resultin the slow
(wh
ile
orward
swing-f
must
ly
of in
forward) eventual
swingsof the iolnt.We'vealreadydiscussedstudies
conto
are
we
if
load)
body
to hold
the otherlegsupportsour
,"nrut" individualswho find it impossible
only
occur
can
This
progression'
that limb
iinu" ou, forward
an outstretchedlimb still unlesstheyview
and
ground
the
contacted
uprigh
whenthe opposltel"c hut
It shouldcomeas no surprisethat standing
asthosein the frontof the
informatio
muscles,-such
sensory
of
tf,"
processing
involvesrapid
"*t"nro,
your entireweight
an
thigh, stiffenadequatelyto bear
by the brain to select appropriatemuscles
muship
the
in
receptors
that
minimiz
suggested
Sherrington
.hung" their level of activationso as to
swingleg
body'
the
of
axis
vertical
clesof the legthat is waitingto becomethe
the
around
sway,motion
leg to begin
doe
usually
sway
may signalthe appropriatetime for the
controlling
of
process
The
locomotion
cat
of
studies
is auto
its forwardswing.Elegant
not requireour attention,so we saythat it
also conrequir
control
this
that
confirmedSherrington'ssuggestionand
discovered
matic.We have
that
o
firmeda similarrol! for receptorsin the tendons
we rapidlypredictthe directionand amount
that
substantial
a
bearing
,,gn"t *h"n the leg is no longer
pJt,ionof bodyload,sothe legcanbe liftedfor swing'
2ln fact, the problem is a bit more complex becauseth
generator
ihe rhythmicoutput of the centralpattern
moving also dete
speed at whkh the center of mass is
shiftingbetweenstandingonthelegandswingingit
get to the edgesc
can
mass
of
your
center
close
mines how
signalsare
forwardis preventedif the propersensory
your
balance
your base of support without losing
not received.
swayfrom sensoryinformationand then selectthe
actionsthat will minimizethe sway'How we control
forwardand backwardswayhasbeenstudiedextensivelyusing a platform that the person standson
that can unexpectedlymove forwardor backward'
Thesestudies have shown that a backwardsway'
from forwardtranslation of the platform, triggers
a coordinatedactivationof musclesthat efficiently
pull the body segmentsforward.The contractions
tegin first with musclesactingaroundthe ankle'
foliowed by activation of muscles acting around
the knee,hips, and finally at the trunk and neck'
Theopposingmusclesare activatedif the platform
movesbackward.
Thesepatternswork becausethe personcan effectivelyerert forcesagainstthe supportsurfacewith
his or her feet.What happenswhen you are standing on a narrowsupport surfacesuch that your toes
andheelshavenothingto pushagainst?In this case
the initialconditionshavechangedcomparedto the
flat supportsurface,and the brain,havingprocessed
sensoryinformationabout the new support conditions,selectsa differentpatternof muscleactivation
thatfocuseson musclesthat will producelargemove'
mentsaroundthe hips (think about balancingon a
tightrope).
nature of these proThe essentiallypredictive
wasdemonstratedwhen investigatorsmixed
cesses
in trialswith a pure platformrotation,which caused
the anklesto rotate without causingsway (Figure
5.5).No swayoccursin this casebecausethe rotation didn't move the base of support in relation
to the verticalproiectionof the centerof mass On
thesetrials people reactedto the imposedankle
motionby generatingthe samesequenceof muscle
activationsas if the platform had moved forward
(whenthe platformrotatedthe toes up) or backward
(whenthe platformrotatedthe toes down)'As a result,the rotation triggeredmuscleresponsesthat
theserequicklysuppressed
sway.lndividuals
caused
the ease
demonstrating
trials,
few
a
within
sponses
transformations
sensory'to'motor
withwhichthese
that arisein
canbe adaptedto new circumstances
theenvironment.
As previouslynoted, posturalcontrol means
morethan controllingthe orientationof the body
in the faceof gravityand other externalforces For
the movementsthat we intentionallygenexample,
erate,like reachingout to graspand lift an obiect'
causeour centerof massto move,which can cause
We'veseenhow the nervoussystemcan react
sway.
to swayquite effectivelyby rapidlyprocessingsensorysignalsaboutswayto generateactionsto minimizeswayin accordancewith support conditions'
Doesthe nervous system use the same strategy
whenthe disturbanceto our stabilityis of our own
Theansweris no.
making?
Backwardmovement
of platform
ra\
r\l
i /1
\(trl
i ,('(/
i \ \ \rl
tl
I l-/
iff/
i\
-o
tp
lo
Induce-Jswaying
four
during
trials
consecutive
lo
lE
_L9
O
B Tiltingof Platform
I
U
!
Directanklerotatlon
duringfour
consecutivetrials
o
o
o
o
E
TO
lo
lo
te
_La
O
Figure5.5 Theposturalcontrolsystemrespondsto
sviayof the bodyaroundthe verticalaxisthat is caused
by the backwardtranslationof a moveableplatform
uponwhichthe personstands.Themotor system
basedon
learnsto triggerthe appropriateresponses
occurs'
actually
sway
much
before
anklerotation,and
rotates
platform
the
when
wrong
prediction
is
This
whilethe anklesstill rotate,no swayoccurs'
because,
Consider the simple act of lifting one leg to the
side (Figure5.6).As your leg rises,your centerof mass
will move to the side, which would lead to a sideways
sway if your postural control system did nothing'
Ratherthan reactingto this sway (as was the case for
Chaoter Five Motor Learning and Motor Control
87
in the face of
adjustmentsneededto preventswaY
thosearm movements
Here'sa simPledemonstrationof anticiPatory
personand an
oosturalcontrolthat requiresanother
Haveyour colobiectlike a bottle of water(Figure5 7).
of him or
leaguebalancethe bottle of water in front
Ankle
Shoulder
Supportslde
Hip
Centerof
pressure
while
5.6 Theactof liftingone'slegsideways
Figure
away
mass
of
center
shiftsin thebody's
rt'"""Ji"ginvolves
an
illustrating
rise'
to
legbegins
iro* *iafin" beforethe
action'
anticiPatory
Postural
discussed
the experimentsusingplatformtranslations
slightly
pt"".rtfyf the brain activatesmusclesiust
you lean slightly
in uauun." of the leg motion so that
you are about to
i" if.r" side awayfrom the leg that
been termed
iifr- rtti, type of postural control has
the reactiveadunii"ip*"w, to di,tinguish it from
out balanceis disturbed
;urt*unt, tirat occur*ihun
system
unexpectedly.Apparentiy,while the nervous
intendedarm
;;ikit the cential commandsfor the
the postural
rnou"*"ntr, it also is determining
c
postural
5.7 A simpleexampleof anticipatory
Fiqure
subiect's
the
on
rests
water
of
co'.,trol.(a) Thebottle
with her
f,""J tnl Whenshequicklylifts the bottle
rested
bottle
the
trand,tire handupon which
;;;;t[J
that
to
commands
motor
dols not movebecausethe
expected
the
for
timing
perfect
with
ur.l"t" adiusted
else
of weighton the hand (c)Whensomeone
;;u;;."
rises
arm
her
r"fiafv lifts the bottle from her hand'
information
;;;;";" her posturalcontrolsvstemlacks
be lifted'
will
bottle
the
quickly
aboutwhenand how
heron an openpalmwith eyesclosed.Askthe person
to use the other hand to quicklylift the bottle off of
the openhand.Observe
the motionof the openhand.
Replace
the bottleon the openhand(yourcolleague's
eyesshouldremainclosed),and don't tell the person
whatis to comenext.Withoutwarning,quicklylift the
bottlefromhisor herhand.Youshouldobserve
a fairly
largeupwardmotion of the hand in the secondcase.
Therelatively
smallhandmovementthat shouldhave
occurredwhen your colleaguelifted the bottle from
his or her own handwas the resultof a reductionin
thedriveto the arm musclesthat weresupportingthe
bottle.Thisreductionin muscledrivewasprecisely
coordinated
withthe removalof the bottlefromthe hand.
Yourcolleague
couldn'tproducethis adiustment
when
goulifled the bottle becausethe centralprocesses
for
producinganticipatoryposturaladlustmentsdidn't
haveaccess
to informationconcerning
whenand how
quickly
the loadwasto be removed.
Thisdemonstrates
thepredictive,
ratherthanreactive,
natureofthe reductionin armmusclecommandsto the supportarm.
PROFESSIONAL
ORGANIZATIONS
AND CERTIFICATIONS
Awide varietyof organizationsand societiesare dedi,
catedto promoting the many professionsthat focus
on the study and application of motor control and
motorlearning.Severalof the more prominent organizationsthat also overseeprofessionalcertification
are discussedhere, along with professional socretiesthat do not overseeprofessionalcertification but
existto organizeand disseminate information about
discipline
or field
Many professional organizations and sciens o c i e t i e sf o s t e r a p r o f e s s i o n w i t h o u t n e c e s r i l y o v e r s e e i n gt h e a c c r e d i t a t i o n o f e d u c a t i o n a l
m s o r t h e c e r t i f i c a t i o no f c l i n i c i a n s o r o r a c ers.They aim to advance the scientific unndingof the discipline,provide professional
ent activities and resources,oromote
i c i n f o r m a t i o na b o u t t h e d i s c i p l i n e , a n d m a n y
rmor lobbylegislators
aboutscientificinformaregarding
the disciplinethat may affectpublic
icy.The Society for Neuroscience is a longn g s o c i e t yi n t h i s m o d e l t h a t d e v e l o p e do u t o f
AmericanPhysiological Society. It is dedicated
ancingthe understandingof the nervous
b y s e r v i n gs c i e n t i s t sa n d s c i e n t i s t s , i n ing,and the public, through the general
i t i e s n o t e d p r e v i o u s l y .T h e a n n u a l m e e t i n g o f
nizationb
, a s e d i n t h e U n i t e d S t a t e s ,d r a w s
imately2t,000to 30,000attendees,
most o[
are scientistsand graduatestudents.The
I n t e r n a t i o n a l B r a i n R e s e a r c hO r g a n i z a t i o n ,b a s e d
i n C a n a d a ,a l s o p r o m o t e s t h e d e v e l o p m e n ta n d d i s s e m i n a t i o no f s c i e n t i f i ci n f o r m a t i o n a b o u t t h e b r a i n
b u t f o c u s e si n a d d i t i o n o n i n t e r n a t i o n a lc o l l a b o r a t i o n a n d i n t e r c h a n g eo f s c i e n t i f i ci n f o r m a t i o n .
Some scientificsocietiesand organizationsfocus
more directlyon the fields of motor control and motor
learning.The InternationalSocietyfor Motor Control
is a relativelynew society aimed at promoting basic
and applied research in the area of the control of
movements of biological systems.A much older society, the North American Society for Psychologyof
Sport and PhysicalActivity, describesitself as "a multidisciplinaryassociationof scholarsfrom the behav,
ioral sciencesand related professions."The society
aims to advancethe scientificstudy of human behavior related to sport and physicalactivity,disseminate
information, and improve the quality of researchand
teaching in the psychologyof sport, motor development, and motor learning and control. The American
Alliance for Health, Physical Education, Recreation
and Dance (AAPHERD)has been important in the
development of scientists and the science of motor
behavior and for professionalswho apply this knowl,
edge, especiallyin physical education,coaching,and
dance instruction. As its name suggests,it is an alliance of severalnational organizationsand research
consortia. (The name of this organization may soon
c h a n g e . )T h e A m e r i c a n C o l l e g e o f S p o r t s M e d i c i n e
(ACSM)likewiseis a professionalorganizationfor scientists and practitionerssome of whom touch upon
motor control and motor learning in their research
and practices.
T h e B i o m e d i c a l E n g i n e e r i n gS o c i e t y e x i s t s t o
"to promote the increaseof biomedical engineering
k n o w l e d g ea n d i t s u t i l i z a t i o n . "I t a l s o p a r t i c i p a t e s
in the accreditation of educational programs. The
d e f i n i t i o n o f b i o m e d i c a le n g i n e e r i n gi s q u i t e b r o a d ,
reflecting the historical interplay between medicine
and technology.According to the National Institutes
of Health,
Biomedicalengineeringintegratesphysical,
chemical,mathematical,and computational
sciencesand engineeringprinciplesto study
biology, medicine,behavior,and health. It
advancesfundamental concepts;createsknowl,
edge from the molecularto the organ systems
level;and developsinnovativebiologics,materials, processes,implants, devicesand informatics
approachesfor the prevention,diagnosis,and
treatment of disease,for patient rehabilitation,
and for improving health." (www.becon.nih.
gov/bioengineering_defi nition.htm)
It is easy to see how motor control and motor
learning can interact with such a broadlv defined en,
g i n e e r i n gd i s c i p l i n e .
A common feature of professionalsthat deliver
h e a l t h c a r e i s t h e r e q u i r e m e n tt o o b t a i n a l i c e n s e
to practice their profession.Just like physiciansand
dentists must obtain the appropriate licenseto prac'
tice medicine and dentistry in their state, so too
m u s t p h y s i c a la n d o c c u p a t i o n a lt h e r a p i s t s ,s p e e c h l a n g u a g e p a t h o l o g i s t s ,a t h l e t i c t r a i n e r s , t e a c h e r s ,
and so on. Before applying for a license,most states
require certification by an approved professional
o r g a n i z a t i o n .T h i s c e r t i f i c a t i o n r e q u i r e s m i n i m u m
standardsof education including graduatingfrom an
accreditededucationalprogram.Theseissuesare discussedfurther in the next section.
CAREERS
Knowledge about motor control can be applied to a
wide variety of clinical, instructional,and engineering
fields. Physical therapists, occupational therapists,
speech-languagepathologists, and athletic trainers
apply their knowledge of motor control and motor
learning on a daily basis as they determine how best
to help their clients establish,modify, or regainmotor
function. lndeed, Vernon Brooks (1986) referred to
physical therapists and occupational therapists as
applied motor control physiologists, a phrase that
therapists
can be applied as well to speech-language
and athletic trainers.
P h y s i c i a n sp r a c t i c i n g i n t h e f i e l d s o f n e u r o l ogy, orthopedic surgery, physical medicine and
r e h a b i l i t a t i o n , a n d o t h e r s p e c i a l t i e sa l s o a r e c o n cerned with how best to improve impaired motor
p e r f o r m a n c e .l n i n s t r u c t i o n a l s e t t i n g s ,p h y s i c a Ie d u c a t o r s , c o a c h e s ,m u s i c i n s t r u c t o r s ,a n d d a n c e i n structorscan, and should, directly apply principles
of motor learning to their teaching techniques ln
industry, those who design devices and environ'
ments that humans engagealso apply knowledge
of motor control, from the designof user interfaces
f o r m a c h i n e c o n t r o l t o t h e d e s i g n o f r o a d w a y s .T h e
fields of ergonomicsand human factors engineering emerged partly out of the realizationthat inj u r y o r s u b o p t i m a l p e r f o r m a n c ea n d l e a r n i n g o f t e n
o c c u r u n l e s s w e a p p l y o u r k n o w l e d g eo f m o v e m e n t
physiology and information processing to engineering design. Indeed, accident investigations
(and subsequent court litigation) routinely make
u s e o f k n o w l e d g ea b o u t m o t o r c o n t r o l i n d e t e r m i n i n g w h o w a s a t f a u l t , h o w a c c i d e n t so c c u r ,a n d h o w
b e s t t o a v o i d f u t u r e a c c i d e n t s .L i k e w i s e ,b i o m e d i '
c a l e n g i n e e r sa n d t h o s e w h o d e s i g n a n d f i t o r t h o t i c
and prosthetic devicesroutinely apply knowledge
of motor physiologY.
As should be clear from this chapter, the disci'
pline of motor behavior has been driven strongly by
r e s e a r c hi n p s y c h o l o g y ,m e d i c i n e , p h y s i o l o g y ,a n d
engineering.Careersfocusedon researchin motor
behaviorare pursuedin academicand industrialsettingsby personswho obtaindoctoraldegreesor their
equivalentin the variousdisciplinesdiscussed.For
more informationabout theseoccupations,consult
(U.S.Department
OutlookHandbook
the Occupational
This excellentresourcedeof Labor, 2006-2007).
scribesthe natureof the work,the workenvironment,
and the employ'
requirededucationand certification,
ment and salaryoutlook in the United States.It is
updatedregularly.
PhysicalTheraPy
of Labor,"Physical
to the U.S.Department
According
that helprestorefunction,
therapistsprovideservices
improvemobility,relievepain,and preventor limit
of patientssuffering
physicaldisabilities
permanent
Theyrestore,maintain,and
frominiuriesor disease.
promoteoverallfitnessand health.Theirpatients
includeaccidentvictimsand individualswith disablingconditionssuch as low-backpain, arthritis,
headiniuries,and cerebral
heartdisease,fractures,
The
palsy"(U.S.Departmentof Labor,2006-2007)'
AmericanPhysicalTherapyAssociation(APTA)is
designedto fosteradorganization
a professional
in physicaltherapypractice,research,
vancements
Thevisionstatementfor this organiand education.
zationstatesthat by the year 2020physicaltherapy
serviceswill be providedby physicaltherapistswho
are doctorsof physicaltherapy.Currentlyindividuals who obtain a master'sdegreefrom a schoolof
physicaltherapy can seek certificationfrom the
APTA,whichwill allowthemto applyfor a licenseto
practicein their state.The trend toward schoolsof
physicaltherapyofferingonly the doctorof physical
therapydegreeis strongin the UnitedStates,and it
appearsthat the vision of the APTAmay well be rethis assoalized.Mirroringthe medicalprofession,
ciationalso overseesboardcertificationin specialty
fieldswithinthe disciplineof physicaltherapy(e.g.,
pediatric,gerentologic,orthopaedicspecialties)
Physicaltherapistsoften are assistedby physical
therapistassistantswho are educatedand licensed
withinthe disciPline.
occupational TheraPY
The AmericanOccupationalTherapyAssociation
Inc. (AOTA)is a professionalorganizationthat
servesa similarfunctionto that of the APTA The
U.S.Departmentof Labor notesthat occupationa
therapistshelp peopleimprovetheir abilityto perform tasksin their daily living and workingenviron'
ments.Occupationaltherapistsserveindividuals
who haveconditionsthat are mentally,physically
or emotionallydisabling.They
developmentally,
helptheir clientsto develop,recover,or maintain
dailyliving and work skills,often by helpingthem
to compensatefor permanentloss of function'
in 2007,a master'sdegreeor higherwill
Beginning
for entry
requirement
be the minimumeducational
practice
oc'
to
license
a
into the field. To obtain
must
one
States,
United
the
in
therapy
cupational
graduatefrom an accreditededucationalprogram
and pass a national certificationexamination'
Uponpassingthe exam,you are awardedthe title
OccupationalTherapistRegistered(OTR) Some
statei also requiretherapistswho work in schools
or earlyinterventionprogramsto havetaken addi'
classes,obtainedan edutionaleducation'related
cationpracticecertificate,or met earlyintervention
certificationrequirements.
guagePathologist
Speech-Lan
Association
TheAmericanSpeech-Language-Hearing
credentialand
scientific,
(ASHA)is the professional,
in
pathologists
ing associationfor speech-language
speech-language
states,
all
the UnitedStates.In nearly
pathologistsmust be licensedto work in a health care
s e t t i n g ,a n d a l l s t a t e s r e q u i r e a m a s t e r ' sd e g r e e o r
equivalentand a passing score on the national examinationon speech'languagepathology Additional
requirementstypically include 300 to 375 hours of
supervisedclinical experienceand 9 months of professionalclinicalexperienceafter graduation'Speechlanguagepathologists can acquire the Certificateof
ClinicalCompetencein Speech-LanguagePathology
(CCC,SLP)
offered by AHSA, which requires a gradu-
atedegreeand 400 hours of supervisedclinicalexperience,
and a postgraduateclinicalfellowship,in
udditionto passingthe nationalexaminationWith
certificate,a speech-languagepathologist can
in hospital,clinic,and educational
seekemployment
,tingsalthoughin some statesa teachinglicense
pathologycan be obtainedwith
speech-language
education.Many speech'languagepathology
ms are moving toward the clinical doctorate as
additionallevel of training
Training
National Athletic Training Association (NATA)
the professionalcertification of individuals
seekemploymentas athletictrainers.Athletic
who specialinersare healthcare professionals
managing,and reharecognizing,
in preventing,
ing injuriesthat result from physicalactivity
chapter7). They work under the direction of a
sed physicianand cooperate with other health
coacnes,
athleticsadministrators,
professionals,
an
accredited
A bachelor'sdegreefrom
Darents.
with a majorin athletictraining
or university
is required for certificationand for almost all iobs as
an athletic trainer. Many trainers further their training with advanceddegrees.
orthotists and Prosthetists
assistpatientswith dis'
Orthotistsand prosthetists
and spine,or with
limbs
the
abling conditionsof
by fitting and pre'
limb,
of
partial or total absence
(devices
prostheses
and
paringorthopedicbraces
artificial
an
as
such
tissues,
that replaceour own
limb). The AmericanAcademyof Orthotistsand
Prosthetistswas foundedto foster the development of practitionersin orthoticsand prosthetics'
the acThis organizationhas been spearheading
prosthetics
and
orthotics
of
creditationof schools
and is activelypromotingthe establishmentof doctoral programsin the discipline.Currentlythe typi'
is a bachelor'sdegree
requirement
cal educational
to the other
program.
Compared
from an accredited
and
orthotics
discussed,
that havebeen
disciplines
advancing
is
rapidly
young
that
field
prostheticsis a
as materialstechnologythrivesand as technology
and refinementof
contributesto the development
poweredprostheses.
SUMMARY
As our knowledgeof brain function has advanced in
the past 30 years,it can be arguedthat motor control
and motor learning are so intimately related in their
physiology that the distinction between these fields
today exists only as a historical legacy.Today many
prominent scientistsworking on issuesof motor control also work on questions concerning motor learning, and vice versa.
Because so much of our daily activity depends
on moving, adapting skills to new conditions,and
learning new movement skills, we are motivated to
understand how all of this comes about for its own
intrinsic value, to perform better, and to better recover function after injury. lt is easy to see why the
scienceof motor control and motor learning has
been applied more and more to issues of health
c a r e , r e c r e a t i o n ,e n g i n e e r i n g ,a n d d e s i g n , a n d w h y
p r o f e s s i o n a lo r g a n i z a t i o n sa n d s c i e n t i f i c s o c i e t i e s
that relate in some way to motor behavior continue
t o g r o w . C a r e e ro p p o r t u n i t i e s a b o u n d , p a r t i c u l a r l y
in the application of this knowledge to health care
a n d r e c r e a t i o n I. n a n y c a s e ,t h e p r a c t i t i o n e ro r s c i e n tist requires a broad knowledge base in physiology,
physics,and psychology.This broad knowledgebase
i s b e c o m i n g i n c r e a s i n g l yi m p o r t a n t t o u n d e r s t a n d
t h e b a s i s o f m o t o r b e h a v i o ra n d t o k e e p p a c e w i t h
the rapid advance of knowledge during this golden
ase of the brain.
Key fournals
andBrainSciences
Behavioral
Ergonomtcs
BrainRes
earch
Experimental
Science
HumanMovement
Phrlsiologg
lournalofApplied
HumanPerception
Psychologu:
lournalofExperimental
andPerformance
Key WebSites
AmericanAcademyof Orthotistsand Prosthetists(www.
oandp.org)
AmericanAlliancefor Health,PhysicalEducation,Recreation
and Dance(www.aapherd.org)
AmericanCollegeof SportsMedicine(www.asm.org)
AmericanOccupationalTherapyAssociation,lnc. (www.
aota.org)
AmericanPhysicalTherapyAssociation(www.apta.org)
Association(www.
AmericanSpeech-Language-Hearing
asha.org)
l. In what keywaydid motor behaviorresearchconducted
and psybefore1950differbetweenneurophysiologists
chologists?What was Bernstein'srole in reducingthis
difference?
2.What evidenceleads us to believethat the central
skilled
nervoussysteminternallystoresor represents
movements?
storedrepresentaleadsustobelievethat
3.Whatevidence
tions of movementsinteractwith sensoryinformation?
4. Givean exampleof how initial conditioninformation
contributesto programminga movement.
5. List three differentwaysin which sensoryinformation
can contributeto executinga movementaccurately.
postural
6. Describewhat is meant by the term anticipatorq
control.Givean exampleof an anticipatorypostural
adiustment.
of MotorBehavior
Iournal
IournalofNeuroscience
gg
IournalofNeurophgsiolo
NatureNeuroscience
andMotorSkills
Perceptual
andSport
Quarterlq
Research
for Exercise
Society(www.bmes.org)
Engineering
Biomedical
Organization(www.ibro.org)
lnternationalBrainResearch
InternationalSocietyfor Motor Control(www.i-s-m-c.org.1
(www.nata.org)
NationalAthleticTrainingAssociation
of Sportand Physical
NorthAmericanSocietyfor Psychology
org)
Activity(www.naspspa.
(www.sfn.org)
Societyfor Neuroscience
U.S. Departmentof Labor'sBureauof Labor Statistics'
OccupationalOutlook Handbook (www.bls.gov/oco/
home.htm)
what is meantby a re7. In motor learningexperiments,
tention test?Why are suchtests importantto discovering the practiceconditionsthat are optimal for motor
learning?
B.What is the Lawof Practice?
9. List three conditionsof practiceknownto affectmotor
learning.
10.Describehow you might structurea practicesessionfor
the optimallearningof threemotorskills.
ll. What is brain plasticity,and why is it importantfor
motor learningand for recoveryof motor functionafter
a stroke?
j
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