Int J HumanComputer Studies doi

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Int. J. Human-Computer Studies (2002) 57, 247�262 doi:10.1006/ijhc.1017 Available online at http://www.idealibrary.com.on Animation:canitfacilitate? arbara verskyand ulie auer orrison Department of Psychology, Jordan Hall; Bldg. #420 Stanford, CA 94305-2130 USA. email: bt{julie}@psych.stanford.edu. ireille etrancourt I.N.R.I.A. Rhone-Alpes, 655, Av. de l Europe, 38330 Montbonnot St-Martin, France. email: mireille.betrancourt@inria.fr. (Received 1 March 2001 and accepted in revised form 4 April 2002) Graphics have been used since ancient times to portray things that are

inherently spatiovisual) like maps and building plans. More recently) graphics have been used to portray things that are metaphorically spatiovisual) like graphs and organizational charts.Theassumptionisthatgraphicscanfacilitatecomprehension)learning)memory) communication and inference. Assumptions aside) research on static graphics has shownthatonlycarefullydesignedandappropriategraphicsprovetobebeneficialfor conveying complex systems. /ffective graphics conform to the 0ongruence 1rinciple according to which the content and format of the graphic should correspond to the

contentandformatoftheconceptstobeconveyed.2romthis)itfollowsthatanimated graphics should be effective in portraying change over time. 3et the research on the efficacy of animated over static graphics is not encouraging. 4n cases where animated graphics seem superior to static ones) scrutiny reveals lack of equivalence between animated and static graphics in content or procedures6 the animated graphics convey more information or involve interactivity. Animations of events may be ineffective because animations violate the second principle of good graphics) the Apprehension

1rinciple)accordingtowhichgraphicsshouldbeaccuratelyperceivedandappropriately conceived. Animations are often too complex or too fast to be accurately perceived. Moreover) many continuous events are conceived of as sequences of discrete steps. Judicioususeofinteractivitymayovercomeboththesedisadvantages.Animationsmay be more effective than comparable static graphics in situations other than conveying complex systems) for example) for real timereorientations intime andspace. 2002 1ublished by/lsevier 7cience 8td. 1. Graphics:TheCongruencePrinciple 1.1. 79M/ 2:;0T49;7 92 GRA1=407 The enthusiasm

for graphics of all kinds rests on the belief that they benefit comprehension and learning) and foster insight (their proponents include 8evie & 8entz)1?8268arkin&7imon)1?876Ainn)1?87)1?8?68evin&Mayer)1??B67chnotz 1071CD81?/02/ECseefrontmatter 20021ublishedby /lsevier7cience8td. JulieBauerMorrisonis nowat Bryant0ollege)7mithfield)R4.
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& Fulhavy) 1??46 Tversky) 1??D) 20016 7caife & Rogers) 1??6). Many advantages of graphics have been proposed. Graphics provide an additional way of representing information6 two codes) pictorial and verbal) are better than one.

Graphics may be aestheticallyappealingorhumorous)attractingattentionandmaintainingmotivation. Graphics)asthesayinggoes)maysavewordsbyshowingthingsthatwouldotherwise need many words to describe. This especially holds for faces) maps) systems) and the like that are naturally spatial and hard to describe or visualize. 7ince shepherds first notchedstickstokeeptrackoftheirflocksorhuntersbenttreestorememberaroute) graphics have been used to record information) historical) political) economic and personal. 7uch records have appeared in myriad forms) including tallies) notches and

tokens(e.g.Gelb) 1?6B67chmandtCBesserat)1??2).Analysisofthesegraphics)ancient andmodern)revealscommonusesofspaceandthethingsinittoconveyotherconcepts (Tversky) 1??D) 2001). Graphics use visual elements and the spatial relations among them to represent elements and relations that may be visuospatial) or may be metaphorically visuospatial) applying the power of spatial inference to other domains (8arkin & 7imon) 1?876 Tversky) 1??D) 2001). Thus) another function of graphic displaysistousespacetoorganizeinformationandtofacilitatememoryandinference. 0omputer menus are a familiar modern example)

but using space to organize and remember is also an ancient practice (e.g. Bower) 1?706 7mall) 1??76 3ates) 1?6?). Graphicsexternalize internalknowledge.Thishasatleasttwobenefits. Thebenefitto the individualmind isreducingthe burdenonmemoryandprocessing byoffCloading. Thebenefittogroupsofmindsisjointconsiderationofthesamesetofideasaswellas collectiverevisionofthem.2inally)graphicshavebeenusedtopromoteinferenceand discovery by making the underlying structures and processes transparent (e.g. Hwyer) 1?786 8arkin & 7imon) 1?876 Mayer) 1?8?6 Bauer & JohnsonC8aird) 1??B6 Tessler)

4wasaki & Fincho 8aw) 1??D). 4nterestingly) for these purposes) simple graphics with lessdetailareoftenmoreeffectivethanmorerealisticones(e.g.Hwyer)1?78))provided that they abstract the essential conceptual information. 1.2. I47:A84JAT49;7 92 T=/ I474B8/ A;H 92 T=/ AB7TRA0T Graphicdisplayscanbelooselydividedintotwokinds:thosethatportraythingsthat areessentiallyvisuospatial)likemaps)moleculesandarchitecturaldrawings)andthose that represent things that are not inherently visual) like organization charts) flow diagrams) and graphs. Graphics that portray essentially visual or spatial

information have a clear and obvious advantage over other means of conveying that same information) notably language) in that they use space to convey space. This natural correspondence does not mean that all space to space graphics are immediately understood. 0ertain aspects of maps are difficult for children (He 8oach) Miller & Rosengren)1??768iben)1???)andevenadults)especiallythreeCdimensionaldepictions (e.g. Gobert) 1???6 2ontaine) 2001). 4n spite of the natural correspondences mapping space to space) there are situations where clear language is as effective as graphics (e.g. Taylor

& Tversky) 1??2). Graphics that portray things that are not inherently visuospatial rely on spatial metaphors. 1ictorial elements can represent abstract meanings through KKfigures of depiction$$) for example) metonymy) where a concrete associaterepresentsanabstractconcept)suchastheAhite=ouseforthepresidencyor B.T VERSKY ET AL. 248
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apairofscissorsforKKdelete$$.7patialproximityisthebasicmetaphorunderlyingusing spacetoexpressabstractrelations.Histanceinspaceconveysdistanceonsomeabstract dimension) such as time) preference) cost orcausality (e.g. Tversky) 1??D) 2001).

Graphicsportrayingthingsthatareessentiallyvisualareinventionsthatareancient andwidespreadacrossmanycultures.Graphicsthatusefiguresofdepictiontoconvey abstract concepts are also ancient. 4n fact) the origins of written language are in pictures.4ncontrast)graphicsthatusespacetoconveynonspatialrelationsare)forthe most part) recent Aestern inventions (e.g. Beniger & Robyn) 1?786 Tufte) 1?8B6 0arswell&Aickens)1?88).Giventhatgraphicscanportrayelementsandrelationsthat are not spatial as well as those that are spatial) their efficacy in learning and

communicationshouldbe)andis)broad.4nfact)itseemsthatitisdifficulttocapture thevastliteratureoneffectsofdiagramsonlearningwithasummarylessgeneralthan graphics aid learning when they present the same information as text in a different formatandalsowhentheypresentinformationcomplementarytotextualinformation (e.g. 8evie & 8entz) 1?82). 1.B. ;AT:RA8 09G;4T4I/ 09RR/719;H/;0/7 4; GRA1=407: T=/ 09;GR:/;0/ 1R4;0418/ Thebenefitsofgraphicsareapparentfrom their ubiquityandintheir naturalness.By naturalness) we mean a convergence of inventions across cultures and ages for using space to

represent space and to represent abstract concepts that suggest cognitive correspondences between mental spaces and real ones. The pictorial languages and petroglyphs found all over the world are one example (e.g. Mallery) 18?B/1?726 Gelb) 1?6B6=arley&Aoodward)1?87)1??260oulmas)1?8?6He2rancis)1?8?6Aoodward& 8ewis) 1??4). The manner of schematizing people) animals) rivers) mountains) foods and houses bear striking similarities across cultures. 4nterestingly) these early written communications resemble contemporary attempts at inventing writing by preliterate children (Fellogg) 1?6?6 Goodnow)

1?776 TolchinskyC8andsman & 8evin) 1?87). 7imilarities in crossCcultural and developmental attempts to externalize mathematical conceptshavebeenobservedby=ughes(1?86)andforgeographicconcepts)especially depictionsofhills)byAood(1??2).2orthemostpart)thesegraphiccommunications haveusedpictorialelements.:seofspatialrelationstoexpresstemporal)quantitative and preference relations was evident in children as young as D and in children from diversecultures(Tversky)Fugelmass&Ainter)1??1).:seofspacehasbeensystematic across young inventors who have used primarily horizontal and vertical lines) with

increases going upwards or to left or right. 4nventors young and old naturally map increasing rates onto increasing slopes (Gattis & =olyoak) 1??66 Gattis) 2001). These naturalcognitivecorrespondencesarecapturedinthe Congruence Principle foreffective graphics:thestructureandcontentoftheexternalrepresentationshouldcorrespondto the desired structure and content ofthe internal representation. 1.4. GRA1=407 G99H A;H ;9T 79 G99H Aithrecentrapidadvancesintechnologyandwithincreasingcontactamong cultures not sharing spoken languages) graphic devices have proliferated. =owever) the A;4MAT49;:0A;

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advances in the technology of producing attractive graphics often seem to drive and outstrip the development of tools and devices rather than research on their utility. Graphicsarenotalwayseffective)orputdifferently)notallgraphicsareeffectiveinall situations.4nfact)theearlyresearchcomparinglearningwithgraphicstolearningwith textalonegavemixedresults)ofteninspiteofenthusiasmforthepictorialdevices(see reviews by 8evin & 8esgold) 1?786 8evie & 8entz) 1?826 Mandl & 8evin) 1?8?). Moreover)muchoftheearlyresearchusedglobalcomparisonsbetweenmediaanddid not address

the subtler questions of what accounted for the facilitation when it occurred. As research progressed) the types of situations) graphics) tasks and learners for which graphics are effective has become clearer. ThreeCdimensional displays are a new case in point. They seem to be everywhere) or at least in software packages) and they do seem to be liked (0arswell) 2rankenberger & Bernhard) 1??16 8evy) Jacks) Tversky & 7chiano) 1??6). =owever) it is simply not clear if BH displays improve performance) speed) accuracy or memory for data (0arswell et al .) 1??16 7pence&8ewandowsky)1??168evy et al

.)1??6).4nsometasks)forexample)memory) there is little difference between BH and 2H displays6 in other tasks) for example) estimation) there is a disadvantage to BH displays (Jacks) 8evy) Tversky & 7chiano) 1??8). 1.D. A;4MAT49; Another of the newer) attractive graphic devices is animation. 9n the surface) animation is compelling. By the 0ongruence 1rinciple) it should be a natural for conveyingconceptsofchange)justasspaceingraphicsisanaturalforconveyingactual space. Animation should) in principle) be effective for expressing processes such as weather patterns or circuit diagrams or the

circulatory system or the mechanics of a bicyclepump. And) justas real space is effective for conveying metaphoric space) real change should be a natural for conveying metaphoric change) such as the spread of culturalinventionslikewriting)agricultureormetallurgy)thetransmissionofcontrolin anorganization)orthechangesinproductionofvariousindustriesovertime.Giventhe breadth of concepts for which animation seems appropriate and the increasing accessibility of computer tools for animating) the enthusiasm for animation is understandable. 1.6. 1R/I4/A Aith this background on graphics in mind) we will

selectively review research on animation(seeBetrancourt&Tversky)2000).KK7electively$$becausesomeofwhathas been called animation has involved other aspects of communication situations) especially interactivity) which is known to benefit learners on its own (e.g. 2erguson &=egarty)1??D).Toevaluateanimation per se )itmustbecomparedtographicsthat do not change with time) as it is change with time that animation adds. The review focuses on uses of animation to teach complex systems) mechanical) biological) physical)operational)computational.4tisinthiscontextthatmostoftheevaluationsof

animation have been done. There are other uses of animation) especially in computer interfaces) and these will be considered briefly at the end. This review will not B.T VERSKY ET AL. 2D0
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provide encouragement for the enthusiasm for animation. That leaves us with a need to explain why animation has not produced the expected benefits. To account for the failures of animation) we step back and take a closer look at how people perceive and comprehend real animations. Aith human perceptual and cognitive limitations in mind) we turn again to the basic question: Ahen

will animation be effectiveL 1.7. F4;H7 92 A;4MAT49;7 9f course) change over time occurs in many different ways) and hence is conveyed by animations differing in complexity. 1erhaps the simplest movement is a path or trajectory. This can be animated as the movement of a dot) providing that the features of the moving object are not relevant. Representing the speed and manner of the moving object may require richer animations. 7ometimes what needs to be conveyed is more complex than a path) for example) the movement of parts of an object or system with respect to each other. The movement or

change of either a path or a system may be in two or three dimensions. 4n these cases) movement is of the object or system itself. 4n other cases) the object or system may be stationary) and the movement is of the viewpoint of the observer) in order to show other aspects of the object or system. The critical information to be conveyed determinestheformoftheanimation.But)whatevertheform)inordertobeeffective) an animation must be perceived and comprehended adequately. 0learly) complexity challenges both. 2. Selectivereviewofresearchonanimation 2.1. 4;09M1ARAB8/ 09;T/;T 4; 7TAT40 A;H A;4MAT/H

GRA1=407 4n order to know if animation per se is facilitatory) animated graphics must be comparedtoinformationallyequivalentstaticgraphics.Thatway)thecontributionsof animation can be separated from the contributions of graphics alone without confounding with content. There may be cases where this control is difficult to instantiate) for example) for an animation that shows a complex manner of motion where both spatial position and timing are of the essence. =owever) the cases of incomparabilityreviewedherewerenotthatsubtle.Theyareallcaseswherethestatic

graphicscouldhaveconveyedthesameinformationastheanimatedones.7howingthat studentslearnmaterialbetterwhenitispresentedthanwhenitisnotpresentedshould not bea goal ofempirical research. Anelegantuseofanimationisapairofmovingdashedlinestoillustratedifferences inspeedforrateMtimeNdistanceproblems(Baek&8ayne)1?88).4nthisanimation) theirrelevantaspectsofthesituationwereeliminated)andtheessentialaspectsreduced to dashes moving proportional to speed. Although students learning from the animation outperformed those learning from a static diagram) little can be concluded aboutanimationassuch.The

staticdiagramwas farfromequivalenttotheanimated one6 in particular) it did not take advantage of spatial distance to convey problem distance. /ssentially) the static graphic was a table listing two sets of distances) times A;4MAT49;:0A; 4T2A0484TAT/L 2D1
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andaveragespeeds.Thus)thereisnowayofknowingiftheanimatedgraphicproduced benefits beyond a comparable static graphic. 8ack of comparability of static and animated diagrams obviate conclusions about the benefits of animation in other studies. 4n a study evaluating graphics for teaching the circulatory system) the

animated diagrams of the heart included blood pathways) but the static diagram did not (8arge) Beheshti) Breuleux & Renaud) 1??6). The static graphics used in Rieber$s (1??0) 1??1 ) computerCbased lesson on ;ewton$s laws of motion did not include information fundamental to understanding the laws. The static graphic for ;ewton$s law of equal and opposite forces depicted the movement of the ball) but not that a single kick to the ball both startedandstoppeditsmotion.Theconceptofinertiaiscriticaltounderstandingthis law)yetcanonlybeextractedfromtheaccompanyingtext.Theanimateddiagram)in

contrast)showedeachkickasitstartedandstoppedtheball$smotion.Although8arge andcolleaguesandRieberbelievetheirfindingssupporttheuseofanimatedgraphics) the lack of equivalence of the static and animated graphics call this conclusion into question. Atfirstglance)forotherstudiesevaluatingstaticandanimatedgraphics)thegraphics appear comparable. But on close examination) the animated graphics present information not available in the static versions) in particular the details of the microsteps between larger steps6 that is) the minute spatialCtemporal actions of components. /vents such as

those portrayed in animations can be reliably segmented into coarser and finerunits by observers (Jacks) Tversky & 4yer) 2001). 2or the most part) the coarse units are segmented by objects or object parts and the fine units by different fineCgrained actions on the same object or part. Many of the static graphics portrayonlythecoarsesegmentswhereastheanimations portrayboththecoarseand fine segments. Thus) there is greater information in the animations than in the static displays.Anybenefits)then)maybeduetotheaddedinformationaloneratherthanthe

formatofthegraphics)informationthatcouldeasilyhavebeenconveyedinthestatic graphics. 4nastudyevaluatingstudents$abilitytolearntheoperationandtroubleshootingof an electronic circuit from a static graphic or from an animated graphic) 1ark and Gittelman (1??2) report better performance in the animated graphic condition. Although both graphics) static and animated) showed the relationships between components in the process) only the animated graphic showed the fine structure. 7pecifically)whenanactionwastakenwiththecircuit)theanimationdepictedthefineC

grainedactionsofthecomponents.Thestaticgraphicshowedthespatialrelationships amongthecomponentsbutdidnotportraythemechanicsofthecircuit$sresponsetoa particular actionandthe consequent changein the circuitstate. Research by Thompson and Riding (1??0) further supports the hypothesis that animation facilitates learning when it presents the fineCgrained actions that static graphicsdonotpresent.Theirprogramtaughtthe1ythagoreantheoremtojuniorhigh schoolstudents.Thegraphicdepictedatriangleandthreesquares)whereeach square sharedoneofthetriangle$ssides.:singshearsandrotations)theprogramshowedthat

theareaofthesquarealongthehypotenusewasthesameasthecombinedareasofthe two other squares. 9ne group viewed a static graphic) a second group saw a discrete animationofthestepsshownonthepapergraphic)andathirdgroupsawacontinuous B.T VERSKY ET AL. 2D2
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animationofthesteps.Thegroupviewingthecontinuousanimationoutperformedthe other two graphic groups. =owever) the results cannot be taken as showing the superiority of animated over static graphics as the authors explicitly state that the information on the paper graphic was equivalent to the discrete animation) but not equivalent to

the continuous animation. The continuous animation depicted all the lower level actions) while that information had to be inferred from both of the other graphics. 2.2. 4;09M1ARAB8/ 1R90/H:R/7 4; 7TAT40 A;H A;4MAT/H GRA1=407 The lack of equivalent information in static and animated graphics is not the only difficulty in assessing possible benefits from animation. 9ther studies comparing animation have not used equivalent procedures. 4n some studies) the animation conditionallowedinteractivitywhilethe staticcondition didnot)sothatbenefitsmay be due to interactivity rather than

animation (e.g. 7chnotz & Grzondziel) 1???). Anotherfactorknowntofacilitatelearning)prediction)hasalsobeenconfoundedwith animation in some studies. 4n prediction) participants anticipate outcomes) and then view graphics (or read text) to check if their predictions were fulfilled. And) indeed) conditionsthatinvolvebothanimationandpredictionofamechanicalsystemdidyield benefitsbeyondgraphicsthatallowneither(=egarty)Ouilici);arayanan)=olmquist& Moreno) 1???). Because prediction alone is known to facilitate learning) facilitation cannot be attributed to animation. 8ater studies by the

same group showed no benefits of animation per se in understanding the workings of a flushing cistern (=egarty) ;arayanan& 2reitas) 2002). Fieras (1??2) investigated the effects of animated and static graphics on students$ abilitytounderstandtheoperationofanenergysystem)theKK7tarTrek1haserBank$$. 7tudentsstudiedconceptualinformationaboutthesystemintheformoftextorinthe formofstaticoranimateddiagrams.7tudentswholearnedfromtheanimatedgraphic performed significantly better on firing the phaser and diagnosing malfunctions tasks than those who learned from a static graphic or

lacked a graphic. 7tudents with the staticoranimatedgraphics)however)wereallowedtousethegraphicsduringthetest phaseoftheexperiment.Thepresenceofgraphicsduringthetestphasemakesthetask one of reading graphics rather than using the information contained in the graphics. That is) the animated graphic may be facilitating execution of the task rather than understanding ofthe concepts. ;athan) Fintsch and 3oung (1??2) developed an animated interactive program (KKAnimate$$) to help students comprehend algebra word problems. The program is

designedtofacilitateunderstandingoftherelationshipbetweentheformalmathematics ofawordproblemandthesituationdescribedintheproblem.7tudentsintheAnimate conditionwroteaformalequationtosolvetheproblemandthenanimatedtheequation to see if it depicted the expected solution. ;one of the other conditions included graphicsandtwoofthethreeconditionshadinterfacessubstantiallydifferentfromthe Animateinterface.AlthoughperformanceintheAnimateconditionwasbetterthanin theotherthreeconditions)thelackofcomparabilityamongconditionsdoesnotallow any conclusions about the relative efficacy ofanimated graphics.

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2.B. 2A48:R/7 92 A;4MAT49; T9 B/;/24T Ahen examined carefully) then) many of the soCcalled successful applications of animation turn out to be a consequence of a superior visualization for the animated thanthestaticcase)orofsuperiorstudyproceduressuchasinteractivityorprediction thatareknowntoimprovelearningindependentofgraphics.4naddition)theliterature isfilledwithoutrightfailurestofind benefitsofanimation) evenwhen animationisin principle ideal: for conveying change over time (e.g. 7chnotz & Grondziel) 1???). Morrison and

Tversky (2001) compared text with text coupled with either static or animated graphics in a task teaching permissible social paths among people or navigationpathsamongobjects.Graphicsyieldedbetterperformancethantextalone) but only for low spatial ability participants. Across all participants) diagrams that animated the path provided no benefit beyond that of the individual static diagrams. Rieber and =annafin (1?88) and Rieber (1?8?) found no facilitation for animation in teaching;ewton$slawsofmotiontoelementaryschoolstudents.4nonecase)bothtext

andanimationwereusedasorientingactivitiespriortothepresentationofeachsection ofthelesson(Rieber&=annafin)1?88))neitherofwhichhadanyeffect.4nthesecond case)elaboratingthetextuallessonwithadditionaltextand/orno) static)oranimated graphics did not lead to performance differences (Rieber) 1?8?). Rieber) Boyce and Assad(1??0)usedthesamedesigntoevaluatetheperformanceofcollegestudentswhen learning;ewton$slaws.Aswiththeearlierexperimentstherewasnoeffectofgraphic condition.Additionally)providingdifferentformsofpractice)oneinvolvinginteractive animation) had no effect in anyof the three

experiments. 7tudents learning about the production of growth hormones during biotechnology were presented with text alone) a static diagram) or an animated diagram (0han8in) 1??8).Ahenlearningproceduralinformation)suchastheformationofapeptidechain) the studentsviewed asingle static diagram whichcombined information aboutallthe steps in the process. 7tudents in the animation group viewed a series of individual animations depicting each step of the process. 7tudents in both conditions performed equally well. 4n fact) the only difference was between the static and no diagram

conditionforthosestudentswhohadabackgroundinbiology.Allotherconditions)for both biology and nonCbiologystudents)wereequal in terms ofperformance. Asasupplementtoabiologycoursetheyweretaking)juniorhighstudentsinteracted withtheAdvanced0omputingfor7cience/ducation(A07/)environment)whichisa multimedia program incorporating textual information) still graphics) movies) and simulations (1ane) 0orbett & John) 1??6).7tudents using the A07/ program did not perform better than students using static graphics except for a slight advantage for information presented only in the A07/ program and not during

the biology course lectures. Byrne) 0atrambone and 7tasko (1???) tested the effectiveness of animated graphics in teaching college students computer algorithms) specifically depthCfirst searches and binomial heaps. The authors were discouraged to find that the benefits of viewing animated graphics were equivalent to making predictions about the outcomes of the algorithms when provided withstatic graphics. Animatedgraphicsareoftenemployedtoteachstudentshowtouseacomputerora computer program. This is also an area where these animations do not appear to be B.T VERSKY ET AL.

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effective. Three groups of researchers investigated the role of animation in teaching students how to use a Macintosh computer) how to use the MacHraw graphics editor) and how to use =yper0ard (1ayne) 0hesworth) & =ill) 1??26 Hyck) 1??D6 =arrison)1??D)respectively).4neachcase)presentinganytypeofagraphic)static(only for=arrison)1??D)oranimated)facilitatedperformancewhencomparedtoproviding noinstruction.7tudentsintheanimatedgraphicconditionsdidnotoutperformthosein the equivalent text (1ayne) 0hesworth & =ill) 1??26 Hyck) 1??D) or static graphic (=arrison) 1??D) conditions.

1almiterandcolleaguescomparedanimatedandstillgraphicsforteachingstudents howtouseanonClinehelpsystemfor=ypercard (1almiter)/lkerton&Baggett)1??16 1almiter&/lkerton)1??B).Althoughthestudentsusingtheanimationcompletedthe training task more quickly) they completed the testing task more slowly. Moreover) after a week) performance of students who had studied the text improved) but performance for those who had studied the animation declined. The longCterm facilitationoftextoveranimationwasattributedtodeeperprocessingofthetextthan ofthe animation.

Thus)most)ifnotall)ofthesuccessesofanimationseemtobeduetoadvantagesin extrainformationconveyedoradditionalprocedures)ratherthantheanimationofthe information per se .Animationsareofteninteractive6interactivityisknowntofacilitate performance but it should not be confused with animation (e.g. 2erguson & =egarty) 1??D). Ahen animations fail to benefit learning) their promoters argue that they are attractiveandmotivating)sotheycouldbepreferredjustforthat(1erez&Ahite)1?8D6 Rieber) 1??1 6 7irikasem & 7hebilske) 1??1). =owever) it turns out that animations

frequentlytakemoretime)sotheyhaveacost./venmoredamagingtothemotivation hypothesis is that animations are not universally preferred) and are often not used (e.g. 1ane et al .) 1??6). 2inally) and to foreshadow our next point) many animations) evenelegantandnaturalones)aredifficulttoperceiveandunderstand)exceptperhaps byexpertswithextensiveexperience(e.g.8owe)1???67locum)3oder)Fessler&7luter) 2000).Theconsequenceofthisisthatanimationsmaybedistracting)orevenharmful) to conveying important ideas. 1roviding animated weather maps to novices) for example) only encouraged them to attend to

perceptually salient information. They were unable to use the animations to extract thematically important information) especiallythecausalinformationthatunderliesadequatementalmodelsofthesystem (8owe) 1???). 3. Whydoanimationsfail?TheApprehensionPrinciple Themanyfailurestofindbenefitsofanimationeveninconveyingchangeovertime)a conceptthatseemsideallysuitedtoanimationissurprising)indeed)disappointing)and calls for deeper inquiry into information processing of animation. The drawback of animation may not be the cognitive congruence between the conceptual material and

thevisualpresentationbutratherperceptualandcognitivelimitationsintheprocessing of a changing visual situation. /ffective graphics should conform not only to the 0ongruence1rinciple)butalsotothe Apprehension Principle :thestructureandcontent A;4MAT49;:0A; 4T2A0484TAT/L 2DD
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of the external representation should be readily and accurately perceived and comprehended. B.1. A;4MAT49;7 MA3 B/ =ARH T9 1/R0/4I/ Generations of masterpieces in galleries and museums all over the world portray the legs of galloping horses incorrectly. Before stopCgap photography) the complex

interactionofhorses$legssimplyhappenedtoofasttobeaccuratelyapprehended./ven when motion is simplified to the path or trajectory of a single object rather than the complex interaction of moving parts) perception of motion may not be accurate. 7ketches of the trajectories of pendula) propelled objects and dropped objects by novicesandexpertsalikeareoftenincorrect)apparentlygovernedmorebyGestaltClike perceptualprinciplesthanlawsofphysics(e.g.0aramazza)Mc0loskey&Green)1?816 Mc0loskey) 1?8B 6 Faiser) 1roffitt) Ahelan & =echt) 1??26 2reyd & Jones) 1??4). 1aths ofmoving objects) for

example) are perceived ascloser tohorizontal orvertical than they actually are (7hiffrar & 7hepard) 1??16 1ani) Jeffres) 7hippey & 7chwartz) 1??6). 2or some kinds of motion) observers can select the correct path from an animation) but still reproduce it incorrectly (Faiser et al .) 1??2). B.2. A;4MAT49;7 MA3 B/ 09M1R/=/;H/H H470R/T/83 /ven when actual motion is smooth and continuous) people may conceive of it as composed of discrete steps Pe.g. =egarty) 1??26 Jacks et al .) 20016 but see 7chwartz (1???) and 7chwartz & Black (1??6) for evidence that for atomic substeps that are

analoginnature)suchastheturningofgears)mentalanimationmaybeanalogaswellQ. 4fmotionisconceivedofindiscretestepsinsteadofcontinuously)thenthenaturalway ofconveyingitistoportrayitindiscretestepsratherthaninacontinuousanimation. Thisisquitecommoninpictorialinstructionsforcomplexmotion)suchasoperatinga machineorassemblinganobject)whereeachstepisportrayedinaseparateframeand theframesareorderedbythesequenceofsteps.2orsimplemotion)asinthepathofan object or the flow of control or electricity through a system) a single diagram can

conveythepath)indicatedbylinesandarrows.4nadditiontocorrespondingtotheway people conceive of animations) multiple diagrams have an additional advantage: they easily allow comparison and reinspection of the details of the actions. By contrast) animationsarefleeting)theydisappear)andwhentheycanbereinspectedtheyusually are reinspected in motion) where itmay bedifficulttoperceive allthe minute changes simultaneously. B.B. 4;T/RA0T4I4T3 0learly) interactivity) a factor known to facilitate learning) can help overcome the difficulties of perception and comprehension. 7topping)

starting and replaying an animation can allow reinspection) focusing on specific parts and actions. Animations that allow closeCups) zooming) alternative perspectives) and control of speed are even more likely to facilitate perception and comprehension. 9f course) the proper experiments have yet to be done) for example) static graphics also allow closeCups B.T VERSKY ET AL. 2D6
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and perspective switches. 0areful studies will reveal the particular aspects) if any) of animation and interactivitythat facilitate conveying specific concepts. B.4. 0AI/AT7 The work

analyzed here is work on the role of animations teaching complex systems) mechanical) biological) computational. The conclusions are restricted to those situations.Animationsareusedinmany othersituations.0ommonusesofanimation include concrete applications such as walks through environments as well as abstract usessuchasthefillbarindicatingtherateofcompletionofafiledownload(see0ard) Mackinlay & 7hneiderman) 1???) for examples). Although rarely tested in highly controlledexperimentsPseeTan)Robertson)&0zerwinski(2001)foranexceptionthat

usesanimationtoconveychangesinorientationQ)theseusesofrealtimeanimationto convey change in time and space have perhaps passed the test of time. They have appeared in many interfaces for many years6 one would think that if they caused problems) user testing and complaints would have eliminated them (this said with hesitation) as unfortunate features have been known to survive) and lamented) e.g. ;orman)1?88).Atthispointthen)themostpromisingusesofanimationseemtobeto conveyrealCtime changes and reorientations in time andspace. 4. Implications

Giventheanalysisofthedifficultyofperceivingandconceptualizationanimations)the failurestofindbenefitsofanimationforconveyingcomplexsystemsbeyondequivalent staticdiagramsislessperplexing.Theapparentsuccessesturnedoutnottobesuccesses. 4nthosecases)theanimatedgraphicsinfactwerenotequivalenttothestaticgraphics) that is) in the animated graphics) more information was presented or the same information was presented differently) better) in the animated than in the static graphics. 4n other studies) animation was confounded with other factors known to

facilitatelearning)interactivityorpredictionoreventhepresenceofgraphics.4nsome of the most carefully controlled cases) the animations conveyed detailed information aboutthefinestructureoftheprocessesthatwasnotavailableinthestaticgraphics.4t maybethatsomekindsofinformationaremoreeasilyconveyedinanimationsthanin static diagrams) and that would be sufficient reason for using them. The information that might be more effectively portrayed in an animated graphic might include the qualitative aspects of motion or the microsteps) the exact sequence and timing of complex operations. Ahether

animations are more effective than static graphics for these subtle aspects ofchangeover time is unknown. This analysis suggests two principles specifying conditions for successful animated graphics) though these principles do not guarantee that animated graphics will be superiorto equivalent static ones. Congruence Principle : The structure and content of the external representation should correspond to the desired structure and content of the internal representation. 2or example) since routes are conceived of as a series of turns) an effective external visual representationof routes will

bebased onturns. A;4MAT49;:0A; 4T2A0484TAT/L 2D7
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Apprehension Principle :Thestructureandcontentoftheexternalrepresentationshouldbe readily and accurately perceived and comprehended. 2or example) since people represent anglesandlengthsingrosscategories)finerdistinctionsindiagramswillnotbeaccurately apprehended. 4n the case of routes) exact angles of turns and lengths of roads are not important. To accord with the 1rinciple of 0ongruence) there should be a natural correspondence between change over time) the core of animation) and the essential

conceptualinformationtobeconveyed.Thatconceptualinformationcouldbechange over time) for example movement or transformation or process. 4t could also be temporal sequence or causal flow. 4t could even be a natural order for attending to a complexarray(Betrancourt&Tversky)inpress).7omeofthesechangesandprocesses willbenaturallymorediscrete)somemorecontinuous.Toaccordwiththe1rincipleof Apprehension) animations must be slow and clear enough for observers to perceive movements) changes) and their timing) and to understand the changes in relations

betweenthepartsandthesequenceofevents.Thismeansthatanimationsshouldlean toward the schematic and away from the realistic) an inclination that does not come naturally to many programmers) who delight in graphic richness and realism. 4t also maymeanannotation)usingarrowsorhighlightingorotherdevicestodirectattention to the critical changes and relations. 7chematizing is simpler than it sounds6 clear understanding is a prerequisite to including only the information essential to the processes to be conveyed and eliminating extraneous but sometimes appealing information.

Accordingtothisanalysis)iftherearebenefitstoanimation)theyshouldbeevident especially for continuous rather than discrete changes) in particular) for manner of change and for microsteps) the subtle and intricate timing relations among parts of a complexsystem.=owever)evenforthesecases)cleverschematizationofstaticdiagrams may be just as effective as animation. 2or example) arrows are effective in indicating temporalsequenceanddirectionofmotion(e.g.Tversky)Jacks)8ee&=eiser) 2000). 4nteractivity may be the key to overcoming the drawbacks of animation as well as

enhancingitsadvantages.4flearnersareincontrol ofthespeedofanimationandcan viewandreview)stopandstart)zoominandout)andchangeorientationofpartsand wholes of the animation at will) then the problems of veridical perception can be alleviated.1articipantscanstudythoseaspectsoftheanimationthattheyneedwithout sufferingthroughportionstheyalreadyunderstand.Then)carefullycraftedanimations canbeapprehended)thosethathighlightthediscreteandhighClevelstepsandthosethat depict the analog and microsteps that animations seem wellCsuited to portray and convey. 8ike all good things) animation must be used with

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