interactive museum exhibits as tools for learning: explorations with light

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This article was downloaded by: [University of Arizona] On: 12 August 2013, At: 21:28 Publisher: Routledge Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK International Journal of Science Education Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tsed20 Interactive museum exhibits as tools for learning: explorations with light Elsa Feher a a San Diego State University, San Diego, California, USA Published online: 25 Feb 2007. To cite this article: Elsa Feher (1990) Interactive museum exhibits as tools for learning: explorations with light, International Journal of Science Education, 12:1, 35-49, DOI: 10.1080/0950069900120104 To link to this article: http://dx.doi.org/10.1080/0950069900120104 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions

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Page 1: Interactive museum exhibits as tools for learning: explorations with light

This article was downloaded by: [University of Arizona]On: 12 August 2013, At: 21:28Publisher: RoutledgeInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

International Journal of Science EducationPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/tsed20

Interactive museum exhibits as tools for learning:explorations with lightElsa Feher aa San Diego State University, San Diego, California, USAPublished online: 25 Feb 2007.

To cite this article: Elsa Feher (1990) Interactive museum exhibits as tools for learning: explorations with light, InternationalJournal of Science Education, 12:1, 35-49, DOI: 10.1080/0950069900120104

To link to this article: http://dx.doi.org/10.1080/0950069900120104

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of theContent. Any opinions and views expressed in this publication are the opinions and views of the authors, andare not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon andshould be independently verified with primary sources of information. Taylor and Francis shall not be liable forany losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use ofthe Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

Page 2: Interactive museum exhibits as tools for learning: explorations with light

INT. J. sci. EDUC., 1990, VOL. 12, NO. 1, 35-49

RESEARCH REPORTS

Interactive museum exhibits as toolsfor learning: explorations with light

Elsa Feher, San Diego State University, San Diego, California, USA

The new generation of science museums is characterized by exhibits that allow the visitors to experimentfreely with natural phenomena. This setting provides a unique type of research laboratory for studyinghow people learn. Using examples from our work with children at the site of exhibits on light and vision,we illustrate the preconceptions the children bring to the situation and how these notions shape theirinterpretation of the phenomena they manipulate and observe. Furthermore, we show how a conceptualanalysis of the exhibit, when tied to the visitors' interpretations, can be used to modify the exhibit in waysthat enhance the user's understanding of the science involved. The study of learning in science museumsis a field in its infancy. In this article we indicate its potential as well as some problems and questions it canfruitfully address.

Introduction

An anecdote about physicist Richard Feynman recounts that during a lecture in Riode Janeiro in 1952 he told his large and distinguished audience: 'The main purpose ofmy talk today is to demonstrate to you that no science is being taught in Brazil.' Tomake his point he opened a textbook at random and read a sentence that turned out tobe the definition of a phenomenon. 'There; have you got science?' stormed Feynman.'No!... You have only told what a word means in terms of other words...'(Feynman and Leighton 1985, p. 217).

Thirty-eight years later, in the USA, we could make a similar demonstration. Atthe start of the chapter on light in the grade 4 textbook in California, the student istold: 'Light is energy that you can see. Light travels through space in the form ofwaves.' This is pretty abstract and quite uninteresting because there is nothing youcan do with it. There's nothing to go home and try out. There's no experience ofnature. The problem is endemic in our schools: teachers teach abstractions,definitions and explanations of phenomena that, for the most part, the students havenever explored, or, worse still, that the students may not even know actually occur.

Exhibits for experiencing and exploring

If schools so often put the cart (explanations) before the horse (first hand experienceof natural phenomena), modern science museums reverse the process. Thesemuseums, most often called 'science centres', present natural phenomena in theform of exhibits that are interactive and manipulable, exhibits whose expresspurpose is to enable the visitors to explore and experiment. The science centre ismuch like a laboratory that is always set up, with all its experiments ready for use atthe discretion of the visitor (Oppenheimer 1976, Semper et al. 1982).

0950-0693/90 $3-00 © 1990 Taylor & Francis Ltd.

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36 RESEARCH REPORTS

A good exhibit presents an interesting phenomenon that is usually not accessibleto the visitor. This might be because the phenomenon is embedded in the fabric ofeveryday things and events and is difficult to isolate and notice; for example, theinterference of water or sound waves. Or, as is the case with a rainbow in the sky,because it is not possible to vary the parameters that give an understanding of howthe phenomenon is caused, or because the technology is not easily available to thevisitor to detect the effect, such as the waveform of his whistle or the sound of hisheartbeat. The interactive aspect of the exhibit is achieved by incorporating elementsthat afford the visitor the possibility of asking and answering 'what if questions:'What would happen if I changed this or that?' The change can involve an action, asis the case in manipulative (or hands-on) exhibits; for perceptual exhibits, it may besimply another way of looking or listening.

Interactive exhibits are designed to be stand-alone teaching devices. This is notan easy task, for when we by-pass the human mediator (the lecturer or the teacher)the exhibit itself must attract and hold the visitor's attention. Experience shows thatcaptions and graphics do not fulfil the role of enticing and engaging the visitor. Thisburden rests on the way in which the exhibit displays the phenomenon. Animportant characteristic of a successful exhibit is its ability to surprise the user.Another is the opportunity it offers the visitor to 'go messing about', like Toad in TheWind in the Willows. This playful exploration, both serious and whimsical, is animportant aspect of the teaching exhibit. Finally, the conceptual content of theexhibit needs to be matched to the prior knowledge of the learner. As we shall explainbelow, carrying out this match entails probing the learner's ideas and finding ways ofaddressing them through the design of the exhibit.

The exhibits that we have been describing are not meant to be didactic, that is tosay, they do not teach with a narrowly defined, focused agenda (even though they canbe so used). They do, however, respond to a clear pedagogical position (Duensing1987), based on the belief that people learn by doing and that the active process ofinquiry and discovery is fundamental in all learning (Hodgkin 1985). -

For its visitors, the science centre provides a unique environment for informallearning about science. Here is a place where people go of their own free choice.Driven by their curiosity, the visitors manage their own learning. Playfullyinteracting with exhibits, they experience natural phenomena directly, first hand.What do these visitors learn? How do they learn? In this article we show how thescience centre environment provides a laboratory for examining these questions and,further, that the results of such research can profitably be fed back into the design ofthe exhibits to make them better learning tools for the visitor.

Probing the explanations of the exhibit users

People are explanatory creatures. They form theories, or mental models, to explainwhat they experience. These models are sometimes naive, often incorrect. 'Thepoint is not that some people have erroneous theories; it is that everyone formstheories to explain what they have observed' (Norman 1988). Museum visitors are acase in point. It is very informative to walk through the science centre and listen tovisitors' comments. The spontaneous reactions to the exhibits are punctuated byremarks like 'Interesting!' and 'Strange!' or 'Weird!' While, they all convey the

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INTERACTIVE MUSEUM EXHIBITS AS TOOLS FOR LEARNING 3 7

visitor's surprise,.each of these remarks carries a different message that we interpretas follows. 'Interesting!' means 'I didn't know that...but I can accept it'. Thisvisitor is saying that although the effect is not in his previous experience, he couldexplain it. In Piagetian terms, he has available a mental model into which theexperience could be assimilated. 'Strange!' or 'Weird!' means 'It's puzzling...Iexpected something else'. Here the visitor is saying 'this effect is contradicting myprevious experience, my previous beliefs, my prior conceptions; I must notunderstand what I thought I understood'. This exhibit displays a discrepant event.Ideally, by confronting the visitor with his preconceived or naive notions, a 'Weird!'exhibit opens the way for conceptual changes to occur.

This loose analysis of people's verbal manifestations of surprise pointy out thatexhibits in the museum are an excellent vehicle for eliciting the visitors' mentalmodels and investigating their ideas about the way nature behaves. In what follows Iwill give examples of visitors' ideas that have been elucidated using exhibits, as partof a systematic research programme at our local science museum, the Reuben FleetScience Center in San Diego.

Subjects and methods

The subjects for our studies are children, aged 8 to 14 years, who come to trie sciencecentre with their school field trips. The children's openness, candidness andwillingness to talk about what they think, make them ideal subjects. Moreover, theirideas give us insight into the cognitive processes of adults. Indeed, we have foundthat adults share many of the children's preconceptions; however, because the adultsexpress their thoughts more subtly, the preconceptions are harder to identify.

Our methodology for this work is a field version of the Piagetian task-basedclinical interview. The interviewer, much like an anthropologist in the field, stationsherself at the chosen exhibit. When a child approaches and starts investigating theexhibit, the interviewer engages the child in dialogue using questions from aprotocol. The protocol is developed from a large number of preliminary testinterviews, to ensure that the wording, content and sequencing of the questions yieldthe best possible information. The questions ask for predictions and explanations ofthe phenomena that occur when the subject carries out specified tasks at the exhibit,e.g., 'What will happen if you do such and such?' and 'How can you explain whathappened? Can you draw it?'

The work we describe deals with children's conceptions of light and vision. Westudied image-formation through apertures, shadow-formation and colour, whichare subject-matter areas where previous research was patchy or scant. In thesestudies we used exhibits that incorporate a source of light that is in some wayunusual: intermittent (rather than steady) (Feher and Rice 1985), extended (ratherthan a point source) (Feher and Rice 1986, Rice and Feher 1987) or coloured (ratherthan white) (Feher and Rice 1989).

The intuitive notions that we will discuss are not simply ad hoc postulatesadvanced by the children to explain an isolated event. They are ideas organized intofull-fledged models that allow for consistent predictions across several differenttasks. We give two examples of such models: one is an explanation of how shadowsare formed; the other is an explanation of how light propagates.

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38 RESEARCH REPORTS

Models

Trigger model of shadow formation

People's ideas about shadow formation tell us a great deal about how they think aboutlight. This has been recognized by thoughtful teachers who have developed excellentshadow activities to foster an understanding of light (ESS 1976). However, the topic ofshadows is seldom dealt with explicitly in schools. It has also received little in-depthattention in studies of concept formation, with the exception of the work of Piaget(1930) and Guesne (1985). In my experience of teaching astronomy to collegestudents, I have found that many of them could not predict the position and length oftheir shadow on the ground. They might verbalize that a shadow is the absence oflight but could not carry out the simple geometrical construction of the shadow byfinding the locus of the points on the ground where the sun's rays did not arrive.There are tacit notions that get in the way of the right explanation. We have gainedinsight into these notions through our interviews with the children in the museumand the extension of this work to the college classroom (Feher and Rice 1987).

Trigger model is the name we have given to the prevalent intuitive model ofshadow formation. It is characterized as follows: when light hits an object, it triggersor initiates the movement of the object's shadow to the screen, or the ground, wherewe can see it; between the object and the screen the shadow either moves on its own,like a projectile shot out by the opaque object, or it is pushed by the light. Once it ison the screen, we need light to see the shadow, just as we need light to see any otherobject, because ambient light is necessary as a medium that enables our eyes to see.An integral component of the trigger model is the reified shadow, that is, the shadowthat has the qualities of a thing, of a material entity: it has a well-defined shape,occupies space, is capable of motion and is susceptible to being pushed. Like PeterPan's shadow, it has a one-to-one correspondence with the object that emits it: thereis only one such shadow per object, and its shape is the same as the shape of theobject.

These ideas appear quite clearly in the interviews with children at two differentexhibits where the phenomena displayed are counter-intuitive to someone thinking interms of a trigger model. In one of these exhibits one obtains a shadow that does nottake the shape of the object but, rather, the shape of the light source. In the otherexhibit the object shows two, differently coloured, shadows instead of the expectedsingle shadow.

The first effect occurs at an exhibit, named Sophisticated Shadows*, where thevisitor holds a small bead in front of a large cross-shaped light and sees a shadow inthe shape of a cross (see figure 1) (Feher and Rice 1986,1988). As part of a protocolthat included other manipulations as well, the children were asked to hold the beadand predict what they would see on the screen when the cross-light was turned on.After seeing the shadow they were asked to explain why it was a cross. In both casesthe interviewer made a skeleton diagram and asked the child to fill it in. The diagramconsisted of a cross (the light source), a small circle (the bead) and a rectangle (thescreen). Figure 2 A shows typical answers, given by one child. The prediction showsa bead-shaped shadow travelling in space to the screen. The explanation after seeingthat the shadow is a cross, shows that the child is trying to save her original model.

• Sophisticated Shadows is the creation of Bob Miller at the Exploratorium in San Francisco. The effectsthat can be seen at this exhibit go well beyond the ones described in this article.

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INTERACTIVE MUSEUM EXHIBITS AS TOOLS FOR LEARNING 39

Figure 1. Schematic representation of the exhibit Sophisticated Shadows.A pinhole and a bead placed in front of a cross-shaped light source (left)form, respectively, a cross-shaped image and a cross-shaped shadowon the screen (right).

CHILD'SPREDICTION

CHILD'SEXPLANATION AFTER

SEEING EFFECT

CORRECT EXPLANATORYDIAGRAM

The shadows are moving*

;+ +N

The light Is going to reflect \over to the screen, but If s going to I

show the bead too."___

The shadow Is the composite ofbead shadows produced by each

point of the light source.

BI ©.

i • -©i i j

•A black The red light Is hitting off theball and hitting the screen and

making It red right there.'

Green light only Illuminates the spoton screen where the red light does

not reach.

Figure 2. Predictions and explanations of shadow effects produced by: A, asmall bead and a large cross-shaped light; B, a ball and two lights, onered and one green: colour coding, ©red , ® green Thechildren are using the trigger model for both effects. The explanatorydiagrams to the right of the figure show how the shadow is formedwhere some of the light rays are blocked by the object and do not arriveat the screen.

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4 0 RESEARCH REPORTS

She insists that the bead's own single shadow, small and round, must still be there,perhaps not easily discernible, but nevertheless present at the centre of the cross. Inthis study's sample of 40 subjects, three-quarters spoke of the shadow as if it were thepresence of something that belongs to the object and is moved about the light. Itshould be pointed out that this effect, the cross-shaped shadow of the bead,sometimes puzzles scientists too, when they first see it. The diagram at the right infigure 2 A shows how the shadow is caused by the partial blocking of some of the lightrays from the source.

The second effect that is puzzling and unexpected to someone who thinks interms of a trigger model, occurs at an exhibit called Primary Lights. At this exhibit aball is placed in front of two light sources, one green and one red. When the red lightonly is turned on, the dark round shadow of the ball appears on a screen. When thegreen light is turned on also, the dark shadow becomes green and a new red shadowappears, i.e., there are two shadows and they are both coloured (Feher and Rice1989).

The children who were interviewed at this exhibit (a different group from thoseat the previous exhibit) were asked to make drawings to accompany their predictionsand explanations. Figure 2 B shows typical answers given by one child for the effectwhen both lights are on and the ball is placed between the lights and the screen. Theprediction shows the characteristic Y-shaped diagram used by children to achieve asingle shadow with two light sources. One half of the 33 subjects in this study gave Y-shaped predictions. After seeing the two shadows, the child could no longer sustainthe idea of a unitary shadow and he altered his diagram accordingly. However, thedynamic light that gets to the screen to make the shadow is still present in theexplanatory V-shaped diagram, showing how the red light forms a red shadow andthe green light forms a green shadow.

When we look at the correct explanatory diagrams to the extreme right of figure 2we see a crucial element that is missing in the children's diagrams, namely, multiplelight rays emanating from every point of the luminous source. The children drawjust one ray coming out of each point of the light source. As we shall see below whenwe discuss the holistic model of light propagation, this incomplete idea gets theminto trouble.

Children's ideas about shadows tell us a great deal about their ideas on light. Forexample, they think light is an agent of force that can push shadows around; lightbounces off things, but is seldom thought of as being absorbed; light enables our eyesto see the shadows. These notions appear in most work done with light. Additionalnotions appear when we study light propagation in the formation of images. Thiswork is the counterpart of the work with shadows and shows how differently thechildren think about the two.

Holistic model of light propagation

At the exhibit Sophisticated Shadows we can appreciate the symmetry betweenimages and shadows. If instead of the bead there is a pinhole aperture in front of thecross-shaped light, the image on the screen is cross-shaped. If the aperture is large(compared to the size of the light source), the image on the screen will approximate tothe shape of the aperture (see figure 3). We worked with another group of children atthis exhibit, asking for predictions, diagrams and explanations of these effects. Fromthe children's answers we inferred the holistic model of light propagation that isexplained below (Rice and Feher 1987).

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INTERACTIVE MUSEUM EXHIBITS AS TOOLS FOR LEARNING 41

The holistic model is rooted in the notion that each point of a light source emitsonly one ray. Furthermore, the direction in which this beam travels is often definedteleologically: the ray travels in a preferential direction toward the screen or theobstacle or aperture that 'matters' in the problem at hand. This is in contrast with thescientifically correct view that each point of a light source emits light rays equally inall directions (isotropically). In the holistic model, a beam made up of one ray fromeach point of an extended source of light carries the shape of the source itself. Inother words, the shape of the light source travels as a whole to the screen. Using thisholistic model, if there is no intervening object, the image of the light source appearson the screen. In actual experience, what results is an evenly illuminated screen.

When there is a finite aperture in the path of the cross-shaped beam, there are twoprevalent ways in which children predict what will happen (see figure 3). One wayassumes that the rays leaving each point of the source are parallel to each other. Whatis seen on the screen is determined by the portion of the parallel beam that 'fits'through the window. This model yields unambiguous—if incorrect—results thatcan be obtained through a simple geometrical construction. Another method ofpredicting uses diagrams that represent light rays funnelling the image through ahole. If the child is not queried in detail about the drawing, these 'squeeze' or doubleV-shaped diagrams (notice the identifying arrows in figure 3) can be interpretederroneously as the standard ray diagrams used by scientists (which are X-shaped).

To the children who use the holistic model, the image that is counter-intuitive isthe lit circle obtained with a large aperture. The small hole offers no major surprises,for the holistic model can predict the shape seen on the screen. In the case of theshadows it is the converse: the cross-shaped shadow of the small bead iscounter-intuitive; a large ball, as expected, casts a fairly circular shadow.

A remarkable feature of the model is the consistency with which a given studentwill use it. This shows in the responses of the individual children and also in those ofadults. Consider, for example, the predictions of college students who were askedwhat they would see on a screen if in front of the cross-light we placed, successively, alarge aperture, a small one, a large ball and a bead. Some of these students had anincipient correct notion about the formation of shadows. Figure 4 shows how theyused a 'fit' model consistently to answer all questions (Feher and Rice 1987). The useof this model by college students is also described by Goldberg and McDermott(1986) in their work with lenses.

From these examples it is clear that the visitors to the science centre just like thestudents in our classrooms, come to the learning situation equipped with stronglyheld ideas. These ideas are often incorrect (for example, the idea of a quasi-materialshadow and the one-to-one correspondence between object and shadow), orincomplete (for example, the notion that each point of the light source emits only oneray). Moreover, these ideas are not generated ad hoc to explain one event as needed,but they are incorporated into well-conceived models. The same models are used bydifferent visitors to explain a variety of phenomena (for example, the cross-shapedand the coloured shadows).

If the trigger and the holistic models are pervasive and robust, it is important in ateaching situation to know who are the students that think this way. Diagnosticprocedures, applicable to the classroom, are readily derived from the researchtechniques. The tasks that we used to elicit the models present the students withqualitative problems to solve. The students' solutions to these problems are theirpredictions, and these predictions are characteristic of the model they use (see

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42 RESEARCH REPORTS

Figure 3. Diagrams drawn by children, using holistic models, to predictthe images produced on a screen when different sized apertures areplaced in front of a cross-shaped light. The actual images produced areshown in the photographs on the right.

ID V

I J t • t ° I

ii MP + 4- +

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INTERACTIVE MUSEUM EXHIBITS AS TOOLS FOR LEARNING 43

WHAT WILL YOU SEE ONTHE SCREEN IF I TURN ON

THE CROSS LIGHT?

WHAT WILL YOU SEE ONTHE SCREEN IF I PLACE

THIS CARDBOARD WITH ALARGE HOLE BETWEENTHE CROSS LIGHT AND

SCREEN?

WHAT WILL YOU SEE ONTHE SCREEN IF I PLACE

THIS CARDBOARD WITH ASMALL HOLE BETWEEN

CROSS LIGHT ANDSCREEN?

WHAT WILL YOU SEE ONTHE SCREEN IF I PLACE

THIS LARGE BALLBETWEEN CROSS LIGHT

AND SCREEN?

WHAT WILL YOU SEE ONTHE SCREEN IF I PLACE

THIS SMALL BEADBETWEEN CROSS LIGHT

AND SCREEN?

-Across win show on thescreen as «reflection ol the

source*

"The targe bole afcws theentire source of iQht

through."

"Only a small beam canpass ihrouQh ths sfnai

hole.-

The beam Is altered bythe bead-

E3"The cross light has nothing

si I t path so It remains across on the screen.*

Tight appeais to be In thecenter ola dicle*

There Is not enough space toshine the entire cross shapethrough; only a speck wBt be

•Only panel the crossshape wSI appear.*

The bead win blockout some Ight"

' ob|Kt• f - * krge

"The hole Is too large tohaveetlect.

4 — * . m i l — * .hole dec

•oK-That Is as that wn pass

through.*

The tad blocks out most J•gM but tNs much.* S

•Al but bead shows up assgnt*

Figure 4. Four college students consistently use the holistic 'fit' model toanswer questions about images and shadows. In each diagram thecross-shaped light source is on the left, the object or aperture is in themiddle and the image or shadow is on the right.

figures 2 and 3). With this knowledge, we can go beyond the detailed individualinterview and construct a diagnostic test made up of the problem-solving tasks (seefigure 4). An analysis of students' responses then serves to determine which studentsare thinking in terms of these models.

Feeding back the cognitive information into the design of theexhibit

In the previous section we have described preconceptions that museum visitorsbring with them to the use of the exhibits. The study of preconceptions is now morethan a decade old. What is novel about the ones we have described is that they werestudied in an environment that had not heretofore been used for this kind of research.Furthermore, the tasks were carried out using a learning tool, the museum exhibit, sothe interviews gave us information that could be fed back into the design of theexhibit to improve its use as a learning tool for the visitor.

I will illustrate the use of this feedback mechanism through an analysis of anotherexhibit, the Wagon Wheel. At this exhibit, a wheel with painted spokes can berotated with the result that the spokes look blurred. When an intermittent(stroboscopic) light is turned on, the spokes become distinct again and the wheel may

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44 RESEARCH REPORTS

Figure 5. The interviewer and a subject at the Wagon Wheel exhibit,which has been modified to include a rotating slitted wheel.

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INTERACTIVE MUSEUM EXHIBITS AS TOOLS FOR LEARNING 4 5

appear to be stopped, or slowly rotating forwards or backwards. This is a captivatingphenomenon that can be seen in old movies, where vehicles sometimes seem to bemoving in the opposite direction to their wheels. To explain the basic effect it isessential to understand that we see the spokes because the light that illuminates theobject is reflected into our eyes. The details of the effect depend on the properties ofthe light source, of the wheel and of the eye/receptor, and cannot be accounted forwithout taking into account all three elements.

Having made this conceptual analysis of what is necessary to interpret thephenomenon in a scientifically acceptable manner, we turn to an analysis of thechildren's interpretations (Feher and Rice 1985). To explain the blurring of thepainted spokes in the rotating wheel, many children focused only on the wheel,without involving either their eye or the light. They explained that in the movingwheel 'the colours mix', that is, the yellow of the painted spokes and the black of thebackground mix to produce a uniform brown; the light simply allows our eyes to seethe wheel, whether it is moving or not; neither the eye nor the light is an activeparticipant in producing the effect. When the intermittent light was turned on, themost common explanation of the effect was that the light hits and stops the wheel.The light, which under normal circumstances played a passive role, was nowendowed with force and conceived to act on the object to cause the effect. However,the receptor of light, the eye that sees the object, was still absent in theseexplanations. Was there a way of moving the children one step further in theirappreciation of visual phenomena and getting them to include the receptor in theirexplanations?

We took our cue from a nearby exhibit where children observed a set of drawingson a rotating wheel through the slits of another rotating wheel. Their explanationshere left out the light but brought in their eye: 'Now I see it, now I don't: I see it whenthe image comes to my eye through the slit'. We modified the Wagon Wheel exhibitby adding a hand-held stroboscope (a slitted wheel which is, in effect, a mechanicaleye blinker; see figure 5). This addition allowed the visitor to produce the same effect(the unblurring of the spokes) in two different ways (using the intermittent light andusing the slitted wheel). Some children who used both methods did, indeed, bring allthree elements — light source, wheel and eye—into their explanations of thestroboscopic effect. For example: 'The light blinks... The spokes catch light; itflashes and reflects to the eye' and 'When the light comes on, you see the spoke'.

In this example there was a detectable three-level hierarchy in the children'sexplanations, from the simplest the-effect-is-in-the-object to the ones that alsoinclude the light and then the receptor. This hierarchy can be generalized since it alsoappears in the work with colour, images and shadows. In the first instance, the actualcolour, the image and the shadow of an object, just like its shape and texture, aretaken by the children to be properties of the object itself. When the light isdramatized (by making it intermittent, or extended, or coloured), second levelexplanations are obtained in which dynamic properties are attributed to the light.For example, coloured light can change an object's colour or it can cause the object toemit a shadow in the colour of the light. Third level explanations are the ones thatbring together the properties of the light source, the interaction of the light with theobject and the eye/receptor. For example, under green light a red object appears darkbecause our eyes do not see all the colours unless the light is white.

The example of the Wagon Wheel shows the usefulness of carrying out aconceptual analysis of the phenomenon displayed by the exhibit and matching it with

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the visitors' interpretation of the phenomenon. By using the exhibit itself to assessthe visitor's interpretations, we obtain information that can be fed back into thedesign of the exhibit. The outcome is an improved exhibit that is a better vehicle forlearning.

The idea that visitors hold naive or intuitive notions that must be taken intoaccount in the design of an exhibit is just beginning to take root in the museum world.Minda Borun at the Franklin Institute is interviewing visitors in order to assess theirideas on gravity and use this information to design exhibits. Judy Diamond at theSan Diego Natural History Museum is doing likewise with visitors' concepts of theproperties of minerals. At the Science Museum of Virginia, William Walton hasdesigned an exhibition on optics taking into account the results on intuitive notionsfrom research done in classrooms and clinical settings.

Learning through interactive exhibits

My argument in this paper is that interactive exhibits are powerful learning tools of adual kind: for the user they constitute an independent, teacher-free, learning device;for the researcher they are the means for rendering explicit the user's conceptionsand studying the learning process. They are both a teaching device and a researchdevice. Users learn subject matter and process; researchers learn how users learn.Each one of these two modes of use of the exhibit reinforces and refines the other.

If we examine the exhibit as a teaching device, we can distinguish severaldifferent levels in the way in which it accomplishes its task. We name each levelaccording to the function it facilitates.1. Experiencing. At its most fundamental level, the exhibit shows the user thatcertain phenomena occur in nature. The visitor experiences phenomena of which hewas unaware or incompletely aware. This experience is perceptual, sensory, drivenby what Zubrowski (1982) calls aesthetic curiosity. Sensual and emotional qualitiesare involved here, more than the purely cognitive ones. A good example of aestheticcuriosity is the fascination of children and adults alike in watching soap bubblesform, turn and twirl in the air, and change colours until they burst. The aestheticimpact of this phenomenon is a precursor of the next level of engagement of thevisitors.

2. Exploring. At the second level, the users discover new features of the phenomenonby manipulating the exhibit. For example, a good follow-up to watching soapbubbles is making your own, testing how to touch them without bursting them,trying to make a non-spherical bubble (Rice 1984). This active exploration serves tointegrate and internalize the sensory and perceptual discoveries that are being made.Gregory (1986) gives a dramatic account that underscores the importance of activeexploration. It is his study of a man who was blind from early infancy and who was inhis fifties when his sight was restored. 'To our astonishment we found that... hecould see some things immediately, without having to learn; though some otherthings took him months or years to see. It turned out that he could at once see thingshe already knew from his earlier exploring of the world by touch.' (p. 20). We do notknow how this type of learning comes about, but it is an important precursor of thenext level.

3. Explaining. The third level is conceptual. It deals more directly with cognitiveissues and is the one most easily interpretable by educators. The examples of mental

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models given in this article belong in this level. The basic premise is that exhibitusers are explanatory beings who compare the results of their experimentation withthe results they expect. If the results are different from what was expected, thevisitors are surprised. We distinguished two different kinds of surprise. One kindarises when the difference between actual occurrence and expectations can beexplained within the visitor's existing mental frameworks. Then the new result isassimilated by the visitor without abrupt cognitive discontinuities. This does notnecessarily mean that the existing mental framework is scientifically acceptable. Wesaw, for example, that children had no trouble explaining pinhole images with a 'fit'model, or postulating intermittent lights that have dynamic qualities.

The other kind of surprise occurs when the difference between the phenomenonobserved and the visitor's expectation cannot be explained within an existing mentalframework. That is, if the exhibit is truly confrontational, we expect that the user ofthe exhibit will need to shift his or her mental framework and that cognitive changewill occur. In our work this happened with learners who were in a transitional stage,almost ready to take the conceptual jump. For example: a few subjects, who had avery strong sense that shadows are formed when light is blocked, were able toabandon the holistic model of their predictions and attribute the cross-shapedshadow to a 'spreading out of the bead by the light', which is not a bad explanation ofwhat is going on. Whereas we do not yet understand precisely what constitutes asubject's 'readiness' to make a conceptual change, the confrontational exhibit acts asa priming agent for such a change to occur. In most instances the confrontationalexperience will need to be reinforced and expanded, as described below, for thechange to become firmly rooted.

4. Expanding. The fourth level involves the generalization of ideas through theinvolvement of other related exhibits. One exhibit by itself cannot carry the wholeconceptual message. Multiple exhibits on one topic are necessary to extend the user'sworld view. As we saw in the case of the exhibits dealing with shadows, thecontradictions inherent in the trigger model showed up in different forms at differentexhibits. Overkill, by repeated exposure to the phenomenon in different forms, isprobably necessary for the user to confront his or her faulty explanatory model. Oncethere has been a change in a visitor's conceptual model, or an insight has been gainedinto the workings of a phenomenon, the exposure to multiple exhibits can serve therole of clarification and verification of the altered or expanded mental model.Ultimately, the visitor's understanding of the phenomenon should be manifest in theconnections he or she can make with similar phenomena in the world outside themuseum. Here is an example of such an application or expansion, in the words of ayoung woman: 'A friend of mine went to a space movie... where... there are loudexplosions and stuff. I said to my friend, "In real life you wouldn't be able to hear allthat. Sound can't travel through empty space." He said I couldn't know that becausewhen you hit two objects together, they make noise. I told him that there was anexhibit here that proved you wouldn't hear it in space. He came to see it because hedidn't believe me and I proved it to him' (Diamond et al. 1987).

Conclusions

We have described the science learning process via the exhibit as an experiential,exploratory and explanatory process. The users first undergo an experience in whichthey can actively participate; they then give meaning to the experience through their

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own interpretations and explanations. These explanations are validated or confron-ted repeatedly as the learners use multiple related exhibits.

Each one of these levels of learning needs further systematic investigation. Weknow very little about the cognitive implications of experiencing and exploring.Explaining poses many problems. For instance, why do some people hold ontenaciously to an erroneous explanatory model, to the extent of ignoring evidencethat contradicts it? We believe that people benefit from exposure to many differentinstances of related phenomena. But we lack studies that document how this occurs.These research questions pose very general problems about learning. The answersare of importance for both the formal and the informal learning environments.

Science museums with interactive exhibits are, nowadays, a readily availableresource. From a handful 15 years ago, their number has grown to several hundred,spread out throughout the world. Apart from their expressed goals as informaleducational environments for their visitors, science centres can and should play animportant role as research laboratories. Using the interaction of the visitors with theexhibits to study general questions about learning serves, in turn, to enhance thequality of the learning experience itself.

Acknowledgements

I thank J. Diamond, S. Duensing and G. Feher for valuable discussions andcomments on the draft of this paper. Laurie Ortiz contributed the illustrations.

References

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Correspondence

Elsa Feher, Center for Research in Mathematics and Science Education, San Diego StateUniversity, San Diego, CA, USA.

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