Pergamon

HOW LATERALISED IS VISUOSPATIAL NEGLECT?

MAKL~N SMALL,* ALAS CowEyt and SISIW. ELLIS:

l blRC Rcscurch Centre in Brain and Bchaviour. Unibcrsity Department uf Clinical Neurolog). The RadclitTc Inlirmary. Woo&tock Road. Oxford OX2 6HE: tAlRC Research Ccntrc in Brain and Behaviour. Departmcnl of Expcrimcntal Psychology. South Parhs Road. Oxford OSI ZUD; and :Univrr\lty Department of Clinical

Neurology. The Radcl~lTe Infirmary. b’oods~och Road. Oxford OS1 6HE. U.K.

IN an cxpcrimcnd investigation of two possible thcorctical cxuscs of visuospatial ncglcct

MIJOVI~, [IX] highlightcd the phcnomcnon of allacsthcsia in which the patient crroncously

Iocaks sliniuli contral;itcral Lo the Icsion 3s ipsilutcral. Such allacsthctic errors can only

occur if Ihc patient’s right side of space allows the inclusion of such misplaccmcnls and

Mijovic slrcsscs thal “the absorption of Icft-siclctl clctails presupposes ;I damagctl or ‘pliant’

rcprcscntation of lhc right hcmispxc”.

Thcsc and other observations indicate ;I more bil;ltcral vistd &licit in visuospatial ncglcct

1han is commonly assumccl. That pcrccptual dclicits (other than altacsthcskl) occur in both

visual licltls in patients with visuospa~ial ncglcc~ has previously been cf~~~~mcntc’cj.

t IOIWNSII~IS antI CASW [IO] dcscribcd inxcur;~tc localisation within the “normd licld in

hcmi:lnopic patients with unilateral, rctrogcniculnk Icsions. The field contratatcral 10 the

Icsion displayed ;I hcmianopic dcfcct with :lpparcnt macular sparing and this arc;1 LV;IS

ncglcctcd. t lowcvcr, pcrsisknt errors of localisn&>n occurred in the “normal” liclcl. the

errors becoming more pronound as an object was plxcd towards the pcriphcry but,

LATT.WALISATIOV I)F VISCOSF’ATIAL \FGLi(‘T 451

(I 7 with left- and one with right-sided visuo-spatial ne_rlect) as soon as possible after their acute cerebrovascular episode.

METHOD

Eighteen patients. eight m;LIc and IO ftmalc. alI adrmttcd to the John RadclltTc Hwpital. Oxford Hlth acute ccrebrwascular accident Here examined. The group mean age was 76.3 years (S.D. X.X. range 55 X7 qcarst. The mcun age for malt’s was 77.4 years (S.D. 6.X. range 6X ~X7 years) and for fern&s. 75.1 jeurs 1S.D. 10.4. range 55 X7 >cdrs). Patients were originally selected because of the presence of anosognusia but all wt’rt’ also fwnd to exhibit \iruoxpatial neglwt. Each patient received a thorough neurological examination (by S.E.1 within 3 d.~)s of udmksion (mean tmic to examination I .3 days. range 0.753 days). NwJect was assessed clinically and by the star cancullution bheot of the Bcha%iourcll Inatlcntion Test which was included in the neurological cwmination. All IS patrents had vi~uosptial neglect: the condition NW loft-sided in I7 and right-sided in one. The I7 wscs of left-sldcd nqlcct fcvm the main patient group for the present study. comprising eight malts and nine females with ;I mean aec of77.C )cars (S.D. 7.2). Fifteen were right- and t~o Icft-handed. Thesingle patient Hith right-sided neglect H:IS~ 5>- )ear-old. left-handed fcmalc: her results will bc rcfcrrcd IO separately.

Patient\ undcrtolak the six suhtcsts of the BIT as soon IIS possible after their axtc admission (usually on d;iy 3. rangy < I Y daysevxpt in onccarc on day 4X). The suitability ofcach patient few e’camination was dictated by their mcdlcal condition. Ic\cI clfarousal and thcrapcutic commitments. They were cwmincd while either confined IO bed (vttlng up)or sitting in ach;~ir.oftcn ;Imld the husy.on-poirle;lctiviticsofar~ ~utcpcncral ward. Whcncker pu\siblc. p.~twnts Hcrc alho ;~sLcd IO carry out the six suhtc~ts of the BIT on ;I wcchly h;k.

Thlrtccn of the 17 patients with Icft-sided ncplcct and the slnglc ~:IIICIII with right neglect undcruont n~llrcir;lJi~,l~lFi~~ll cv;llu;tticm by compulcriacd toniogr;~phy (CT) scan.

The u\u;d rncthd of scoring the HI I’ whtc\t> (hy taking ;I ICII;II scow) doa MI indicxtc Hhcthcr the error\ of or1w4on arc rn:~lc in right or 1cf1 hcmiqwc. WC thsrcforc ;~n:~lywd the d;~ta in ;I u:~y which cn:thlcd the Iatsralid CITCCI crf~~a~qxlti;~l ncpl~c~ IO bc prcscntcd hut it \\a> only pobsiblc IO do thih on >ymmctric;ll BtT stimulu\ \hccr>. \VC thcrcforc split ths scows from the (symmetric:~l) stimulus shcs~> provided for 111x (I’ig. la). Icttcr (k’ig. I b) and \t;lr c;~nc~II~~t~on into their rcspcclivs scctitln~ (c’.g. thrcs right- and thrcr kft-dcd colu~nr~s for hoth llnc and slar c~~nccll~~t~~n: IHO right-and IUO Icft-sided columns for Isttcr~arlu~ll;ltion). Th~~~divi~ions;lruCIL’LIrIy markstl on thr platic BIT wwing cards. Thr numhcr ofcorrcctly c;~n~cIIcd .rtimuli in cxh of thr right- ;~nd left-sided wctions was counlcd for each p~lllcnl and for sach nornml suhjcct. Thssc rcqinws Hcrc then contcrtcd into ;I pcrcsntagc of the m.~ximtml p&hlc scow.

51. SCL\LL. A. COWEY and S. ELLIS

E&R

* 4*“4 LEG +

y- * ARE*

M Y

LEG _k M ,, LEG

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*

LATI'I(.\LISATIOV OF VISI'OSP~TIAL %tGLE(‘T 453

RESULTS

Three patients were not tested. Acuity ranged from N5 to N-M with one patient blind in the

right eye. For controls acuity ranged from N5 to N IO. with one male subject able to see only

finger movements with his left eye.

Eleven (65%) of the I7 patients with left-sided neglect had ;1 left homonymous

hemianopia. The six remaining patients had no field deficit as detected by confrontation and

no patient had an occular palsy. The one patient with right-sided neglect had full visual fields.

The presence or absence of field defects is shown in Table I. It should be noted that the

presence of a hemianopia does not necessarily indicate visual neglect. Most hemianopic

patients do not show contralateral neglect because they scrutinise the space within their

defective visual field with the intact hemifield.

The patients’ ages and total BIT subtest scores arc shown in Table I. The I7 patients with

left-sided neglect had i1 mean total BIT score (all sin subtests) of 50.3. S.D. 35.1. range

12 -IX!. Paticnt H.W., with right-s&xi neglect. had ;1 BIT total score of 176.

The normal control’s total BIT score ranpcd from I32 to I46 with a mean total score of

143.9. S.D. 3.58. No normal subject’s total score fell below the rccommcndcd cut-otT point of

129. The dillkrcnce bctwecn the scores of the two groups was significant at f’<O.OOl

((i= 153. Mann -Whitney test).

/_irw crrrrcdlcr/ior~. The mean pcrccntagc correct line cancellations in the three right- and

three Icft-sided columns. for both the patient :IIICI control groups, are S~OWII below and

appear in Fig. 2. The patient and control groups were signilicantly dillkrcnt (Friedman’s

Z-way Analysis of Varklncc (ANOVA), x2 = 6.0. f’=O.O143).

I’crcctlldgc corrccl wore Tow lirw c;~nccll;~l~~m~

l:;lr IdI Ldl I (hlitllinc) Right I

Compared to the almost frlultlcss performance of the control group the patients showed ;L

progressive improvcmcnt from left to right but did not reach ;I perfect score cvcn in the far

right column.

f_ctfcr c.cl,~~.c’//trriolt. The mean percentage correct Icttcr cancellations on the two right- ad

two MI-sided sections, for the normal controls ar,d the patient group. arc shown below ancl

also appear in Fig. 2. There was ;I statistically significant dilkrence bctwccr: the patient ~mJ

control groups (x2 =4.0. P=O.O455, Friedman’s Z-way ANOVA).

D.A. 59 B.W. 77 \v Xl 76 E.51. x3 R.Sc. s7

S.S. 6X R.Sh. 6s

A.C. 76 H.C. RO

H.hl. 81 I.Str. 78 V.B. 83 MD. 77

H.L. x7 I..Stu. 75 H.P. 7h

J.L. x-l

l H.W. 55

+ + +

Owe again the controls pcrfornul al ;I ilnili~mly high lcvcl \vlicrc;is the patients iniprovcrl

systcnialic;illy from Icft to right hut rcaclictl ;I ailing of only 63%. S/or c.trr~c.c,//tr/iorr. Tlw tnc;111 pcrccntagc dstar unccll;~tions on tho three right- and three

Id-sitlccl scclions, for the patient 2nd control groups , appear below and arc also shown in

I:ig. 2. I‘hcrc was ;I st;itically signilicant dilkrcncc bclwccn the patient and control groups (f~‘ricdman’s Z-Way ANOVA. x2 = 6.0. /‘=O.OIJ.1).

I.‘ar Idl

Normal controlscancellctl 98 100% ofstars in all scctiuns whcrus the p;iticnts rcxhd only S7”!<, correct in Lhc far right column.

Ibxt~sc thcsc ;~vcr;lgccl group results sccmcd to intlkxtc that patients made ;I cnnsidcrxblc numhcr of omissions on cvcry sp;itial section of wch canccllalion lask (lines. luttcrs and

stars) it \vas important IO ascertain tllc contrihtrtion from each patient to the avcragt score.

ioa

9a

60

70

6a

60

40

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4 P.ll.“l. I,“. + p.ll.n,. I.,,., % P.ll.“,. .t.,

Et 00111,101. II”. x oontro,. I.,,., 0 oontro,. .I., I

The individu;d results on the Icticr and star cancellation tasks of the eight p;tticnts with the

lowest BIT scow :lrc shown graphkxlly in Figs 3(a) :lnJ (b). rcspcotivcly.

Ths results ol’ 11.W.. the only palicnt with ;I unil;ltcr:ll I&-sided Icsion and right-sided

ncglcct. xc cxprcsscd x pcrccnlagc wrrcct canccll;ttions on the three tasks Mow. In her

ipsilcsional Id1 licld she w;ls substanli~dly txltcr than any of lhc other 17 p;llicnts in their

ipsilcsional right licld.

LlllC Glncell~ll~rn Fllr Id-t Let-r 2

D .A IN) I(N) B IV. 100 I(H) E.kl. 67 INI R.SC. 0 17 s.s ?? 50 \v 51 I(W) I(H) H.C. 0 0 R.Sh. 0 0 .4.c-. 0 0 H P. 0 0 XI D. 0 0 H L. 0 0 H 11. 0 0 v.11. 0 0 I SIU. 0 0 1 S1r 0 I7 J I. 0 0

Letrcr c.lnccll.lll~~tl Far ICfl

D fi\. IO II M’. 4-J 1: 11 30 R.SC 30 s s. 0 w Xl 20 II (‘. 0 R.Sh 0 AC‘. 0 II I’. 0 hl.0. 0 II 1.. 0 II Xl. 0 v Ii 0 I.SllI. 0 I.Srr. 0 J I.. 0

Sldr c;IwAl;llion I.;1r ICfl Idl 2

IL\. 7s 50

Ii w (11 I(H) fI.XI. 0 0 R SC. 0 11.5 S.S. 0 25 \V.XI. 0 0 f I .C‘. 0 (1 R.Sh. 0 0 ,\ (‘ 0 0 II I’ 0 0 h1.f). 0 0 II I.. 0 0 II Xl. 0 0 v.11. 0 (1 I.SllI. 0 0 ISIr. 0 0 J I.. 0 0

L&t I loo IW I(H) loo

67 loo

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IA1 SO JO 50 00

IO 41

0 0 0 0 0 0 0 0 0 0 0

I.dr I x2 Xl

0 is 45

0 0 0 0 0 0 0 0 0 0 0 0

(\lldllnc I Right I Rtsht 1 F,lr rlghr I(H) I(W) I(W)

s-1 I(H) I(H) l(M) I(W) IN) I(H) IOU IOU

67 I(H) I(X) I(H) IIN) loo

0 I(W) I(H) l(H) I(H) loo I(W) I(H) loo

0 CO 50 0 67 x.3 0 I CM) I(H)

17 I(H) l(H) 67 50 67 50 33 50 50 32 I(H)

0 0 R!

Rlghl I;.Ir rlytll I(H) loo

30 HO SO ‘JO

IO0 IOU JO ‘JO SO I(H) IO ‘JO so ‘JO 20 so

0 30 0 30 0 IO

to 70 0 50 0 to 0 JO 0 to

t~lidlltlcl RIgtI1 t Right 1 t,‘;lr righr I(H) I(H) I(H) t(M) I(H) IO0

0 50 75 30 12.5 100 27 71 IO0 0-I IIMI I(M) 3, 50 IOU

0 0 I(M) 0 0 50 0 0 02 0 0 x7 0 0 75 0 (12 I(H) 0 0 02 0 0 IIX1 0 12.5 x7 0 0 75

R~s~rlrs (!/‘\~,c~c~k/?,~i,llo~~-~rp ft’st.s. The results of testing the eight patients svith the lo\vrst

BIT score during subsequent \veekly follow-ups on the Ictter and star cancellation tasks

produced similar consistent findings from week to week. (Five pnticnts bverc followed up for

I month or longer but testing could not bc continued in three patients for medical or sociul

reasons.) The follow-up results of patient J.L.. on the letter and star cancellation tasks. arc shown in Fig. 4.

E.~~c~tktl cw-siorl ofsttrr c.cmdltrtior~. Five patients wxx tested with the lattxally ostcnded version of the star cancellation task. Three patients began to cancel the small stars by starting

at the same point whcrc they had previously begun on the original A-t-sized stimulus sheet

(ix. the original far right column). On the new version. cxtcndcd on the right, they then continued rightwards from this point and procccdcd to cancel additional stars. moving

to~vards the right-hand side of the cxtcndcd page and crossing the small stars within the “cxtcnsion”. In contrast, the other two paticnts canccllcd only the stars at the cxtrcmc right-

h;irltl cdgc of the new c?ctcndcd shcot, complctcly omitting to cancel any stimuli to the Icft of

this point which they had previously dctcctcd and canccllcd. It should :I~SO bc noted that one patient (I l.l’.) produced both types of result outlined above on this cxtondcd version of star

c~iriccll:ition whcri tcstcd at dilkrcnt times, I month apart.

k‘igurc 2, which shows the group nicin psrccntago of correct rcsponscs for the lint, Icttcr

and star c:inccllation tasks indicates ;I continuous dccrcmcnt in the pcrformancc of patients

;tcross columns, from right to Isft. The scores for the star cancellation show ;I very similar

slope to that dcscribcd by MARSIIAI.I. and ~IAL.I.IGAN [IG] for their Incan pcrccnt omissions per column on the s:imc test. t lowcvcr. as Marshall and t lalligan also noted. once the inclivitlu~d patients’ scores arc plottctl it immcdiatcly becomes obvious that the continuous

tlcsrcmcnt implied by the IIXII~ group scores is not ;I true rcprcscnt;ltion of pcrformancc. cvcn \vhcn testing in all patients has taken place within days of the vascul;[r xcidcnt.

The results of the tight pnticnts with the lowest BIT scores show that on exh of the three

canccll~~tion tasks [lcttcr, Fig. 3(a), and star, Fig. 3(b)] patients show not only clear left-sided

ncglcct but m:u4xdly poor pcrformancc on columns within r@-sided space. cvcn including the far right columns. The results arc almost idclntical for the tight patients on the Icttcr and star

c~mccllation tasks. On thcsc two tests in p;[rticul;lr, most patients score zero on all IA-sided

sections of the page iis well ;IS on the Columbus imm~diatcly to the right of the midlinc. I’crformancc then “improves”, though not usually to 3 maximum. on the fur right column. at

approximately I-1 from the midline. This observation prompted further invcstigltion to

discover whcthcr the phcnomcnon was ;I consistent. rcpcatablc finding. The results of w&l) prcscntation of lcttcr and star canccll;~tion taslis to the group of live patients with scvcrc Icft-

sided visuospatial ncglcct who could be folknvcd-up clearly shorvcd that markedly reduced

60

50

40

30

20

10

0

h1. SMALL. A. CO\~EY and S. ELLIS

I.11 ,lQhl

position of targets

I., ,lDh,

r - -- 8 H.P. uu.0. ++H.L. -H.M. *v.e. +l.s,.. __.____._ _- ..__-. _ _~ - ~_ - .._~ -._ __..-- - _.- . .

z I slr-:-~q

Fig. 3 (a)

;~tlontion in both left :intl ri!/hl visual space was not just ;i trxnsilory event. Little change

occurred during the I month follow-up period, as shown by patient J.L. in Fig. 4. In an :ittempt to cxplorc whcthcr in:lttcntion shows ;I boundary (in this C;ISC the far right 01

the stimulus sheets) at the same visual angle in a large group of patients Lvith scvcrc ncglcct WC

asked five patients from this group to cancel stars on ;I latcral~y extcndcd version of the: star c;lnccll;~tion sheet. Whcrc the “in;lttcntion border” occtlrs 1x1 this clongat~ti contintution 01 stimuli ought to indicate whcthcr it rcllccts ;I fixccl visual angle or whcthcr it arises bcc~~usc

atkmtion is focused at the Iir right sitlc of the display. kvhatcvcr its xigul;ir Sk. The outcome of

this subsqucnt cnpcrimcnt W;IS suggcstivc but inconclusive. LVhilc the results from three

patients suggest that the boundary for visual ncglcct is in&xi ;I tixcd visual angle. in the other

two patients this is clearly not the cxc and the right-hand cdg~ of the stimulus display scum to

L,\TERALISATIOX OF VISUOSP4TIAL NEGLECT

100

90

60

70

60

50

40

30

20

10

0 _ I., I.11 3 I.11 2 I.11 1 tIphI 1 rlphl 2 I., rIglIt 5

positnon of targets

IL _ t+H P. -yu 0. $#li.L. -H u. *v.s. + I 51”. &,.str. c+ J.L. - --~ .~ - _~___._ -I

specify lhc point of inattention. Further invcstiyntions arc in progress to try to rcsolvc this issue.

Although other investigators hnvc occasionally rcportcd ipsilxtcral omissions on cancella- tion tasks in patients with right homisphcrc damage [I , 243 this right-sided inattention has always been dcscribcd as less scvcre than the contralatcral neglect. While this is indubitable if the cntirc hcmiliclds arc compared (91 hloc~. it is ncvcrthclcss striking that in many of our patients the right&id, ipsilatcral omissions up to about IO from the midline wcrc often as frqucnt or only slightly Icss common than the contralntcrd errors at the S;IIIIC eccentricity.

Procasing of right-sided space in patients with Id-sided ncglcct has been previously invcstigatcd using expcrimcntal methods other than cancellation tasks. CALVANIO PI rrl. [?I.

bl. SMALL. A. COREY and S. ELLIS

(b) 100

. 80

: = 70 2 ;

‘: IO

: 00

; : .o ; ” JO

+

IO

0 :

20

I., ,.I, I

whose right hcmisphcrc stroke patients wcrc :Iskcd to report objects or words from :I 5 x 5

array. dcscribc an abnormal rightward starting tcndcncy relative to controls. Their data also

clearly show suboptimal pcrformancc by patients in both body and cnvironmcnt centrcd

right halfofspacc whcrcas control subjects correctly rcportcd all itcms in :lII arrays under all

conditions. In patients with right hcmisphcrc &ions of mixed actiology who undertook ;L

scorch task whcrcby four letters lvcrc displayed to the right ofccntral fixation, DI: RKNZI cr (11.

[5] found that reaction timcs (KTs) bccamc progrcssivcly longer as the target position

approached the central fixation point (i.e. KTs wcrc sloivcr in ;I right to Icft direction in the

right halfofspncc). The rcsponsc latency in thcextrcmc right position was approximately the

L,\TE:RALISATIO\ OF VISLOSPATIAL hE5LEC-T 461

same for patients with right hemisphere lesions.either with or without neglect. although both

groups were slower in this position than the non-cerebral patient controls. LADAVAS if (11.

[I51 compared RTs of patients with right hemisphere lesions with or without left-sided

neglect who were required to disciminate between distracters and targets presented in the

ipsilesional. intact. right half field. They also reported faster RTs to the most right-sided

targets in the patient group with neglect and in fact these neglect patients were actually faster

in this position than the control patients without neglect. Similarly. RAPCSAR ef cd. [19]. examining visual extinction Lvith double simultaneous stimulation in a single patient with a

right hemisphere infarct and left neglect. noted that it was the lateral location of the

contralateral stimulus which determined the severity ofextinction (i.e. the stimulus on the left

side of a pair presented simultaneously). The patient’s pcrformunce was essentially normal

\vhen the more contralateral stimulus was in the peripheral part of the right visual half field or

the right hemispatial field. The authors suggest that inattention has a gradient of severity

from a maximum in the extreme contralateral hemifield or hemispace to a minimum in the

extreme ipsilateral hemificld or hemispace.

Although these previous reports indicate impovcrishcd processing in the supposedly

“intact” right half of space in patients with left-sided neglect. none of them reports complete

non-attendance to stimuli to the right of centre. ;i clcnr finding in many of our patients

particularly on lcttcr and star cancellation. Previous investigations also dcscribcs the results

with stimuli in the extrcmc right of space to be cithcr cclu;~l to those of control pilticnts

without neglect [S]. fastor than lhc control group [IS] or csscntinlly normal [ 191. However,

in our ncglcct paticnts omissions occurred in the far right section of the stimulus arrays in

5,: I7 patients on lint cancellation, 13/l 7 bvith letters and Xi I7 on star canccllution.

Our results cannot be attributable to the prcscncc of a Icft-sidsd field dcfcct. Two patients

(tl.M. and I.Str.) had full visual fields yet both showcd omissions on the far right section of

the lcttcr cancellation sheet ;ind, cvcn more noticcahly. in the portion lo the right of the

midline. I~urthcrmorc. Isrll~l (‘I trl. [I I]. recorded cyc movcmcnts during ;I lint bisection task

in hcmianopic patients with or willlout unilateral spatial neglect. Patients with both ;L

hcminnopi:l and ncglcct fixated their ~;ILL’ on the righI of the lint and matlc a few rightward

scarchcs bill ncvcr looked to the Icfl. t lu\vevcr, hcmianopic patients without neglect made

scvcral scarchcs to the entlpoinl of the line on the hcmianopic side ;lnd, using iI compcnsalory

eye-lixativn pattern, contrived to SW the whole line which was subsequently biscctcd almost

correctly. Our patients with ;I left hcmianopia should therefore have produccd errorless

pcrformanccs on right-sided targets because these stimuli fccll into the preserved visual half

lieId ilnd, to rsitcratc. the cnncckltion sheets were ccntrcd at the patient’s midline with head

and cyc 1iiovciiic1ils in no way restricted.

While it is :ko known that the number of latcralised omissions GIII be manipulated by the

clTccts ofcucing [ 12. 211 and by the addition ofdistractors to the stimulus array [ 131, neither

of thcsc techniques was included in our experiment:11 design.

Thcrc is ;I growing consensus that ncglcct reflects a11 attentional deficit although the

proposed cxpl;inations arc divcrsc. Our findings ;lre not readily reconcilable with ;I possible

attcnlional expl;lniltion as suggcstcd by AIJIXT [I] who proposed that disturbances in

overall general attcnlion might account for at least sorbic of the dclicicnt performance

obscrvcd on [hc side ipsilatcral to the Icsion. A dccrcasc in the lcvcl of pnticnts’ gcncral

ilttcntion could perhaps explilin occasional ipsiiatcral errors but not the very marked

omissions wc have described or, in particul:tr. their greater frequency in central rather than

pcriphcral vision. Such qro.s.s ipsilatcral neglect is also not easily reconciled with the proposal

-62 Xl. SMALL. A. Coun and S. ELLIS

that there is an asymnictrical hcniisphcric contrihtion to visual space in the sc’nsc that the

right posterior region contributes lo the pcrccption of both right and Idi visual spacc whcrcas the kft hanisphcrc is conccrncd only with the contralatcral side [X. 241. With this tlic~~ry. which is iIndotIbtcdly ;itlraclivc bcc;iiIsc it so rcxlily ilCCOl~lltS for the rarity dscvcrc

ncglcct following lcfi hcmisphcrc: Icsions. ipsilatcr;d (right-sitlcd) errors ought to lx

IIII~~~II~~I~ bcc;ItIsc right visual space should contintrc to bc proccssctl normally by ;III intact

lcli hcniisphcrc. Al~liougl~ WIiIN’rxAt:II iInd MI.s\;I.A\I [‘Z-I] to attention may. in some indivitlualS;. bc minor so that

unilateral right hcmisphcrc in scvcrc attcntional Jisturbancc I5 out of the I7 patients

on the lcttcr and star cancellation I3 patients

IZ hd iIiiil;ilcral. right-sitlcd 01

bil;Itcral involvcmcnt. WC obviously cannot comment lesion location in the four

in detail. four It thcrcforc seems impossible ~nadc in right-sided slxu \vcrc iI result ol’ bilateral ccrcfbr:Il invol\cmcIIt (ix. a

tl;~rii:~gctl Id1 hcmisphcrc Lvhich wotiltl prcclucls “normal” right-sided visuospatial proccss-

ing). KINSHO~~I~NII’S [l-t] proposal that ncglcct rssults from an attcnticxul bias postulates that the

right~v;Irtl dircotccl processor is more poknt and when disinhibitcd gcncratcs ;I more extrcnic

lateral orientating tcndcncy resulting in ;I rightward attcntional bias.ThtIs. patients nsglcct not

only stimuli contraliItcral to lhc Icsioii (ix. ;I right hcniisphcrc patient ncglccts lllc ldt sick) hut

also those stimuli prcscntcd in the right visual liclil and cspccially those cioscr to the miillins. Although with Kinsbournc’s view thcrc CiIII bc marl& imp;Iirmcnt within the ‘intact’ hcmilicld, more pcriphcraI stimuli should bc tlctcctcrl. Again. our patients’ markal ipsilcsional ixiiissions 011 far right targcts remain iIncxplaincil cspcci;illy in two p:itisnls on Ihc cxtcnilcil

version of lhc slar candlation t;isk who nixlc errors at an ccccntricity of 30 As H’C had only one patient (I 1.W.) \vith ;I ldt hcmisphcrc Icsiori ad right-sidcrl ncglcct it

L.\TtKALIS,\TIOS OF \IISI OSP\1lAL V1(;Lf.(‘T 363

w;~s not possible to comment on the finding [24] that ipsilateral neglect is found only in

p;lticnts with right-sided injury and not in those with left cerebral damage. Wt: can only state

that H.U’.‘s o\crull BIT score of 126 1-M \v;1s only six points lower than that of our poorest

normal control and. although there is some evidence of ipsilateral (left-sided) terrors on all

three cancellation tasks her contralateral (right-sided) omissions are not gross. Her CT scan

revcalcd ;I unilateral left hemisphere infarct.

Perhaps the most plausible hypothesis to explain the marked ip.silofutll ;LS well as

contralateral neglect we have described is to suggest that there are two components to the

phenomenon. ;I visuospatiul field dckct (representing dcfcctivc spatial representation within

the damaged right parietal cortex) and a severe directional bias in automatic orientation or

selective attention caused by a loss of inhibitory mechanisms that undoubtedly underlie

selcctivc attention. In order to explain our results it seems that there has to be ;III additional

attcntional component kvhich precludes normal processing of right visual space by an intact

left hemisphere.

That other brain areas apart from retro-rolnndic cortex may contribute to some of the

complcs components of ncglcct has alrcndy been suggcstcd [7, 8. 171 but, again, these

thcnrics consider only contralatcral ncglcct. Even with the recent “premotor theory ofspatial

attention” by RIZZOIATTI and CASIAKDA [Xl. which incorpnratcs ;I distributed system of

sclcctivc attention, it is dillicult to explain how ipsik1tcral spacc would bc markedly afkcIcd.

The Iargc right-sided arcas ofdamagc (including the frontal lobe in IO out of I7 of our casts)

without cvitlcncc of bilateral involvcmcnt. as rcportcd in many patients who undcrwcnt CT

sc;111. rnahcs such ;I multi-contrcd proposal for atIcntic)n c1nincnIly knablc. Contributions by

fronl;il regions to Ik~ii~cr sc;irch tinics in contral~itcral sp;icc (in Ihc absoncc of any clinically

obvious parks in lateral g~c) have hccn dcscrihcd by TI:I;IIIX [X] and. more rcccntly.

iicglccl caiiscd by frontal lobe IcGiis has been rcporlcd by I Ilrlr.slAN and V,\I IiNs-r1:IN [h].

l‘hcy tlcscrihc throc patkilts with Icsioiis of lhc medial surfcicc of Ihc right frontal lobe and

three c;iscs wilh Icsions of the right dorsol;ilcraI surfcicc: howcvcr, the ncglcct was

contr~1l;itcr;il in ;iII six c;iscs. l~~\al~\slo (*I trl. [4] dcscrihc ;I similar condition following

damage to the frorit~il lohc or b;is;il g;iiigli;i. Again the tic&t was contr:iI;iIcraI cxccpt for

011~ p;iticilI who showctl scvcrc /q/i-sidctl (ipsil;itcral) visuzl neglect although CT SC;III rcvcakd ;I circumsoribctl arc;1 in the k/i basal ganglia region. They suggest that their

“dcvi;1nt” USC with ipsilatcral ncglcct might bc rclatcd to ;I dysfunction in basal gangli;l

rather than frontal cortex. This may bc the anatomical corrclatc which cxpl;1ins our findings

although such ;I suggestion mtlst remain spccul;1tivc bccausc CT SC;III was not obtainsd in AII

C;IS;CS and not all patients had front;11 d~magc. It should bc poinIcd out thcrc is gcncrally

scant cvidcncc for frontal involvcmcnt in spti;~l attention (with 111~: cxccption ofd;~magc that

involves the frontal cyc-lickis) and our hypothesis ;ISSLIIIICS that any d&it prod IICCCI by the

right frontal arc;1 would bc limited to sp;Itial proccssing bccausc our paticnIs did not show

any of the classical and prornincnt signs of frontal Iobc clam;lgc.

Although our p;iticnI group was small. Ihc results strongly suggest th;1t the inilial

prcscntation of visuospatial nq$cct may bc cluitc divcrsc. At the carlicst time possible for

objccIivc IcsIing of inattention using Ihc HIT, patients \vith the s;1mc Iypc of ;1cIiology (i.e.

ccrcbruv;lscul;1r) sho\vcd \viclcly discrepant pcrformancc. The fact that tight patients with

the Iowcst BIT subtcst scores all sho\vcd dclicicnt pcrformancc of ;I remarkably similar

n;iturc on the Icttcr and slar c;inccllaIion Iasks indicates lhal dilkrcnl dcgrccs of this

condition csist within tbc broad classilication of visuosp~~ti~~l ncglcct. Th;~t ;I considcrablc part of right-skid visit21 space includiii~ Ihc far right side is ~ilso oftcu complctcly ncglccted.

and not just ;1s a transitory occurrence. must also be ucceptcd and incorporated Into nca

theories that endtxvour to explain this puz.xlins condition.