Task diffiutlty and hand differences
in peg moving, circle marking and square tracing
J.D. Van Homi
I.C. McManus
Dcpanmcnt of' Ps1'choiogl'
Univcrsin' Collcgc London
cr)wcr strccI
London WClE 68T
Engiano
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Task difficrtltlt and hand dffirences
in peg movinq, circle marking and square tracing
J.D. Van Homl
I.C. McManus
Dcpartmcnt
ol
Psychology,
Univcrsitv Collcgc London
Cowcr Strcct
London WCIE 68T
England
'Prcscnr addrcss lor corrcsnontit ncc.. N I M
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9(XX)
Task difficulty and hand diffcrences
Abstract
Tasks such as the Annen pegboard. Taplcy and Brydcn circlc marking rask. and Bishop squarc
tracing task. are commonlv used to asscss thc diffcrcnce in pcrlormancc of right and
lclt hands, and
thereby to construct indiccs of laterality. Howeve r almost no srudics havc systcmatically askcd how
perfbrmance on the two hancis varies as a function of task difficulty, and yct without such information
there is no theoretical basis tor choosing bctwcen a rangc
ol possiblc lltcrality
indiccs.
In this studv we show that thc overall difliculty ol'thc Annctt pcgboard can rcadiiy
bc
increascd by making the rows of pegs furthcr apart, by putting targct holcs closcr togcthcr, or by using
pcgs which are larger or are cut squarc at thc cnd. Howcvcr in clch crsc thc difrcrence bctwccn hands
rcmains constant. rhe non-dominant hand
t*ing lbout 600 msccs longcr to movc thc tcn pcgs.
Likewisc. rcducing thc size oi the tlrgct circlcs makcs thc Taplcv and Bn'dcn circlc-markinc task morc
,Jil'{rcuit ovcrail: how'cver r.hc tiut-crencc bctwccn hands rcmarns constant, thc non-dominant hand
marking about
incrcascs thc
l0 circlcs
ie'ss
in clch 20 scconds. Finally, rcducrng rhe distancc bctwccn thc squarcs
ovcrlil dilficultv ol'thc Bishop squarc-tracing msk: ind only on this task did
hand
diflcrcnccs incrcasc ro somc cxtcnt ls ovcralldilllcultv incrcascd. Trrkcn togcthcrour findings suggest
scrious llaw,s in currL'nt mcthods tbr caiculating indiccs
ol Iltcraiitr'. such that intcrprctations of
dil'lcrcnccs in'dcsre'c ol' i.rtcrliisrrtion' urc highly qucstionablc.
Corrclations in dcgrr--c ot llrtcralisation bctrvccn Lhc thrcc tlsks wcrc low tc.g. 0. l2 lor thc
,\nncu. with Taplcl'und Bndcntdcspitc trigh intra-mcAsurc rclilbilitics (Cronbuch's alpha =.879 and
0.li-1-5
rcspcctivclvr. Thc irnnircltiorr is thtt dil'lcrcnt proccsscs mccjiulc irand dil'[crcnccs lbr thc thrcc
tasks. and that thcv rjo not
lii
rctlcct a sinslc pnmarv continuum ot'Irrrndcdncss. Thc data also suggcst
that dillcrcnccs in nrc-lcrcnce'urc prior to dil'[crcnccs in skill.
Task difficulty and hand differences
Introduction
Thc right and lcil hanos of most individuals diffcr in thcir abiiity to car.v out unimanuai tasks,
with about 907o of the populauon showing supcrior skill with thcir right hand. Thc mechanism of thc
supenority ot the oominanr hano is not at all clcar, although specuiations have includcd improved
force controi (Pcten. 1980), a iess noisy output mcchanism (Annett et al. 1979), and supcriorvisuo-
motor co-ordination (Honda, 1984). Diffcrcntial hand perlbrmance is usually assesscd by one of
scvcral standard tesrs.
of which thc most popular is thc Annctt pcgboard (Annett, 1985), aithough
orhcrs includc the circlc-marfiing task olTaplcv and Brydcn (1985). and thc squarc-tracing task of
Bishop (1980: 1984: 1990). Despite thc popularity olthcse mc&sures, thcrc is very littlc publishcd data
conceming how <iifferences in hand performancc rclatc to task difficulty, or indccd to how skill
diffcrences on one rask reiate to diffcrcnccs on anothcr task. In this paper we cxaminc these thrce
frequently used tasks in dctaii. examrning how difficulty rclatcs to task paramctcrs. and how thc tasks
rclate to one another.
The Annett pegbottrd. Thc pi;gboard task
Kilshaw
&
Annert. 1983; .{nnert
of Annett and
collcagucs (Annctt. 1970; Anncn, 1985;
& Kilshaw. 1984: Annctt.
measuremcnt ot'diitcrcnccs in ocrfbrrnancc
1992) is a popular instrumcnt fbr the
ol'thc right and lcli hanos (scc for exunplc, Pctcrs
and
Scn,os (1989). !{c\lanus et ti!. r1993)). Thc task is attractivc i-rccausc it.s rationalc is straight[orward,
it is simple fbr
subiccts ro undenirand.
it is straightfbrward to ldministcr.
and
it can bc administcrcd
cven to quite 1,oung childrcn or pcrsons with motor handicaps. Tl,pically pcrlbrmancc is mcasured
as
thc timc takcn to complctc rhc msk with thc right (rr) and thc Iclt (r,.) hlnd (oftcn asscsscd in an RLLR
or LRRL ordcr):. Dil'lcrcnccs irctrr'ccn thc hands arc asscsscd t'irhcr by looking at thc simplc
diflcrencc (DIFB i.crwcen rhe' irands (tt.-til, or by calculating r iltcralitv indcx tLI) in which
dilltrenccs bctu,ccn rhc hands rrc cxprcssctl rs a l'unction oi'total pcrlbrmancc
ld.mc. 100.(
t,,-till(tr-+til,
thcrcby taking inro lccounr ovc'rlil dil'l'crcnccs in pcrlbrmancc bctuccn subjccts. Although thc two
mcasurcs arc
vcn'irighll,corrcirtcd. and do not obviouslv givc ciil-lcrcnt irnstvcrs in practicc tc.g.
!lcManus cr a/ (1!)t)l)). it courri
brc
argucd that thcrc arc thcorcticlri r.'lrsons lbr prct'crnng a measurc
ttt asvmmctn,which is a dimcnsionlcss numbcr. rathcr th:tn onc uiticit is mcasurcd in units ol'timc.
: It should bc norcd that lirhough ir is normally morc convcniL.nt to rr'r.cr to thc dominant (D)
and non-
dominant hand (N) 1^-rtormance ot'subiccts, irrcspcctivc ol'whcthcr thcv nclrmally prct'cr to usc thcir right or
lcl't hand lbr rasks such ls u'nung. thlt usagc is not cntircly thcorv l'rcc rn tic contcxt ol Annctt's right-shift
rnrxicl. anci that one should thcrctorc rct'cr in ahsolutc lcrms to thc pcrlbrmancc ot'right (R) and lcli (L) hands,
irrcspcctivc ol othcr hr.hlvi0urs. Hr'rc \\,c rrsc /? ltnti
hrrt othcrwrsc usc D rtnri N.
L *,hcn
thaL rni.rkcs nrorc thcorctical or dcscript.ivc scnsc,
Task difficuity and hand differences
That notwithstanding,
it is clear from the developmcntal
remains almost constant over the age range 5-15. despitc
4_
data
of Annett (1985) (p.al9) that
rr-rn
and r, each showing considcrable decreases
with age (and therebv producing a situation in which 100.(t,.-r*t'it_+r"/ would bc incrcasing with age).
The interprctation of such a resuit is diificult: it could bc argueci rhat larcralisation (exprcsscd
a.s
rr-rp)
should indced bc invariant with age, on the grounds that latcralisation sccms to be prcsent even in
neonates, and thcreibre probably has a l'ixcd biological substratc: or rt could be argued that on this test
of skill, latera.lisation {expressed as 100.(tr-tr)l(t,_+rrl is truly incrcasing with age, in thc same way
as degree
of hand preference incrcases with age (McManus et al.198$, and that it would be expectcd
that this task shouid also increase its latcralisation with agc. Thc choicc of an appropriatc Iatcrality
index thercfore has rmponant theorctical implications.
The difference in performancc on thc pcgboard bctwecn right and lclt hands displays a rcliablc
rightward bias,
extensiveiv
or "right shift" (Annctt. i985); Annctt and her collcagues have used this task
as the theoreticai and
1984: Kiishaw
&
.{nnen.
cmprrical basis of a gcnctic modcl ol handcdncss lAnnctt & Kilshaw,
19831
Annctt. i9ti5). O[ somc imponancc in this thcory is that
the
distribution ol skiil dilfercnces between thc hands is unimodal and approximatcly normally distributcd,
with its mode shiltcd towards the right, thc tail ol the maror distribution conccaling a minor
distnbution with a mern oi zcro.
Although mc pcgooaro tlsk is
r
popuiar mcasurc ot'hmd dif'lcrcnccs thcrc is e strong
suegestion that othcr mcasurcs ot'dil'lcrcntinl hand pcrlbrmancc rc'.g. tTrrplcy
1990: Mcltlanus. 19.\5b)) do ncrrproducc
instcad producc rvhat has bc-cn
thcrc arc trvo cicar rrcuks.
l
l
& Bn,dcn. 1985: Bishop,
unimodal distribution simiilr to that
olthc
pcgboard, but
clllcd tt.symmetric birnodttl distribuilon (McManus. 1985b), in which
llrrgcr. hroadlv corrcspondins to rir:irr-hunocn whiclr is shiltcd to thc right,
lnd a smailcr. corrcsponding to lctt-handcn. ivhich is shificd to ri.rL'ir'l'r. Rcccnt rvork by Annctt t1992)
usinq a rangc ol'othe'r pcncii ilnd pilpcr tcsts suggcsts th:rt sucn svmmL'tric bimodal distnbutions arc
probably *re normai pattcm
ol
rcsults. and arc also associatcd *'ith
pcrfbrmancc bctrvccn thc irlnds tiran is lound on thc pcgboard
thaL thc
ra.sk.
r
grcatcr rclativc diflcrcncc in
Tlic possibilitv thcrclbrc cxists
unimodal distnbution tirund with thc pcrboaro task is prL'0omlnxntly thc' rcsult ol'its panicular
dit'ficulty lcvcl. lrnd fiat it'drc tusk wcrc madc harricr thcn u s\mmcrnc bimodal .iistnbution should
cmcrsc, along with lrrrgcr rclatirc
Dcspitc rts popuilnty as
vuriclus comDoncnrs
r
cii
l'l'crcncc-s
in pcrlormancL- (rr tJrc nght and lcli hands.
mcasudng instrumcnt. littlc rcscurch lras bccn camcd out on
fic
thrt mlkc up lhc pcgboard task. lrnd thcir inllucncc on thc dillcrcntial
l
Task dilficulty and hand differences
performance of
tie two
hands, and we are only aware of thc single paper by Annett, Annett, Hudson
and Tumer (1979\ which looked at right-handcrs. In thcir cxpcriment
I they constructcd
vcrsions of
thc pegboard task in which w'ere varicd thc distancc betwcen thc rows of the pcgboard (movement
amplitudc), and the size of rhe holes (movcment tolcrancc)to dctcrmine if hand pcrformance followed
Fitts' Law (Fitts. 1954). The inirial expenment showed that incrcascs in movement amplitude produccd
uniform increases in task compietion timc; however thcre was no evidence that this was associatcd
wrth a change in difference of performancc bctween thc hands. In contrast, rcductions in holc size did
alter the differences bctween the right and lcft hands, with thc smailest hole size producing thc greatest
difierence between hands.
The earlier work of Annctt, Golby and Kay (1958) had notcd that thc positioning clcment of
peg moving time was the most sensitive to changes in thc ratio of pcg sizc to holc size. Thercfore in
Expenment
II. Annett
et al. (1979) fiimcd subjccts whilc thcy performed thc standard pegboard task
and reported data suggesting that the major dillcrencc bctwccn thc hands was in thc locating of pegs
in rhe dcstination hole. In addition. thc lcft hand (of thcir ri-r]ht-hanocrs) produccd morc corrective
movements to placc the pegs. Thc authom concludcd that lhc motor output
ol the worsc
hand is
"simply morc noisy than that oi thc prcl'crrcd hand", and that it was unlikcly that diffcrcnccs betwccn
hancis
in the aiming movcments wcrc thc rcsult of dillcrcnccs in thc ct'ficicncy in lccdback proccssing.
Nevcnhclcss
it is notewonhl'rhat thcir clata showcd
sigrrilicant diilercnccs bctwcen hands in the
'rransporr empry' phrsc ol lhc movcmcnt in which thc cmpty hand is rctuming and picking up the next
pcg.
It should aiso
be emDhasiscrj that although Annctt ct rtl (1979)
*ishcd to usc thc rcsults olthcir
cxpcnmcnt II in orocrto cxpiain dil'fcrcnccs in pcrt'ormancc bctrvccn pegboards ot'dillcrcnt diificuitv,
thcir experimcnt II lctuallv oniv uscd lt st:tndard pcgbolrd ol'onc de'grcc ol'di{'ficulty.
Thc prcscnt studf invcstigatcd lhc ct;ccts upon ovcrall pcnbrmlncc. md upon diffcrcnccs
hctwccn hands. ot'changing
rr
numbcr ol'tiil'fcrcnt aspccts ol'thc stanrrlrd pcgboard.
witr thc intcntion
ot'r'arving thc ditllculty ot'thc trsk.
Pcgboard
i
*as simii.rr to that uscd in cxpcrimcnt I ol ,A,nncrt.,\nnctt. Hudson and Tumcr
i 197!)). in that wc vuncd thc rri.rr,lncc bcnytut the row.t tR0ll'Dl,\T) ot holcs, itnci thc di:;tancc betn-een
lutles (HOLEDIST) within
:.r
rou'. in
l
total ot twclvc comhinrtions. It rvus hopcd that varying distancc
hctrvccn rows would pnncipallv all'cc[ thc transpon pan ol thc ta.sk. uhcrcas vrtrving distancc bctwcen
holcs would al'fcct thc lrnal. pilcing pan ot'thc task, which should
h: panicularlv dcpcndcnt on fine
ntotor skills. riuc ro thc prcscncc ol'othcr pcgs alrcady in holcs limiring thc l'rccdom ol movcmcnt
thc iund in placrnr: thc rcmrtinins pcss.
-l
of
Task difficulty and hand diffcrences
Pegboard
II allowed
a companson
of the effccts of thc finai stages of peg placing, and hence
the need for corrective movemens. Thc task was made morc difficulty by varying peg DIAMETER
rclative to hole diamerer, anci bv varving pes SHAPE, all pcgs bcing *'lindrical but with thc cnd cithcr
bcing cut square or being semicircuiar in section. Thc squarc-enocd pegs required a much narrower
ancie of entrv into the hole in order to prcvent 'jamming'. Thc basic condition
oi pcgboard II
was
dcsigned to be as similar as possibic to Annett's standard pegboarci, based upon published dimensions
(Annett, 19701 Kilshaw & Annen, 1983: Annctt
& Kilshaw,
1984: Annctt, 1985: Annctt. 1992).
In totai each of our subiects was tcstcd on 20 pcgboards. Although Annett et al. (1979) tcstcd
mainlv right-handcd fcmaics, hcre wc havc tcstcd thc pcrtbrmancc of equal numbcrs of right and lcft
dominant subjects of both sexes.
The Taple-v and Bryden circle-markins msk. Taplcy an<i Brydcn ri985) dcscribcd a group tcst for
in skill, which is broadly similar to the 'dotting' task of
Each hand was used scparatcly to placc marks in a scrics ol'circlcs'(in lact
assessing diffcrences between hands
Stcingrueber (1975).
UpperCase lctter'O's, as typed on a standard typcwritcr). Thc numbcrof marks madc in 20 scconds
was countcd. and a standard laterality score, (nR-n,.11(n*+n,_), rvas cllculatcd. That such a standard
latcniitl, indcx mrght not bc complctcly satislactory lbr thc Taplcl, mci Brydcn task is suggcstcd,
wirh rhc Anncrr pcgboard. bv o*'clopmcntal data l.Carlicr et ai.
1t)9-1).
as
Carlicr er al ( 1993) studied thc
Tapicl,and Brydcn rask in cnridrcn agcd 7 to 14. Although thc total numbcr ol'marks madc by
the
non-prelcrrcd hand neariy doubicd over that agc rangc thc absolutc dil-lL-rcncc bctrvccn hands changed
vcn,tittle (rcgrcssion ol marks on ilgc: dominant hand.
-1.991.11
mlnis pcr vcar: non-dominant hand
+.1-+10.18 marks frcr vcar). .\lthough a simplc dillcrcncc scorc shoue'd.somc o'idcncc
of increaning
larcrliisation with agc. convcntlonill latcralitv scorcs showcd u r/t't','c:r.slnq lutcrliisation with age.
In
this^ \^tudv
wc rr.ili rcport tbur vlnations ol'thc Tapicv mtl Bn,dcn tl.sk in which wc vary
thc sizc ol-thc circlc rciativc to thc sizc ol'thc marking in.strumcnt
tl
tclt-tip pcn). In vicw ol'thc lack
ttl'dcscnptivc dctaii in thc ongrnal papcr ol'Taplcy and Brvdcn ir is ,.jit'tlcult to bc prcciscly sure of
thc rrccisc comparabili[\,
ol our task u'ith thcir
task.
Thc Bi.rhop suuur(-rrdL'it( rir.ir. Bishop (l9ll0) dcscribcd a task ol'ncht and lcti hand skill in which
childrcn uscd a pcn to draw lr continuous linc bctwccn two conccnrnc squarcs.i mms apart. thc outcr
squarc having a sidc lcngth
ol
102 mms. In thc onginal vcrsion ot'thc tcst thc dcpcndcnt variablc was
thc numbcr ol'crron. dcl'incd as thc pcn crossing ouLsidc thc trlck rtctlncd b1' thc two squarcs. Thc
lnctsurc was panicullrrlv succcsstul in u group ol'cight-vcur oltJs lt showinq problcms with thc non-
Task difliculty and hand differences
dominant hand. In the present study we modificd the task somcwhat. principally because we wished
to use it in a group of adults, and wc wishcd to vary its difficulry across a wide range.
Since
pertormance in such a population showcd very f'cw errors. cspeciailv whcn thc task was easier than
in Bishop's version. we used the total Limc ro travcrse thc track
as the outcome measure; Pcters and
Servos t1989) have previousiy used a similar modification. Thc difflculty of thc task was altercd by
vanrng the distance between the squarcs. Whcn thc di.stancc is large rhcn it is possiblc for subjects
to 'round off' the comers to
a largc extcnt, and we thcrclorc al.so modificd thc task by placing a small
square at the centre of each comer. and instructcd subjccts that thc linc had to pas.s through the comcr
squares. That rcsuited
in sudden, abrupt changcs of dircction. in a similar manner to that requircd in
the original task.
For convenience we wili describc the pcgboard, circlc-marking tasks, and squarc-tracing tasks
separately, and then considertheirinter-rclations. Forcach task wc wcre intcrcstcd in scvcrai diilcrcnt
qucstions: thc cffccts of overali task dil-ficulty upon thc pcrlbrmancc ol'dominant and non-dominant
hands: thc inter-rclationship bctwecn latcrality measurcs of'tasks varying
lactor anaiysis and rcliabiiitv analvsis; a comparison of Iatcralitv
and by conventional latcralitv indices; and thc distribution
ol
in dilficulty,
as scorcd by
mcasurcs
simplc diffcrcnce scorcs
of Iatcraiisation in right
and
of hand skill
are
lcft-handcrs. Finailr'we wcrc intercstcd in thc cxtcnt to which dillcrcnt mcasurcs
intcr-corrclatcd. ano hcncc c.:.n DC sL-cn
ls mcasurins
asscsscd by
Lhc samc'undcriving proccss.
Tlrc ,lnnctt Derboord tusk.
.\l cthod.
Subieus: Onc hunijrcd and t*civc sublccts took pan in this cxtL-nmcnt ovcrall.
lll
bcing tcstcd on
lhc Annctt pcgboards. Thcrc wcrc lifir,-six malc and llfit,-six ltmaic univcr.silv studcnts having
mcan+SD agcs ol' 15.716.6 and 16.7+7.(16. rcspcctivclv. Thc sub-icct.s wcrc dividcd into groups of
right- and lcl't-hanci domrnant bascd on thcir rvriting hrnd rcsponscs (rn thc lS-itcm qucstionnairc ol'
VIcN'lanus 11919). Thcrc rvcrc trltr'-six riuht und
Iilty-six lcl't-lrano titrminant suhtccts, with mcantSD
agcs crt-25.6t6.1 rnd 26.ti+7.6. rc'spcctivclv. Thc bctwccn suhjr'cr iTlcasurcs rrc'rc lhcrclbrc hand
dominancc (DOMHAND) and SEX.
Pcg,bodrd
1. Pcgirolrd I rvas buscd upon thc pcgboard task ol'Annctt (.{nnctt.
1970: Annctt, Hud.son,
& Tumcr. 1974: Kilshaw & .{nncrt, lt)tl3: .\nnctt. I992), rnd in punicuiar lhc studv ol Annctt. Annctt,
Task difficulty and hand differences
Hudson and Tumer (Annett et
al. 1979). The pegboard was constructcd to the same
dimensions
commonly given for the pegboard (see bclow I but was adaptcd such that the distance bctwecn the rows
coulci be set anywhere between
5 and 64 ccntimctrcs along a dovetailed guide. Once placcd into
key. Thc distanccs bctwecn
posruon. the row couid be locked into position using an Allcn
rows
(ROWDIST) used in this expenment werc the same as thosc of Annen et al. (1979), bcing 20322,
30.48. and40.64 centimetres apan. The distancc bctwccn holcs is more convenicntly reponcd hcre
as
berween their ccntres, as opposed to thc distancc bctwccn the edges oi thc holes as reportcd by Annett.
Each row was constructed such that
it could be rotated 90o around its horizontal axis in order
to
engageoneoffourseriesofholesscparatcdbyadiffcrcntdistance. Thcrewcrctcnholcsineachrow,
scparated by distances
Pegs were made
of 1.5,2.15,3.0. and 3.75 ccntimctrcs^ bctween the holc ccntres (HOLEDIST).
of red perspex, and were 5cm long and 0.95cm in diamctcr. A schcmatic diagram
oIPegboard I is prcsented in Figure 1a. Furthcrdctails arc givcn in Van Hom (199D.
Procedure: Subjects were asked to begin with thcir right hand lrom thc right sidc oIthc pcgboard,
and with thcir
At
each
lcll
hand from thc icit sidc. so that thcy werc working across thcirbody on cvcrJ'trial.
row and hole distance setting, subjccts pcrlbrmcd thc tesk witlt thcir dominanr and non-
domrnant hands
in a randomiscd ordcr. Altcr both hands had bcen uscd, thc distancc bctwcen
holcs (HOLEDIST) was chanccd. This was donc until
all lbur
the
distanccs bctwccn holcs had been
varicd. also in a randomiscd orocr. Thcn thc distancc bctwccn lhc rorvs (ROWDIST) was changcd,
ano
fic holc distancc tnals
\\'ere rcpcatcd. and so
lbnh. Thc timc l-or l subjcct to movc ail of thc
l'rom one sidc of thc pcgboard to the othcr rvas mcasurcd to thc ncarcst hundrcdth
a hand-hckl stop watch.
'.vas sroppcd and bcgun
If
pcgs
ol'a sccond using
at anv timc dunng a trial. a subjcct droppccl or misirandlcd a pcg thc trial
again. This was donc
as of'tcn as ncccssarv
untii thc subjcct complctcd placing
rril thc pcgs in thcir holcs r.vithout crror.
Pt,;itrtard
l/
This pcgboard uls bascd lliriv closciy,on that originliir dcscribcd by Annctt (Annctt,
i970: .\nnctt. 1972. Annctt. ltlt)l: .-\nnctt. l9tl5: Annctt. I{udson. & Tumcr. i974: Bishop, 1990).
Ilowc.vcr inlormation about mcasurcmcnts ot'thc pcghnard *as not complctcll'spccilicd, md whcrc
litcrc *,as insut'flcicnt inlbrmarion tr.(. ircisirt ol'thc pcgboar(l. \\'idrtt ot
drawn t'rom othcrciimcnsions and l'rom Figurcs
l1.l
and
ii.l
l
row. ctc.) inlcrcnccs wcrc
ol .{nnctt ii9ll-5). Fortcchnical rcasons.
duc to rhc availabilirv rrt'matcnuis. Lhc'"ridth ol'thc rows on tlic prcscnt pcgborrrd is a littlc smallcr
Lhan thosc uscd
by Annctt. [-icl*cvcr. in most ot-hcr rcspccts thc pcrnourd is comparablc to that uscd
bv Annctt. Tirc dimcnsions ol our pcgboard:trc givcn in ligurc lb.
Task difficulty and hand differcnces
Annett et al. (1979; Experiment I) varied thc peg-to-hole size ratio by incrcasing the size
of
the holes rclative to the size of the pegs. In this cxperimcnt, the pcg-to-hole sizc ratio is also
manipuiated, however
this is done by using two diflcrcnt pcg sizcs (0.95 cm and 1.25
DIAN{ETER), keeping the hole size constant. In acidition to t}ris, tre shape of thc end
also examined (SHAPE).
increases the need
A roundcd
ol
cm;
the pcgs is
shapc to the peg hclps to guidc peg placcment, whilc a flat end
lor correctivc movemenrs bctorc thc Ilnal placement of thc peg. Thc pcgs
were
made of red perspex and were of the standard lcngth.
Procedure: Each subjcct sat facing the pcgboard that was positioncd on a tablc at about waist hcight.
As with pegboard I, the pegs werc piaccd in thc row closest to thc sub3ect with cithcr thc roundcd end
or the t-Iat end downward in the hole. SHAPE was randomiscd across trials and across
subjects.
DIAN1ETER with which the subiect bcgan each condition was also randomiscd across trials. Subjects
were rold that with their right hand they should bcgin lrom thc right sidc of tJrc board, md with thcir
lcft hand from thc Ieft side of thc board. Il rt any timc a pcg was dropped, thc trial was stopped and
restaned.
The time for a subjcct to compiete rhc task was rccordcd to the ncarcst hundrcdth of a second
using a hand-hcld clectronic sropwatch. Elch condition was pcrlbrmcd twicc rvith cach HAND,
dominant and non-dominant. cithcr in thc onicr D-ND-ND-D or thc ordcr ND-D-D-ND, to balancc
lbriinearcl'lcctsolpracticc. Uponcomoictionoi'ail tnalslbrasivcnpcgshapc.thcpcgswcrcturncd
over in thc holes ro the nerv shape and thc ncxt tnal bcgun. Thc
t*o right hutd and two lclt hand
vaiucs fbr cach condition wcrc thcn avcragcd ltnd thc avcragc uscd ior subscqucnt analysis.
Rcsuits
Pctboord
[.
Statistical anaivsis ot'pcrtbrmlncc timcs
wls
by'
l ]rlxlx3x.l (DO\IHAND
x SEX
x
ROWDIST x HOLEDIST x IJAND) split-piot unalvsis ol varirncc du'sign: bctrvccn-subjcct vanablcs
wcrc DOIvIHAND and SEX and',r'ithin-sub-icct variablcs wcrc HAND. ROWDIST lnd HOLEDIST.
Whcrc signilicanr e'lf'ccts
ol
ROWDIST und I-IOLEDIST rrcrc lbund tlrcv $crc penitioncd into
pol vnomial componcnts.
Considcring bctrvccn-subiccts cllccts. thcrc was no ovcrall dil'l'crcncc bclr','ccn subjcct-s who
wcrc right-handcd rtr lcli-handcd lirr wnting (DOMHAND). Thcrc rvas. ltowcvcr. a significant
dil'{'crcncc bcrwccn malcs and tcmalcs (SEX) in rimc to complcrc'rhc rlsk
(F(l,l0S) = (r.tJI, p<0.fi)l),
lcmrics bcing slowcrovcrall ti\lalcs: rncan = ''l'l'l'.), sd = l'l'l'l sccs: lL'muics: Incan = !'!'!'!'!, sd = sccs).
Task difficulty and hand differenccs
Performance with the dominant hand (HAND) was significantly bctter than performance with
the non-dominanthand
G(1,i08) = 126.43. p<0.001). Although the HAND x DOMHAND interaction
;ust laiied to reach significance (F(1.108)
=
-i.22.
p = 0.075), the HAND x DOMHAND x SEX
interaction was significant, (F(1.108) = 7,20. p = 0.tX)ti): it shows that'l???l?'l??????2?.
There was
a highly
signif-icant ct'lcct
ol' distancc bctween the rows of thc
pegboard
(ROWDIST) (F(2,216) = 1064.45. p < 0.tX)l). which polynomial contrasts showed to be principally
a iinear increase in performancc time with distancc betwecn rows (F(1,216)
the non-linear component was 'l?????????. Thc HAND
=
2127.73, p < 0.001);
x ROWDIST intcraction
wa.s
not significant
rF(???.1'???)= l???), indicating that the dilfcrcncc bctwcen thc hands did not systcmatically change as
thc cjistance between the rows incrcased. Figure 2a shows ovcrall performancc, scparately for rightand left-handen, and dominant and non-dominant hands,
in rclation to
tJrc distancc bctwcen rows:
although total time increa.ses with distancc. the dillcrcncc bctwcen dominant and non-dominant hands
is unreiated to movement ampiitudc. No group-by-rows
cffcct l????-which is this'l???? was significant
{F(???.1'}??)=???), but thcrc was a sicnificant ROWDIST x SEX interaction (F(2,21S) = 4.21 , p =0.016),
the diffcrencc bctween malcs and lcmalcs bccoming '????grcatcr???? as ROWDIST incrcascd.
Thcrc was a signil'icant cil'cct ol'distancc bc[wccn thc holcs ol'thc pcgboard lHOLEDIST;
Ff3.,rl-1) =
)i8.17, p<0.001). *hich
had signitrcant Iincar. quadratic and cubic components (Linear,
Fi1.ll-l)=i12.'16. p<0.001: Q)uadratic.Frl.-lll)= i17.50.p<0.001:Cubic.FLl.-:l-{)-5.2-1,p=
0.016). Thc HAND x HOLEDIST intcrrction \r'as not signilicant (F(???.1'??)=.)'l'.)'l). indicating,
as
with
ROWDIST. that thc diffcrcncc bct*'cen dominant and non-dominant hands u'as not a function of
distancc bctwccn holes. dcspitc ovcrdl timc incrcasing with distancc bctwccn holcs (scc figurc 2b).
\cithcr thc grouo-by-holcs l'l'lDO\IHAND r HOLEDIST intcraction
thc SEX
x HOLEDIST intcractron. \o hiqhcr
orcicr intcractions
rrrrs not signillcunt. and norwas
uirh HOLEDIST rvcrc si[nificant.
.xccpt lbrthc group-by-gcndcr-br'-lrand-br,-holcs'l'l'.''l'l'l DOIvIHAND r SEX x H.\ND x HOLEDIST
intcrlction (F(3.32.1) =
pcrtbrmxncc
--i.3-{.
in thc holc
p = ().01). duc to l'l'l'l'l'l'l'l'lbcttcr tlcscnptionll'l'l indicating ditl-cring
distlmccs conditions bctwccn
thc sc\cs ol' onc ot- thc groups. Thc
mcrninslulncss ol'such an unanticiputcd lour-wllv intcrlction is not rrt lll obvious.
Pcibrtord
ll.
Statistical anrlrsrs was by mcilns
oi a fx2x2x2xl iDONIHAND x SEX x SHAPE x
DIA\tETER x I{AND) split-olot rtnalvsis ol vuriancc. wiLh thrcc rcpc:rtcd mcasurcs. Bctwccn-subjcct
vanlblcs wL-rc DOMHAND und SEX: rv'ithin-subjcct vlnlblc's wcrc Ur\ND. SHAPE,
DIANIETER.
and
Task dilficuity and hand diffcrences
Overall performance on the pegboard did not diftcr in right and lcft handers (DOMHAND;
F(?.????)=???), and neither were there diffcrcnces bctween malcs and fcmales (SEXI F(??,????)=???).
There was a highiy significant differencc bctwcen dominant and non-dominant hands (HAND:
F(l.108)
=
107.82,
p < 0.001), the non-dominant hand bcing slower than the dominant hand. A
signit-rcant effect of SHAPE (F(1,108)
=
1459.80, p < 0.001) showed rhat the usc
of flat ended
pegs
incrcased performance time as compared wirh round-cndcd pcgs. Similarly the effcct oiDIAMETER
was significant (F(1,108) = 9i3.06, p < 0.001). pcrlbrmancc bcing fasterwith a iarserpeg-to-hole sizc
ratio. Thc SHAPE
x DIAMETER intcraction
was also signilicrnt (F(1,108)
= 213.?5, p <
0.001),
large. flat pegs bcing particuiarly slow. Thcre arc also significant SEX x HAND x SIZE (F(1,108) =
4.07.p=0.046)andSEXxHANDxSHAPE(F(1,108)=5.79,p=0.02)interactions,dueto
.'}????????what???????
and ?????what'l???? rcspcctivcly. Of particular intcrcst is that none of thc
HAND x SHAPE. HAND x DIAMETER or HAND x SHAPE x DIAMETER interactions werc
signiticant (F(??,???=???: F(???.???)='l???: F(l'}l',?l?)='l??), showing that diffcrcnccs in pcrformance
between hands were unrelated to peg size or shapc (as is shown
in ligurc 3, scparatcly, lbr right
and
lcft-handed subjects ).
Fdcnr
analvsi.s and
reliahilin'onaivsis. Elch ol'thc
task on 20 diffcrcnt occasions usinu rhc right and
ll2
lcli
subjccts has carricd out thc Annctt pcgboard
hand. Analvsis ol' variancc suggests that the
diffcrcnce in perfbrmance bctween thc hands is almost constanl across conditions. That implics both
that a DIFF mcasurc is an adcquatc dcscnprion ol'hand diflcrcnccs. rnd that diflcrcnccs bctwcen thc
hands arc unifactorial across conciitions. If'thc'lattcr is truc thcn it shouid bc possiblc to dcrivc a singlc
mcrsurc ol' Iatcralisation dcnvcci l'rom ail ot lr subicct's data.
,{ companson ol' DIFF trnd LI
sub.;cct
mcasurcs '"vas carricd out b)' caiculating clch indcx lor cach
lbr thc 20 dil'fcrcnt pcgboarci conditit'lns. Thc 20x20 corrciltion matrix was rhcn llctor analyscd
bv a principal lltctor analvsis. Figurc
ln clch ca.sc it is clcar that
l
-1
shows thc l'irst tcn cigcn valucs lbr thc DIFF and
mcasurcs.
scrce-siopc unaivsis suugcsl.s thc prcscncc ol'onlv a singlc main lactor,
;tccounting lor -11.6% ul'Lhc vanancc in DItrF scorcs and -12.3!i.ol thc vuriancc in
basrs
LI
tlut tltc scorcs wcrc thcrctbrc uniluctonli.
LI scorcs. On thc
a rciiabilitt,analvsis rvls carricd our on a singlc scalc
dcnvcd by summing all twcnty mcasurcs. On thc DIFF lncasurc rhc summcd scllc lud a mcan of
11.96
tSD I I.02), indic;rting an avemqc dil'fcrcncc bctwccn hantls on cach task ol'0.59U sccond.s: lor
thc LI mcasurc thc summcd scalc had a mcan ol'0.5t17.1(SD 0.-5-ll6). indicating an ilvcragc LI on cach
trtsk ol'0.019-l (SD 0.0271). Thc uvcrasc currclution hctwccn tusks rvas 0.2(t13lbr DIFF mcasurcs and
Task difficulty and hand diffcrences
LI measures. Cronbach's aipha lbr the total scale was 0.8791 for DIFF measures and
for LI measures. Thus across all statistics. tie LI mcasurcs account lbr a slightly higher
0.2785 for
0.8860
proponion of total variance, have slightly highcr intcr-itcm conclations, and rcsult in a slightly higher
rcliabiiity for thc dcnved scale. \cverthclcss these dilfercnccs arc a]most ccnainly not significant (and
neither is it clear how to tcst them for significrncc). What is clcar is that latcraiitv differcnces across
a range of task difficultics are unifactonai.
Distribution of scores. Figure 5a shows the distnbution olovcrall Iateraiit.v scorcs. crlculatcd from the
l0
r'ersions of thc pegboard, for incjividual subjccts. dividcd according to hand dominancc. It can bc
seen that the distribution is approximatelv normal. Although
it might secm Lhat thcrc arc a number of
outiiers. only 4 (3.67o) of the data points lie outsidc thc 2.5-97.5 pcrccntilcs (-4.78 to 7.76), about the
proponion that would be expectcd rvirh a normal distribution \5Vo). Thc
3.32: SD = 2.85) is not significantlv diffcrcnr liom that
LI in lcli-handcrs
(mean =
in right-handers (mean = 1.55: SD = 2.52; t
= -i.-<J. 110 di. NS).
Di.rcussion: ,Annett pegboard. The most striking rcsult lbund
in
thcse studics
is that, dcspite our
cxocctations. thc dilfcrcnccs bctrvccn hanos rcmains almost constant across conditions which vary
diiflcuitv. Ourmanipulations allmociitlcd dil'llculn,in thc cxpcctcd dircctions, and produccd rclativcly
llrgc r't'fccts tscc Fig:rcs 2 and -l). Thc
be a.scribcd to a lack
aoscncc ol-un cl'lcct upon hand dil'lcrcnccs cannot thcrcfbrc
oi scnsitivitv in thc dcsign. It might bc
argucd thrt some
oi our manipuiations,
in panicular that ol'thc distancc bcrrvccn thc rows. u'ould not bc cxpccrcd to modilv rhc llnal transport
corrccdvc movcmcnts that Annctt et
dl tlt)7t)) idcntillcd as thc ponion ol'thc rltsk most scnsitivc
iteno dill'crcnccs. Howcvcrsincc ht'lic'sizc rcmlilns er)nstant. incrclsing distancc sitould. by
rcqulrc a morc accuratc movcmcnt.
*hich shouid bc
to
Fitts'Law,
Icss clrsilv pcrt'ormcd w'ith thc non-tiominant
itand. thcrcbl'rc'sulting in morc corrc'ctivc mo\/cmcnts. In any casc. Lirltt argumcnI ccrtlinly cannol bc
lppiicd to thc oftcrmanipuiations. ail ot'which can hrc conslrucd as atttcting thc rinal panol-thc task.
\\'c lrc not thcrctbrc compciicd bv rhc
rrrgumcnr ol',A,nnct[ cr
rri
Lhat hand dit-lcrcnccs dcpend
pnnctoallv on lt nosicr output lrom tire'ncln-dclminlrnt hand. rcsuitinrt tn morc corrcclivc movcmcnts.
,'\dministration
ol'tic
t-L.*sDoard
tlsk ls
ticscnhrcd hcrc is siightlt,di['lcrcnr lrom that uscd by
.\nnctt. In particular subjccts wcrc .rc(rrcd ut a lahrlc on which thc pcgnolrd was pllccd ut thc subjcct's
ivrtist hcight. and thc sub_icct movcd thc pcgs l'rom lhc row closcsl to rhcm ro thL' row Jfurthe.st from
tlrcm. 'fitis dil'f'crs lrom thc prcvrous r,'ork ol ."\nnctt (1970) und Annctt t'r ul.(lt)7i). ivho had subjccts
r0
Task difllculty and hand diffcrences
stand in front of the pegboard and asked subjects to move pegs to thc holes closest to thcir bodies.
Moving pegs awav from the body rather fian towards it mav makc thc task somewhat more difficult
sincc the final adjusting (or conecting) movemcnls arc madc with thc arm cxtcnded which would
cnhance the need
for finer motor skill. in addition. thc targct holes tend to appear eilipticai. with
increasing eccentricity as distance liom the subjcct is incrcascd. Both facton arc Iikcly to increase
the task's difficuity. Nevertheiess the timcs oi our subjccts on pcgboard 2, in thc round-endcd, large-
hole conciition (Dominant hand mean = ti.03 sccs. Non-dominant mean = t1.57 scconds), which is
closest to Annett's standard pegboard. are broadly comparablc with thosc rcponed
by Annett et al
(1979\ (Dominant hand mean = 8.50 secs: non-dominant hand mcan =9.73 secs). so that any effccts
of task differences must bc smail.
The only substantial difference between our rcsults and that of Annctt et al conccms the effcct
of the peg and hole size. Annett er al (Annct et al. 1979) uscd a 0.95 cm diamctcr pcg which was
piaced in hoics 1.27,1.91 and
2.-<-1
cms in diamctcr and lound that the diffcrencc bctwccn hands
bccame greater as thc hole:peg ratro bccamc lcss. In our study thc holc ri'as 1.27 cms in diamcter and
the pegs were either 0.95
or
1.25 cms
in diamctcr and wc lbund no eflcct upon hand diffcrenccs.
However it should be noted that our task is rcally quitc diffcrcnt lrom that ol Annett et al. for whom
the vrnant conditions arc ail easier than thc standard task. In our studv wc spccilicallv wishcd to
producc variants ot thc pegboard
thlt wcrc morc diificult than thc standard pcgboard.
and
ourdifficult
conoition rs vcry much morc dilllcult than rhat ol'Annctt cr rrl. rcquinng an almost vc'nicai cntry to
cnsure corrcct docking of thc peg inro thc holc.
Thc linding that thcrc 0rc no dilf'crcnccs in ovcrall pcrlbrmancc bctwccn right and lclt handcrs
is inconsistcnt rvith thc prcvious tinding ot Kilshaw and Annctt (1483) and.A,nnctt and Manning
(
i989) that lclt handcrs show supcnor skill * hcn pcrlbrming thc pcgbolrd task {supposcdlv associatcd
with srcetcr intclligcncc among non-dcxtrlls). Thcir tindings urc tlkcn as cvidcncc crplaining thc
prcscn'ationol-non-dcxtralityinthcpopuiritionlsaballnccdpoli,morphism.
thc prcscnt analysis that
lcli
Tl:crcisnosupponliom
handcrs show supcriur pcrlbrmlncc whcn using thc' pcgboard task as a
rrcasurc ol'motor usvmmctrv. lrithouth thcrc is lr trcnd
lirr
lcl't-hanoL-rs to show'rr
sliulttly rcduccd
dil'l'crcnc:c bctwccn thc hands.
Tlkcn togcthcr thcsc rcsuits providc compclling cvidcncc
uhat
on thc pcgboard task thc
dil'lcrcncc bctwccn thc hands rcmains broldlv unchanscd rcsilrdlcss ol'incrcascs in trtsk dil-ficulty.
Tltc fttoict' dttd ilryd(n circlc-rnurkint tdsk.
II
Ta.sk
difficulry and hand diffcrcnces
Merhod.
Subjects: The subjects consisted
ol a subset of 56 oi thc same
subjccts who had carricd out the
cxpenment on the Annen pegboard dcscribcd previously. Half wcre maie, half lemale. and half were
left-handed and haif right-handed. with equal numbcrs in cach combination. Thc mean age
handers was 23..1 (SD 6.3) and
ol
oi right-
left-hancicrs was 26.3 (SD 6.9).
Apparatus. The Tapiey and Bryden circlc-marking task consists of a serics of *,enly spaced circles
in which the subject must use a pen to placc a mark. a dot. insidc cach circlc. Circics were placcd in
a similar lavout to that used bv Taplcy and Brvdcn (198-5). Circlcs wcrc 1.5 cms apan, and the
CIRCLES were cither of diameter 0.25 cms. 0.33 cms. 0.55 cms and 1.00 cms. llarks wcre madc
using a fclt-tipped pen of approximate diameter 0.2cms. Fitts' Law-tvpc indcx oldiificulties suggests
that based on thc size of pen and circles. thc rclativc difllcultics
olthc tasks wcrc -i.2. 3.3,2.2 and
1.3
respectiveiy.
Procedure. Each subjcct carricd out cach ot'thc lour task dit-t'icultics twicc with rhcir <lominant and
non-dominant hands. the tasks bcing in a randomiscd ordcr. Taplcy and Brydcn (l9tt-5) do not dcscribc
thc ordcr in which circlcs shouid bc markcd. lnd in this stud1, thcrcfbrc subjccts stancd with thc uppcr-
lcli circlc ano markcd in a lell-to-nght dircction. which is consistcnt with thc dircction ot-hand-wnting.
On each tnal sub_iccts wcrc
asi<ed
to mark ls many circlcs as pxrssibic in 20 scconos. Scoring was
in Tlplev and Brydcn. with marks onlv bcing considcrcd as valid
il
as
thc mark *as cntircly includcd
',vithin thc circic.
Rr'.slril.r.
Statistical analvsis was by mclns ol'a
rtnairsis ot'r'liriancc.
lxl\l\+
(DON'IHAND x SEX
r
HAND r CIRCLES) split plot
witit DO\IHAND;rnrt SEX hcing bctwccn subicct
mL.lrsurcs.
rvith thc two
rcplicatrons ol' cach condition bcin[ avcragco bcl'orc analvsis.
-ihc
bctwccn-subjcct lnaivsis siro"rcd no dill'crcnccs ils ir rcsuit ol'SEX iFrl.-52)=0.3-1, NS),
DO\IHAND (F(1.51)=0.ttl. \S). trr thcir inrcnrcrion tF(1.-5lr=0.,U. \S).
CIRCLES di{'f'crcd vcn'sisnilicanrlv rn dil'f iculry tF(3,156)=o93.25, p<<.(X)l). Thcrc was also
It highlv signiticant diffcrcncc r*utrvccn thc H,\NDs (F(1,-52)=318.tt7.6<.001). Thcrc was. howcvcr,
no intcraction bclwccn HAND and CIRCLE rF(1.].1-56)=0.93. NS). indic:uing rhlr thc diffcrcncc in
Itum0cr ot'circlcs markcd
hr thc dominunt
lrnd rron-tlomirurnt hands wu.s sirrriilr tbr all circlcs.
rl
Task difficulty and hand differences
irrespective of difficulty (figure 6). There was also a significant interaction of DOMHAND x HAND
(F(1,52)=5.20, p<.05), with left-handcrs showing a somcwhat smallcr diffcrence between dominant and
non-dominant hands than did right-handcn (sce figure 6). The only other significant effcct
ANOVA was
a smail interaction of
CIRCLES
x SEX (F(3,156)=3.49),
p<.05),
in
in
the
which
???????????????? ?????????????.
Facnr analysis and reliabiliry
analy"sis. Diffcrcnccs bctwccn the hands werc calculatcd both
as
difference scores (no-n7,) and as standardiscd latcrality indiccs as uscd by Tapley a:d Brydcn (
100.(no-n")l(no+nr)). Eight such indices were calculatcd, two lor each difficult1,, onc lrom the first
time rhat the dominant and non-dominant hand carricd out thc
ta.sk, and the
othcr irom the second timc
that they carried out the task. Factor analvsis of thc dilfcrcncc scorcs found cigen-valucs of 3.977,
.895,.760, .736,.586,.480, .328, and .294. From a scrce-slopc analysis
it is clcar that the data arc
unifactorial, with the first factor accounting ior 49.07o of thc variancc. Factor anaivsis oi thc laterality
indices found very similar eigen-valucs, wirh thc first factor accounting for 4t1.8% ol' t}tc variance.
Reliabiiity anaiysis of the eight oiffcrencc scores on thc basis that thcv lbrmcd a singlc scalc showcd
a mean correiation between items o[0.4]-+, and a Cronbach's alpha
oi0.8453. Rcliability analysis of
the eight lateraiity indices found a mcan inrcr-itcm corrclation of 0.112, and a Cronbach's alpha
0.8158.
It thus appcars that thc oiffcrcncc scorcs account lor
a siightlv highcr proponion
of
oi thc total
variancc. and show a slightiy hishcr alpha than do thc latcrality indiccs.
Distrtbution o.iscores. Figurc -ib shows thc distnbution ol'/?D-l,\. scorcs tbr right and left-handcrs,
avcraged across thc cight tasks. Thc distnbution ol' scorcs
is approximatclv normal rvith
somc
suggcsrion o[ a singlc outlying nsht-handcd subjc'ct who pcrlorms substantiallr bcttcr rvith thc nondomrnant.
icli. hand. All othcr
non-dominant hand.
suLr_iccts
shorv rr grcatcr numbcr
ol'trps with thcir iominant thnn thcir
It is ot' intcrcst that T.roicv lnd Brydcn notcd that a smail numbcr ol'subjccts
tl'l/15-i6: 0.-517) showcd supcrior pcrtbrmancc rvirh thcir non-dominant hand. Tire'mcut dilfcrcnce
bctwccn dominant and non-dominant hantis is signil'icuntly lrighcr in right-handcrs (mcan
=
12.04,
SD=,i.17) rhan in lcti-handcrs (mL'an = q..ii. SD = j.73) usins a r-rcsr (r = 2.1S.51 dl'. p<.05).
Dist'ttssion: Tapict'ontl Brvden t'trc'lc-rrutrkur(
riz.iA.
TIrc ovcruil pilttcm ol rcsults orr tltc tlsk ot Tapley
and Brvdcn 1lt)ll-5) is similar to that rcponcd clscrvlrcrc. rvith
domrnanr and non-dominant hlnds. and lirrlc cvidcncc
non-dominanr hand. cxccpt in
tcrms
ol'a
I
ol
clclr di.scrinrinltion bctwccn thc
irrdividuals who pcrl'onn bcttcr with thcir
singlc clsc. .\llhough Taplcy and Brydcn rcponcd thcir rcsulLs in
standardiscd latcralitv coclllcicnt
riil-lcrcncc scorc t'lctr,,'ccn thc circlcs mlrkcd
it is lpparcn[ llom our lactor lmlll'scs that a simplc
*irlr
thc dominunt und non-tlominant !rrrnd is cqullll'good
l-1
Task difflculty and hand diffcrences
at expiaining the total variance in the data. and indced a scalc'calculated kom such diffcrences has
a slightly (although probably non-significant) highcr valuc of Cronbach's alpha than does a scalc
composed of iatcrality indices.
Of some interest in these resuits is that as thc task incrcases in difficulty so thc total number
of circies markcd
expressed as
decrcases substantially, but
thc diffcrcncc in pcrtormancc of the rwo
hands,
fte number of circies. remains constant. That rcsult was uncxpectcd.
Comparing our results with those ol Taplcl, and Bn,dcn.
index llcft-handcrs: mean
= 11.56. SD=5.0:
right-handcrs: mcan
it is clcar [hat thc overal] Iatcrality
=
l-5.93, SD=7.5) is similar to that
reponed for their data. It is not possible to comparc thc absolutc numbcrs
ol
marks madc since that
is not reported by Tapley and Bryden.
The Bisltop ,rquarc-tracing task.
Metlnd.
Subjects: Thc 56 subjccts werc thc samc 0s thosc who crrricd out the Taplcl,
lnd Brydcn circlc-
markinc task rcponcd prcviouslv.
.4pporarus:Scvcn oiffcrcnt squarcs w'crc uscd. cach with an avcragc sidc lcngth ol'-5 cms. Thc distance
bctween the inncrand outersquarc was vancd to altcrthc dit'ficulty, thc distanccs bcing ???, ???, ????,
'l'l'l?. l'l?,'l'l'l and'l'l'l cms. thcse valucs bcing choscn so lhat thcv rrcrc approrimrtclv cquidistant
along a scalc oi dilficulty, usinc thc thcorctical modcl ol'Vlct,cr
thc rnncr and outcr iargc squarcs thcrc rvas ;r small squarc.
e
t
al t19ltl). At
l'l'l x l'l'l
rvas rcquircd to pass. Each task was prescntcd individuallv on tr shcct
L'ilch comcr. bctwccn
mms, Lhrough which thc track
ol'A4 parrr.
Proc'edure. Each sub-icct camcd out cach ot'thc squlrcs t*,icc usine thc dominlnr md non-dominant
hand in a randomiscd ordcr. Timc rvas mcasurcd using
I hlnd-hcld
cicctronic stoprvatch.
*'ils bv mc:rns ol' u lrlxlx-{ tDOIvIHAND r SEX r Il,{ND x
DIFFICULT\') split plot analvsis ol r,lnlncc. rritlr DOi\I1"1,{ND lnd SEX lrcing bctrvccn subjcct
Rc'.srrir.r.
Statistical lnalysis
mci.lsurcs, and tlrc tvvo rcplications ol'cuch condition bcing uvcragcd
bclilrc lnaivsis.
Thc r^srwccn-subjccts analvsis shou,ctl no sirrnilicant cll'ccts ol'cithcr SEX tF(1..52)=1.63, NS),
DO\lHAND
(
Ir( I ..51)=0.40. NS)
or thcir inrcnrction rfr( I ..51)=0.05. NS). Thc wirlrin-sutrjccLs analysis
tl
Task difficulty and hand diffcrences
showed a highiy significant effect of HAND (F(1,52)=136.53, p<<.001), aurd a highly significant effect
of DIFFICULTY (F(6,312)=130.43, p<<.001). Thcre was aiso a significant intcraction of HAND
x
DIFFICULTY G(6.312)=3.01, p<.01) (sce Figurc 7), all ot'which was accountcd for by the lincar
of
with no significant non-linear term
(F(5,312)4.78. NS). The only other significant cflcct was thc HAND x DOMHAND interaction
component
DIFFICLTI-TY tF(1,312)=1.1.23, p<.001),
(F(1,52)=10.03. p<.05) (see Figure 7).
Factor analvsis and reliabiliry analysis. Diflcrcncc scorcs (tti-til and latcrality
indiccs
(100.(tr-tr1l(t*+ro)) rvere caiculated for crch ol thc scvcn diiliculty conditions. Factor analysis of the
difference scores lbund cigen values o12.0955, 1.213, 1.099,.912..636,..5-13 and.498. Scrcc-slopc
anaiysis suggested that the data were unifactorial, with thc fi rst lactor accounting lor 29.97o of the total
variance. Analysis of lateraiity indices gave almost idcntical rcsults, thc first cigcn-valuc bcing 2.097,
accounting lbr 30.07o of the total variance. Rcliability analysis of a singlc scalc bascd on the seven
difference scores showed amean correlation bctween pain olscorcs o10.162, and a Cronbach's alpha
of
0.5829; anaivsis
of laterality indiccs showcd cocl-ficicnts
ol- 0.15.1 and 0.5813 rcspcctivcly,
suggesting a minimai superiority in scalc rcliability lbr thc dil'lcrencc scorcs.
Di.strtbution ry scores. Figure 5c shows thc distribution ol'scorcs lbr individual subjccts bascd on the
mean dilfcrcnce score across
diffcrcncc scorcs
t.-ri
ali
scr.,cn conoitions. T.,vo lcli-handcrs^ and
onc lcli-handcrs showed
lcss than zcro. suggcsting that thc),wcrc pcribrming bcttcr r,vith Lhcir non-
dominant hand. Lcit-handers showcd a smallcr dif'lcrcncc (mcan = 0.ll116 scconcis: SD
0.-5-52) than
did
right-handen (mcirn = 1.33[i scconds: SD 0.S]7). ivhich is srarisricalll,signil'icanr (r=2.-11.57. p<.05).
Di.st'its.rion: Bi,slutlt .tituare-rracinq m.sk. Takcn ovcrril thc rcsuils ol thc Bishop squtrc-tracing task arc
simiiar to thosc or'thc Annctt pcgboard and tlrc Taplcl' und Brvdcn circlc-marking t:rsk in that. rt lcast
{br iclt-handcru. thc diffcrcncc in timc lbr thc dominant and non-dominant h:.rnds shows almost no
rciationship to
ovcrlil task diflicuitv. For nght-handcn dil-['crcncc bctwccn hlnci.s docs incrcrse
as
difllcuitv incrcascs.llthough thc cl'fcc[ is small rclativc to thc t()ul incrcasc in task.iil-liculty. Thc task
lulso shows a simrlrtrphcnomcnon to thc pcgnolrrd lmti circlc-rnlrrking ta.sks irr tlurt tuctorltnalvsis and
rcliabiiitv analvsis shows no basis lbr bclicvins that lutcrllitv inriiccs llrc supcnor ro srrnplc dil'lcrcncc
SCOTCS.
lnter-reldtton.sltip.s berween rc.rt.r. Pclrson corrclations wcrc cltlculatcd bctwccn
fic
dil-fcrcncc scorcs
Ibr Lnc dominant irnd non-dominlnt hands ol'thc thrcc rasks (in clch casc ad.iusring signs so
positrvc numbcrs mcrnt thal thc dominant hend was JL-rlbrminq bcttcr).
1<
thaL
Task dilllculty and hand diffcrcnces
The overall coneiation between subjects on the Annctt pcgboard and the Taplcy and Bryden
circle-marking task was 0.1265, which is not significantly diffcrcnt from zero. That this low conelation
does not merely resuit from attenuation due to low rcliabilitl,
of thc
measurcs is clcar from thcir
It must thcrctbre bc conciudcd that the two
Cronbach's alphas. were 0.879 and 0.845 rcspcctivcly.
measures are assessing separate functions which arc dissociablc across subjccts. Figure 8 shows a
scatterplot of the resuits and shows a scconci intcrcsting phcnomenon. Thc corrciation within righthanders is eifectively zero and non-significanr
(r=-.l18ti)
a rcsuit which rcmains unchurged whcn the
two ouriiers are removed ft=-.M2D. However within lcft-handcrs thc corrclation is substantially highcr
(e0.5806),
a vaiue',vhich is
significantly diffcrcnt from zcro tp<.01) and is significantly diffcrent from
that ior n-sht-handers tp<.01). Of panicular inrcrcst is that a simiiar pattcm oI rcsuits has bccn found
by Bryden er al (personal communication. Julv 1993).
Thc overali correlation between diffcrencc scorcs on thc pcgboard and squarc-tracing tasks is
0.O18 (NS), rvith similar values
for right-handcn 1r=.1175) and lcft-handcrs (e-.0724). Thc overall
correlation berween difference scorcs on thc circlc-marking task and squarc-tracing tasks is 0.356
(p=.007), wirh non-significanrly diffcrcnt vaiucs lbr right-handcrs tr=0.386, p<.1)5) and lclt-handcrs
tr=.0870. NS).
It must bc emphasiscd that in pan trc low corrclations rcponcd abovc rcllcct our analysis of
degree
oi hurocdness. rcllcctcd in usrng scorcs
l-rom ciominant and non-dominant hands.
raticr than
lrom nght and lclt hurds. In contrast. directiott ol'hundcdncss is vcn'consistcrtt ]cross tasks (as can
bc secn in ligurc 8. in which most of thosc right-handcd on thc Tuplcl,and Brydcn tmk arc also righthandcd on rhc Annctt task). Indccd
r.r'hich hand r,crtbrms
if'on clch task wc
cir.rssil'r,
right and lcli-hundcrs according to
bcttcrthcn thc phi cocttlcicnts bct*'ccn dircctions ol'handcdncss arc.96{ lorthc
.{nnctr rno Bishop n.sk.s. .713 lbr thc .A,nncrt lnti Taplu'und Brydcn tasks, and .070 lbr thc .{nnctt
tund Bishop rasks.
rrirh onlv l/-56. 3/-56 and l)i56 suhrjccts hcinr: discordant across tlsks. Likcwisc thc
phi cocl'iicicnls ol'*'nting hand r.vith thc
ta.sks
arc .9(r4 lirr thc Taplcv and Brvrjcn task.
.9211
for the
Bishop rask. and .133 tbr [he Anncu tusK. 1r'5(r. ]/-56 und l-5/l l2 subjccts bcing discordant,
r"cspcctivcir'.
Lli.rt'trs.rirrn
'fhis .studv has lbund a numbcr ol'surpnsinu lnd complicltcd rcsults. *,itich raisc imponant
pracrical and thcorL'tical problcms lbr thc undcrstandins
pcrl'ormancc.
I(l
ol
hand dil'fcrcnccs in prcl'crcncc and
Task difficulty and hand differences
The calculation of lateraliry scores,
There is a modest iiterature on the pr"oblcm ol calculating lppropnate lateralitv indiccs for dichotic
listening and tachistopic iateralisation tasks, with vanous mcasurcs bcing proposed (Rcpp, 1977; Kuhn,
1973: Bryden
&
Sprott, 1981; Marshall. Caplan,
both in empiricai (Hellige, Zatkin,
& Holmcs. 1975), thcir limitations bcing asscssed
& Wong. 198i) and Lhcorcrical tcrms (Stonc, 1980: Levy,1977)
being ciiscussed, and several authors arguing strongiy that an adcquatc laterality measurc is not possiblc
without appropnate theoretical modei (Birkctt. 1977; Colboum, 1978; Richardson, 1976). However
there is almost no discussion of the similar problcm lor tcsts asscssins hand diffcrcnccs in motor skill.
That the probiem matters can bc demonstratcd by a bricf' comparison of thc prcscnt rcsults on thc
pegboard and the circie-marking task.
If
simplc dillcrcncc scorcs arc calculatcd on cither tcst then
there is I'lO RELATIONSHIP betvveen lateralin, and task difficuln': in contrast
il
a conventional
lateraiity score is calculated then for thc pcgboard lutcrolin' DECREASES cts ciifficulry increases
tt
whereas for the circle-marking task lateralin'INCREA.IES
clfficultt' increa.re,r. Which sct of rcsults
we choose depends cntircly on our mcasurc ol latcralisation: iurd on that dcpends our thcorctical
interpretation of the rclationship bctween task difficulty and larcralisation. Similar problcms have also
been describcd cariicr in this papcr lor thc rciationship bctrvccn agc and dcgrcc of latcralisation.
Thc Lhcorcrrcel problcms ol companng latcraiity cocl'llcicnts can also bc scen by cxamining
the most common lureralitv indcx in its appiication to both thc pcgboard and thc circlc-marking task,
when
it
prociuccs scorcs
oi (tr-to1l(t,+rr)
and (nD-n\)i(nD+ir..l rcspcctivcly. Although supcrlicially
simiiar. lhcsc scorcs dilfcr in onc vcrv imponant w'av. In lirc llrst casc. bcttcr pcrtbrmancc produccs
lower t scorcs (lcss time takcn). whcrcas in thc sccond casc bcttcr pcrlbrrnancc produccs ltiqher n
scorcs (morc circlcs mlrkcd).
t7n-tt\.t
If trvo subjccts
huvc idcnticul tlillcrcnccs bc'lwccn hlnds (i.c. Ir-r,, and
but t}tcv dil-l-'r in ovcrall pcrlbrmancc. thcn rhc sutrjcct rvlro is
marks morc circlcs on thc' circlc-marking tusk r,.rll bc sccmingll,
on
Lhc
h
Lhc
llstcron thc ncgboard
and also
rnrtrc latcraiiscd ol'thc subjccts
ocgbolrd tr-sk and vet wiil lhc /c.r'.r'li.ltcr:.]iiscd subjcct on thc circlc-markins task: which is
surcil' not a scnsiblc outcomc.
Thc problcm oi'cllculaiing llrtcralitv scorcs is
tllrl
thcv ull havc un ilnpiicit thcorcticai
undcminnins rrhich is rarclv cxplicitlv statcd lrnd its blsis usscsscd. As a staning point lct us rcconsrdcr thc justi lrcltion givcn bv Taplcy und Brvdcn
lR-L)lR+L): 'lt
wlrs choscn. in part, bccausc
ot'l
lilr
calcuil.rting a lal.cralil.r'iniicx
ol'thc lbrm
l'cciing tlrlt thc diffcrcncc bctwccn I(D and 98
circlcsllllcdrcrrrcsr'ntcdpcrlbrmanccsimilartothatsccnirrapcrlbrmanccol'2(X)and
l96,rathcrLhan
l(X) and l9ti" tp.2ltr). Fintlv it is quitc cicur rhut tlrcrc urc situurions in which this rrrgume'nt is corrccl..
ll
Task dilficulty and hand differcnces
If in a time, r, a subject marks
100 and 98 circies with thc right and lc{t hands, and in a timc 2t they
complete 200 and 196 circles then the rate ol circlc-filling pcr sccond is constant in each case. The
assumption is that the rate is constant over a reasonable timc-range, and thcrcfore standardising for
totai time is a scnsrbie strategy. The proceciurc is probablv icgitimatc in ury situation in which
a
subject carries out tasks forvarving timc intervals, and wc rvish to know how rates of bchaviourvary
between subjects.
A probiem anses however when *re scorcs rcl'cr to tiiJferent subjccrs who produce fie scores
i00/98 and 200/196 The implicit assumption ola latcrality indcx of thc form (R-L)/(R+L) is that tltc
subjects diJfer onlt, in their clock speed.
It is
as
il
thc tlrst subjcct wcrc simply running more slowly
than the second. and the subjects could bc made cquivalcnt by spccding up thc first subject: that is,
by taking their data and slretching the timc-scalc. thc abscissa. But that is probably not a scnsible
assumpdon.
If two subjects diffcr in thcir ovcrall
rcspon.sc ratc
it is almost ccrtainlv nar (unlikc with
two computers) because the brain of one subjcct has a slorvcr 'clock speed' l.han thc othcr. Ncural
transmission
in both subjects will probablv occur at almost idcntical ratcs. And to take a panicular
example peninent to laterality,
was a consequencc of
rve *'ouid probablv
if it werc [rc cesc that poorcr pcrlormancc by thc non-dominant
fie cxtra time rcquircd to transmit inlonnation
na
hand
across thc corpus callosum. then
expcct cailosal trunsmission timc to bc doublcd in thc slowcr subjcct.
Diffcrenccs bctrvccn subjccts in such a casc ',rouid morc iikclv bc a constant timc incrcmcnt tbrcach
action by the non-drrminant hand. An cxacdl simiier i.rrgumcnl cen bc appiicd to dil'lcrcnccs ixtwecn
tasks within sublcct-s.
Thc initial conclusion must thcrclbrc nc lhal thc culculrtion ol'a latcralitv mcasurc olanv sort
-lhcrc
is not;.r thcorr-l'rcc.rction. *'hosc rcsuil. is rclrlilr ilrtcrprctuDlc.
is a strong irnplicit thcorv,
thcon,which makcs scvcral assumDtions. nor
lil
a
ot'r,'hich lrc ohrviousll' ju.stiliabic. urd thc sclcction
ol'diflcrcnt lrtcralin mcasurcs can rcsult in cntircir,oppositc conclusions whcn compansons arc madc
bctrvcen diilcrcnt groups ol'subJccts. or bctuccn dil-ltrcnt tusks. Thc choicc ol'an appropnatc latcrality
measure is thcrclorc both a thcorcdcal issuc. srncc ir rctluircs lrrr cxpiicit modcl. and rn cmpirical issue,
sincc
it rcquircs
rr Lir'monstration
ilrat particuilr thcorcticll rnodcls urc supcriur to othcrs. Nc'ithcr ol
thosc nccds iras vct i',ccn udcqultciv mct lor mca.\urcs
carc musl bc
tlkcn
rrt studics rv'hich lrttcmpt to provitic ilcc()ur)ts
tasks in thc crtcnt ot thcir latcralisation.
,l{ ode lli n q
r
irc ttl'ec
rll ilrndcdrrcss.'fhc crlroilerv is tltat cxtrcmc
t.s
tt'
ttt.t
k dilf
ic
ultv.
IS
ol dil'lcrcnccs i^.^trvccn subtccls or
Task difficulty and hand differences
We wish to develop a model
tlat
can be applicd cithcr to tasks such as the Annett pegboard,
in which the time is measured for making a fjxcd numbcr ol'movemcnls, or thc Taplcy and Bryden
circic marking task in which is measured thc numbcr ol'movcmcnts madc in a fixcd amount of time.
The Bishop square-rracing task. which cannot readiiy bc sub-diviticd into discrctc componcnts, is less
readiiy modeilcd using this approach.
Consider an acrion whose difficulty ior thc dominant hand, measurcd as thc timc taken to carry
out the action. is Dr. Let the total task consist
IhC
total time to carry out the task,
r,
ol thc action bcing carricd out n, timcs. In that case
is:
n
Let the difficulty of rhe action for the non-dominant hand bc rcprcsentcd as a lincar function, bcing
the difficuity for the dominant hand multiplicd by rn. and with thc addition of a constant. Dy.
If
thc
non-ciominant action is carricd out n^- times. Lhcn thc total timc lbr thc non-dominant hand canf ing
out the task. r", is:
t"=r..i. (n, Do*P,,1
.\lodeilinq rhe pcqnctrtra: With thc pcgboaro
ta.sk thc
numbcrol'uctions carncd out with hc dominant
and non-dominant hands is the same, nD=n\:n. TIrc dil'f'crcncc scorc fbr thc
tlsk is rr-rrr, which.
dcnved lrom thc tundamcntal cquations sivcn abovc. is:
Thc rcsults ot'thc ercscnt studv suggcst thAt r.-t,, is indcpcndcnt ol' thc ovcrall dil'f icultv ol' thc task
,,vith thc dominant hrnd. D,r. Civcn thc :rhnvc cquation thlrt c::n onlv bc thc
clsc i!' m=1. in *hich
CASC:
i- -r
=n
f)
That is. on thc pcgt'oard trsk thc hanos dil'lcr bcclusc ol tlrc lddition ol a lixcd timc constant tor
carn'ing out clch rtction with thc non-dominant hand. Sincc lirr thc data rcponcd hcrc. rr-r, = 600
mscc.\.lnd r=it). rrc can cstimltc Dy=60
/n.rc.'.T.
l()
Task difficulty and hand differences
Modelling the circle-marking task. For the circlc-marking ta.sk. fie total timc for carrying out the task
with the dominant and non-dominant hands is the same, i.e. tu=1,-1. Using thc ba.sic cquations given
above, then the difference in perfbrmancc of the hands. np-t\t can bc modcllcd by thc equarion:
tJD
:,l(m-t)
JtN -
,Do+D,o)
Do. (n.Do*Dy)
For the pegboard it was conciuded that m=/.
If
that wcrc also lhe casc lor thc upping usk. rhen thc
above equation would reduce to:
L'uv
n-n
De, (Do+D*)
Since ilris equation contains components
ol tlrc ovcrall difliculty,
actions bctween the hands should be inversciv rclatcd to thc ovcrall
DD, thc diflcrcnce
in number of
diiliculty ol thc task. casicr
tasks
shou'ing a somewhat larger difference bctween hands than dil'ficult tasks. Considcr an easy task. lor
rvhich Dr=-it)Q rnsec.s (i.c. 50 marks in 20 scconds). and a dil'ficult task lor which
l0
marks in
l0
Df
1000 m.sec.s (i.c.
scconds), and usc thc cstimmc l'rom thc,A,nnctt pcgboard tha[ D\=o0 m.\cc.t. thcn. lor
i=r1,) .rcc.r. rr,.-irr is
;.rbour acceptablc
o.5l lbr thc casv tlsk ano l.l3 lor thc dil'llcuit
ta.sk.
Although thc cstimerc is just
in rhe casy condition. it is broth countcr-irrtuitivc and incompatibic witit thc prescnt
data that thc dillcrcnce bctwcen hands should bc ic.rs in thc
dilllcult condition. Thc ovcrallmodci must
thcrcrbrc bc rcgardcd as unacccptablc. sincc ttrcrc is no sct ()l'paramctcm which cln makc thc modcl
compatiblc
*ith
thc circlc marking data. It shouid bc cmphusiscd that that conclusion docs not dcpcnd
irt
1,,-n' is
"rnicit
rtoproximatciv constant ovcrLhc rantc D,, =:i)0 to l()00 tnlct.t cvcn il'rn is not ctiull to i ('sc'c tlgurc
on thc ltssumDtion rnadc prcvrousir that rn=i: iltcrc lrrc \nnplv no
()a). Thc
onir soiutions occur bv rrllowrns D. io bc ol
Ll'lc
ordcr ot
situnLior-is
--1(X) msccs.
I
rcsuit v'"'hich can bc
rcjcctcd sincc such lt larsc ncgativc valuc mlrkcs no thcorctic;ri scnsc at all.
A
ptrttr mttLtci.ll is clcar liom thc abovc
lnlrivscs thut lr simplc linclr modci. irr uhich non-tiominant
liand dil'{'icuitv is tr lincar lunction ot dominunt hanci dil'l-icuirr. elnnoI account tirr thc rllta ti'om thc
'fuplcv and Brvticn cxpcrimcnt. Lincar mortcls incvitablv prcdict Lhut thc dil-le'rcncc hct'*e'cn thc
dominant and non-dominant hands shouid bc'comc smalicr lrs
tusk.s bccomc
morc dil'llcult. rvhcreas thc
tlata sutgc.st thtl. ovcr thc nrngc uscd hcrc thcv rcmain consrlrnl (xnd intuitivciv u'c suspcct
tasks bccomc r'(,rl nruch morc
diificult - us in spccd-wntins - that thc- dif'{'crcncc wtll
:0
tiat
as
hc'comc grcatcr
Task difficulty and hand diffcrcnces
still). The implicadon is that the difficulty of tasks camcd out with the non-dominant hand should not
rise as a linear function of Do, but as a power function, bcing disproportionatcly difficult forthe nondomrnant hand as difficulty rises for the dominant hand. A straightforward powcr modcl is
a.s
follows:
t--an u5
uD-trD.
tr=Dn. (D*+)r. (1 *a ,Di)
Note that if p=Q then
em-1,
)
and thc modcl is cquivalcnt to that givcn carlicr. As a rcsult
a=-/ then the modei is equivaient to lhat dcscribcd prcviousiv lor the pcgboard
cannot also bc tltted. to a first approximation. to thc circlc marking data.
6d
data. This modcl
If a=1, p=2.5
then over the range Do=400 to 1000 msecs, nr-n, is alwal,s within lhc rangc 9.1
if p=0
to
and D*=0.06,
10.3, which is
compatible with the results obtaincd earlicr. The lunction also cxtrapolates wcll (scc figurc 9b); cven
whcn
D, is as long
as
five seconds, so tiat thc dominant hand is only carrying out thc task four timcs
within the 20 second period (e.g. as in writing an cxtrcmcly dif'ficult phrasc), thc lunction prcdicts that
the non-dominant
wiil not
be carrying out the task at all
- rvhich is surcly a scnsible result. since it
is clear that as tasks such as hand-writing bccomc vcry diificult thcn cvcntually thc non-dominant hand
lails to canJ, out those tasks at all.
Thc lbove modcls suggest that thc dlta on thc Tlplcv rrnd Brydcn task arc incomoatiblc with
env simplc iincar moocl. md *rat instcad
it is nc'ccssan' to invokc a powcr lunction whcrcbv
as thc
dominant hand cames out difficult tasks so thc non-dominant hand bccomcs rapidly much worsc at
those samc tasks. Such a situation is comprchcnsiblc in computational tcrms: manv problcm-soiving
algonthms scaic
ls
NP
-
sce Pcnrosc (1990), pp.1tt1-187)
-
whcrctly difllcuitv uccclcratcs as
polvnomial l-unction ot'task complcxitv. [n thc clrsc ol'hund tlil'l'crcnccs, this mlv
diffcrcnt ncuro-computational archil.ccturc in thc
t*o
hc-mispircrcs. pcrhaps
Lrc
l
a
lunction of
mcrcir duc to a smallcr
distnbutcd network.
A
soiul.ion ro thc problcm
ol'a corrcct latcr:riitv indcx should by now Lr' :rpparent. Civcn
a
prnicular tvpc ot'tlsk. bc it pcg-board or dot-marking. thcn rrn lppropriatc Iatcralitv coct'llcicnt is onc
which rcmains consrant ucross il ransc ol task dil'ficultics. In tlrc casc ol thc Annctt pcgboard that
-sccms to bc rr-r,,. .ind l'or thc Taplcv and
Bn'dcn circic-mulking tlt.sk it sccms tt) I'c n,,-rt.,.. OIcourse
such alustilication rs mcrcil,cmpirical at this stagc. It is ho*'cvcr il prccursor to thc complctc proccss
ol'litring a lbrmal rtrcorcticui modcl to account lor dit'lcrcnccs r^stlccn hands anti task.s. Whcn
i.s done
licn
it.shouid bc upparcnt that thc appropnltc ltrtcnrlit_r'indcx lbr
11
,t
r
that
punicuiar task is onc ol'
Task difllculty and hand diffcrcnces
the parameters in a model such as the power modcl shown earlicr. Only with such a theoretical
underpinning can be we truly certain that our latcrality mcasures are strictly appropriatc.
The inter-relationship berween rcs&s.
A surprising finding in thc prcscnt studf is that thcrc is a
surprisingly low correlation between latcralisation on thc threc dilfcrcnt tasks. That finding had
previousiy been anticipated by Tapley urci Brydcn tl9tt5), who argucd, on the basis
ol the
distributional differences bctween their tcst and thc pcgboard task that "it sccms [...] reasonabie to
conclude that different tests of hand performance measurc somewhat diffcrcnt factors" (p.219). md
they note the impiications for such a conclusion lor Anncrt's right-shil't theory of handcdness. More
rccently Brycien and Singh (1993) have reponcd a corrclation rvithin handcdncss groups of onlv.188
between pegboard and circie-marking pcrtbrmance. although only one lcvcl of
If,
as Annetr has argued. thcrc is a singlc cnriry
clllcd
dilficulty was uscd.
handcdncss. that that cntity
is
a
continuum, rathcr than simply being two discrctc classcs. and that variation along this continuum is
inheritcd, and is the primary source of othcr hand diil-crcnccs (including hand prcl-crcncc forwriting),
thcn
it is essenriai that strongil, right-handcd
individual.s on onc task should also be strongiy handed
on all other rasks. However the present data suggcst vcry strongly that aithough direcdon of
handcdness is strongly consen,cd across tasks.
r/c(rrs ol'hlrrrdcdncss is at bcst oniv r,vcakly corrclatcd
bctween subrccts.
That linding has major implications lor rhc imporrant ontogcnctic qucstion
ol
whcthcr
dillcrcnces in prciercncc cause diffcrcnccs in skill. or di{'l'crcnccs in skill causc diffcrcnces in
prct'crence (lvlorgan
& McN'lanus.
191t8: N{c\lanus et al.1t)t)2).
bcrwccn Anncu s gcnctic moitcl ol'handcdnc'ss (Annctt.
lnd is also imponant in distinruishing
I9t-i). rririch argucs thlt skill dillcrcnccs
cuusc prcf'crcncc.lrnd McManus'gcnctic mocici (Mcftlanus. l9S,5u:
argucs that prclcrcncc ciluscs skill dil'fcrcnccs (McNlunus.
\lc\'lanus & Brvdcn, l99l) *hich
l9()l). ll' tlsks do not conciltc in ficir
dcgrcc ol'latcraiisation hcn thc implication is that tirc proccss ot'lrcqursitir)n
dif'f'cr bctwccn thc rlsks. Howcvcr thc lact
thll dirccrion ol
ol
rsymmctrics musl
Iarcralisurion is highlv corrclatcd across
ttsks suggcsrs that thcrc is probablv a sinsie'undcrlving proccss. Ii is dil'tlcult to rcconciic such
eonclusions
uiti.l,nnctt's modcl. lbr rt.sccms to rcquirc lhtil thcrc arc at lc;.ist thrcc
sc'oaratcly
inhcritcd nghr shitts. onc lbr cach task, thcrcbl,producinu Iittlc corrclation t-rctrvccn tasks in ticir
dcgrcc ot'lrtcrliisation: but
it
is thcn almost irnpossitrlc lo crpiain how dircction ol'Iatcraiisation is
highly corrcletcd across tasks. ,\ morc parsimonious conclusitlrr is thut. probabll' lbr gcnctic rc&sons,
individuals havc wnal'faplcv imd Brydcn cuilcd "u dircct nrccllurism
tp.2l0). and Lhlt such prctcrcncc thcn manrtcsrs on lrll skiilcd
lilr gcncratirtg lcl't-handcdncss"
Lusks thut
thcy sui'rscqucntlv lcam. so
Task diiliculty and hand differences
that direction of lateralisation between tasks is highly corrclatcdt howcver since tasks necessarily differ
in the details of their movements. and since it is clcar that all voluntary movements contain strategic
dccisions which differ berween subjects and task vanants (Cottlicb, Corcos,
&
Agarwal. 1989:
Mcuienbroek et aI,1993), as weil as biomcchanicai lactors that can diifcr bctwccn hands and subjects
(Meuienbroek & Thomassen. i993; Mculcnbrock & Van Calcn, 1989), it is not surpnsing that dcgrce
of handedness does not correlate across tasks lor, to put it irnothcr wav. that the paramcters of a power
model of the sort described eariier can dilfcr radically bctwccn tasks). Thcsc results therefore support
a model of handedness in which prefcrence is prior to skill, probabiy bccause it. is inheritcd. and
manifests ar a rciatively earlv age, with skill diffcrcnccs onlv manifcsting later.
Acknowledgments
We thank Phil Bryden and Gina Grimshaw lor thcir hclpl'ul discussion ol'lhc issues raiscd in this
study.
,.)
Task dilficulty and hand differences
References
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9, 150-157
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Lcvv, J. (1977\. Thc conciltion ol'thc Phi l'unction ol'thc dillcrcncc scorc with pcrlbrm:mcc and its
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t-5
Task dif{lculty anci hand differences
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a
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Task dilllculty and hand differenccs
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\'1.P. rl9ll-5). ,,\ group tcst
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lbr thc lsscssnrcnr ol pcrlormuncc bctwccn
thc
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Van Hom. J.D. (l!192). Brain.ttructural ubnrtrmaiin,dtkl ituttttlity in.t'c'hi;ttphrenia. Univcrsity
Collegc London: Llnoublishcd PhD thcsis.
)'7
Task difficulty and hand diffcrences
Figure
l:
Schematic diagrams of the two pcgboards:
a). Pegboard I. showing top, side. and front vicws. Thc row l-urthcst lrom thc subjcct can bc adjustcd
along a dove-taii guide at distanccs of
5 to 64 ccntimctrcs lrom the row closest to
subjccts
(ROWDIST). The rows themselves can bc rotatcd 90o around thcir long axcs in ordcr to show prescnt
tour sets of target hoies rvith dilfercnt inter-holc distanccs (HOLEDIST).
b). Pegboard
II.
Thc lcncrs inciicatc thc various mcasurcmcnts tlut dctcrmincd as lar as possible from
other descriptions in the literature ot'thc pcgboard. Also prcscnrcd
lrc thc two dilfcrent pcg stylcs
uscd in cxpcriment II. having t*'o diffcrcnt diamctcrs and round and
lllt cnds. A = 38.5 cms. B =
l-1.0 cms. C = 5.08 cms. D = l.-i-l cms: E = 2.54 cms; F = l.-5-l cms: G = 20.32cms; H
= l0 holcs:
I=1.?7cms: J=l.llcms: K=-1.7-5cms:L=-5.0llcms: NI=r).9.5cms(small)orl.25cms(largc).
,n
I
I
I
A
'I'oU
Il,
1--
Il
tr*
ill
'|
t
-,t-.,
.,I
li'ro!rt
Side
Task dilficuity and hand differences
Ficure 2:
Pcgboard
hands.
I.
Pcrlbrmancc times
oi right- and lclt-handcrs using thcir dominant- and non-dominant
in rclation to at the distancc bctwccn rows of pcgs (RO\\'DIST) and b) thc distance bctween
holes within rows iHOLEDIST). Standard crror bars rcprcscnt lcrtormancc
t9
+I
SE.
[Jnlversal Pegboard
IJniversal Pegboard
13.0
1.1
I nrrzool.,r
n IrII/NONDOM
rr l.JIll)()N{
lil
ll
l2
l,!l/N()NlloM
nrvoonaI
RIr/NoNDoM
L2.6
I
Ii
I
t2.o
I
-l
I,I I/DO
M
LIIlNoNDoM
I
I
I
I r.5
ll
,a 1t.o
a
-10
a
o
()
a0)
0)
9e
10.6
0)
o
d
t{
E
.j.8
t-{
H
10.0
9.5
9.0
o
8.5
5
8.0
,L
20
.32
30.4
B
40.64
llow fJistances (c*)
1.6
2.26
3.O
IIoIe Dlstances (cm)
3.7 6
Task di[flculty and hand differences
Figure 3:
Pcgboard II. Pcrfbrmance of right- anci lcft-handcrs, using dontinant and non-dominant hands, for two
peg diameters and oegs with r"oundcd and squarc-cut (flat) cnd.s. Standard crror bars rcpresent
perlbrmance
+t
SE.
i0
Standard Pegboard
L2.0
I
r
E
N
11.5
11.0
RH/DOM
RH/NONDOM
LH/DOM
LHINONDOM
10.5
10.0
9.5
-a
9.0
3
a
\/
U.D
0)
E 8.0
F
7.5
7.0
I
I
6.5
I
6.0 _l
_l
tr
i
,-
U.t)
.
5.0
I
I
I
Smail/Rounci Smail/Flat Lar gelRounci Lar ge/Fl at
Peg Styi
e
Task difllculty and hand differences
Figure 4:
Shows rhe
llrst tcn eigen-vaiues lor the lactor analysis ol'dil'icrcncc bctwccn irands on thc twcnty
pegboard measurcs. using either a simplc dilfcrcncc scorc
latcrility indcx ( (t\-tD)l(t.+tD;: soiid
barst.
.11
( r.-r,r; .small
point.s)
or a conventional
Eigenvalues
Difference score
Laterality index
l
I
I
I
l
I
4l
I
l
I
Ji
I
L
i
I
I
I
I
2l
0
2
a
5
7
Factor number
Task dilficulty and hand diffcrences
Figure 5:
Distnbutions of combined differcncc scores lbr thc thrcc tasks, scparatcll, lor right- and lcft-handcn,
a) on rhc Annett pegboard. r"-ro: b) on thc
Tlplcy and Brydcn task circlc-marking tsk. nr-nr:
on rhc Bishop squarc-tracing tasK. /\-tD.
.12
and c)
Annett pegboard
Numbsr ol subl6cls
12i
--
-
l
'
Tapley and Bryden
task
.t
f'lufri,ui ol sublecls
o,
f
*1&
r'nr,.*,.
Bishop square-tracing task
I
nsnrr,",o.'__,1
.il
:\,L
I
_l
Task diitlculty and hand diffcrences
Figure 6:
Pcrformance on the Tapley urd Brvden task by right- and lcli-handcrs using thc dominant and non-
dominant hands. lbr fourdiffcrent degrecs ol'task dilficulty, cxprcsscci as a Fitts'Law tvpc indcx (sce
tcxt). Standard error bars reprcsent pcrtbrmancc
handedness and hand used.
-) -1
+I
SE. Rcgrcssion lincs arc tittcd scparatcly by
The
TaPleY
and BrYden Task
e RlVDom
7A
I
11 RH/NDom
o
o
65
LHlDom
LHlNDom
@
r{
;60
o
O
o
.oss
c\r
H50
?
tt{
'+{
945
r-
t{
,4t
=40
C')
o
O
.
FI
eE
Ut/
,-Ft
:30
Z
25
2A
1.0
1.5
2.A
2.5
lnciex of
3.0
D
3.5
iff ic u ltY
4,0
4,5
Ta.sk
difficulty and hand diffcrences
Figure 7:
The time taken on the Bishop square-tracing task, by right- antl lclt-handcrs using thc dominant and
non-dominant hands, for seven rjifferent dcgrees of ta.sk difli culr1,, cxprcsscd as a Fius' Law t-vpe indcx
(see text).Standard error bars represent pcrformancc
handedness and hand used.
-1+
t
1 SE. Rcgrcssion lincs arc titrcrl scparatcly by
The Square Tracigg Task:
Pen ind PaPer Version
9.0
9.5
I
RH/Dom
RH/NDom
LHIDom
LHINDom
i'J
I
_
i
I
8.0
U)
7.5
a
I 1.0
C)
o
a 6.5
l't
o
F
}.r
_
_
_
6.0
5.5
t
5.0
l.i
L
,1.5
\
\Y
+/
-/
/-
+.0
,/./
U.IJ
3.0
,/
t.
=
r'l
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4'0
S q uare Dif f icultY
Task difficulty and hand differences
Figure 8:
Scanergram
of reiationship between performance on thc Tapley and Brydcn task (abscissa) and
the
Annen pcgboard task (ordinate), separateiy lor right- and left-handcrs. Note: in ordcr that the
distnbutions of right- and left-handers are both clcarly visiblc we havc plottcd
than rr,-/, versus /rD-l,v.
l-5
t,.-rR
versus nR-nLruther
tL-tR (Annett pegboard)
2.
i
Left.handers
X
7t
Right-handers
l,/
rz /t\
-jt\1/
'1
-
)il
^
:Z
/\
Y
\
rlz
/i\
\,
'v'\
l
tl
.-J
-1
tl
l
-2
-20
-15
-10
10
nR-nL (Tapley and Bryden task)
Task dil'liculty and hand differences
Fiqtrre g. Shows the predictions of two modcls l'or nn,nn, and no-nriurhc Tapley and Brydcn task.
The heavy dark line indicates nr-n. when
it
i.s
in thc approximate rangc ol thc present study tor thc
Tapley and Bryden task, and the thin soiid linc shows its cxtrapolation ovcr thc ranse D,r=1 to 5
a). Predictions tbr a iinearmodci when
D,
secs.
is in thc rangc 0.4 to 5, D^ = 60 msccs, t=20, and m=l.3
(i.e. equivalent to a=0.3 and p--l in thc power modcl). This modcl was chosen so that D" was
compatible with the value estimated {iom thc Annctt pcgboard, and thc modcl llttcd with a differcnce
score
of 10 tbr Do=0.4.
b). Predictions lbr a power model when
l- _\
D,
is in thc rangc 0.4 to 5.
D, = 60 msccs. a=1. p=-i.-i.
and
t-
In cach casc thc values choscn are illustrativc ol't"hc potcntial ol thc modcls. rathcr rhan intcndcd to
be precisc cstimatcs lltted to thc panicular cmpirical valucs obtaincd
-r6
clrlicr
Linear model
nD, nN
Power model
nD-nN
50
nD, nN
50
nD-nN
50
40
40
30
30
50
\,
30
nD
nN
nDnN
20
20
10
.l
0.5 1 1.5 2 2.5 3 3.5 4 4.5
Difficulty of dominant hand (DD) - secs
5
0
-
20
\-----f
10
r
I
05
1
15
I
'
I
?
2,i
3
t-_
35
4
4.)
Dilticulty of dominant hand (DD) - secs