Olivier Piller
email: olivier.piller@irstea.fr

Fereshte Sedehizade

Thomas Bernard

Mathias Braun

Nicolas Cheifetz

Jochen Deuerlein

Martin Wagner

Emmanuel Lapébie

Iris Trick

Jean-Marc Weber

Caty Werey

Augmented Resilience of Water Distribution Systems following Severe Abnormal Events

Keywords: Secure sensor networks, Robust simulation models, Resilience assessment

des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

BACKGROUND

Water Distribution Systems (WDSs) are critical infrastructures that may fail to distribute drinking water of adequate quantity and quality. Given their distributed topology and interconnectivity with other infrastructure systems, such as power supply and telecommunication, WDSs are exposed to a variety of risks including terrorist attacks, natural hazards and widespread technical failures that may be caused by cascade effects. The ResiWater project [1] aims to improve prevention, surveillance and response regarding realistic case studies of collapse of WDS, water quality deterioration and cascade effects between water, energy and IT infrastructures.

The prevention and level of required preparation include the development of new hydraulic analysis software solutions, and of training and resilience strengthening tools. The surveillance includes the continuous recording of the real system state with a network of high-performance sensors for fast detection of water quality deterioration or system breakdown. To serve in case of connectivity loss, modelling tools should be more robust for solving numerically difficult problems (or poorly conditioned) than those of the normal state. Knowing the degree of uncertainty of the model results, which depends on the level and on the quality of the instrumentation, the modelling error but also the parameter uncertainty, is a strong request for the operator decision-making.

For the realization of the ResiWater project, five main steps were defined: specification of critical case studies, design of integrated and secure sensor networks, development of a self-learning module for abnormal event detection, development of robust hydraulic and water quality simulation tools for modelling of extreme events, and decision support tools for improving resilience of WDSs. [START_REF] Piller | Porteau: An Object-Oriented programming hydraulic toolkit for water distribution system analysis[END_REF] and SIR 3S for 3S Consult [START_REF] Sir | [END_REF]. The three water utilities benefit from the outputs, training and decision support tools.

Among the main results that will be presented to the CCWI 2017 conference: Ø Three use cases per water utility were chosen: WDS collapse, water quality deterioration and cyber-attack. Ø A resilience framework has been fitted to the ResiWater needs with a ranking method devised for each case studies of the three project end users. Ø Two spectroscopic sensors (absorption, fluorescence) have been installed at Berliner Wasserbetriebe (BWB) for testing their functionality under practical conditions at water utilities.

Here below are listed additional main results beneficial for the project: Ø A database for the detection potential of a variety of substances by fluorescence as well as absorption sensors was developed. Ø A multi-step approach is proposed for monitoring water quality into the distribution network.

As a first step, a temporal segmentation has been implemented and validated on a real hydraulic sector at Veolia Eau d'Ile de France [START_REF] Cheifetz | Extracting Temporal Patterns for Contamination Event Detection in a Large Water Distribution System[END_REF]. Ø A first software solution was delivered for alarm generation that is based on Dynamic and Incremental Principal Component Analysis [START_REF] Kühnert | Ereignisdetektion in Trinkwassernetzen mittels PCA und DPCA. Datengetriebene Detektion von Kontaminationen und Reduktion von Fehlalarmen (Event detection in drinking water distribution networks using PCA and DPCA. Data-driven contaminant detection and reduction of false alarms[END_REF]. Ø An optimisation framework was developed that enables the fast and robust solving of a range of algorithms for the pressure-driven modelling (PDM) system of equation [START_REF] Elhay | A Robust, Rapidly Convergent Method That Solves the Water Distribution Equations for Pressure-Dependent Models[END_REF]. Ø The optimisation framework has been extended to afford for pumps and control devices under abnormal operational conditions [START_REF] Deuerlein | On Solvability of The Pressure Driven Hydraulic Steady-State Equations Considering Feedback-Control Devices[END_REF]. Ø Spectral Propagation of Parameter Uncertainties in Water Distribution Networks is done by chaos polynomial method to infer the model output uncertainty [START_REF] Braun | Spectral Propagation of Parameter Uncertainties in Water Distribution Networks[END_REF]. Other developments are underway, within this project, for instance, cyber security analysis, EU, French and German Law analysis, crisis costs valuation and resilience cost benefit analysis including vulnerability of natural and human environments.

In the following, the resilience framework and the development of sensor network in the project are described.

Results

Vulnerability and Resilience Framework in ResiWater

In the context of the project, vulnerability is composed of the following four items (cf. The three first items describe the internal vulnerability of the system. In contrast, the 4th item, external vulnerability, measures the impacts of the system outside its own boundaries on consumers and human activities but also on the natural environment.

Figure 1. The four vulnerability components in the ResiWater project.

System vulnerability Vsystem describes both the interaction of system functions (for instance the influence of closing a valve on the network topology) and the physical evolution of the system (for instance a sudden pressure drop causing pump cavitation). It is assessed through the loss of performance P (see Fig. 2) of the WDS during the passive phase (before any reaction). Vsystem is defined as the difference of system performance (in case of performance loss) between the pristine system and the residual system measured at a characteristic time. The residual performance (Figure 2) at time t is thus given by (Pinitial -Vsystem(t)), where P initial denotes the initial performance. The performance evolution is computed by the hydraulic and transport models, considering the initial physical and functional vulnerability. From the other side, resilience is composed of three capacities: Absorptive (linked to vulnerability), adaptive and restorative capacity (see Fig. 3). It is adapted from [START_REF] Francis | A metric and frameworks for resilience analysis of engineered and infrastructure systems[END_REF]. The absorptive capacity is defined as "the degree to which a system can absorb the impacts of system perturbations and minimize consequences with little effort". It is merely the passive evolution of the system facing a performance loss, whereas adaptive and restorative capacities both involve system reactions. The absorptive capacity includes the robustness and redundancy (both physical and functional) aspects of the Bruneau 4Rs [START_REF] Bruneau | A Framework to Quantitatively Assess and Enhance the Seismic Resilience of Communities[END_REF].

The adaptive capacity is defined as "ability of a system to adjust to undesirable situations by undergoing some changes […] if absorptive capacity has been exceeded" [START_REF] Francis | A metric and frameworks for resilience analysis of engineered and infrastructure systems[END_REF]. It focuses on the emergency responses from the preparedness level up to the implementation of temporary solutions, considering the ability of detection and of decision making by the operator. The adaptive capacity includes preparedness (not explicitly mentioned in the 4Rs approach), resourcefulness (internal resources) and part of rapidity (to overcome the disruption and tend to a stable state).

Finally, the restorative capacity focuses on long-term solutions. It is "characterized by rapidity of return on normal or improved operations and system reliability. This capacity should be assessed against a defined set of requirements derived from a desirable level of service or control" [START_REF] Francis | A metric and frameworks for resilience analysis of engineered and infrastructure systems[END_REF]. The duration of the restorative phase is usually much larger than the delay to implement emergency solutions. The restorative capacity also includes from the 4Rs resourcefulness (external resources) and part of rapidity (restoring service).

Vulnerability and resilience signatures are also assessed on a simple three-level scale (see Figure 4). Defining the end of the passive evolution of the system (t palliative value) requires estimating the average time of detection, the delay of decision making and the estimated time for implementing the "emergency" reactions in such cases. Ideally, the operators should react before t failure , which corresponds to the delay before a failure if the system evolves without reaction at all (Figure 4). The internal system vulnerability ranking is a mirror of the absorptive capacity ranking (R absorptive ): Vsystem(t palliative ) = 4 -R absorptive . The vulnerability ranking helps to detail the steps for modelling the passive evolution of the system. Vulnerability assessment at system level requires a hydraulic and transport model (Porteau, SIR 3S), given an initial state of perturbed infrastructures and functions. Resilience can be assessed by using characteristic times and residual levels of performance (analysis of past events), or using simple survey, when no past event is available. Two waterworks are cutting off by a regional power cut; 2.

Contamination (by a non-pathogen bacteria) in south east of Berlin; 3.

Cyber-attack at control systems (stuxnet). For EMS (Strasbourg) also three case studies are investigated:

1.

Main production unit stopped by major flood event; 2.

Water quality degradation by intentional network contamination; 3.

IT attack stopped Oberhausbergen power, event masked by false data (replicated data set). And for Veolia Eau d'Ile de France, four case studies are defined:

1.

Fire Hydrants operation in "Street Pooling" situation; 2.

Terrorist attack on network in the situation of a major International Event (COP 21); 3.

Centennial Flood; 4.

Above Centennial Flood -Establishment of the major crisis emergency plan. The vulnerability and the resilience was assessed for the nine case studies at the beginning of the project. They will be assessed again at the end to evaluate the solutions proposed by the project.

Water quality sensors and flow measurements

For a better management of networks for the routine status as well as for accidents or CBRN attacks, online information of water quantity and quality of the whole water network is needed, i.e. a higher number of sensors should be installed [START_REF] Aisopou | In pipe water quality monitoring in water supply systems under steady and und unsteady state flow conditions[END_REF]. To overcome the limitation of sensor placement through monetary restrictions low cost products are available. However, the performance of such low-cost products for an online and long term running is unknown. In this project, non-specific multi-probe sensors are used together with spectroscopic sensors, biosensors and accurate flow metering systems.

Spectroscopic sensors.

Spectroscopic sensors become more relevant due to their ability to detect a broad range of contaminants (see Table 1). Routine and test equipment is available for UV-VIS1 absorption and fluorescence, the mid and near infrared including Raman-spectroscopy as well as flow cytometry [START_REF] Wagner | Charakterisierung des aquatischen DOC mittels Fluoreszenzspektroskopie[END_REF]. NMR2 techniques are in designing phase [START_REF] Maiwald | Hochauflösende online-NMR-Spektroskopie für das Reaktions-und Prozessmonitoring: Beispiele zur Anwendung in der Verfahrenstechnik[END_REF] These spectrometers are small, robust and produce colossal data sets (in frequency spectrum). However, the assessment and interpretation of this spectrum data is a challenge up to now. With the appropriate interpretation, chemical-structural knowledge can be obtained, see e.g. the detection of single compounds as pesticides and pharmaceuticals as well as algal-like toxins. A decisive higher quality level can be reached by combination of "classical" physicochemical sensors with spectroscopic sensors. Currently, there are worldwide only a few biological sensors available that are capable to measure a broad spectrum of toxic components in drinking water online (e.g. DaphToxII of bbe moldaenke, MicroTox CTM of ModernWater, iToxControl of microLAN). All these systems have the drawback that the maintenance effort is very high and consequently, the systems are not well suited for an operation in the drinking water network.

The partners Fraunhofer IOSB and IGB have developed a prototype of a biological sensor system see Figure 5 which has the potential for a fully automated system and hence can be installed even directly in the water supply network. The sensitivity of the AquaBioTox for a wide spectrum of substances and concentrations has been proved (see also Table 1). During the project, the AquaBioTox prototype shall be fully automated, enabling its installation in the pipe network.

Low-Cost flow rate measurement system. The most currently monitoring parameter is the flow rate and several devices end technologies are available and the uncertainties well known. For economic reasons, mostly simple devices are installed, e.g. electromagnetic insertion flow meters. The accuracy depends on the precise knowledge of the pipe diameter, which is needed for calculation of the volume flow. However, the inner pipe diameter is very often not precisely known. Currently, no method exists to obtain the wet section from the inside of the pipe, giving the best way to minimize uncertainties on flow.

Sensors, sensor data as well as the communication network of water distribution systems have become an increased target from the cyber space in recent years. Thus, the project investigates the impact and the risk of cyber incidences and develops new concepts for security and authentication of sensor networks in water supply.

CONCLUSIONS

The project ResiWater aims to increase the resilience of water infrastructures by means of enhanced sensors and secure sensor networks, self-learning monitoring tools, robust simulation models and training simulator, vulnerability and resilience assessment tools.

A new vulnerability resilience framework is proposed for ranking the crisis case studies defined by the project end users. A simple three-level scale was chosen and is illustrated in the paper.

New spectroscopic, biological sensors and a low-cost flow rate measurement system are under investigation in the project. They will be part of a broad and secure sensor network for monitoring the systems.

Other solutions were also studied in the project for the prevention and response of critical events. Among the main results, we may put forward the robust modelling for training in presence of large disconnected network parts, the enhanced event detection by PCA and Gaussian mixture model (oscillating data and drifting sensor data) and the economic evaluation by cost benefit analysis.

Once the robust simulation software solutions for severe abnormal situations and the uncertainty quantification tool will be released in the project, they will be used for assessing the resilience of WDN by simulating the scenarios.

Figure 1 )

 1 : a) Vphysical = Physical vulnerability (initial). b) Vfunctional = Functional vulnerability (initial). c) Vsystem = System vulnerability (time-dependent) . d) Vexternal = External vulnerability (time-dependent).

Figure 2 .

 2 Figure 2. Residual performance at time t.

Figure 3 .

 3 Figure 3. Timeline for the three resilience phases in the ResiWater project.The absorptive capacity is defined as "the degree to which a system can absorb the impacts of system perturbations and minimize consequences with little effort". It is merely the passive evolution of the system facing a performance loss, whereas adaptive and restorative capacities both involve system reactions. The absorptive capacity includes the robustness and redundancy (both physical and functional) aspects of the Bruneau 4Rs[START_REF] Bruneau | A Framework to Quantitatively Assess and Enhance the Seismic Resilience of Communities[END_REF].

Figure 4 .

 4 Figure 4. Ranking of the absorptive resilience from green (low system vulnerability) to the worst red case (critical system vulnerability). For BWB (Berlin) three case studies are defined:1.Two waterworks are cutting off by a regional power cut; 2.Contamination (by a non-pathogen bacteria) in south east of Berlin; 3.Cyber-attack at control systems (stuxnet). For EMS (Strasbourg) also three case studies are investigated:

Table 1 :Figure 5 :

 15 Figure 5: Prototype of biosensor AquaBioTox.

  The French-German cooperative research project integrates end users (BWB Berlin in Germany, EMS Strasbourg in France and Veolia Eau d'Ile de France around Paris), technical and socioeconomic research institutions (Fraunhofer IOSB, Fraunhofer IGB, TZW, CEA, Irstea, ENGEES) and industrial partners on French and German sides (Veolia Eau d'Ile de France, 3S Consult). Two simulation software tools are extended for crisis management and preparedness: Porteau for Irstea

Ultraviolet-visible spectroscopy or ultraviolet-visible spectrophotometry (UV-Vis or UV/Vis) refers to absorption spectroscopy or reflectance spectroscopy in the ultraviolet-visible spectral region.

Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy, is a research technique that exploits the magnetic properties of certain atomic nuclei. This type of spectroscopy determines the physical and chemical properties of atoms or the molecules in which they are contained.

Acknowledgements

The work presented in the paper is part of the French-German collaborative research project ResiWater that is funded by the French National Research Agency (ANR; project: ANR-14-PICS-0003) and the German Federal Ministry of Education and Research (BMBF; project: BMBF-13N13690).


Sabine Madsen
email: sabinemadsen@live.dk

Lene Nielsen

Heidi Hautopp
email: heidi.hautopp@gmail.com

Iben Jensen

An Empirical Investigation of the Practices and Challenges Specific to International User Studies

Keywords: Design, International user studies, Application, Practice-study 1

des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

The HCI field has traditionally focused on two key research areas, namely (1) methods, tools and guidelines for designing and testing interfaces to enhance the usability hereof and (2) approaches for understanding the users and the context and situational aspects that influence their use of a given (IT) product or service. Within both of these research areas, the implications of globalization and the internationalization of pro ducts and services have over the years become important topics of study [START_REF] Camara | Augmenting Usability: Cultural Elicitation in HCI[END_REF][START_REF] Clemmensen | An Overview of a Decade of Journal Publications about Culture and Human-Computer Interaction (HCI)[END_REF][START_REF] Siegel | International Contextual Field Research[END_REF][START_REF] Young | Integrating Culture in the Design of ICTs[END_REF].

Our research is positioned within the second stream of research concerned with approaches for understanding users and contextual product use. In particular, we aim to contribute to the HCI literature with insights about how companies conduct intern a-tional user studies to get a foundation for meeting the n eeds of and designing products and services for users on international markets.

An earlier research project discovered that companies found it difficult to decide which markets to approach and how to incorporate cultural differences when co mmunicating the findings from the user studies as personas [START_REF] Nielsen | Personas is Applicable: A Study On the Use of Personas in Denmark[END_REF]. Looking at the literature within HCI very little address these aspects in a scientific way and most address data collection and communication from an experience-based perspective, see e.g. [START_REF] Schumacher | The Handbook of Global User Research[END_REF][START_REF] Siegel | International Contextual Field Research[END_REF]. An exception is [START_REF] Boztepe | Toward a Framework of Product Development For Global M arkets: a uservalue-based approach[END_REF], who draws on empirical data to propose a conceptual framework that, among other things, assists designers in global companies in planning user studies that take local and cultural aspects into account.

The purpose of this research is to inves tigate how companies conduct international user studies; and more specifically to identify the practices and challenges that are particular to the process of collecting data and presenting insights about users on international markets.

The research is based on a qualitative interview study with 15 practitioners from 11 different companies. All interviews were held in Denmark, either in Danish comp anies that have users and subdivisions around the world or in Danish subdivisions of large international corporations. This means that what is considered "international" is seen from a Danish perspective.

On culture and intercultural communication

All user studies are concerned with understanding the important differences and similarities among users. However, one of the aspects that make international user studies different from national user studies is that they are explicitly concerned with culture and intercultural communication. Thus, international user studies require attention to cultural differences and similarities during the planning and data collection phases of the study. Moreover, an important outcome of these studies is an increased unde rstanding of which cultural differences and similarities that exist among users on different markets and which of these that are -and are notimportant to take into account when designing a given product.

Recent theories point out that in today's globalized world it is useful to think about culture as a concept and phenomenon that refers to much more than just national culture [START_REF] Jensen | Introduction to Cultural Understanding[END_REF]. This allows for other understandings of the significant differences and similarities between groups of people and of the complexity of peoples' everyday lives. A complex understanding of culture facilitates ways of group ing people based on their everyday practices and the communities (i.e. cultures) they participate in; e.g., by focusing on their practices with regard to work, leisure, sport, parenting, language, gender, and religion [START_REF] Jensen | If Culture Is Practice …? A Practice Theoretical Perspective on Intercultural Communication and M ediation[END_REF].

A complex understanding of culture does not exclude a focus on national culture; rather the emphasis is on, for example, understanding what it means to be Danish and at the same time that there are many ways in which to be Danish. However, as the theories stress, even for people with a high level of intercultural competence it remains a challenge to avoid interpretations, linguistic expressions , and actions that are informed by more simplistic national and geographical stereotypes. This is due to, among other things, the strong influence of the very notion of national culture as well as to the often more one-sided representations and discourses presented in the media.

This complex understanding of culture is very different from the understanding of culture as represented by methods, tools and guidelines for designing interfaces as suggested by e.g. [START_REF] Gould | Cultural Dimensions and Global User-Interface Design: What? So What? Now What?[END_REF] or the application of methods on new frontiers as described by e.g. [START_REF] Putnam | Adapting User-Centered Design M ethods to Design for Diverse Populations[END_REF][START_REF] Walsh | Cross-Cultural Design of M obile M athematics Learning Service for South African Schools[END_REF].

In this paper, we use the distinction between the concept of national culture and the complex understanding of culture as our theoretical foundation for understanding the role that perceptions of cultural differences and similarities play when companies collect and present data about international users.

3

Research method

The research presented in this paper is based on a qualitative interview study with 15 user researchers from 11 different companies . The aim of the interviews was to investigate how companies collect and present data about users on international markets. The companies/interviewees were selected from the involved researchers' professional network based on the following criteria. [START_REF] Boztepe | Toward a Framework of Product Development For Global M arkets: a uservalue-based approach[END_REF] The most important criterion was that they were operating on international markets. (2) The second criterion was that they had experience with international user studies and/or that they were using methods (such as, e.g. the persona method or segmentation into target groups) to delineate and incorporate user insights into their work and design processes.

The interviews were carried out from February -April 2014. All interviews took place in Denmark, either in Danish companies that have users and subdivisions around the world or in Danish subdivisions of large international companies.

The interviews were semi-structured and held in accordance with an interview guide. Each interview lasted 1-1,5 hour, was audio-recorded and subsequently transcribed. All interviews were held in the Danish language. The included interview quotes have therefore been translated from Danish to English by the paper authors.

As all interviews took place in Denmark what constitutes "international" is viewed from a Danish perspective. This can be useful to keep in mind when reading interview quotes that compare Denmark to other countries or when differences and similarities are mentioned. For example, when the interviewees make comparisons and statements about differences and similarities they seem to do so based on a number of taken -forgranted notions, such as the assumption that the Danish work culture is less hiera rchical and more characterized by employee autonomy than work culture in other countries and that Danes in general are task oriented and prioritize efficiency.

Moreover, as all interviews were held in Danish it means that the two interviewers and the interviewee shared the same language and that much could be taken for granted with regard to contextual understandings, body language, humor, etc. It has been suggested that in such data collection situations (characterized by shared language and background) interviewer(s) and interviewee(s) create an 'ad hoc' national community as 'fellow travellers' [START_REF] Gabriel | Storytelling in organizations: Facts, fictions and fantasies[END_REF][START_REF] Gertsen | Intercultural Collaboration Stories: On narrative inquiry and analysis as tools for research in international business[END_REF] that jointly aim to understand the world around them.

However, it also means that taken for granted notions, national stereotypes, etc. might go unnoticed and that statements about national differences and similarities might be more expressed, because they are intendedand understood -as jokes in the interview situation. This is also useful to keep in mind when reading the in terview quotes in this paper. All interviewees work in companies, where digital solutions and/or software d evelopment is the main area of expertise or an important part of the products and pro duct portfolio. They have many years of professional experience and are currently holding positions as design researchers, user experience (UX) researchers, innovation consultants and so on. A part of their job is to plan and carry out user studies. We will hereafter refer to them as user researchers. Table 1 provides an overview of the characteristics of the involved companies and participants.

The analysis of the interview data was structured into several rounds of analysis, where we used a thematic approach to organize the interview data into relevant units of text and themes, which were then interpreted and meaning condensed into our research findings [6].

An important part of the analysis was to distinguish between on the one hand, themes that the interviewees described as specific to international user studies and on the other hand, themes related to national studies or inherent to all types of user research. In this paper, we focus on the practices and challenges that are specific to (or magnified by) the process of doing international user research.

Empirical findings: A process perspective on international user studies

In this section, we describe the strategies and practices that the companies and inte rviewees use when conducting international user studies. We present our research findings in accordance with a process perspective, because this was how the interviewees structured their practice descriptions. Thus, we look at the practices and challenges related to: (1) Initial planning, (2) International data collection, (3) Perceptions of end users , and (4) Presentation of user insights.

We do not address data analysis and implementation of user insights into design processes. This delimitation has been chosen, because the interviewees reported that the practices and challenges for these two process steps (i.e. analysis and implementation) were similar for national and international user studies. See [START_REF] Nielsen | Personas is Applicable: A Study On the Use of Personas in Denmark[END_REF] for research findings about the practices and challenges that relate to analysis and implementation of user insights in a national context.

Initial planning

There are a number of initial decisions and planning activities that have to be made before an international user study can commence.

Strategic markets are prioritized.

For companies operating on international markets a key decision is where, geographically, to collect data about the users. In most cases it is the management/client who makes the decision about which countries/regions to include in the study. The dec ision is typically based on what they consider to be the company's most important, strategic markets.

"It has to do with which strategic markets we want to be strong in. It is not so much that now we need to find four [countries] that are very different…of course India is included because they are very different from the US, but India is also included because they have a very large population who could use [our products]…" (Inn ovation specialist, N)

Thus, our analysis shows that the management's/client's decision about where to collect data is driven more by strategic business considerations and a marketorientation than by a focus on specific countries and national culture. Moreover, while it is not possible to say that it is a distinct pattern in the interview data, there does seem to be a slight difference in the way the interviewees use the words "markets" and "countries". When the word "market" is used, it seems to have more of a business connotation and to be used in connection with economic and pragmatic considerations. When the word "country" is used, it more intuitively invites the interviewee to talk about differences and similarities between countries/regions, and whether they matter or not for decision-making, data collection, and the product in question.

Pragmatic issues sometimes overrule strategy.

The interviewees report that normally it is quite clear which markets the manag ement/client want to collect data about or what kind of knowledge they want to obtain about a particular geographical area. However, economic and pragmatic c onsiderations related to, e.g., easier and cheaper travelling and language barriers mean that data sometimes is collected in other countries than originally decided. And also in other countries/regions than what might yield optimal knowledge. For example, it might be decided to do user interviews in England instead of an Eastern European country, because it reduces the language barrier for all involved.

Strategies for planning the user study

While it typically is the management/client that makes the decision about where to collect data, it is the task of the user researchers to plan the study. There are two different strategies for planning an international user study:  A research design oriented strategy. Some user researchers plan the study to cover as many users and user groups in the chosen countries/regions as thoroughly as the budget allows. This planning strategy is driven by the notion of validity and tends to lead to large-scale studies that involve many end users.  A use oriented strategy. Other user researchers plan the study with the aim of being able to provide the employees (i.e., product designers, system developers, and marketing personnel) with insights about the important differences and similarities between countries/regions, between the employees and their users, and between the many different types of users. When this planning strategy is used, the notion of validity still plays a role, but designing a study that addresses knowledge gaps is considered just as or more important than scientific method and rigor.

International data collection

The planning and the logistics that surround data collection for international user studies are much more demanding and time consuming than for national studies. This is because they typically involve: planning of international field studies, travel planning, use of external resources (e.g., agencies and translators from the countries where the study takes place), and many end users. All this adds to the scale and complexity of carrying out this type of user studies. In this section we look at the interviewees' reported practices and concerns about data collection.

The importance of going to the field.

User researchers consider it very important to go to the field and participate in the data collection, for two reasons:  To gain rich insights, i.e. to gain contextual knowledge and to interact directly with each of the users. It is also considered important for other employees, such as d esigners and developers to go to the field and meet the users.  To ensure the quality of the data, i.e. to ensure the consistency of the data collection across countries and in general to ensure that the data collection is carried out in the way the user researchers has planned it. This is considered especially important if the data collection takes place in "new" or less familiar countries.

We have identified three different field study strategies. Thus, when user researchers go to the field they use one or more of the strategies mentioned below. Strategy 1: The user researchers prefer to perform the data collection themselves , if possible from a language perspective. This approach provides much contextual knowledge about the particular country. Moreover, the experience of interacting with each of the users in person allows for a nuanced understanding of who the users are, how they live and work, and what their needs and motivations are.

Strategy 2: The user researchers perform the data collection with the help of a translator. This provides all the advantages of the abovementioned approach. However, different experiences are reported. Some state that it works well with a translator and especially if the translator is skilled and unobtrusive; others feel that they miss out on many nuances in what the user is saying and that t hey are unable to build a relationship with the user in the same way.

"It is always a challenge to use a translator because you never really have that d irect contact. You always depend on the translator. But when it is a good translator it works surprisingly well." (Design researcher, L)

Strategy 3: The user researchers participate as observers despite language barriers. Five of the 15 interviewees mention that they have used this strategy, and while they consider it the least desirable option, it has advantages. Thus, even in cases where language barriers mean that they cannot understand the actual interaction between a local resource and a user, observation provides them with contextual knowledge and is a great aid to memory during the subsequent data analysis.

"We made sure that at least one of us was present at all interviews in all cou n-tries…" ( Choosing which external resources to use is an important decision. The user researchers state that it is essential for them to be able to trust that the external resources can perform and deliver the results of the study with the expected quality.

"…Just to find an agency that understands what we are talking about and…is able to do it with the quality we expect. We don't understand Russian for example…how can I know that what they are talking about is a good persona interview? A good observation? And they will probably report back with phrases and language that has many implicit understandings, which I might not get, so, yes, there are many cha llenges." (Senior interaction designer, B)

The user researchers prefer to use resources that they have used before. If this is not possible, e.g., because the study is performed in a country where they have not previously collected data, they prefer to participate in all or selected data collection activities to control the process.

As the data collection often involves the use of different agencies and resources in different countries, the external resources are typically briefed very thoroughly. Thus, to ensure that the data is collected in the same way and with the desired quality, the user researchers provide the external resources with:  Detailed criteria for recruiting relevant users  An interview guide with detailed explanations of why and how to ask each que stion  Detailed guidelines for how to transcribe the interviews "We used agencies in all four countries…it has the advantage that they speak the language and that they do it for us…but it of course also has the disadvantage that we used quite a lot of time on explaining very thoroughly what it was we wanted…When we delivered something to them there was a column wit h a question and then there was a long explanation of why we were asking about this and what we wanted to do with it…so we were very thorough and it also worked." (Design researcher, C)

The common way of working with external resources is to be very thorou gh when choosing and briefing the resources. In general, the user researchers view internatio nal data collection as a collaborative effort and they work closely with the external resources throughout the data collection process to ensure that they get good quality data.

Large-scale studies involving many end users . International user studies typically involve many end users. The prevailing approach is that data collection should cover the same number of users in each country/region that is included in the study. In other words, a research design oriented approach informed by the notion of validity is preferred. As one of the interviewees explain: "…of course, identical in the four countries" (Design researcher, C).

This means that if a company normally performs 15 user interviews for a national study, they will plan an international user study in four countries to cover 60 inte rviews.

Another example is from a user study that involved two countries, Denmark and an Eastern European country. It was prioritized that the same number of interviews should be held in both countries and that several user groups should be covered in each country. As a result, the number of interviews became quite extensive.

"…we did 72 qualitative interviews in total, half in Denma rk and half in Hungary." (Design researcher, L)

Strategies for recruitment of end users .

As international user studies typically involve many end users, recruitment is a big task that takes up much time in the initial phases of a project. The user research ers choose between or mix two different strategies, depending on whether money or time is the more important aspect for the particular project.

The prevailing strategy is that the user researchers do all, most or some of the recruitment themselves. This is primarily because it is expensive to use external recruiters, but also because it often is possible (if time-consuming) for them to find the end users, based on customer lists or by drawing on their own social network.

Another strategy is to use external recruiters to minimize the time spend, and also because it sometimes is not possible (or too time-consuming) to find relevant users in other countries.

The user researchers state that they give much thought to determining the recruitment criteria and that they typically use the same criteria to recruit the end users in all the involved countries/regions.

Concerns about national culture create barriers for data collection.

In addition to travel expenses, language issues, and data quality, concerns about national culture create barriers for data collection.

The user researchers express many concerns about lack of education in culture and about insufficient understandings particular countries and national cultures.

"…if you are going to do user studies, e.g., with Chinese people, it has to be in collaboration with somebody who knows something about China, about the Chinese market. Someone with an education. We wouldn't know enough." (Consultant, J)

They are especially worried about their lack of knowledge about Asia and Africa, but also areas that are geographically closer to Denmark such as Eastern European countries.

Some interviewees explain that they are much more comfortable doing user studies in countries and regions they are familiar with and where they do not perceive the culture to differ significantly from Danish culture. In some cases, the consequence of this respect for differences in national culture is that they do not conduct user studies in countries/regions they feel too unfamiliar with, even when these countries/regions are or could be relevant for their business.

"…India, China, Brazil, which are big markets, and yes, well, we know that we have a huge knowledge gap and we haven't really done anything…" (Senior intera ction designer, B) Dealing with cultural differences in the data collection situation. Our analysis shows that (too much) focus on differences in national cultural can give rise to concerns that significantly delimits a company's approach to international data collection. However, our analysis also shows examples of user researchers that acknowledge cultural differences as inherent to the data collection situation, also in a national context. They therefore see it as an important part of their job and skill set to be able to build a trusting and empathic relationship with the user, despite such differences (in nationality, educational background, work culture etc.).

"I try to achieve this closeness and that is difficult to achieve…[when] you meet a complete stranger and also from a different country…even in that cultural distance, which always is there, I have to establish empathy, trust, so she also can tell me about those aspects of her job where she is not so successful or where she does work arounds, how they tinker [with the system]…" (Design researcher, A)

4.3

Perceptions of international end users

In this section, we focus on perceptions of international end users, as an important outcome of the process as well as something that shapes the way the user study is planned and carried out.

End users share many similarities across nationalities . The user researchers stress that one of the most important outcomes of international user studies is the insight that there are many similarities among end users across nationalities -as humans, consumers (of particular products), parents, workers, etc. This insight reflects a complex understanding of culture, i.e. an understanding that foregrounds the similarities of the users' everyday practices and the communities they participate in rather than national differences.

However, the user researchers also explain that employees have many preconce ptions about different nationalities and the (large) role that national culture plays. It is therefore important to explicitly communicate insights about the similarities that the company's end users share across nationalities to the employees. Otherwise stereoty pical understandings of national differences might go unquestioned and influence the designers' work and ultimately the company's products.

"The user studies we have done have shown that at the personal level our end u sers have very similar motivations and approaches across borders…and this is very, very important and we make a big deal out of communicating this to employees." (Design researcher, C) "…[this disability] effects end users in the same way no matter where they live in the world." (Innovation specialist, N)

There are important differences in market conditions . There are also important differences among end users. Interestingly, it is pointed out that the most important differences often do not stem from national culture as such, but instead from differences in the economy, legislation, education, and societal structures and structural developments in different countries and regions.

"…it has to do with how the economy is…[and the] legislation. Legislation promotes a particular behavior in a particular country. And this is actually the two things [i.e. economy and legislation] that we have seen consequences of." (Design researcher, C) "…the differences that we see when we talk about [our end users] are that there can be a difference in how much money they have and this has something to do with whether the country they live in gives refunds, or health insurance, or whether the state is paying the full amount, and things like that. There are many different [health care] models in the different countries. And that effects this very much." ( Innovation specialist, N)

Knowledge about differences in national/regional market conditions cannot be o btained through user studies alone. Other types of internal data from databases, reports, social network, etc. as well as secondary sources about the socio -economic situation, societal structures and legal systems are also important in order to be able to distinguish between and understand the different types of users.

Perceived differences in national culture are used to explain behavior. In addition to the complex understanding of culture demonstrated above, the interview data contains many examples of how perceived differences in national culture are used to explain expected and experienced behavior when collecting data in other countries.

The interviewees explain that challenges might arise because the communication partners have different expectations and may place different emphasis on efficiency and/versus politeness.

"I have just received an email from one of my colleagues who is trying to get [a user study] in Japan in place for me. He says that you just have to be aware that they are…traditionally speaking, they are not so willing to say what they really think…you have to be aware of that, especially if their opinion is negative, so I have to take that into account." (Senior UX researcher, F) "We have experienced the classical thing, in Brazil [they] were expressive about it and in Asia much shorter replies. We have used the same type of test in both places, and in Brazil they were very expressive, the Japanese gave very short statements, the Chinese were very polite and the Germans made jokes that were kind of dirty, which was a little strange, but it was also in Berlin [laughs] so maybe it was that." ( Company owner, M)

In the examples, perceived differences in communication styles are associated with and explained by national culture. The consequence of this is that more general u nderstandings based on one factor, namely national culture, are foregrounded, while the more complex aspects of culture and the uniqueness of th e actual situations and the individual communication partners are played down. As can be seen from our highlights in the quotes , the interviewees use words such as "traditionally speaking" and "the classical thing" to signal that they are aware of using general and somewhat stereotypical descriptions to explain the behavior of people from the countries in question.

National stereotypes develop over time as stories, examples , and jokes about the characteristics of people with a particular nationality are to ld and retold in the media, in literature, at social gatherings, etc. Moreover, they tend to cohere well with the experiences we have of interacting with people from these countries [START_REF] Risberg | National Talk: The construction of national stereotypes in a merging multinational[END_REF]. In this way, stereotypes come to influence the way we make sense of and talk about other nationalities. This can be problematic if stereotypical understandings gain too much expla natory power. Moreover, it can be problematic if stereotypes shape interpretations and decision-making in unreflective or unrecognized ways, e.g., when interacting with a person from a particular nationality or when making decisions about where and how to conduct international user studies.

Linguistic simplifications create distance between people.

In addition to stereotypes, language can in subtle, and often unconscious, ways serve to create distinctions between "us" and "them". For example, when the interviewees say that "those from Norway" prefer this or that "some lady from Mongolia" has that type of education, a distance is created. This is because the choice of the seemingly insignificant words "those" and "some" refer to a generalized group or person diffe rent from oneselfand therefore by implication more difficult to understand and relate to.

Likewise, communication theory shows that we always position ourselves as either: superior, equal, or subordinate in relation to other people when we communicate [START_REF] Jensen | Introduction to Cultural Understanding[END_REF][START_REF] Jensen | If Culture Is Practice …? A Practice Theoretical Perspective on Intercultural Communication and M ediation[END_REF]. This can be seen in the above examples, where the generalization to "those" and "some" positioned the interviewee as superior and th e others as subordinate. Other examples include the interviewees' use of linguistic images to explain that even though their company has a very diverse user group much data collection is conducted with "the white middle class" and "pale Europeans". Or to explain that the software their company produces is used by different groups, and therefore has to be designed so that it can be used by both "engineering types" and "a Russian cosmetologist". Such expressions are very powerful in communicating a point, because (positive and negative) stereotypes are used to create a vivid image. However, they also gloss over complex understandings and create distance (rather than empathy and identification) because of the use of general, value-laden categories.

Such linguistic images and simplifications cannot be avoided no matter how cu lturally competent one becomes. However, it is possible to become more aware of the language that one self and others use and to gain a better understanding of how linguistic structures create distance and cause people to take value-laden positions in relation to others.

This awareness of language is especially important when presenting the obtained user insights to the employees who have to use them for product design.

Presentation of the user insights

The companies that have participated in this research project use three different types of methods for presenting the user insights that they obtain through international user studies, namely personas, segmentation, or profiles of actual users. It is clear from our interview data that different types of companies use the three methods for different reasons.

 Personas is used by companies that wish to capture and apply the user insights for a period of time and for several purposes, i.e. in design activities, development projects, marketing campaigns, etc.  Segmentation is used in companies where the company culture enforces a focus on logical arguments and decisions based on quantitative data.  Profiles of actual users (rather than personas) are used by design agencies. For the design agencies we have talked to, the priority is to identify design insights for a particular client project. The profiles and user insights are not meant to live on a fter the project is over and therefore in-depth analysis leading to personas is not economically feasible unless they constitute an outcome, which the client is inte rested in and willing to pay for.

In this section, we look first at how the companies work with international pe rsonas and subsequently we des cribe the use of the two other methods.

Strategies for creating international personas .

The user researchers stress that the strength of the persona method is its ability to create recognition and empathic identification, but they disagree about how to ac hieve this in international personas. There are two different overall strategies for presenting international user insights as a set of personas:

(1) To create personas according to nationality. When this strategy is used there is typically one persona per country/region covered by the user study (e.g., if the user study was conducted in Denmark, India and USA, there will be one Danish, one Indian, and one US persona). In other words, this strategy results in country specific persona descriptions. (2) To create personas according to other criteria, such as, e.g., differences in user preferences, profession, education level, level of involvement, learning styles, digital maturity, autonomy at the work place, etc. This is similar to the criteria that are used to create national personas. This results in general persona descriptions.

"We have tried two different models. One is to have a persona that is very focused on how people in this job think and what kind of goals they have. It [the persona d escription] can be quite general…the other model we have tried is to map different personas to different regions." (Senior interaction designer, B).

However, some compensate for what the choice of main strategy leaves out by adding text fields that delineate:  What would be different about the persona compared to the country specific d escription if s/he was living in different countries/regions  What would be unique to the persona compared to the general persona description if s/he was living in a particular country/region This indicates that neither strategy is entirely successful. In line with this, one of the interviewed user researchers states that he would prefer if people did not have to read about the differences between, e.g., Japan and Europe, in added text fields and that he is planning to experiment with other ways of presenting the information about cultural differences.

When it comes to the content of the persona descriptions, some user researchers prefer to use pictures or drawings that contain very little backgroun d that could place the persona in a specific context. Moreover, they avoid geographical references in the text and they give the personas as general names as possible. The argument for this is that employees around the world should be able to recognize and use the personas and therefore the focus should be on the persona as a person rather than a person in a specific place.

Other user researchers prefer to use pictures, names, titles, etc. which draw attention to and challenge the employees' stereotypical understandings of who the users are. The argument for this is to communicate the diversity of the users to the employees and therefore the focus is on the persona as a person who has both expected and unexpected features. One of the interviewees explain that she puts much effort into finding the right pictures for the personas and that she deliberately chooses pictures that challenge stereotypical understandings: "Generally for personas in firms: the top manager is a woman, the creative leader is a dark man . That is how you try to challenge stereotypes." (Design researcher, A).

The choice of strategy is not only based on data.

In general, the user researchers have strong opinions about which strategy they prefer. One of the interviewees for example states that: "I would rather not divide [

personas] according to nationality." (Innovation specialist, N).

There are also several examples of how the choice of strategy for creating personas is made based on other considerations than the differences that emerge d uring data analysis. In one example, political considerations led to the use of strategy one, i.e. one persona for each of the company's main markets (even though nationality was not reflected as a significant difference in the data).

In another example the client had requested personas specifically to be able to d evelop 'the Swedish market', 'the Norwegian market', etc. and it was therefore natural to use strategy one. In other words, the decision to create personas based on nationality was made early on in the project, due to the client's way of conceptualizing their users in terms of markets that could be developed.

Profiles and segments.

Not all the companies we have talked to use personas. In the design agencies, for example, they do not use personas. Instead they create a profile of each user who has participated in the user study. The profile contains one or more pictures of the user and the home-or work context where the data collection took place as well as quotes and key insights. Thus, if the study covers 72 interviews, 72 user profiles are subs equently createdand in this particular example hung in a project room in order for the project team to be continuously reminded of the users an d whom they were designing for.

Another company currently uses segmentation as the method for gathering and presenting user insights. Some companies conduct and use quantitative segmentation surveys, among other things, for planning a qualitative user study that results in pe rsonas. Yet again, in other companies they use and need both personas and segmentation as: "Personas are a strong tool to communicate user behavior and intentions, but many "number people" want to be able to use them to prioritize, so they want to know exactly how many "of those" there are in each country." (Innovation specialist, N).

Conclusion

In this paper, we have presented the results of an empirical investigation of how co mpanies conduct international user studies. Key findings are as follows.

Companies do not collect data about end us ers in all the countries/regions they operate in. Instead, they focus on a few strategic markets. These can be new markets the company wants to develop, but more often it is relatively well-known markets where the company is already conducting much of its business.

Our research also shows that for some geographical areas and countries the companies/user researchers have almost too much respect for the national culture. This in turn means that, even though it would be highly relevant for the business, there are parts of the world where they do not conduct user stud ies.

International user studies tend to be large-scale studies that involve many human resources, including company employees as well as external agencies, translators, etc. from the countries where the studies take place. The studies typically cover 2-4 countries/regions and many end users in each country/region. It is not uncommon that more than 50 qualitative interviews are conducted (in total), among other things, to ensure validity.

The preferred data collection method is field studies. If possible, user researchers choose to go to the field themselves to gain rich insights and to control the data co llection process.

The main insights that companies gain from international user studies are (1) that there are many similarities among end users across nationalities and (2) that it often is more important to focus on and take differences in market conditions (i.e. legislation, socio-economic situation, healthcare system, education, etc.) into account rather than national culture per se. This indicates that one of the important outcomes of intern ational user studies is a complex understanding of the role of culture. However, we also saw examples of stereotyping the users and of an "us versus them" attitude, even though the goal of the user studies is to gain a nuanced understanding of the users and to provide other employees with user insights that allow for recognition and empathic identification.

Companies are in the process of finding out how best to present the insights about international end users to the employees (i.e., product designers, project participants and marketing personnel). Currently, two strategies are used, namely to distinguish among end users (1) according to nationality or (2) according to other criteria (e.g., user preferences, education level, and IT maturity). However, neither strategy is e ntirely successful, as it either foregrounds the differences between nationalities or downplays the unique aspects of the different countries/regions. Thus, so far, no best practice for incorporating both national differences and crosscultural similarities into persona descriptions, segmentations, etc. has been esta blished.

This study contributes to the HCI literature with empirical findings about how companies conduct international user studies and the specific practices and challenges hereof. In particular, we show that strategic considerations, perceived differences in national culture, and concerns about data quality play an importan t role in shaping and delimiting the approach that companies take to international user studies.

Our findings points to the need for more research that addresses how to plan and carry out user studies in countries that are perceived as culturally very different, how to ensure data quality and understand the notion of validity when conducting multicountry studies, and how to incorporate both national differences and cross -cultural similarities into persona descriptions, segmentations, etc.

  Design researcher, C) External resources: A matter of trust and control. International user studies often involve the use of external resources, such as:  Recruiters/recruitment agencies  User research agencies  Local resource persons (e.g. freelance user researchers and translators )  Danes with a relevant ethnic or educational background (e.g. a person with Danish-Kenyan ethnicity or a Danish anthropologist)

Table 1 .

 1 Overview of the participants

	Inter-	Job title	Type of company	Method for presenting
	viewee			user insights
	A	Design re-	Danish subdivision of a large inter-	M ore than 10 years of
		searcher	national software development	experience with the
			company	persona method (interna-
	B	Senior inter-		tional personas)
		action design-
		er
	C	Design re-	Large financial company with	Around 5 years of expe-
		searcher	headquarter in Denmark and subdi-	rience with the persona
			visions in Northern Europe	method (international
				personas)
	D	Head of digi-	Large financial company with	Preferred method: Seg-
		tal experience	headquarter in Denmark and subdi-	mentation; considers
		and global	visions around the world	using personas
		marketing
	E	Technical	Software development company	Development of a set of
		writer	(financial systems), headquarter in	international personas is
			Denmark and subdivisions around	under consideration
			the world
	F	Senior UX	Software development company	Development of a set of
		researcher	(content management systems),	international personas
			headquarter in Denmark and subdi-	has been initiated
			visions round the world
	G	Innovation	Organization that specializes in	The method for present-
		consultant	development of digital health-care	ing user insights is cho-
			solutions; many projects are funded	sen from project to pro-
	H	Innovation consultant	by EU and involve development of solutions for several EU countries at a time	ject; experience with national personas
	I	Senior inno-
		vation con-
		sultant
	J	Consultant	Design agency that specializes in	(National and interna-
			tourism, events and city develop-	tional) Personas often
	K	User re-searcher	ment (project work for clients)	constitute an important result of the projects/for the clients
	L	Design re-	Design agency that specializes in	One-page profiles of
		searcher	product, service, graphical and	actual users, with pic-
			digital design (project work for	tures and quotes

Acknowledgement. This research is supported by InfinIT-Danish Network for Innovative Utilization of IT.


Bin Yu

Loe M G Feijs

Mathias Funk

Jun Hu

J Hu}

Breathe with Touch: A Tactile Interface for Breathing Assistance System

Keywords: tactile interface, biofeedback, breathing assistance, relaxation

Breathing techniques have been widely used as an aid in stressreduction and relaxation exercises. M ost breathing assistance systems present breathing guidance in visual or auditory forms. In this study, we explored a tactile interface of a breathing assistance system by using a shape-changing airbag. We hypothesized that it would help users perform the breathing exercise more effectively and enhance their relaxing experience. The feasibility of the tactile interface was evaluated from three aspects: stress reduction, breathing training and interface usability. The results showed that for most participants, the overall heart rate variability were improved after breathing training. M oreover, "Breathe with Touch" brought users better satisfaction during the exercise. We discuss these results and future design implications for designing tactile interfaces for breathing guidance.

Introduction

In modem society, the pace of life is fast and the competition is fierce. An increasing number of people are suffering fro m chronic stress in their daily life. Breathing techniques have been widely used in mind-body practices for stress reduction and relaxation [1]. Breathing techniques offer a simple tool to improve the balance of autonomic nervous system, strengthen its capability to adapt to stress and further mit igate the negative effects of stress on the health [2]. W ith a variety of breathing assistance devices, individuals learn to regulate their b reathing into an optimal pattern with the aim of stress reduction. But this is not an easy task for most people to achieve a real relaxed state physically and mentally; because besides an improved breathing skills, the users' psycho-physiologic relaxing experience also affects the stress mit igation. To put it simp ly, users should also "feel good" during a breathing exercise. Therefore, the interface of breathing assistance device should not only offer an effective breathing guidance, but also a "feeling good" relaxing experience.

In medical applications, breathing guidance is usually presented in graphic or numeric forms, which tend to be technical and performance-oriented. In recent years, several new audiovisual interfaces with more aesthetic qualities have been created for daily use. Fo r instance, Yongqiang Qin et al. developed an immersive breathing train-ing game "Balloon" to train the user to improve breathing pattern [3]. In [4], the authors presented "Sonic Respiration" to provide breathing feedback by modifying the quality of musical interface. However, very little work has exp lored the feasibility of tactile interface for breathing guidance.

The sense of touch enables us to interact with real objects around us, meanwhile, to perceive these interactions. In [5], the authors suggested that the characteristic bidirectional property of touch sense provides a basis to further enhance motor learning and somatic experience. Studies in [6] revealed that tactile feedback could also reduce the perceived workload in learning tasks and enhance the user's feeling of p resence. Moreover, stimulating the tactile sense can give people strong relaxing experiences or even emotional experiences, which are beneficial for stress mit igation and health. Therefore, tactile stimu li are often used as a way to reduce stress and make people feel better, such as in massaging techniques and physiotherapy. Tactile feedback is often integrated into mult imodal interfaces to enhance the user experience. For exa mple in [7] the authors developed a breathing guidance system to provide the users with an immersive experience through a mult imodal interface of auditory, vib ratile and light stimuli.

In this study, we aim to investigate whether the tactile interface would help users perform breathing exercise more effectively and enhance user experience during the exercise. We present the concept of "Breathe with Touch": a tactile interface of breathing assistance device that provides breathing guidance through a shapechanging airbag. The airbag inflates and deflates at a specific rhythm to simulate the targeted respiratory pattern. We assume that the changes in the shape of airbag can be mirrored by the user resulting in a better and more relaxing breathing pattern. The tactile interface was evaluated fro m three aspects: the effect on stress reduction, the efficacy of breathing guidance and the usability. We synthesized the results with valuable qualitative responses from users .

Design & Implementation

The concept "Breathe with Touch" entails a tactile interface for b reathing exercises. By touching the interface, the user follows the shape change of the interface to receive the feedback informat ion. To design the proper form of tactile feedback, we observe the nature of human's breathing movement. Breathing is accompanied by diaphragm fluctuation activities. As an individual inhale, the diaphragm contracts and flattens, causing the expansion of the lungs. Conversely, on exhale, the diaphrag m relaxes and moves upward to reduce the space in the chest cavity (see Fig 1). The lungs are like two air balloons inside of our body. The changes in its shape depend on the airflow. "Breathe with Touch" simu lates human's breathing movements through the shape changes of an inflatable airbag. The expansion and contraction of the lungs are mirrored by the inflation and deflat ion of the airbag. We assume that this kind of na tural mapping between the targeted behavior and the interface could minimize cogn itive workload thanks to the intuitive interpretation of the interface. Besides, we think the gradual shape-changing process of airbag could render the breathing guidance in a more soothing way, which helps users slow down their breathing and calm down as well. A hand-sized ellipsoid airbag was made of thermoplastic textile covered by a layer of soft velvet. The user rests her hand on the airbag to "feel" the targeted breathing rhythm (see Figure 2b). The breathing guidance is mapped to the airbag in the fo llo wing way: when the airbag in flates, an inhale activity is imp lied. When the airbag deflates, an exhale activity is implied. The maximu m volu me of airbag is around 120ml that is the same size o f a mouse appro ximately. This enables the user to identify subtle changes of the shape easily and accurately by hand. The sensitive tactile feelings fro m the hand and fingers ensure that users can receive the guidance precisely as well. An air pu mp and a solenoid vent valves implement the inflation and deflation of the airbag. During the inflation, the air-pu mp pu mps air into the airbag and the valve is closed. During the deflation, the air-pu mp stops working and the valve turn opened. Then, with the hand own weight, the air will be pushed out of airbag gently.

In this study, we focus on the design and evaluation of the tactile interface. A feed forward system was built with a pre -set breathing rate of 6 breathing cycles per minute (c/min). According to literature [8], most people could achieve a h igh HRV level under a respiration of 6 c/ min. The airbag starts from the deflated state to inflated state then return to deflated state again. The duration of this inflat ion/deflation process is 10 seconds and this process repeats for the whole training session. As shown in Fig 2(a), the p roposed tactile interface in this work can be embedded into a co mplete closed-loop biofeedback breathing assistance system in our future research.

Study One:Evaluation of the effects on stress reduction

We admin istered the first user study to investigate whether the proposed tactile interface would enhance breathing train ing and reduce stress effectively. 12 subjects (six The experiment follo wed a procedure as shown in Figure 4. On arrival at the laboratory, the participants were instructed how to use the breathing assistance system. The pulse sensor and respiration sensor were applied to the participants. Then participants were instructed to rela x with their eyes closed for 5 minutes. After the resting period and without moving, part icipants were instructed to open their eyes and complete a pre-training mathematical task wh ich lasted 10 minutes during which time measurements of HRV and respiratory rate were calculated. After the task, participants completed a pre-train ing STAIS questionnaire. After further 5-minute rest with eyes closed, then participants completed a 10-minute breathing training session with "Breath with touch". The instructions given to participants were: "Please follow the changes of the airbag to breathe, when the airbag inflates, you should breathe in. When airbag begins to deflate, you should breathe out. This session will last for 10 minutes." After the training, part icipants comp leted a further 10-minute mathematical task. Pulse signal and respiratory data were also recorded throughout this period. Then, a post-training STAIS questionnaire was completed.

Study two: Evaluation of interface usability

As tactile interfaces are seldom used in breathing assistance, we conducted another study to investigate the user's perception on the usability of tactile interface. To gain more insightful feedback and reco mmendations for further design, ten students with interaction design background (four females and six males, age range: 20 to 35) were recruited for this study. All part icipants complete three 10-minute breathing training sessions using the same breathing guidance, but with three different interfaces: v isual, auditory and tactile interfaces. The experiment follows a within-subjects design with counter balancing to avoid carry-over effects.

We introduced visual and auditory interfaces for breathing assistance as shown in Fig 7 . In visual interface, an ellipse with varying radius represents the breathing guidance. When the ellipse grows, an inhale process is imp lied. In auditory feedback, we used the changes in sound volume to present breathing guidance. An increasing sound volume pro mpted user to breathe in, and the fading sound imp lied breathing out. The usability of the interface was measured using an adapted Lund's USE Questionnaire [10]. The questionnaire was designed for three d imensions: ease of use, ease of learning and satisfaction. All the questions used a seven-point Likert scale (1=strongly disagree, 7=strongly agree).

The results are shown in Figure 7. In terms of " Ease of Use", all of three interfaces received high scores; there were no significant differences between tactile, auditory and visual interfaces (19±2 vs. 17±2 vs. 17±2; Tactile vs. Auditory vs. Visual). In terms of "Ease of Learn ing", there were also no significant differences between three interfaces (19±2 vs. 18±2 vs. 17±2; Tactile vs. Auditory vs. Visual). In terms of "Satisfaction", the score of visual interface was significant lo wer than tactile and auditory interfaces (15±3, 14±3 vs. 11±2; Haptic, Auditory vs. Visual, respectively, p<0.05).

Fro m the open-ended interview, we got more positive feedback about tactile interface. More than 70% participants chose the tactile interface as their favorite interface. Sp ecifically, they expressed a strong interest in working with the tactile interface and emphasized that it was more comfortable due to the touch experience.

General discussion

During a breathing train ing, users need to recognize the breathing guidance and follow it to regulate their breathing. In other words, the breathing training is a learning process, in which the users should take an active role, rather than just being exposed to it. Therefore, in breathing train ing, although the learning tasks are very simp le (i.e. to regulate breathing to a specific rate), some participants still regard it as a serious task, which keep them away fro m a pure relaxat ion. We think this might be an interesting "paradox" in the design of self-t rain ing system for relaxat ion. It appeals to us and drive us to think about the interaction design in these products or systems that aim to promote relaxation. The training session requires user's mental effort to achieve optimal training effect, such as improved breathing skills, positive imagination or more concentration. However, such mental effort of learn ing might leads to new stress.

In this design, we tried to lower the workload and enhance the relaxing experience by using a tactile interface. The touch airbag was used as a tangible commun ication med ia between the training system and the user. It is assumed that the user can adapt her breathing movements to an optimal pattern mo re effort lessly by mirroring the shape changes of the tangible interface. The results of user study confirm that the proposed "natural-mapping" interface could help the users perform breathing exercise more spontaneously. The users do not need to put much effort into understanding the instructions, and the transition between inflat ion and deflat ion of airbag might naturally trigger a slow and smooth transition between inhalation and exhalation.

The effectiveness of tactile breathing guidance in aid ing relaxat ion and reducing stress was shown by the results of SAITS self-report. However, there is no significant reduction of stress level during the post-training mathemat ics task. There might be two possible explanations. For most participants, it was their first time to use breathing assistance system; the unfamiliarity with the system brings about new stresses. We also have reservations about the acute effect of 10-minute breathing e xercise on stress reduction. Although in some clinical use [11], the minimu m time of each training session could be 5 minutes; a short-period exercise may be repeated several times throughout a day to achieve a greater effect on stress mitigation. Fro m physiological measurements, the results suggested that there was a significant imp rovement in HRV during the post-training task, wh ich suggests that tactile breathing train ing could enhance the users'physical ability to adapt to stress.

The users' ratings on the usability of visual, auditory and lighting interface were shown in Fig 7 . The tactile interface shows the potential in improving user experience during the relaxat ion exercise as seen from significantly higher user rat ings on satisfaction. Improvements in user experience were also evidenced by the participants' feedback fro m the interviews at the end of the experiment. During a breathing training process, repeated breathing instructions become boring easily. Th is is a major problem of most breathing guidance systems for long-term use. To some extent, the touch airbag shifts the focus from the superficial interface to users' own regulating behavior, wh ich helps to relieve users of tedium. Besides, the users thought tactile feedback offers a condition for them to perfo rm breathing train ing with eyes closed, wh ich also helped relax. They also gave us a lot of insightful reco mmendations for further design of the interface, for instance, changing the size or position of airbag, integrating the airbag into regular items, and combining tactile and auditory feedback.

Fig. 1 .

 1 Fig. 1. The shape change of the airbag might be naturally associated with breathing movement s

Fig. 2 .

 2 Fig. 2. (a). Touch Airbag schematic diagram. (b). The user's right hand on the airbag

  females and six males, age range: 25 to 35) part icipated in the study. Each part icipant performed two stress-induced tasks (mathematical test) before and after breathing training. For each task, the physiological data (pulse signals and respiration data) and subjective stress reports were collected. For each participant, A PPG sensor was placed on the left index finger and a respiratory sensor was placed at the abdominal level. Pu lse signals were measured by a data acquisition unit developed by our lab, and then beat-to-beat intervals (RR intervals) were calculated and transmitted to a Processing program for data storage. The standard deviation of the beat-to-beat intervals (SDNN ) was calcu lated as the index of HRV. Respiration data was recorded by the ANT system 1 with a sampling rate of 256 Hz. The part icipant's stress level were measured by the state component of a Spie lberger State-Trait Anxiety Inventory (STAIS)[9].

Fig. 3 .

 3 Fig. 3. (a). The experiment set up (b). Right hand on the airbag

Fig. 4 .

 4 Fig. 4. The experiment procedure

Fig. 5 .

 5 Fig. 5. HRV (SDNN) and respiration rate before and after the breathing training.

Fig. 6 .

 6 Fig. 6. Scores of STAIS questionnaires pre-and post-the breathing training (N=12)

Fig. 7 .

 7 Fig. 7. The results of Evaluation of interface usability

ANT, the Netherlands, http://www.ant-neuro.com/