Christos Fidas
email: christos.fidas@cs.ucy.ac.cy

Artemios G Voyiatzis

On Users' Preference on Localized vs. Latin-based CAPTCHA Challenges

Keywords: CAPTCHA, Usability, Security, Native Language (non-Latin) systems, localized CAPTCHA

A Completely Automated Public Turing test to tell Computers and Humans Apart (CAPTCHA) is a widely used security mechanism for constructing a high-confidence proof that the entity interacting with a remote service is actually a human being. Stimulated by the facts that: a) nowadays CAPTCHA challenges are solely based on the Latin alphabet, b) currently Internet population consists in its majority of non-native-English speakers and c) numerous web sites consist of exclusively localized content, we conducted an empirical study aiming to examine the effect of various factors on users' preference in solving localized vs. Latin-based text CAPTCHA challenges. The study embraced a between-subject design using a self-developed localized CAPTCHA mechanism, capable of producing text challenges based on the participants' native alphabet. A total of 384 non-native English speakers participated in the frame of the reported study which followed an ecological valid experimental design. Analysis of interaction results provides interesting insights which can be taken into consideration for designing more usable CAPTCHA mechanisms.

Introduction

A Completely Automated Public Turing test to tell Computers and Humans Apart (CAPTCHA) is nowadays utilized by numerous application service providers in order to defend themselves against automated software agents whose purpose is to degrade the quality of a provided service, whether due to misuse or resource expenditure. CAPTCHA challenges are utilized worldwide by millions of users and thus, it becomes obvious that having usability flaws in the design of CAPTCHA mechanisms, results in unacceptable tradeoffs for the users in terms of time and money. Thus, considering usability aspects in designing CAPTCHA mechanisms becomes nowadays a necessity.

Nowadays, the vast majority of deployed CAPTCHA mechanisms rely on recognition of distorted text with audio as an alternative means for those with vision problems. Research on CAPTCHA design has received significant attention lately. There is a growing demand to enhance both the security and the usability aspects of CAPTCHA mechanisms, aiming to offer high security standards to application service providers and interaction transparency to actual users. Therefore, the design of secure and usable CAPTCHA mechanisms is considered to be a challenging endeavor [START_REF] Yan | Usability of CAPTCHAs or usability issues in CAPTCHA design[END_REF].

There are two main research directions for improving usable security of CAPTCHA mechanisms. The first one is towards breaking and improving existing mechanisms, resulting in the development of design guidelines for increased security [START_REF] Burzstein | Text-based CAPTCHA Strengths and Weaknesses[END_REF][START_REF] Ahmad | The Robustness of Google CAPTCHAs[END_REF]. Being focused on security, CAPTCHA mechanisms are currently designed as tasks which are not integrated smoothly in the primary user interaction flow and many attempts exists aiming to provide more usable mechanisms [START_REF] Matthews | Scene tagging: image-based CAPTCHA using image composition and object relationships[END_REF][START_REF] He | Filtering short message spam of group sending using CAPTCHA[END_REF][START_REF] Kluever | Balancing usability and security in a video CAPTCHA[END_REF][START_REF] Zhang | Dealing with telephone fraud using CAPTCHA[END_REF][START_REF] Datta | IMAGINATION: A robust image-based CAPTCHA generation system[END_REF][START_REF] Cui | A 3layer dynamic CAPTCHA implementation[END_REF][START_REF] Lin | A new CAPTCHA interface design for mobile devices[END_REF][START_REF] Banday | Image Fip CAPTCHA. ISeCure[END_REF][START_REF] Ho | DevilTyper: a game for CAPTCHA usability evaluation[END_REF][START_REF] Holman | Developing usable CAPTCHAs for blind users[END_REF][START_REF] Ross | Sketcha: a CAPTCHA based on line drawings of 3D models[END_REF][START_REF] Wei | GeoCAPTCHA -A novel personalized CAPTCHA using geographic concept to defend against 3rd Party Human Attack[END_REF].

Existing text-based CAPTCHA mechanisms produce challenges with characters solely from the Latin alphabet. This is a "one-size-fits-all" approach that may not provide a viable long-term solution or even a good usability tradeoff, considering that not all Internet users are familiar with this alphabet. This argument is further strengthened bearing in mind that the Internet population consists in its majority of nonnative-English speakers 1 and numerous web sites consist of exclusively localized content.

In this context, it is necessary to explore alternative constructs that consider the diversity of Internet users in terms of conventions, cultural, and cognitive backgrounds; tools and resources; and contexts in which CAPTCHA challenges are required to be solved. Towards this direction, we aim to explore the applicability of localized CAPTCHA i.e., a system that presents challenges with characters, glyphs, or other symbols in users' native language and cultural context. In contrast, a Latin-based one presents challenges using characters only from the Latin alphabet i.e., lowercase and/or uppercase letters from "a" to "z".

A localized CAPTCHA adapted to users' contextual factors may actually increase the usability of a system, in terms of efficiency and effectiveness, while not decreasing the security level needed for protecting the system. In this context, the work presented in this paper is primarily driven by the need to apply User Centered Design (UCD) methodologies related to design and evaluation of CAPTCHA mechanisms and contributes towards this direction by investigating whether individual differences, focusing mainly on users' lingual characteristics, affect efficiency and effectiveness on interacting with text-based CAPTCHA mechanisms.

The rest of the paper is structured as follows: first, we review the related works. Subsequently, we describe the context of an empirical study, the methods, and the developed hypotheses. Then, we analyze and discuss the findings of the study. Finally, we summarize and outline the implications of the reported research.

Related Works

The role and involvement of the real users and their unique characteristics is getting the attention of the research community lately. Based on over a million collected responses, an overall success rate of 96.1% was observed on the ReCAPTCHA service [START_REF] Von Ahn | reCAPTCHA: Human-Based Character Recognition via Web Security Measures[END_REF]. The service presents garbled words from English scanned books that OCR software failed to recognize. The authors noticed that "non-English speakers seem to perform slightly worse than English speakers"' based on statistically significant differences in success rates correlated with the origin of the respondent's IP address [START_REF] Bursztein | How good are humans at solving CAPTCHAs? A large scale evaluation[END_REF].

A large-scale study involving over 1,000 volunteers and 21 different text-based CAPTCHA systems revealed among other that "non-native speakers of English take longer to solve CAPTCHAs and are less accurate on CAPTCHAs that include English words" [START_REF] Banday | Challenges of CAPTCHA in the accessibility of Indian regional websites[END_REF]. Users needed on average 9.8 seconds to solve a text challenge and between 12 and 25 seconds for an audio challenge. Overall, native-English speakers were substantially faster and slightly more accurate on solving the challenges. We note that the recruitment platform that was used in the study (Amazon Mechanical Turk) is currently available only in the US and thus, it might be the case of bilingual speakers. The study neither evaluated CAPTCHA challenges in languages other than English nor the performance of non-native English speakers.

As part of one accessibility studies, a localized CAPTCHA based on the Urdu language was developed for web-based applications [START_REF] Banday | Challenges of CAPTCHA in the accessibility of Indian regional websites[END_REF]. Urdu is widely spoken in India. A small-scale evaluation of the system involved 50 Urdu-knowing users with no or elementary knowledge of English language. The study found that users were more accurate and solved faster challenges in Urdu rather than in English. Similar results were reported in a recent study with Arab participants [START_REF] Khalil | Script Familiarity and Its Effect on CAPTCHA Usability: An Experiment with Arab Participants[END_REF].

Furthermore, a lab usability study of text-based English CAPTCHA involved 24 participants who spoke Chinese and learned English as a second language [START_REF] Lee | Usability study of text-based CAPTCHAs[END_REF]. The authors observed that "When reading a string of alphanumeric characters, the participants spoke the alphabets in English, but the numbers in Chinese." This resulted in erroneous responses as for example due to the similar-sounding number "one" in Chinese and letter "e" in English.

Another study investigated users' perceptions towards localized and Latin-based CAPTCHA challenges [START_REF] Fidas | On the necessity of user-friendly CAPTCHA[END_REF]. According to the perceptions of the participants, current implementations do not provide an acceptable tradeoff solution with regards to usability. Analysis of responses revealed that even experienced users had severe difficulties in coping with current CAPTCHA challenges: "every other participant claimed to need two or more tries each time to solve a challenge." Furthermore, participants stated to be positively attributed with regards to localized CAPTCHA challenges, especially when visiting web sites with localized content, since their interaction flow tends to be more natural.

A follow-up work examined the relation between the cognitive style of the user and their preference and performance upon interacting with text-and picture-based challenges [START_REF] Belk | Do Cognitive Styles of User Affect Preference and Performance related to CAPTCHA?[END_REF]. The results of the study revealed an existing main effect relating to users' cognitive styles (Verbalizer or Imager) and a respective performance issue in solving text-vs. picture-based CAPTCHA challenges.

We build on top of these findings aiming to investigate whether individual differences affect preference to localized-vs. Latin-based CAPTCHA challenges. We describe in the next section a study that utilized the developed localized CAPTCHA mechanism, the hypotheses that have been formulated for the purpose of our research together with analysis of interactions and the interpretation of results.

3

Method of Study

Procedure and research hypotheses

A research prototype of a localized CAPTCHA mechanism was designed and developed aiming to produce challenges of random characters based on different national alphabets. The research prototype was based on an open source CAPTCHA mechanism which has been enhanced as to produce CAPTCHA challenges based on UTF-8 and thus capable to produce challenges in a variety of national alphabets. The research prototype produced challenges in Latin and non-Latin alphabet with a similar level of text distortion. We formulated the following null hypotheses for the purpose of this research: H 0 . There is no general preference of users towards Latin or non-Latin CAPTCHA challenges, considering also various main effects and interactions with respect to language presentation of the web site and users' national alphabet.

Experimental design

The aim of the experiment was to examine user preference towards a specific type of CAPTCHA challenge by considering also various main effects and interactions with respect to language presentation of the web site and users' national alphabet. The participants were asked to visit a web page which was placed in front of a web application that announced the students' marks for the course assignments. In this study, the web page content appeared equal randomly in either local language (in Greek) or translated in the English language. The aim was to examine whether the web page content presentation language influenced the user preference towards selecting a specific type of CAPTCHA challenge.

Once a student initiated a session, a random process chose if the student would receive content in English or local language. This choice was fixed for the whole session. The page explained what a CAPTCHA challenge is and presented two example challenges, one in local language and one in English. It then asked the user to select the CAPTCHA type of preference. The placement of the two challenges was equally split: in half cases the localized CAPTCHA example challenge appeared on the left side of the screen and the English one on the right; in the other half this order was reversed. Once the CAPTCHA type choice was made, the participant was faced with the actual CAPTCHA challenge and was asked to provide the correct response. If a correct answer was received, the system displayed the marks for the course assign-ments or else it challenged again the participant with a new challenge in the same (previously selected) language of preference.

Demographics of the participants and validity of the study

The participants of the experiment were juniors and seniors of two different academic institutions studying computing science and applications. They were all native non-English speakers. We recruited 384 students in total for this experiment. The age of the students was between 20 and 25 years old with only minor exceptions. In total, 440 different challenges were presented to these students.

The validity of a study is related to its internal and external validity, and ecological factors. There has been an effort to increase ecological validity of the research, since the participants were involved at their own working conditions and physical environments (without the intervention of any experimental equipment or person). Furthermore, participants were asked to solve the CAPTCHA challenge during a real-life task (the primary task of the participants has been to view their course marks). This closely resembles a typical usage scenario related to CAPTCHA usage in which the challenge is as a secondary task. In terms of external validity, we mention that further empirical research with a larger sample is needed aiming to compare the findings of this study with ones performed using other alphabets, more representative samples, and diverse cultural contexts.

Study Results and Discussion

In this section, we present and discuss the main findings of the study based on the analysis of the collected responses.

The experimental design explored the actual user preference and the effect of content presentation in this choice. The users visited a web page that contained an example of both a Latin-based and a localized CAPTCHA and asked them which language they prefer to be actually challenged. The page appeared either in local language or in English and the appearance order of the two examples (left-right) was random. For the purpose of the study, we separated the participants in two groups based on their skills with regards to the English language. The control Group (A) consisted of N=298 participants who were proficient in English. The experimental group (B) consisted of N=86 participants who were not proficient in English.

In Table 1, we summarize the CAPTCHA preferences for each group according to the users' choice. Those participants belonging to Group (A) select to solve the English challenge in the majority of cases (188/298), while those participants belonging to Group (B) select to solve the localized one (72/86). This difference in preference is significant x 2 (1,N=384)=58.650, p<0.001. Furthermore, we examined the effect of the language presentation of the web content towards users' preference for a specific type of CAPTCHA challenge. The choice of the participants in both groups is not affected by the page content language: control group x 2 (1,N=298)=0.220, p=0.639 and experimental group x 2 (1,N=86)=0.332, p=0.564. The choice is also not affected by the order in which the two example chal-lenges appear: control group x 2 (1,N=286)=1.828, p=0.176 and experimental group x 2 (1,N=86)=3.084, p=0.079.

The aforementioned results suggest that there is a main factor between the user preference on CAPTCHA challenges and their familiarity with the Latin alphabet. It appears that, if the users are given a choice, then the users belonging to the experimental Group (B) prefer to solve challenges in their native language, whereas users belonging to the control group (A) prefer to solve the Latin-based CAPTCHA challenges. The aforementioned results are based on objectively measured interaction data and are in line with the results presented in [START_REF] Fidas | On the necessity of user-friendly CAPTCHA[END_REF], which investigated users' preference in solving localized vs. Latin-based CAPTCHA challenges through a questionnaire based survey. Bearing in mind that these recent studies followed different methodological approaches (objective vs. subjective self-reporting data) it seems promising to consider user's diversity with regards to their lingual characteristics in the design of CAPTCHA challenges, as nowadays CAPTCHA designs and implementations clearly fail to consider in their iteration design cycles such individual characteristics of the users as they produce challenges with characters solely from the Latin alphabet.

Simultaneously, such an approach would have as well some positive side effects, especially in use cases in which the users interact with a web application in native language content presentation, as it is preferable to have a uniform presentation, including the actual site content and the CAPTCHA challenge. Thus, we argue that enhancing existing Latin-based CAPTCHA mechanisms with the capability to provide localized text-based challenges would result to a better user experience.

Conclusions

The purpose of this paper is to presented results of an empirical study with the aim to gain knowledge for enhancing usability and user experience related to CAPTCHA challenges as an effort to apply User Centered Design (UCD) approaches related to CAPTCHA mechanisms. We argue that for designing more usable mechanisms, research in this area should partially move its focus away from the technical security issues towards understanding the users and developing approaches which can be applied for increasing usability and offering a better user experience to users who are engaged in solving CAPTCHA challenges.

In this context, given that current CAPTCHA designs provide challenges solely in Latin alphabet and considering the diversity of World Wide Web users with regards to their lingual characteristics we developed a CAPTCHA mechanism capable to produce challenges of different alphabets. We utilized the developed CAPTCHA mechanism in the frame of an ecological valid experimental design aiming to examine users' preference towards Latin and localized CAPTCHA challenges. The analysis of results was mainly focused on users' preference towards localized and Latin-based CAPTCHA challenges. However, we also looked at the language presentation factor of the web page in which the CAPTCHA mechanism was embedded aiming to examine if this factor has a main effect towards users' preference to a specific type of CAPTCHA challenge. We recruited overall 384 non-native English-speaking users aiming to investigate the aforementioned factors and revealed that there is a statistical significant preference of users towards using specific type of CAPTCHA challenges depending on their profession in using the Latin-alphabet.

A future research direction, aiming to examine in wider perspective human factors on CAPTCHA designs, is to investigate preference and performance factors in localized and Latin-based CAPTCHA challenges in comparative cross-national studies. Bearing in mind that CAPTCHA tasks are not embedded smoothly into the primary task of a user (e.g. a user not familiar with the Latin alphabet performs a registration on a local content web site that requires to solve a Latinbased CAPTCHA challenge) and that every second millions of users world wide are solving CAPTCHA challenges, studies like the reported one could have an impact on making these tasks more affordable as even a small improvements will have massive benefits for users.

Table 1 .

 1 Group Preference on challenge language by page content.

		Page Content Latin Localized	Total
		Group (A)
	English	87	54	141
	Localized	101	56	157
	Total	188	110	298
		Group (B)
	English	7	42	49
	Localized	7	30	37
	Total	14	72	86

http://www.internetworldstats.com/stats.htm


Michael Heidt

Kalja Kanellopoulos
email: kalja.kanellopoulos@phil.tu-chemnitz.de

Linda Pfeiffer
email: linda.pfeiffer@s2011.tu-chemnitz.de

Paul Rosenthal

Diverse Ecologies -Interdisciplinary Development for Cultural Education

Keywords: interdisciplinarity, museum informatics, design for cultural experience

de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Devices geared towards product development aim at producing artefacts amenable to concepts such as efficiency, effectiveness and usability. Cultural contexts usually require a different development perspective. Most interfaces constructed for exhibition spaces do not aim at enabling the user to fulfil specific and predetermined tasks as quickly as possible, but offer the possibility to explore and experience the exhibited artefacts or the narratives connected to them. They have to enrich visitor experience and at the same time need to refer to the context they are placed in. Therefore, the actual situation of deployment and use gains enormous importance. It consequently needs to be accounted for within the design process at an early stage. What is to be observed on the contrary is that technological developments for museums are often decontextualised during the process of design. They are frequently outsourced to external production companies, while cooperation between these companies and the museums during the design process remains rudimentary. This leads to the fact, that the highly deployment specific actual contexts of use for these technologies often are neglected. Consequently, many of the developed technologies are not well received by their end users, the museum visitors. In order to overcome the mentioned problems, we state the necessity of realigning technological systems with the cultural contexts they are to be operated in.

Project Context

The project described here is tasked with developing interactive installations and mobile applications for the domain of cultural education within museums. It is situated within a collective of researchers with diverse backgrounds. These range from informatics and engineering over psychology and sociology to philosophy, rhetoric, and literary studies. Installations are developed in close collaboration with a local museum of industry, while collaborations with other museums exist as well. Among the installations developed are tangible user interfaces, mobile applications and multitouch tables. The design processes are informed by an exploratory pre-study and a concurrent ethnography. Some of the results of the pre-study and their implications for design will be outlined in the following.

Concerning new media and interfaces in museums and exhibitions the discursive focus often lies on learning [START_REF] Reussner | New Technologies for Learning in Museums: An Interdisciplinary Research Project[END_REF]. What can be observed empirically on the contrary, is the importance of the visitor experience during a museum visit. This experience is influenced by several factors. Not only is the museum an environment for cultural education, but also one for strolling, interaction and communication with others. The museum environment connects visitors to those far in time and space: to past events, persons deceased, artefacts, concepts and narratives rendered strange by the passing of time. At the same time visitors have to interact and connect with those close to them in space and time. This includes interaction with other visitors as well as the interactivity with exhibits and technical artefacts. It is this dynamic interplay of times, spaces, persons and artefacts that forms the unique ensemble of situations that constitutes the museum experience itself. It is characterised by the contrast of an immersive present environment with the invoked feelings of something far removed. Consequently, the aim of our design process is not to transform the experience of the museum visit in a spectacular way, but to support it gently and on a playful basis.

In the subsequent phase of the project, prototyping techniques were deployed in order to generate ideas for improvement of existing systems. The overarching narrative was that of a museum-visit. It exhibits a three-part structure: preparation, actual visit and recapitulation. It has proven essential to develop overarching scenarios in order to contain specialists' affinities to disregard context specifics and to selectively optimise their respective system components regarding technological impressiveness and feasibility.

Among the prototypes developed were:

1. A recommender engine, trying to foster communication by pointing users towards fellow visitors, possessing relevant knowledge.

A multitouch-table installation, allowing users to engage in playful interactions

with exhibit related information. 3. An interactive role-playing device. Optical recognition of props present in the museum is used to present users with relevant narratives. The development of the first set of prototypes and scenarios was followed by interdisciplinary discussions. Subsequently and regarding the outcome of this exchange, the attempt was made to break up monolithic deployments into their conceptual and material parts.

To this end usage scenarios for individual prototypes were discussed. Considering the observations made by social scientists in the field, usage scenarios were elaborated into mini-narratives accounting for situational factors within the deployment context. These mini-narratives now can be composed in a non-linear fashion, thereby allowing for exploring possible patterns of system usage.

For example, the analysis unveiled that though prototypes i) and ii) had been developed with two distinct sets of goals in mind, they share a functional characteristic. Both facilitate communication between visitors. The recommender system does this by virtue of direct proposals for communication. The table installation reduces communicative inhibitions by allowing visitors to perceive each other during technologically mediated interactions. The analysis thus allowed for a more conscious and strategic utilisation of the communicative incentives provided.

In a next step individual elements will be orchestrated into new functional ensembles according to the requirements of the museum ecology.

Implications of Interdisciplinarity

The value of technological virtuosity is not to produce ever more spectacular displays of its own prowess. It is twofold in nature. First, it allows more degrees of freedom when designing technology. As social practice is diverse, reproduced within a web of disparate sites of practice, the technical possibilities for cultural embedding of technology likewise are diverse and disparate. It is an informatician's job to recognize and exploit these possibilities. This requires a vast level of mastery of technological skills as well as insights in the social and cultural structures the developed technology will be deployed in. Therein lies one of the main reasons for interdisciplinary cooperation with social scientists in system development. Collaborations of this type are based on a high level of communication between heterogeneous actorsapart from information professionals and social scientists, system users and other professionals within the technological field itself have to be included as well.

The key in facilitating communication in these kinds of interdisciplinary working contexts lies in the realisation that system development too contains theory building aspects. Whenever confronted with a new domain, developers usually develop informal theories describing how this domain is structured. They do not do so by means of ethnographic analysis and generally do not apply social theory. At this point, the theory building process is usually implicit and remains opaque to other project participants. This does not mean, however, that the theories themselves are unstructured or inherently informal. On the contrary, system designers with a background in engineering tend to construe social practices observed with the same formal concepts used to understand technical components. This creates potentials for misconstruction of the social. While diverse perspectives and ambiguities can have catastrophic effects within the sphere of the technical, understanding of social practice necessitates embracing diversity, heterogeneity, multi-perspectivityand calls for acceptance of its inherent ambiguities.

The relationship between design, social science and informatics has been discussed extensively within the HCI community [START_REF] Mackay | HCI, natural science and design: a framework for triangulation across disciplines[END_REF][START_REF] Hughes | Designing with Ethnography : A Presentation Framework for Design[END_REF][START_REF] Hughes | Moving out from the control room : ethnography in system design Moving out from the control room : ethnography in system design[END_REF]. Following the authors cited, we acknowledge that there is tension inherent in the cooperation of engineers and social scientists. We argue, however, that this tension can be made productive by employment of adequate methodologies. Therefore, our approach does not try to integrate differing perspectives within one conceptual framework. We rather try to create sensitivity of project participants towards the perspectives of the others, as outlined in Fig. 1. We do not expect to achieve fundamental perspective transformations, but aim at repeated chiastic crossing of boundaries. While it is not necessary for social scientists to fully grasp technical intricacies and engineers do not need to follow involved discussions of social theory or methodologies to their conceptual origins, it is paramount that project participants develop a feeling of 'how they are different'. Inside the disciplinary terrain the same demand needs to be made, as researchers from the same discipline can differ broadly concerning research paradigms, methods and methodologies as well as favoured theoretical approaches. We developed a set of communicative devices in order to highlight these differences and make them tractable within the design process. These are detailed in the following subsection. Among the techniques employed are different forms of diagrams as well as other visual aids and narrative devices.

Communicative devices

In order to aid the communicative process within the interdisciplinary setting, different forms of analytical description were employed. These ranged from formaltechnical diagrams employing mathematical language over pictures and photos to informally presented narratives. It has proven both necessary as well as beneficial to encourage participants to discuss their work at an early stage. Furthermore, scientists had to explain their different backgrounds to each other, including previous work and methods employed. A multitude of mutual misconceptions could thus be caught at an early stagewhile others may still be present.

Additionally, it has to be stressed that both spatial proximity of researchers from diverse fields, as well as their spatial distance to the surrounding everyday university processes, has proven to be an invaluable asset in producing ideas. As so often is the case, communal trips to the canteen, spontaneous doodle sessions during coffee breaks and seemingly random prototyping sessions in the printer-room have dwarfed official and semi-official design workshop appointments regarding creative power.

However, this should not point to the conclusion that informal talk is enough, rendering formal appointments obsolete. On the contrary, regular meetings have proven to be an integral and invaluable constituent of the communicative ecosystem. They provided helpful incentives to translate work into a language accessible to the other. Frequently, forcing to take these fresh perspectives resulted in the emergence of new ideas and a firmer grasp of the tacit assumptions underlying the own work process. Consequently, a practice similar to that of SCRUM [START_REF] Schwaber | Agile software development with Scrum[END_REF] was adopted: Participants were encouraged to explain what they have been working on since the last regular meeting. Encouraging participants to pose questions to each other also proved to be helpful. Within these discussions it proved helpful to develop a certain discipline: Before presenting an argument, dialogue partners had to adequately sum up the position of their predecessor. Furthermore, conducting clustering sessions where participants had to cluster thoughts and concepts produced by researchers from another discipline furthered mutual understanding. A set of visual devices was also employed, these are detailed further in an accompanying publication [START_REF] Heidt | Examining Interdisciplinary Prototyping in the Context of Cultural Communication[END_REF].

The most essential communicative device was that of prototyping. Prototyping provides means to overcome communicative boundaries by employing the integrating power of the material. Thereby, prototypes produced create unique communicative opportunities. Problems and perspectives can be discussed across disciplinary languages and vocabularies with respect to artefacts, which literally are graspable. They allow researchers and developers to derive descriptions from concrete material objects. At the same time, they can be discussed as material correlates of ideas. In the outlined project prototypes were cut out of paper and cardboard, assembled using everyday objects forming structures bearing similarity to an assemblage or made from dough or lego bricks. However, prototyping can also gloss over antagonistic perspectives: Since the prototype already has been built, utterances can easily be misunderstood by presupposing the own construal of the artefact at hand. Frequently, the opportunity to shatter and question presuppositions is missed during the process, especially if it is geared towards rapid development. Therefore, it proved imperative to embed the prototyping process into the network of communicative support detailed above. Every prototype developed has to be discussed prior to inception, during the respective prototyping session as well as afterwards during a regular meeting.

Related Work

At this point it is important to address the inherent contradictions of user-centered design (UCD). Central to the UCD process usually is an understanding of users' tasks and goals. However, in most domains the users' tasks will not be their own. They are determined by organisational and institutional settings. Actual users' wishes and desires will entertain a dialectical tension with those environmental requirements. Furthermore, we highlight the role of UCD as being rooted in a rhetorical situation. UCD is not employed by uninterested third parties but by persons and organisations wishing to achieve certain goals. Our treatment of system design is informed by the notion that concepts have politics [START_REF] Suchman | Do Categories Have Politics ? The language/action perspective reconsidered[END_REF] and that artefacts facilitate social practices. System development cannot merely be considered as an instrumental process. It is a site of struggle, where different interests and views of the world engage with each other. Our methodologies try to account for these productive antagonisms while trying to enable productive discussion and struggle within the embodied practices themselves. Our goals are distinct from UCD in that we do not aim at merely identifying user expectations or desires. What we envision is not exclusive development for the user but a critical dialogue between project stakeholders as well as end users.

Embodied Interaction developed by Paul Dourish [START_REF] Dourish | Where the action is: the foundations of embodied interaction[END_REF] proposes a blend of methods from social-sciences and humanities. He builds on a phenomenological understanding of the realm computing systems are part of. Drawing on Lucy Suchman's research [START_REF] Suchman | Plans and situated actions: the problem of human-machine communication[END_REF], he develops a processual conception of reality in conjunction with a situational multi-level conception of meaning. The key concept is that of embodiment, reminding designers how each artefact always is used in the context of practice and that practice in turn takes part in a meaning making process. Dourish goes on to develop a set of practical design guidelines. We found the argumentation to be cogent and the specification of practical guidelines refreshing. Embodied Interaction provides a site for common understanding between social-scientists and informaticians, due to its roots both in anthropology as well as informatics. It has consequently informed our design process and proved to be one of the most beneficial conceptual toolsets. However, it focusses more on the analysis of the socio-ontological status of HCI artefacts while temporarily neglecting production processes. Consequently, we found that it needs to be combined with further methodological tools in order to realise its inner potential.

Participatory Design aims at communicative integration of all stakeholders potentially affected by an artefact [START_REF] Muller | Participatory design[END_REF]. It centres on democratic discussion and deliberative processes. Although our own approach is informed by Participatory Design, we do not conceive of our design project as an instance of public service. The design team follows convictions not identical with that of potential users. Consequently, we do not try to simulate a consensus. Rather, we try to articulate the privileged nature as well as the limitations of our own position as scientists, developers, designers.

Value-Sensitive Design [START_REF] Friedman | Value Sensitive Design as a Pattern: Examples from Informed Consent in Web Browsers and from Urban Simulation[END_REF][START_REF] Friedman | A Value-Sensitive Design Approach to Augmented Reality[END_REF][START_REF] Louise | Value Sensitive Design of Interactions with UrbanSim Indicators[END_REF][START_REF] Borning | Next steps for value sensitive design[END_REF] describes itself as an alternative paradigm to participatory approaches. Whereas Participatory Design highlights the need for valuing every participant's opinion, here adhering to human values is given preference. Value Sensitive approaches emphasise the need to acknowledge trade-offs between conflicting values. Consequently, the design process is aimed at enabling reasonable ethically informed decisions, while stating that these must remain publicly accountable.

Our design process is informed by extensive discussions of ethical implications. In contrast to Value Sensitive Design, we do not try to create a deliberative space integrating each and every stakeholder. This first of all is not feasible from an organisational perspective within our project parameters. While we do try to involve potential system users early in the process, this is not done in order to reach a consensus. On the contrary, we think it is imperative to make our own goals very clear and embody them into artefacts. These should be contestable in a wider realm of discussion. In effect, we view our design actions as being accountable to others, while not trying to speak from a position of consensus.

Critical Technical Practice as initially put forward by Phil Agre constituted itself as an effort to reform the field of Artificial Intelligence [START_REF] Agre | Toward a Critical Technical Practice: Lessons Learned in Trying to Reform Al[END_REF][START_REF] Agre | The soul gained and lost: artificial intelligence as a philosophical project[END_REF][START_REF] Agre | Computation and Human Experience[END_REF] . Within the works cited, Agre argues for a situational approach towards AI problems, trying to highlight shortcomings inhering in the idea of universal cognition. Our research efforts align themselves with some of the basic stances put forward by Agre. Namely, we try to reflect on the untested assumptions underlying practices of technology design. Critical Technical Practice has since informed a multitude of concepts within the field of HCI. One of these influences is Reflective HCI [START_REF] Dourish | Reflective HCI : Towards a Critical Technical Practice[END_REF], a joint effort of theorists affiliated with Embodied Interaction, AI centred Critical Technical Practice and other paradigms within the HCI community.

Conclusion

We have described an interdisciplinary development project in the domain of museum education. Highlighting the specificity of cultural contexts, we argued for the necessity of customising existing design methods. Viewing the diversity of differing perspectives as assets rather than problems, we have described communicative devices to inform interdisciplinary development. Consequently, our process aims for repeated chiastic crossing of boundaries in order to sensitise participants for the otherness of the other. We do not expect to achieve fundamental perspective transformations on a short or medium timescale.

Fig. 1 .

 1 Fig. 1. Differing perspectives are made productive by means of translations and mutual sensitivity.


Susumu Harada
email: haradas@jp.ibm.com

Daisuke Sato
email: dsato@jp.ibm.com

Hironobu Takagi
email: takagih@jp.ibm.com

Chieko Asakawa

Characteristics of Elderly User Behavior on Mobile Multi-Touch Devices

Keywords: Mobile, Multi-touch, Smartphones, Tablet, Aging, Elderly

Smartphones and tablet devices have been rapidly proliferating, and multi-touch interaction, powerful processors and rich array of sensors make these devices an attractive service platform for older users. While there is an increasing number of work investigating the issues that elderly users experience through their interaction with mobile devices, most have focused either on evaluation of low-level interaction characteristics or on qualitative survey. Therefore, we conducted a user study with 21 elderly participants to analyze the needs and issues faced by this user group under naturalistic usage scenarios. Specifically, we interviewed each participant about their experiences, had them perform various practical tasks using our custom testing application, and analyzed the operation logs using our custom visualizations. Based on our results, we summarize the types of issues observed, present design considerations for the applications studied, and future research directions.

Introduction

Over the past several years, mobile multi-touch devices such as smartphones and tablets have been rapidly proliferating. While the primary growth has been among younger users, there is a growing number of elderly people who are beginning to adopt such new technology [START_REF] Plaza | Mobile applications in an aging society: Status and trends[END_REF]. The direct manipulation interaction afforded by their multi-touch displays, their ability to run numerous applications both on the device as well as over the network, combined with powerful processors and a rich array of sensors, make these devices an attractive platform for making a wide range of services available to benefit older users. While the multi-touch interfaces enable intuitive direct-manipulation interaction that mimic real-world metaphors, they also introduce a number of potential challenges, such as non-intuitive multi-finger gestures, unexpected sensitivity of the touch surface, and a conceptual model that differ significantly from traditional desktop computers and other preceding technologies.

Younger users may be able to quickly learn to navigate around such challenges through trial-and-error and relying on their mental models of recent technologies, but the hurdle may be bigger for older users. A study by Docampo Rama, Ridder, and Bouma [START_REF] Rama | Technology generation and age in using layered user interfaces[END_REF] indicates that generational difference in exposure levels to various technology during one's formative years (before the age of 25) has a significant effect on the performance on and the level of understanding of new technologies. A survey with 131 respondents from three age groups (20-49, 50-64, 65+) conducted by Leung and others [START_REF] Leung | How older adults learn to use mobile devices: Survey and field investigations[END_REF] suggests that significantly fewer older people choose trial-and-error as a method for learning new technology compared to younger people, opting for more traditional methods such as instruction manuals despite citing difficulties using them. It is clear that the needs and characteristics of the older population are quite different from those of the younger population in the context of mobile device usage. In our investigation, we focus on the issues surrounding the usability of such devices from the perspective of elderly users.

There have been many works seeking to better capture the needs and characteristics of older users and their interaction with mobile devices. On the one hand, there have been various interview and questionnaire studies [START_REF] Leung | How older adults learn to use mobile devices: Survey and field investigations[END_REF][START_REF] Kurniawan | Older people and mobile phones: A multi-method investigation[END_REF][START_REF] Lee | Older adults' user experiences with mobile phones: Identification of user clusters and user requirements[END_REF][START_REF] Renaud | Worth-centred mobile phone design for older users[END_REF][START_REF] Van Dyk | Mosesmethod for selecting senior mobile phones: Supporting design & choice for the elderly[END_REF] that have identified characteristics unique to the elderly user population. While these interview and questionnaire studies provide valuable insight into elderly user's attitudes towards and perceptions of mobile devices, they do not reveal much about the interaction tendencies of and challenges faced by elderly users throughout their actual use of such devices.

On the other hand, there have also been works that sought to capture more concretely the patterns and tendencies of elderly users' interaction with mobile touchscreen devices through measurement and analysis of low-level interaction metrics such as task speed and accuracy [START_REF] Jastrzembski | The model human processor and the older adult: Parameter estimation and validation within a mobile phone task[END_REF][START_REF] Kobayashi | Elderly user evaluation of mobile touchscreen interactions[END_REF][START_REF] Leitão | Target and spacing sizes for smartphone user interfaces for older adults[END_REF][START_REF] Nicolau | Elderly text-entry performance on touchscreens[END_REF][START_REF] Wacharamanotham | Evaluating swabbing: A touchscreen input method for elderly users with tremor[END_REF][START_REF] Ziefle | How older adults meet complexity: Aging effects on the usability of different mobile phones[END_REF]. Most of these works involved experiments in which the participants performed primitive actions such as tap or swipe gestures in isolation within their custom test applications. While these studies provide concrete data, the data may not be representative of what users experience in actual usage of mobile devices, since real tasks require not only primitive gesture skills but also skills to develop strategy to complete tasks by effectively selecting a series of gestures in real-time, in-situ, within the context of full application user interfaces.

In our work, we build upon the above studies by combining an observational study approach with an experimental approach that include detailed instrumentation of elderly users' interaction with mobile touch-screen devices as they perform tasks within realistic application contexts. Our aim was to uncover issues that elderly users may encounter during their typical usage of smartphones and tablets, such as errors, unexpected results, standstills, ineffective operational strategy and so on, and delve deeper into each issue by analyzing the instrumented log data.

We conducted a user study with 21 elderly participants with diverse experience levels, from first time users to active intermediate level users, to observe and analyze specific issues and challenges that they experience when using mobile touch-screen devices. We built a custom experiment application for multi-touch smartphones and tablets that mimicked the appearance and functionality of actual applications, augmenting them with instrumentation capability to capture and log all multi-touch events and application state changes. Our focus, however, was less on statistically analyzing aggregate results but more on carefully observing interaction characteristics such as errors, unexpected results, operational strategies and so on, of each individual participant. We also conducted interviews with each participant to solicit their com-ments and better understand their perceptions and past experiences with mobile devices. Based on these results, we present a number of design considerations and future research directions for creating smartphone and tablet devices and applications that are more accessible and easily adoptable by elderly users. Our contributions are as follows:

-Quantitative analysis of elderly users' interaction behaviors within realistic application settings -Qualitative analysis of elderly users' specific tendencies and obstacles encountered during their interaction with multi-touch smartphones and tablets

Related Work

There are many prior work that have investigated elderly users' perceptions and use of traditional mobile phones [START_REF] Caprani | Touch screens for the older user[END_REF][START_REF] Czaja | Factors predicting the use of technology: findings from the Center for Research and Education on Aging and Technology Enhancement (CREATE)[END_REF][START_REF] Pattison | Inclusive design and human factors: Designing mobile phones for older users[END_REF][START_REF] Morris | Internet use and non-use: Views of older users[END_REF], as well as those that have examined elderly users' interactions with large touch-screen displays, but not much work has yet looked into elderly people's use of mobile touch-screen devices such as recent multi-touch smartphones and tablets.

Elderly Users and Mobile Phones

A number of interview and questionnaire studies have been conducted to investigate the general perceptions and practices of elderly users regarding mobile phones, and several resources provide a comprehensive overview of the literature [START_REF] Plaza | Mobile applications in an aging society: Status and trends[END_REF][START_REF] Zhou | Use and design of handheld computers for older adults: A review and appraisal[END_REF]. We present some of the representative works here. Kurniawan [START_REF] Kurniawan | Older people and mobile phones: A multi-method investigation[END_REF] conducted a set of expert interviews with two domain experts, focus group discussions with 14 elderly participants, and an online questionnaire that resulted in 100 responses from people over 60 years old. The study reports on various findings about elderly people's perceptions of and issues with mobile phones, such as their preference for features that aid their declining functional abilities. Leung and others [START_REF] Leung | How older adults learn to use mobile devices: Survey and field investigations[END_REF] also conducted a large-scale online survey with 131 respondents across three age groups (20-49, 50-64, 65+) to identify unique tendencies among the older population, including their preference for traditional methods such as instruction manuals for learning new technologies over trial-and-error. Van Dyk, Renaund, and van Biljon [START_REF] Van Dyk | Mosesmethod for selecting senior mobile phones: Supporting design & choice for the elderly[END_REF] conducted an extensive interview with 147 mobile phone users between the ages of 60 and 89 to construct a prioritized checklist of features that should be considered in the design of mobile phones catered to the elderly users.

There have also been some observational studies as well as experimental studies that delve into more detail about the elderly's use of such technologies. Renaud and Biljon [START_REF] Renaud | Worth-centred mobile phone design for older users[END_REF] used worth-centered design process to interview and conduct a participatory design experiment with elderly users, resulting in a prototype mobile phone design. Weilenmann [START_REF] Weilenmann | Learning to text: An interaction analytic study of how seniors learn to enter text on mobile phones[END_REF] conducted an observational study of elderly users learning to enter text on mobile phones, highlighting specific issues they encountered. Ziefle and Bay [START_REF] Ziefle | How older adults meet complexity: Aging effects on the usability of different mobile phones[END_REF] conducted comparative evaluation of two mobile phones of different complexity between younger and older participant groups. Jastrzembski and Charness [START_REF] Jastrzembski | The model human processor and the older adult: Parameter estimation and validation within a mobile phone task[END_REF] proposed and validated the parameters of a Model Human Processor for older adults.

While these studies provide valuable insight into the overall tendencies and preferences of elderly people as well as their usage characteristics within the context of mobile phones in general, they have not focused on issues that surround the more recent mobile multi-touch devices.

Elderly Users and Touch-Screen Displays

Touch interaction is one of the key features that differentiate recent smartphones and tablets from prior mobile devices. Leonardi and others [START_REF] Leonardi | An exploratory study of a touchbased gestural interface for elderly[END_REF] conducted experiments with a tabletop touch panel interface and found that the direct interaction metaphor was easy to understand and had a pleasing effect that attracted and motivated elderly participants in their study. Lepicard and Vigouroux [21] had a group of younger and older participants interact with their test application on a 12" Tablet PC and found that two-handed touchscreen input was difficult for elderly users. There have also been other observational studies of elderly people's use of touchscreen interfaces [START_REF] Caprani | Designing a touch-screen sensecam browser to support an aging population[END_REF][START_REF] Tsai | Connecting communities: Designing a social media platform for older adults living in a senior village[END_REF], and a survey of other work is provided by Caprani, O'Connor, and Gurrin [START_REF] Caprani | Touch screens for the older user[END_REF]. While the results from these studies offer insight into the issues that elderly users experience with touch-screen devices, there are several key differences between tabletop and desktop touchscreen devices and mobile multi-touch devices that warrant further investigation looking specifically at the latter category of devices. For one, the smaller form factor of mobile devices mean that the users are often holding the device with one hand while they touch the screen with the other hand or even the same hand. This factor, combined with the multi-touch sensing, can potentially lead to greater chances of inadvertent or accidental touches of the screen by the holding hand or some other part of their manipulating hand. Furthermore, the smaller screen estate can lead to the need for more touch manipulation to view the desired information as well as potential errors when touch targets are too close or too small. Therefore, more research is needed to investigate the more recent multi-touch smartphones and tablets.

Elderly Users and Mobile Multi-Touch Smartphones and Tablets

While still few in number, there have been recent works that have specifically focused on mobile multi-touch smartphones and tablets as the target of their study. One part of the extensive study conducted by Leung and others [START_REF] Leung | How older adults learn to use mobile devices: Survey and field investigations[END_REF] involved a field study observing two middle-aged and four older users learning to use smartphones. Kobayashi and others [START_REF] Kobayashi | Elderly user evaluation of mobile touchscreen interactions[END_REF] observed 20 participants in their 60s and 70s using various applications on multi-touch smartphones and tablets. They also conducted controlled experiments involving execution of primitive gestures on smartphones and tablets, finding that the elderly participants' performance of dragging and pinching gestures improved after one week of practice but not tapping. Leitão and Silva [START_REF] Leitão | Target and spacing sizes for smartphone user interfaces for older adults[END_REF] used a custom "game" on a multi-touch smartphone to analyze the effects of target size and spacing on tapping and swiping tasks. Nicolau and Jorge [START_REF] Nicolau | Elderly text-entry performance on touchscreens[END_REF] evaluated typing performance and typing patterns of 15 participants over the age of 65 using a virtual keyboard on a multitouch smartphone and tablet.

Our goal was to build upon these works by observing and looking for specific challenges, stumbling points, and possible coping strategies employed by individual users.

While our results do not provide statistical significance or sweeping generalizations, we believe that the concrete observations, both qualitative as well as quantitative, situated within the context of realistic application usage, provide valuable insight into specific issues that elderly users may encounter in their typical interaction with multitouch smartphones and tablets.

User Study

We conducted seven half-day-long user study sessions with a total of 21 elderly participants to investigate their perceptions of smartphones and tablets as well as specific usage characteristics as they performed tasks on the devices. Our goals were: 1) to better understand elderly users' perception of smartphones and tablets, 2) to identify "realistic issues" encountered by elderly users as they interacted with real and "realistic" apps, 3) to quantitatively analyze the issues identified in 2) to see if we could systematically identify and potentially circumvent such issues, and 4) to uncover design considerations that could inform design of more senior-friendly smartphones and tablets.

Participants

We recruited participants for our study through email announcements distributed to retiree mailing list for a large corporation, as well as to local computer classes for seniors. The condition for participation was specified as being 60 years of age or older with some interest in smartphones and tablet devices. A total of 21 participants ranging in age from 63 to 79 (12 females and 9 males) took part in our study. Fifteen of the participants were members of the local computer class, and six were from the retiree group. The participants were divided into seven groups, each consisting of two to four members, so that we could conduct a focusgroup-style discussion. Each group was invited to our lab for a half-day session, and each participant was compensated for their time with a gift valued at approximately $25. All of the participants owned a mobile phone. Eight of them owned multi-touch smartphones while 14 owned a tablet, and six owned both devices.

Procedure

Each of the half-day user study sessions was structured into two parts: 1) open discussion about each participant's experiences with and perceptions of smartphones and tablets, and 2) execution of controlled tasks on smartphones and tablets. The sessions were audio recorded for later analysis, and with participants' permission, video was also recorded to capture the user's hands operating the devices during various tasks.

During each session, two experimenters were present, one to primarily engage with the participants, and another to take notes and to tend to the video cameras.

Open Discussion. At the start of the user study session, we first had all participants individually fill out a questionnaire soliciting demographic information as well as specifics about their experiences with smartphones and tablets. In particular, we prepared different questionnaires for those who did or did not own a smartphone or a tablet. To those who did not own the devices, we asked whether they had considered owning one, and if so, what factors had interested them and what factors had prevented them from actually owning one. To those who owned the devices, we asked for their reasons for purchasing them and what they most use them for. After the questionnaires were filled out, about 30 minutes was spent on open group discussion about each participant's experiences and perceptions about smartphones and tablets as well as their current mobile phones. The discussion was led by the experimenter based on a prepared set of guiding questions, but the participants were free to expound upon or add any stories about their experiences. The group discussion format was adopted so that the participants were able to engage in a more casual conversation, feeding off of each other's responses and stories.

Controlled Task Experiment. In the controlled task experiment session, we had the participants perform various tasks on both the smartphone and tablet using the data collection application we built to gather logs of quantitative usage data. The purpose of this session was to attempt to gain an objective view of any tendencies or unique characteristics in the interaction styles of each participant in using various touchoperated apps. The primary objective of this investigation was not to obtain statistically significant aggregate data, but rather to observe and analyze the usage patterns of individual participants so that we may gain specific insight into concrete manifestations of errors, operation difficulties, and other issues. Ideally we would have liked to evaluate the usage of real applications under actual usage scenarios, but we resorted to an in-lab study to more closely observe the interaction issues as they happened. Each participant performed in an order of Address Book, Phone, and Map tasks on both smartphone and tablet. The order of devices was counterbalanced. All participants performed the same set of tasks on both devices. For the Phone task, they input three 11-digit phone numbers printed on a sheet paper. For the Address Book task, the participant was presented with a same list of 160 names but with different initial starting position in the list, and were prompted to search for and tap on a particular name. A total of 10 pre-chosen names were presented one by one and were shown at the top of the application. For the Map task, the participants were asked to find three locations (Hokkaido, Okinawa, and England) on a map, zooming in to fill up the screen with the target island as the completion condition for each trial. The map was reset to show the Tokyo Bay area at the beginning of each trial. While not all apps required multi-touch gestures, we wanted to see if the multi-touch-enabled screen would lead to various errors caused by unintentional touches during the tasks, a common symptom observed especially among novice multi-touch device users.

Apparatus for the Controlled Task Experiment

For the controlled task experiment, we used Apple's iPod Touch (fourth generation) and iPad (third generation). Both devices were running iOS version 5. We built a custom test application that included three application interfaces that closely mimicked the appearance and behavior actual applications found on standard iOS devices (Phone, Address Book, and Map). The test application logged all multi-touch events and application events for later analysis.

Phone Application Interface. The phone application interface consisted of the standard telephone keypad, and an entry display at the top showing the numbers entered.

The actual visual of the user interface was directly copied from the original application. The app was set up such that after the participant entered the correct phone number for a particular trial and tapped the dial button, the screen returned to the main screen. If the user tapped the dial button but the phone number entered was incorrect, a dialog was displayed to prompt the user to re-enter the correct number.

Address Book Application Interface. The address book application interface consisted of a vertical list of contact names sorted and grouped alphabetically, with an index bar on the right side of the screen that support jumping to the section of the list corresponding to the tapped index letter. During each task trial, the participant was first presented with a dialog displaying the target name to find in the contact list. After dismissing the dialog, the target name remained visible at the top of the screen as the user scrolled through the list.

Map Application Interface. The map application interface simply presented the standard iOS map control, with the ability to use two-finger pinch-in and pinch-out gestures to zoom out and in, respectively, as well as to pan the map using either one or two fingers. Double tapping with a single finger to zoom in by a fixed amount and single tapping with two fingers to zoom out by a fixed amount were also possible.

Controlled Experiment Results

Phone Application Task Results

Position of Touches. Participants completed each trial on average in 13.2 seconds on the smartphone and in 11.9 seconds on the tablet. For each of the 63 (3 x 21) trials on smartphone and tablet, the numbers of incorrect touches were 32 and 15 in total, respectively. Figure 2 shows the plots of correct touches and incorrect touches made by Phone Address Book Map Figure 1. Screenshots of the three application interfaces in our test application. all participants on both devices. With the tablet, five participants made incorrect taps with their palm, which can be seen at the bottom-right of the plot for the tablet. With the smartphone, three participants made an incorrect "call" while intending to tap "0". Most of the other incorrect taps were due to misreading the phone numbers.

We observed P13 input one extra digit with an unexpected repeat of the "8" button. By checking the recorded video for the trial, she did only tap once on the "8" button but the system accidentally recognized two distinct taps within 0.13 seconds. Also many unregistered taps were observed, in which participants physically tapped on the screen but the system failed to recognize them.

Not Confirming Before Moving On.

There was an instance when P13 tapped the "call" button with one too many digit entered, and the dialog prompted her to correct the entry. She then tried to re-input the number from the beginning but only tapped the delete button once, not checking the number display at the top, resulting in an even longer sequence of numbers. P04 and P15 also got the dialog prompt during the task by tapping "call" button with too few digits of input. After they dismissed the dialog, they also tried re-entering the digits from the beginning without deleting or checking the display at the top of the screen.

Address Book Application Task Results

Participants completed each trial on average in 9.7 seconds on the smartphone and in 8.9 seconds on the tablet. P09 and P11 made 15 and 12 miss-taps, respectively, significantly more than the maximum of four miss-taps made by the other participants. Most of the mistakes by P09 on the tablet were miss-selection of list item while intending to tap on the index bar. All miss-taps by P11 were on the smartphone, and seemed to be due to her hand tremor. Difficulties With The Index Bar. P4, P5, P9, P18 and P23 experienced a number of instanced in which they unintentionally manipulated the index bar. In particular, the participants were especially confused when they were attempting to drag the list vertically but instead accidentally started their gesture on the index bar. As they moved their finger, the list jumped discretely across the index groups instead of smoothly following the participant's finger movement. P4, P5 and P9 experienced these issues even though they were aware of the index bar function previously. P4 also exhibited confusion when she tapped the index bar my mistake when attempting to tap the target row. Similar to the case with the Phone application interface, we also observed a number of unintentional touches primarily by the participants' palms. Due to the index bar being on the right side of the screen and all participants being right handed, this often led to the index bar being accidentally tapped, resulting in the list jumping to a grouping unexpectedly. As a result, P23 commented, "the screen just 'flew away'… I just touched it lightly just like this, and then it just flew away somewhere…"

Nudge-Flicking Instead of Stroke-

Flicking. There were distinct differences among the participants in their finger movements for scrolling the list up or down. It is typical for experienced users to use short, quick "flick" gestures to "throw" the list towards a given direction to take advantage of the inertial scrolling to scroll over a long distance, and to use controlled "dragging" gesture to keep the list pinned below the firmly touching finger to move the list by a small amount. Figure 3 shows a visualization of users' gestures during a particular trial of the Address Book task. Each stroke represents the user's gesture on Figure 4 shows the trajectories of all gestures across all trials on the smartphone by P11, P12, P04, and P20. P11 and P12 taped on the left side of the smartphone when selecting a name on the list. Each list item has a full screen width, and all participants except P4 and P20 tended to tap on the side of the screen with the names displayed.

Map Application Task Results

Participants completed each trial on average in 23.8 seconds with the smartphone and in 23.7 seconds with the tablet. Figure 5 shows a visualization of users' operations as they navigated from Tokyo to England on the map (P6 on the tablet and P15 on the smartphone). Each rectangle in the visualizations shows what the device showed when they performed the corresponding gestures and the solid lines within the rectangles represent the gesture trajectories. They used zoom-out gestures but the zoom-out level was not enough to explorer the world map, and they tried to find the goal (England) by executing numerous swiping gestures. Figure 6 and Figure 7 visualizes the zoom level sequence of the task by P19 and P17, respectively. Vertical axis shows the zoom level from world (small-scale) to town (large-scale) and horizontal axis shows the time since the task started in seconds. Thick lines indicate zoom level change while touching and thin lines indicate zoom level change without touching (inertial, double tap, or single tap with two fingers). P19 used two fingers for both zooming and panning and each gesture was very short, causing unexpected zoom-outs during operations. Three dashed circles in Figure 6 indicate where the map recognized single tap with two fingers to zoom out for a certain step. This type of miss operations was also found in P13, P14, P15, P17, P20, P21 and P23. Two dashed circles in Figure 7 show that P17 attempted many pinch-in (zoom out) gestures at the minimum scale. He was aware that something was not going as expected (i.e., the map was not zooming out any further than its current level), but he did not stop executing the zoom-out gesture.

Figure 8 shows a good example of operation by P23 from Tokyo to England. He could zoom out smoothly and easily found the target after a few swipes and then zoomed into the target. By comparing such participants' log traces, it becomes clear that there are distinct differences in the characteristics of the performed gestures as well as their strategy in performing the task of locating a target on a map.

The smaller and incremental pan and zoom gestures were observed more among those who had less experience with smartphones and tablets (i.e., those who did not own the corresponding devices), so we looked into the differences in the ratio of zoom operations of varying magnitudes, grouped by device experience (Figure 9a). A similar analysis was performed for panning movement distance as well (Figure 9b). Figure 9a shows that people who do not own smart devices tend to use smaller scale factor of zoom-in and zoom-out. Figure 9b shows that people who do not own smart devices tend to use shorter panning, most of the panning were less than 300 pixels, while people having smart devices use various length of panning.

Comparing to the other two apps, many difficulties of operations were observed with map application. P6 and P19 use more than two fingers for zoom-in and zoomout. Unfortunately, since the tablet has a function to close application by four fingers pinch-in gesture, the experiment app was terminated sometimes by the four fingers gesture when they wanted to zoom-out on the map. Two hands were used to perform for pinch-in/out gestures by P17 and P20 on smartphone and tablet respectively. P17 had difficulty zooming with two fingers on smartphone. Many participants performed a single tap gesture on the map instead of a double tap gesture when they saw their target location at a low zoom level, seemingly in an attempt to zoom in to the target location.

Interview Results and Observations

Here we report on other observations across the experimental tasks and through our conversations with the participants.

Unexpected Touch Screen Responses

There were a number of instances when a participant either intended to touch the screen but the system did not register (unregistered touches), or did not intend to touch the screen but the system registered a touch event (unintentional touches). Such unexpected responses seemed to be a major cause for frustration and confusion expressed by the participants. Regarding unregistered touches, the primary cause seemed to be that the participants' fingers were too dry for the touch-sensitive display to detect. P4, P5, and P6 mentioned frequently having problems during their daily life with dry finger resulting in ATMs and other touch screens not responding. P14, P18, and P20 all commented during their experimental tasks that their fingers felt dry and that the device seemed not to be responding to their touches. Unintentional touches were also observed across many participants. There were several patterns of unintentional touches. First was when the participant's noncontrolling hand that was holding or resting near the device accidentally touched the screen surface. Another was when the participant was hovering above the touch screen surface contemplating what to tap, and got too close to the surface of the display and triggered a touch event. Finally, there were cases when the user was performing some gesture such as a single tap or a swipe, during which some other part of their hand also accidentally contacted the display surface, resulting in multi-touch events being registered. P10, P13, and P14 mentioned that they often experience situations in which unintentional touches are triggered by the sleeve of their clothing making contact with the touch screen at ATMs or when using their tablet. While we do not know for certain whether it is actually the sleeve of their clothing that was making contact with the touch screen or a part of their hand, but it is clear that unintentional touches are quite a common phenomenon that is noticed by these elderly users. P6, P11, P12 and P22 all mentioned that they experienced difficulty with such unintentional touches when they first purchased their touch screen devices but that they had now gotten used to it.

Not Seeing the State of the Entire Screen

A number of participants tried to start scrolling before dismissing the popup dialog in the address book task. In the phone app, when using the backspace button, some users seemed to assume that it deleted not just the most recent digit but all digits entered so far. When such a user miss-entered a digit in the middle of a sequence, they tapped the delete button once but then proceeded to reenter the entire number sequence from the first digit, and not being aware of their mistake as they did not seem to be checking the number display at the top.

During the interview session, we observed some users entering text into a search textbox. During this process, these users were focused on the on-screen keyboard keys, and were not looking at the actual text being entered in the text box, which was at the upper left corner of the screen. Unlike physical keyboard where touch-typing is possible due to the tactile feedback from the physical keys, touch-screen keyboard inherently requires user to direct visual attention to each key the user is about to tap. For elderly, seems especially challenging to shift attention back and forth from keys to the textbox where text is being entered. As a result, they type away until they finish their phrase, and only then go to check what they typed, which may include surprising results due to mistyped characters and auto-suggestions.

"Unfriendly" Interface

During the interview session, a number of participants tried entering text into a memo application using the on-screen keyboard. There were several keyboard layouts available, and to switch among them, a particular button had to be pressed. However, if the user stays in contact on that button for slightly longer than a quick tap, to bring up a popup menu with a list of available keyboards is shown. The popup, however, automatically fades away after a few seconds. P3, P4 and P5 had difficulty with this, as they would tap the button once, and before they could finish reading the list of options and tap on a selection, the popup faded away. Tap-and-hold menus are tricky, especially because by holding the finger down, it may be visually covering the available options. Tap should show the menu and keep it shown, but the issue is, how to dismiss the menu without making a selection. Tapping "outside" the menu should be used, but sometimes, since the background behind the popup menu is still highly visible, one may be reluctant to tap on the "background" for fear of activating something else. A clearer indication of which part of the interface is actionable at any time may be needed.

5.4

The "Aha" Moments When Being Shown a New Technique After the controlled task experiments were completed, the experimenters debriefed the participants by describing and demonstrating some techniques for performing some of the interactions more accurately and precisely. There were a number of instances when users expressed particular surprise and joy at learning about such new method of interaction that was more effective than what they had been used to. For instance, P4 and P5 were excited to be shown that the device can also respond with the side of the finger instead of just the tip. P10, P11, and P12 also expressed excitement at learning how to perform the pinch-in gesture on the map by not flicking the two fingers together but by assuming that the map is like a rubber sheet in which the points under the fingers remain fixed as the fingers are moved.

As elderly people may be less reluctant to experiment [START_REF] Leung | How older adults learn to use mobile devices: Survey and field investigations[END_REF], it may be good to show various alternative interaction approaches, preferably gradually and repeatedly, to accommodate for their slower learning pace.

Discussion

This section describes a number of design considerations for enhancing the three applications we used in our study, based on the above results, to address some of the issues encountered by our elderly participants.

Phone Application Interface

As described in Section 4.1, the main issues experienced by the elderly participants in the phone application interface were accidental taps of buttons adjacent to the target buttons, especially problematic between the "zero" and the "call" buttons, and also not being aware of the top part of the screen showing the phone number. The issues of unexpected touch screen responses are one of major issues across applications (Section 5.1). One way to mitigate these issues may be to provide better feedback through both audio and visual. The phone application currently provides dial-tone feedback whenever a key is pressed, but this could be enhanced by having the tapped digit be spoken out. Work by Sato and others [START_REF] Sato | How voice augmentation supports elderly web users[END_REF] have shown that such spoken feedback during online web form entry helped elderly users feel more confident and reassured. Such feedback mechanism will help various situations such as misrecognition caused by "dry" finger or cloths (Section 5.1) In addition to sound feedback, visual feedbacks may be effective. The phone application also highlights the pressed button. In addition to this visual feedback, showing a fading "fingerprint" on the display to show the actual touch position may be helpful for the users. This could be combined with auditory icon and/or color feedback to indicate number of touches detected.

Furthermore, the application could determine whether the input number is a valid phone number or not to change behavior of the "call" button dynamically. For example, if the phone number is not valid, the system can show a confirmation dialog to the user. More implicit way to handle the situation may be for the system to ignore the press of the "call" button once but letting the second press invoke the actual call.

Address Book Interface

Although using the index bar to navigate to an entry in a list can be effective (Section 4.2), a number of our participants experienced difficulties in manipulating the index bar. Some participants unintentionally tapped on a row entry instead of on the index bar, some participants operated index bar before dismissing the popup dialog (Section 5.2) and some participants touched the index bar at the beginning of their swipe gesture when scroll the list (Section 4.2). There may be several reasons for these mistakes, including the index bar being too narrow, the touchable area of the index bar not being visible (it temporarily becomes visible while the user is touching the index bar), and the index bar being laid out on the right edge of the screen. One possible solution for the current index bar design is to place the bar on the left edge of the screen for right-handed users and making the labels bolder and more visible. If this design is not acceptable from an aesthetic point of view, the index bar may be better off being removed altogether. As the scroll list component handles both tap gestures as well as swipe gestures, there is a greater possibility that the user's gesture may be misinterpreted compared to the phone application that only handles tap gestures.

Map Interface

Under the map interface, there are more gestures available than with the address book interface, including pinch to zoom, double tap, two-finger single-tap, etc. While our map interface did not implement them, there are other map applications that support even more gestures such as tap and hold for dropping pins on the map and using two fingers to rotate the map, making maps one of the more comprehensive apps in terms of the types of gestures supported. Furthermore, the notion of an "incorrect" operation on map interface is not as clear as with the phone or the address book interfaces. As a possibility for enhancing the map application interface for elderly users, it may be desirable to support the ability to disable or enable various gestures to match the skill level of the user. Furthermore, a training mode that teaches the user about each available gesture and assesses users' skill of gestures by analyzing their panning and zooming behaviors (Figure 9) allows the user to practice them and to be aware of the correct concept of map operation (Section 5.4). It would not only benefit the map application interface but other applications in general as well.

We also observed a participant repeatedly attempt to pinch out beyond the maximum supported zoom level (Section 4.3), but such a behavior of repeatedly attempting ineffective gestures was not seen in the address book interface. The reason could be that in the address book interface, when the end of the list is reached, any attempt to scroll further results in a bouncing animation where the list bounces back to its limit position. By adopting a similar animation feedback for the map's zoom function, it could more clearly communicate to the user that the attempted action is ineffective.

Conclusion

We investigated the issues and challenges that elderly people may encounter when using multi-touch smartphones and tablets by conducting a user study with 21 elderly participants. The user study sessions comprised of open discussion about each participant's experiences with and perceptions of smartphones and tablets, and an experiment involving controlled tasks on smartphones and tablets to gather interaction characteristics. By creating our logging application that captured detailed interaction logs while mimicking the appearance and functionality of actual application interfaces, we were able to observe realistic issues that the participants encountered, while also being able to visualize and analyze the details of their interaction styles and the difficulties they encountered.

Our observations revealed a number of specific issues and challenges encountered by our participants. For instance, a number of them experienced unintentional taps due to parts of their hand accidentally making contact with the touch screen, as well as unregistered taps due most likely to their fingers being dry. Our log visualizations also revealed specific interaction behaviors, such as differences in panning and zoom-ing strategies on the map application, with some users not utilizing zooming much at all and simply panning long distances to find the desired target.

Based on these and other observations from our study, we provided some design considerations for enhancing the three applications as well as suggested methods to train and guide the user towards gaining a better understanding of the issues they may encounter and how to deal with them.

Our exploration is preliminary, but the approach we adopted of gathering detailed logs while users performed tasks on realistic interfaces can yield many interesting and insightful findings. Since "elderly users" is a very broad sweeping category of users, no one study can comprehensively cover a representative collection of users from the category. Therefore, there is a need for a greater number of studies to be conducted looking at specific issues encountered by a wide variety of users. Further work also needs to be done to explore a wider range of applications and interaction methods, to explore other ways of effectively visualizing the interaction logs, and to implement and validate the proposed enhancements.

Figure 2 .

 2 Figure 2. Correct and incorrect touches in the Phone task on smartphone and tablet.

Figure 3 .

 3 Figure 3. Trajectories of all gestures within representative trials for the scroll task on the smartphone across three participants. (Nudge-flicking: P11 and P14, Stroke-flicking: P18)

Figure 4 .

 4 Figure 4. Trajectories of all gestures for the Scroll task on the smartphone. P11 P11 P20 P20 P12 P12 P04 P04

Figure 5 .

 5 Figure 5. Operation sequence for a particular Map task trial by P06 and P15.

Figure 6 .

 6 Figure 6. Zoom level sequence for a particular Map task trial by P19.

Figure 7 .

 7 Figure 7. Zoom level sequence for a particular Map task trial by P17.

Figure 8 .

 8 Figure 8. Operation sequence for a particular Map task trial by P23.

Figure 9 .

 9 Figure 9. (a) Comparison of frequency of zoom scale factor in the Map task across users who do and do not own mobile multi-touch devices. (b) Comparison of ratio of panning gesture lengths in the Map task across users who do and do not own mobile multi-touch devices.