The control of discrete and reciprocal target-aiming responses: Evidence for the exploitation of mechanics

Human hlo\cmrnt North

Scwnce I2

(IYY)i) ;5:-?6-I

Holland

The control of discrete and reciprocal target-aiming responses: Evidence for the exploitation of mechanics ”

Introduction

Recently. Chamberlm and Mng~ll (1989) reported that ‘I movement toward a single target has n shorter movement time I e IS ewcuted

t,l\tt‘r. th,w the Fame movement \\hen It IS tollwed t-q ;I wzond rno\ement twxd d wcond taget Chaniberlrn and M;lgrll (IYSY) rnterpreted thl\ otwtot,qtv rrtirwltrzge phenomenon a e\wlrnce tor on-lme programm~np 111\thlch some ot the progr,m~mtng fog the second movement occurs durmg ewcutron of the trrst movement Ftschman and Reese (1903) proposed an altern,ltn’r e~pl,lnatwn tar the one-target ad\,mt,lg? The\. argued that mcnement time to a tttrt target (hIT1) Is lengthened because the addltmndl requirement ot ewcutlng ‘I wcond movement plxes cowtranth on the ewcutlon ot the tlrbt movement Sprc~trc;ill~. thti) rewxwd that Mhen cublects ‘Ire tnlng to mo\tz through ‘1 multr-segment responw as raprdly AS powMe. the! must conwan the Irmb (or shluc) ‘IF rt completes the Inrtlnl wgment at the tlrbt target III order to moothly aid qu~chly ewcute the nelt mwement wgment (p 133) kxordtng to Fwhman and Rtwe f lYY7). thl\ ,iddrtlon,ll denw~d for control could be entrrel! ~~rt~progranimed Flschmdn ad Ree\e I lYY2) tested the on-ltne progr,~mmtng h\,puthesls by dtxgntng n procedure which mJwmlzed the opportunlo tar complete programming pt Ior to response rnrtl,ttlon The) xcompltbhed this b> ;Illo\rrn_g subyxts dn unlmirted amount of respone pl,mnmg ttmt: betore response Inltldtlon and by srrnpllt\lng the second movement Thus. the\ ,lrhsd subwt5 to t&e rhelr time ,ind plan the entire respone before Inltl,ltrng It. the response D;IS to \trlhe the tlr\t target and then slrnpl), lrtt the shlus ott and rno\e rt c)\er the xcond target \rtthout rtrrhlny It E\en though this procedure mlnlmrzed the need tar on-line progr:~mmrng the rewltb shw’ed ‘1 robust one-tLllrget ahCmtagr r~ltlence

Flschmnn that

aid

the longer

not due to on-line

Rer\e MT1

(lYY2I

Interpreted this tlndlng ,I\ responws I\ prob,ibll the) Lnored ,I wnwalnt

rn t\fo-element

progranmlng

Insteal

conceptron Mhlch clarms that subtectb tmng ‘1 hio-ekment ta-get amIng re~p~~nrs adopt ;I crtateg> ot ~e~tr~unlng the limb
to ta\or &i constraint

r\plm,ltwn

Hwe\er

not cornpletelv term

mlsblng

ccmtrain The

gwl

their

first

mer

;Ind Reoe

It IS e\prrrsed

,ind does not ~peclflc‘all~

wbJect3 xtlon

csplamtion

Flcchrnm

dddresr mwerncnt

dn on-lrntz \ comtr,ilnt

In cery gent’rdl the questIon, rn

progrmmnin~ explancttwn r‘lther

ot N~/z\cmf Irm

a trio-element

14

~c~gut‘ strrhlng

nt thrs study \ias to shed some Irght on thrs ISSW

Many

studies

(Adam

1992. Te;lsdale

1087. Teasdale

,md Schmidt

1991. Waters and Strlch. 1981. Zelaznlk et aI lc)86) hae pointed to the Importance of the 7t77pocr trifle f/w rnrger a\ an essentlA contrlbutor to movement deceleratwn That IS. at the tak ~rnpows some Impact constramts. part ot the deceleration ot the mo\srnent rnq be xcompllshed pnss~vsly or mechanlcall) t-q txget rmpxt thl\ IS slmph a consequence ot prlnclplec of Ne\vtonl;ln mechanics (TeardAe and Schmidt 1991) For Instance. Te,lsd;lle ( 1087. cited 111Tensdale ,jnd Schmidt 1991) reported that the pe,lk Impact force ot td5t clngle aiming movements (mean movement duration 1hO ms) b;ls 205”~ larger than that ot slower movements (mean rno\‘ement duration 2-M ms) This recult strongly suggests th,lt pawve Impxt tortes contribute to movement decelerntlon The Insight that the Impxt \ilth ;I target surtxe c;111 pro\lde movement tlon

decelerdtron

ot the

wo-element

response

tlon

txget

through

he $0 because rel?asr

might

one-target

Impact

hitting

th,m

target

and

ewcutlon

ot

the

cecond

response.

theretore.

such

It

movement might

I\ charactcrlzed

tx

deceleration

In order

to ensure

mirth target

1 ~111 not

Intertere

smaller

xcordlng

,idLnnt‘lge

one-target tion In

;Ind

xe

larger

this

tested

stud\

ue

ad\ant,ye

t\\o-element target

srnhg

ments

tward

target

hto-element

nlmlng

mwements targets

the

t-q studying

orw

response

\\lth

mixfement

torte

;Ind

Impxt

wblects

brst

mai

In

1

ot

uct1lv’

Impxt

time

Inltl,ltlon

choose

nwement

quick cmooth

J ti\o-t,lrgst

to progr,im

qu~ch ,tnd wwoth

ot

to progr,lm

d hio-element

response con,tl,llnt

‘1 motor

Impxt

e\pl,ln,ltlon.

control

\LLZ asked

str,~teg!

tg rel,~tnel> th,tn

conw;llnt Hoiie\‘t:r. sublects

h!pothesls Inste,ld

to m;tke

movement

\ihlch

decelera-

of one-element

r/w wrtc7ccP of 17cirg7rr~tv

that

shorter

the oneIn

the colre5pondlng

the hlnematlcs

rerponws

such

,lnd

that

Mlth

peak velocltles

response

t,lced

mrght

may hinder

Inltldtlon

portlon

characterized

in d trio-target

one-target

When

Impxt

tram

Impact

delq

rn a

deceler,lThl\

Ixge

the

to the

on paswe movement

choose

s\pl,m,l-

mwwnent

‘1 rel,ltlvel>

re
tar

results

movements

phase

ment

the

the same

than tar a one-element

sum

target

For

peal\ \elocltw

response In

3

twent

‘1 large

theretore

sulqsctc

the constr,llnt

I$. the trrst

d one-element

1 \tlth

target

this

mo\femsnt

eMorate That

rely to a lesser

rn,l!

trom

th,lt

help

ad\ant,lge

moieot

the ,lnd

ot employing ~l~l~rzg

mo\e-

Also we dwgned 1 M~S a right-lett

movement. and movement 2 a lett-right mwement. that 15. (I re\ers;ll of the tlrst movement Thus. the one-element movement HIS a d~screw. rrght-left moi’ement and the t\\o-element maement a recrprocdl. &-left.

Iett-right

responw

The ratlon;lle tar employmg drscrete and teclprocA slldlng mo\w mats \\a that It created the poss~b~l~~ to stud\ the control ot one-element and hfo-element movements in the &wnce ,ind proencr ot target Impact constrnlnts That IS. 4rdlng movementr MZ rl~twzsel~~t~rcall kx- ~ctll’e control ot the \i hole deceleration phase since there IS no opportunity for pestle deceleration through target Impact Hcwee\vr. by Introducmg n mechanIcal stop. I e A btooden barrier ,tt txget 1. subjects could. at leait pxth. under thew circumsLlnces nchws deceleration ot the mwement pawvely or mechanIcally lx w-get Impact The ~mpxt conwant hypothew ot the one-target ;id\ant,lge predicts that. for sliding ma’ements wrth a mech,lnlcA stop ,~t target I. MT1 IS shorter for the one-element (I e discrete) movement thm for the hto-element (I e reclpiocA) mw’ement Moreover. these shorter movement times die xcomp~imed by larger pe,ih velocitie and shorter decelerntlon phases For slldlng mwements \ilthout mechdnvxl stop dt target 1. the Impact constrant hypotherls would predict no dotterences III MTI. pedk ~eloc~tv. and duration ot the deceleration phase toI discrete and reaproc;ll mo\emrnts since both type ot movements rely completely on actne. deceleratne control Since target SIX ha been sho\fn to Influence mwtmenn time, peak velocrty and the rel,ltne duration ot the acceler;ltlon dnd deceleration phases (Adam 1992 hlacKenzle et
hlet hod

NIneteen students (1-I female and 5 malet) ot the Unr\el\In ot Lunburg partlclpated In this study (mean ‘lge. 22 2 years. range 20 to 31) The) \iere nil rght-hnnded nnd volunteered to partlclpdte None

ot them had any e\perlence behmd

\ilth

the eupermxntal

task or the loge

the study

A 61 x 91 cm X-Y dlgltlzmg tablet (Scrlptel Corporation), mounted on a 80 cm high table. was used In conynctmn i\lth a MS-DOS AT computer to record time-X data paws Sampling rate ~a?s 135 Hz. and spatial accuracy ot the dygtlzmg tablet was set at 0 1 mm T\\o target sheets ivere constructed. each consisting of hvo equally sized circular targets horlzontallly separated by 10 cm The diameter of the two targets was either 3 mm or 24 mm Target sheets uere placed on top of the dlgltlzer and coxred by a pvxe of clear glas Subjects were asked to execute one-element (I e discrete) and twoelement (reciprocal) target almmg responses The discrete amilng response required subjects to moie the stylus from the right target to the left target The reciprocal aiming response required subjects to move trom the right target to the lett target and then back to the right target SubJects had to produce the amimg movements either In the absence or presence ot a mechanical stop This mechanlcal stop conswed ot a \\ooden barrier idImensIons. 32 x 9 x 9 cm. Height 606 gr) covering the left side of the left target Subjects had to keep this wooden barrier m place by pressrng It l\lth their left hand In total. three Independent variables \\ere orthogonally combined - Type of Response (dlscrete/reclprocal). Target Size (3/2-l mm). and Mechanreal Stop (wlth/wthout) - resulting In 8 movement conditions

Subjects stood taclng a table on which the X-Y dlgltlzlng tablet was mounted They L\ere Instructed to powon themsehes such that their body midline wac biased toward the center ot the left target They were ashed to hold a stylus m a pen-grip fashion and to slide the stylus smoothly and as quickly as possible toward the target(c) It was emphasized that the) had to stop (for discrete movements) or to reverse (for reciprocal movements) the movement wthln the boundaries of the left target In order to ensure optlmal response preparation. response rnitratron \%as under subJect control Subjects per-

Movements here program The follw! mwenient 1 and 2 (time tram initi‘ition dtwn

time (time

dncil>zed otf-line using n nomnterxti~e computei ing dependent mesuw \\ere cnlcul,~ted tar both nio\ement time. pr,A ielocrty. ncceletdtion time ot a mo\sment to that ot peak ~~IocIQ). deceler-

tram

pe,lk \eloat>

to zero \eloclt>

‘It the end ot the

movement). normalized nccelerat~on (percentage ot mo~enient time spent In acceleration). awl normalized deceleration (percentage ot mo~ernent time spent in deceleration) In dddition tar the reciproccil aiming recponw d~iell time was calculated the period ot tmw the
zero during the re\erwl ot the rno\wiient dependent \xl;lbles l\erts termed tram 10 tot trials

on the

Results and Discussion

The means ot the hlTI5 tar the discrete and reclproc;il dlmlng rwxements to\\;ird the sm,~ll tdrget(s)
MOVEMENT

% DECELERATION

TIME

I

MT (ms)

RECIPROCU

600,

550

5 \\

500

RECIPROCAL 450 I-

400

-

350

-

300

-

PEAK VELOCITY

,ooP” ILnb.,

DISCRETE s k

wI

b

80 10.

250i

WITHOUT

MECHANICAL

, DISCRETE ’ I

’

WITH

STOP

chnracterlzed by smaller portlons of normJlze:d decelerCltwn. F( 1. 120 = 103. p < 0 001. ;Ind larger peak \!elocltles. F( 1. 18) = 136. /I < 0 001. than movements m the condltlon iblthout mechanlcal stop (37 vs YE. ;Ind 81 is 56 cm/s. respectnely) In addition. slgnlflcant Interactions lndlcated that nlthout mechdnlcal stop. the first movement of the reclprocdl response \\a~ not dlfterent trom that of the discrete response m term5 of normalized deceler;ltron and pe& \eloclty. howe\er. \\lth mechanIcal stop dwrete mowments had shorter normAlzed deceleration phases and Idrger peak \elocltles (F( 1. 18) = 6 31. p < 0 025. and F( 1. 18) = 8 33. p < 0 01. for normalized deceler&lon and peak \elocq. respectnely) Thrs pattern of result IS consistent wth the predlctlons dernred from the Impact ccmstralnt hypothesis of the one-target ;Id\,mtage \\hrln the physlcal constraints ot the task allow paswe deceleratron of the movement through target Impact. MT1 of a discrete rno\ement IS

shorter

than

MT1

ot d reciprocal

movement

,md.

moraxer.

has d

Ixger ped \eloc~t~ ,Ind a shorter normalized deceleration phase HoweLet-. ashen the t,lsk constrants do not permit passive decekratwn through txget Irnpxt there IS no one-target aivantage T&en together. contrlhute important zation

The

thee results \trongll wggest that passne Impact force to mwernent deceler~tlon and that Impact with target IS dn control parameter of movement programming and organi-

means

mwements

MTlr

tar

the

the large t,lrgt:t(~)

(wthout/wth)

stop X t)pe

(ANOVA)

the

toward

stop condltlon cdl

of

of

shwed

discrete In fig

\tithin-subject

‘1 slgnltrclmt

MOVEMENT

reaprocA

as a tunctlon

are shwn

response)

,md

maIn

ettect

of the mechanlcxl

2a A 2 x 2 (mechanlan;ll!sis

tar

wnmg

of

idridnce

the mrchanvxl

stop

TIME

MT (ms) 350 I-

250 PEAK VELOCITY

+

200

RECIPROCAL

l-8 F

J”

Ic”3.l

condltlon.

F( 1. 18) = 17 1. p < 0 001. lndlcatlng

the condltlon tlon

wth

wthout

taster

responses

for

stop (M = 218 rns) than tor the condlstop (A1 = 2-W ms) Howe\vr. the slgnlflcant

mechanlcal

mechanical

InteractIon between mechanical stop and ape of response. F( 1. 18) = 29 3. p < 0 001. quaIltIed this maln effect by lndlcatrng that the ddiantage

for the mechanical stop only materlallzed tor the discrete response but not for the recrproc;il response That IS. MT1 ot the reciprocal response was virtually the same for the condltlons ~lth ,md \vlthout mechanical stop Apparently. MT1 ot reciprocal almrng responses toH;Irds large targets does not seem to be affected b) the presence or Axence of a mechanlcal stop at txget 1 Importantly. the slgnltlcant mteractlon ;~lso Indicated that wth mechanlcal 5top MT1 ot the discrete and the reciprocal response \iere the same. and that wthout mechanlcJ stop MT1 of the reciprocal response was fl7swl than that ot the discrete response (313 versus 285 ms. respectrvely) The tlrst flndrng reflects d Lulure to obtain the one-target ad\;lntage. ithilt: the second flndlnp demonstrates a fnw tnrger ~7~11~712~~7g:~~ This InteractIon WAS also eLIdent tor the \;lr~Ales normalized deceleration. F( 1. 18) = 13 0. P < 0 001. and peak \eloclb. F( 1. 18) = h 36. ~1 < 0 03 (see fig 2b and ?c. respectIveI!) Clearly. the pattern of results tor discrete and reciprocal moiements toward lc7rge targets IS quite different from the pattern ot result\ tor movements toward snznll targets HON to e\plam these unexpected fIndIngs” A promrslng dIrectIon tor possible elplanatlon would be an account that postulates that a reciprocal response toi\xd k7rg~ targets does not ha\e to stop but rather to rt’lvvse twl twtwt tlumwt~ on the first target ImportantI!. the control mechnnrsmg ot stopping a movement and re\erslng a movement are different The e’recutlon EMG agonist faate

of

a discrete

pattern actl\lty the

limb

1975

Hannatord

other

hand.

usually

of

dnmpmg (or

s@lus)

absent

19X5)

1988)

(Enoka

IS controlled wersal

pattern touxd

typ~call\

require\

bl

movement

might

account

large target($)

198X.

three-burst

fact that

three-burst

IS controlled for

the shorter

\\lth

In order

(Enoha

In a fast reversal of this

The J

target

d three-burst

xtlvrty

osclllatlons

on the

and Stark

reciprocal. response

possible

the last component

movement xtwlty

movement

agonlst-Clntagonlst-agonlst

xtnlty

and et al

on the

pattern

IS

unldlrectlon;il

pattern

b\ a wo-burst MT1

last

to stop Hallett

movement.

a discrete

actlk~ty

the

Mhlle

d

EMG

ot the reclproc;ll

For

recqxwxl

mwemrntc

the dlstlnctlon

brt\ieeen

not be tele\‘lnt

This

and reclprocA

subwts

can evaluate

other

words.

their

period this

of

ot

2s

stCmdstlll’

suggectmn

diiell

two

almrng

mcnernentr mwemrntc

dwell

~n~lgses

tlme

rng

to

the

twxd

llns

small

h.mctlon;lllg

ot

the wme.

and peak \eloclt) The

presence

ad\,tnt;igt: that

reclprocA

hit,

CI rrlatl\ely

small

/rrt~~//ztvst~l~

h,l\e shied

awa\ tram

iiould

c‘\usz

At

this

the tlrst

movements

constrdlnts

are

deceler~~tlon

Ixge

i\lth

targets

eftect’

require

d Ltrger

the

Impact

bxrler

I&t

IS. ‘3

‘1 dwxete

Mi

hand,

re-

than

since the mechanIcA Mooden

In the

Th,\t

the

stop was

111phc-e h\

SubJects

the b,irrlsr

Mlth such ‘I Large Irnpxt

be

that

Possibly.

th,lt

tollowed

b! J mwement

tlon

warrant5

cdutlon

reverse regarding

the klnematlc

the

might th‘lt

the one-t,lrget protrle

In the opposite

ewcuted

t,lsl\ dfter

ad\ant;tge

In the dlrectlon of
This

tIndIng

ot

rtwement

dltterent

dlrectwn

the present

rmxements

prewnt

dlrrctlon

In the same dIrectIon

gener;lllzlng

to multwlement

Mhlle

mwement

the second mwement

b> A second mcnement III

noted

to

studies

to continue

movement

pret‘itmns

tar


would

i\lth

IF.

subwx

1. previous

wblects

tollwed

hrttlnp should

it

rsqurred

txget

required

(that

th,in

Accord-

be dl\plxed

to

point.

constraints hrttlng

it

;Ind Ight-iieelghted

longer

(see top I)

ref-kct

stop

I support5

dwrete

nornwllzed

\~ould do Hweer.

r/w dwtr

\fds much

hlT1.

w-get5

mechanlcA

mai

by ‘1 dlstlnct

Impact

‘id\ant;lge

large

target<

small

ot target

InterpretCltmn

stop mght

tar

the

responw

this

one-txget

the

ot A mech~inlc~il

one-txpet sponw

ot

IS. In

15 m\. respectnel))

datd concerning

support

dxence

that

accurxv

time on t,u-get

‘lnd

both

so that

accurxy.

sepx,lted

reclprocJ

In the Jxence

might

that

txget

endpoint

w-get

( 130 iersub

re;lsonlng.

targets

tlrst

toward

ot d\tell

on the small

time on the large txget

lequlre

5 endpoint

dnd xhleved

dlscrrte

The

a mwement

target\

~rcy~ on the

mwement

Intended

reciprocal

be thought

wiall

moiementz

ha\e to cornplus

rcrtgerr ( Z I~WZL hwe\el.

vmll

and re\erslng

IS so. bsc;luse

dwrete they

tward

jtoppmg

tram

obsew,l,md Inter-

In the sxntl

dlrec-

tICIt

The

lmplwxtmns

twotold

FII~;~.

affected ph,ws not

the

reldtwe

the notion

suppo~

ot the present

because

t?d This

the

durdtwn

ot simrnetq outcome

txget

result5

tar motor

Impxt

ot the

acceler~itlon

or bell-shaped IS not compatible

control

constr,ilnt~ ;Ind

lelocltv-time wth

theon

drt:

dr;lmatlcall\ deceler‘itlon protlles

the aswmptwn

IS ot

ot relatwe

rmnrlance theories

of motor

sptw~ic

movements

dom,un

(e g . Meyer

results

tune.

control

and

theretore

In l\hich

by adJustlng

et al

questwns

a general

motor

d sckibie

1982. Munh,lll

the \1ab111ty ot program

pa-ameter

et ‘11 19S5)

in

produces the

trme

Rather.

the

support

a VKN of motor control that 15 fund;lment,llly pragmatIc and spec~hc to the oblectlves ot the pertormer and the constraints ot the task (Adam 1W2. A-bib 1985. Cole and Abbs 1986. Marteniuh et al 1087) Second. phenomen;l

the

one-target

alled

ad\,mtdge

cotItc’\f

quence are not Independent exh

other

Studies

shape and tlmlng wh,it

letter

tollous

ot each other

ot h‘md\irltlng.

ot a letter

belongs

to

movements

effrcfs

but mnq mutuAli

tar Instance.

depends

It (Rosenbaum


on \i hdt letter 1991)

Conkit

class In

ot

A se-

Inf’luenct: th,tt

the

precedec It and on eftew

A;0

hnw

been described In the stud! of bpwrltlng (Terzuolo ,md VnICmr 1080) The present research points to the Importwce of mechCmlcdl constraints (I e Impact l\lth txget) In producing contekt ettects. a point corrobor‘ited b! Gentner et al (1988l \vho shwed that contekt etkcts In tqpewrltlng can be centr,illy based but also mech,mlcall) Importantly the rele\~nce ot mechanIcal constralnt5 In the control ot mo\‘ements has been emphasrzed b> Rosenbnum ( 1991) M ho drpued that rel)Ing on mechanics’ cdn smipll~ the degrees-of-freedom problem (see also. BIZZI and Muss,l-I\xldl 1989) In conclwnn The one-target ;Idvantnge m;lterlnllzes when t;lrk constrdlntc rtqurre d mwernent 5top and Jlo\.\ tar target Impact. It 5 underlyng mechdnlsm IS the e\ploltatlon of paw\e. mech,mlcal deceleration ithen

through

target

task constrarnts

mwemrnt

underhung ant;lgonlst tuo-target

reysterlng

References

re\erwl

Impact

The

do not require

In the absence mechamsm IS prob;lblv actlilt\ Future rewxch ‘idvantage more directly EhlG xtnlty pattterns

advantage IS tound \top but ctllo~ a tart of target Imp;lct constraints. It s d txo-burst pattern ot ;Igonlstshould Imestlg;lte the one- and by monltorlng rmpxt tortes ,md t\\o-target

a mcxement