Searching with Unilateral Neglect

Searching with Unilateral Neglect

Marina Pavlovskaya1 Haim Ring1 Zeev Groswasser1and Shaul Hochstein2

Abstract

amp We address two longstanding conflicts in the visual searchand unilateral neglect literature by studying feature andconjunction search performance of neglect patients usinglaterally presented search arrays The first issue relates towhether feature search is performed independently ofattention or rather requires lsquolsquospread attentionrsquorsquo If featuresearch is lsquolsquopreattentiversquorsquo it should survive neglect Howeverwe find neglect effects for both feature and conjunctionsearch suggesting that feature search too has an attentionalrequirement The second controversy refers to the space- orobject-based nature of neglect following unilateral right-

hemisphere parietal lobe damage If neglect were a purelyspatial phenomenon then we would expect no detriment inperformance in the right (nonneglect) field and diminishedperformance for the whole left (neglect) field On the otherhand if neglect were purely object-based we would expectdiminished performance on the left side of the search arrayirrespective of its location in the visual field We nowdemonstrate a combination of strong object-based andspace-based neglect effects for conjunction search withlaterally placed element arrays suggesting that these twomechanisms work in tandem amp

INTRODUCTION

There is some controversy as to the nature of neglectfollowing unilateral right hemisphere damage involvingthe parietal lobe Does neglect affect the left side of thevisual field relative egocentric position andor the leftside of each object in the field Furthermore doesneglect have to do only with focusing attention Ifindeed neglect syndrome affects only attentional aspectsof perception then tasks that can be performed withoutattention called lsquolsquopreattentiversquorsquo tasks should be unaf-fected by neglect These questions address the verynature of attention and of feature search Is featuresearch performed preattentively that is independentlyof attention or does it require at least lsquolsquospread atten-tionrsquorsquo The latter alternative would imply that featuresearch performance could be independent of the num-ber of (distractor) elements while it nevertheless re-tains an attentional demand Treisman who performedthe classical studies on feature and conjunction searchand coined the relevant terminology revised her earlieruse of the term preattentive (Treisman amp Gelade 1980)for the more accurate term in her view of lsquolsquodividedrsquorsquo orlsquolsquospreadrsquorsquo attention (Treisman 1988) Nevertheless nu-merous more recent articles use the older terminologyThis issue is not simply semantic It leads to a parallelcontroversy regarding our ability to perform a secondtask simultaneously with feature search If feature

search is preattentive in the sense that it does notrequire allocation of rare resources it should not inter-fere with performance of another task (Braun amp Sagi1990 Braun 1998) Nevertheless some studies reportthat under appropriate conditions interference is seen(Ahissar Laiwand amp Hochstein 2001 Joseph Chun ampNakayama 1997) In line with the possibility of featuresearch having a (spread) attention requirement werecently reported that for eccentrically presented arrayseven feature search has a set-size dependence (Pavlov-skaya Ring Groswasser Keren amp Hochstein 2001) Wereport here confirming results for feature search inneglect patients for both centrally and laterally placedelement arrays

The second issue refers to the space- or object-basednature of neglect (Driver amp Pouget 2000 Behrmann ampTipper 1999 Pouget amp Driver 1999 Pavlovskaya GlassSoroker Blum amp Groswasser 1997) While the neglectsyndrome was originally described in terms of a space-based deficit (Mesulam 1999 Moscovitch amp Behrmann1994 Karnath Christ amp Hartje 1993 Vallar GuarigliaNico amp Bisiach 1993 Farah Brunn Wong Wallace ampCarpenter 1990) later findings argued that neglect wasalso object centered (Vallar 1998 Humphreys OlsonRomani amp Riddoch 1996 Walker 1995 Halligan ampMarshall 1994 Arguin amp Bub 1993 Grabovecky Robert-son amp Treisman 1993 Young Hellawell amp Welsch1992 Driver amp Halligan 1991) or even predominantlyallocentric (Pavlovskaya et al 1997 Tipper amp Behrmann1996 Behrmann amp Moscovitch 1994 Driver amp Halligan1991 Caramazza amp Hills 1990) Most interestingly the

1Loewenstein Rehabilitation Hospital Raanana and Tel AvivUniversity 2Hebrew University

copy 2002 Massachusetts Institu te of Technology Jou rnal of Cogn itive Neuroscience 145 pp 745ndash756

possibility was raised that neglect may simultaneouslyaffect multiple attentional frames of reference (Behr-mann amp Tipper 1999) A recent report by Driver andPouget (2000) opened the question once again by claim-ing that some results suggesting allocentric effects may infact be readily explained by egocentric neglect We nowshow that both space-based and object-based neglecteffects occur for lateral arrays and conjunction search

We tested neglect syndrome patients with both afeature and a conjunction search task as demonstratedin Figure 1 (See Methods) Five neglect patients and sixnormal controls were tested in two sessions each Wefound neglect effects for both feature and conjunctionsearch suggesting that feature search too depends onattention albeit on spread attention and that this typeof attention too is affected by neglect We found space-based neglect effects for both feature and conjunction

search and a strong object-centered neglect effect forconjunction search For feature search there is a com-mon (left or right) degradation of detection perform-ance with target eccentricity added to a large superiorityof performance in the right hemifield For the conjunc-tion task left neglect overrides eccentricity so thatwithin the right hemifield performance is actually betterfurther out (ie more to the right of the array) than it iscentrally In contrast with left hemifield arrays theeccentricity and neglect effects sum to produce anextremely sharp performance slope with eccentricityIn addition object-centered neglect is evident in thepoorer performance on the left side of arrays in the righthemifield compared to the right side of arrays in the leftThus in addition to space-based neglect for eithersearch task there is a strong object-based componentof neglect with the focused attention search task

Figure 1 Schematic diagramof feature (A B) andconjunction (C) search stimuliAn example of the orientationfeature search task stimuluswith a 7 pound 7 array of verticallight bars with (A) and without(B) an odd element oriented at458 from the horizontal A maskcomprising elements each withbars of various orientations(D) was presented followingeach stimulus The conjunctionvisual search task (C) wherethe target was a yellow lineelement with an orientation of608 embedded in a group ofblue elements with the sameorientation (608) and yellowelements with a differentorientation (308) The mask forthe color and conjunction taskswas as in D but with blue andyellow lines Actual stimuli had3 pound 3 5 pound 5 or 7 pound 7 elementsand were placed centrally orlaterally in the visual field

746 Jou rnal of Cogn itive Neuroscience Volum e 14 Nu m ber 5

RESULTS

Feature and Conjunction Search Tasks withCentral Arrays

The first question we addressed is the performance offeature and conjunction search tasks by neglect patientscompared to normal control subjects If neglect has todo only with attention and feature search is a purelypreattentive taskmdashor if neglect impairs only focusedattention and feature search requires only spread atten-tionmdashthen we would expect that feature search per-formance should be quite normal despite neglect since itdoes not require focused attention while performanceon the conjunction task should show severe signs ofneglect when the target is contralateral to the braindamage

Figure 2 displays results for three patients with severeneglect syndrome MP and SS with right hemispherebrain damage (Figure 2a and b) and UL with left hemi-sphere damage (Figure 2c) Specific detailed clinical dataconcerning the patients are included in table format inthe Methods section For comparison we display resultsfor the patient with traumatic brain injury (TBI notshowing unilateral effects Figure 2d) as well as theaverage for six healthy control subjects (Figure 2e)

In these experiments the test array had 49 elements(in a 7 pound 7 array) with the target in 1 of 24 locations (the5 pound 5 central locations excluding the fixation point itself)The array was positioned in the center of the screen withthe central element replacing the fixation cross

Note first that for all control subjects (Figure 2d and e)there is nearly no performance dependence on thetarget laterality (slopes were never significantly differentthan zerolt3 per unit interelement distance from thecenter R2 lt 5)1 Detection (percentage of trials withsubject correctly reporting the presence of the target)was better for feature than for conjunction search (95vs 67 for normal subjects 86 vs 80 for the patientwith TBI) But the stimulus-to-mask onset asynchronies(SOAs) used were entirely different 33ndash150 msec forfeature detection for all subjects 50 ndash250 msec forconjunction search in normal controls 1500ndash3000 msecfor TBI and neglect subjects (up to 10 sec for UL)Feature detection was somewhat better for the controlsubjects than for the patient with TBI

Turning to the three neglect patients we find a dra-matically different picture In each case (Figure 2a ndashc)there is a significant dependence of detection perform-ance on target position As we go from left to right onthe array there is an upward slope for MP and SS (13and 4 per unit interelement distance from the centerfor feature search and 11 and 18 per elementdistance for conjunction search respectively) and adownward slope for UL (iexcl8 and iexcl6 per elementfor feature and conjunction search respectively R

2 gt 6for all neglect patient data) For MP there is poorerperformance for both tasks when the target was on the

left side of the array while for SS there is a strongerdeficit on the left for the conjunction task than for thefeature task Performance is quite acceptable when the

central presentation 7x7

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d

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Figure 2 Performance with central array presentation Results areshown for feature search (filled circles) and conjunction search(open circles) for three neglect subjects (graphs andashc) one subject withdiffuse TBI (d) and average for six normal control subjects (e) all witha 7 pound 7 element array Note strong downward slope towards neglectedhemifield (to the left MP and SS or right UL) but not for TBI ornormal controls There is a considerable deficit for both conjunctionand feature search on the contralesional side of the array Abscissarefers to relative lateral position within the array summing over allvertical positions Absolute levels of feature search results shouldnot be compared with those of conjunction search becausestimulus-to-mask onset asynchronies (SOAs) differed See text

Pavlovskaya et al 747

target was on the right for either feature or conjunctionsearch For UL performance is quite poor in generalwith a slightly stronger dependence on laterality forfeature search

We conclude that there is an effect of neglect also forthe feature search task suggesting that feature search isnot preattentive but rather requires spread attentionand that neglect affects also this type of attention Wewere concerned however that this test did not differ-entiate between space-centered and object-centeredneglect that is between hemifield neglect and hemi-object neglect The elements in the array could be seenas separate objects in and of themselves (Scholl 2001)and patients could be neglecting to attend to those inone hemifield or alternatively the array could be seenas a single object with the subjects neglecting to attendto one half of the object Furthermore even the latteralternative object neglect could be interpreted in twoways with subjects not attending to the half objectwithin the neglected hemifield or with subjects neglect-ing the half object itself wherever it be To differentiatebetween these alternatives we tested patients andcontrols with arrays that were laterally placed withinone or the other hemifield (For a discussion of per-formance with laterally placed arrays see Pavlovskayaet al 2001)

Feature and Conjunction Search Tasks withLaterally Located Arrays

We tested neglect and control subjects with the entirearray in either the left or the right hemifield againtesting them with feature and conjunction search Ifneglect is a purely spatial hemifield phenomenon thenwe expect no detriment to performance in the right(nonneglect) field and diminished performance for thewhole left (neglect) field On the other hand if attentionwere purely object based we would expect diminishedperformance on the left side of the search array irre-spective of its location in the visual field

Three patients all with left hemifield neglect weretested on feature and conjunction search tasks withlaterally located arrays (see Methods)

One patient SS with left neglect was included inboth groups first tested with central array presentationand then with lateral presentation and we analyze firstthis patientrsquos results Figure 3a shows his results forfeature search For either central or left hemifield pre-sentation there is a gradual rise from left to right withperformance being superior for central than for leftpresentation This is a clear sign of the neglect effectPerformance is worse on the left than on the right andworse in the left hemifield than in the center (or right)These results contrast with normal control results whereperformance depends mainly on eccentricity (Figure 2ecentral Figure 5endashh lateral) Thus for central presen-tation best performance of controls is for central array

locations with decreased performance at extreme rightor left array locations (iexcl2 and +2 Figure 2e) For lateralpresentation performance again increases toward 0eccentricity that is improvement is to the right for leftpresentation and towards the left for right presentation(Figure 5e) Returning to SS feature search performancefor the right hemifield should show competition be-tween two effects The eccentricity effect would lead tobetter performance on the left of the array (that is closerto the center of the visual field) and the neglect effectwould lead to better performance on the right of thearray (which is further into the better hemifield and onthe better side of the object) In fact between the twothere is only a small decline to the right of the arraywhich is not significantly different than that of controls(see Figure 5e)2

conjunction test

00

05

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SS

feature search

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SS

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con junction testfeature search

Figure 3 Search performance with central or lateral arraypresentation Results for left-neglect subject SS are shown for featuresearch (top) or conjunction search (bottom) with central arrays(circles) or laterally placed arrays (in all graphs triangles representresults for left hemifield and squares for right hemifield in either casefilled symbols represent data for feature search and open symbols forconjunction search) Note strong downward displacement when thefeature search array was placed in the left hemifield In contrastconjunction search results are quite similar independent of arrayposition suggesting a strong lsquolsquoobject centeredrsquorsquo neglect effect Allgraphs (except Figure 2) present averaged results for different arraysizes and lateral placements


The picture is different for conjunction search Herefor patient SS we find a very small difference betweenthe performance with the array placed centrally orlaterally There is a major gradient of performance fromleft to right Clearly there is left array element neglect inall cases The similar performance for the three presen-tation locations is most directly explained by assumingobject-based neglect It does not matter where the arrayis it matters where on the array the element is foundHowever there is an alternative explanation Perhapswith these long search times (15ndash3 sec) the neglectpatient is able to notice the single object in their visualfield namely the array of elements and to turn theirgaze and explicit attention to the arraymdashand presumablyto the right side of the array Then they are reduced toequivalent situations in all three cases and we wouldexpect no difference in the gradient from left to rightHowever if there is some visual field aspect to neglect atall we would expect it to be harder for this subject toturn their attention to a left hemifield array than to aright hemifield array There is indeed a small but sig-nificant difference between right and left hemifield (orcentral) presentation The lack of a large differencemdashthat is there is a far greater difference between the left

and right positions on the array than there is betweenthe left and right side presentations of the arraymdashiscertainly surprising and may support the object-basedneglect hypothesis

To further test these conclusions we tested twomore neglect patients IZ and RR both also with leftneglect They were tested only with lateral (left andright) presentation Figure 4 left presents their resultsfor feature search For left presentation (triangles)performance improves for elements on the right ofthe feature search array for both subjects as we foundfor SS For right presentation (squares) where weexpect a competition between neglect and eccentricityeffects IZ (like SS) shows more of the eccentricityeffect while RR shows more of the neglect effectexcept for the most extreme point Most dramaticallyhowever there is a strong shift of the curves so that thecurve for left array presentation is far below that forright presentation Thus performance is considerablypoorer in the left neglected hemifield than on theright For the conjunction search task (Figure 4 right)the picture is pretty much the same for these subjectsas for subject SS There is a sharp increase in perform-ance when going from left to right positions in thearray with a small difference between left and rightarray presentation location which is almost always infavor of right presentation

Thus the conclusions concerning neglect in SS arecorroborated in IZ and RR Figure 5 shows averaged datafor the three neglect subjects for left and right arraypresentation and for feature and conjunction searchtasks (Figure 5a and b) Note that feature search ismuch easier in the right hemifield than in the left andthat there is a gradual increase in performance forlocations further to the right of the array for arrays inthe left hemifield and a decreased (or inverted) eccen-tricity effect on the right (Figure 5a) Conjunction searchshows a very large performance dependence on targetlocation within the arraymdasha strong object-centered leftneglect with a somewhat poorer performance for arraysin the left hemifield compared to those in the right(Figure 5b) There is a very significant difference be-tween the data for these neglect subjects and those fornormal subjects (shown in Figure 5e and f )

To elucidate the eccentricity and neglect effects weplot the average data for neglect versus normal subjectsin another way as well In Figure 5c and d (neglectsubjects) and 5g and h (normal controls) we presentthe data by position within the array for left and righthemifields plotted on the left and right sides of thegraph respectively Note the dramatic difference forneglect subjects in the forms of the feature and con-junction search graphs (Figure 5c and d respectively)The feature search plot has a sharp rise to the rightflattening off and slightly falling again only for mosteccentric positions on the right demonstrating aneccentricity effect on both sides but an increased

feature search conjunction test

position on object (distance from center - of elements)

0 0

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05

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SS

00

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IZ

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IZ

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0 00 20 40 6

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Figure 4 Search performance with lateral array presentationResults for 3 left neglect subjects are shown for feature search(leftmdashfilled symbols) and conjunction search (rightmdashopen symbols)with arrays in the left (triangles) or right (squares) hemifield Majoraspects of results of subject SS (Figure 3) are confirmed in othersubjects Note consistent neglect effect even for feature search seen incurve for left hemifield array presentation being shifted dramaticallydownward and having a somewhat stronger slope Subject RR evenshows signs of an upward slope with eccentricity for right hemifieldarraysmdashwhere eccentricity and neglect effects work in oppositedirections For conjunction search slopes are similar with a smallbut consistent shift downward for left hemifield array presentationsuggesting mainly an object-centered neglect effect


eccentricity effect on the left and a reduced effect onthe right In contrast the conjunction data rise from leftto right and fall again dramatically for the left positionsin the right hemifieldmdashthat is for near foveal posi-tionsmdashonly to rise again with more rightward positionsin the array These data may be contrasted with thoseof normal control subjects in Figure 5g and h Forfeature search neglect patients show a strong rise inperformance with position on the array and in spacewhile controls have only a small degradation witheccentricity For conjunction search neglect patientsshow a strong performance dependence on position inthe arraymdashfor either hemifieldmdashwhile controls havethe best performance in the middle of the array (Theslight degradation at locations plusmn2 for conjunctionsearch includes a set-size effect since these points weremeasured only for the 7 pound 7 array while other pointsare averages for the three array sizes Note the absence

of this effect for feature search For the neglect patientsthe set-size effect is present but swamped by object-centered neglect)

We conclude that there is a very significant differ-ence between the performance of neglect subjects andcontrols for lateral array presentation The similarperformance in neglect-syndrome subjects for the threepresentation locations is most directly explained byassuming object-based neglect It does not matterwhere the array is it matters where on the array theelement is found

Object- and Space-Centered Neglect Effects inSearch Task Performance

The above results suggest that there is a strong object-centered neglect effect and a small space-centeredneglect effect for conjunction search in these patients

Figure 5 Search performancewith lateral array presentationmdashcomparing neglect with controlsubjects Averaged results for3 left neglect subjects ofFigure 4 (graphs andashd) arecompared with those for 6control subjects (graphs endashh)for feature search (filledsymbols) and conjunctionsearch (open symbols) and witharrays in the left (triangles) orright (squares) hemifield Inaddition results are replottedwith curves for left hemifieldplaced on the left and those ofthe right hemifield placed onthe right to demonstrate thecomparative overall visual fieldsensitivity for patients andcontrols Note symmetric curvesfor controls and in contrast forneglect patients an overallslope for feature search and arepeated slope for conjunctionsearch The differences betweenthe shapes of the graphs forfeature and conjunction searchmay reflect mainly a space-based effect for feature searchand mainly an object-basedeffect for conjunction search

position on object ( of elements from center)

conjunction test

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tion

corr

ect


We were concerned however that there might be analternative explanation to our results besides the con-clusion of object-centered neglect Perhaps with theselong search times (15ndash30 sec) the neglect patients areable to notice the single object in their visual fieldnamely the array of elements and to turn their gazeand explicit attention to the arraymdashand presumably tothe right side of the array Then they are reduced toequivalent situations in all three cases and we wouldexpect no difference in the gradient from left to rightHowever if there is some visual field aspect to neglectat all we would expect it to be harder for these

subjects to turn their attention to a left hemifield arraythan to a right hemifield array In fact most studieshave found that neglect patients miss objects in theirleft hemifields Furthermore when asked to bisect aline they miss the center Thus if performance for theeccentric arrays depends on patients moving their gazeto the center of the arrays we would expect them tomiss the center

To study the results more thoroughly and to clarifythe strength of the space-centered effect we replot-ted the data not on the basis of position within thearray (as in Figures 3ndash5) but rather on the basis of

Figure 6 Object-centered andspace-centered neglect effectsResults of Figure 5 are replottedon the basis of absoluteposition in space rather thanposition on array thereforeaveraging data for differentarray sizes and lateralplacements on the basis ofcoinciding absolute spatiallocation Note that the abscissafor the left column of thegraphs is the absolute value ofthe eccentricity so that thedownward slope to the rightseen for most graphs reflects aneccentricity effect and theopposing slopes for conjunc-tion search in neglect subjectsreflect a strong object-centeredeffect Still the large shiftdownward for neglect subjectsfor both search types indicatesa strong space-based neglecteffect for both tasks Right sideas in Figure 5 see text InsertTarget positions Each pointindicates a possible targetlocation for arrays with3 pound 3 (squares) 5 pound 5 (circles)or 7 pound 7 (triangles) elementsThe ordinate is the eccentricityof array edge from fixationArrows indicate (nearly)coinciding groups of positionsused for other graphs of thisfigure

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ccen

tric

ity

3x3

5x5

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position in space We averaged the data from differentarray presentations and at three different eccentricitiesand three sizes always taking data for coinciding lat-eral (x-coordinate) positions

The results are displayed in Figure 6andashd for feature andconjunction search for the neglect-syndrome subjectsand in Figure 6endashh for the controls The general featuresof Figure 5andashh are maintained but new characteristicscome to light There is a definite lsquolsquoeccentricityrsquorsquo effect forfeature search as seen in Figure 6cmdashthat is performanceslopes downward with left or right eccentricity (regres-sion slope = 5 and iexcl5 per degree for left and righthemifields respectively) These slopes are very similar tothose seen for normal control subjects in Figure 6e and gFigure 6a also demonstrates the presence of a lsquolsquoneglectrsquorsquoeffect by plotting the two curves one above the other(the x-axis is now the absolute value of the eccentricity)Note that together with the similar slopes (ie similareccentricity effects) there is a large offset of the curvesreflecting a much poorer performance on the left than onthe right for feature search This is in stark contrast to theresults of control subjects as seen in Figure 6e where leftand right hemifield performances are identical

For conjunction search on the other hand there areindeed both space-centered and object-centered neglecteffects The object-centered effect is seen in the strongslope from left to right in both curves (Figure 6d) Notethat for control subjects the slope for the right hemifieldis negative However one can see strong indications of aspace-centered hemifield-neglect effect for conjunctionsearch as well For neglect subjects the slope for the lefthemifield is much stronger than that for the right hemi-field (10 vs 6 per degree) Thus while performancenear the center (eccentricity 2ndash68) is similar for bothhemifields it is much poorer on the left for more distantlocations (5ndash88) as seen in Figure 6b Again this is instrong contrast to the results for normal controls whereperformance as a function of (absolute value of ) eccen-tricity is identical for the two hemifields as demonstra-ted in Figure 6h

Note that even the neglect-syndrome model suggestedby Driver and Pouget (2000) does not work Theyproposed that there might be a single right to leftdownward slope of attention throughout the visual fieldwhich would lead to better performance on the rightthan on the left of an objectmdashwherever it is located Thismodel was seen as explaining many previously reportedresults as resulting from a space-based rather than aninferred object-based neglect (Vallar 1998 Pavlovskayaet al 1997 Humphreys et al 1996 Walker 1995Halligan amp Marshall 1994 Arguin amp Bub 1993 DriverBaylis amp Rafal 1992 Young et al 1992 Driver ampHalligan 1991) However their model would mean thatfor two points in space near but on opposite sides ofcentral fixation there would be better performance onthe right than on the leftmdasheven when they are on objectsplaced in the right versus left hemifields We find the

opposite As seen in Figure 6d for positions between 08and plusmn48 there is considerably better performance to theleft of center than to the right This could only resultfrom object-centered neglect On the other hand thisneglect effect could not derive only from subjects movingtheir gaze to the array center There is also a significantdifference between left and right hemifield performanceboth in average performance and slope with eccentricityThus we conclude that there are both spatial-positionand object-centered neglect effects

DISCUSSION

We addressed two central issues relating to perceptualattention and its dysfunction due to brain damagemdashtheneglect effect Is feature search really preattentive andtherefore immune to neglect effects Are the effects ofattention and its related deficits for example the ne-glect syndrome only space-based or are there insteador in addition object-based attention and object-basedneglect effects

We demonstrate conclusively that feature search isdefinitely susceptible to inattention effects When searcharrays are placed centrally neglect subjects have a moredifficult time finding targets that fall in the neglectedhemi-array When arrays are placed laterally there is atremendous difference between neglect subject per-formance in finding lsquolsquopop-outrsquorsquo targets when the arrayis in their neglected hemifield than when it is in theattended hemifield Note that these results differ some-what from those of other studies but methods usedwere very different as well Riddoch and Humphreys(1987)mdashbilateral displays 23 subjects with visual fielddefect Eglin Robertson and Knight (1989)mdashlong dis-plays with a target always present response for locationof the target Arguin Joanette and Cavanagh (1993)mdashleft hemifield damage very small very lateral arrays allmeasured RT see Driver (1998) We conclude thatlsquolsquofeature searchrsquorsquo should be so named and the termpreattentive search should be avoided as already sug-gested by Treisman (1988) The difference betweenfeature and conjunction search is indeed related toattention not to the need for or to independence ofattention but rather in the type of attention neededFeature search requires spread attention as indicated byits parallel processing mode while conjunction searchrequires focused attention giving it a serial nature andset-size dependence (Treisman 1988) Some recentstudies have found early deficits or delays in detectingchanges in the environment that hamper involuntarytriggering of attention in neglect patients (Losier ampKlein 2001 Deouell Bentin amp Soroker 2000 SpinelliBurr amp Morrone 1994 Spinelli Angelelli De Luca ampBurr 1996) It remains to be seen if these deficits tooare attention related rather than being preattentive

For conjunction search our results confirm and ex-tend those of previous studies (despite the use of


somewhat different methods) For central presentationperformance is superior for targets in the right side ofthe array than for those on the left and for lateralpresentation performance is better for right hemifieldarrays than for left hemifield arrays (Arguin et al 1993Grabovecky et al 1993 Eglin et al 1989 Riddoch ampHumphreys 1987)

As discussed in the Introduction there is a great dealof controversy regarding object-based neglect The issueis extremely important since it reflects the very nature ofattention itself (Scholl 2001 Driver amp Baylis 1998) Arewe able to attend selectively only to specific spatialregionsmdashoften referred to as using a spotlight of atten-tionmdashor are we also capable of attending to a specificobject in our view Furthermore are we able to focus onspecific subregions in our visual fields or are we able tofocus on subparts of objects as well The latter requirestwo selection stages first selection of an object andthen selection of part of an object If neglect subjectssuffer from the inability to disengage attention from theirright hemifield (Posner Walker Friedrich amp Rafal 1984)are they also unable to disengage attention from theright side of (selected) objects Is this inability foundboth for objects placed in their right or their left hemi-fields (Rapcsak Varfaellie Fleet amp Heilman 1989 Bi-siach Luzatti amp Perani 1981 Bowers Leilman amp Vanden Abel 1981) By using an array of elements as anlsquolsquoobjectrsquorsquo we demonstrate that neglect subjects automati-cally select the object if it is in their right hemifield andhave difficulty selecting it if it is in their left Furthermorethey select and attend more to the right side of theobject (array) and have great difficulty with findingconjunction targets located in the left half of the arrayirrespective of whether the array is centrally placed or intheir right or left hemifield We conclude that there isindeed a strong object-centered neglect effect and smallspace-centered neglect effect for conjunction search

METHODS

Stimuli and Tasks

The experimental paradigm is based on a methodconceived by Treisman and Gelade (1980) as developedby Ahissar and Hochstein (1993 1996 1997) and othersTwo basic experimental procedures were used (onseparate days) to test search task abilities The first isdesigned to test the performance of the feature searchtask (pop-out) which does not require focused atten-tion and the other to test subjectsrsquo ability to perform avisual search task involving focused attention the lsquolsquocon-junctionrsquorsquo task

The Feature Search Task (Pop-Ou t)

Stimulus arrays were composed of 3 pound 3 5 pound 5 or 7 pound 7elements so that array sizes were 28 338 and 468 visual

angle respectively The arrays were presented centrallyor in the left or right hemifield at three possibleeccentricities with the array proximal edge at 158 38or 48 (so that array centers for the 3 pound 3 array were at 08258 and 48 and 58 for the 5 pound 5 array at 98 318 and468 and 568 and for the 7 pound 7 array at 98 388 and 538and 638 from the fixation cross) Each stimulus elementwas a light bar subtending 22 pound 10 To avoid periodicityeffects element positions were jittered randomly by upto plusmn40 The distractor elements were vertical light barsand the odd element was oriented at 458 from thehorizontal The odd element was randomly positionedat any location within the array except its border forthe 5 pound 5 and 7 pound 7 arrays Thus the nearest target forlateral presentation (for the nearest 3 pound 3 array) was at188 and the furthest (for the furthest 7 pound 7 array) wasat 768 from fixation Figure 6 (insert) shows possibletarget positions for each array size An example stimulusis illustrated in Figure 1 with an array of 7 pound 7 elementsThe odd element was present on half of the trials(Figure 1A) while on the other half the stimulus arraywas composed only of distractors (Figure 1B) Theobserverrsquos task was to report the presence or absenceof an odd element

A mask followed each stimulus (Figure 1D) com-posed of asterisk-like elements at the grid points ofthe same stimulus lattice (plusmn40 jitter) Mask elementswere superpositions of four lines (vertical horizontaland the two 458 diagonals) two of which coincided withthe test target and distractor orientations

The Conjun ction Visual Search Task

The conjunction visual search task (Figure 1C) is de-signed to require focused attention The odd elementdiffers from half the distractors by one feature (color)and from the other half by another feature (orientation)The target was a yellow line element with an orientationof 608 embedded in an array of blue elements with thesame orientation (608) and yellow elements with anorientation of 308 Other test parameters were the sameas in the case of the feature search task

Trial Temporal Sequence and Data Analysis

Each trial started with the presentation of a fixation crossWhen the observer pressed the ready key the stimulusappeared briefly on the computer monitor (for normalcontrols generally 16 msec for patients 16 ndash 750 msecfor feature search and 250 ndash 5000 msec for the conjunc-tion task) Following a variable delay (SOA) a mask wasdisplayed for 100 msec Finally following a 133-msecdark period the fixation point reappeared while thesubject pressed a response key (top two rows on key-board Yes bottom rows No) A computer tone signaledincorrect responses Stimuli were presented in 24 blocksof 50 trials each with the same stimulus duration SOA


array size and eccentricity Within each block leftrighthemifield target presenceabsence and target location(when present) were interleaved in pseudorandom or-der Detection scores were evaluated for each subject asa function of SOA array size location of odd elementand eccentricity in two hemifields separately We areinterested here in the position of the target when it isdetected or neglected Thus we tally only the proportionof hits for target present and ignore data for targetabsent for which location is irrelevant

Subjects

We tested 5 first-episode stroke patients with unilateralcerebral damage and one patient with TBI all admittedto Loewenstein Hospital for rehabilitation (see Table 1for a detailed description of these subjects) as well as 6normal controls The 5 patients with unilateral damage(3 women 2 men age 38 ndash65 mean 53 years educa-tion level 7ndash18 mean 13 years) had extensive middlecerebral artery infarctions (ischemic in four hemorrha-gic in one right hemisphere SS IZ RR MP left UL)affecting parts of the frontal temporal and parietallobes except SS whose lesion was confined to theparietal lobe and external capsule Occipital lobes andthe geniculo-striate pathways were preserved in allpatients except UL (whose lesion involved the lateraloccipital gyri but not the primary visual cortex) Patientshad normal visual fields (again UL was exceptional inshowing a right upper-quadrant scotoma in perimetricexamination but no effect within the eccentricity rangetested here) Soon after stroke onset all patients man-ifested contralesional neglect in activities of daily livingand performed abnormally on the standardized Behav-ioral Inattention Test for visual neglect (Wilson Cock-burn amp Halligan 1987 cut-off for normality 130 patientrange 63ndash110)

The TBI patient IR (male 25 years old with 12 yearseducation) had repeated brain CT scans at about 1month post injury with no marked focal areas of dam-age The patient became unconscious immediately postinjury and his initial Glasgow coma score was 8 (thisscale with range 3ndash15 is in common use for assessingthe initial severity of coma Teasdale amp Jennett 1974)Upon recovery he had no neglect or aphasia and scored6 on the Rancho Los Amigos Cognitive Scale (a scaleassessing long-term recovery of TBI patients range 1ndash8Hagen Milkmus amp Durham 1979)

Six healthy right-handed subjects with normal or cor-rected-to-normal vision served as controls (age 32ndash62mean 47 years educational level 15ndash18 mean 17 years)Five of them were paid subjects with only limited practicein visual psychophysics and were unaware of the purposeof the experiment The sixth was author M P

Acknowledgments

We thank Drs Nachum Soroker and Marlene Behrmann forhelpful comments This study was supported by grants fromthe Smith Family Laboratory for Collaborative Research inPsychobiology the USndashIsrael Binational Science Foundation(BSF) and the Israel Science Foundation of the Israel Academyof Sciences and Humanities (Center of Excellence grant)

Reprint requests should be sent to Shaul Hochstein Instituteof Life Sciences Hebrew University Jerusalem 91904 Israel orvia e-mail shaulvmshujiacil

Notes

1 We would expect some dependence of performance oneccentricity However these array elements are all quitecentrally located (up to about 28 eccentricity) Part of theexpected effect is also smoothed by plotting performanceversus medial ndashlateral position while averaging over elevationThus position 0 has a mean distance from the center of foveaof 450 while position 2 has an average distance of 1050

Table 1 Patientsrsquo Demographic and Clinical Data

No Patien t Agesex Hand EducMotorIm p

SensoryImp VFD BIT

TAO(weeks) Pathology

1 SS 53M L 18 ++ ++ iexcln 70 16 H Rt P C-P CSO

2 RR 65F R 8 ++ ++ iexcln 68 16 I Rt F T P C-P CSO

3 IZ 38F R 13 ++ ++ iexcln 63 18 I Rt T P C-P CSO

4 MP 58F R 13 ++ ++ iexcln 110 18 I Rt F T P C-P CSO

5 UL 47M L 18 + ++ Rightupper-quadrantscotoman

60 16 I Lt T O

Hand = handedness (R = right L = left) Educ = education (years of formal schooling) Imp = impairment (+ = moderate ++ = severe)VFD = visual field defect (iexcl = no field defect on perimetry test n = hemifield neglect on behavioral inattention test) BIT = BehavioralInattention Test (cut off score for normality 130 maximal score 146 Scores presented were obtained on admission to rehabilitation Patientswere studied later but neglect behavior persisted to this stage) TAO = time after onset of stroke (weeks) when testing began I = ischemicinfarction H = parenchymal hemorrhage Rt = right hemisphere Lt = left hemisphere P = parietal F = frontal T = temporal O = occipitalCSO = centrum semi-ovale C-P = capsular-putaminal region


2 Similarly performance improvement from earlier centralto later lateral testing may overshadow the expected eccen-tricity effect which would lead to better performance withcentral than with right hemifield presentation

REFERENCES

Ahissar M amp Hochstein S (1993) Attentional control of earlyperceptual learning Proceedings of the National Academ yof Science USA 90 5718 ndash5722

Ahissar M amp Hochstein S (1996) Learning pop-outdetection Specificities to stimulus characteristics VisionResearch 36 3487 ndash3500

Ahissar M amp Hochstein S (1997) Task difficulty and thespecificity of perceptual learning Nature 387 401ndash406

Ahissar M Laiwand R amp Hochstein S (2001) Attentionaldemands following perceptual skill training PsychologicalScience 12 56ndash62

Arguin M amp Bub D N (1993) Evidence for an independentstimulus-centered reference frame from a case of visualhemineglect Cortex 29 349 ndash357

Arguin M Joanette Y amp Cavanagh P (1993) Visual searchfor feature and conjunction targets with an attention deficitJou rnal of Cogn itive Neuroscience 5 436 ndash452

Behrmann M amp Moscovitch M (1994) Object-centeredneglect in patients with unilateral neglect Effects ofleftndash right coordinates of objects Jou rnal of Cogn itiveNeuroscience 6 151 ndash155

Behrmann M amp Tipper S T (1999) Attention accessesmultiple reference frames Evidence from visual neglectJou rnal of Experim ental Psychology Hu m an Perceptionand Perform ance 25 83ndash101

Bisiach E Luzatti C amp Perani D (1981) Unilateral neglectrepresentational schema and consciousness Brain 102757 ndash765

Bowers D Leilman K M amp Van den Abel T (1981)Hemi-spacendashVHF compatibility Neuropsychologia 19757 ndash765

Braun J (1998) Vision and attention The role of trainingNature 393 424 ndash425

Braun J amp Sagi D (1990) Vision outside the focus ofattention Perception an d Psychophysics 48 45ndash58

Caramazza A amp Hills A E (1990) Spatial representation ofwords in the brain implied by studies of a unilateral neglectpatient Nature 346 267 ndash269

Deouell L Y Bentin S amp Soroker N (2000) Electrophy-siological evidence for an early (preattentive) informationprocessing deficit in patients with right hemisphere damageand unilateral neglect Brain 123 353 ndash365

Driver J (1998) The neuropsychology of spatial attentionIn H Pashler (Ed) Attention (pp 297ndash340) Hove UKPsychology Press

Driver J amp Baylis G (1998) Attention and visual objectsegmentation In R Parasuraman (Ed) The atten tion brain(pp 299ndash325) Cambridge MIT Press

Driver J Baylis G C amp Rafal R D (1992) Preservedfigurendashground segregation and symmetry perception invisual neglect Nature 360 73ndash75

Driver J amp Halligan P W (1991) Can visual neglect operateon object-centered co-ordinates An affirmative single casestudy Cogn itive Neuropsychology 8 475 ndash496

Driver J amp Pouget A (2000) Object-centered visual neglector relative egocentric neglect Jou rnal of Cogn itiveNeuroscience 12 542 ndash545

Eglin M Robertson L C amp Knight R T (1989) Visual searchperformance in the neglect syndrome Jou rnal of Cogn itiveNeuroscience 1 372 ndash385

Farah M J Brunn J I Wong A B Wallace M Aamp Carpenter P A (1990) Frames of reference for allocatingattention to space Evidence from the neglect syndromeNeuropsychologia 28 335 ndash347

Grabovecky M Robertson L amp Treisman A (1993)Preattentive processes guide visual search Evidence frompatients with unilateral visual neglect Journal of Cogn itiveNeuroscience 5 288 ndash302

Hagen C Milkmus D amp Durham P (1979) Levels ofcognitive functioning In Rehabilitation of the head in juredadu lt Com prehensive physical m anagem ent Downey CAProfessional Staff Association of Rancho Los Amigos Hospital

Halligan P W amp Marshall J C (1994) Toward aprincipled explanation of unilateral neglect Cogn itiveNeuropsychology 11 167 ndash206

Humphreys G W Olson A Romani C amp Riddoch M J(1996) Competitive mechanisms of selection by space andobject A neuropsychological approach In A F KramerM G H Coles amp G D Logan (Eds) Converging operationsin the study of visual selective attention (pp 365ndash393)Washington DC American Psychological Association

Joseph J S Chun M M amp Nakayama K (1997) Attentionalrequirements in a lsquopreattentiversquo feature search task Nature387 805 ndash807

Karnath H O Christ K amp Hartje W (1993) Decrease ofcontralateral neglect by neck muscle vibration and spatialorientation of trunk midline Brain 116 383 ndash396

Losier B J amp Klein R M (2001) A review of the evidencefor a disengage deficit following parietal lobe damageNeuroscience and Biobehavior Review 25 1ndash13

Mesulam M (1999) Spatial attention and neglect Parietalfrontal and cingulate contributions to the mentalrepresentations and attentional targeting of salientextrapersonal events Philosophical Transactions of theRoyal Society of Lon don 54 1325 ndash1346

Moscovitch M amp Behrmann M (1994) Coding of spatialinformation in the somatosensory system Evidence frompatients with neglect following parietal lobe damageJou rnal of Cogn itive Neuroscience 6 151 ndash155

Pavlovskaya M Glass I Soroker N Blum B amp Groswasser Z(1997) Coordinate frame for pattern recognition in unilateralspatial neglect Jou rnal of Cogn itive Neuroscience 9824 ndash834

Pavlovskaya M Ring H Groswasser Z Keren Oamp Hochstein S (2001) Visual search in peripheral visionLearning effect and set-size dependence Spatial Vision 14151 ndash173

Posner M I Walker J A Friedrich F A amp Rafal R D (1984)Effects of parietal lobe injury on covert orienting ofattention Jou rnal of Neuroscience 4 1863 ndash1874

Pouget A amp Driver J (1999) Visual neglect In R Wilsonamp F Keil (Eds) MIT encyclopedia of cogn itive sciencesCambridge MIT Press

Rapcsak S Z Varfaellie M Fleet W S amp Heilman K M(1989) Selective attention in hemispatial neglect Archivesof Neurology 46 178 ndash182

Riddoch M J amp Humphreys G W (1987) Perceptual andaction systems in unilateral visual neglect In M Jeanneford(Ed) Neurophysiological and neuropsychological aspectsof spatial neglect Amsterdam Elsevier

Scholl B J (2001) Objects and attention The state of the artCogn ition 80 1ndash46

Spinelli D Burr D C amp Morrone M C (1994) Spatialneglect is associated with increased latencies of visualevoked potentials Visual Neuroscience 11 909 ndash918

Spinelli D Angelelli P De Luca M amp Burr D C (1996) VEPin neglect patients have longer latencies for luminance butnot for chromatic patterns NeuroReport 7 815ndash819


Teasdale G amp Jennett B (1974) Assessment of coma andimpaired consciousness A practical scale Lancet 13 81ndash84

Tipper S P amp Behrmann M (1996) Object-centered notscene-based visual neglect Jou rnal of Experim entalPsychology Hu m an Perception and Perform ance 221261 ndash1278

Treisman A (1988) Features and objects The fourteenthBartlett memorial lecture Qu arterly Jou rnal ofExperim ental Psychology A 40 201 ndash237

Treisman A amp Gelade G A (1980) A feature integrationtheory of attention Cogn itive Psychology 12 97ndash136

Vallar G (1998) Spatial hemineglect in humans Trends inCogn itive Neuroscience 2 87ndash98

Vallar G Guariglia C Nico D amp Bisiach F (1993) Spatialhemineglect in back space Brain 118 467 ndash472

Walker R (1995) Spatial and object-based neglect Neurocase1 371ndash383

Wilson B Cockburn J amp Halligan P (1987) Developmentof a behavioural test of visual ndashspatial neglect Archives ofPhysical Medicine and Rehabilitation 68 98ndash102

Young A W Hellawell D J amp Welsch J (1992) Neglect andvisual recognition Brain 115 51ndash71


possibility was raised that neglect may simultaneouslyaffect multiple attentional frames of reference (Behr-mann amp Tipper 1999) A recent report by Driver andPouget (2000) opened the question once again by claim-ing that some results suggesting allocentric effects may infact be readily explained by egocentric neglect We nowshow that both space-based and object-based neglecteffects occur for lateral arrays and conjunction search

We tested neglect syndrome patients with both afeature and a conjunction search task as demonstratedin Figure 1 (See Methods) Five neglect patients and sixnormal controls were tested in two sessions each Wefound neglect effects for both feature and conjunctionsearch suggesting that feature search too depends onattention albeit on spread attention and that this typeof attention too is affected by neglect We found space-based neglect effects for both feature and conjunction

search and a strong object-centered neglect effect forconjunction search For feature search there is a com-mon (left or right) degradation of detection perform-ance with target eccentricity added to a large superiorityof performance in the right hemifield For the conjunc-tion task left neglect overrides eccentricity so thatwithin the right hemifield performance is actually betterfurther out (ie more to the right of the array) than it iscentrally In contrast with left hemifield arrays theeccentricity and neglect effects sum to produce anextremely sharp performance slope with eccentricityIn addition object-centered neglect is evident in thepoorer performance on the left side of arrays in the righthemifield compared to the right side of arrays in the leftThus in addition to space-based neglect for eithersearch task there is a strong object-based componentof neglect with the focused attention search task

Figure 1 Schematic diagramof feature (A B) andconjunction (C) search stimuliAn example of the orientationfeature search task stimuluswith a 7 pound 7 array of verticallight bars with (A) and without(B) an odd element oriented at458 from the horizontal A maskcomprising elements each withbars of various orientations(D) was presented followingeach stimulus The conjunctionvisual search task (C) wherethe target was a yellow lineelement with an orientation of608 embedded in a group ofblue elements with the sameorientation (608) and yellowelements with a differentorientation (308) The mask forthe color and conjunction taskswas as in D but with blue andyellow lines Actual stimuli had3 pound 3 5 pound 5 or 7 pound 7 elementsand were placed centrally orlaterally in the visual field


RESULTS










0 0

0 5

1 0

0 0

0 5

1 0

00

05

10


center)

0 0

0 5

1 0

0 0

0 5

1 0

a

b

c

e

feature search

conjunction

d




IR- TBI

6 controls

fra

cti

on

co

rre

ct










conjunction test

00

05

10


SS

feature search

0 0

0 5

1 0

SS

fra

ctio

n

co

rre

ct

LHF

c e n t r a l

RHF

LHF

ce n t r a l

RHF











0 0

0 5

1 0

00

05

10

SS

00

05

10

-2 -1 0 1 2

R R

00

05

10

IZ

00

05

10

00

05

10

-2 - 1 0 1 2

IZ

fra

cti

on

co

rre

ct

0 00 20 40 6

0 81 0

- 2 0 2

LHF RHF LHF RHF

SS

R R










conjunction test

00

05

10

feature search

00

05

10 feature search

0 0

0 5

1 0

conjunction test

00

05

10

conjunction test

00

05

10

-2L H F

-1 0 1 2 -2R H F

-1 0 1 2

feature search

00

05

10feature search

00

05

10

conjunction test

00

05

10

-2 -1 0 1 2

e

f

g

h

3 patients

6 controls

LHF RHF LHF RHF

feature search

d

ca

b

conjunction test

frac

tion

corr

ect






feature search

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

feature search

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

0 2 4 6 8 10

f

feature search

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

-10 -5 0 5 10

feature search

0

02

04

06

08

1

a

b

c

g

h

d


6 controls

3 patients

frac

tio

n c

orr

ect

LHF

RHF

LHF

RHF


e


0

1

2

3

4

5


arra

y ed

ge e

ccen

tric

ity

3x3

5x5

7x7







DISCUSSION







METHODS

Stimuli and Tasks












Subjects




Acknowledgments



Notes




SensoryImp VFD BIT







60 16 I Lt T O




REFERENCES



















































RESULTS










0 0

0 5

1 0

0 0

0 5

1 0

00

05

10


center)

0 0

0 5

1 0

0 0

0 5

1 0

a

b

c

e

feature search

conjunction

d




IR- TBI

6 controls

fra

cti

on

co

rre

ct










conjunction test

00

05

10


SS

feature search

0 0

0 5

1 0

SS

fra

ctio

n

co

rre

ct

LHF

c e n t r a l

RHF

LHF

ce n t r a l

RHF











0 0

0 5

1 0

00

05

10

SS

00

05

10

-2 -1 0 1 2

R R

00

05

10

IZ

00

05

10

00

05

10

-2 - 1 0 1 2

IZ

fra

cti

on

co

rre

ct

0 00 20 40 6

0 81 0

- 2 0 2

LHF RHF LHF RHF

SS

R R










conjunction test

00

05

10

feature search

00

05

10 feature search

0 0

0 5

1 0

conjunction test

00

05

10

conjunction test

00

05

10

-2L H F

-1 0 1 2 -2R H F

-1 0 1 2

feature search

00

05

10feature search

00

05

10

conjunction test

00

05

10

-2 -1 0 1 2

e

f

g

h

3 patients

6 controls

LHF RHF LHF RHF

feature search

d

ca

b

conjunction test

frac

tion

corr

ect






feature search

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

feature search

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

0 2 4 6 8 10

f

feature search

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

-10 -5 0 5 10

feature search

0

02

04

06

08

1

a

b

c

g

h

d


6 controls

3 patients

frac

tio

n c

orr

ect

LHF

RHF

LHF

RHF


e


0

1

2

3

4

5


arra

y ed

ge e

ccen

tric

ity

3x3

5x5

7x7







DISCUSSION







METHODS

Stimuli and Tasks












Subjects




Acknowledgments



Notes




SensoryImp VFD BIT







60 16 I Lt T O




REFERENCES


























































conjunction test

00

05

10


SS

feature search

0 0

0 5

1 0

SS

fra

ctio

n

co

rre

ct

LHF

c e n t r a l

RHF

LHF

ce n t r a l

RHF











0 0

0 5

1 0

00

05

10

SS

00

05

10

-2 -1 0 1 2

R R

00

05

10

IZ

00

05

10

00

05

10

-2 - 1 0 1 2

IZ

fra

cti

on

co

rre

ct

0 00 20 40 6

0 81 0

- 2 0 2

LHF RHF LHF RHF

SS

R R










conjunction test

00

05

10

feature search

00

05

10 feature search

0 0

0 5

1 0

conjunction test

00

05

10

conjunction test

00

05

10

-2L H F

-1 0 1 2 -2R H F

-1 0 1 2

feature search

00

05

10feature search

00

05

10

conjunction test

00

05

10

-2 -1 0 1 2

e

f

g

h

3 patients

6 controls

LHF RHF LHF RHF

feature search

d

ca

b

conjunction test

frac

tion

corr

ect






feature search

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

feature search

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

0 2 4 6 8 10

f

feature search

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

-10 -5 0 5 10

feature search

0

02

04

06

08

1

a

b

c

g

h

d


6 controls

3 patients

frac

tio

n c

orr

ect

LHF

RHF

LHF

RHF


e


0

1

2

3

4

5


arra

y ed

ge e

ccen

tric

ity

3x3

5x5

7x7







DISCUSSION







METHODS

Stimuli and Tasks












Subjects




Acknowledgments



Notes




SensoryImp VFD BIT







60 16 I Lt T O




REFERENCES


























































0 0

0 5

1 0

00

05

10

SS

00

05

10

-2 -1 0 1 2

R R

00

05

10

IZ

00

05

10

00

05

10

-2 - 1 0 1 2

IZ

fra

cti

on

co

rre

ct

0 00 20 40 6

0 81 0

- 2 0 2

LHF RHF LHF RHF

SS

R R










conjunction test

00

05

10

feature search

00

05

10 feature search

0 0

0 5

1 0

conjunction test

00

05

10

conjunction test

00

05

10

-2L H F

-1 0 1 2 -2R H F

-1 0 1 2

feature search

00

05

10feature search

00

05

10

conjunction test

00

05

10

-2 -1 0 1 2

e

f

g

h

3 patients

6 controls

LHF RHF LHF RHF

feature search

d

ca

b

conjunction test

frac

tion

corr

ect






feature search

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

feature search

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

0 2 4 6 8 10

f

feature search

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

-10 -5 0 5 10

feature search

0

02

04

06

08

1

a

b

c

g

h

d


6 controls

3 patients

frac

tio

n c

orr

ect

LHF

RHF

LHF

RHF


e


0

1

2

3

4

5


arra

y ed

ge e

ccen

tric

ity

3x3

5x5

7x7







DISCUSSION







METHODS

Stimuli and Tasks












Subjects




Acknowledgments



Notes




SensoryImp VFD BIT







60 16 I Lt T O




REFERENCES


























































conjunction test

00

05

10

feature search

00

05

10 feature search

0 0

0 5

1 0

conjunction test

00

05

10

conjunction test

00

05

10

-2L H F

-1 0 1 2 -2R H F

-1 0 1 2

feature search

00

05

10feature search

00

05

10

conjunction test

00

05

10

-2 -1 0 1 2

e

f

g

h

3 patients

6 controls

LHF RHF LHF RHF

feature search

d

ca

b

conjunction test

frac

tion

corr

ect






feature search

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

feature search

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

0 2 4 6 8 10

f

feature search

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

-10 -5 0 5 10

feature search

0

02

04

06

08

1

a

b

c

g

h

d


6 controls

3 patients

frac

tio

n c

orr

ect

LHF

RHF

LHF

RHF


e


0

1

2

3

4

5


arra

y ed

ge e

ccen

tric

ity

3x3

5x5

7x7







DISCUSSION







METHODS

Stimuli and Tasks












Subjects




Acknowledgments



Notes




SensoryImp VFD BIT







60 16 I Lt T O




REFERENCES























































feature search

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

feature search

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

0 2 4 6 8 10

f

feature search

0

02

04

06

08

1

conjunction test

0

02

04

06

08

1

-10 -5 0 5 10

feature search

0

02

04

06

08

1

a

b

c

g

h

d


6 controls

3 patients

frac

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ect

LHF

RHF

LHF

RHF


e


0

1

2

3

4

5


arra

y ed

ge e

ccen

tric

ity

3x3

5x5

7x7







DISCUSSION







METHODS

Stimuli and Tasks












Subjects




Acknowledgments



Notes




SensoryImp VFD BIT







60 16 I Lt T O




REFERENCES
























































DISCUSSION







METHODS

Stimuli and Tasks












Subjects




Acknowledgments



Notes




SensoryImp VFD BIT







60 16 I Lt T O




REFERENCES





















































METHODS

Stimuli and Tasks












Subjects




Acknowledgments



Notes




SensoryImp VFD BIT







60 16 I Lt T O




REFERENCES




















































Subjects




Acknowledgments



Notes




SensoryImp VFD BIT







60 16 I Lt T O




REFERENCES




















































REFERENCES





























































Documents

Searching with Unilateral Neglect