Dokshin Lim
email: dokshin@hotmail.com

Carole Bouchard

Améziane Aoussat Running

Iterative process of design and evaluation of icons for menu structure interface of interactive TV services

Keywords: icon usability, user interface design, interactive TV, design process

This paper shows an iterative process of design and evaluation of icons for future interactive TV services. In doing RNRT (French National Network of Research in Telecommunications) iTV project, we tried to generate icons easy to identify, to associate and to memorize for 32 categories and services related to menu structure of our iTV system.

We processed several iterations between design and evaluation at the end of which we obtained a set of valid icons. First iterations were processed in the multidisciplinary project team.

Once we got more or less valid icons, we went through user tests. On the basis of the Multiple Index Approach, we evaluated icons in terms of intuitiveness, associativeness, preference and suitability with the subjective certainty of users.

We extended this approach by adding a delayed session of recall test. As a conclusion, we propose a methodology of icon design and evaluation.

INTRODUCTION

The RNRT (French National Research Network in Telecommunications) sponsors researches in telecommunication. Since 2001, they specially call for researches centred on usage. This is because it is now being realized that considering users in developing innovative technologies is of great importance. This governmental support allows researches highly centred on user while usually interactive products released on the market tend to be produced to be well sold, not to be well used by common users.

The RNRT Interactive TV project is a multidisciplinary collaboration project: usability engineer, specialist in multimodal interaction, psychologist, product designer, computer programmer, innovator and president of a small sized enterprise. The goal of the project was to anticipate future iTV services.

In the iTV domain, technologies are being developed so vigorously that the definition changes everyday. [START_REF] Gawlinski | Interactive television production[END_REF] defined iTV as anything that lets the television viewer or viewers and the people making the television channel, programme or service engage in a dialogue. More specifically, it can be defined as a dialogue that takes the viewers beyond the passive experience of watching and lets them make choices and take actions -even if the action is as simple as filling in a postcard and popping it into the mail, or drawing a picture on the television screen.

According to statistics (IDATE, 4 March, 2003) ITV users now count 52.7 million (TV households) and will continue to increase at an annual rate of 16 %. However, there are few studies questioning on which services are really useful from users' perspective and how to design them usable by majority users. As a result of the project, we proposed a model of future iTV including 90 services that we consider useful for common users. The services are also organized in a usable way. All services are accessible by navigating 2-depth menu designed on the basis of the results obtained by card sorting method with 18 users.

Why was it necessary to add icons to our system? Icons are used more and more frequently in the context of the controls and indications of a large variety of devices. In common usage, the term, icon, has come to denote any small raster image appearing in a GUI (Graphic User Interface) display [START_REF] Mullet | Designing visual interfaces[END_REF]. Well designed icons offer the speed and directness with which recognition and identification take place.

We tried to take account of existing guidelines proposed by THERASIS and Multimedia User Interfaces for Interactive Systems and TV [MUSIST] when designing icons for our system. This research aims, when defining appropriate icons for iTV services, to evaluate icons by user tests and in the end to propose design recommendations for iTV icon design and evaluation.

In many cases, icons require less learning time and effort than text-based alternatives.

However, as [START_REF] Wiedenbeck | The use of icons and labels in an end user application program: an empirical study of learning and retention[END_REF] pointed out, using only icons without label can lead the system much poorer performance than when using texts only or icon-text combination. In particular, when users don't intend to use this interface frequently, which may be the case for certain interactive services of our model, it seemed us necessary to display icons with their text label.

Designing icons is a creative process. Considering that today few guidelines that guarantee usable icons for iTV exist, they should, as [START_REF] Nielsen | Usability Engineering[END_REF] emphasized, be subjected to early usability testing to gain a useful assessment from users. Our iterative process of design and evaluation continued till a set of wholly new icons replacing precedent ones is sufficiently small (see Figure 1).

Figure 1. Iterative process of design and evaluation of icons for iTV services

GENERATION OF FIRST ICON SET

A designer in the multidisciplinary iTV project team was charged of the generation of icons for 32 items (main or sub categories, services and functions) figuring in the menu structure of our interactive TV services.

When there exist already largely adapted icons for common users or standards, we adopted the existing idea and adjusted it to fit our system. For example, we referred to existing standards (European Telecommunications Standards Institute [START_REF] Etsi | Human Factors; The Multiple Index Approach (MIA) for the evaluation of pictograms[END_REF][ETSI], , 1994) ) (MUSIST) and universal public signs (Yang, Kumekawa, & Hotta, 2003) (see Figure 2). We tried not to limit ourselves to copy icons that are familiar to frequent PC users but not for non PC users. However, for some items, essentially known for their functionality in PC environment and so largely accepted that it seems us difficult to invent another, we used existing icons for PC environment (ex: "Print" and "Help" functions and "Mail", see Figure 2).

For services such as "Going out", "Cyber sightseeing" or "Multimedia encyclopedia" for which there isn't yet well adapted icons, rapid brainstorming sessions were organized to generate ideas. Icons proposed in this way (search for existings, creativity) were at first gone through an internal preselection.

The task of designing icons, whether the designer creates new icons or he adapts existing ones, leaves him a great deal of artistic freedom. Some icons may be highly ambiguous and lessen the usability of the device. So, it is imperative that icons be empirically tested in order to establish whether the user does indeed associate the function to the represented (from this point known "referent").

PRESELECTION OF ICONS BY THE DESIGN TEAM

The designer, when designing icons, tried to propose several alternatives for each item. The first icon set was presented to our multidisciplinary design team and passed by a brief preselection. All project team members participated to several votes. The quantity of the icon set went through up and downs. Finally, 51 icons (among 32 referents, 19 had two alternatives) were internally selected to be tested by users.

USER TESTING METHOD

The Multiple Index Approach (MIA) had been developed, tested and employed in the context of an European Telecommunications Standards Institute [ETSI] study on pictograms for basic videophone functions (see also [START_REF] Böcker | A multiple index approach for the evaluation of pictograms[END_REF]). [START_REF] Piamonte | Across the seas a user-based evaluation of candidate telecommunication icons[END_REF][START_REF] Piamonte | Using Multiple Performance Parameters in Testing Small Graphical Symbols[END_REF] found that this method had been found to be suitable as a general testing method for pictograms from all areas. Our test method relied mainly on this MIA.

The main purpose of evaluation was to collect data with the help of which the best suited icons of a number of icon proposals (for some items, two candidates were proposed) could be selected. Three tests (User Test 1, 2 and 3) were designed. Each test aims to measure some of the following indices:

(1) Test of icon intuitiveness: Icon intuitiveness is a measure employed in the work of [START_REF] Nielsen | Design of SunWeb -Sun Microsystems' Intranet[END_REF][START_REF] Nielsen | Icon Usability[END_REF]. Our icons will be normally presented with text labels. Anyway, it would be ideal that icons possess immediacy that allows them to be recognized at a glance as the intended meaning even when they are not associated with text label. In icon intuitiveness test, respondents were shown icons one by one without their label and were asked to describe what each icon was supposed to represent.

(2) Test of icon associativeness: One referent (name and description of an item) is presented on a questionnaire. A group of icons is presented on the TV screen. The respondent's task is to choose the appropriate icon for the referent in question. His choice can be analysed in terms of the hit rate, false alarms and missing values. In addition, subjective certainty is required for each rating. The following is the description of each index.

-Hit rate: Score of correct associations between the referent and icon -False alarms: For a given referent, to which other icons, it is associated when it should be associated to its relevant icon -Missing values: How many instances a respondent doesn't answer a question presumably because he did not know the answer -Subjective certainty: This index indicates how certain the respondents feel in their identification and association. For example, if the user is extremely uncertain about a choice on a test of icon associativeness, he may decide, in a real situation of use, not to use it at all.

(3) Test of icon preference: The respondents indicate which of the candidate icon for one referent represents best the referent in question. Calculating p-values of each pair will show if there exists a significant difference between two candidates.

(4) Test of subjective suitability: The subjective suitability indicates how certain the user is in the given association in question of an icon and a referent. The multiple scale dimension analysis will allow to dissociate icons in groups depending on their mean of subjective suitability. The groups with low suitability should seriously be redesigned.

Each test needed to use different orders of presenting icons to counter-balance learning effects. Icons were displayed on the TV screen (Sony 70 cm in diagonal standard cathode screen).

The distance between the television screen and the users' faces was set to 3 m as Gawlinsk recommended (2003) 1 .

Each step of iteration needed different composition of performance measures described above (see Figure 1). We also collected some descriptive data from respondents on their technical experience (PC, Internet, mobile phone, …).

RESULTS

User Test 1 (icon intuitiveness / icon associativeness)

We showed icons, on by one, to four users 2 without its label. Users were asked to state their best guess as to what the icon was supposed to represent. This test assessed the degree to which the graphic chosen for the icon represented the intended concept. Subjective uncertainty let us have conviction on making decisions. Some icons passed the test easily, with most users guessing the intended meaning or at least guessing something that was very close and would not be misleading in the context of the full 1 The distance between television viewers' faces and the television screen is typically 2-3.5 m [START_REF] Gawlinski | Interactive television production[END_REF]. 2 This type of test can be done by a small number of users, typically five [START_REF] Nielsen | Icon Usability[END_REF]. Four students (22 -26 years old) participated to our test.

system. For example, only one user explicitly used the word "See and Listen (in French Voir et écouter)" to describe our "Watch/Listen (Regarder/écouter)" icon, but descriptions like "Audiovisual (Audiovisuel)" and "Image and sound (Image et son)" actually showed that people got the general idea. In cases like this, we were satisfied that users would understand the icon when it was combined with its label in the full system. So we did not feel a need to change it, especially given that we had planned several additional user tests that would reveal any hidden problems. For these icons, only minor adjustments were made, (see Figure 3).

In other cases, users did not get exactly the correct meaning of an icon but we decided to keep it anyway. "Learn (Apprendre)" was one such example, because we thought that it could be easily accepted when it is presented with the text label. The underlying problem was that sub categories were not coherent to the main category icon. So, we reused the "teacher" image to all sub categories of the main menu "Learn" (see Figure 3).

With respect to the "Going out (Sorties)", people didn't get the intended meaning. They identified the icon as "Assisting a person at home" and "Home automation appliance" (two subjects over four had no idea). At this stage, the project team generated wholly different concept. An icon using a "chick" going out of the egg. Major change was made also to the icon of main menu "Practical life (Vie pratique)". A thumb recognized as "Nice", "OK" and "More information" didn't seem appropriate. It was redesigned as a Swiss knife (see Figure 3).

Figure 3. Example of changes made from the results of User Test 1

The intuitiveness is the principal factor that defines the usability of icon in an absolute condition. However, in real context of use, the correlation between co-existing icons should also be considered. According to the hit rate and false alarms, we were able to make decisions on some icon sets. For example, we discovered poor associativeness of three icons in the main menu "Communicate": "Visiophone", "Dialogue on line" and "Discussion forum" (all 3 errors over 4).

They were redesigned using ordinary smile head and empty smile head at the same time (see Figure 3) because one of the distinguishing factors among the three services is if the correspondent is anonymous or not.

At the end of the User Test 1, we achieved a set of 43 icons. 18 icons could already be considered to be able to pass easily. 15 wholly new icons were added either as new alternatives or as replacing ones. 10 icons seemed necessary to improve (see Figure 4) but we kept them hoping that it would be better when they were to be labelled because we didn't have better idea.

User Test 2 (icon associativeness / icon preference / icon suitability)

At this stage, the laborious icon intuitiveness test was replaced by the icon suitability test at the end. Instead of asking users to state what the icons inspired them, referents were given with associated icons for users to evaluate the suitability among four choices (very bad, bad, good, very good).

Icon preference test was added in order to choose better icons when there were more than two alternatives for one referent (we had 10 referent having more than two alternatives).

Thirteen subjects (student or staff of the New Product Design Laboratory) whose age varied from 22 to 59 participated to the test. Tests were performed in a group of 3 or 4 subjects at a time.

By integrating the associativeness and the subjective certainty (see Figure 5) and by using pvalues of the significant difference in the mean of subjective preference, we were able to eliminate 7 alternatives among 10 couples of icons.

Figure 5. Associativeness and subjective certainty on User Test 2

We also found that with respect to the main category "My garden (Mon jardin)" missing values were high (6 and 7 over 13 for two alternatives), because of the imaginative label, subjects strongly tended to think of gardening related TV programs or shops. We renamed this category as "Perso" and redesigned it as a drawer that would let people think that one can keep personal data in it.

Nine subjects (over 13) chose the icon of "Dialogue" when asked to find the icon for "Discussion forum". The category "Communicate" leaves users to learn the difference among "Visiophone", "Dialogue" and "Discussion forum".

User Test 3 *Delayed session (icon associativeness / icon intuitiveness)

Nine subjects who had participated to the User Test 2 were gathered again two weeks later.

We asked them to associate two referents on each category to the icons. They were also asked to describe what would happen if they choose that item. The aim was to see if users were able to recall well the attribution of icons and services contents.

For icons such as "Friendly TV (TV amie)", "Discussion Forum (Forum de discussion)", "On demand (A la demande)" and "Live (En direct)" which had showed poorer intuitiveness and associativeness during previous tests, we found that most of users associated them well as we intended (at least 8 correct answer over 9 for all categories).

On the contrary, only by seeing icons and labels, they had difficulty in describing exactly what function the items were designed to do.

At the end of the User Test 2 and 3, we finally achieved 32 icons to use for a working prototype of iTV services. Two icons were new proposition, not yet tested. One icon in the

User test in the context of real use using a working prototype

The limit of the above experiments is that we were not able to test icons in real context of use because at that moment, our mock-up was not working. We couldn't see if users given real use tasks like "Save or visualize your personal multimedia data" choose the intended icon "My garden" (modified as "Perso" on User Test 2).

A final usability test in which the icons were shown as a part of the full user interface of the global system was followed. Twenty-four adults and adolescents (6 over 55 years old, 12 between 22 and 40 years old and 6 under 17 years old) participated to the test. Users were given scenarios of use and asked to "think aloud" when they used the system to perform given tasks.

The aim of the test was multiple: the usability of categories and hierarchy of services, using PDA remote control, contents of services as well as the usability of icons. The tested a working prototype looked like Figure 7.

We observed that at first users paid more attention to the text labels than on the icons to use the system. For example, the main menu "Perso" reminded "Personalization" or "Personal configuration" rather than "Personal data". The icon of a drawer didn't orient users to the intended meaning. This main menu was finally renamed as "My data (Mes données)".

When at the end of the test we asked users to recall icons, they were not able to draw exact concepts. Except some adolescents, subjects showed tendency to draw geometric forms (ex: diagonal line, rectangle) but not precise concepts (ex: Swiss knife, drawer) of icon. Did icons contribute to the ease of use of our iTV service system? We didn't find it through the test because users depended more on text labels than on icons. Some exceptions were observed when users were navigating on the two categories: "Watch/Listen" and "Communicate". In the former category, three unfamiliar items -"Diffused programmes", "Ondemand" and "Mediatheque" -needed users to figure out what they are for. The latter ("Communicate") has three services that caused confusion: "Visiophone", "Discussion Forum" and "Dialogue". With respect to these items, text labels were not sufficient enough to understand the contents of the items that users paid attention to icons. We observed that users tried to figure out the contents by analysing the differences in icon design.

CONTENTS 1 .

 1 INTRODUCTION …………………………………………………………………….. 2. GENERATION OF FIRST ICON SET ………………………………………………. 3. PRESELECTION OF ICONS BY THE DESIGN TEAM ……………………………. 4. USER TESTING METHOD …………………………………………………………... 5. RESULTS ……………………………………………………………………………… 5.1. User Test 1 (icon intuitiveness / icon associativeness) 5.2. User Test 2 (icon associativeness / icon preference / icon suitability) 5.3. User Test 3 *Delayed session (icon associativeness / icon intuitiveness) 5.1. User Test in the context of real use using a working prototype 6. CONCLUSION ……………………………………………………………………….. REFERENCES …………………………………………………………………………..

Figure 2 .

 2 Figure 2. Example of icons using existing standards

Figure 4 .

 4 Figure 4. Example of icons proved not easy to identify and to associate on User Test 1

Figure 7 .

 7 Figure 7. Screen of television and PDA remote control of the working prototype

FIGURE CAPTIONS Figure 1 .Figure 2 .Figure 3 . 1 Figure 4 . 1 Figure 5 .Figure 7 .FIGURESFigure 1 .

 CAPTIONS123141571 FIGURE CAPTIONS

Figure 2. Example of icons using existing standards

Figure 3. Example of changes made from the results of User Test 1

Figure 5. Associativeness and subjective certainty on User Test 2

Figure 6. 32 icons of interactive TV services

Acknowledgments. We are indebted to Michel Naël for critical discussion during the project. We are also grateful to Jean-Claude Martin and Stéphanie Buisine of the Laboratoire d'Informatique pour la Mécanique et les Sciences de l'Ingénieur-Centre National de la Recherche Scientifique [LIMSI-CNRS] for their helpful comments. Support. The Interactive Television Project was supported by the Réseau National de Recherche en Télécommunications [RNRT] and the Ministry of Research in France from November 2002 to December 2003.

category "Communicate" seemed not easily associable to its referent "Discussion forum", but we maintained it in hoping that in learning through several uses, users can memorize it. We could say that other twenty nine icons were comprehensible and suit for represent the related items. The final icon set ready to be integrated into the working prototype is shown in Figure 6.

Figure 6. 32 icons of interactive TV services

Our experience let us think that the major role of icon when users are not familiar with the system may be to bring user-friend environment of use. When users are familiar with the system after successive uses, we expect that users depend more and more on icons than on text labels due to the speed and directness of icons with which recognition and identification take place. In that case, we can consider icon-only interfaces for expert users.

CONCLUSION

We used the Multiple Index Approach (MIA) for iterative process of design and evaluation of icons structured in menu. We showed that the choice of indexes should be varied throughout iterations depending on the evolution of icon sets. Initial user test (User Test 1) needed most of all icon intuitiveness test and then associativeness test. Spontaneous icon identification may seem laborious but it would be better to do it at least once in the early phase of iteration, even with a small number of users, in order to get productive assessment from users. For further iterations, the spontaneous identification may be replaced by simple closed questionnaire of subjective suitability. The associativeness test is well adapted for navigation system structured in hierarchical menu.

User Test 2 was composed of icon associativeness test, preference test and suitability test. At this stage, by the preference test, it was possible to eliminate some less powerful alternatives.

User Test 3 aimed to verify for suspicious icons if they can be well associated and well memorized after some delay. With respect to today's information appliances, we emphasize on the importance of the learning effect through time. Common users encounter more and more new products in everyday life. New features having no predators need to be learnt and memorized. In this context, even if a new feature (icon, contents, …) shows poor performance at first because it isn't familiar to users, if it can be easily learnt and accepted, it can be considered as well designed one. The importance lies on the rate of improvement, not on the performance at first glance.

The main contribution of the present work is that we improved the multiple index approach of icon test by adding a recall test session. We empirically did the recall test after two weeks from the first usage test. Further research should define optimal length of delay to perform such king of recall test.

We briefly explained the final test with a working prototype during which we tested once again the icons. We found that the major role of icons was rather to let the system more user friendly than to make easier to use the system because users didn't pay particular attention to icons. It seemed that users relied more on text labels than on icons to figure out items. We also found that user began to pay attention to icons in order to figure out the service contents by analysing icons when the text labels were not sufficient.

In this paper, we showed a way of iterative design and evaluation of icons. User test of icons may begin very early in the process, even when any working prototype is not yet ready (generally when the designer begins to design icons, the working prototype doesn't exist yet). When major corrections were made in early phases, further development becomes simpler (ex: less charge for programmer). However, a final test of icons in real context of use with a working prototype is also necessary.


Carole Bouchard
email: carole.bouchard@paris.ensam.fr

Roger Camous
email: roger.francis.camous@montreal.ca

Ame  Ziane

Nature and role of intermediate representations (IR) in the design process: case studies in car design

Keywords: car design, design process, intermediate representations, materialisation, mental and physical representations

This paper aims to show the key role of the intermediate representations (IR) in the design process and especially in the car design process. For a better understanding of the concept of design, which is by nature conceptual, we propose to study the concept of IR. To this end, we will present the three following parts: description of IR in the design process; nature of IR; and role of IR in the design process. We chose to illustrate this paper with our experience essentially in car design because the design process in this field is historically formatted and very formalised and complex. Besides, this activity is based on the intervention of many professional teams.

Introduction

The elaboration of IR is a main part of the design activity. As cognitive psychologists and design theorists point out, designers need to create multiple representations at different levels of abstraction in order to support their cognitive processes. In industrial design, the most used words are objects or models [START_REF] Mohaved-Khah | Les objets Interme diaires de conception dans un processus de conception aÁ distance[END_REF]. In fact, mechanical engineers with design interests speak about intermediate objects in order to define the different digital or physical objects produced during the design process. The more and more widespread issues related to the cognitive processes involved in design emphasise the immaterial side of the intermediate objects, that is to say the manner they are produced. While we can also find the term model in sociology, we often find the notion of representations in psychology [START_REF] Piaget | L'image mentale chez l'enfant, Collection BSI-PUI[END_REF][START_REF] Rasmussen | Skills, rules and knowledge; signals, signs and symbols, and other distinction in human performance models[END_REF][START_REF] Richard | Les ActiviteÂs Mentales: Comprendre, Raisonner[END_REF][START_REF] Richard | Functioning logic and using logic[END_REF], and cogniticians sometimes use the word artefact [START_REF] Norman | Cognitive Artefacts in Designing Interaction: Psychology at the Human-Computer Interface[END_REF]. Nowadays, the elaboration and communication of design mental and physical representations in the design activity is all the more crucial because it constitutes an essential experimental focus of interest for the elaboration of new digital tools. Digital tools are now widely used in industry for detailed design phases (Computer Aided Design, Computer Aided Manufacturing, . . .). The digital chain tends to spread out into the earliest phases of general concept design.

In the earliest design process phases, any formalised objects cannot be found. For that reason, the notion of IR has to be introduced. In these phases, the term representations means mental representations, which are more individual for this stage. The first explicit IR are produced for individual use, in the sense that they help the reflexive conversation described by SchoÈ n (1994). As soon as they become explicit, the IR can be shared and exchanged with other actors in the design process. Explicit IR are more commonly produced by digital tools now. The word intermediate comes from the evolutionary character of the representations in the design process: we define IR as every representation which appears during the design process, from its beginning to its end.

The design process can be seen as the space problem transformation, either an initial system of signs into a space solution, or a final system of signs. Then the diachronous design process is characterised by a global progressive reconfiguration of the space problem (or brief) into a space solution (3D model), according to a recursive cycle in which a partial transformation takes place from the space problem to intermediate space solutions at every representation level (see Figure 1). This partial transformation first occurs by way of the designers mental representations, followed by the generation of physical solutions and feedback evaluation. The term cycle is used here in order to express the repetitive loops of materialisation including information, generation and evaluation parts. [START_REF] Bouchard | Modellization of the car design process[END_REF] A design project begins with a finality expressed in the form of a brief variable in terms of length and precision. The passing on of the brief to the work team constitutes an important step. The brief can be considered as the first formal and shared representation of the space problem including the different constraints to fulfil through the solutions. It leads to a collective exploration process aiming at a clear definition of the problem. In car design, the brief is a formal document written by the design comity, relatively open at the beginning and including development planning and the future product specifications. The brief is verbally explained to the staff and the team exchange different ideas to explore it with an early brainstorming. If the brief is very imprecise, complementary information is searched by the designers in order to complete it.

The different arrows on Figure 1 show the information flow and its transformation:

* the first corresponds to the constitution of the complete initial brief from the given brief and the information searched by the designer to complete it * the second illustrates the data processing made by the designer in order to produce a first mental representation of the space problem, and iteratively of the space solution

Those representations are co-built in order to provide a formalised exchange support. The reduction of the whole design process duration time and the diversification of the proposed design solutions to address the increasing number of needs in personalisation, as well as the limited cognitive capabilities of the designers and their needs in memorisation and communication, prevail not only to the formalisation of the design process but to its digitalisation too.

Shared representations are privileged media for the coordination of different partners involved in a co-design transdisciplinary process. They are formulated, reformulated and elaborated individually or collectively by the cooperation of participants, according to a process that we tried to define in that paper. Working in a context of co-design, the aim of this paper is to attempt to identify the specific role of IR in design, through the three following parts: The first part is a descriptive part based on our experience in the car design field; the second part is related to different definitions of the IR concept from cognitive science and from engineering design; and the fourth part is an illustration from the case studies presented in the third part, which one essentially of automotive design projects where we were involved as consultants in order to improve the integration of trends and creativity.

Intermediate representations in products design

The design process consists of reducing abstraction through the use of various successive levels of representation integrating more and more constraints. [START_REF] Lloyd | Discovering the design problem[END_REF] describe the design process as generative, deductive and evaluative statements in the activity of design. The generative part, creativity, is involved from early idea generation until production of the technical detailed design.

This part consists in the generation of new ideas and new solutions: by means of numerous mental images and from brief data and other information contained in any design project, designers can generate lexical data, digital or physical representations as 2D and 3D models. This requires the use of manual or digital tools, depending mainly on designer skills and on corporate culture. The generative part can be performed in accordance with various applied creativity methods and tools, which enable the generation of a large volume of ideas, possibly even including the points of view of other non-designer players (ergonomists, sociologists etc.).

The generative part of the design process intervenes at different levels, but the nature of the constraints and of the generated design solutions becomes more and more precise, with the transformation of imprecise data into dimensional ones. The integration of constraints is often considered as a reduction of the creative potential. However, certain constraints are sometimes considered as stimulating for creativity when they are open enough (in green design for example). The design process is characterised by [START_REF] Wang | An approach to computer-aided styling[END_REF] as a conceptualisation including an iterative cycle of mental solutions shown with a given problem, where: * the selection of a solution or partial solutions enables the reduction of uncertainty, keeping in mind the necessary level of vagueness in modifications during subsequent phases [START_REF] Lebahar | Quelques formes de planifications significatives de l'activite de conception en design industriel[END_REF][START_REF] Lebahar | Aspects cognitifs du travail du designer industriel[END_REF] * new constraints are then added while preserving shape and initial ideas * the display of a new physical representation is going to generate new ideas and new solutions.

Abstract finalised information is transformed step by step into material information, by way of mental representations (transfer of information: darkened part in Figure 2). [START_REF] Mackay | Information, Mechanism and Meaning[END_REF] proposes a generalisation of the theory of information: ``information is what forms or what transforms a representation.'' Here, a comparison can be set between the transformation of images and the representations generated by a message containing information. The information modifies the representations so communication can be measured by measuring these changes. A physical system supplies an external memory that modifies the problem of perception in a decisive way. The space problem (expressed goals) as well as the space solution (physical representations) are punctually made explicit by the production of signs, as with verbal codes in the case of the brief, or formal codes in the case of solutions. Adapted from [START_REF] Lebahar | Quelques formes de planifications significatives de l'activite de conception en design industriel[END_REF][START_REF] Lebahar | Aspects cognitifs du travail du designer industriel[END_REF] Each cycle Brief1, m1, M1, corresponds to a specific state of representation. The evolution of the brief is defined by the transformation of ends in purposes, from purposes to objectives, from objectives to criteria, from criteria to more and more concrete technical specifications. The mental representations corresponds partially, as does the physical model. By the definition of every model in a set of attributes, the design process P is then characterised by the succession of cycles: Brief1M1 (A11, A12, A1n), Brief 2M2 (A21, A22 . . . A2n), Brief NMN (An1, An2, Ann). 1 For the industrial designers corporation, a semiotic (which pertains to structuralist signs) point of view is very important as well: any process develops a system of information (objectives) in a signs system (solutions), of which recognition and evaluation allow the production of new signs. This point of view is also very relevant because a design representation constitutes an image of the reality. Everything can be considered as a sign. The semiotic approach by the IR allows emphasis on the importance of this phenomena. Signs emanate from the process of the mental composition of an imaginary object into an object readily comprehensible by anyone.

The design process fits into the global plan of the design process presented above (see Figure 3). The space solution, in the context of design activity, has in particular the passage of iconic signs (trend boards, graphic representations, . . .) in plastic signs (3D physical models, . . .). The space solution is established by a succession of modelled forms. Each new modelled form will progressively integrate more and more precise objects through more and more concrete models: this is called the sign sequence [START_REF] Toyama | Semiotic studies on the design methods[END_REF]. The space problem (ends expressed) as well as the space solution (physical representations) are punctually made explicit by the production of signs, as verbal codes in the case of the brief, and formal codes in the case of solutions. From a semiotic point of view, each representation is a sign composed by a signifier (a symbol or label) and a signified (the physical object or conceptual structure). Each form M1, M2, constitutes a signified which is bound by a known referent: the real object which has its own appropriate physical characteristics. The signified is linked to the referent by a relation of transformations (isomorphism, specific to the socio-cultural character of the recognition codes) (Groupe [START_REF] Mu | Traite du signe visuel[END_REF].

Nature of the intermediate representations

Nowadays, empirical research about the design process is beginning to produce reasonably consistent evidence on which to base models and develop theories [START_REF] Gero | Towards a theory of designing as situated acts[END_REF]. In fact, it is essential to explain the cognitive mechanisms through the representations in the case of the product design process, because the generation of representations is a main part of the design activity. Firstly, we define the general notion of mental representation according to the specific points of view of sociology and cognitive psychology. Secondly, we clarify the notion of explicit physical model with the particular case of the graphic representation, and illustrate this notion in the context of car design.

Definitions of the mental representations

According to [START_REF] Jodelet | Les repreÂsentations sociales[END_REF], a social representation is socially elaborated and shared not only from our experiences, but equally from information, knowledge and models of thought which are received and transmitted by tradition, education and social communication. These social representations aim to organise, control our environment and to build behaviours and communications to establish a common vision in any socio-cultural group. In fact, they are action guides or reading guides. Considering that reality is socially built, then one of the most important characteristics to define the organisations lies on existing perceptions and on the consensually shared visions of the world. The cognitive consensus makes the organisational action easier [START_REF] Ehlinger | Les repre sentations partage es au sein des organisations: entre mythe et re aliteÂ[END_REF]. In fact, this interpretation is very specific to sociology and couldn't be easily transferred to the field of industrial design. The socialisation of an object is more a fundamental property of marketing, but for the designers, the emergence of innovation often lies in contradiction to the recognition of an object by the majority.

In cognitive psychology, the notion of mental representation has two different definitions. In the first definition, the notion of mental representation is related to a set of cognitive elements (knowledge, opinions, believes, ideas . . .) linked to a given object [START_REF] Ehlinger | Les repre sentations partage es au sein des organisations: entre mythe et re aliteÂ[END_REF]. The expression of mental schema is used as well, with the same meaning. This definition is very closed from the previous one in sociology. In the second definition, the notion of mental representation is more linked to the structures of stabilised knowledge which are stored in our long-term memory (see Figure 4). These structures are searched and temporarily activated in order to be used in a particular context for the realisation of a specific task. In the same way, a mental representation can be defined as ``an incidental construction created in a given situation so as to meet the requirements of the current task.'' [START_REF] Richard | Les ActiviteÂs Mentales: Comprendre, Raisonner[END_REF] For Piaget (1948), a mental representation differs from a perception. The first one either constitutes an evocation of objects that are absent at the time, or it doubles the perception of present objects, by referring to other images as well as to similar things. This corresponds to the building of the interpretation, with situated constructions [START_REF] Gero | Towards a theory of designing as situated acts[END_REF] done in a particular context for specific purposes elaborated in a given situation and faced to the requirements of the current task [START_REF] Richard | Functioning logic and using logic[END_REF]. In other terms, [START_REF] Falzon | Les activite s de conception: re flexions introductives[END_REF] speaks about an internal model elaborated by the subject to treat situations. This internal model results from a construction which is based on a data analysis of the situation and on the evocation of memorised knowledge. [START_REF] Dubois | Evaluation et connaissance e valuative: une the orie dualiste de la connaissance[END_REF] sets it against the concept of knowledge: knowledge is often conceived scientific, general knowledge and non contextual while mental representations are linked to the action of the subject, to the specificity of local situations and to their variability. On one hand, mental representations are contextual, temporary and evolve as soon as the situation is changing. They are, on the other hand, quickly available and constitute the operational memory. [START_REF] Rasmussen | Skills, rules and knowledge; signals, signs and symbols, and other distinction in human performance models[END_REF] The term of representation in that sense differentiates the representations from the shared knowledge accepted in a specific field, as described in the first definition. This second kind of representations or knowledge are, in fact, coloured by our vision of the world and consequently more individual. If these representations are then stored in our operational memory, they will become knowledge or belief stored and organised in our memory. The content of the following paper is especially linked with this second definition.

Cognitive processes are made by representations and treatments. As regards the symbolic information, representations are knowledge and interpretations, treatments are inferences and judgments directed to activities of understanding or to decisions of action [START_REF] Richard | Les ActiviteÂs Mentales: Comprendre, Raisonner[END_REF]. The function of representation consists in introducing a mental object producing a mediation between the subject and the world. At the same time, it is functional, by reflecting certain properties of the reality (those that the subject perceives of its experience of the reality, and allows to operate on its mental objects and thus to determine rules of action). The notion of operative image, introduced by Ochanine (1966), specifies the notion of representation by simultaneously introducing understanding or evocation and the operativity: ``image of an object which adequately reflects its major distinguishing features and which is by the same way appropriate for human action/intervention.'' This statement can be linked with the triadic relation of [START_REF] Pierce | Logic as semiotic: the theory of signs[END_REF]. According to Pierce, these three components are: The interpretant is the dimension that gives sense to the correspondence of the two others, as does the IR (Figure 5). In relation to design activities, the initial representation which stems from the brief's treatment will gradually evolve as the uncertainty is reduced, due to the application of the acquisitive process of information, of interpretation (i.e. the construction of a representation which is compatible with expectations), and of the monitoring of the representation's construction by knowledge (activation and transfer of knowledge from long-term memory towards working memory) [START_REF] Akin | How do architects design?[END_REF]. A design problem is characterised by the simultaneous construction of the problem and the solution, with incomplete data and a multitude of solutions [START_REF] Falzon | Les activite s de conception: re flexions introductives[END_REF]. The designer gradually constructs an individual representation of the problem ± solution space; the result of the latter will be in any case original, in that it will be particular and different from those that would have been produced by a panel of any experts in the field facing the same problem (Bisseret et al., 1988;[START_REF] Carrol | Introduction to a special issue on design rationale[END_REF].

Physical representations or intermediates materialisation:

the particular case of the graphic representation Physical representations or intermediate materialisations act as mediators between us and the world, both in execution between actions and the resulting changes to the world state and in perception between changes in the world and our detection and interpretation of the state [START_REF] Norman | Cognitive Artefacts in Designing Interaction: Psychology at the Human-Computer Interface[END_REF]. Norman states that physical representations are cognitive artefacts: cognitive artefacts are artificial devices that maintain, display, or operate upon information in order to serve a representational function and that affect human cognitive performance. Two main aspects of cognitive artefacts are: * the relationship between those aspects of artefacts that serve the execution of acts and those that serve the evaluation of environmental states with the resulting feeling of directness of control * the representational properties of cognitive artefacts: the relationship between the system state and its representation in the artefact. By this analysis, the physical representations enhance human ability by the amplification of the cognitive power of human memory and by the ability to be communicated because of their external form. It allows the cognitive effort to be distributed across time and people and to change the actions required of individuals involved in the related activity.

In the design process earliest stages, graphic realisations make it possible to fix a mental image as well as to render it physical, in a space that gradually gets closer to the product space. In a setting of a complex of actors, the physical object expresses an unambiguous representation of which the reading is immediate by all the actors, whatever their origin, skills or function. Besides its operative character, realisation thus entices communication. But before being shared, the graphic realisation is used to mediate directly between the person and the object: the artefact presents a virtual object upon which operations are performed to be reflected onto the real object. Actions are performed through a feedback mechanism involving both execution and evaluation phases. The gulfs of execution and evaluation refer to the mismatch between our internal goals and expectations and the availability and representation of information about the state of the world and how it might be changed: the gulf of execution refers to the difficulty of acting upon the environment and the gulf of evaluation refers to the difficulty of assessing the state of the environment [START_REF] Norman | Cognitive Artefacts in Designing Interaction: Psychology at the Human-Computer Interface[END_REF].

Graphic representation in design can be alternately considered as:

* the realisation of a part of the space problem (state of evolution of the mental representation) * a ``set of means adapted to find solutions to the definition and to the object dimensioning problem.'' [START_REF] Lebahar | Aspects cognitifs du travail du designer industriel[END_REF] Graphic practice intervenes the upstream phase of the process, as soon as data and knowledge can be understood in spatial terms. It establishes a physical visual support for generating and structuring new ideas. Given its nature and particular position in the genesis and the progressive construction of the object, nowadays more and more research is undertaken on the sketching activities [START_REF] Scrievener | Sketching in collaborative design[END_REF], with the hope of integrating this capacity into computer-aided styling tools. The resulting realisation stems from the immediate fixation of a mental image dictated as a whole in sketch form. According to Lebahar, the first graphic performances have to be ``quick enough and limited to the information necessary to solve the predicament, by expressing a minimum set of solutions on the object to be designed.'' Elaborated forms stem from the:

``graphic encoding of the constraints which are held in the space problem, as well as the choices that come from the anticipating mental image of an overall picture and ®nally, from the anticipations of the process. These forms should ensure that the solution research can still be undertaken without interrupting the design process.'' [START_REF] Lebahar | Aspects cognitifs du travail du designer industriel[END_REF] In order to do so, the designer keeps the volumes he creates vague as long as possible, the strategy being to specify at the right time. The representation is precise enough to express the problem and indistinct enough to enable changes that will not altogether question its very existence. This explains the elastic and distortable signifiers of its composition. For instance, freehand drawing is an effective method of simulation where each graphic simulation is an operative reversible image. This simulation uses incomplete figures as graphic bases of simulation, which are indistinct and possibly distorted. It also uses a system of signifiers (indications, symbols, icons and plans) that are appropriate for the combined evocation of concrete objects (inspiration sources, whole object or parts of it), as well as of abstracted objects (classes of problems). Thus, research and gradual definition of the object are made by the realisation of graphic representations, which will be increased in accuracy and in information as a result of an assimilation ± accommodation cycle. The quest for certainty is carried out by fixating certitudes, variables, coordinating different point of views and dimensional coordination (by comparison). In other words, graphic representations make possible the display and preservation of symbols.

The manual realisation of sketches is a means to progressively reduce uncertainty. It enables contemplation of eventual solutions regarding issues such as aesthetic, ergonomic, spatial, technological and economic features. In this sense, ``the manual drawing makes it possible to write and erase at the pace of the thought, thus leaving traces of the mental process of the reasoning.'' [START_REF] Lebahar | Aspects cognitifs du travail du designer industriel[END_REF] The latter is plastic and appears to be indispensable in the phases of volume search (3D thinking). This gives birth to an analogical relation of the drawings with the concept, thus enabling to manipulate them as transformable mock-ups.

To conclude, the form of representation used by the graphic representation carries great weight in determining its functionality and utility. The choice of representation is not arbitrary: each particular representation provides a set of constraints and intrinsic and extrinsic properties. Each representation emphasises some mappings at the expense of others, making some of them explicit and visible, while others are neglected and the physical form suggests and reminds the person of the set of possible operations. Appropriate use of intrinsic properties can constrain behaviour in desirable or undesirable ways [START_REF] Norman | Cognitive Artefacts in Designing Interaction: Psychology at the Human-Computer Interface[END_REF].

Notion of shared representations

Current interest in the design of computer interfaces has forced consideration for the role of real tasks and environments, and therefore for groups of cooperating individuals, for artefacts and culture. Even though individuals build different representations of a same artefact, the social life in which they are involved during the design process induces them to communicate with each other, to influence each other, and to share information. An individual's knowledge has to be shared with other people in order to be diffused [START_REF] Nonaka | Die Organisation des Wissens[END_REF]. That point constitutes the base of the culture which can be seen as a system of shared knowledge or shared meanings [START_REF] Goodenough | Culture, Language and Society[END_REF]. Collectives or organisational representations are mainly described as shared representations. However, [START_REF] Ehlinger | Les repre sentations partage es au sein des organisations: entre mythe et re aliteÂ[END_REF] indicates a questioning of the existence of shared representations within organisations, in spite of the existence of interaction and communication mechanisms.

The notion of sharing can also be seen as the ability to communicate one's own representations and to understand those of other people, to introduce diversity in the teamwork and so to arouse confrontations and fruitful questionings.

Knowledge and belief exchanges have to be emphasised, as well as the product of these exchanges, more than their sharing in the sense of appropriation of similar beliefs. As such, the concept of organisational representations which we use here must not be understood as a synonym for shared representations, but rather as a sociological cognitive process which allows the members of an organisation to make decisions and to act together.

According to [START_REF] Nonaka | Die Organisation des Wissens[END_REF], there cannot be creation of organisational knowledge without exchange of individual tacit knowledge (specific personal knowledge in the context, belief and concrete knowledge). Tacit knowledge cannot be communicated easily because it is mainly acquired by experience and not easily expressed by words. Tacit knowledge clarifies that feelings, sensibilities and mental models of individuals must be shared in specific contexts to build a mutual confidence, only the transfer of information not having enough effect. To reach this notion of tacit knowledge, Baumard (cited in [START_REF] Ehlinger | Les repre sentations partage es au sein des organisations: entre mythe et re aliteÂ[END_REF] proposes several methodologies of access to tacit knowledge, such as the strategies of confrontation, against-expertise or wear methods.

The notion of sharing does not mean that the organisation's members adhere to common representations, but that the group leaders adhere to it. For the others, it is more about consensus or about mutual understanding which allows the decision taking and the possible collective action. The term of sharing is ambiguous as well, meaning to possess in common as well as to distribute in equal parts. So from the various manners of the ``shared term, it seems that mental collective models make reference to an identical cognitive representation for the group (i.e. common knowledge), as well as a distributed configuration of representations (i.e. any stepping)''; or in a configuration of representations which confirm each other between the members of a group (Klimoski and Mohammed, cited in [START_REF] Ehlinger | Les repre sentations partage es au sein des organisations: entre mythe et re aliteÂ[END_REF].

Most recently, the concept of Design Intermediate Object (DIO) appeared in the engineering design community [START_REF] Mohaved-Khah | Les objets Interme diaires de conception dans un processus de conception aÁ distance[END_REF][START_REF] Vinck | Mediating and commissioning objects in the sociotechnical process of product design: a conceptual approach[END_REF] in the context of Computer Aided Supported Collaborative Work (CASCW). The results of the studies in this field concern the DIO, which contain internal elements (entities) associated with external elements (relations), which are taken as coordinators and indicators of design project progress. The centre of interest focuses on collective computer systems for the exchange and the sharing of the IDO with the aim of defining the classes of entity and relation of an DIO (Mohaved-Khah et al., 2003).

Illustration of the representations levels: the example of car design

The preceding considerations about the representations in the design process constitute a synthesis of the actual works from a theoretical point of view. The purpose of this section is to illustrate the theory with more practical reflections coming from the field of car design. We will present various ideas resulting from our experience in the automotive sector, completed by the point of view of several professionals of this sector.

In architecture, the operative representation of the problem ± solution space refers to a set of normative references [START_REF] Prost | Conception architecturale, Une investigation meÂthodologique[END_REF], which stems from the designers active cultural collection (signified references and signifiers: archetypes, proportions, sources of inspiration, personal experience and spatio-temporal position) and are projected in the object. The same phenomena happens in car design, where designers assimilate the brief's data from the outset of the project. During the brainstorming phase, their mental image integrate forms associated to a type of vehicle and often to a brand. Each designer then orally describes her or his own representation to the others, which ultimately results in the verbal description of a common representation (see Figure 6). The language used often refers to objects or to human beings by analogy. Thus, individual mental interpretation is beginning to appear on paper. The designers become so impregnated with strong verbal and visual codes (type, brand image, target consumers . . .) that they can materialise with notes or sketches. The latter, in turn, will be completed by an informative watch, which will enable the designers to formally imagine the concept. In the first sketches elaboration, mental representation is characterised by a succession of global and vague 2 images of the concept (outline, lines, proportions) that go hand in hand with a particular atmosphere, for example a hostile city. The vehicle is thought of as if it was in movement, denoted by a dynamic tension. At this stage of the process, no precise geographic environment nor any detail are imagined. The global shape, which leads to a structure and the basic lines are only envisioned at this point. Here, the stylist is the unique actor able to estimate the gap between his mental representation and the first realised sketch. To reduce this mismatch, the stylist attempts several endeavours until he finally reaches satisfaction. The succession of mental representations expresses itself partially through the succession of drawn sights (3/4 left, perspective, 1/4 front, 3/4 right, 1/4 rear and orthogonal sights). According to this chronology, one might think that the designer imagines a concept that revolves on itself in a movement which is here punctuated by mental and graphic fixations. The undertaking of numerous different sights thus enables oneself to fully imagine the vehicle. This revolving is dictated by a compromise between the informative need, which is necessary to completely imagine the volume and the convenience to construct graphic representations. Most designers say they mentally visualise various images prior to the drawing of the first sketched lines.

A famous car designer in the USA, Edson Armi, wrote his point of view about the traditional design process. According to him: ``the automotive designers, in order to have control on the complex sculptural forms on which they work, imagine forms in the mental space while they conceive them. This simulation and visualisation of the imagined real space establish the ®eld in which the conceptual battle takes place. It can be said that the mental process goes back and forth in this space, as if the designer was trying to grasp the latter mentally as well as physically. It also appears that the space itself seems to undergo a distortion, a blur, as if ideas oscillated through itself.'' [START_REF] Edson Armi | The Art of American Car Design: The Profession and Personalities: `Not Simple Like Simon[END_REF] Kim, another car designer, adds: ``the visual thinker (. . .) makes several drawings, which are quickly drawn. Searching and forming an idea does not correspond to a static image. Besides, ideas are rarely grasped in a faithful representation, they change and disappear.'' [START_REF] Kim | Protocol Trace Analysis Based on Formal Specifications[END_REF] According to [START_REF] Birtley | Body styling[END_REF], during the realisation of sketches the space problem corresponds to, ``an objective which the designer is going to estimate in an almost subconscious way'': it is only by the means of the interpretation of physical visual messages that the designer knows that the image corresponds to the one he had originally intended to make. Kim puts forward the notion of intuition: presentiments, feelings and intuition are major steps in a field which is usually approached in small steps. He underlines that intuitive capacity, which increases with experience, is crucial at this stage. Car designers try to find innovations in researching something bizarre. To this end, they tend to avoid any clarification in the earliest phases of the design process, or certain constraints as well. If the mental representations were to precisely defined, they could be blocked. It is then by this back and forth process with many readjustments, that they will be able to integrate more and more constraints. The designer can eventually explain this intuitive process aÁ poste riori.

These considerations build a common corpus among designers, of which holistic activity is connected to a wide action of watch [START_REF] Tovey | Intuitive and objective processes in automotive design[END_REF][START_REF] Tovey | Styling and design: intuition and analysis in industrial design[END_REF]. During the making of the final sketches, mental representation consists of a succession of accurate and detailed images (shape, constituents, aspect, impressions linked to the environment, coloured background or detailed environment of the vehicle with individuals), which offer more acuteness and a more realism.

``In spite of a precise de®nition of the concept by means of sketches, the interpretation of the 3D sketches can only be mental, thus without measurement, and subsequently entails inevitable exaggerations during the realisation.'' (Birtley, 1995) During the 3D modelling, it is only when all the surfaces of the model are clearly defined, that the stylist exactly imagines the details and constituents that had only been represented until then by simple lines of outline (for example bumper lines). Mental 3D images play an important part in the decision process and advice of the stylist to the modeller. The natural capacity of the modellers to think in 3D and to express their own interpretation is an undeniable help. Satisfaction is never absolute or unanimous in regards to the adequacy between expected and produced images.

Case studies

Our understanding related to the role of the intermediate representations in the design process has been based on our experience in collaboration with European companies, mainly on three case studies in the field of car design coming from three different design projects where we can find a common ground as well as specificities (see Table 1). In this way, their theoretical contribution will be presented in Section 4 under the form of a common model. The field of car design constitutes a very closed circle. Consequently all of these projects will be partially illustrated because of confidentiality.

Table 1

Case studies [START_REF] Bouchard | Modellization of the car design process[END_REF] professional field. This level of concretisation by professionals is necessary at this stage for further exploitation of the results. Previous experience showed that if concept generation is not followed by field characterisation, the passing from creativity to innovation is not possible.

Project 2

This project was a specific innovative experimental project with the intention of developing a concept of interior vehicle partially dedicated to serial production. It was especially oriented towards the generation of customised parts. The innovative side of this project was centred on communication aspects. There was a preparation phase before the creative session where each specific professional field had to produce corresponding representations in the form of cards, able to show their most recent innovations and fields of influence. These representations had to be very simple and easy to understand by the other corporations. In that way, each corporation had to prepare an explicit representation of his own point of view on innovation in order to share it during the creative session. Cards have a playful effect, recognised for its efficiency during creative sessions involving sometimes conflictual debates between different corporations. Each card was composed of visual and lexical contents allowing the description of an universe (Figure 7). The use of visual matter, such as illustrations and photographs, and of simple keywords, answered the need for very simple representations.

Project 3

As in the preceding project, this project was a specific innovative experimental project with the intention of developing a new concept of interior vehicle partially dedicated to serial production. As in the preceding case, cards were produced by each professional field in order to have some popularised matter to share during the creative session. This project was initiated by ergonomics. The creative session came later and it was difficult to realise a phase of divergence, because some people already had solutions in their mind. The maturity level on the project differed from person to person. The specific use of cards helped to bring people into line.

Common ground and specificities

The three projects were supported by applied creativity methods. These involved many professional skills like ergonomics, design, innovation, architecture and marketing. These methods enhance innovation by way of a multidisciplinary approach, based on communication and allowing the generate and memorisation a great number of ideas with the in-real-time solutions accepted by all the different corporations. The use of cards is relevant for the communication between people of different professional fields. This new representation plays two major roles: makes for easier communication between different professional fields involving conflicts of constraints and stimulates collective creativity. The comparison between the first project (without any cards) and the two others shows that the convergence phase is more difficult in the first case. A long time is spent in solving misunderstandings coming from the specific jargon of the different corporations. These misunderstandings increase the notion of conflict of constraints.

The advantages of the formalism in this case is very clear. A design project related to a complex product, like an automotive vehicle, requires many skills. The communication among these different skills plays an important role in innovation. In each specific professional field, people propose innovations based on a state-of-the-art. No other corporation would be able to propose an innovation in this specific field. The global innovation side of a concept car lies in a good integration of the different skills very early in the design process, following the way of concurrent engineering. Concurrent activities between the different corporations need to be supported by specific representations in order to solve the language and conflicts of constraints problems.

Role of the intermediate representations in the design process

As presented, the design process can be seen as an information process, as a set of successive cycles of realisations of the design information with the manipulation of more and more concrete representations of physical objects until the final solution. The realisations mentioned here concern the formalisation of input data in the form of intermediate mental and physical representations from the technical specifications. In this information process, the design space problem is progressively transformed into a space solution. IR and materialisations are intermediate objects in two ways: the active and constructive perception of the environment and the elaboration of answer and action [START_REF] Avenier | La StrateÂgie Chemin Faisant[END_REF]. In that sense, the communication impact of the explicit representations between the different actors is also crucial.

Through the preceding case studies in the field of car design, we propose in Figure 7 a common model of the design process with its explicit representations. The corresponding projects were mentioned as research and innovation projects in the company. This kind of project aimed to prepare innovative concepts for future vehicles. These concepts were centred on the onboard life in the cockpit. They had mainly to take into account comfort and pleasure. The Both of the projects that allowed us to build a common model of the collective design process and its representations, were centred on interior design, emphasising mainly the ambience design and the usability, and other skills, such as man machine interfaces, interior equipment design, and synthesis.

In fact the different actors in the design team seem systematically to have to go through the three following phases (see Figure 8). Our purpose is finally to produce explicit representations at least at the end of each of these phases, in order to facilitate the communication and appropriation process concerned in teamwork. These three phases are the following: * Phase 1 ± impregnation: the building of specific explicit skill representations related to the initial brief: we illustrated our example in car design with the following skills ± design, ergonomics, and so on. * Phase 2 ± integration: the initial integration of skills through a discussion about the explicit skills representations of preliminary concepts and their mutual validation.

* Phase 3 ± implementation: the building of a common inter-skills representation where the integration of details will follow a more or less synchronic process between the different skills.

Phase 1: impregnation

The initial brief is formulated around a common goal. Where the context deals with a complex design process, as in the field of car design for instance, the first mental and physical representations are more related to a single skill. In other terms, the first steps from the initial brief involve specific skill representations (design representations for industrial design IRD, usability representations for ergonomics IRE, technological representations for engineering IRT and so on), which have to be formalised and made explicit before building common representations. At this stage, we experimented with several paths, and found a very useful approach based on the preparation of the second phase with appropriated inputs. These inputs were the different specific skills representations translated in the form of cards for the creativity sessions, in a unique format with simplified contents such as keywords and illustrations. The illustrations concern watch inputs as well as the innovative productions of the different skills. The specific skills cards are helpful for the following processes involved in the second phase.

Phase 2: integration

After defining the brief, the global design takes place. This phase is crucial because it corresponds to the inter-skills communication based on a collaborative work and more particularly on collective creativity. Actually the cooperation process is a characteristic of the emergence. Each skill group presented their own point of view, with skills representations that are inevitably coded. Decoding is done between skills language by way of an organised creative process (the creative session), using the cards which have been produced in the preceding phase. The applied creativity process allows a privileged open-minded context for compromise, communication and finally the elaboration of a new shared representation between the different specialised skills (common representations). The new convictions generated during the interactions are re-appropriated by the individuals, in order to find out progressively a new common representation through the global design of new concepts. The challenge is here to build a common ground based on a common vision of the design process to achieve the goal of new product development. To this end, the organisation becomes a learning organisation to attain the elaboration of a shared vision (Senge, 1990, cited in Ehlinger, 1998). But the end result is not obtained in summing up the results provided by each skill. It takes place in a more complex move which results from the confrontation and the adjustment of the different skills, bringing in heterogeneous constraints. The shared experience allows any actor to project themselves in the thought process of other actors, through direct dialogue, to reach the common goal. Conflicts and disagreements will push the different members to give a new sense to their experience. Richness and, in this sense, originality come from the divergence of points of views as well as the ability of the actors to rebound mutually on the ideas of each other in real time. Finally a shared vision leads to a certain degree of compromise. In the case of a design plate-form organisation, the compromise comes very early in the process. The advantage of the new common representation is that it is instantaneously decodable by all the actors

Phase 3: implementation

In this last phase, which is more linked with detailed design, the common representation RI3 will be progressively implemented by the team until the production of a final solution, through several refinement phases, by refined briefs, and by evaluation, selection and implementation processes. The implementation corresponds to a skills and project oriented deepening of the common representation. The end of this phase corresponds to the 3D validation of the detailed concept. The early, possible conflict, phases will finally tend to a progressive consensus with plenty of discussions. In this way the risk of errors coming from misunderstandings between the different skills (as in a more sequential process) becomes reduced. New specialised skills have to be involved at this stage, such as transverse skills or hybrid skills. The skill of engineers/ designers, for instance, led in the projects because engineers/designers have a more pragmatic point of view than traditional designers. They are more turned toward the development phases and can be very creative as well. However, both skills are necessary, the traditional and the new. This point sometimes becomes problematic because of certain actors who fear to see themselves dispossessed of their own functions, or of their status.

In order to reduce costs and delays with more variability for personalisation, it is necessary to apply new approaches too, based on the collaborative work and supported by New Technologies of Information and Communication (NTIC). These evolutions towards innovation have to be reinforced by high management levels and require fundamental changes and acceptance in the company's corporate culture.

Discussion

Each of these phases involve an iterative conceptualisation process, with many go-and-back loops. Finally it is essential to organise the innovation to rationalise design, but in practice there is much uncertainty in the conceptualisation process. The mental images are indispensable in imagining the two correlated spaces with constraints and without constraints, but they don't reflect all the richness of the stage in which one is. Sketches (digital or manual) are the representation objects which enable more dynamic progression. IR allow to make the thought process more explicit: they clarify by their explicit character the different phases of the design process, and support in this sense the collective work.

The links between the different points of view of the various skills can be more or less conflictual. The divergence and convergence between the different points of view will emerge explicitly by the use of common representations. The explicit common representations (or Design Intermediate Objects; DIO) depend on different dimensions, such as their autonomy (faced to the other DIO) and their concretisation level (more or less detailed design). The concretisation level evolves until the final implementation phase, while the autonomy between the different skills representations becomes more and more reduced.

As we can see in the following example (Figure 9), the different skills ± ergonomics, design, etc. ± couldn't be worked separately, and the IR are the only relevant supports for communication between the different points of view and skills, for collaborative building and implementation.

Conclusion

In the traditional design approach, different skills were acting relatively sequentially in the collective design process, with very costly iterations in time/energy. In the car industry, a new concept of design, platforms, was introduced to solve the early communication problems between different skills. Platforms are:

``geographic places regrouping the various actors during the project's reviews, where various physical models are exposed to quickly show the problems, and to stimulate creativity while generating a strong constituent of collective learning.'' (Midler) Midler explains how the car design project managers ensure a management by projects, which supports according to him: Simultaneous engineering allows the anticipation of problems by the simultaneity of points of view, and so avoids delays and additional costs due to late modifications (reduction of the times of development from 30 to 50%). This innovative approach is based on a logic of compromise by the definition of common objectives among the various partners, and is given the name `concurrent engineering'. While designing a new vehicle, the treatment of the various conceptual or technical objectives on a hierarchical basis is all the more difficult as they vary according to the skills point of views. In that process, physical representations play an important role in design performance, because of their role in enhancing cognition, as well as their representational format and because of their communication impact in design teams. They provide an earliest consensus between the different skills, allowing consequently a reduction of costs and delays. Models constitute common explicit representations which are progressively developed in an individual ± collective cycle, with the possibility of simulation and adjustment of the action. The explicit IR bring a formalisation of the interactions to the interfaces (assemblies, style, manufacture . . .), and make explicit the problems ignored during the sequential process. The modifications take place before the execution of these representations, thanks to a compromise induced by simultaneity.

Major occurring problems in concurrent engineering organisation are linked to its superposition with the traditional hierarchic organisation. The managers have to reinforce communication aspects to facilitate transition within the existing structure. Besides, communications problems linked to the variety of expertise persist at the beginning, and generate conflicts. The use of physical supports allows thus to improve decision making aspect according to global goals and to reduce risks, while favouring innovation.

To our mind, the ideal conditions to support the emergence of this approach and to diffuse it in the company concerns the relevant association between applied creativity methods and IR, allowing improvement of the generation, evaluation and decision processes in design, both during specific skills phases and collective ones. Even if the creativity sessions allow the provision of systematically early generated shared IR, difficulties often remain in the evaluation and formalisation processes supporting decisions. IR must help in the evaluation and decision phases too. The future of the IR should actually move towards these two phases of the industrial design activity.

Figure 1

 1 Figure1Description of a materialisation cycle[START_REF] Bouchard | Modellization of the car design process[END_REF]

*

  description of IR in the design process * nature of IR * role of IR in the design process.

Figure 2

 2 Figure 2 Representation of the diachronous design process

Figure 3

 3 Figure 3 Design process considered as a sign sequence

Figure 4

 4 Figure4Simplified model of human information system by[START_REF] Rasmussen | Skills, rules and knowledge; signals, signs and symbols, and other distinction in human performance models[END_REF]

Figure 5

 5 Figure 5 Example of the three components of Pierce's triadic model

Figure 6

 6 Figure 6 Transformation of the representation levels and their function in the traditional process

Figure 7

 7 Figure 7 Example of products/usability card as input for the creativity session in car design

  final outputs are demonstrators (internal concept cars), which have to pass by obtaining intermediate results in the form of sketches and intermediate models. The purposes of the demonstrators are the following: * to emphasise the proposals of new performances * to make a synthesis of all the innovative work in the company * to consolidate the methods of consumer and user centred design * to provide a support for the diffusion of knowledge and the evaluation of the synthesis.

Figure 8

 8 Figure 8 Evolution of the IR through the concurrent design process

Figure 9

 9 Figure 9 The different points of view of the various skills related to the seats in interior vehicle design

*

  the acceleration of informational flows * the resolution of the problems * the optimisation of the assignment-use of the resources.

Project 1

This project aimed at developing a new modular platform for automotive vehicles, in order to meet the needs arising from the new shapes of innovative vehicles. At the beginning, the creative session was not supported by any object (physical representation), except by the people themselves. In fact there was no preparation from the different professional fields. After concept generation, people participating in the creative session characterised these concepts according to their specific Notes 1 We can find models M1 sketches, M2 model 3D in the scale, M3 final 3D models, M4 digital models, M5 produced prototype, M6 produced pre-serial, M7 produced serial, as well as for the global concept, that for subsets or finally parts. Attributes vary according to the type of model. In every case they send back to internal characteristics of the made object (materials, process), and external in reference to the utility and to the features of the end product. 2 According to many designers, their premature mental image of vehicles or forms/shapes are very vague (and subject to fluctuation). They are able to see a real image but the latter fluctuates. The shape and details change just as would a myriad of diverse thoughts. What is fixed/written on paper might be a mixture of these different thoughts.