Impairment of grasping movements following a bilateral posterior parietal lesion

IMPAIRMENT OF GRASPING MOVEMENTS BILATERAL POSTERIOR PARIETAL JEASNEROD.J. DECETYand F.

M. Vision et hlotricit2.

TIII:

invotvcmcnt

targc number

U.9-l dc 1‘1,s S.E.R.kl.. Neurops)chol@e.

of posterior

tobutc product

;L reaching d&it.

their arm con~ratatcrat poslcrior

parktat

conliguration. objects. with

Monkeys

with such tcsions

Tactitc

cuts

In man. the classical

posterior

obscrvcd

pariutal

systematically movcmcn1s

arc impaired

trigger

with

following

whcrc

rcniain

Restoration

stwvcr

Second,

than

grasping

of visual

normal

[I-!.

vision

with Of

to object six

or

small

contact occurs

the object

p:lrictat shows

reaching arm

arc

is seized

This

made by and

often

In addition.

thcsc

is increased,

bccomcs particularly

10 and during

the rcxhin,

has been similarity

movcmcnts

inaccurate

ones; their JuraCon

phase is longer.

ol the hand prior

lesions

;I striking

lo the side of the Icsion).

feedback rcduccs

misroach

t 0, 211. Lesions

palmor

whcrc

posterior

of thcsc clkcts

attcrcd with rcspcct to normal

apparcnl

unlit

grasp

visually-dircctcd

~lnd their dccclcration

in Ihc condition

animals

by a

parktat

[3, 91.

contralcsional

(usually

de

in graspin, 0 and manipulating

an inadcctuatc

their peak vcloci~y is lower,, prcvcntcd.

The

fictd [Z, 2,

strctchcd

and the tinycrs

First, their

biased in one direction arc kincmaticalty

remain

R cccnt rcdcscriplion

in monkeys.

patients

[Xl.

of Lhc inkrior

to shape the hand according

optic ataxia syndrome

for ;I long time [4,2X].

with the deticils

then

by I’I:I;I.I;

lSmiw

is now attcstcd

tcsions

part of the visual

open and the fingers

surfacesof the hand

bchaviour

In monkeys.

mcn(ioncd

also ;~tTcct the ability

The hand remains

the object.

tirst

Lcpine. 6Y5OO Bran: and Lynn. France

in visuomok~r

sludics.

to the tcsion in cilhcr

;lrc;Is

bctwccn the palmar known

and clinical

A

MICHEL*

16. a\cnuc du Dqen Hopikd Ncuroloptquc,

paric~at cortex

ofcapcrimcnlat

FOLLOWING LESION

~7errors.

the movcmcnt

is

but the movcmcn~s

171.

and manipulation

movcmcn1s

arc also allcred.

PaticnLs

misplace

their

370

51. Jf-ASWWII. J. DECET~ and F.

MICH~L

fingers when they have to visually guide their hand to a slit [27.30]. During prehension of objects. they open their finger grip too wide with no or poor preshaping and close it when they are in contact with the object [l-l.

171. These patients. as observed by Perenin and

Viphetto and by Jeannerod. have usually

intact somutosensory

anaesthesia. no loss of position sense) and intact visuospatial localize objects visually).

control of their hand (no

functions (they can correctly

A classical interpretation of these lesionrtl effects holds that parietal areas have the primary function of coding spatial relationships between the body and external objects, and directing the arm at the object location. Accordingly, the grasping deficit observed following parietal lesion was often implicitly attributed to a secondary strategy for compensating the reaching deficit and increasing probability ofcontact of the hand with the object. This interpretation, however, was recently challenged by new findings in monkey, showing the existonce of a group of neurons in area 7a specifically related to the action of grasping visual objects [ZY] and distinct from those activated during reaching [?3]. This

finding suggests that reaching

and grasping are separate functional entities represented in different (albeit neighbouring) parictal areas [S] and that they should in principle be dissociable by selective &ions. papa, we report the case of one patient where this dissociation

CLINICAL The

patient (A.T.)

;I 35year-old

In this

occurred.

CASE

right-handed

woman, sustained

a bilateral

pnricto-

occipital infarct during cclampsia. During the early stage of the Icsion, she prcscntcd with ;I complex set ofsymptoms rcminisccnt ofa l~~~lint’ssyndromc: transient cortical blindness and pseudo-tubular

vision.

scverc visual

disorientation,

bilateral

optic

atnxin,

right

left

disoricntntion. Aprasia, aprnxic agraphia, ~lutotopo;l_cnosia wcrc also obscrvcd. Four years later, at the time of the currcnt examination. A.T. was normal regarding global attention, language, memory and clcmcntary motor and tnctilo-kincsthctic functions. f’osition SCIISC was normal: body schema was intact. Right left orientation was still mildly impaired. Static pcrimetry showed normal visual fields apart for ;L few dcgrccs scotoma in the right inferior

qu:idrant

frlccs had always

ncnr the fovea. Visual

been normal.

In

addition

recognition of shape, tcxturc, depth. color, A.T.

ncvcr complained

of any difliculty

concerning pcrccption of movcmcnt. Formal cvnluation of line length and size ofdrawn figures was poor. Tnchistoscopic testing proved ;I difliculty to see scvcral itcms at once. Reading was normal, cxccpt that A.T. would often loose the beginning of the next lint in ;I paragraph. Despite some recovery with the passing years and rehabilitation

programs.

A.T.

still

prcscntcd a severe disorientation. lndccd she was hampcrod in her cvcryday lift for actions like dressing. cooking. ironing, sewing or driving. Symbolic gcsturcs were correctly cxccutcd. Writing was still slow and clumsy, drawing was impossible, as well as playing cards or scrabble, nsscmbling puzzles. etc. MRI pcrformcd in 1092 showed extcnsivc bilatcrnl lesions involving arcas I8 (above the calcarinc upper lip), 19, 39 and 7. Areas 17, 40 and 5 were spared (Fig.

I).

HILATLR\L

POSTERIOR

P4ltIET4L

LESIOk

I

If

BILATEKAL

373

P”STEKIOK PAKIETAL LESION

During the experimental sessions the subjects sat in rront ofa large plastic box (68 cm high. IOOcm wide and 7Ocm dL*Ip) placed on a table top [l6]. The box was divided horizontally into two equal compartments separated by a semi-reflecting mirror. The subjects placed their forehead on the front panel at the level of the upper compartment and looked in the mirror. They placed their arm on the table top. in the lower compartment. Two diferent situations of visual control of arm movements could be created. In one condition. the subjects saw their arm in the lower compartment through the mirror. They could also see target objects placed on the table (visual-feedback situation. V). In the other condition. a mask was inserted below the mirror. and the subjects could no longer see the lower compartment. Instead. rhey saw the ceiling of the box. Target objects were displayed irom an aperture in the ceiling. the virtual image of which projected at the table lebel in the lower compartment. Another object identical to that displayed in the mirror was placed directly on the table in exact coincidence with the virtual image seen in the mirror. When subjects (without seeing their arm) reached toward the virtual object. they met the real one at the expected location (no visual-feedback situation. NV).

Grrrspin~qrhjrcts. Blocks of trials were run. involving reach and grasp movements with either arm. in both the visual feedback and the no-visual feedback situations. Each trial started with subjectsclosing their eyes and placing thclr hand on the table next to their body. with the ulnar edge in contact with the table and with the tips orthe thumb and index linger in contact with each other. A target object was placed on the table at 30 cm lrom the subject in a direction corresponding to the sagi~tal axis of the body. Depending on the situation (NV or V) an identical object was or was not displayed at the top ofihe box. A vocal signal indicated the start ofihe trial. The instructions were 10 open the eyes, reach for the object, grasp it between the thumb and index finger tips and lift it from Ihe table. Target objects were of IWO kinds. NPIIITCI/ objects were six plastic cylinders placed vertically. They had the same height (5 cm I but varied in diameter l’rom I .5to 7Scm. Ftrmilicrrohjecls weresix cylinder-shaped objects (a lipstick. a reel ol’ thread. dilTercnt types of glasses). with approximalely the same height as the neutral objects and with diamcbzrs wIthin the same range (I 5X.5 cm). Small objecls wcrc more rcprcsenled in the Familiar series than in the Neutral series. which was justilied hy the Iact that the patient had more dillicultics in grasping smaller objects. Neutral and Familiar ohjccts were prcscntcd in dill’ercnt sessions. In each given session. each object was prcscntcd five Linics in a randomized sequences. ~\/rt/~/tr~/,si:c* o/‘rirrurr/ IJ/,~WI.S.This lest was run in the patient and the control subject. The NV condition was used. The virtual ‘images of the Nculral ohjccts were prcscnrcd in randomized scqucncc from the lop of the upper compar(mcnI. The paticnl placed her (invisihlc) right hand in the lower compartment at the level where the object images projcclcd. On each trial. she was inslruclctl IO match with her thumb and index linger Ihe size of Ihe object prcscn(cd. Thirty trials were run (six ohjccts. live prcscnlalions). /~~tr)/i~~irr~/ ol,jc*c.rsize,. This tcsl W;IS run in lhc patient only. Aricr inspecting the Familiar ohjcc(s li)r several minulcs. A.T. was inslructcd. with her cycs closed throughout Ihc s&on. to place her right hand in the lower comparlmcn(. The cxpcrimcnhzr named the ohjc~ls in ;I randomircd scquencc. For each name ofobjecL the patient had to open her linger grip al the corresponding imagined sire. as ifshc had to grasp the object. The six ohjccls were named live limes (30 trials).

A video camera was placed XI the level of Ihe lower compartment. The optical axis of the camera was made to roughly coincide with the dire&m orthe moving arm. so Ihat a rronlal view of both the approaching hand and the target object could bc rocordcd. Subjsc~s lingcrtips were marked with hlach dots. The distance bctwecn the thumb and the index linger was measured directly on lhc screen ol the monitor by playing hack the videotape Iramr-byframe. For Ihr Grasping lest. rhc measure of interlinger distance corresponding IO Ihe maximum grip aperture b&rc lhc grasp was rctaincd. For the other two tcs(s (Matching and Imagining size). the in(crlingcr distance at the end of linger opening was rctaincd.

RESULTS

GL,rlrrn/t/cscriprio,l ~1 striking

dissociation.

oj’llw

I~I~I~~I~JIII~.

Patient’s

movements

during

the grasping

task

olTered

In all cilscs the reach was correctly oriented: while the hand approached the object. the wrist was dorsillexed and the middle of the first interosscous space was aligned with the object’s vertical axis. No locillkltion errors were observed throughout the session. ncithcr in V nor in NV conditions. Reaching wils formally tested only for objects placed in the sagittal plane. Casual observation, however, showed that the patient was not impaired in reaching targets at other locations.

By contrast. the trial

the grasp was incorrect.

kvith the object in contact.

more proximal resulted

phalanges

in a\vkward

specially

not with

or even with

and inaccurate

the object. On n few occasions.

the palmar

grasps

analysis

fingers

in contact with

delayed and the reach tended to overshoot ivith

Grip

the right

size I~It’tl.sIITt’IIIt’II~.~. In A.T..

conditions.

In A.T..

by vision

were r=O.35 r=0.83

3 compares

in NV.

in V and r=0.63

in NV.

in V: r=0.31

The poor correlation

incrcasc 0.36

lhc

control

This

objects

corrclatcd

bcttcr

cocllicicnts

kvcrc ~=0.77

small

objscts.

behaviour

for right

the \vas

\vas more

and left hands

hand was studied

in both V and

hand in the two subjects.

Correlation

cocllicients

values

in the control

pcrformcd

\vas not

for the right

hand

subject

bcttcr than with

grip size and object size in A.T.

cxaggcratcd

for the smaller

with

in A.T.

the patient’s

used

object

were

her right

thrl

subject.

due to

3. upper).

in grip apcrturc

than in the control

This

for

As ;I I cm

value w;ls

and 0.41 cm in the NV condition.

right

hand only.

k‘igurc

wlwn

was incrcascd

A.T.‘s

4 shows

Neutral

in V and I’ =0.5 I in NV.

the rate of apcrlurc

\vas mostly (Fig.

In the

cm in NV.

as targets.

skc

objects

as the nican incrcao

cm in V and 0.70

wcrc

with

bring

with object size. and this correlation

hand in the V condition

it was 0.95

Familiar

2 ). This

of the right

her left hand A.T.

was much smaller

task ~vas pcrformcd

when

aperture

normally

in NV). was grossly

right

subject,

With

around

condition.

only the right

corresponding

rtrfc o/‘c~pertm~ (nicnsurctl

in ohjcct siLc)

WI for A.T.‘s

The

(Fig.

grip size was measured

poorly

of

behaviour

finger closed

which should

in the NV

the grasp.

between maximum

the f:lct that grip apcrturc conscqucncc.

and index

surface

This

as the object was pushed down by

target position

performances

grip size corrolnted

in V: r=0.28

hand (r=O.%

of the hand itself.

the thumb

patient ended

the object at the time when the reach stops.

subject,

of the hand during

The

the palmar

of the grasp revealed an exaggerated

maximum

In the normal

Figure

maximum

improved

surface

hand and was aggravated

in V and NV conditions. NV

with

objects.

but with

such that the end of the tinger enclosure,

tips of the opposing marked

the smaller

the grasp was not possible.

the palm of the hand. Frame-by-frame of the finger grip,

with

the tingcrtips,

objects

grasping that wcrc

As the grip apcrturc up to normal

v;tIucs

was improved

ni;tsiniuni

grip

\v;ts clearly (0.M

sk

usccf. Correlation smaller

for

cm in V and 0.70

cm in NV).

This A.T.‘s

task \v;~s performed performance

5a and b). In b<)th subjects 1.=0.60;

in control

cm in the control

This strongly

This

task

was

corrclatcd

clinical

impairment

with six Neutral

with her right

the intcrfingcr

subject,

objects rangin, 0 in ske from 0.5 cm up to 5.5 cm.

hand was closely

r = I ). The

similar

dist:lncc

to that of the control

incrcascd

rate of apcrturc

linearly

subject

Lvith object hia

was 0.86 cm in A.T.

(f-ig.

(in A.T.,

compared

to

I .OS

subject.

pcrformcd with

case revcnls

in grasping.

with

object sia

:I pure

without

the

Famili;Ir

(r =0.79)

bil;ltcral

reaching &licit.

objects. (Fig.

In

5c). The

(although follo\ring

i\.T.,

the intcrfingcr

rate of apcrturc

predominating ;I posterior

ciist;lncc

\v;~s I .O:! cm.

on the right parictal

Icsion.

side) This

is

HIL.\TtK

\L

PO\II

KIOK

P \KIt

T.\L

LLSIl)\

A.T. (right hand)

l

V

0

NV

Cont. (tight hand)

10’

.

v

CI NV

t~nt~st~al, x

C;ISCS previously

rcportcd

with

Icsions

in this ;lrc;~ had combined

reaching

:tntl

(c.c. In fact, A.T. initially prcscntcd the two z(*rapine c impairments c Rcfs [ I71 and [27]). clclicits. \vith the typical clinical picture of the optic ;ltaxi;t syndrome. The rcxhing &licit rccoccrcd simple

and

the

co~~scq~~c~~c

graspin, (1 clclicit of inaccuracy

T\vo aspects of this clinical

A.T.‘s

GISC is highly

&licit

rclcvant

clcscrvc

inckpcnclcncc

of visuomotor

I~xation

(the transport

component)

coniponcnt)

[I.

Therefore,

motfcl

components and for shaping

IS]. This

the grasping stands

clcficit cannot

by itselfas

bc ;I

;L gcnuinc deficit.

discussion.

to the current

rc’I;Iti\c

(the grasp

pcrsistccl.

of the reach. but rather

model

of prchcnsion,

for transporting

which

postulates

the linger grip bcforc grasping

is grounded

on

;I

the hand at the object

functional

the object

and anotomicul

376

hl. JLAS~EROU.

J. DECETY and F. MIC‘HEL

A.T. Neutral objects, right hand, vision

1 I.

y - 0.359x

+ 7.568

r = 0.35

10.5.

7,s7

0

0

-

0

. 2

1

0

3

4

S

Object

6

t 8

7

51X

A.T. Familiar objects, right hand, vision

4J

c

1

2

3

4

5

6

7

0

9

object %ze Fig. 4. Comparison of I’aficnt A.T.‘s perform;lncc with her right hand during prehcnsicm movcmc’nts directed ul Neutral (upper diagram) ;md Familiar (louer diagram) objects in the Visual-fwdh:cb sifuation. Slop ol rcgrcsion liw and corrcl;ilion cocllicicnt~ arc g,ivcn on the upper Icft: Ncutrxl ohjccts, r=O.35; NS: Familiar ohjscts. r =0.77. I’-zO.(X)I. Grip WC and object G/c’ arc in cm.

considerations: (concerning shnpc)

Visual

should

organization and

bc widely for

cxpcrimcnts.

Transport

processing

ncedcd

for

the

in space) and for the grasp component

dilrcrcnt;

the proximal

howcvcr,

grasping:

formation

information

object location

thcsc components and distal

motor

have also rcvcalcd ;I significant kinematics

involve commands, amount

can bc inllucnccd

of the finger grip can bc modiliod

diflcrcnt

component object size or

modalities

respectively. ofcoupling

by object

by pcrturbntions

transport

(concerning

of

bctwccn reaching

size

aliccting

of neural

A number

[S.

131,

the trajectory

whereas of the

WLATEKAL

A.T.

POSTEICIOR PAKIETAL

377

LLSI0-b

Virtual objects

A.T.

Imagined objects

7,

3.5. 3 2.5 2, 1.5’

CONT. Virtual objects

reach

[6,

rcquircd Ref. [

251.

This

coupling

forcnsuring

in&xc1

simultaneity

rcllccts

the existcncc

of the itrrcst

of coordination

of the reach with the closure

mechanisms

of the finfcrs

(SW

I8]).

The

patient

the two objects)

hcrc seems. at first

rcportcd

components.

The

with exag~crxtion

bctwccn

the two,

Howcvcr,

another

object distance, impairment

it might

with

posterior

grasping

C;W. &licit)

howcvcr.

(at Icast

with respect to the object six

be discussed

First

for an indepcndcnt

altered

component

of the grasp component.

in patients

;I good wsc

W;IS clearly

the transport

aspect of the &licit.

must

sight,

component

of tho grip six

whcrcas

overshoot. prcscnt

grasp

Scvcral

this

SCC‘IIIS

were obscrvcd

only

possible

cllixts

unlikely.

of

and poor correlation dircctcd

at the object.

specially

can bc attributed

cxpkrnations

was ovcrcstimatcd.

Icsions,

controi

the neutral

the fact that the reach tcndcd to overshoot

bcforc the observed

bc that distance pnrictal

namely

was accurately

for

This

by HOI.MI:S

;IS the overshooting

with the neutral

objects.

solely

can bc considcrcd possibility ;lnd

W;IS mentioned

f4orcK,\s

(nnd

but not with

to an for this

[I?].

In the

the corrcspondinf the usual objects.

‘Another

explanation

did not come with

into

could

contact

the palmar \kin. This

camponcnt~

to ;I tactile

compatible with the lelocit>

of the reach

be that.

with

because

the object

the fingers

did not close in time.

and the trun$port

explanation would attribute

signal

arising

ohwr\cd during

from

contact

;wcuracv

of

the late phase

continued

the coordination

with

the object.

prehension

of transport

until

This

occurred

betucen

the two

mechanism \vould be

molcments: dots

the fingerpads

contact

Assuming

not ewccd

that

IO cm s and

that

the the

time for ;I tactile signal to intlucnce an ongoing movement i, around 60 msec [?I]. the movement c~~uldcome to ;I stop within about half ;I ccntimcter. The validit) of this “tactiic” explanation of coc~rdinxtinn betbvccnreach and gasp \bould hate to be kerilicd in subjects with tactile anxsthesia. It remains. howckcr. that it does not account for normal grasping bcha\ iour. hlowmcnts directed at virtual targets approslmatcl! stop at the perceikccl object location

in the alxence

f.‘inally.

the third

of any

tactile

cut.

most

likely

c?cplanation

and

distance is that the deticit in grip form;ltion

for A.T.‘s

tendency to overshoot

disrupted the normal coordination

nb_iect

bctbvecnthe

two components of the moxmcnt. This csplanation rcfcrs to the notion of ~1time-based covrdination [I I]. whcrchy compnncnts pcrL1inin, ‘7 to a _civen action exchange signals for keeping in time with each nthcr. In the prcscnt GISL’. one could spcculatc that. bccausc the linger opening did not stop at the rquircd grip si/c, the on’ict of the finger closure was As the closure tiriic i< ;I rclatiwly lixctl proportion of mo\cmcnt time (1,~. 75’;;~. see Kcf. [ IO]). the reach was proIon& in clr-tlcr to rcnx1in ccwrdiriatcd with the grasp. According

dcl;~~cd.

IO (Iii5 c\plan;itiori. the f;lctor ultimately rcsponsiblc for the inxxuratc yap in our p,aticnt \vould bc the impaired calibration of yrip si/c as ;I function of object si/c. The posterior p;1rictal ;Irc;i ~\oultl tht14 plxy ;I iii:l~ior role in this function. Thi5 h!pLthcsis predicts 111x1the of IIII~~CIIICIIIS 10 nsutral obiccts should bc tlillcrcnt from those of movcmc~~t~ to

kinematics f:lmiliar yr;l
obiccls.

i\ltliough

f;lmili;lr

ohjcct5

this co11ltl 1i0t lx seems

tcstcd

1~ go iii that

in A.T.,

I)i.\,\cU~itrric~,r /~~~1~c’l’c’rr /,rc~c~lrtr,ri.\/tr.~/;w f~/~~C’C~/ it/~~rl/i/ic~trri,~/l .f’hc sccontl grasping;~nd

striking

fcaturc

thcclosc-to-lll)rnlal

of the objects.

A.T.

wxs

able.

ofA.T.‘s

the fact that

.shc \v;ls xcuratc

for

tlirccti~~n.

Ixllaviour

wx

c/,d

f,l,j~‘c.l-or.ir,/r/~,~~

111~dissociation

trclirur

bctwccn

the impair4

when the task consistcd in perceptual :1nalyGs in the :~bwncc of visu;tl or tactile cues about her hand. to pcrform;~nce

correctly rn;~tch with her lingers the sia of ;I visually cx;lrnincd object. Normal subjects (inclrlding our control subject in the pr’cxnt study) perform this task with ;I linear incrcmcnt in intcrlingcr dlstancc [ZO]; A.T.‘s performance M’;IS thus \vithin the normal range. This result. togsthcr with that of the task of imagining the si,x of well-known usual objects is thus ;i good argument in Tabor of ati intact pcrccptual and rcprcsent:1tivn~1l procsssing in A.T. dissociation bct\vccn impaired grip si/c during prchcnsion of objects and normal

This

m;~tching of size ofthc s;~mc objects suggests that tho visual primitives for object si/c arc not proccswxl in the same neural pathways whether they arc used for guiding a motor action toward an object. or for pcrccptual ;~nalysis. Thcsc complcmcntary functions have been assigned diCrent neural palh\vays [Z-l. 3 I]. One pathway is the ventral occipitotenipor;ll route linkingstriatecortc,~ to prestriatcarcas and from thcrc. rcxhing inferotcmporal cortex 011 both Gtlcs vi;1 c;~llosal connections. In monkey cxpcrimcnts. interruption of this pathway abolishes objects.

object

discrimin;ition

The other.

dorsal.

pathuay

ivithout

;Irc;1s to the posterior part of lhc parictal spatial

disoricnt:ltion

charactcri/ccl.

aIl&ting

di\crgcs lobe.

from

pcrccption

of spatial

the previous

Intcrruplion

relations

ens by linking

of this

path~vay

bctwen

the prcstrialc produces

\isu;ll

not only by mispcrccption of the rclativc positions

of

KILATEKAL I’OSTTKIOK PAKILTAL

spatial

landmarks.

patient,

be damaged. This

but also

by localization

whereas

anatomical

agnosia. picture:

These

the ventral

model

patients,

although

who have a lesion

object size or orientation These

observations

\\cll as intrinsic)

with her fingers

suggest

rcprcscntation

(tentatively

is, to the extent

opposes

another

can bc named,

that

specific

motor

the process

ofovert This

dill&at

vantage points

(see Ref. [ 191). A.T.‘s

functions

of the two pathways

the graspingdclicit objects. tlonc

observed

through

the transfer

No other cues can be cognitive ;tlbut syslcm.

:~natomical

used,

as

cues can bc used thcsc objects.

This

patterns. implies

entity

ofneutral

primitives

suggests

This

transfer

would

connections

existing

bclwccn

grasp them

This relates

is illustrated

to the pragmatic

by the fxt system

through

In fact, the that. in A.T.. with usual can

only bc

the appropriate

of ~hc object.

based

cues c;m be transferred

he made anatomically the two pathw;~ys

across

In the c;lsc of usual objects,

the six

that semantic

of the

invariant

objects was less marked to size

an object

a representation

cues in the pragmatic rclatod

to the

representation

and by which

limited

possihlc

[_24]_

OS

mode of

as affordanccs.

aspect was normal.

all objects look alike. to determine

thus therein

and remains

was obviously

This

One

for those (extrinsic

Pragmatic

recognition.

the semantic

the use of six

of the visual

pathway. Lnowlctlgc

prehension

ohjccts

contrast, pr;igni:1lic

dclicit

arc complcmcntury. during

In the case of neutral

whereas

object

way.

representation)

process

type, whcrc the object appears as an identifiable bchaviour.

with

the reverse clinical

the movement.

are represented

semantic

aspect of object oricntcrl

In our

seemed to

this patient could not match

of a specific representation

and memorized.

categorized

of patients present

object size in a “normal’*

object attributes

trigger

mode. used during

action.

pathway

they can handle them normally.

Interestingly.

here ;I “pragmatic”

The

they

pathtvay.

which are used for controlling

called

object as a go:11 for an action.

the dorsal

and hand, but she was able to correctly with

the existence

object attributes

objects,

et 01. [7].

grip size correlated

object-oriented

only

by the observation

in the ventral

they arc unable to recognize

and her maximum

379

was spared.

validated

by GOODALE

during

of the lesion.

pathway

is further

such patient was observed

that

deficits

in accordance with the topography

LLSIO~

on

b)

prior to the

by the numerous

3x0

M. JEAS~U)U.

J. DEUTY

and F. MK’HI.L

IO. HARUE. W. and ETTLIS~XR, G. Reachmg in hght UKI Jarh after un~latcral postcrlor parietsl ablations m the monks). C~wrrr 9. 316 354. 1973. I I. HOFF. B. and ARRIM. Xl. A. A model of the e&Is of speed. accurucy and perturbation on visually-guided rcachlng. In Control rj/ .-Imt .\l~~rrmrnr in .Sput~~. ~Vt,uroph~~\r,~l,~~~~.ul und Compurtrrionul ..(pprw~~hrx R. CAIII\ITI. P. B. JUH>SOX and y. BLIOOII (Editors). E.\ptv%w~ru/ Br~rn Rtwwth .%rw.s 22, 285 306. IYYI. I?. HOL\IU. G.. HOKKAI. G. Disturbances of spatial orientation and visual attention mcith Icw, of ~tereo,rcopvz vision. .4rch. .Vrurol. Pswhidr. I. 385 407. 1919. 13. J\KOHSO~. L. S. and GO(~ALE. hl. A. Factors a&tine higher-order movement planning. .A kinematic anulksis of human prehension. Esp. Bwirl Rrs. 86. IYY-XX. IYYI. I-l. J~\KOHSOU.L. S., ARCHIH,\LD, y. hl.. C,\K~.Y. D. P. and G(x)I).u_~. hl ,A A h~nsmat~c analysis of reachln$ and Brasping movements in II patient recoberinp from optic ntaiia. .~ultrr)p\~~.h,rLrl/ilr 29. SO3- SOY. IYYI. IS. JE.\SVEKOI>. 51. Intersegmental coordination during rexhlnp at nclt;ral \~suaI O~JCC~S. In .-lrr~rt~~w cwcl f’rry/~~rrrr~n~v1.v. J. LOU and A. B..WUEL~Y (Editors). pp. I53 -16s. Lawrence Erlbaum. Hillsdale. NJ. IYSI. hl. The timing of natural prehension movements. J. .\/(,I. Bzhcrc-. 16. 235 25-l. IYSJ. 16. JEr\VUf.fwD. 17. JFAVSFROI). b1. The formation of finger grip during prehension. ;I corticalI> mediated visuomotor pattern. Bchcrr~. Brcrin Res. 19. YY -I 16. IYX6. IS. I Y. 20.

21. 2’. 23. 24. 25. 16. 27. 2rc. 2’). 30. 31.