Raquel Bertoldo
email: raquel.bohn-bertoldo@univ-amu.fr.

Disaster Risk Reduction, ref IJDRR_101945 A comparative frame for a contextualised analysis of local natural risk management

Modern natural risk management presupposes that once natural risks are understood, the necessary measures will be taken by the locally competent bodies. Field observations however show that scientific knowledge encounters locally other sources of environmental knowledge which can present resistance to risk management propositions. This special issue adopted a constructivist frame to analyse how natural risks (coastal floods and earthquakes) are locally understood, remembered, and avoided. The comparative fieldwork approach across national contexts (Italy, France and Morocco) in which different natural risks were considered revealed similar local psychosocial dynamics which may be summarised as follows: (1) Knowledge diversity; (2) Local history and trust; (3) Shifting risk rationalisations and (4) Risk objectification.

"The environment is an instrument of hybridisation that questions old dichotomies: nature and culture, local and national, particular and general, vernacular and scientific knowledge" (Claeys-Mekdade & Allard, 2007, p. 51).

Over the course of their local history, Mediterranean communities have learned to adapt to their local environments. Their local knowledge has greatly contributed to the success of their long implantation [START_REF] Nazarea | Local Knowledge and memory in biodiversity conservation[END_REF]. This is why efforts to understand human societies' adaptation to natural risks have underlined the need to understand how risk adaptation and preparedness make sense contextually [START_REF] Joffe | Social representations of earthquakes: A Study of people living in three highly seismic areas[END_REF][START_REF] Luís | Raising awareness of climate change causes? Cross-national evidence for the normalization of societal risk perception of climate change[END_REF][START_REF] Solberg | The social psychology of seismic hazard adjustment : re-evaluating the international literature[END_REF]. On the other hand, modern risk management agencies are bound to propose risk management policies that are also technically and scientifically sound. The institutions from which natural risk management emanates propose understandings of risks that are generalized and must be 'translated' to a given context [START_REF] Castro | Psycho-Social processes in dealing with legal innovation in the community: Insights from biodiversity conservation[END_REF] where risk preparedness might already exist. Risk management can be in this sense at odds with local cultures that "incessantly problematise their own relationships with expertise of all kinds, as part of their negotiation of their own identities" (Wynne, 1996, p. 50).

The coexistence and cooperation between social groups around the same localities, and the differences between how these entities understand and respond to threats [START_REF] Breakwell | Mistrust, uncertainty and health risks[END_REF] illustrate how natural risk management is reinforced when it accounts for the diversity of actors, local histories and identities. We propose in this special issue to analyse how psychosocial processes involved in natural risk knowledge contribute to reinforcingor to underminingcommunity resilience. More precisely the analyses presented here explore (1) how scientific arguments about natural risks are understood locally and (2) how this knowledge contributes (or not) to building natural risk adaptation strategies. The articles taken together analyse both how different types of natural risksin particular coastal floods and earthquakesare contextually understood and how this local knowledge influences collective vulnerability around the Mediterranean basin (France, Italy and Morocco).

Throughout the studies presented in this special issue the question 'who learns with whom' was posed often with different intentions. Across the generations local inhabitants have learned to understand the intricate behaviour of their surrounding environment; while specialists (scientists, technicians) may dispose of generalised, longitudinal data, risk prevention and mitigation solutions. Any mismatch between specialist logics and their local appropriation for risk preparedness was seen to contribute to the vulnerability of local populations to natural risks [START_REF] Solberg | The social psychology of seismic hazard adjustment : re-evaluating the international literature[END_REF]. In this sense a coordinated contextualised set of analyses would help to enlighten how science-society relations support or hamper natural risk management (earthquakes, marine submersions, landslides, erosion, floods, etc.) around the Mediterranean. This special issue presents the results of different field investigations in localities where catastrophic natural events are anticipated to take place, but where risk management or local adaptation couldfrom the specialist's perspectivebe improved. The RiskMed1 project took an interdisciplinary approach to analysing collective intelligence around naturally observed local risk management. Scientists of different disciplinary perspectives contributed to the study of commonalities and differences in knowledge construction and processes seen in communities around the Mediterranean that are exposed to natural risks (earthquakes, coastal floods, landslides, erosion).

Comparisons of how these different Mediterranean communities use knowledge to adapt

to natural risks soon identified common psychosocial factors or processes that impact their adaptation potential. These are presented below and can be summarised as: (1) Knowledge diversity (2) Local history and trust; and (3) Shifting risk rationalisations and (4) Risk objectification. Certain of these points were part of the upstream analytical frame with which we approached the fieldwork, while others emerged from the data and from their comparison.

Each of these points will be illustrated with concrete elements from different fieldwork.

Knowledge diversity: Scientific and 'other' knowledge

Adaptation to natural risks has been a matter of tradition for generations. The rapid urbanisation of Mediterranean communities created several vulnerabilities that were absent in traditional land management. Since the 1990s European member states have relied on common strategies to direct the management of natural risks at local level -European Water Framework Directive (2000) and, more recently, the Floods Directive (2007). These common strategies raise the question of how these technical or scientific approaches to one's local environment are adapted and understood by communities that used to manage risks on their own [START_REF] Wynne | Elephants in the rooms where publics encounter "science"?: A response to Darrin Durant[END_REF].

The conversation between different sources of knowledge is of particular interest to social representations theory (SRT) (Moscovici, 1961(Moscovici, /1976[START_REF] Moscovici | Why a theory of social representations[END_REF]. This theory of social knowledge describes the process by which knowledge emanating from scientific (formalised, reified) spheres becomes invested with 'new' meanings by different social groups. When these new knowledges become familiar in a consensual sphere, it then becomes part of common sense (Moscovici 1961[START_REF] Moscovici | Why a theory of social representations[END_REF]. This diffusion process involves sharing new information and, with it, new meanings [START_REF] Joffe | Risk: From perception to social representation[END_REF]: laypeople resort to metaphors and images to translate these novel ideas into familiar ones [START_REF] Wagner | Everyday discourse and common-sense: The theory of social representations[END_REF].

The symbolism implicit in shared and mediated meaning is part of the reason why SRT can provide a more refined response to the needs of risk communicators. 'Risk perception' approaches have constituted the mainstream research in risk analysis [START_REF] Breakwell | Identiy process theory: Clarifications and elaborations[END_REF] by raising awareness to the logics over which the lay public rely on to judge different types of risks: from everyday life, health, natural or catastrophic risks [START_REF] Slovic | The Perception of Risk[END_REF]. The focus of this approach on individual level cognitive processes left a less theorized aspect of risk perception: how they are based in collective level meaning structures, representations. Constructivist approaches such as the SRT have proposed theoretical frames capable of explaining interindividual systematic risk perception differences through cultural or symbolic differences.

These approaches are more "concerned with symbols, social reality and social knowledge" (Joffe, 2003, p.60). As a constructivist theory, SRT understands social knowledge as symbolic.

Meaning mediates shared realities, which gains their status as reality by being recognised as socially shared [START_REF] Raudsepp | Why is it so difficult to understand the theory of social representations[END_REF]. Because the sharedness of a representation within social groups greatly contributes to its reality status, the biding force of social groups or the social identity is pivotal to how shared meanings are organised, and how these meanings can also play an identity protective role [START_REF] Breakwell | Mental models and social representations of hazards: The significance of identity processes[END_REF].

Since for SRT all knowledge is relative and context-bound [START_REF] Moscovici | Why a theory of social representations[END_REF], it considers scientific knowledge also to be a source of social knowledge. Here an important distinction is warranted between "science as research, scientific knowledge-culture, and science as aspirant public authority knowledge" (Wynne, 2008. p. 24). Scientific institutions arelike publics -reflexive institutions often positioned in relation to policymaking closer to 'science in the making' [START_REF] Latour | Laboratory life: The social construction of scientific facts[END_REF] in the quest for answers to new and still ill-identified problems for which the context plays a fundamental role [START_REF] Patterson | Maintaining research traditions on place: Diversity of thought and scientific progress[END_REF]. The realisation of this fact is crucial in interdisciplinary research: the more colleagues from different disciplines approach risk management as societal issues for which lay publics have past experiences and share valid knowledge, the more resilient and adaptable our adaptation responses will be.

Local history and trust

Risk experiences are described in the literature as important predictors of protective behaviour [START_REF] Gruev-Vintila | Social thinking about collective risk: How do risk-related practice and personal involvement impact its social representations[END_REF][START_REF] Lo | Seismic risk perception in the aftermath of Wenchuan earthquakes in southwestern China[END_REF] and knowledge [START_REF] Luís | Raising awareness of climate change causes? Cross-national evidence for the normalization of societal risk perception of climate change[END_REF]. For this reason, the studies presented here identify direct or indirect (collective history) experiences as paramount elements to understand how local communities consider themselves vulnerable to a risk. These experiences include memories about how local authorities have managed risks in the past, which may also lead to an increase (or decrease) in perceived vulnerability.

Participants interviewed on the southern coast of France (Bertoldo et al., this issue) described their risk experience through personal temporal landmarks (e.g. 'that was the year my daughter was born'; 'my mother was still living'). Environmental experiences are intertwined with personal histories in a place (e.g. Bertoldo et al, this issue). For example, people who have lived their whole life in Port-Saint-Louis-du-Rhône (PSLR) are able to describe exactly what the meteorological conditions should be for the Rhône river to attain its maximum level. Simultaneous high risk awareness and deep place attachment has been described as a paradox [START_REF] Meur-Ferec | Interest of social representations theory to grasp coastal vulnerability and to enhance coastal risk management[END_REF]. Our comparative study between two communities with different coastal risk cultures (PSLR and Fréjus) found that PSLR inhabitants, who share a strong place attachment, also demonstrate a deep understanding of how their environment works and how dangerous it can be (Bertoldo et al., this issue). On the other hand, inhabitants of Fréjus -a popular Côte d'Azur retirement destinationhave a limited and recent first-hand experience with their surrounding environment. Not only are these participants less aware of the natural risks to which they are exposed, but they also share fewer memories and talk about their environment in less emotional terms. These observations can illustrate the ambivalent relationship found in the literature between place attachment and risk perception [START_REF] Bonaiuto | Place attachment and natural environmental risk: Research review and agenda[END_REF].

Shared local history has also been observed to be a central indicator of how existing natural risks have been managed previously and who can be trusted with managing them (Brondi et al., this issue). Our comparative fieldwork has allowed us to illustrate the strong trust of French local inhabitants in state-run risk management bodies (c.f. Gilli, Velez, Bueso, & Réaud, 2020). In contrast, Italian participants exposed to earthquakes are more directly critical of their local administrations, in relation to whom they display fatalism and powerlessness in face of management problems they consider overwhelming (Brondi et al., this issue).

French participants in the studies presented here show general support to state and local risk management despite locally active and critical associative networks. Interestingly, the type of criticism local associations address to state-run environmental bodies (see Bertoldo et al., this issue) is formulated in the same highly technical terms as are used by these agencies. The resort to a hermetic technical language has historically contributed to 'dissuade' local communities from engaging in risk management decisions that concern them directly and to which they otherwise would be able to contribute [START_REF] Claeys-Mekdade | Managing the environment and metamorphoses of the State: the French experience[END_REF]. The French tradition of centralized state management of national infrastructure through the Corps des Ponts et Chaussées ["Bridges and Roads Body"] dates back to 1740; it was reinforced in the Napoleonic era with the task of "carrying out all major planning and development projects, roads, railway lines, canals, drainage of wet areas (after the 1807 Act), river embankments, irrigation canals and water supply to towns" (Claeys-Mekdade & Allard, 2007, p. 42). This approach to environmental management has been greatly questioned because of its expansionist approach treating nature as a 'resource'. Because of the complex dynamics of how climate change disrupts global and local environments, inflexible top-down territorial management might limit the potential of our territories to find climate change adaptation solutions. Highly structured and powerful techno-scientific organisations continuously reproduce the same power relations and imbalances between national and local, specialist and vernacular [START_REF] Claeys-Mekdade | Managing the environment and metamorphoses of the State: the French experience[END_REF].

The studies presented in this issue suggest that different types of trust seem to be at play in the case of French or Italian natural risk management (Brondi, et al., this issue). More precisely, considering that 'trust' might be expressed through two complementary dimensions [START_REF] Bertoldo | Calculative and relational trust in the management of coastal floods and earthquakes: A comparative study[END_REF], one might observe a 'relational' trusthot or social type of trust that is resilient to inconsistent information; and a 'calculative' trustcold and cognitive [START_REF] Engdahl | Risk, communication and trust: Towards an emotional understanding of trust[END_REF]. Here, participants from PSLR apparently make use of a calculative trust when they refer to local authorities' 'technical' competence for managing coastal floods, something they have already done in the past [START_REF] Bertoldo | Calculative and relational trust in the management of coastal floods and earthquakes: A comparative study[END_REF]Bertoldo, this issue). By contrast, Italian participants argue on the basis of a relational type of trust how sceptical they are about local earthquake management [START_REF] Bertoldo | Calculative and relational trust in the management of coastal floods and earthquakes: A comparative study[END_REF]. These results illustrate how communities understand their vulnerability to natural risks, the responsibility of local authorities and how these elements are combined to contribute to a local identity sense of continuity [START_REF] Breakwell | Mental models and social representations of hazards: The significance of identity processes[END_REF][START_REF] Breakwell | Identiy process theory: Clarifications and elaborations[END_REF]. In the next section we will discuss examples of how these socially shared meanings are present in individuals' discursive strategies.

Shifting' rationalisations

Faced with the fear caused by our exposure to a risk, we can adopt different action strategies: either acknowledge this risk's existencediscuss it and describe how we would adapt to it; or adopt the opposed strategy of risk rationalization and willingly downplay its existence as part of an identity protective strategy [START_REF] Breakwell | Mental models and social representations of hazards: The significance of identity processes[END_REF][START_REF] Breakwell | Identiy process theory: Clarifications and elaborations[END_REF]. In this latter case, our effort could be directed towards justifying a lack of action: either because the risk could be seen as too small to warrant action, or too overwhelming for action to make a difference, or too removed in the future for it to be considered our own concern.

In the course of the studies described in this special issue we have seen both strategiesacknowledgement and rationalisation -being used, sometimes by the same individual at different moments of the interview (Bertoldo et al., this issue). Here the risk rationalisations could be designated as: social comparison (e.g. 'we are not as exposed as they are'); risk comparison ('what about this other, more important, risk?') and fatalism ('it is all so overwhelmingly bad, what can we do?'). Rationalisations were often used when the individuals expressed little concern for local coastal risks, or when they did little to reduce their exposure despite acknowledging the natural risk. Such rationalizations of risk exposure have been widely described in risk analytic research (e.g. [START_REF] Luís | Is it all about awareness? The normalization of coastal risk[END_REF][START_REF] Joffe | Risk: From perception to social representation[END_REF] as part of individual or collective processes. [START_REF] Breakwell | Mental models and social representations of hazards: The significance of identity processes[END_REF] proposes that these rationalisations become part of social representations and that these representations also contain information about which groups can be trusted or not [START_REF] Breakwell | Mistrust, uncertainty and health risks[END_REF], as part of identity defensive strategies. What is interesting in the rationalisations identified in the studies presented in Bertoldo et al. (this issue) is that their main objective seems to be to justify individual inaction in the face of natural risks while local authorities and the state are taken to be responsible for their protection.

These shifting rationalisations rely on inconsistent and sometimes antagonistic arguments, demonstrating how social representations can support communicative acts as if they were 'tools' addressing different needs at different places and times [START_REF] Raudsepp | Why is it so difficult to understand the theory of social representations[END_REF]. In this sense [START_REF] Joffe | Social representations of earthquakes: A Study of people living in three highly seismic areas[END_REF] describes the profound differences in how Americans, Turkish and Japanese people regard their responsibility for earthquake preparedness: Americans are more inclined to regard individuals as primarily responsible, whereas at the other extreme Japanese see the state as responsible for household seismic protection. As cultural resources, these risk representations are used to address different contextual needs, serving for example as a personal reassurance or to project the blame onto local authorities for not doing enough to manage a community's risk exposure.

Risk objectification

Scientific knowledge about natural risks has evolved in the understanding of natural phenomena that are generalisable across contexts, times and places [START_REF] Beck | Risk society: Towards a new modernity[END_REF]. Still, societies have repeatedly demonstrated their difficulty to act in the face of abstract, distant (Spence, Poortinga, & Pidgeon, 2011;[START_REF] Trope | Temporal construal[END_REF] or never-before-experienced phenomena such as climate change (e.g [START_REF] Marshall | Don't even think about it: Why our brains are wired to ignore climate change?[END_REF].

Previous psychosocial analysis has illustrated how when faced with real direct [START_REF] Sarrica | Shaken and stirred: Social representations, social media, and community empowerment in emergency contexts[END_REF] or indirect [START_REF] Smith | Climate change in the British press: the role of the visual[END_REF]) consequences of natural events, social groups find in shared images a support to exchange about previously abstract ideas. When coupled with images and shared emotions, catastrophic events can galvanise ideas about how a natural risk is thought, remembered, recognised and communicated.

The studies presented in this special issue have also shown how past experience sets important precedent for how the risk of a natural event is imagined and thought possible (Bertoldo et al., this issue; Brondi et al., this issue). Interviews showed how past risk events are often used as a basis to discuss present and future exposure. More precisely, local communities were able to acknowledge the existence of natural risk when they were able to 'see' it, imagine and therefore communicate about it. In the absence of a past risk event providing a concrete representational basis, these events were easily rationalised as distant possibilities that did not affect them directly. This difficulty of communities or societies to prepare for natural risks that are anticipated by experts but that arestillabsent from the collective memory is here interpreted as a limitation in how objectifiable a representation is. Anchoring and objectification are the psychosocial processes Moscovici (1961Moscovici ( /1976) uses to explain the emergence of new representations. These two processes are complementary in their use of shared memories to comprehend new events or threats. By anchoring new phenomena in old ones, groups use already existing categories as basis to understand newer, not yet familiar ones. This process explains the resort to approximations with past natural events, metaphors and the like when groups are confronted with unfamiliar objects. Objectification on the other hand is what renders these shared memories accessible on the first place. When abstract ideas or are objectified, they acquire materiality and "become expressions of a reality thought as natural" (Vala, 2000, p. 465, our translation). When representations are materialized, they become an icon that summarises quickly and intuitively an idea that become easily communicated and remembered.

Objectification describes therefore a paramount process for how risks are represented and come to assume a "concrete shape" [START_REF] Moscovici | Preconditions for explanation in social psychology[END_REF] through risk management institutions.

When a risk fails to be objectified, we can consider this risk to be yet in a state of 'latency', where it possibility exists as a certitude for some individuals or groups, but not for society's shared scheme of reality. Based on observations presented in this special issue we propose that ill-objectified risks remain in an epistemic state that is typical of socially attenuated risks [START_REF] Kasperson | The Social Amplification of Risk: A conceptual framework[END_REF]. The collective experience of a natural catastrophe can surely contribute to the objectification of a risk, but as described elsewhere [START_REF] Poumadère | The 2003 heat wave in France: Dangerous climate change here and now[END_REF] the amplification of a risk, and its objectification, depends on how an event unfolds in relation to a context shaped by risk management institutions, policymakers and individuals, all of these nested in a culture. For this reason, we consider the objectification of a risk as part of the representational process in the absence of which an idea (or representation) is doomed to be forgotten [START_REF] Moscovici | Notes towards a description of social representations[END_REF].

In the understanding of our participants, unless 'something happens' in relation to coastal floods in southern France (Bertoldo et al., this issue), policymakers have little incentive to invest in avoiding them, even in the face of scientific advice. In this manner, unless a threat is remembered, objectified in the shared symbolic tissue, it would also fail to leverage popular mobilisation and state response.

Special issue articles

The articles included in this special issue mirror in different ways the need to apprehend risk management contextually in order to understand societal response. The articles that compose this special issue frame the local knowledge in different ways and propose different pictures of how publics organise local scientific issues. Our shared approach to local understandings of natural risks is not one that proposes this source of knowledge as being 'better' than scientific views (see [START_REF] Wynne | Elephants in the rooms where publics encounter "science"?: A response to Darrin Durant[END_REF] but rather focuses on local "multiple knowledges, reflecting their different sets of priority concerns […], accountably validated as far as possible, and if necessary (but unity or consensus should not be presumed) negotiated together as such" (Wynne, 2008, p. 28).

The article by Bertoldo, Guignard, Dias and Schleyer-Lindenmann describes a comparative study of two localities at risk for coastal floods. Qualitative analysis was able to show how the two places studied (Port-Saint-Louis-du-Rhône and Fréjus) involve different types of community ties to the environment and consequently different ideas of what local issues are [START_REF] Wynne | Elephants in the rooms where publics encounter "science"?: A response to Darrin Durant[END_REF].

The article by Brondi, Benedetti, Tanga and Bertoldo (this issue) describes a comparative study between two localities of the Italian Apennine region with different recent earthquake experiences. Based on different environmental cues in their local environment these two localities prioritize earthquake risks differently as a function of their recent seismic experience.

Ivcevic and collaborators (this issue) take us to the southern Mediterranean coast where the northern Morocco region of Tangier-Tetouan-Al Hoceima can be characterised as a multirisk zone (floods and earthquakes). The article analyses how different variables explain residents' willingness to protect themselves and to invest financially in their protection from natural risks. The study shows that regional differences associated with varied sociodemographic profiles significantly contribute to risk management strategies. Ivcevic, Statzu, Satta and Bertoldo (this issue) also analysed in Sardinia (Italy) local publics' interpretation of wetlands as a protective feature against coastal floods, coupled with an economic analysis of how willing they are to invest in theseoften regarded as unpleasantenvironments.

Our Mediterranean-centered approach to risk management is complemented by invited

Conclusion

This special issue was proposed with a common assumption of how natural risks are understood locally. Contributors made use of widely different methodological approachesstructural equation modelling, qualitative analysis or econometry. Still they shared a common view about how natural risks acquire the thick reality conveyed by through being socially shared.

These international comparisons across nations, cities, social groups and risks have contributed very contextualized descriptions of how local natural risks are based on social memories. Despite their differences, they also revealed similar dynamics in locally embedded processes involving knowledge status, institutional trust, experience, rationalisation or risk objectification.

Taken together, the synthesis presented above illustrates the role of socially constructed realities [START_REF] Joffe | Risk: From perception to social representation[END_REF] engrained in Disaster Risk Reduction. Shared memories, social knowledge, and symbols are enacted through social relations and communications that might explain why risk management strategies succeed or fail.

Special issue references

  comparative contributions analysing risk management on different Atlantic coasts: French, Canadian and Colombian. The first of these invited contributions includes the article by Navarro and colleagues (this issue) which presents a study interested in the adoption of protective behaviours regarding erosion and coastal flooding risks in the French Atlantic coast. They use qualitative and regression modelling to identify the variables explaining the adoption of coastal flood protective behaviour. Mocaer, Guillou et Chouinard (this issue) compare the 'systemic vulnerability' of atlantic coast dwellers in France and Canada to erosion and floodig risks. This comparative analysis considered how different people-place variables (e.g. place attachment, dependance, social identity, coastal risk experience) contribute to reinforce the resilience of these two communities. This analysis also proposes a dialogue between the theory of social representaitons and the concept of systemic vulnerabilities. Also in the Atlantic, Duque-Muñoz, Navarro, Restrepo and Fleury-Bahi (this issue) bring us to the Caribean to explore how Cartagena (Colombia) inhabitants understand and protect themselves from coastal flood hazards. Our last invited article by Guillard, Navarro and Fleury-Bahi (this issue) presents an analysis of how psychological distance and place attachment predict risk perception and the adoption of climate change adaptation measures across groups of Colombian participants who had experienced floods or droughts.

This project was funded by the Labex OT-Med (ANR-11-LABEX-0061), supported by the Investissements d'Avenir, French Government project of the French National Research Agency (ANR) through the A*Midex project (ANR-11-IDEX-0001-02).

Acknowledgements

This work is a contribution to Labex OT-Med (n° ANR-11-LABX-0061) and received funding from Excellence Initiative of Aix-Marseille University-A*MIDEX, a French "Investissements d'Avenir" programme (RISKMED project). Additional funding was provided for the study in France by the European Union-FEDER programme (DIGUE 2020 project). I also like to thank Claire Mays for carefully reviweing a first version of this manuscript.

This project (2016)(2017)(2018)(2019) was funded by the Labex OT-Med (ANR-11-LABEX-0061), supported by the Investissements d'Avenir, French Government project of the French National Research Agency (ANR) through the A*Midex project (ANR-11-IDEX-0001-02). I also thank Claire Mays for carefully reviewing a first version of this manuscript.


Hyunyoung Kim
email: hyunyoung.kim@univ-grenoble-alpes.fr

Céline Coutrix
email: celine.coutrix@univ-grenoble-alpes.fr

Anne Roudaut
email: roudauta@gmail.com

KnobSlider: Design of a Shape-Changing UI for Parameter Control

Keywords: Shape-changing interfaces, knob, slider, contextual inquiry. ACM Classification H5.2 [Information interfaces and presentation]: User Interfaces

Physical controls are widely used by professionals such as sound engineers or aircraft pilots. In particular knobs and sliders are the most prevalent in such interfaces. They have advantages over touchscreen GUIs, especially when users require quick and eyes-free control. However, their interfaces (e.g., mixing consoles) are often bulky and crowded. To improve this, we present the results of a formative study with professionals who use physical controllers. Based on their feedback, we propose design requirements for future interfaces for parameters control. We then introduce the design of our KnobSlider that combines the advantages of a knob and a slider in one unique shape-changing device. A qualitative study with professionals shows how KnobSlider supports the design requirements, and inspired new interactions and applications.

INTRODUCTION

Many professionals (e.g., sound and light engineers, graphic designers, camera operators and pilots) use physical controls to interact with a large number of parameters. The interfaces have evolved little in the past 30 years, and these still use physical controls despite touchscreen technology being widely used. In fact, physical interfaces are ideal for such professions as they provide haptic feedback and thus eyes free manipulation. Each type of controls has different interactive advantages: the most prevalent are knobs for fine adjustment and sliders for absolute positioning. Knobs, or dials [START_REF] Michelitsch | Haptic chameleon: a new concept of shapechanging user interface controls with force feedback[END_REF], are buttons controlled via rotation. Sliders are linear control elements consisting of rails and cursors. There is a variety of controllers, varying in angular or linear range, size, shape, torque or friction, with or without detents, and implemented via diverse technologies (of various resolution). Their interfaces allow users to simultaneously access a large number of parameters. As a consequence of exploiting the advantages of physical controls, such interfaces are inevitably bulky and crowded. For instance, one of the sound systems we observed in this work offers more than 400 parameters through 3 banks of 112 controls -28 sliders with 4 layers each-and 65 knobs (Figure 2, P5-6). Such large interfaces are thus not portable, which can hinder users in many ways: e.g., sounds engineers cannot move around the stage to test sounds while adjusting parameters. Furthermore, they are also cognitively demanding: for example, users must remember and reach the position of each parameter control. Touchscreen GUIs, which offer more flexibility by providing consecutively different interfaces on a surface, could solve some of these issues. However, they lack haptic feedback and hinder eyes-free interaction.

A B C

As a result, there is a tradeoff between the space occupied by input devices (e.g. sliders and knobs) and the number and types of controls they offer. Current solutions such as remappable banks or GUIs force users to choose either sticking to one type of device or losing physicality. In this paper, we offer KnobSlider, which provides both a physical knob and a slider through shape changing. It decreases the interface size and gains portability without losing the different types of controls or their physicality. We believe this is a strong advantage which was additionally suggested by our user population. Our bottom-up research procedure described below has the following contributions:

1. Through a formative study, we gain an understanding of professional users' needs regarding parameter control. We conducted contextual inquiries to learn about use of physical and touch screen controllers. 2. We derive design requirements for a flexible physical interface element based on the formative study. Users need fast, precise, eyes-free and mobile interaction with a large number of parameters. They also need retrocompatibility with current interaction. 3. We present KnobSlider, a shape-changing physical control that shifts between a knob and a slider (Figure 1). It combines the advantages of both types of controls while increasing the flexibility of the interface. 4. We report a qualitative study with professional users interacting with a KnobSlider. Results reveal that they appreciate the flexible control, and suggest promising applications for shape changing parameter controls.

RELATED WORK

Our work aims to provide flexible physical interaction for the control of continuous parameters, through knobs and sliders. We survey previous works that investigated flexible and physical continuous input devices.

Flexibility of a Single Device

An early height-changing knob was proposed by Hemmert et al. [START_REF] Hemmert | Dynamic knobs: shape change as a means of interaction on a mobile phone[END_REF]. It was dedicated to cell phone notifications such as missed calls. Button+ [START_REF] Suh | Button+: Supporting User and Context Aware Interaction through Shape-Changing Interfaces[END_REF] also changed the knob height to give distinctive control access to different users or to change the level of control difficulty for games. Haptic Chameleon [START_REF] Michelitsch | Haptic chameleon: a new concept of shapechanging user interface controls with force feedback[END_REF] was a shape-changing knob that changed its function according to its deformed shape to control videos. InGen [START_REF] Badshah | Interactive generator: a self-powered haptic feedback device[END_REF] was a passive knob with dynamic detent, stiffness and abrupt stops to help users scroll a list.

Many studies have explored the flexibility of sliders focusing on dynamic haptic/force feedbacks. Some motorized slider cursors have been proposed for physics education [START_REF] Shahrokni | Onedimensional force feedback slider: going from an analogue to a digital platform[END_REF], haptic cues of sound amplitude [START_REF] Shahrokni | Onedimensional force feedback slider: going from an analogue to a digital platform[END_REF][START_REF] Tanaka | Haptic Wave: A Cross-Modal Interface for Visually Impaired Audio Producers[END_REF], and creating music loop [START_REF] Gabriel | BounceSlider: actuated sliders for music performance and composition[END_REF]. Vázquez et al. [START_REF] Vázquez | 3D Printing Pneumatic Device Controls with Variable Activation Force Capabilities[END_REF] changed the haptic feedback of knobs and sliders by changing pressure in air chambers around the knob/slider axes. Zoomable TUIs explored physically zoomable sliders to balance between device footprint and pointing performance [START_REF] Coutrix | Shape-change for zoomable tuis: Opportunities and limits of a resizable slider[END_REF]. In addition to knobs and sliders, a volume-changing mouse was designed to allow zooming and scrolling through the control of the pressure [START_REF] Kim | Inflatable mouse: volumeadjustable mouse with air-pressure-sensitive input and haptic feedback[END_REF].

Space-Multiplexing

One approach to enable flexibility is to provide multiple devices in different locations simultaneously. There have been two approaches taken in spatially arranging controls. First, next to each other, like on sound mixing boards. Here, users manipulate sets of physical controls, including sliding and rotating joints [START_REF] Blackwell | Articulating tangible interfaces[END_REF]. Their drawback is their footprint when space is a critical resource. Second, on top of each other, like in Zebra Widgets [START_REF] Chan | CapStones and ZebraWidgets: sensing stacks of building blocks, dials and sliders on capacitive touch screens[END_REF] and a rotary knob control for microwave oven [START_REF] Djajadiningrat | Easy doesn't do it: skill and expression in tangible aesthetics[END_REF]. They required less surface than the first arrangement. However, Zebra Widgets do not allow stacking a dial on a slider or vice versa. With the microwave control, moving one device might cause unwanted movement of the other device.

Time-Multiplexing

Another approach is to have knobs and sliders in a sequence at the same location. With Paddle [START_REF] Ramakers | Paddle: highly deformable mobile devices with physical controls[END_REF], users can make a flat surface for swipe (linear input), then deform it to a ring for rotational input. inFORM and Emergeables [START_REF] Follmer | inFORM: dynamic physical affordances and constraints through shape and object actuation[END_REF][START_REF] Robinson | Emergeables: Deformable Displays for Continuous Eyes-Free Mobile Interaction[END_REF] provided a slider and a knob at the very same location. With ForceForm [START_REF] Tsimeris | Achieving soft and directly deformable interaction on tabletop interactive surfaces[END_REF], users molded a placeholder to make a slider or knob on a touch surface. ChainFORM [START_REF] Nakagaki | ChainFORM: A Linear Integrated Modular Hardware System for Shape Changing Interfaces[END_REF] provided a linear or a round shape with actuation and touch sensing. However, in these implementations, the manipulation of the sliders was very different from that of the physical sliders, either lacking a physical cursor [START_REF] Follmer | inFORM: dynamic physical affordances and constraints through shape and object actuation[END_REF][START_REF] Nakagaki | ChainFORM: A Linear Integrated Modular Hardware System for Shape Changing Interfaces[END_REF][START_REF] Ramakers | Paddle: highly deformable mobile devices with physical controls[END_REF][START_REF] Tsimeris | Achieving soft and directly deformable interaction on tabletop interactive surfaces[END_REF] or continuity [START_REF] Robinson | Emergeables: Deformable Displays for Continuous Eyes-Free Mobile Interaction[END_REF].

Both Space-and Time-Multiplexing

Some research approaches allowed both spatial and temporal multiplexing. With inFORM and related approach [START_REF] Follmer | inFORM: dynamic physical affordances and constraints through shape and object actuation[END_REF][START_REF] Robinson | Emergeables: Deformable Displays for Continuous Eyes-Free Mobile Interaction[END_REF][START_REF] Tsimeris | Achieving soft and directly deformable interaction on tabletop interactive surfaces[END_REF], it was also possible to provide several sliders and knobs sequentially in one place and simultaneously in different places. Our approach incorporates a combination of spatial and temporal multiplexing. In contrast to using widgets on touch surfaces [START_REF] Jansen | Tangible remote controllers for wall-size displays[END_REF][START_REF] Weiss | SLAP widgets: bridging the gap between virtual and physical controls on tabletops[END_REF], we want to avoid the need to place widgets on surfaces. In contract of using discrete control points on a slider [START_REF] Follmer | inFORM: dynamic physical affordances and constraints through shape and object actuation[END_REF][START_REF] Robinson | Emergeables: Deformable Displays for Continuous Eyes-Free Mobile Interaction[END_REF][START_REF] Tsimeris | Achieving soft and directly deformable interaction on tabletop interactive surfaces[END_REF], we allow for both continuous and physical manipulation of the cursor.

Balancing between Space-and Time-Multiplexing

Space-and time-multiplexing provide different advantages. Space-multiplexing allows spatial arrangements [START_REF] Fitzmaurice | An empirical evaluation of graspable user interfaces: towards specialized, space-multiplexed input[END_REF], persistence of attachment between devices and parameters [START_REF] Badshah | Interactive generator: a self-powered haptic feedback device[END_REF][START_REF] Fitzmaurice | An empirical evaluation of graspable user interfaces: towards specialized, space-multiplexed input[END_REF], exploiting spatial memory [START_REF] Scarr | Supporting and exploiting spatial memory in user interfaces[END_REF][START_REF] Shaer | Tangible User Interfaces: Past, Present, and Future Directions[END_REF], simultaneous control of several parameters [START_REF] Badshah | Interactive generator: a self-powered haptic feedback device[END_REF][START_REF] Fitzmaurice | An empirical evaluation of graspable user interfaces: towards specialized, space-multiplexed input[END_REF], and specialized physical form factors [START_REF] Fitzmaurice | An empirical evaluation of graspable user interfaces: towards specialized, space-multiplexed input[END_REF]. Time-multiplexing lowers hardware and maintenance costs [START_REF] Fitzmaurice | An empirical evaluation of graspable user interfaces: towards specialized, space-multiplexed input[END_REF] and avoids physical clutter [START_REF] Shaer | Tangible User Interfaces: Past, Present, and Future Directions[END_REF]. Two extremes of these different multiplexing approached are "hundreds of potentiometers" and a "single mouse" [START_REF] Badshah | Interactive generator: a self-powered haptic feedback device[END_REF]. Fitzmaurice et al. [START_REF] Fitzmaurice | An empirical evaluation of graspable user interfaces: towards specialized, space-multiplexed input[END_REF] and Beaudouin-Lafon [START_REF] Badshah | Interactive generator: a self-powered haptic feedback device[END_REF] say that the challenge lies in finding the optimal balance between the two types of multiplexing. We aim to fill in this gap and combine both multiplexing.

FORMATIVE STUDY

We used contextual inquiry [START_REF] Holtzblatt | Rapid Contextual Design: A How-to Guide to Key Techniques for User-Centered Design[END_REF] to gather users' requirements. Our observation and interviews of experts targeted specifically unresolved usability problems related to physicality and flexibility of devices for continuous parameters control -mostly knobs and sliders.

Participants

We first identified the most widespread professions extensively using physical input control. According to the US Bureau of Labor Statistics 2) using knobs and sliders in their professional activities: 1 movie operator (P1), 1 graphic designer (P2), 2 light engineers (P3, P4), 2 sound engineers (P5, P6), and 2 pilots (P7, P8). All participants were voluntary and consented to photo and video recording. The interfaces participants were using were mainly physical, although a few recently started using touchscreens.

Procedure

All sessions took place in ecologically valid settings and we observed all participants doing live activities, e.g., shooting a movie (P1), drawing (P2), preparing a show (P3-6) and piloting (P7-8) (Figure 2). We asked them to explain what was happening each time a sequence of actions was not clear. We interviewed them after the activities. At the end, we asked for situations where they needed to balance flexibility and tangibility. When the activities required concentration or silence (P1, P3) and it was not possible to ask a question, we asked questions during the follow-up interview. Each session took around 2 hours.

Data collection and analysis

We collected 8640 words of written notes, 141 drawings and photos (i.e., finger posture or devices used), and 2h34m26s of video and audio recordings of particular sequences of actions or interview. When possible, we performed the analysis no later than 48 hours after the interview. First, we described every sequence of observed actions. We used the collected notes, photo and video recordings from our observations to help the description.

We then used thematic analysis [START_REF] Braun | Using thematic analysis in psychology[END_REF] to analyze user needs regarding their controllers. We started with a research question: "what is needed for the users to perform their task?" A coder first labeled the observations with initial categories (codes) answering the question. An additional two coders joined to discuss, and agreed on them as well as identifying particular topics to regroup codes by themes.

Our final scheme had six final main themes.

Results

We identified six needs regarding the control of parameters. We illustrate them with examples of actions we observed or comments made by the participants.

Most knobs were potentiometers with no bounds or detents, of around 1cm diameter with small lobes on their sides. We observed fewer varied knobs: e.g., with position mark (P1), concentric ones (P8), discrete arrow-shaped ones (P8) or large knob with a concave notch for rotation with a single finger (P4). In the following, we focus on the requirements that encompass knobs and sliders.

Interaction with a large number of parameters

All participants interacted with a large number of parameters. For instance, the fewest number of parameters was ten to control P1's stereoscopic cameras' 3D position, 3D orientation, focal length, 1D focus distance, interaxial distance and convergence. P2 used many of the ~60 Photoshop tools and their parameters (e.g., brush size, tip, roundness, hardness, etc.). During his show, P3 adjusted ~50 parameters in total. P4 -P8 (sound and light engineers and pilots) had more than 100 parameters to deal with.

Fast interaction

Fast access to parameters: In many situations, the users needed to quickly acquire the devices. For example, to quickly access the parameters of a fan and a fog machine during the show, P3 (light artist) chose to permanently display two dedicated knobs on the left-hand side of his interface (Figure 2). P2 explained that her desk is always tidy: she needed a clear space to go from one device to another without losing time. P5 told that he never used the sliders that are too far away, and preferred pressing a button to quickly switch the parameters associated with the sliders that are close to him.

Fast manipulation of parameters:

For instance, P7 related that the throttle was used by default for quick, coarse adjustments. P1, P3-P6 worked "live," i.e., during the shooting or the show, so they must manipulate the parameters promptly. When working for music concerts, they needed to be very reactive as musicians never play the same way. The need for fast manipulation required some participants (P3-P6) to use several fingers on sliders or two hands on different devices. P2 explained that she started using the computer to work faster: her work requires several back and forth exchanges with the client who asks for modifications. She used the computer to do quick corrections (undo) that physical brushes and pens could not.

Fast observations of parameters: For example, P1 was manipulating interaxial distance between stereoscopic cameras and the bounds of the slider were clearly showing her the physical constraints of cameras. She also used red tape to mark a particular value of the interaxial distance during the shooting (see Figure 2 P1, the left side of the slider). P5 and P6 sometimes quickly glanced at their interfaces to observe a parameter value during the show.

During manipulation, the knobs of the cockpits (P7-P8) provided haptic feedback through haptic detents. For quick observations of parameters, P7-P8 looked or touched the corresponding devices. P7 explained that in emergency situations, quick observation of parameters is critical. Overall, sliders were preferred for rapid observation of parameters.

Precise interaction

For precise interaction, most participants used large sliders (~8-10cm), with very smooth friction to allow tiny movements. The only small slider we observed was a tactile one with a placeholder (Figure 2, P2), to zoom in on the screen. When operating a slider, P1 placed her hand carefully to avoid mistakenly moving the dials next to it (Figure 2).

Knobs, even when small, also offered high precision as most of them were multiturn. Using the knob for precise control was done by P2 who used her tactile dial with a placeholder to scroll webpages. We observed P4 (light engineer) using a knob before the show to very precisely set a projector angle (Figure 2, P4). For this, he performed many rotations on a knob with low control-display (CD) gain. Similarly, P7 and P8 (pilots) used knobs to accurately input decimal values of radio frequencies. P7 related that the extremity of his aircraft's throttle could be turned for precise adjustments. P6 needed to adjust the curve of sound level (dB) for each frequency (Hz) of each instrument and microphone on stage. He preferred using the physical knobs for this rather than the touchscreen. P1 (movie operator) used a knob to adjust, at pixel precision, the horizontal shift between stereoscopic images, by performing multiple rotations. Overall, knobs were preferred for precise interaction.

Eyes-free interaction P1 needed eyes-free interaction because her screens were not collocated with her knobs and sliders. Similarly, P2 focused on her canvas on the screen and looked away to modify her tool, thus lost time finding her object on the canvas again. P3-P6 watched the stage while interacting (Figure 2). P5 explained that he preferred physical controllers, and never used the touchscreen of his console, which our observations corroborated. P5 and P6 said that interacting with bounded parameters on multiturn -i.e. unbounded-knobs was not comfortable, as they have to look away from the stage to watch the LEDs around the knob. Bounded knobs were not available on the mixing console we observed, and participants said that they also seldom find them on other mixing consoles.

P3's problem with touchscreens was that he felt "blind" as there was no haptic feedback. We observed P3 missing his intended trajectory of a knob on the screen: he started to follow the knob on the tablet. While looking at the stage, he drifted from the knob, losing control of it. When he realized it, he looked down to reacquire the knob. We observed him trying to grasp two touchscreen sliders eyes-free: one with the index finger and the second with the middle finger, both unsuccessfully. He then looked down to re-grasp the sliders. He recouped the lack of tangibility with extra-large widgets, but it was not satisfactory for him: he lost space, and still lacked tangibility, which caused critical errors.

P7 and P8 (pilots) used push/pull handle for power and mixture (of air and fuel) and often placed their hand on the handles to know their status without looking (Figure 2, P8). P7 said, "If you put your hand on [the control device], you know in which mode you are." They commented that physical devices were particularly useful when visibility in the cockpit was altered by smoke. P7 and P8 both explained that aircraft manufacturers were introducing touch screen interfaces. Both agreed that the idea was dangerous. Their comments strengthened the cockpit design requirements in previous work [START_REF] Angel | The aircraft of the future: towards the tangible cockpit[END_REF][START_REF] Vinot | Could tangibility improve the safety of touch-based interaction?: exploring a new physical design space for pilot-system interfaces[END_REF].

Mobile interaction

All users needed mobility. P1 used her cameras and control devices at different locations. P2 sometimes worked away from her desk, e.g., in a van during a vacation. P3 explained that moving around the stage was crucial for him: when not possible, he communicated with someone in front of the stage as a proxy. Unfortunately, this person might not understand what he wanted or did not have the same demand on the final quality. To avoid losing time or quality, he used a tablet, but sub-optimally moved back and forth between his desk and the stage. P4 went on the stage to better see his projectors, and then came back to the console. We observed P5 going on the stage to ease the communication with musicians. He said this was the only reason he used the tablet, as he did not like using the sliders/knobs on touch screens. To avoid using the tablet, he communicated with musicians via a microphone (Figure 2, P5), or even shouted or signed. Sometimes a third person was necessary to help communication with drummers who did not have a microphone. Thus, all solutions were suboptimal. Mobility was also necessary during the show: P6 walked around the venue to hear the sound from other locations. He then had to come back to the mixing desk to adjust the parameters. P7 and P8 (pilots) had a compact interface that fits in the cockpit.

Retro-compatibility

The professional users needed to leverage their existing expertise with current interfaces. For example, P2 explicitly commented that she was not keen to change interface because her workflow was efficient and she was not ready to lose income for a short term. The only participant that explicitly showed no interest in retro-compatibility was P3. He built a new interface dedicated for each show and improved it with practice. Yet, his touchscreen controllers were mimicking physical ones (knobs, sliders, buttons, etc.).

DESIGN REQUIREMENTS

We derived the following six requirements directly from the themes of our formative study. R1. Interaction with a large number of parameters was requested by all participants. The cameraman had the least [START_REF] Esteves | Informing design by recording tangible interaction[END_REF]. The sound and light engineers can deal with more than 100. Types of parameters were diverse: some were discrete (e.g., tool in Palette) or continuous (e.g., sound volume). Some were bounded (e.g., flaps' angle) or not (e.g., shift between cameras). Some were cyclic (e.g., projector's angle). R2. Fast interaction. Quick access to parameters can be supported by placing devices within users' reach. Rapid manipulation of parameters can be supported through smooth trajectories. Fast observation of parameter value can be carried by visual and/or haptic display, including min/max value or value of interest. R3. Precise interaction can be supported through a large interaction area (multiturn knob or large slider) and little friction. Enough space between devices prevents errors. A stable grip on the device also allows its operation without slipping. R4. Eyes-free interaction. Eyes-free access to parameters can be supported by spatial stability of the device to leverage motor-spatial memory.

Eyes-free manipulation of parameters can be supported through physical trajectory guide (e.g., slider's rail, knob' rotational axis) and haptic feedback. Eyes-free observation of parameters' value can be supported through a physical cursor or haptic feedback (detent). R5. Mobile interaction can be supported by small devices. R6. Retro-compatibility with current interaction: it is arduous for users to give up current UIs -even though new ones can be beneficial in the long term [START_REF] Scarr | Dips and ceilings: understanding and supporting transitions to expertise in user interfaces[END_REF]. This can be supported by standard operations of standard devices and customizability.

Some of these requirements are incompatible (e.g., a slider should be large for precision and small for mobility). As a consequence, a good design needs to find a compromise in order to maximize users' satisfaction.

KNOBSLIDER DESIGN

We first present the design space of the previous work to reveal space for improvement. We then present KnobSlider, a shape-changing device for rotary and linear input, and how it supports the target design space and requirements.

Design Space Exploration

We focus on the physical interfaces that have some retrocompatibility (R6) with physical knobs and sliders (rotational/linear interaction). They have different spatial and temporal combinations as shown in Table 1. The current solutions largely cover the design space but lack some of the requirements: A. A single knob would hinder the fast and eyes-free operation of a parameter (R2,R4). A small single slider would either hinder precision (R3) and a large single slider would take too much space (R5) on a surface. B. A knob or slider sequentially morphing out of a surface currently lacks continuity (R1) or physical cursors (R4). Manually placing a knob or a slider on a surface is time-consuming (R2). C. Adjacent knob and slider are space-consuming (R5). A knob on top of a slider (and vice-versa) would cause unwanted movement thus lack precision (R3). D. Physical knobs and sliders anywhere, anytime are not fully supported yet. As in B, manually placing knobs and sliders on a surface is time-consuming (R2) and knobs and sliders morphing out currently lacks continuity (R1) or physical cursors (R4). Current systems partially support time-multiplexing through banks of sliders only.

We aim a novel solution improving the tradeoff between users' requirements: a device that takes the shape of either a knob or a slider in sequence, improving time-multiplexed solutions (B). Several of such devices combined will improve time-and space-multiplexed solutions (D).

Design Principle

After exploring with low-fi prototypes (Figure 3.A), we converged on a particular design that better supports the requirements. The design has six triangular prism blocks connected to each other (Figure 3 B-D). When folded (D) the prisms form a hexagonal prism (knob). When unfolded (B), the prisms are aligned, thus creating a connected surface. A cursor can move along the surface. The design is originally inspired by the Sensitive Rolypoly [START_REF] Fulda | Raising user impulse awareness: the sensitive rolypoly[END_REF], and the final design looks similar to the InGen [START_REF] Badshah | Interactive generator: a self-powered haptic feedback device[END_REF] when folded.

Working prototype

To open/close each hinge between two blocks, we embed a servomotor (SG90) at each hinge between two blocks (Figure 3.B, block #1 to #5 from left to right). Each motor is individually controlled by an Arduino. The housing is 3D printed with ABS. For sensing the knob or the slider value, we place a manufactured clickable knob 2 at the base of the sensor center (see Figure 4).

R2. Fast interaction

Knob and slider interactions are as fast as standard ones. The shape change takes 0.1s.

R3. Precise interaction

Knob: 100 control positions/rotation, diameter is around 75mm. Slider: ~237 control positions/112mm (cursor travel length). Silicon base sticks on the surface. R4. Eyes-free interaction KnobSlider offers physical knob, button and slider.

R5. Mobile interaction

KnobSlider is small enough so that several are available on a mobile surface. R6. Retro-compatibility KnobSlider provides a button, knob and slider.

Table 2 summarizes how our prototype supports the requirements. The device can support two continuous parameters, and several can be used in parallel. The peak motor speed is 60° per 0.1s, enabling the shape change in ~0.1s. The KnobSlider can reach similar precision than knob/slider on their own; in our prototype, knob has 100 control positions per rotation, and slider has ~237 control positions per 112mm (cursor traveling length). The knob diameter is ~75mm. The outer length of the slider is around 182mm, and the cursor's traveling distance is 112mm due to the gears at the corners of slider. When it is a slider, the footprint is about 68.2 cm 2 . When it is a knob, the footprint becomes around 43.6 cm 2 . Additionally, the silicon base ensures stability. The KnobSlider has physical cursors for both knob and slider, but the slider friction varies because of the gaps between the blocks. Future engineering effort includes miniaturization, haptic feedback, cursor automation and cable removal to ensure better mobility and multiturn knob. Even though the prototype is low fidelity, it is suitable to collect early feedback from users.

QUALITATIVE STUDY

We evaluate the KnobSlider and gather feedback of professional users in ecological setups. We also gather possible uses and future developments of the KnobSlider. For this, we use technological probing [START_REF] Hutchinson | Technology probes: inspiring design for and with families[END_REF]. Note that we chose to conduct a qualitative study over a quantitative one for two reasons: First, previous work conducting performance evaluation of shape-changing UI [START_REF] Robinson | Emergeables: Deformable Displays for Continuous Eyes-Free Mobile Interaction[END_REF] showed that a low-res prototype does not perform as well as the envisioned concept. For this reason, researchers seldom conduct quantitative evaluation of shape-changing UI [START_REF] Hemmert | Dynamic knobs: shape change as a means of interaction on a mobile phone[END_REF][START_REF] Nakagaki | ChainFORM: A Linear Integrated Modular Hardware System for Shape Changing Interfaces[END_REF][START_REF] Suh | Button+: Supporting User and Context Aware Interaction through Shape-Changing Interfaces[END_REF][START_REF] Vázquez | 3D Printing Pneumatic Device Controls with Variable Activation Force Capabilities[END_REF][START_REF] Yao | PneUI: pneumatically actuated soft composite materials for shape changing interfaces[END_REF]. Second, quantitative experiments are hard to generalize to real use as the tasks performed by participants might be too simplistic [START_REF] Esteves | Informing design by recording tangible interaction[END_REF] or the participant groups can be artificial: often young students and/or colleagues of the authors. We wanted to avoid this by bringing the KnobSlider to its real target users for a task as real as possible. Accordingly, we conducted a qualitative experiment where we asked professionals to use the KnobSlider in a situation as close as possible to their actual work (Figure 5). This allowed us to gather diverse and real feedback on its benefits and drawbacks.

Participants

We recruited 10 participants: 6 from the first study (P2,3,5,6,7,8), and 4 new via our extended social network or calling/emailing local professionals: PI and PII (light engineers), PIII (graphic designer), PIX (photographer using Photoshop like P2 and PIII). They (2 females) were between 32 and 63 years old. All participants were voluntary and consented to photo and video recording.

Procedure

Each participant was interviewed while interacting with the probe for ~1 hour at their workplace when possible (for P3 at a café and P7,P8 in their office). We demonstrated how the prototype worked. The participants were asked to perform given tasks in thinking-aloud protocol. We then conducted semi-structured interviews to assess our requirements. At the end, we asked them to explain a recent situation where the KnobSlider might, or not, be useful.

Apparatus

Most systems used by our participants3 had very diverse and/or proprietary communication protocols. Instead of investing a lot of resources for interfacing a low-fidelity KnobSlider with them, we wanted to gather early feedback and prototyped custom applications tailored for each profession. This enabled close-to-real world tasks while providing simplicity and flexibility as required by technology probes [START_REF] Hutchinson | Technology probes: inspiring design for and with families[END_REF]. One exception was Photoshop, used by three participants (graphic designers P2,PIII,PIX), which allowed us to easily interface the KnobSlider directly through mouse and keyboard events.

All participants manipulated the same hardware prototype (described in the previous section). The prototype was linked via USB connection and an Arduino to a MacBook Pro running the task applications.

Tasks

To ensure each participant uses the KnobSlider in situations similar to their actual work, we implemented different tasks representing what each professional were frequently observed doing in our formative study (Table 3). We proposed a mapping between these tasks and the KnobSlider's inputs and shapes (Figure 5) in order to support the user requirements.

For graphic designers (P2,PII,PIX), we implemented a script to control Photoshop functions through the KnobSlider. With the slider shape, users switched among tools in Tools Palette. With knob shape, users changed tool size, such as Brush and Burn tools. For the rest of participants, we implemented stand-alone Processing applications because their interfaces were not compatible with our device. The light artist's (P3) task was changing the size of a moving laser light with the slider, and changing its movement speed with the knob. The light engineers (PI,PII) were asked to control the intensity (brightness) of a projector with the slider and angle of the projector with the knob. Sound engineers (P5,6) could control volume of a song with both slider and knob. Pilots (P7,8) controlled two different flap angles with the slider and knob.

Data collection and analysis

We collected 313 words of written notes, 1 photo and 7h14m33s of audio and video recording of particular sequences of the interview and use of the KnobSlider. We

PIX PII

transcribed the audio of the recordings. As in the first study, we used thematic analysis to analyze our results.

Results: Meeting the users' requirements

For each requirement, we first present the ways KnobSlider supported them and then report on areas for improvement.

Interaction with a large number of parameters

Participants immediately confirmed that the KnobSlider allows them to interact with a large number of parameters. First, its ability for time-multiplexing was praised. As P6 explained: "I have a volume slider, and when I adjust the pan, I have a knob. I gain space. Instead of having both a slider and a knob, I have two in one". PII even further wanted to have the central button dedicated to the control of a third parameter. Second, they saw its ability for spacemultiplexing. Several participants, mostly sound and light engineers, mentioned that they would like to have several KnobSliders next to each other.

Fast interaction

Fast access to parameters. Most participants said the change of shape was fast. Expecting a slow change of shape, we observed two participants (P3, P5) first holding down the button, instead of a short click on the button (Figure 5). We noticed that for some of them, the change of shape was scary at first: "it seems that it is going to explode" (PIII), "it scares me […] because it moves" (P5). However, after a few trials they liked it and appreciated its speed: "it needs to be fast" (PIII), "it is not disturbing" (PIII), "it is fun, like an animal" (PII). We observed participants clearly playing with the shape-change capability and getting used to its speed. P7 even said that it might take too much time to change the shape: "There is a time between both [shapes], so it has to be two different steps of my work. […] It is for two distinct tasks, two ways to work on the same data". This suggests that the change of shape can be even faster for an expert user.

In particular, participants liked the way to trigger the change of shape (button). PIII said it allowed her to use her thumb for this, leaving other fingers in place, ready for adjustment of the parameter. Improving stability would ensure even faster access to parameters: P5 complained that the prototype sometimes fell when deformed.

Fast manipulation of parameters. All participants liked the smoothness of the knob. Seven participants mentioned or agreed that KnobSlider in slider shape (Figure 5, P2 and PIX) helps quickly reach the vicinity of a value. Even faster manipulation of parameters can be achieved through lower friction. Five out of ten participants complained that the slider had too much friction. For instance, PII said that "it needs to be smooth", like "velvet".

Fast observation of parameters. While the lack of smoothness of the slider was critical for sound and light engineers, P7 and PIII said that the detents of the slider are useful. P7 (pilot) said that army pilots use detents for feedback, as they focus on external elements for survival. PIII (graphic designer) suggested using them as haptic feedback for switching between Photoshop tools with the slider. Further observation of parameters can be achieved through motorization: after the adjustment of a parameter with the knob, P6 (sound engineer) wanted the cursor of the slider to be updated.

Precise interaction

Seven participants mentioned or agreed to use the KnobSlider in knob shape (Figure 5, P6) for precisely reach a parameter's value. For instance, P7 said "[in a cockpit], rotary means precision" and P6 "and then I need precision and shazam! It transforms to a knob". P6 cited example of parameters that can be controlled on mixing consoles with either knobs or sliders, e.g., pan (whether the sound comes from left or right) or volume, depending on the required precision. In addition to multiturn with a low CD gain, the stability of the knob shape further helped fine adjustments: "I can rest my hand on it" (P7), "I feel I play with something solid" (PIX). Its shape further helped precision by preventing fingers from slipping: PII liked that the knob was not round, but provided edges for a secure grip. More precise interaction can be achieved through longer slider shape. Light and sound engineers mentioned that they like sliders to be as long as possible. Stable slider would also help precise interaction. Eight participants said that the slider was not stable. In Figure 5, PII is holding it with his left hand. The rotation axis needs to be locked and supported on the surface when in slider state. Lastly, lower knob would increase precision in interaction. Sitting participants (PIII, PIX) found that the hand operating the prototype lacked support because the prototype is too high.

Eyes-free interaction

Probably because KnobSlider leverages standard physical interaction and its eyes-free capabilities [START_REF] Jansen | Tangible remote controllers for wall-size displays[END_REF], this requirement was less discussed. For example, three participants mentioned that the slider's shape allows for adjustment and haptic feel of bounded parameters. When in knob shape, the slider's cursor protrudes from the knob. P3 found it "efficient" to use it as a handle to rotate the knob.

Mobile interaction

Most participants saw the KnobSlider as a solution to bring a few physical devices on a mobile surface: "I take it, I go there and I do my balance for real" (P5), "If you need it to be transportable, then this is a solution" (P6). They saw its abilities for deciding on the go which device they want. Either for (1) a different parameter: "I have a volume slider, and when I adjust the pan, I have a knob. I gain space. Instead of having both a slider and a knob, I have two in one" (P6); or (2) for the same parameter, but with a different footprint: P5 wanted to have eight KnobSliders, and take them out of his mixing table to put them on a tablet-like surface and go on stage with the musicians or in the public with only the necessary channels to adjust. If eight do not fit on his surface, then he would change a few to knobs. Even more mobile interaction can be achieved through removing cables (as half of the participant suggested), and miniaturizing the prototype. Five participants complained about the size of the prototype. Light and sound engineers (PI,PII,P3,P5,P6) were comparing the prototype to the sliders and knobs they daily use, and mentioned that they like knobs as small as possible.

Retro-compatibility

They understood it was either a knob or a slider and all participants manipulated the device without difficulty. They were particularly happy it could support their preference: P6 cited examples of parameters that can be controlled on mixing consoles with either knobs or sliders, e.g. pan or volume, depending on preference. He preferred "[…] a volume slider, and a knob to adjust the pan." Not hindering retro-compatibility, the novelty of shape-change had a positive impact on participants, e.g. one reacted saying "Wow!", "I want to play with it!" The participants further suggested device features to improve retro-compatibility: 1) Actuating the slider's orientation to vertical after a shape change: it was a concern for two participants (PII and P6, used to vertically arrange banks of sliders). Similarly, most participants wanted to use the slider vertically, i.e. with flexion/extension movement of the finger, even when the virtual parameter was displayed horizontally (e.g., in Photoshop). 2) The slider's cursor should disappear on knob. It currently protrudes from the knob and P7 says it "interferes". 3) Further improvement of the knob's edges: because the knob has an even number of edges, the base cannot be centered when in slider's state, which confused P8. Also, PIII would like round edges for a circular knob. 4) Further studying its integration with other devices. At a table, P2,PIII,PIX already use a tablet/mouse and a keyboard with Photoshop. These participants wondered how to further combine the KnobSlider with other devices, e.g., having a mouse sensor in KnobSlider. 5) Extreme solidity: Pilots might not accept a change of shape during the flight: "A system that deploys during the flight is not in the culture" (P7).

Results: envisioned interactions and applications

We now present feedback relative to possible future interactions and applications of the KnobSlider.

Envisioned interaction

Novel manipulation of the same prototype: Eight participants suggested novel interactions. E.g. P3 was holding the knob shape in one hand while turning with the other, and deforming the flexible slider. The additional rotational axis of the slider gave P8 (pilot) the idea to explore the surroundings' visualization with polar coordinates, by orienting the slider (angle) and sliding the cursor (distance or scale). Two participants asked the interviewer if it was possible to use the slider's cursor when in knob shape.

Beyond knobs and sliders: P3 suggested adding accelerometers, gyroscopes and compass for the KnobSlider tracked when moved in hand. P3 suggested bending the KnobSlider as a way to interact. P6 mentioned that the slider could be bent to mark values of interest.

Beyond mixing tables: PI and P3 also thought about using the KnobSlider on a flat table and tracking its displacement on the table (PI mentioned the reacTable [START_REF] Jordà | The reacTable: a tangible tabletop musical instrument and collaborative workbench[END_REF]). P3 also mention holding the KnobSlider in its knob shape in a hand, without any support.

Envisioned applications

Participants gave feedback on the applications we prototyped and proposed new ones. Graphic designers agreed that the prototype allowed them to balance their need for a tidy desk with few devices and dedicated devices, either for fast navigation in Photoshop's tools or precise adjustment of a parameter like the size. They expected to gain time by avoiding mouse movements and clicks [START_REF] Fitzmaurice | An empirical evaluation of graspable user interfaces: towards specialized, space-multiplexed input[END_REF]. They further envisioned easier access to parameters through a physical shape analog to the GUI widget: e.g., slider shape for red levels, displayed as sliders on the screen, and knob shape for rotating the canvas.

Sound and light engineers agreed that the prototype allowed gaining space when parameter adjustment happens in sequence: e.g., the slider to control the gain, and the knob the frequency, or the slider for the volume of an effect, (e.g. a reverb), and then the knob to send this effect to the master channel. They also agreed that the device allowed adapting to users' preferences: some prefer to control volume or pan with a fader, while others prefer to do it with a knob. They further envisioned the flexible footprint of the device. If physical sliders do not fit any more on P5's mobile surface, he would switch to physical knobs rather than graphical sliders or constantly switch between banks of sliders.

Pilots agreed that the prototype allowed adaption to the preferred control because they control flaps only twice (takeoff/landing). However, changing the shape of other controls might lead to errors, as the logic of each aircraft is different. Pilots further proposed to leverage the different precision of both shapes: When taking off, P7 wanted to coarsely slide from 0 to maximum power, and while cruising, he wanted the knob to precisely adjust the power. P7 proposed to have the KnobSlider in flight simulators so that trainees can train on different controls while reducing costs. Pilots imagined prototype improvements to perform tasks that are currently not supported, like seeing backwards before performing a U-turn.

Our participants also proposed new application domains based on their experience. For example, P6 proposed to use the change of shape in the manufacturing industry. It could indicate that a security requirement is met after a first adjustment -e.g. the pressure is low enough after rotating the knob -and that the worker can proceed to adjust the porosity with the slider if its shape is unlocked.

DISCUSSION AND FUTURE WORK

Implications for Shape-Changing Interfaces (SCIs)

This paper provides a solution for users with diverse professions that use linear and rotary controls, in contrast to previous work that has often targeted single professions (e.g., musicians [START_REF] Maria Troiano | Deformable Interfaces for Performing Music[END_REF] or cooks [START_REF] Vinot | Could tangibility improve the safety of touch-based interaction?: exploring a new physical design space for pilot-system interfaces[END_REF]) or the general public [START_REF] Grönvall | Causing commotion with a shape-changing bench: experiencing shapechanging interfaces in use[END_REF]. From this study, we can draw implications for future SCIs for professional users.

First, the participants were excited by the reconfigurable aspect, suggesting they are open to adopting timemultiplexing through shape change. The current approach for time-multiplexing in the industry is to provide touchscreen interfaces (e.g., THALES Avionics 2020 or Slate Media Technology RAVEN MTi2), while others add back physical devices on GUIs (e.g., Microsoft Surface Dial or Neff Point and Twist dial). SCIs can be a next step to provide both tangibility and time-multiplexing. In addition, they can provide eyes-free situational awareness, which is useful in degraded work conditions [START_REF] Vinot | Could tangibility improve the safety of touch-based interaction?: exploring a new physical design space for pilot-system interfaces[END_REF].

Second, the retro-compatibility users require should be studied to ensure SCIs' adoption by professionals. Although KnobSliders could provide better retro-compatibility than touchscreen interfaces, the time-multiplexing of physical device introduced surprising feelings and waiting time for shape change. A follow up study can investigate the impact of shape change on users' perceptual response and find a compromising point. For instance, it can study the impact of proximity of device to users, speed of shape-change, and possibility of hurting users (e.g., device snaps on user's fingers) on user's subjective feelings.

Lastly, a long-term field study should be conducted to let more professionals adapt SCIs into their daily workflow. The interviewed users needed dynamic interaction in timely manner and mistakes could be critical. The long-term study should study how to design SCIs to support various context including emergencies. It can also study how to promote users' transition to expert functions, as SCIs will get more sophisticated. It can refer research in GUI, e.g., [START_REF] Scarr | Dips and ceilings: understanding and supporting transitions to expertise in user interfaces[END_REF].

KnobSlider design and prototype

The qualitative study unveiled advantages and future directions of KnobSlider before a quantitative study.

Benefits of KnobSlider over current solutions

Small footprint is critical for both mobile interaction and mixing desks, as participants reported not using devices beyond arm's reach. Participants found that KnobSlider allows fast and coarse manipulation of the slider combined with slow but precise manipulation of the knob, with a smaller footprint than previous work [START_REF] Coutrix | Shape-change for zoomable tuis: Opportunities and limits of a resizable slider[END_REF][START_REF] Djajadiningrat | Easy doesn't do it: skill and expression in tangible aesthetics[END_REF]. This particular benefit needs to be quantitatively measured in future work. KnobSlider also allows users to only use a knob when space is limited. In addition, KnobSlider better supports customization to a preferred control. This is also important as participants reported that they want to leverage their expertise of their current interface.

Future high-fidelity implementation

Although the KnobSlider was enough for our study, several aspects of the device should be improved for quantitative study in comparison with commercial knobs and sliders. A future work can miniaturize the device to increase the spatial benefit of KnobSlider. Stability during the slider status and shape change should be also improved for fast and precise interaction. The friction of slider needs to be low and even. Seamless joints between blocks can resolve this problem. It can be useful to motorize the slider cursor and the knob to improve retro-compatibility. Adjacent KnobSliders should not get in the way of each other. A central motor could ensure that the unfolded part always stays vertical. Most importantly, the device's safety should be improved as current design allows the device to collide with user's fingers.

Open issues and novel interactions

Even though we seek generality from the five professions, future work should study the applicability of our requirements to further professions, situations, and tasks.

Currently the ratio of slider length and knob diameter is limited to 𝜋 at best. Considering that many participants preferred large sliders and small knobs, folding in spiral could be explored.

Further work is needed where there was no consensus, e.g., 1) The presence of the slider's cursor when in knob shape that cause lower retro-compatibility (R6) but better eyesfree interaction (R4). 2) The locking of the slider's orientation, wanted by most, whereas it gave an idea of an interaction to a pilot.

New interaction techniques should be explored in future work. For instance, participants suggested bending the slider. This could allow physical implementation of the graphical corner by Tsandilas et al. [START_REF] Tsandilas | SketchSliders: Sketching Widgets for Visual Exploration on Wall Displays[END_REF], or changing slider length as suggested in Zoomable TUIs [START_REF] Coutrix | Shape-change for zoomable tuis: Opportunities and limits of a resizable slider[END_REF].

CONCLUSION

In this paper, we identified six requirements for a physical interface for flexible continuous parameters control. Based on these requirements, we designed a working prototype, KnobSlider. It combines the benefits of a physical knob and a physical slider through on-demand shape change. We evaluated the KnobSlider with target users. Results suggested future improvements of the KnobSlider and implications for shape-changing interfaces. In future work, we will iterate the design so that we can conduct a longterm field study with professionals. We will also explore novel interaction techniques based on this device.

Figure 1 .

 1 Figure 1. KnobSlider is a shape-changing device that changes between a rotational knob and a linear slider to accommodate users' needs. In the situation depicted (a) a sound engineer uses it as a slider to coarsely control a sound volume. He then presses the central button to trigger the change into (b) a low control-display (CD) gain knob, and (c) he can use it for fine adjustment.

Figure 2 .

 2 Figure 2. Participants using knobs and sliders in their professional activity: (P1) a cameraman with 4 knobs and a slider on a custom made device; (P2) a graphic designer using a graphic tablet and a slider placeholder; (P3) a light artist using custom knobs and sliders on a tablet in a dark environment; (P4) a light engineer using physical knobs and sliders while observing a stage; (P5) a sound engineer communicating with musicians on the far stage while using sliders; (P6) a sound engineer controlling a knob while watching a screen; (P7) a pilot using flight simulator for his training; (P8) a pilot using physical controls in a flight.

  The sensor is connected to the bottom and top central gear, and used for both knob and slider states of the KnobSlider. When the joints are closed, the block edges interlock with the bottom central gear making a knob state. User's rotation of the knob then translates to the sensor axis, and the device works as a knob. When the joints are open, the device makes a slider 2 griffintechnology.com/us/powermate state. The central block is supported on the bottom central gear, but the rotation of the block doesn't affect the gear. Instead, the movement of the slider cursor is conveyed to the top central gear through the timing belt.

Figure 4 .Figure 3 .

 43 Figure 4. Different elements of the KnobSlider, here without the top cover to expose the slider's timing belt.Sensor center

Figure 5 .

 5 Figure 5. Seven out of our 10 participants interacting with the probe. P2, PII and PIX use the slider. P3 and P5 are about the change the shape by clicking on the central button. P6 and P8 use the rotary knob.

Table 1 . Design space and related work.

 1

		No time-multiplexing:	Time-multiplexing:
		Device(s) available	Devices available
		all the time	in sequence
	No space-multiplexing: One device available at the workspace	A. A single knob or slider [8,24,34,40]	B. A knob and a slider in sequence [12,25,28,29,39]
	Space-multiplexing: Multi-devices available at the workspace	C. Adjacent knobs and sliders and stacked knobs and sliders [3,6,9] and current systems	D. Knobs and sliders anywhere, anytime: [12,21,29,39,43] and current systems

Table 2 . Summary of the prototype specification Requirements Assessment R1. Many parameters One

 2

KnobSlider accommodates two continuous parameters in sequence. Several KnobSliders can be used simultaneously.

Table 3 : Tasks performed in the qualitative study.

 3

	Participant(s)	Slider shape allows…	Knob shape allows…
	P2,III,IX Graphic designers	Switching between tools	Adjusting a tool's size
	P3	Adjusting the size of a	Adjusting the speed of
	Light artist	rotating laser	laser dot's movement
	PI,II	Controlling the intensity	Controlling the rotation
	Light engineers	of a projector	of the projector
	P5,6 Sound engineers	Controlling the sound volume
	P7,8 Pilots	Controlling the flaps angle

https://www.bls.gov

Allen&heath iLive T112, LICON CX, MA Scancommander et grandMA mixing consoles, CESSNA 172 aircraft and Cirrus Aircraft Avidyne Entegra SR20 with Avidyne FlightMax Entegra EX5000C R 6.2.1 software, custom hardware and software developed by the participant or by its company, etc.

ACKNOWLEDGEMENT

This work was supported by the French National Research Agency (ANR-11-LABX-0025-01, ANR-11-EQPX-0002, ANR-15-CE23-0011-01), the Leverhulme Trust, the Alexander von Humboldt Foundation, the German Research Foundation through the projects C02 & C04 of SFB/TRR 161, and the German Federal Ministry of Education and Research as part of the project Be-greifen (grant no. 16SV7527). The prototype has been partially made in AmiQual4home (https://amiqual4home.inria.fr/ fr/tools/cl/) and MSTIC (http://fabmstic.liglab.fr/). We would like to thank the participants of both studies, and colleagues and reviewers for their feedback.