rigid and nonrigid objects in canonical and noncanonical views: hemisphere-specific effects on...

RIGID AND NONRIGID OBJECTS IN CANONICAL ANDNONCANONICAL VIEWS HEMISPHERE-SPECIFIC

EFFECTS ON OBJECT IDENTIFICATION

Bruno LaengUniversity of Tromsoslash Norway

Giovanni Augusto Carlesimo and Carlo CaltagironeIRCCS S Lucia Hospital and Universitagrave Tor Vergata Rome Italy

Rita CapassoIRCCS S Lucia Hospital Universitagrave Tor Vergata and Universitagrave Cattolica Rome Italy

Gabriele MiceliUniversitagrave Cattolica Rome Italy

We compared the performance in a picture-name matching task of 10 patients suffering from left cere-bral hemisphere (LH) damage and 10 from right hemisphere (RH) damage The tasks showed detailedfigures of nonrigid objects (animals) and rigid objects (artefacts) and each object was shown in twoseparate views a noncanonical view (an unusual perspective for rigid objects or a contorted pose for thenonrigid ones) and a canonical view (a typical perspective and pose) Patients with LH damage werespecifically impaired in identifying noncanonical (contorted) poses of nonrigid objects (animals) In asecond picture-name matching experiment using the divided visual field technique normal subjectsmatched names to images of nonrigid shapes (animals) shown in canonical and noncanonical perspec-tives of noncontorted typical poses of the animals It was found that the normal subjectsrsquo RH identifiedthese perspectives better than their LH We conclude that computationally different problems aresolved by different cerebral mechanisms when identifying flexible objects and when identifying rigidobjects We propose the idea that identifying flexible objects when their shapes contort relies on access-ing stored descriptions of objectsrsquo parts and their ldquocategoricalrdquo spatial relations and that both types ofinformation are encoded better by the LH In contrast we propose that the RH is more adept at identi-fying different perspectives of rigid objects (and flexible objects when their shapes do not contort)because of this hemispherersquos superiority in encoding specific global shapes and their views and incoordinate spatial transformation

Very few objects project the same or a highly similarshape image onto our retinae when seen from dif-ferent viewpoints Yet all these different images

must somehow be recognised as arising from thesame object According to one theoretical accountwe recognise objects despite such extraordinary

COGNITIVE NEUROPSYCHOLOGY 2002 19 (8) 697ndash720

Oacute 2002 Psychology Press Ltdhttpwwwtandfcoukjournalspp02643294html DOI10108002643290244000121

697

Requests for reprints should be addressed to Bruno Laeng PhD Department of Psychology University of Tromsoslash Aringsgaringrdveien9 9037 Tromsoslash Norway (Tel +47 77646372 Email brunopsykuitno)

Bruno Laeng was supported by a grant from the Norges Forskningsraringd (No 137350300) Giovanni Augusto Carlesimo and CarloCaltagirone were supported by the S Lucia Hospital Gabriele Miceli and Rita Capasso were supported by a grant from MURST andone from NIH (grant NS 34073)

Q0285ndashCN5000 Nov 11 02 (Mon) [24 pages 1 tables 9 figures 0 footnotes] ndash S endings Edited from Disk [jg] Fig-ures from Word doc file edited into cdr files Figures 4-7 9 [scanned] need to be redrawn at proof stage

variation of viewing conditions by using a ldquostruc-tural descriptionrdquo that specifies parts and their con-nections or spatial relations (eg cf Biederman1985 1987 Marr 1982) However according toanother theoretical view the brain stores a largenumber of images or views for each shape and canretrieve them in a parallel manner (cf Koenderinkamp Van Doorn 1979 Logothetis Pauls amp Poggio1995 Perrett et al 1985 Poggio amp Edelman1990 Tarr amp Buumllthoff 1995 Ullman 1996)

These multiple images belonging to the sameobject would be stored while we experience a shapethrough changes in viewpoint and rotations indepth Thus when the object is flexible anddynamic in shape (eg a human being anumbrella) it would also seem necessary to store thedifferent poses (eg for animate objects the defor-mations of its surface across different types ofmovements or actions cf Kourtzi amp Shiffrar1999) Clearly animals and other flexible objects

LAENG ET AL

698 COGNITIVE NEUROPSYCHOLOGY 2002 19 (8)

Figure 1 Contorted human body (from Lois Greenfield Breaking Bounds London Thames and Hudson 1992)

(eg plants) have joints that can bend or surfacesthat can be stretched creased and folded either byinternal or external forces (eg a cat curling upasleep) Rigid objects also project different imageswith changes of viewpoint but their parts and sur-faces always remain at fixed locations relative to oneanother Thus it would seem that computationallydifferent problems must be solved by a system thatidentifies flexible objects rather than by one thatidentifies rigid objects and different mechanismsmay be used in the two cases

Our hypothesis is that structural descriptionswill be most useful in recognising flexible objectssince parts and surfaces of flexible objects changetheir relative locations when these objects contortand therefore their global shape is altered How-ever some spatial relations descriptions remaininvariant across changes in the relative locations ofparts and surfaces (ie when these objects contort)This spatial information is of an abstract kinddescribing qualitative properties of the connections(that one part is to the side of another or end-to-endconnected etc cf Hummel amp Biederman 1992Richards Dawson amp Whittington 1988) accord-ingly the structure of an object remains invariant atsuch an abstract spatial level and different views ofthe same parts will end up with the same abstractdescription Indeed several theories of structuraldescriptions have posited that qualitative classes ofspatial relations are an integral part of the represen-tation (cf Biederman 1987 Marr 1982 pp 305ndash307) Stephen Kosslyn has labelled such abstractspatial representations ldquocategoricalrdquo because theydefine an equivalence class independent of any pre-cise position (Kosslyn 1987 1994Laeng Chabrisamp Kosslyn in press)

We specifically propose that when the viewedshape does not match a global template in visualmemory as when a familiar flexible object is seen ina novel contortion (eg see Figures 1 and 2) anactive ldquotop-down hypothesis-testingrdquo mechanismwill come into play and this will make use of cate-gorical spatial relations stored with the objectrsquosstructural description in searching for a flexibleobjectrsquos parts in the perceived image Alternativelywhen the object is rigid and this is also seen in anovel or less familiar view (eg see Figure 3) the

visual system could attempt to transform withincoordinate (quantitative) space an internal canoni-cal description of the candidate shape This strategywould also be engaged by a perceptual hypothesisbut it would be characterised by the mental align-ment (eg a rotation) of a stored possibly holisticobjectrsquos model to the perceived image (cf Jolicoeur1985 1988 1990 Tarr 1995 Ullman 1996) Thisvisual matching method would be based on coordi-nate spatial transformations and it would seem aneffective strategy for recognising rigid objects fromnoncanonical views (eg a water bucket seen per-pendicularly from above or from the bottom so thatits main axis is foreshortened) as well as non-canonical perspectives of flexible objects whenthese appear in typical poses (eg see Figure 8)However and crucially this method would not besuccessful in matching a flexible object seen in anunusual contortion

Given these considerations it is then relevant tonote that parts and categorical spatial relationsamong them are both encoded better by the leftcerebral hemisphere (LH) than the right hemi-sphere (RH) Studies of patients with unilateralbrain damage have revealed a LH selective deficit inthe encoding of constituent parts of objects andnormal subjects can encode local elements of a hier-archical display (cf Navon 1977) better when thestimuli are presented in the right visual field (henceencoded initially by the LH) than in the left visualfield (Delis Robertson amp Efron 1986 Robertsonamp Delis 1986 Robertson amp Lamb 1991 VanKleeck 1989) Moreover there is evidence fromclinical and normal lateralisation studies and brainimaging studies as well as studies of nonhumanprimates that categorical spatial relations represen-tations are encoded better by the LH (eg Baciu etal 1999 Banich amp Federmeier 1999 BruyerScailquin amp Coibon 1997 Deacutepy Fagot ampVauclair 1998 Hellige amp Michimata 1989Kessels Kappelle De Haan amp Postma 2002Kogure amp Hatta 1999 Kosslyn 1987 KosslynChabris Marsolek amp Koenig 1992 Kosslyn et al1989 Laeng 1994 Laeng amp Peters 1995 LaengPeters amp McCabe 1997 Parrot DoyonDemonet amp Cardebat 1999 Trojano et al 2002)In contrast the RHrsquos perceptual specialisations can

COGNITIVE NEUROPSYCHOLOGY 2002 19 (8) 699

CANONICAL AND NONCANONICAL VIEWS

be described as complementary to those of the LHNamely in spatial tasks where it is necessary tospecify the precise metric distances among objectsor parts (also defined as ldquocoordinaterdquo spatial rela-tions Kosslyn 1987) RH damage disrupts perfor-mance (Laeng 1994) Normal subjects also showbetter encoding of this type of spatial relation intheir left visual field (hence by the RH) than in theright visual field (eg Hellige amp Michimata 1989Laeng amp Peters 1995 see Chabris amp Kosslyn1998 for a review) In addition global forms areencoded better when presented in the left visualfield and RH lesions selectively disrupt the memoryof the global form of a hierarchical structure but notof its constituent parts (Delis et al 1986 Robert-son amp Delis 1986 Robertson amp Lamb 1991)Finally there is also evidence that the visual repre-sentations of specific shapes are matched moreeffectively in the RH and that lesions to this hemi-spherersquos temporal lobe disrupt the memory of spe-cific pictures of objects more than lesions to the LH(Marsolek Kosslyn amp Squire 1994a MarsolekSquire Kosslyn amp Lulenski 1994b MetcalfeFunnell amp Gazzaniga 1995 Milner 1968 Phelpsamp Gazzaniga 1992 Vilkki 1987 Warrington1984) Therefore we expect that if people are veryfamiliar with a shape (and likely to have stored it assuch) they identify it more effectively in the RH(Laeng Shah amp Kosslyn 1999)

In the present study we investigate the effects ofunilateral brain damage on the recognition ofnonrigid objects (animals) as well as of rigid objects(artefacts) seen at different perspectives or posesBased on the evidence mentioned earlier that theLH is specialised for parts and abstract spatial rela-tion representations we hypothesise that the LHplays a key role in supporting structural descriptionsand that these are most effective for the recognitionof difficult or unusual views but not for the recogni-tion of conventional and familiar views of objectsHence lesions to the LH should cause a deficit inthe recognition of unconventional poses but not ofconventional poses of objects Specifically wehypothesise that the effect of LH damage should bemost clear when patients identify unusual views offlexible objects (eg animals viewed in contortedposes) than when seeing rigid objects (eg

artefacts) even when the latter forms are seen inunusual noncanonical perspectives Previous workby Warrington and colleagues (eg Warrington ampJames 1986 Warrington amp Taylor 1973 1978)has revealed perceptual impairments of patientswith lesions to the RH (especially those with dam-age to the parietal lobe) when they identified rigidobjects seen in noncanonical views Within ouraccount RH damage would also be expected toaffect rigid objectsrsquo recognition In particular dor-sal damage to the RH could affect (1) the extractionof depth cues such as slant or shading from two-dimensional pictures (cf Carmon amp Bechtold1969 Durnford amp Kimura 1971 HumphreySymons Herbert amp Goodale 1993 Layman ampGreen 1988 Sakata Taira Kusunoki amp Tanaka1997) or (2) the mental transformation of a storedmodel to match the input (eg alignment and rota-tion cf Alivisatos amp Petrides 1997 Cohen 1975Corballis amp Sergent 1989 Ditunno amp Mann1990 Harris et al 2000 Layman amp Green 1988Ratcliff 1979 Tagaris et al 1997 Wendt ampRisberg 1994Zacks Rypma Gabrieli Tversky ampGlover 1999) Moreover dorsal lesions to the RHcan result in deficits in coordinate space representa-tion (Laeng 1994) which in turn could affect theability to perform rigid transformations of storedmodels Finally we surmise that ventral lesions tothe RH could disrupt either the memory for specificviews of objects or the matching of the objectrsquos per-ceptual image to stored viewer-centred global rep-resentations of the same object (or of an object inthe same class cf Tarr amp Pinker 1989)

EXPERIMENT 1

Two groups of unilaterally damaged patients and agroup of control subjects were examined in two pic-ture-name matching tasks where objects appearedin either the canonical view or in one noncanonicalview In each trial a name was presented along withthe picture half of the time the names matched theobjects and half of the time they named otherobjects Each subject decided whether the wordcorrectly named the picture or not Specifically inthe Animals task subjects saw on a computer screen


LAENG ET AL

figures of individual animals (eg a giraffe) whilehearing words that could be appropriate names forthe pictured objects or not (eg ldquohorserdquo) In someinstances the body position of the animal was unfa-miliar and clearly ldquocontortedrdquo (eg the animalcould bend its torso or limbs thus causing unusualjuxtapositions and occlusions of relevant bodyparts see Figure 2) In the Objects task the subjectssaw figures of common objects (eg a teapot) whileagain hearing words that could be appropriatenames or not (eg ldquofrying panrdquo) In some instancesthe view was either from a perpendicular angle to

the top or bottom of the object so that the projectedshape was noncanonical (ie there were occlusionsof relevant parts as well as foreshortening of theobjectrsquos main axis see examples in Figure 3) Inother instances the view was either from the side orslightly from above so that the most relevant partsas well as the objectrsquos principal axis were clearlyvisible



Table 1 Details of experimental subjects

AreaGroupSubject no of lesion Sex Age

Left-hemisphere lesion1 P+T F 312 P M 593 P F 614 P+T+F F 625 P+T F 646 P+T+F M 687 P M 708 P+T M 719 P+O M 75

10 T+O F 76Right-hemisphere lesion1 T F 572 P F 663 P+T+O M 664 (p) M 675 P+T+F M 686 P M 697 P M 708 P F 709 P+T M 73

10 P+T M 76Control1 - M 312 - F 613 - F 624 - M 665 - M 686 - M 707 - M 708 - F 739 - F 75

10 - M 76

F = frontal lobe T = temporal lobe O = occipital lobe P =parietal lobe (p) = putamen

Canonical Noncanonical

Figure 2 Nonrigid objects In the left column canonical views ofanimals in the right column noncanonical views (contorted poses)of the same animals

LAENG ET AL



Figure 3 Rigid objects In the left column canonical views of artefacts in the right column noncanonical views of the same artefacts

Because we hypothesise that the LH supportsrecognition processes that are essential for the iden-tification of novel images of nonrigid objects we pre-dict that performance should be worse for LHpatients than RH patients (and control subjects) inmatching the name of a nonrigid object or animal to acontortedpose In contrast we hypothesise that eachhemisphere supports recognition processes that arecomplementary for the identification of novelimages of rigid objects therefore we predict lessimpairment in identifying unusual views of artefactsthan animals for both patient groups Because sev-eral of the recognition mechanisms that are sup-ported by RH lateralised processes may be effectivefor rigid object recognition we are also led to predictthat LH patients should be less impaired than RHpatients in the identification of noncanonical imagesof rigid objects Finally we expect that conventionalpictures of either nonrigid or rigid shapes shouldcause no specific problem to any of the unilateralbrain-damaged patient groups since these views areover-learned easily identifiable by definition andlikely to be matched equally well by each hemi-spherersquos pattern recognition processes

Method

Subjects Twenty unilateral stroke patients withlesions confined to one cerebral hemisphereaccording to brain imaging analyses (ie CT andMRI) were recruited in the IRCCS S Lucia Hos-pital and the Gemelli Hospital of the UniversitagraveCattolica (Rome Italy) Ten neurologically normalindividuals (five females and five males) in thesame age group as the patients (mean age = 65 yearsSD = 13) were recruited as controls subjects inTromsoslash Norway Table 1 shows each subjectrsquos agesex and the patientsrsquo area of lesion The two groupsof patients did not differ in terms of age (LH meanage = 637 SD = 129 RH mean age = 68 SD =50) F(1 18) = 11 p lt 32

Stimuli and apparatus The pictures used in theanimal task were the same set of pictures used in astudy by Laeng et al (1999) that is black and whiteline drawings of animals (either engravings or fineink pen drawings) selected from zoology books

(eg Buffon 1993 Harter 1979) These drawingsare realistic depictions in which the correct propor-tions natural texture and shading of the animalsrsquobodies are clearly represented (see Figure 2) InLaeng et alrsquos study three independent judgeschose from several pictures of each animal oneconventional pose in which the animalrsquos bodyappeared in a natural standing position (from eithera side or frac34 ldquocanonical perspectiverdquo cf PalmerRosch amp Chase 1981) and one contorted orhighly unconventional unfamiliar (noncanonical)pose The pictures used in the Objectsrsquo task wereselected from the Tarrlab image database (BrownUniversity) These are computer-rendered picturesof several common objects mostly artefacts (seeFigure 3) Each objectrsquos views were selected accord-ing to the same criterions for the Animal task Allimages were presented in gray-scale at a distance sothat each image occupied approximately 5 degreesof visual angle the animalsrsquo heads towards the rightside of the screen Laeng and colleagues have foundthat the head was most often rated as the mostinformative part of the body for identity judge-ments Animalsrsquo and objectsrsquo names (in Italian orNorwegian) were recorded digitally for auditorypresentations while spoken slowly and clearly bytwo native speakers On foil trials names of dissim-ilar animalsobjects used in the task were pairedwith an inappropriate picture (eg a picture of alion and the name ldquohorserdquo) each name appearedequally often as a distractor and a target The foilfigures in both the Animals and Artefacts taskswere selected on the basis of structural similarity(which also correlates with semantic neighbour-hood) between the perceived and named objects

Procedure Each task was divided in two blocksand these blocks were presented in ABBA orderbeginning with the Animal task for each subjectEach block showed the complete set of picturesonce (ie all animals or artefacts in both views) andpresented the stimuli in the same order howeverthe truth or falsity (50 likelihood) of the namematches for one drawing in one block were reversedin the other block There were no practice trialsSubjects sat upright at a distance of about 45 cmaway from the computer screen For a few RH



patients who had evidence of spatial neglect fromindependent neurological testing the computerscreen was moved about 40 cm towards the rightside of the patientrsquos body midline all patientsreported seeing a stimulus in every trial and gave ayesno response to the verbal match Each trial hadthe following sequence of events (1) a blank screenthe subject initiated a trial by pressing the space barof the computerrsquos keyboard (2) a visual stimulus(eg an animal in a box) appeared in the centre ofthe screen an auditory stimulus (eg an animalname) was presented simultaneously (3) the sub-ject indicated whether the name was appropriate asquickly and accurately as possible by pressing oneof two adjacent keys (B or N) marked ldquoyesrdquo and ldquonordquoin their language The computer recorded eachanswer together with its latency from the onset ofthe picture Following each response the picturewould disappear from the screen and the subjectcould initiate a new trial

Results

We first obtained descriptive statistics for each sub-ject Mean percentage of () errors and responsetimes (RTs) were calculated for each combinationof the factor of View (canonical versus non-canonical) The data were pooled over type ofmatch (yes versus no) since a preliminary analysisshowed that this factor did not interact with any ofthe other factors Data were also pooled over thetwo separate blocks since there was no evidence fora reduction of error rates in the second block Timesfrom trials on which errors occurred were excludedfrom computation of the RTs In addition trialswith RTs longer than 3 SDs from each individualrsquosmean RT for that condition were excluded from allthe statistics (on average 2 of correct responseswere discarded for each of the control subjects and4 of data for both types of patients) The results(mean errors and RTs) for each task (Animalsand Objects) were then analysed with four separaterepeated-measures analyses of variance

Animals taskError rates In the analysis on the mean errorsdata View (canonical versus noncanonical) was

the within-subject factor and Group (LH RHcontrols) the between-subjects factor This analysisrevealed a reliable difference in error rate betweenthe groups F(2 27) = 38 p lt 03 power = 6 Thecontrol subjects committed fewer errors (mean error = 56 SE = 05) than either the LH strokegroup (mean error = 128 SE = 26) or the RHstroke group (mean error = 92 SE = 11) How-ever post hoc Fisherrsquos LSD tests (crit diff = 49)showed that only the LH group differed reliablyfrom the control group (p lt 006) whereas the dif-ference between the LH and RH groupsapproached significance (p lt 08) and the RHpatients did not reliably differ from the control sub-jects (p lt 25) The main effect of View was also sig-nificant F(1 27) = 395 p lt 0001 power = 10 Allsubjects found it more difficult to match labels tononcanonical views (mean error = 126 SE = 17)than canonical views (mean error= 51 SE = 07)

Importantly this analysis of variance revealed asignificant interaction between the factors ofGroup and View F(2 27) = 72 p lt 003 power =9 LH patients showed more difficulty as wewould expect than RH patients and control sub-jects (see Figure 4) in identifying animals innoncanonical contorted poses (LH mean error =194 SE = 41 RH mean error = 111 SE = 16control subjects mean error = 72 SE = 03) Aseparate ANOVA on the mean error rates fornoncanonical views confirmed these effects F(227) = 60 p lt 006 power = 85 Post hoc FisherrsquosLSD tests (crit diff = 74) showed that the LHgroup differed reliably from both the RH group (p lt03) and the control group (p lt 002) whereas theRH patients did not reliably differ from the controlsubjects (p lt 29) In contrast (see Figure 4) therewas no difference between the three groups whenthey viewed canonical or typical poses of animals(control subjects mean error = 40 SE = 04 LHmean error = 61 SE = 17 RH mean error =59 SE = 10) A separate ANOVA on the meanerror rates for canonical views failed to reveal anydifference F(2 27) = 10 p lt 40 power = 2

Response times Similar analyses were performedon the response time data with View (canonical ver-sus noncanonical) as the within-subject factor and

LAENG ET AL


Group (LH RH controls) as the between-subjectsfactor The main effect of Group approached sig-nificance F(2 27) = 29 p lt 07 power = 58 Con-sistent with their high error rate LH patients wereslower than normal subjects in matching names ofanimals to noncanonical poses (LH mean RTs =1943 ms SE = 162 control subjects mean RTs =1572 SE = 36) also consistent with their low errorrate the RH patients (mean RTs = 1792 ms SE =72) were neither slower than the control subjectsnor faster than the LH patients Post hoc FisherrsquosLSD tests (crit diff = 32) confirmed that the LHgroup differed reliably from the control group (p lt02) whereas the RH patients did not reliably differfrom the control subjects (p lt 17) or the LHpatients (p lt 33) The main effect of View was alsosignificant F(1 27) = 79 p lt 002 power = 10Subjects were overall slower in matching labels tononcanonical views (mean RTs = 1940 ms SE =104) than canonical views (mean RTs = 1597 msSE = 55)

Most importantly the analysis of variance onRTs revealed a significant interaction between thefactors of Group and View F(2 27) = 79 p lt 002power = 95 As we predicted LH patients wereslower than RH patients and control subjects inidentifying animals in noncanonical contortedposes (LH mean RTs = 2340 ms SE = 252 RH

mean RTs = 1851 ms SE = 99 control subjectsmean RTs = 1628 ms SE = 45) A separateANOVA on the mean RTs for these noncanonicalviews confirmed these differences F(2 27) = 53p lt 01 power = 80 Post hoc Fisherrsquos LSD tests(crit diff = 469 ms) revealed a reliably slower per-formance for the LH group versus both the RHgroup (p lt 04) and the control group (p lt 004) incontrast with no difference between the RH andthe control subjects (p lt 33) Moreover there wasno difference between the three groups when theyviewed canonical or typical poses of animals (LHmean RTs = 1546 ms SE = 109 RH mean RTs =1732 ms SE = 106 control subjects mean RTs =1515 ms SE = 53) A separate ANOVA on themean RTs for canonical views failed to reveal anydifference F(2 27) = 16 p lt 22 power = 30Figure 5 illustrates these findings

Objects taskError rates Identical analyses to those describedfor the Animals task were applied to the data fromthe Objects task First one repeated measures anal-ysis of variance was performed on the mean errorswith View (canonical versus noncanonical) as thewithin-subject factor and Group (LH RH con-trols) as the between-subjects factor There was areliable difference in error rates betweenthe groups



Figure 4 Animals task Means and standard errors of percenterror rates to canonical and noncanonical views of nonrigid shapesfor the left-hemisphere patients (LH) the right-hemispherepatients (RH) and the control subjects (Ns)

Figure 5 Animals task Means and standard errors of RTs tocanonical and noncanonical views of nonrigid shapes for the lefthemisphere patients (LH) the right hemisphere patients (RH)and the control subjects (Ns)

F(2 27) = 49 p lt 01power = 77The control sub-jects committed fewer errors (mean error = 49SE = 04) than either the LH stroke group (mean error = 76 SE = 11) or the RH stroke group (mean error = 100SE = 15) However in contrast withthe Animals task findings post hoc Fisherrsquos LSDtests (crit diff = 33) showed that only the RHgroup differed reliably from the control group (p lt004) whereas there was no difference between theRH and LH groups (p lt 15) or between the lattergroup and the controls (p lt 11) The main effect ofView was also significant F(1 27) = 534p lt 0001power = 10 All subjects found it more difficult tomatch labels to noncanonical views (mean error =126 SE = 17) than canonical views (mean error= 51 SE = 07)

The analysis of variance revealed also a signifi-cant interaction between the factors of Group andView F(2 27) = 59 p lt 008 power = 84 In con-trast with the previous findings in the Animals taskthe RH patients showed more difficulty than LHpatients or the control subjects (see Figure 6) inmatching labels to artefacts seen in noncanonicalatypical views (LH mean error = 76 SE = 11RH mean error = 100 SE = 15 control sub-jects mean error = 49 SE = 04) A separateANOVA on the mean error rates for just thenoncanonical views confirmed these effect F(2 27)

= 65 p lt 005 power = 88 and post hoc FisherrsquosLSD tests (crit diff = 46) showed that the RHgroup differed reliably from the control group (p lt001) whereas group differences only approachedsignificance for the comparisons of the LH groupand the RH group (p lt 09) or the LH and the con-trol group (p lt 07) There was clearly no differencebetween the three groups when they viewed canon-ical views of these objects (LH mean error = 49SE = 13 RH mean error = 58 SE = 09 controlsubjects mean error = 38 SE = 03) A separateANOVA on the mean error rates for canonicalviews failed to reveal any difference F(2 27) = 11p lt 33

Response times An analysis on the response timedata with View (canonical versus noncanonical) asthe within-subject factor and Group (LH RHcontrols) as the between-subjects factor showed amain effect of Group F(2 27) = 47 p lt 02 power= 48 Post hoc Fisherrsquos LSD tests (crit diff = 204ms) showed that the control group differed reliablyfrom both the LH group (p lt 02) and the RHgroup (p lt 01) but also that the LH and RHgroups were far from showing a difference (p lt 86)Thus LH and RH patients were equally impairedin their performance speed when matching namesof rigid objects to noncanonical poses (LH meanRTs = 1441 ms SE = 76 RH mean RTs = 1459msSE = 62 control subjects mean RTs = 1186 SE =23) The main effect of View was also significantF(1 27) = 671 p lt 0001 power = 10 All subjectswere on average slower in matching labels tononcanonical views (mean RTs = 1474ms SE = 57)than canonical views (mean RTs = 1251 ms SE =34)

We expected an interactive effect between thefactors of Group and View and indeed the analysisconfirmed its presence F(2 27) = 64 p lt 001power = 41 Both patient groups were equallyimpaired in their efficiency in matching labels toobjects seen in noncanonical unusual perspectives(LH mean RTs = 1586 ms SE = 114 RH meanRTs = 1607 ms SE = 87 control subjects meanRTs = 1229 ms SE = 35) A separate ANOVA onthe mean RTs for these noncanonical views con-firmed these differences F(2 27) = 62 p lt 006

LAENG ET AL


Figure 6 Objects task Means and standard errors of percent errorrates to canonical and noncanonical views of rigid shapes for theleft-hemisphere patients (LH) the right-hemisphere patients(RH) and the control subjects (Ns)

power = 57 as well as post hoc Fisherrsquos LSD tests(crit diff = 247 ms) revealed a reliably slower per-formance of both the LH and RH groups (p lt 006and p lt 004 respectively) when compared to thecontrol group (p lt 004) Instead there was no dif-ference between the two groups of patients (p lt86) Also there was no difference between thepatientsrsquo groups and between these and the controlsubjects when they matched canonical views ofthese rigid objects (LH mean RTs = 1297 ms SE =83 RH mean RTs = 1311 ms SE = 61 controlsubjects mean RTs = 1143 ms SE = 24) A separateANOVA on the mean RTs for canonical viewsfailed to reveal any difference F(2 27)= 23 p lt 12power = 028 Figure 7 illustrates these findings

Discussion

We found a specific deficit in LH patients whenanimals in contorted poses were matched to theirnames The deficit cannot be accounted for by aproblem in encoding words or other lexical process-ing per se because the effect was dependent on viewor shape transformations (ie with contortedposes) and there was no deficit in the same patientsin matching labels to canonical views of either ani-mals or objects Instead these findings are consis-tent with the hypothesis that the superior abilities

of the LH in encoding categorical spatial relationsandor parts play a role in the initial identificationof a novel contorted pose of a flexible shape Indeedwe surmise that LH lesions may disrupt the onlyperceptual strategy that is likely to succeed in theseextremely challenging visual conditions

This study may be the first to report the effects ofunilateral brain damage on the perception ofnonrigid or flexible objects Previous research hadexamined perceptual deficits in neurologicalpatients when identifying rigid objects seen eitherin noncanonical or canonical views Warringtonand colleagues (eg Warrington amp James 1986Warrington amp Taylor 1973 1978) observed thatpatients with lesions to the RH (especially thosewith damage to the parietal lobe) had perceptualimpairments in identifying rigid objects when thesewere seen in noncanonical views Their results wereoriginally interpreted in terms of Marrrsquos theory (cfMarr 1982 p 328) that is RH damage causes afailure to derive the correct object-centred refer-ence frame on foreshortened objects Warringtonand James (1986) later argued that some foreshort-ened views can hide several of the objectrsquos ldquofeaturesrdquo(parts) that need to be mapped onto stored struc-tural descriptions in order to achieve identificationHowever this account seems inconsistent with evi-dence from damage to the brain of human and non-human primates These studies implicate theventral system but not the dorsal in visual shaperepresentations (eg Maunsell amp Newsome 1987Ungerleider amp Mishkin 1982) thus it seemsunlikely that damage to the parietal lobe coulddirectly affect the description of features or thememory of objects or partsrsquo representations as seenfrom specific views since pattern recognition neu-rons that are specifically tuned to objects or parts aretypically found in the temporal lobes (cf PerrettOram amp Ashbridge 1998) Therefore it is morelikely that dorsal (eg right parietal) damage inter-feres with procedures that operate in processes thatrequire ldquovisual problem solvingrdquo and that engagedifferent types of visual top-down processingIndeednumerous studies suggest an important roleof the parietal cortex in attention-related processesas well as in the control of eye fixations (eg ColbyDuhamel amp Goldberg 1995 Corbetta 1998



Figure 7 Objects task Means and standard errors of RTs tocanonical and noncanonical views of rigid shapes for the left-hemisphere patients (LH) the right-hemisphere patients (RH)and the control subjects (Ns)

Wojciulik amp Kanwisher 1999) The parietal role inattentional processing (both overt and covert) mayexplain the presence of parietal activations inhuman neuroimaging studies of shape processing(eg Kraut Hart Soher amp Gordon 1997 PriceMooreHumphreys Frachowiak amp Friston 1996)as well as some shape selectivity of parietal singlecells as seen in nonhuman primate studies (egSereno amp Maunsell 1998)

Interestingly Warrington and Taylor (19731978) reported a difference in the error rates of 35LH patients and 39 RH patients when they named20 common objects seen in gray-scale photoimages Each object was shown either in a canonicalview (typically showing an objectrsquos side) or a non-canonical view (typically an end-on view) Thesephotos showed rigid objects or artefacts (eg abucket a ladder a typewriter) although one itemincluded pictures of a kitten (see Warrington1982) In Warrington and Taylorrsquos (1973) studyRH patients made more errors (25) than LHpatients (17) or control subjects (25) How-ever the patientsrsquo latencies in naming the pictureswere not reported Therefore it remains unclearwhether this group of LH patients despite beingmore accurate than RH patients would have shownimpairment in their speed of response (as did thepatients in the present study)

We found that RH patients were less accuratethan LH patients in the recognition of non-canonical views of rigid objects This result repli-cates Warrington and colleaguesrsquo findingsHowever we also found that the two unilateralpatient groups were equally inefficient (ie slowerthan control subjects) in matching names to pic-tures Within our account we expected a LH lesionto impair the top-down hypothesis testing (basedon parts extraction and categorical relations) whilesparing other matching strategies that are moredependent on RH functioning These spared RHperceptual abilities alone may be sufficient for accu-rate recognition of rigid objects eg either byretrieval of the global pattern of specific(noncanonical) views (cf Kosslyn 1994) mappingof the objectrsquos surface depth (cf Marr 1982) ormentally transforming an internal holistic model ofthe rigid shape (cf Tarr amp Pinker 1989 Ullman

1996) As mentioned earlier independent evidencewithin cognitive neuroscience converges in show-ing a superior role of the RH both in surface depthperception and in coordinate mental transforma-tions of shapes

EXPERIMENT 2

A potential problem with the interpretation of thefindings of the previous experiment is that the Ani-mal and Object tasks did not differ solely in terms ofshape properties and their spatial transformations(nonrigid versus rigid) but they also differed interms of their object class (animals versus artefacts)Thus the semantic domains of the stimuli couldhave confounded the observed dissociations Spe-cifically the LH may support a domain-specificknowledge system for living (animate) thingswhereas the RH may support a domain-specificknowledge system for nonliving (inanimate)things

Several neuropsychological studies have investi-gated the selective loss of knowledge about specificcategories of objects (eg animals artefacts foodsfruits vegetables musical instruments etc cfWarrington amp Shallice 1984) In a study with alarge number of brain-damaged patients (N = 30)Damasio and colleagues (Damasio GrabowskiTranel Hichwa amp Damasio 1996) found thatimpairments for both the category of animals andthat of toolswere associated with damage to the LHinfero-temporal areas Caramazza and Shelton(1998) reviewed the neuroanatomical evidence ofcategory-specific deficit studies and concluded thatthe majority of patients showing deficits for livingor animate things had sustained damage to the LHtemporal lobe There are however instances ofpatients (typically recovering from herpes simplexencephalitis) that implicate the RH temporal lobefor a selective deficit for living things (see Saffran ampSchwartz 1994) In contrast there seems to be noevidence pointing to a RH specialisation for thesemantic knowledge of artefacts On the contraryartefact recognition most predominantly engages aLH network (eg Damasio et al 1996 MartinWiggs Ungerleider amp Haxby 1996 Perani et al

LAENG ET AL


1995) Last Gainotti and colleagues (GainottiSilveri Daniele amp Giustolisi 1995)concluded thatpatients who present category impairment on bothverbal and nonverbal tasks almost always showbilateral brain lesions

The available evidence from the (rapidly grow-ing) literature on functional imaging of the humanbrain supports the observation that semantic andlexical processing for animals plants and artefactscan activate regions of temporal lobes Howeverthe results of these neuroimaging studies areambiguous and often difficult to compare In theirPET study Damasio and colleagues (1996) foundthat pictures of animals artefacts and people allactivated (separate) areas within the temporal lobeof the LH Perani and colleagues (1995) as well asMartin and colleagues (1996) found that namingpictures of animals and tools activated areas of theLH temporal lobe Other studies involving namingof visual stimuli have shown similar findings (seeMoore amp Price 1997 Moscovitch Kapur Koumlhleramp Houle 1995 Price et al 1996 Rosier et al1997 Sergent Ohta amp MacDonald 1992Zelkovicz Herbster Nebes Mintun amp Becker1998) In contrast other neuroimaging studies(eg Gauthier Anderson Tarr Skudlarski ampGore 1997 Kawashima et al 2001 Leube ErbGrodd Bartels amp Kircher 2001) have found thatthe RH fusiform cortex was specifically activated inassociation with the naming of animals In an objectdecision task Gerlach Law Gade and Paulson(1999) found that perceiving natural objectsrecruited parts of the RH temporal lobe in a subse-quent study (2000) they also used a categorisationtask and found that whereas the RH was activatedduring object decision the LH was activated duringcategorisation Stewart Meyer Frith andRothwell (2001) sought to obtain convergingevidence for the different rolesof the cerebral hemi-spheres by delivering transcranial magnetic stimu-lation (TMS) to different parts of the brain Theydelivered TMS that selectively interfered with pro-cessing in BA 37 in the LH or RH while subjectsnamed words pseudowords colour patches orSnodgrass and Vanderwart drawings Stewart et alfound that TMS increased naming latency onlyfor the line drawings of objects and only after LH

stimulation The selectivity of the interferenceclearly indicates that the LHrsquos role in object namingdoes not simply reflect phonological and lexicalprocesses (cf Levelt Praamstra Meyer Heleniusamp Salmelin 1998) but also specific types of visualprocessing

Regarding artefacts (eg tools) the evidence ismore consistent since there appears convergencefrom single-case studies and neuroimaging studiesof normal subjects that (temporal) areas of the LHare specifically implicated (eg Damasio et al1996 Ilmberger Rau Noachtar Arnold ampWinkler 2002 Martin et al 1996) Note how-ever that such evidence runs contrary to the find-ings of this study as well as those of previous studieson brain-damaged patientsrsquo identification ofnoncanonical perspectives (eg Warrington ampTaylor 1978) These overall contrasting resultsstrongly suggest that other factors beside ldquocate-goryrdquo could contribute to the observed patterns ofbrain activation and the functional effects oflateralised lesions Such factors may be many forexample task demands and difficulty whetherretrieving semantic nonvisual information or giv-ing a lexical response is required or not the level oftaxonomy of the required identification or lexicalaccess and the subjectsrsquo expertise with the stimuliWe add to this list the perceptual attributes of theparticular stimuli used (ie perspective and forflexible objects whether they appear contorted ornot) as one factor determining which brain mecha-nisms will be functionally implicated in the task

In sum the evidence for the substrates for twosemantic domains of animals and artefacts beingsplit between the two hemispheres is not in itselfvery strong and the LH lateralisation pattern forartefacts runs contrary to the evidence on brain-damaged patientsrsquo identification of noncanonicalperspectives Nevertheless we cannot ignore suchan alternative account and consequently we per-formed a second experiment aimed to tease apartwhether the two hemispheres are differentiallyengaged (1) by the presentation of stimuli belong-ing to one semantic class or (2) by the type of spatialtransformation required when processing the stim-uli In particular if semantic domain is the mostrelevant variable and the previously observed LH



deficit for contorted views of animals reflected therepeated priming of the class ldquoanimalsrdquo then pre-senting rigidly rotated noncanonical views of ani-mals in typical poses should yield once again a LHeffect Alternatively semantic domain may not bethe relevant factor behind these hemisphere-specific effects which are due instead to the type ofspatial transformations then presenting (rigid)rotations of animalsrsquo shapes should yield a RHeffect The two accounts lead to opposite predic-tions and our account would also predict a reversalof the hemisphere-based effects if artefacts wereviewed in contorted shapes However only the pre-diction on rigid rotations of animals was tested inthe present experiment whereas the prediction oncontorted artefacts was not nevertheless only a fewreal-world artefacts are flexible and allow contor-tions (eg umbrellas bicycles some desk lampsand chairs) but all animals allow noncanonicalcoordinate transformation of the same rigid pose

The following experiment makes use of a well-known method for revealing lateralisation of func-tion in normal subjects namely the divided visualfield technique (see Hellige 1993 Springer ampDeutsch 1996) This method relies on showingthat the cerebral hemispheres differ in their ease ofcarrying out different processes That is if the LHperforms one process better than the RH and theRH performs another process better than the LHthen the two processes must rely on distinct under-lying mechanisms If the same mechanism wereused in both cases either one hemisphere wouldperform both processes better or there would be nodifference between the hemispheres Specificallyvisual stimuli appear tachistoscopically in one of thetwo lateral visual hemifields while participantsmaintain central fixation As in Experiment 1 weused a picture-name verification task in which eachpicture was followed by the visual presentation of aname for an animal (half of the time correct) andthe participants decided whether the name wasappropriate for that specific animal Some of thepictures showed the animal from a canonical view(eg a horse standing in its typical four-leggedposition and viewed frontally from a slightlyskewed angle) in contrast some of the picturesshowed the same animal in the same position but

seen in a noncanonical perspective (eg the horseviewed from the rear see Figure 8 for examples)Crucially all of these noncanonical perspectivesrepresent a rigid rotation of a typical or conven-tional pose of each animal as discussed earlier theidentification of these shapes should be most effi-ciently solved by perceptual mechanisms that wehypothesise to depend more prevalently on RHstructures

Method

Subjects Ten right-handed students (fourfemales and six males) at the University of TromsoslashDepartment of Psychology volunteeredas subjectsHandedness was assessed by self-report

Stimuli and apparatus Twenty-two colour-rendered digital drawings of animals were selectedfrom the Viewpoint Premier models online data-base All drawings were realistic depictions (polyg-onal meshes and NURBS models of animate andinanimate objects) in which the correct propor-tions natural texture and shading of the animalsrsquobodies were clearly represented For this experi-ment two views were selected for each of the 22selected species according to the following criteria(1) One drawing depicted a specific view of the ani-mal that was judged by the authors to be ldquoconven-tionalrdquo (ie the body appeared in a natural standingposition and typically as seen from either a sideor frac34 ldquocanonical perspectiverdquo cf Palmer 1999Palmer et al 1981) (2) the other drawing depictedthe animal in the same pose but viewed fromanother angle of perspective (rotated in depth) thatwas judged by the authors to be unconventional andnoncanonical ie a rear view of the animal

Specifically the set of images included an ant-eater bat bee bull camel chicken cockroach dogdolphin eagle elephant elk finch fox goat horseowl penguin pig polar bear reindeer and sharkThese animalsrsquo names were also presented visuallyin Norwegian and in Geneva font (size 24) In foiltrials names of animals from the same visual stim-uli set were paired with an inappropriate picture(eg a picture of a ldquodogrdquo was followed by the name

LAENG ET AL





Figure 8 Examples of rigid rotations of animalsrsquo shapes used in Experiment 3 The left column shows canonical views and the right columnnoncanonical views of the same animalsrsquo shapes

ldquohorserdquo) each name appeared equally often as adistractor and a target

Images were downloaded from the World WideWeb resized by fitting each drawing into the frameof a 7 times 7 cm empty box and edited with AdobePhotoshop software The boundary of the animalrsquosimage was no more than 5 mm from any side of theframe The box with an animal inside could appearin one of two different positions on the central hori-zontal meridian of a PowerBook Macintosh screeneither 27 cm to the left or 27 cm to the right of cen-tral fixation The distance of the screen from theobserver was adjusted so that each image occupiedapproximately 5deg of visual angle The head of theanimal was always toward the screen centre (ierightward for left visual field trials and leftward forright visual field ones) in order to facilitate recogni-tion (details of the head are typically smaller thanthose of other parts of the body and would thereforebenefit from the higher resolution of retinal loca-tions near to the fovea) Two versions of each of thelateralised stimuli were prepared one in each visualfield (which allowed counterbalancing of thelateralised presentations) All sequences of trialsand storage of key presses were controlled byMacLab software (Costin 1988)

Procedure Subjects sat upright and placed theirheads on a chinrest There were no practice trialssubjects were told that they would see drawings andread names of animals and their task was to deter-mine whether the name was appropriate for thatanimal Each trial had the following sequence ofevents (1) a blank screen the subjects would initi-ate a trial by pressing the space bar of the computerrsquoskeyboard (2) a small fixation cross then appeared atthe centre of the screen which remained visible for450 ms the subjects were asked to gaze directly atthe cross and maintain fixation until the end of thetrial (3) a lateralised visual stimulus (ie an animalin a box) appeared for 100 ms to the left or right ofthe fixation cross (4) the written name of an animalappeared centred in the lower portion of the screen(so as to appear in the portion of the screen belowthat occupied by the animalsrsquo images) and over auniform white background (5) the subject indi-cated as quickly and accurately as possible whether

the name of the animal was appropriate by pressingwith the index finger of each hand one of two keysmarked ldquojardquo and ldquoneirdquo (corresponding to the A andAElig keys of the Norwegian keyboard) For half of thesubjects the ldquojardquo label corresponded to a left handresponse whereas for the other subjects it corre-sponded to a right hand response Following eachkey press a blank screen would appear and the sub-ject would initiate a new trial

Results

We first obtained descriptive statistics for each sub-ject Means of errors and response times (RTs)were calculated for each combination of the follow-ing factors View (canonical versus noncanonical)and Hemisphere (LH versus RH) The data werepooled over type of match (correct versus incorrect)and subjectsrsquo groups (left hand versus right handresponse = a correct match) since preliminary anal-yses showed that none of these factors interactedwith any of the other factors Times from trials onwhich errors occurred were excluded from compu-tation of the RTs (about 1 of the trials) and trialswith RTs longer than 3 SDs from each individualrsquosmean RT for that condition were excluded from allthe statistics (also about 1 of the trials)

Response times A repeated-measures analysisof variance with View (canonical versusnoncanonical) and Hemisphere (LH versus RH)as the within-participants variables was performedon RT as the dependent variable Most impor-tantly this analysis revealed the predicted interac-tion between View and Hemisphere F(1 9) =804 p lt 02 power = 72 As expected the sub-jects evaluated noncanonical views faster whenimages were presented initially to the RH (meanRT = 837 ms SD = 132 versus LH mean RT = 912ms SD = 148) as confirmed by a separate t-testt(9) = 27 p lt 03 Instead the subjectsrsquo matchingof names to canonical views of animals did not reli-ably differ between the LH and the RH (RH meanRT = 753 ms SD = 71 LH mean RT = 793 ms SD= 115) t(9) = 14 ns Figure 9 illustrates theseresults The main effect of View was also signifi-

LAENG ET AL


cant F(1 9) = 82 p lt 02 power = 73 Subjectsevaluated canonical views (mean RT = 772 ms SD= 95) faster than the noncanonical views (meanRT = 874 ms SD = 142) The main effect of VisualField failed to reach significance F(1 9) = 23 p =12 power = 33

Error rates A separate repeated-measures analy-sis of variance with View (canonical versusnoncanonical) and Hemisphere (LH versus RH) asthe within-participants variables was performed onthe mean error rates as the dependent variableThe main effect of View was significant F(1 9) =56 p lt 04 power = 56 Subjects made more errorsin matching names to noncanonical views (mean error = 44 SD = 63) than to canonical views (mean error = 75 SD = 79) The main effect of Hemi-sphere approached significance F(1 9) = 48 p lt06 power = 49 Subjects tended to make moreerrors in the LH (mean error = 67 SD = 81)than in the RH (mean error = 52 SD = 64)Similarly the interaction between View and Hemi-sphere approached significance F(1 9) = 39 p lt07 power = 42 Subjects tended to make moreerrors when noncanonical views were presented ini-tially to the LH (mean error = 101SD = 91 ver-sus RH mean error = 48 SD = 58) or whencanonical views were presented to either hemi-sphere (LH mean error = 55 SD = 72RH mean error = 32 SD = 53)

Discussion

Names of animals seen in noncanonicalnoncontorted views were better matched when thepictures were presented initially to the RH (ieafter left visual field presentations) whereas nohemispheric difference was observed for canonicalviews of the same shapes We hypothesised thatnoncanonical perspectives of nonrigid objects in aconventional pose would engage a RH viewer-centred perceptual memory subsystem as well as aRH coordinate spatial transformation subsystemThis prediction was also derived in our originalaccount but crucially runs opposite to the predic-tion of Experiment 1 where nonrigid objects (ani-mals) were shown in contorted poses Thus thefindings of the second experiment are difficult toreconcile with the account that the observed hemi-sphere-specific effects are due to the visual stimulibelonging to a particular semantic domain class orcategory We also note that the results of Experi-ment 1 showed equal performance of either LH orRH patient groups when seeing conventional orcanonical views of either animals or objects and itwas only when the shapes were spatially trans-formed that a differential effect of the lateralisedlesions was observed

A few other divided-fields studies (Humphreyamp Jolicoeur 1993 Sergent amp Lorber 1983 StJohn 1981) have previously attempted to evaluatehemisphere-specific advantages in normal subjectsfor processing different views of an object Novisual differences were found in these studiesHowever null findings in divided visual field stud-ies are common The effects can be fragile andundetectable when the design exceeds an optimalnarrow window of parameters For example StJohnrsquos study lateralised pictures of objects viewed indifferent perspectives (eg a shoe) but the stimulipresentations were longer than the optimal timingto guarantee central fixation Also the choice of thedependent variable seems crucial Humphrey andJolicoeur measured only the percentage of objectsnamed correctly and no RTs were recorded Partialinformation relayed from one hemisphere toanother via the corpus callosum could result inaccurate performance but more sensitive measure-



Figure 9 Divided-fields task Means and standard errors of RTsto left visual field presentations (LVF) and right visual fieldpresentations (RVF) for canonical and noncanonical views of asame animalrsquos pose

ments based on the efficiency (speed) of responseshould have been able to pick up the relative differ-ences in performance (cf Laeng amp Caviness 2001)In the present study the hemisphere-based effectswere detected by the RT measure whereas accuracymerely approached statistical significance

The RH advantage in identifying noncanonicalviews of rigidly rotated animal shapes allows us todocument a double dissociation with anotherdivided visual field study on normal subjects byLaeng et al (1999) which showed drawings of ani-mals in contorted poses (ie the same stimuli weused in Experiment 1) In that study a LH advan-tage was found when subjects first encoded the ani-malsrsquo contorted poses and a RH advantage wasfound for identifications of the same contortedposes after they had become familiar Moreovercorrelation analyses between the subjectsrsquo visual-field asymmetries between (1) matching whole pic-tures to names (2) matching body parts to thewhole body and (3) judging categorical spatial rela-tions between separate objects revealed that thedegree and polarity of lateralisation of categoricalspatial encoding predicted the hemispheric advan-tage in the first time identification of the wholecontorted shapes

GENERAL DISCUSSION

A perceptual impairment was found specifically inLH patients when they matched names of animalsto contorted poses of the animalsrsquo bodies In con-trast RH patients were more inaccurate relative toLH patients when they matched names of artefactswith noncanonical views of such rigid objectsHowever LH patients were as slow as RH patientsin matching noncanonical views of rigid objects Inaddition the two patient groups showed no impair-ment (either in accuracy or in speed of response) inmatching canonical or typical views of either rigidor nonrigid objects Last when patterns of advan-tages or ease of processing for the identification ofnonrigid shapes (animals) were examined in normalsubjects with a divided field task it was found thatthe RH identified noncanonical perspectives ofanimals in conventional (rigid) poses best

We conclude that lateralised damage can disruptparallel perceptual strategies LH damage wouldaffect a top-down hypothesis-testing mechanismbased on parts and relations (structural descrip-tions) which is most useful for the recognition ofnonrigid objects (eg animals) When viewingnovel or unusual configurations (contortions) of aflexible shape this parts-based processing couldprovide an efficient (or even the only successful)recognition scheme To specify this account fur-ther we suggest that when initially viewing a con-torted flexible object a few visible parts of theobject may be able to find a match with stored rep-resentations of parts in visual pattern memory Forexample in a contorted human shape (like thedancerrsquos in Figure 1) a foot a hand or part of thearm may be clearly recognisable even when the posealters the global shape The information availablefrom nonoccluded parts as well as visible spatialrelations among these parts could provide clues asto the identity of the whole If so a strategy forgathering more visual information could be exe-cuted For example we would argue that whenlooking at Figure 1 a global shape subsystem wouldfirst attempt unsuccessfully to find a match At thesame time a series of eye fixations would gatherinformation about salient parts One first eye fixa-tion may be directed to portions of the outlinewhere the contours suggest the presence of a naturalpart (eg the hand see Figure 1) We assume thatparts information is extracted automatically and inparallel based on simple features like convexity (cfDriver amp Baylis 1995 Wolfe amp Bennett 1997)Subsequently the identified parts could activate aninternally stored structural description whichwould act as a perceptual hypothesis (cf Deco ampSchuumlrmann 2000 Rybak Gusakova GolovanPodladchickova amp Shevstova 1998) This storedinformation which contains the complete set ofparts and their arrangement into an abstract struc-ture in concert with the information that the eyefixations feed in about the orientation and size ofthe parts would then formulate a prediction rela-tive to the location of other parts This predictionby taking also into account the current eye positionwould command the shifts of the eyes onto a newlocation so as to focus central vision (and the atten-

LAENG ET AL


tion window) on other candidate parts (eg thearm) Thus predictions from the perceptualhypothesis can be translated cyclically into actionsThis ldquotop-down hypothesis testingrdquo guidance ofseries of fixations would allow in turn a refinementof the perceptual analysis and of further predictionsabout the location of parts The cycle of successivefixations analyses and predictions may thus unfoldin time until sufficient information is gathered toreach an object identification decision (Deco ampSchuumlrmann 2000 Rybak et al 1998)

A ldquotop-down hypothesis testingrdquo mechanismcould also assist in the recognition of rigid shapesalthough it may not be essential for this We foundthat LH lesions were more likely to affect thepatientsrsquo efficiency in speedmdashinstead of accuracymdashfor rigid shape recognition In contrast RHpatients may benefit from the intact LH processingabilities and therefore be able to identify most rigidshapes seen in noncanonical views Interestinglyboth in our study as well as in Warrington and Tay-lorrsquos (1973) the RH patientsrsquo accuracy rates fornoncanonical views were significantly reduced butnever completely abolished For example in theirstudy RH patients were correct in 83 of thenoncanonical views trials and the 13 most impairedRH patients mostly with parietal lesions showed amean correct naming rate of 75 of these ldquouncon-ventionalrdquo views As Warrington and James (1988)have already pointed out the RH parietal lobe maysupport an added or ldquooptional resourcerdquo to severalother mechanisms of visual analysis

In our account information about both theglobal shape and the parts of an object is extractedautomatically and in parallel and once an object hasbeen identified by one subsystem processing is ter-minated readying the system for the next stimulusIn visually familiar and unambiguous circum-stances global shape extraction and immediatematching to stored perceptual templates would be amore efficient strategy than one based on the recog-nition and description of parts (cf Cave amp Kosslyn1989) Hence the two sorts of information (globaland parts-based) are not used to the same extent inall circumstances Crucially if the object and itspose are familiar the entire shape will be matchedas a single representation before the parts-and-

relations processing would reach the sameconclusion

Research on the effects of perspective or pose onobject identification has focused on the perfor-mance of normal subjects (eg Biederman ampGerhardstein 1993 Buumllthoff amp Edelman 1992Jolicoeur 1990 Lawson 1999 Rock amp Di Vita1987 Tarr amp Pinker 1989) A few clinical studieshave examined the effects of brain damage onthe identification of objects seen in noncanonicalviews or other unusual viewing conditions (egBulla-Hellwig Ettlinger Dommasch Ebel ampSkreczeck 1992 Humphreys amp Riddoch 1984Lawson amp Humphreys 1999 Layman amp Greene1988 Warrington amp James 1986 1991Warrington amp Taylor 1973 1978) These indi-cated that damage to dorsal especially parietalareas is likely to result in impairments in recognis-ing noncanonical views Our observations appearconsistent with those of Warrington and colleaguesin that damage to parietal areas can result in objectrsquosidentification impairments We propose that rigidshapes (eg common artefacts) can be recognisedby a variety of perceptual mechanisms (eg mem-ory for specific views transformations in coordinatespace) We also propose that a conventional pose ofa flexible familiar object could benefit from mecha-nisms that perform rigid transformations in coordi-nate space (eg mental rotation or interpolation ofviews) of a shapersquos internal model All of thesemechanisms have been hypothesised to depend onthe processing of ventral and dorsal areas of theRH

Recently neuroimaging studies have specificallyexamined the perspective effects on the activationof brain subsystems In a PET study Kosslyn andcolleagues (1994) found that subjects performing apicture-name matching task of canonical andnoncanonical views of rigid objects showed massiveactivation of areas in the dorsal (spatial relationsencoding) systems Specifically the inferior parietallobe in the RH was active when objects were shownin noncanonical views This brain imaging evidenceconverges with that on the effects of brain damageon noncanonical views of rigid objects as reportedin the present study as well as that gathered byWarrington and colleagues In addition Kosslyn



and colleagues found no selective activation in theLH parietal lobe when subjects saw noncanonicalviews of rigid objects in comparison to the activa-tion found when judging canonical views of thesame objects This finding is also consistent withthe findings of Warrington and Taylor (1973) andWarrington and James (1991) on the effects of LHlesions Our study also appears consistent with suchevidence in that the error rates of our LH patientsfor noncanonical views of artefacts were smallercompared to those of patients with RH lesionsalthough both groups were equally impaired interms of their speed of response or efficiency Onepossibility entertained by Kosslyn and colleagues(1994) is that top-down processing mechanismsrun virtually all the time reflexively and in parallel(in ldquocascaderdquo) even when their engagement is notessential and other mechanisms terminate the pro-cessing before they can contribute to the objectrsquosrecognition

In conclusion properties of the visible shapeappear to determine in a predictable way whichstrategy the visual system will use to identify anobject and in turn which (lateralised) neural sys-tems will be recruited and play a functional role inan object recognition task

Manuscript received 6 November 2000Revised manuscript received 22 November 2001

Revised manuscript accepted 11 June 2002

REFERENCES

Alivisatos B amp Petrides M (1997) Functional activa-tion of the human brain during mental rotationNeuropsychologia 35 111ndash118

Baciu M Koenig O Vernier M-P Bedoin NRubin C amp Segebarth C (1999) Categorical andcoordinate spatial relations fMRI evidence for hemi-spheric specialisation Neuroreport 10 1373ndash1378

Banich MT amp Federmeier KD (1999) Categoricaland metric spatial processes distinguished by taskdemands and practice Journal of Cognitive Neurosci-ence 11 153ndash166

Biederman I (1985) Human image understandingRecent research and a theory Computer VisionGraphics and Image Processing 32 29ndash73

Biederman I (1987) Recognition-by-components Atheory of human image understanding PsychologicalReview 94 115ndash147

Biederman I amp Gerhardstein P (1993) Recognisingdepth-rotated objects Evidence and conditions forthree-dimensional viewpoint invariance Journal ofExperimental Psychology Human Perception andPerformance 19 1162ndash1182

Bruyer R Scailquin JC amp Coibon P (1997) Disso-ciation between categorical and coordinate spatialcomputations Modulation by cerebral hemispherestask properties mode of response and age Brain andCognition 33 245ndash277

Buffon GL (1993) 368 animal illustrations fromBuffonrsquos ldquoNatural historyrdquo New York DoverPublications

Bulla-Hellwig M Ettlinger G Dommasch D EbelE amp Skreczeck W (1992) Impaired visual percep-tual categorization in right-brain-damaged patientsFailure to replicate Cortex 28 261ndash272

Caramazza A amp Shelton JR (1998)Domain-specificknowledge systems in the brain The animate-inanimate distinction Journal of Cognitive Neurosci-ence 10 1ndash34

Carmon A amp Bechtold HP (1969) Dominance ofthe right hemisphere for stereopsis Neuropsychologia7 29ndash40

Cave CB amp Kosslyn SM (1989) The role of partsand spatial relations in object identification Percep-tion 22 229ndash248

Chabris CF amp Kosslyn SM (1998) How do thecerebral hemispheres contribute to encoding spatialrelationships Current Directions in PsychologicalScience 7 8ndash14

Cohen G (1975) Hemispheric differences in the utili-sation of advance information In PM Rabbitt amp SDornic (Eds) Attention and performance V (pp 20ndash32) London Academic Press

Colby CL Duhamel JR amp Goldberg ME (1995)Oculocentric spatial representation in parietal cortexCerebral Cortex 5 470ndash481

Corballis M amp Sergent J (1989) Mental rotation in acommissurotomised subject Neuropsychologia 27585ndash597

Corbetta M (1998) Frontoparietal cortical networksfor directing attention and the eye to visual locationsIdentical independent or overlapping neuralsystems Proceedings of the National Academy ofSciences 95 831ndash838

LAENG ET AL


Costin D (1988) MacLab A Macintosh system forpsychology labs Behavior Research Methods andComputers 20 197ndash200

Damasio H Grabowski TJ Tranel D HichwaRD amp Damasio AR (1996) A neural basis forlexical retrieval Nature 380 499ndash505

Deco G amp Schuumlrmann B (2000) A neuro-cognitivevisual system for object recognition based on testingthe interactive attentional top-down hypothesesPerception 29 1249ndash1264

Delis DC Robertson LC amp Efron R (1986)Hemispheric specialization of memory for visual hier-archical stimuli Neuropsychologia 24 205ndash214

Deacutepy D Fagot J amp Vauclair J (1998) Comparativeassessment of distance processing and hemisphericspecialisation in humans and baboons (Papio papio)Brain and Cognition 38 165ndash182

Ditunno PL amp Mann VA (1990)Right hemispherespecialisation for mental rotation in normals andbrain-damaged subjects Cortex 26 177ndash188

Driver J amp Baylis G (1995) One-side edge assign-ment in vision 2 Part decomposition shape descrip-tion and attention to objects Current Directions inPsychological Science 4 201ndash206

Durnford M amp Kimura D (1971) Right hemispherespecialization for depth perception reflected in visualfield differences Nature 231 394ndash395

Edelman S amp Buumllthoff HH (1992) Orientationdependence in the recognition of familiar and novelviews of three-dimensional objects Vision Research32 2385ndash2400

Gainotti G Silveri MC Daniele A amp Giustolisi L(1995) Neuroanatomical correlates of category-specific semantic disorders A critical survey Memory3 247ndash264

Gauthier I Anderson AW Tarr MJ SkudlarskiP amp Gore JC (1997) Levels of categorisation invisual recognition studied using functionalmagnetic resonance imaging Current Biology 7645ndash651

Gerlach C Law I Gade A amp Paulson OB (1999)Perceptual differentiation and category effects innormal object recognition A PET study Brain 1222519ndash2170

Gerlach C Law I Gade A amp Paulson OB (2000)Categorisation and category effects in normal objectrecognition A PET study Neuropsychologia 381693ndash1703

Harris IM Egan GF Sonkkila C Tochon-Danguy HJ Paxinos G amp Watson JDG

(2000) Selective right parietal lobe activation duringmental rotation Brain 123 65ndash73

Harter J (1979) Animals 1419 copyright-free illustra-tions of mammals birds fish insects etc New YorkDover Publications

Hellige JB (1993) Hemispheric asymmetry CambridgeMA Harvard University Press

Hellige JB amp Michimata C (1989) Categorisationversus distance Hemispheric differences for process-ing spatial information Memory and Cognition 17770ndash776

Hummel JE amp Biederman I (1992) Dynamic bind-ing in a neural network for shape recognition Psycho-logical Review 99 480ndash517

Humphrey GK amp Jolicoeur P (1993) Visual objectidentification Some effects of image foreshorteningmonocular depth cues and visual field on object iden-tification The Quarterly Journal of ExperimentalPsychology 46A 137ndash159

Humphrey GK Symons LA Herbert AM ampGoodale MA (1993) A neurological dissociationbetween shape from shading and shape from edgesBehavioral Brain Research 76 117ndash125

Humphreys GW amp Riddoch MJ (1984) Routes toobject constancy Implications from neurologicalimpairments of object constancy The Quarterly Jour-nal of Experimental Psychology 36A 385ndash415

Ilmberger J Rau S Noachtar S Arnold S ampWinkler P (2002) Naming tools and animalsAsymmetries observed during direct electrical corticalstimulation Neuropsychologia 40 695ndash700

Jolicoeur P (1985) The time to name disoriented natu-ral objects Memory and Cognition 13 289ndash303

Jolicoeur P (1988) Mental rotation and the identifica-tion of natural objects Canadian Journal of Psychology42 461ndash478

Jolicoeur P (1990) Identification of disoriented objectsA dual-systems theory Mind and Language 5 387ndash410

Kawashima R Hatano G Oizumi K Sugiura MFukuda H Itoh K Kato T Nakamura AHatano K amp Kojima S (2001) Different neuralsystems for recognising plants animals and artefactsBrain Research Bulletin 54 313ndash317

Kessels RPC Kappelle LJ De Haan EHF ampPostma A (2002) Lateralisation of spatial-memoryprocesses Evidence on spatial span maze learningand memory for object locations Neuropsychologia40 1465ndash1473



Koenderink JJ amp Van Doorn AJ (1982) The shapeof smooth objects and the way the contours endPerception 11 129ndash137

Kogure T amp Hatta T (1999) Hemisphere specialisa-tion and categorical spatial relations representationsLaterality 4 321ndash331

Kosslyn SM (1987) Seeing and imagining in the cere-bral hemispheres A computational approach Psycho-logical Review 94 148ndash175

KosslynSM (1994) Image and brain Cambridge MAThe MIT Press

KosslynSMAlpert NAThompson WLChabrisCF Rauch SL amp Anderson AK (1994) Iden-tifying objects seen from different viewpoints A PETinvestigation Brain 117 1055ndash1071

Kosslyn SM Chabris CF Marsolek CJ amp KoenigO (1992) Categorical versus coordinate spatial rela-tions Computational analyses and computer simula-tions Journal of Experimental Psychology HumanPerception and Performance 18 562ndash577

Kosslyn SM Koenig O Barrett A Cave CBTang J amp Gabrieli JDE (1989)Evidence for twotypes of spatial representations Hemisphericspecialisation for categorical and coordinate relationsJournal of Experimental Psychology Human Perceptionand Performance 15 723ndash735

Kourtzi Z amp Shiffrar M (1999) The visual represen-tation of three-dimensional rotating objects ActaPsychologica 102 265ndash292

Kraut M Hart Jr J Soher BJ amp Gordon B (1997)Object shape processing in the visual system evaluatedusing functional MRI Neurology 48 1416ndash1420

Laeng B (1994) Lateralisation of categorical and coor-dinate spatial functions A study of unilateral strokepatients Journal of Cognitive Neuroscience 6 189ndash203

Laeng B amp Caviness V (2001) Prosopagnosia as adeficit in encoding curved surface Journal of CognitiveNeuroscience 13 556ndash557

Laeng B Chabris CF amp Kosslyn SM (in press)Asymmetries in encoding spatial relations In RDavidson amp K Hugdahl (Eds) Brain asymmetry(2nd ed) Cambridge MA MIT Press

Laeng B amp Peters M (1995) Cerebral lateralisationfor the processing of spatial coordinates and catego-ries in left- and right-handers Neuropsychologia 33421ndash439

Laeng B Peters M amp McCabe B (1998) Memoryfor locations within regions Spatial biases and visual

hemifield differences Memory and Cognition 26 97ndash107

Laeng B Shah J amp Kosslyn SM (1999) Identifyingobjects in conventional and contorted poses Contri-butions of hemisphere-specific mechanisms Cogni-tion 70 53ndash85

Lawson R (1999) Achieving visual object constancyacross plane rotation and depth rotation ActaPsychologica 102 221ndash245

Lawson R amp Humphreys GW (1999) The effects ofview in depth on the identification of line drawingsand silhouettes of familiar objects Normality andpathology Visual Cognition 6 165ndash195

Layman S amp Greene E (1988)The effect of stroke onobject recognition Brain and Cognition 7 87ndash114

Levelt WJM Praamstra P Meyer AS HeleniusP amp Salmelin R (1998) An MEG study of picturenaming Journal of Cognitive Neuroscience 10 553ndash567

Leube DT Erb M Grodd W Bartels M ampKircher TTJ (2001) Activation of right fronto-temporal cortex characterises the ldquolivingrdquo category insemantic processing Cognitive Brain Research 12425ndash430

Logothetis NK Pauls J amp Poggio T (1995) Shaperepresentation in the inferior temporal cortex ofmonkeys Current Biology 5 552ndash563

Marr D (1982) Vision San Francisco FreemanMarsolek CJ Kosslyn SM amp Squire LR (1994a)

Form-specific visual priming in the right cerebralhemisphere Journal of Experimental PsychologyLearning Memory and Cognition 18 492ndash508

Marsolek CJ Squire LR Kosslyn SM amp LulenskiME (1994b) Form-specific explicit and implicitmemory in the right cerebral hemisphereNeuropsychology 8 588ndash597

Martin A Wiggs CL Ungerleider LG amp HaxbyJV (1996) Neural correlates of category-specificknowledge Nature 379 649ndash652

Maunsell JHR amp Newsome WT (1987) Visualprocessing in monkey extrastriate cortex AnnualReview of Neuroscience 10 363ndash401

Metcalfe J Funnell M amp Gazzaniga MS (1995)Right-hemisphere memory superiority Studies of asplit-brain patient Psychological Science 6 157ndash164

Milner B (1968) Visual recognition and recall afterright temporal lobe excision in man Neuropsychologia6 191ndash209

Moore C amp Price CJ (1997) Category-specificobject-naming differences A functional imaging

LAENG ET AL


study 27th Annual Meeting of the Society for Neurosci-ence 414 5

Moscovitch C Kapur S Koumlhler S amp Houle S(1995) Distinct neural correlates of visual long-termmemory for spatial location and object identity Apositron emission tomography study in humansProceedings of the National Academy of Sciences USA 923721ndash3725

Navon D (1977)Forest before trees The precedence ofglobal features in visual perception Cognitive Psychol-ogy 9 353ndash383

Palmer SE (1981) Vision science Photons to phenomen-ology Cambridge MA MIT Press

Palmer SE (1999)Vision science Cambridge MA TheMIT Press

Palmer SE Rosch E amp Chase P (1981) Canonicalperspective and the perception of objects In J Longamp A Baddeley (Eds) Attention and performance IX(pp 131ndash151) Hillsdale NJ Lawrence ErlbaumAssociates Inc

Parrot M Doyon B Demonet JF amp Cardebat D(1999) Hemispheric preponderance in categoricaland coordinate visual processes Neuropsychologia 371215ndash1225

Perani D Cappa SF Bettinardi V Bressi SGorno-Tempini M Mattarese M et al (1995)Different neural systems for the recognition ofanimals and man-made tools NeuroReport 6 1637ndash1641

Perrett DI Oram MW amp Ashbridge E (1998)Evidence accumulation in cell populations responsiveto faces An account and generalisation of recognitionwithout mental transformations Cognition 67 111ndash145

Perrett DI Smith PA Potter DD Mistlin AJHead AS Milner AD amp Jeeves MA (1985)Visual cells in the temporal cortex sensitive to faceview and gaze direction Proceedings of the Royal Societyof London 223 293ndash317

Phelps E amp Gazzaniga M (1992) Hemisphericdifferences in mnemonic processing The effects ofleft hemisphere interpretation Neuropsychologia 30293ndash297

Poggio T amp Edelman S (1990)A network that learnsto recognise three-dimensional objects Nature 343263

Price CJ Moore CJ Humphreys GWFrackowiak RS amp Friston KJ (1996) The neuralregions sustaining object recognition and naming

Proceeding of the Royal Society London Series B 2631501ndash1507

Ratcliff G (1979) Spatial thought mental rotation andthe right cerebral hemisphere Neuropsychologia 1749ndash54

Richards W Dawson B amp Whittington D (1988)Encoding contour shape by curvature extrema In WRichards (Ed) Natural computation (pp 83ndash98)Cambridge MA MIT Press

Robertson LC amp Delis DC (1986) ldquoPart-wholerdquoprocessing in unilateral brain-damaged patientsDysfunctions of hierarchical organization Neuro-psychologia 24 363ndash370

Robertson LC amp Lamb MR (1991) Neuro-psychological contributions to theories of part-wholeorganization Cognitive Psychology 24 363ndash370

Rock I amp Di Vita J (1987) A case of viewer-centredobject perception Cognitive Psychology 19 280ndash293

Rosier A Cornette L Dupont P Bormans GMichiels J Mortelmans L amp Orban GA (1997)Positron-emission tomography imaging of long-termshape recognition challenges Proceedings of theNational Academy of Sciences USA 94 7627ndash7632

Rybak IA Gusakova VI Golovan AVPodladchikova LN amp Shevstova NA (1998) Amodel of attention-guided visual perception andrecognition Visual Research 38 2387ndash2400

Saffran EM amp Schwartz MF (1994) Of cabbagesand things Semantic memory from a neuro-psychological perspective A tutorial review In CUmiltagrave amp M Moscovitch (Eds) Attention andPerformance XV Conscious and nonconscious informa-tion processing (pp 507ndash536) Cambridge MA MITPress

Sakata H Taira M Kusunoki A amp Tanaka Y(1997) The parietal association cortex in depthperception and visual control of hand action Trends inNeurosciences 20 350ndash357

Sereno AB amp Maunsell JH (1998) Shape selectivityin primate lateral intraparietal cortex Nature 395500ndash503

Sergent J amp Lorber E (1983) Perceptualcategorisation in the cerebral hemispheres Brain andCognition 2 39ndash54

Sergent J Ohta S amp MacDonald B (1992) Func-tional neuroanatomy of face and object processing Apositron emission tomography Brain 115 15ndash36

Springer SP amp Deutsch G (1998) Left brain rightbrain Perspectives from cognitive neuroscience (5th ed)New York Freeman



Stewart L Meyer BU Frith U amp Rothwell J(2001) Left posterior BA 37 is involved in objectrecognition A TMS study Neuropsychologia 39 1ndash6

St John RC (1981) Lateral asymmetry in face percep-tion Canadian Journal of Psychology 35 213ndash223

Tagaris GA Kim S-G Strupp JP Andersen PUgurbil K amp Georgopoulos AP (1997) Mentalrotation studied by functional magnetic resonanceimaging at high field (4 Tesla) Performance andcortical activation Journal of Cognitive Neuroscience 9419ndash432

Tarr MJ (1995) Rotating objects to recognise them Acase study of the role of the viewpoint dependency inthe recognition of three-dimensional objectsPsychonomic Bulletin and Review 2 55ndash82

Tarr MJ amp Buumllthoff HB (1995) Is human objectrecognition better described by geon-structural-descriptions or by multiple-views Journal of Experi-mental Psychology Human Perception and Performance21 1494ndash1505

Tarr MJ amp Pinker S (1989) Mental rotation andorientation-dependence in shape recognition Cogni-tive Psychology 21 233ndash282

Trojano L Grossi D Linden DEJ Formisano EGoebel R Cirillo S Elefante R amp Di Salle F(2002) Coordinate and categorical judgments inspatial imagery An fMRI study Neuropsychologia 401666ndash1674

Ullman S (1996) High-level vision Object recognitionand visual cognition Cambridge MA MIT Press

Ungerleider LG amp Mishkin M (1982) In DJ IngleMA Goodale amp RJW Mansfield (Eds) Theanalysis of visual behavior Cambridge MA MITPress

Van Kleeck MH (1989) Hemispheric differences inglobal versus local processing of hierarchical visualstimuli by normal subjects New data and a meta-analysis of previous studies Neuropsychologia 271165ndash1178

Vilkki J (1987) Incidental and deliberate memory forwords and faces after focal cerebral lesionsNeuropsychologia 25 221ndash230

Warrington EK (1982) Neuropsychological studies ofobject recognition Philosophical Transactions of theRoyal Society London B 298 15ndash33

Warrington EK (1984) Recognition Memory TestWindsor UK Nelson

Warrington EK amp James M (1986) Visual objectrecognition in patients with right hemisphere lesionsAxes or features Perception 15 355ndash366

Warrington EK amp James (1988) Visual apperceptiveagnosia A clinico-anatomical study of three casesCortex 24 13ndash32

Warrington EK amp James M (1991) A new test ofobject decision 2D silhouettes featuring a minimalview Cortex 27 370ndash383

Warrington EK amp Shallice T (1984) Category-specific semantic impairments Brain 107 829ndash854

Warrington EK amp Taylor AM (1973) The contri-bution of the right parietal lobe to object recognitionCortex 9 152ndash164

Warrington EK amp Taylor AM(1978)Two categor-ical stages of object recognition Perception 7 695ndash705

Wendt PE amp Risberg J (1994) Cortical activationduring visual spatial processing Relation betweenhemispheric asymmetry of blood flow and perfor-mance Brain and Cognition 24 87ndash103

Wojciulik E amp Kanwisher N (1999) The generalityof parietal involvement in visual attention Neuron23 747ndash764

Wolfe JM amp Bennett SC (1997)Preattentive objectfiles Shapeless bundles of basic features VisionResearch 37 25ndash43

Zacks J Rypma B Gabrieli JDE Tversky B ampGlover GH (1999) Imagined transformations ofbodies An fMRI investigation Neuropsychologia 371029ndash1040

Zelkovicz BJ Herbster AN Nebes RD MintunMA amp Becker JT (1998) An examination ofregional cerebral blood flow during object namingtasks Journal of the International NeuropsychologicalSociety 4 160ndash166

LAENG ET AL


variation of viewing conditions by using a ldquostruc-tural descriptionrdquo that specifies parts and their con-nections or spatial relations (eg cf Biederman1985 1987 Marr 1982) However according toanother theoretical view the brain stores a largenumber of images or views for each shape and canretrieve them in a parallel manner (cf Koenderinkamp Van Doorn 1979 Logothetis Pauls amp Poggio1995 Perrett et al 1985 Poggio amp Edelman1990 Tarr amp Buumllthoff 1995 Ullman 1996)

These multiple images belonging to the sameobject would be stored while we experience a shapethrough changes in viewpoint and rotations indepth Thus when the object is flexible anddynamic in shape (eg a human being anumbrella) it would also seem necessary to store thedifferent poses (eg for animate objects the defor-mations of its surface across different types ofmovements or actions cf Kourtzi amp Shiffrar1999) Clearly animals and other flexible objects

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Figure 1 Contorted human body (from Lois Greenfield Breaking Bounds London Thames and Hudson 1992)











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rigid and nonrigid objects in canonical and noncanonical views: hemisphere-specific effects on...

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