Journal ofNeurology, Neurosurgery, and Psychiatry 1991;54:1082-1089

Early orientation of attention toward the halfspace ipsilateral to the lesion in patients withunilateral brain damage

Guido Gainotti, Patrizia D'Erme, Paolo Bartolomeo

AbstractPosner has suggested that unilateralspatial neglect could be due to a

difficulty in disengaging attention fromits current focus to orient it toward theneglected half space. Clinical andexperimental data suggest, however, thatthis disengaging difficulty could be onlyone aspect of a more complex distur-bance also characterised by an earlyautomatic orienting of attention towardthe half space ipsilateral to the lesion. Totest this hypothesis, two different inves-tigations in unselected groups of patientswith right and left brain-damage were

carried out. The first investigation, toevaluate forms of lateral orienting ofattention severe enough to provoke an

overt gaze deviation, consisted of the sys-

tematic assessment of the phenomenonof "magnetic gaze attraction". Thesecond investigation, to detect milderforms of automatic orienting of atten-tion, analysed the temporal sequencefollowed in identifying the picturesrepresented in an "Overlapping Figurestask", to see if patients tended to identifyfirst figures lying in the half spaceipsilateral to the lesion. In both inves-tigations results consistently showed: a)that patients with right brain damagetend to orient attention automaticallytoward the ipsilateral half space morethan patients with left brain damage; b)that this tendency is tightly linked to thepresence of behavioural manifestationsof hemi-neglect. These results are

therefore consistent with the hypothesisthat hemi-neglect is a multi-componentsyndrome with an early orienting ofattention toward the half space ipsi-lateral to the lesion as the first of thesecomponents.

Institute of Neurologyof the CatholicUniversity, Rome,ItalyG GainottiP D'ErmeP BartolomeoCorrespondence to:Dr Gainotti, NeurologicalClinic, Catholic University,Policilinco Gemelli, largo AGemelli 8, 00168 Rome,Italy.Received 25 April 1990and in revised form10 December 1990.Accepted 17 January 1991

Among the "attentional" theories recentlyadvanced explaining the unilateral spatialneglect syndrome, the cognitive interpretationproposed by Posner et al stems from thedetailed analysis of the act of covert orientingof visual attention. According to the authorsthis orientation consists of three successivemental operations: 1) disengaging from thecurrent focus of attention; 2) moving towardthe target; and 3) engaging the target.

Posner et al'3 suggested that parietal lobeinjuries specifically affect the ability to disen-gage attention from its previous focus auto-

matically, and viewed the extinctionphenomenon as a consequence of this in-ability.Although this interpretation may ad-

equately explain the extinction phenomenon,it can hardly account for some of the aspectsof the unilateral spatial neglect syndrome.Clinical observations and neuropsychologicaldata45 suggest that the difficulty in disengag-ing attention from its current focus could bebut an aspect of a more complex disturbancealso characterised by an early automatic orien-ting of attention toward the half spaceipsilateral to the lesion. To verify this hypo-thesis, we carried out two simple neuro-psychological investigations, which aimed toseparately take into account severe and subtleforms of automatic lateral orienting of atten-tion in patients with and without unilateralspatial neglect.A clinical phenomenon which seems to

express a severe form of automatic lateralorienting of attention is the "magnetic gazeattraction," described by Cohn' in patientswith homonymous hemianopia and con-sidered by Friedland and Weinstein' as anocular motor disorder analogous to visualextinction. This phenomenon, which isusually observed while assessing the visualfields of the patient with the confrontationtechnique, consists of a tendency to orient thegaze toward the side ipsilateral to the brainlesion spontaneously as soon as the examineroutstretches his or her arms and before theadministration of the stimuli. To study therelationships between "magnetic gaze attrac-tion" and unilateral spatial neglect, we as-sessed systematically, in our first investiga-tion, the frequency of this phenomenon inunselected groups of patients with right andleft brain damage, with and without evidenceof unilateral spatial neglect.A second clinical phenomenon which

seemed appropriate to study milder forms ofearly automatic orienting of attention was thescanning pattern shown by patients with braindamage while identifying pictures representedin an Overlapping Figures Test. It could bepredicted that if patients tend to orient firsttoward stimuli lying in one half of space, theyshould identify first pictures placed in thatpart of the composite diagram, turning onlylater to pictures lying on the other side of thedisplay. An analysis of the temporal sequencefollowed by right and left brain-damagedpatients while identifying the pictures repre-sented in an Overlapping Figures Test wastherefore performed in our second investiga-tion.

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Our general hypothesis was that ifautomatic orienting of attention toward thehalf space ipsilateral to the lesion is an impor-tant component of unilateral spatial neglect,then a strong relationship should exist be-tween presence and severity of lateral orient-ing of attention and presence and severity ofunilateral spatial neglect.Thus a magnetic gaze attraction should be

mainly (or almost only) observed in patientswith severe hemi-neglect, whereas a tendencyto point first to figures lying in the half spaceipsilateral to the lesion should also beobserved in patients with mild forms of hemi-inattention.

EXPERIMENT 1Although the phenomenon of the "magneticgaze attraction" has been described by Cohn6in patients with both right and left hemi-anopia and has not been considered as part ofunilateral spatial neglect syndrome, westudied more closely the relationships be-tween magnetic gaze attraction and unilateralspatial neglect, particularly taking intoaccount two problems: a) The relationshipbetween magnetic attraction and laterality oflesions, to see whether magnetic attractionprevails in patients with right brain damage,as is usual with unilateral spatial neglect."'0 b)The relation between magnetic attraction,homonymous hemianopia, visual extinctionand unilateral spatial neglect. We predictedthat if 'the magnetic attraction is part of theunilateral spatial neglect syndrome, then itshould clearly prevail in patients with rightbrain damage with severe signs of hemi-neglect.

Subjects and methodsSubjectsFifty three patients with right brain damage(RBD) and thirty three with left brain damage(LBD) participated in this experiment. Ourpatients were selected on the basis of clinicaland neuroradiological evidence of unilateralbrain damage. Mean age was 60-8 in RBD and54-8 in LBD patients (t = 1-99; p = notsignificant) and mean educational level (yearsof schooling) was very similar in patients withright (9-8) and in those with left (9 5) braindamage. The two groups were also wellmatched for cause (in each group vascularpatients represented about 80% of the wholesample) and the intra-hemispheric locus oflesion.

Testing Procedures Four aspects of thepatients' behaviour were considered in ourfirst experiment:1) The presence of a visual field defect, as-sessed by means of a perimetric examination;2) The presence and severity of unilateralspatial neglect, assessed by means of a stan-dard battery comprising tests of: overlappingfigures identification;" searching for animalson a large board;"1 lines cancellation;'2 linesbisection;'3 copying drawings;'4 3) The

incidence and severity of visual extinction;4) The presence of magnetic gaze attraction.For each test used to study visual neglect,

the normative data obtained in controlsubjects distinguished normal from patho-logical performances. Within the latter,arbitrary cut-off points were drawn to distin-guish two levels of severity of hemi-neglect.The following criteria were chosen to define"severe' and "mild to moderate"' forms ofunilateral spatial neglect: a rate of more than40% omissions in the tests of line cancella-tion, copying drawings, overlapping figuresidentification and searching for animals wasconsidered as an index of severe neglect. Adisplacement of the subjective centre exceed-ing 20% of line length in lines bisection taskswas also considered as an index of severeneglect. Conversely, performances character-ised by less than 40% omissions (or by lessthan 20% displacement in lines bisection)were judged as indicative of mild to moderateforms of visual neglect.

Patients were classified as affected by asevere form of unilateral spatial neglect whentheir neglect was scored as severe in at leastthree out of the five tests of the battery. Theywere, however, considered to show mild tomoderate forms of hemi-neglect when theirperformances had been rated as mild tomoderate in at least three out of the five tests.To detect visual extinction and magnetic

gaze attraction toward the unaffected field,patients were submitted to a visual fieldassessment with the confrontation technique.They were seated at a distance of about 1metre from the confronting examiner whoheld the arms outstretched and moved thefingers either in one hemifield or in bothhemifields simultaneously, according to apreviously randomised pattern. The sequenceconsisted of 36 stimuli distributed as follows:nine right and nine left single stimuli, 18double simultaneous stimulations, adminis-tered in the superior or inferior quadrant ofeach hemifield or on the horizontal midline.For 12 RBD and for seven LBD patients ashortened version of 24 stimuli was used. Thesequence was administered twice on a fewoccasions.

Patients were asked to fixate their gaze on theexaminer's nose and to report each movementof the examiner's fingers. Patients were con-sidered to show extinction when at least threeout of 18 stimuli of the double stimulationseries were not detected, whereas the omissionof single stimuli was the exception. Further-more, extinction was obviously also found inpatients with visual field defect (quadrantan-opia or hemianopia), together with a highernumber of omissions of single stimuli appliedto the affected field.

Patients were defined as affected by a severeform of visual extinction when more than 60%of contralateral stimuli were omitted on doublesimultaneous stimulation. Rates of unilateralextinction ranging from 16-60% were con-sidered as mild.

Patients presented magnetic gaze attractionwhen the examiner detected the occurrence of

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Table 1 Incidence of magnetic attraction, visualfield defect (VFD), unilateral spatial neglect and visual extinction(VE) in patients with right and left brain damage. Incidence of VE and relative statistics after having excludedpatients with VFD are reported in brackets

Right brain damage Left brain damage Statistics

Magnetic attraction+ 12 1 chi squared = 6-1 p = 0-013Magnetic attraction - 41 32Total 53 33

Visual field defect + 17 11 chi squared = 0-00 p = 0 30 (n.s.)Visual field defect - 34 22Total 51 33

Unilateral spatial neglect + 40 6 chi squared = 26-8 p < 0 001Unilateral spatial neglect - 13 27Total 53 33

Visual extinction + 39 (23) I5 (4) chi squared = 8-4 (clhi squared = 13-1)Visual extinction- 12 (11) 18 (18) , = 0-004 (p < 0-001)Total 51 (34) 33 (22)

spontaneous, automatic shifts of the patient'seyes toward the side ipsilateral to the lesion,as soon as the arms of the examiner wereoutstretched and before the administration ofthe stimuli. This phenomenon showeddifferent degrees of severity, ranging from a

brief eye shift followed by spontaneous re-engagement offixation point to a gaze deviationwhich occurred for each item of the series ofstimuli, and required verbal command toregain fixation. Patients were classified asshowing magnetic attraction of gaze towardsthe ipsilesional side on the basis of the consis-tency of the phenomenon throughout theexamination; progressively better control onmaintenance of central fixation was acquired asthe examination proceeded.

Results1 Incidence of magnetic gaze attraction, visualfield defect, unilateral spatial neglect and visualextinction in patients with right and left braindamage.Table 1 reports the incidence of magneticattraction, visual field defect, unilateral spatialneglect, and visual extinction in patients withright and left brain damage.On confrontation test, a shift of the eyes

toward the side ipsilateral to the lesionoccurred in 12 of 53 (23%) RBD patients butonly in one of 33 (3%) LBD patient. Themagnetic attraction was brief and reversible inmost patients, but was strong and persistent intwo RBD patients, preventing them fromcorrectly performing the confrontation test andthe perimetric assessment of the visual field

defects. These patients were therefore discar-ded from the statistical analysis concerningthese behavioural defects.The incidence of visual field defect was very

similar in patients with right and left braindamage, as there was a homonymous hemi-anopia or quadrantanopia in 17 of 51 patientswith right brain damage and in 11 of 33 withleft brain damage. A highly significantdifference between the two hemispheric groupswas observed when the incidence of unilateralspatial neglect was taken into account.

Finally, there was a highly significantdifference between RBD and LBD patientswhen the incidence of visual extinction was

considered (and this difference persisted evenwhen patients with visual field defect wereexcluded from analysis).

2 Relationship between magnetic gaze attraction,unilateral spatial neglect, visual extinction andvisualfield defects.To analyse the relationship between magneticattraction, unilateral spatial neglect and visualextinction, we distinguished within the RBDpatients, two levels of severity of visual neglect(mild to moderate versus severe) and two levelsof consistency of visual extinction according tothe criteria described in methods. Table 2reports the incidence of the magnetic attractionin patients with right and left brain damage, asa function of the presence/absence of visualfield defects and of the presence and severity ofvisual extinction and hemi-neglect.Magnetic attraction was almost always found

in patients with severe unilateral spatial neglectand with consistent visual extinction. Less

Table 2 Incidence of magnetic attraction in patients with right and left brain damage as related to the absence orpresence of visualfield defect and mild or severeforms of visual extinction and unilateral spatial neglect

Right brain damage (n = 51) Left brain damage (n = 33)

Magnetic Magnetic Magnetic Magneticattraction - attraction + attraction- attraction +

Visual field defect - 27 7 22 0Visual field defect + 14 3 10 1

Visual extinction - 1 1 1 18 0Visual extinction+ 10 1 7 0Visual extinction + ± 20 8 7 1

Unilateral spatial neglect - 13 0 27 0Unilateral spatial neglect + 12 2 5 1Unilateral spatial neglect + + 16 8 0 0

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striking is the link between magnetic attractionand visual field defect, as seven out of 10 RBDpatients showed magnetic attraction in theabsence of homonymous hemianopia orquadrantanopia.Taken together, these results seem to show

that magnetic gaze attraction and unilateralspatial neglect are highly interconnected. Bothare significantly more frequent in right than inleft brain-damaged patients and a magneticattraction is almost only observed in patientswith severe neglect for the contralateral halfspace.

EXPERIMENT 2The results of experiment 1 showed thatpatients with right brain damage with severeunilateral spatial neglect often present a mag-netic gaze attraction toward stimuli arising inthe right half space. We aimed in experiment 2to check if milder forms of lateral orienting ofattention could be detected in patients with lessstriking signs of unilateral spatial neglect. Ananalysis of the scanning patterns shown bypatients with right and left brain damage while

Figure An itemfrom the Overlapping Figures Test. During the test, the diwhich is shown to the right of the composite diagram, was placedjust below tpattern.

identifying pictures represented in an Overlap-ping Figures Test," was deemed appropriate tosolve this issue. The following hypothesis wasadvanced: if the first component of unilateralspatial neglect consists of an automatic orient-ing ofattention toward the half space ipsilateralto the damaged hemisphere, then: A) Patientswith right brain damage (presenting a higherincidence of unilateral spatial neglect) shouldtend first to identify figures lying in the halfspace ipsilateral to the brain lesion more thanpatients with left brain damage; B) The ten-dency to recognise first figures lying on theright side of the composite diagram shouldprevail in RBD patients with severe manifesta-tions of unilateral spatial neglect, but shouldalso be present in patients with milder forms ofhemi-inattention.

Subjects and MethodsSubjectsThirty five control subjects, 88 patients withright and 64 with left brain damage wereexamined. There was a partial overlap betweenthe two experiments, as 46 patients with rightand 28 with left brain damage who participatedin experiment 1 also entered experiment 2.Control subjects had been admitted to hospitalwith neurological lesions below the brainstemor for symptoms not affecting the CNS. Thelocalisation of lesions of patients with braindamage was determined by neurologicalexamination, EEG and neuroradiological find-ings. No significant difference existed betweencontrol subjects and patients with right or leftbrain damage for age and education; aetiologyand site of lesion of patients with brain damagewere also well matched in the two groups.

11:4 Overlapping Figures Testf::, ~ Six cards (14 x 21 cm) each bearing five

overlapping figures of common objects werepresented one at a time to the subjects at adistance ofapproximately 40 cm, thus subtend-ing less than 20° of the subject's visual field.Each pattern consists of two figures overlap-ping on the right and two on the left side of thecard, all of them overlapping a fifth centrallylocated figure. The first item was used as an

(@j introductory procedure, and the subjects werethen requested to recognise the figures bypointing to identical figures interspersed with"distractors" on a multiple choice board placedjust below the test card. An item from theOverlapping Figures Test is shown in thefigure.Three aspects of the subjects' behaviour

were taken into account in this part of thestudy: 1) The tendency to explore first one sideof the composite diagrams; 2) The presence ofunilateral spatial neglect, evaluated with acriterion intrinsic to the Overlapping FiguresTest; 3) The severity of neglect for figuresplaced on the half space contralateral to the

> damaged hemisphere.1) The tendency to explore first one side of

the overlapping figures was evaluated by re-splay borld, cording the (right or left) space location of the

figure first recognised by the subjects in each of

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Table 3 Mean valuesfor the first choice scores obtainedby control subjects, and by patients with right and leftbrain damage in the Overlapping Figures Test

n Mean (SD)

Control subjects 35 1 40 (1-03)Patients with right brain damage 88 3 28 (1-59)Patients with left brain damage 64 1 01 (1-07)

the five cards forming the test and counting thenumber of first recognitions made on the rightside. The score ranged therefore from 0 (noright sided first choices) to five (five times firstchoices on the right side).

2) The presence of unilateral spatial neglectwas evaluated by considering as affected byhemi-neglect patients who presented one ormore omissions on the side contralateral to thedamaged hemisphere, in the absence of ipsi-lateral omissions and patients who presentedomissions on both sides, but at least twice asoften on the contralateral as on the ipsilateralside."

3) Finally, the severity of hemi-neglect wasassessed as severe when patients were unable toidentify figures lying in the half space con-tralateral to the damaged hemisphere in themajority of items (at least three out of five) andas mild to moderate when patients were able toidentify figures on both sides of space in themajority of items. This distinction aimed tocheck whether a tendency to orient their atten-tion first to the ipsilateral side was also presentin patients with mild forms or no signs ofneglect. Although the Overlapping FiguresTest had already been used in experiment 1,only the presence of neglect was evaluated inthe same way as in that experiment, whereas theseverity of neglect was assessed in a differentmanner. This was because in experiment 1 anoverall evaluation of the severity of neglect wasconsidered appropriate and that severalindependent tasks were used, choosing forsimplicity a similar criterion of assessingseverity across all these tasks. In experiment 2,a more specific aspect of the severity of neglect(namely the capacity to draw information fromboth sides of the stimulus) ought to beevaluated. We needed this procedure to ensurethat at least in patients with mild or moderateneglect, the tendency to first report items on the

Table4 Mean values for thefirst choice scores obtained by control subjects and bypatients with right and left brain damage showing respectively: no neglect, a mild tomoderate neglect, or a severe neglect

Number Mean (SD) One-way ANOVA

Controls 35 1-40 (1-03) F = 31-063RBD USN- 51 2-64 (1.55)

USN+ 26 3-92 (1-35) p < 0-001USN+ + 11 4-72 (0-46)

LBD USN- 57 1-05 (1 10)USN + 7 0-71 (0-75)

Post-hoc statistics (non-orthogonal comparisons):RBD USN- versus Controls F = 2100 p < 001RBD USN + versus Controls F = 61-78 p < 0 01RBD USN + + versus Controls F = 60 29 p < 0-01LBD USN - versus Controls F = 1-70 p nsLBD USN + versus Controls F = 1-78 p ns

right side of the display was due to an earlyorienting of attention toward that side, ratherthan to a complete inability to explore the lefthalf space.The criterion of taking into account in the

majority of items figures also lying in the halfspace contralateral to the damaged hemispherewas considered appropriate to solve thisspecific issue.

Results1 Tendency to identify first figures lying on theright and left side of the composite diagram inpatients with unilateral brain damage and incontrol subjects.Table 3 gives the mean values for the firstchoice scores obtained by the three groups ofsubjects. Results show that RBD patients con-sistently analysed the stimulus pattern by iden-tifying first figures lying on the right side ofspace. This behaviour significantly differs fromthat observed in control subjects and inpatients with left brain damage: both groupsshowed a marked tendency to make their firstchoice on the left side of space and did not differsignificantly from each other.2 Relationships between severity of unilateralneglect and early orienting-of attention.Thirty seven of 88 (42%) RBD patients andseven of 64 (11%) LBD patients showedunilateral spatial neglect according to thecriteria mentioned in methods. Eleven of 37RBD neglect patients showed an almost com-plete inability to identify figures lying in the lefthalf space and showed a severe form of uni-lateral spatial neglect, whereas the other 26RBD neglect patients (and all the LBDpatients) accomplished the task by identifyingfigures on both sides of space and showed amild to moderate form of hemi-neglect. Thedifference between the frequency of unilateralspatial neglect in patients with right and leftbrain damage was highly significant at thestatistical control (chi squared = 17-4, p <0001).Table 4 reports the mean values of the first

choice scores obtained by normal controls andby patients with right and left brain damageshowing: a) no neglect; b) a mild to moderateneglect; c) a severe form of neglect.Data reported in table 4 show that patients

with left brain damage (with and withoutunilateral spatial neglect) are indistinguishablefrom the normal controls, whereas all threegroups of patients with right brain damage(without, with moderate and with severeunilateral spatial neglect) significantly tend tostart their indentification from figures lying onthe right side of space, more than the controls.Also patients with right brain damage who donot make omissions show a statistically sig-nificant tendency to identify first items on theright side of the pattern, compared with controlsubjects.

Legends: RBD = patients with right brain damage; LBD = patients with left brain damage; DiscussionUSN - = patients without unilateral spatial neglect; USN + = patients with mild to modeate rSUlOfsneglect; USN + + = patients with severe neglect. The results of our research strongly suggest

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that a bias in early orienting ofattention towardthe half space ipsilateral to the damaged hemi-sphere represents a mechanism underlyingboth dramatic and less severe forms ofunilateral spatial neglect.

In experiment 1 the phenomenon of mag-netic attraction of gaze toward the unaffectedfield during the confrontation test occurred farmore frequently in patients with right braindamage than in those with left brain damageand was much more strongly associated withsevere hemi-neglect than with homonymoushemianopia. Both these results are at variancewith Cohn's findings which pointed to arelationship between magnetic attraction andvisual field defects6 and suggest that the mag-netic attraction is a part of the most severeforms of unilateral spatial neglect. Further-more, since the gaze orientation toward thehand placed in the half space ipsilateral to thedamaged hemisphere occurred before an actualstimulus was presented, these data show thathemi-neglect cannot be reduced to a difficultyin disengaging attention from its previousfocus. They suggest that a series of events,beginning with an early orienting of attentiontoward the ipsilesional side, followed by adifficulty in disengaging attention from thatside in order to orient it toward the con-tralateral half space, subserves the clinicalsyndrome of unilateral spatial neglect.The results of experiment 2 confirm this and

show that it can be generalised from the severeto the milder forms of hemi-neglect. When wesubstituted a subtler index of lateral orientingof attention (such as, the tendency to identifyfirst the parts of a composite diagram lying justto the right or to the left of the midline) for astrong indicator (such as, an overt gaze devia-tion), the following results were obtained: a)Patients with right brain damage tended toidentify first figures lying on the right side ofthe pattern, whereas the opposite trend wasshown by normal controls and by patients withleft brain damage; b) The tendency to identifyfirst figures lying in the right half space wasparticularly strong in patients with right braindamage with severe unilateral spatial neglect,but was also clear in those with moderate hemi-neglect. Furthermore, even patients with rightbrain damage without clinical signs of uni-lateral spatial neglect on the OverlappingFigures Test tended to identify figures lying onthe right side of the composite pattern sig-nificantly more than control subjects.The tendency to identify first figures lying on

the right side of the pattem was not limited topatients with severe hemi-neglect, but was alsopresent in those with mild or no clinical signs ofhemi-inattention; this is an important meth-odological point. It shows that neglect patientsdo not begin their identification from figureslying on the right side of the diagram simplybecause they limit their exploration to this partof the composite picture, as a similar pattern ofbehaviour is also present in patients with rightbrain damage with mild or no neglect whoidentify first the right-sided figures, but sub-sequently report also the left-sided stimuli.Together, these findings strongly suggest that a

bias in early orienting of attention toward theright half space is an important and frequentcomponent of unilateral spatial neglect shownby patients with right hemisphere damage.Similar conclusions have been recently reachedby Mark, Kooistra and Heilman."5 In an ingen-ious experiment they tested 10 RBD neglectpatients on two versions of a cancellation task.In the control task, patients cancelled lines bydrawing over them, whereas in the experimen-tal task they erased them. Since patients madesignificantly more omissions in the drawing-over condition than in the erasing condition,the authors concluded that in the first conditionneglect was increased by stimuli which stilloccupied the non-neglected half space, over-attracting the patients' attention. Thus theclaim that an attentional bias may account forpart ofunilateral spatial neglect shown by RBDpatients seems supported by data obtained withdifferent methods in different laboratories.

Conversely, the observation that patientswith right brain damage without clinical signsof neglect also tended more than controlsubjects to begin their identification from theright side of space clearly shows that this earlyorientation bias is only the first component of aseries of events involved in the neglect syn-drome. This component almost inevitablyleads to the clinical syndrome of unilateralspatial neglect when it is very strong (as in ourtwo patients with a persistent gaze deviationtoward the extreme right side of space) andwhen it is accompanied by other components ofthe unilateral spatial neglect syndrome. If,however, patients are conscious ofthe tendencyto orient automatically their attention towardone half of space and if therefore they manageto intentionally direct it toward the contra-lateral halfspace, then the early orientation biascan be counterbalanced and patients canachieve a complete space exploration. In thiscase patients invert the left-to-right scanningpattern usually shown by normal controls andby patients with left brain damage and progres-sively extend their exploration from the right tothe left side of space.Thus the results of experiments 1 and 2

clearly support the hypothesis, recently advan-ced by Karnath,'6 that unilateral spatial neglectmust be considered as a multi-componentsyndrome and that the first of its componentsconsists of a spontaneous orienting of attentiontoward the half space ipsilateral to the lesion.Our data also show that this early ipsilateral

orienting of attention is much more frequentand severe in patients with right brain damagethan in those with left brain damage, thusraising the problem of the mechanism underly-ing this asymmetry in orientation bias.

It might seem that Kinsbourne's theory,'7 18viewing neglect as a bias in lateral orientingtendencies, should be the model which best fitsour data. Even this theory, however, seemsunable to fully account for our results. Kins-bourne8views the preponderance of left-sidedover right-sided hemi-neglect as an exaggera-tion of a physiological asymmetry betweenrightward and leftward orienting tendencies.This asymmetry should be present but is very

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subtle in normal subjects and should be mag-nified in patients with brain damage by adisruption of the interhemispheric inhibitionsystems. If this interpretation was correct,normal subjects should show a mild tendencyto orient first their attention to the right-sidedfigures of the Overlapping Figures Task,because of their more powerful rightwardorienting tendencies. This prediction wasrefuted by our results, as normal controlsshowed an early orientation bias, but in thedirection opposite to that anticipated byKinsbourne's theory. They tended more sig-nificantly than it would be expected by chanceto identify first figures lying on the left side ofthe composite diagram (t = -6.289; p <0001).

Further, our results are consistent with thoseobtained by other authors (for example, DeRenzi, Faglioni and Scotti;`9 Chedru, Leblancand Lhermitte,20) who have studied theactivities of visual searching in normal controlsand in patients with unilateral brain damage.Despite the different methods used in theseinvestigations, in each case control subjectsshowed a consistent tendency to begin theiractivity of visual searching from the left side ofthe display.

It is therefore very unlikely that the strikingprevalence in patients with right brain damageof the phenomenon of magnetic gaze attractionand of other subtler indicators of ipsilateralorienting of attention simply reflects the mag-nification of physiological asymmetries inlateral orienting tendencies.

It may be that these major interhemisphericdifferences reflect the selective disruption inpatients with right brain damage of a mechan-ism linked to the orienting reaction. If oneaccepts that this automatic activity might bedisrupted much more by right-sided than byleft-sided lesions, then a series of outcomescould be predicted: a) The field of automaticorienting of attention should be severelyimbalanced by large right hemispheric lesions,so that stimuli arising in the right half spacecould easily capture a patient's attention andautomatically orient the gaze in that direction.Observations consistent with this predictionhave been made by several authors (forexample, Mesulam,21 Riddoch andHumphreys,22 Karnath,'6 De Renzi, Gentilini,Faglioni and Barbieri,4 Marshall andHalligan.5)A rightward orienting behaviour could also

be provoked by non lateralised stimuli or byconditions which act phasically increasing thearousal level and hence activating the orientingtendencies of the patient. The strikingprevalence of magnetic gaze attraction inpatients with right brain damage could beexplained on these grounds. b) The prevalenceof unilateral spatial neglect in patients withright brain damage should be greater in tasksrequiring a partly automatic orienting of atten-tion than in those based on a more intentionalactivity of visual searching. This prediction isalso confirmed by the literature available on theunilateral neglect syndrome (Gainotti, D'Ermeand De Bonis23). The most striking differences

between patients with right and left braindamage have been obtained on tasks (such asdrawing tasks or overlapping figures) whichrequire partly automatic orienting of attentiontoward the parts of the figures lying in theneglected half space, whereas less clear (or evennon significant) interhemispheric differenceshave been obtained on visual searching tasksbased on the active voluntary exploration oflarge parts of extrapersonal space." '92024 c)Finally, the notion of a possible dissociationbetween lost automatic orienting tendenciesand preserved possibility ofintentionally direc-ting attention toward the contralateral halfspace could have important implications for therehabilitation processes.The behavioural difficulties resulting from

an impaired tendency to automatically orientattention toward new or behaviourally relevantstimuli arising on the neglected half spacecould be overcome by teaching the patient topay a deliberate, continuous attention to thatpart of space. Although this rehabilitativestrategy has been explicitly mentioned by onlya few authors (Seron, Deloche and Coyette25),some techniques empirically used in rehabilita-tion programmes probably act through thismechanism. Thus Weinberg et al26 suggestpacing the patient's visual exploration of thecontralateral half space to improve hemi-neglect, but the efficacy of this trainingprocedure probably results from causing a shiftin the patient's scanning strategy, thus forcinghim to pass from a partly automatic to a muchmore controlled use of the scanning eyemovements.

1 Posner MI. Orienting of attention. The VIIth Sir FredericBartlett Lecture. Quart J Exp Psychol 1980;32:3-25.

2 Posner MI, Cohen Y, Rafal RD. Neural system control ofspatial orienting. Phil TransR Soc Lond 1982;298:187-98.

3 Posner MI, Walker JA, Friedrich FA, Rafal RD. Effects ofparietal injury on covert orienting of attention. J Neurosci1984;4:1863-74.

4 De Renzi E, Gentilini M, Faglioni P, Barbieri C. Attentionalshifts towards the rightmost stimuli in patients with leftvisual neglect. Cortex 1989;25:231-7.

5 Marshall JC, Halligan PW. Does the Midsagittal PManePlay Any Privileged Role in "Left" Neglect? Cognitive.Neuropsychology 1989;6(4):403-22.

6 Cohn R. Eyeball movements in homonymous hemianopiafollowing simultaneous bitemporal- object presentation.Neurology 1972;22:12-4.

7 Friedland RP, Weinstein EA. Hemi-inattention and hemi-sphere specialization: introduction and historical review.In: Weinstein EA, FriedlandiRP, eds. Advances inNeurology, 18. New York: Raven Press, 1977.

8 Brain WR. Visual disorientation with special reference tolesions of the right cerebral hemisphere. Brain 1941;64:244-72.

9 Gainotti G, Messerli P, Tissot R. Qualitative analysis ofunilateral spatial neglect in relation to laterality ofcerebrallesion. J Neurol Neurosurg Psychiatry 1972;35:545-50.

10 Heilman KM, Valenstein E, Watson RT. The neglectsyndrome. In: Vinken PJ, Bruyn GJ, eds. Handbook ofclinical neurology, Vol 1. Amsterdam: North Holland,1985:153-83.

11 Gainotti G, D'Erme P, Monteleone D, Silveri MC.Mechanisms of unilateral spatial neglect in relation tolaterality of cerebral lesion. Brain 1986;109:599-612.

12 Albert ML. A simple test of visual neglect. Neurology1973;23:658-64.

13 D'Erme P, De Bonis C, Gainotti G. Influenza dell'emi-inattenzione e dell'emianopsia sui compiti di bisezione dilinee nei pazienti cerebrolesi. Archivio di Psicologia,Neurologia e Psichiatria 1987;48(2):193-207.

14 Gainotti G, D'Erme P, De Bonis C. Aspects cliniques etmecanismes de la negligence visuo-spatiale. Rev Neurol(Paris) 1989;145 (8-9):626-34.

15 MarkVW, Kooistra CA, Heilnan KM. Hemispatial neglectaffected by non-neglected stimuli. Neurology 1988;38:1207-11.

16 Kamath HO. Deficits of attention in acute and recoveredvisual hemi-neglect. Neuropsychologia 1988;20:27-45.

17 Kinsboume M. The mechanisms of hemispheric control of

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Early orientation of attention toward the half space ipsilateral to the lesion in patients with unilateral brain damage

the lateral gradient of attention. In: Rabbitt PMA, DornicS, eds. Attention and performance. London: AcademicPress, 1975.

18 Kinsbourne M. Mechanisms of unilateral neglect. In:Jeannerod M, ed. Neurophysiological and neuropsycho-logical aspects of spatial neglect. Amsterdam: Elsevier,1987:69-86.

19 De Renzi E, Faglioni P, Scotti G. Hemispheric contributionto the exploration of space through the visual and tactilemodality. Cortex 1970;6:191-203.

20 Chedru F, Leblanc M, Lhermitte F. Visual searching innormal and brain-damaged subjects (contribution to thestudy of unilateral inattention). Cortex 1973;9:94- 1i1.

21 Mesulam M. Attention, confusional states and neglect. In:Mesulam MM, ed. Principles of behavioral neurology.Philadelphia: FA Davis, 1985.

22 Riddoch MJ, Humphreys GW. Perceptual and action sys-tems in unilateral visual neglect. In: Jeannerod M, ed.

Neurophysiological and neuropsychological aspects ofspatialneglect. Amsterdam: Elsevier, 1987:151-81.

23 Gainotti G, D'Erme P, De Bonis C. Visual attentiondisrupted in unilateral neglect. in: Brown JW, ed. Neuro-psychology of Visual Perception, Hillsdale. New Jersey:Lawrence Erlbaum, 1989.

24 Colombo A, De Renzi E, Faglioni P. The occurrence ofvisual neglect in patients with unilateral cerebral disease.Cortex 1986;12:221-31.

25 Seron X, Deloche G, Coyette F. A retrospective analysis ofasingle case neglect therapy: a point of theory. In: Seron X,Deloche G, eds. Cognitive approach to neuropsychologicalrehabilitation, Hillsdale, New Jersey: Lawrence Erlbaum,1989.

26 Weinberg J, Diller L, Gordon A, et al. Training sensoryawareness and spatial organization in people with braindamage. Archives of Physical Medicine and Rehabilitation1979;60:491-6.

Depictions of an odysseyby Peter MacKarell.Edited by Sheila Paine.Published by NSEAD, Corsham, Wiltshire.

On the walls of a top floor at Guy's Hospital, London, are a

series ofsmall gouache paintings. Visitors and hospital staffare captivated by the colourful works which painfullyillustrate the impact of optic neuritis on an artist's percep-tion of light and form. This book is a posthumous andtouching tribute to the painter and patient, PeterMacKarell.

In 1980 Peter MacKarell experienced the onset ofmultiple sclerosis to which he succumbed eight years later.The artist's struggle with his illness, his fortitude andpersistently enquiring nature are described in various waysin the book. It is well written, but the text is eclipsed byMacKarell's paintings.The foreword is by Richard Hoggart who was warden of

Goldsmith's College where the artist was a teacher. It is a

warm and generous introduction which describes theartist's "incarceration" in various hospitals, each of whichaffected the artist's creativity. For example, gloom anddespair characterised a period in a ward for the young andchronically disabled. The first chapter by the writer BevisHillier covers the artist's career as an illustrator andcartoonist. The second is by a fellow painter, StanislavFrenkiel, who movingly describes the changing styles,techniques and subjects of the painter as his circumstancesand vision alter with the illness.The last two chapters are by the artist himself. He writes

about the optic neuritis which heralded the onset of hisdisease. He describes the puzzling circumstances ofdeteriorating vision, blindness and recovery. His series ofhighly personal pictures illustrate this experience. A latersequence of pictures painted during convalescence now

hang in the Institute of Ophthalmology.The last chapter contains some excerpts from an illus-

trated journal he kept for his daughter whilst he was in a

nursing home. His decline is all too apparent. In the closingpages he struggles to make sense of the confused images of

s K .~~~'

C.,c

,Q- %14t*%* 4-

Pageswim. "One evening my lad asked me to look up a word in the

French dictionary and I found that I could not make out the printbecause at each point I attempted to focus, the individual letters were

obscured by an infuriating and irritating bouncing grey dot. AlthoughI was alarmed I was somewhat relieved to find I was able to watch the

television pictures on the News at Ten. Somewhat shaken by these

events I went to bed." (From Depictions of an Odyssey, Peter

MacKarell 1990, National Society for Education in Art and Design.)

shape and colour, analysing them with an artist's training,and reflecting fondly on earlier painters who had influencedhim.

Peter MacKarell was a supremely talented artist whomust have been a great inspiration to his family and friends.

T GIBSON

Journal of Neurology, Neurosurgery, and Psychiatry 1991;54:000-000

DEPICTIONS OFAN ODYSSEY

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