Fernando Garcia-Sanjuan

Alejandro Catala
email: acatala@dsic.upv.es

Geraldine Fitzpatrick
email: geraldine.fitzpatrick@tuwien.ac.at

Javier Jaen
email: fjaen@dsic.upv.es

Around-Device Interactions: A Usability Study of Frame Markers in Acquisition Tasks

Keywords: Around-Device Interaction (ADI), tablets, fiducial markers, frame markers, M ulti-Display Environments (M DE), usability study

Digital tabletops present numerous benefits in face-to-face collaboration environments. However, their integration in real settings is complicated by cost and fixed location. In this respect, building table-like environments using several handheld devices such as tablets or smartphones provides a promising alternative but is limited to touch interaction only. We propose instead another kind of "around-device" interaction (ADI) technique using the built-in front camera of these devices and fiducial frame markers, which presents advantages including better awareness and less interference. This paper contributes a first step in exploring the potential of this interaction technique by conducting a usability test comparing several ergonomic factors that may have an effect on the very first operation of the interaction: the acquisition of the marker.

Introduction

Digital tabletops have been shown to be very suitable to ols for use in collaborative environments [START_REF] Gutwin | Designing digital tables for highly integrated collaboration[END_REF][START_REF] Hornecker | Collaboration and interference: Awareness with mice or touch input[END_REF]. Their form factor improves workspace awareness [START_REF] Hornecker | Collaboration and interference: Awareness with mice or touch input[END_REF], and their multi-touch capabilities allow simultaneous interaction. Together, this increases parallelism, allows more democratized access, and leads to an increased collaborative performance, which produces better results [START_REF] Hornecker | Collaboration and interference: Awareness with mice or touch input[END_REF][START_REF] Rick | Beyond one-size-fits-all: How interactive tabletops support collaborative learning[END_REF]. Nevertheless, it is rare to see tabletops embedded in real settings. This is due to a number of disadvantages: their high cost; their limited workspace dimensions , which can only accommodate a certain number of participants; and the fact that their form factor complicates mobility in a way that, nowadays, if a digital tabletop is available, it is fixed to a single location and users are forced to move to a specific place if they want to engage in a collaborative activity around it. Ideally, it would be desirable for users to be able to form groups in an improvised way, in virtually any place, and of any size, using the devices they have with them to dynamically create a tabletop-like collaborative space. This allows us to take advantage of the benefits of tabletops in terms of awareness and parallel interaction, but using a different approach to tabletop working based on handheld devices. Devices such as smartphones or tablets are becoming increasingly popular and will be in common use in the near future. The portability of these devices implies that it could be possible to build multi-display environments (MDE) to support colocated collaborative activities on a table-like setting by coordinating interaction across several devices put together on the same table. However, this scenario raises a new challenge. As Gutwin et al. [START_REF] Gutwin | Designing digital tables for highly integrated collaboration[END_REF] found out, in highly integrated collaborative scenarios, users often have the need to acquire elements that are out of reach. Therefore, since interaction with handhelds is usually carried out by touch contact, in a situation where several users are gathered around the same table, interference problems may arise related to simultaneous touch actions from different users on the same surface.

The immediate solution comes by asking others to hand over the elements. However, this could interfere with the task another user is currently carrying out. Another possible solution is Around-Device Interactions (ADI) [START_REF] Kratz | Expanding the design space of around-device interaction[END_REF], where a user could interact with an out-of-reach tablet which is at the same time being manipulated via touch by a nother user, and without interfering with the latter's actions . We explore the potential of fiducial frame markers as an enabler of ADI.

Our end future goal is to design MDE collaborative environments around a table like the one shown in Fig. 1, where users bring their own devices and where they may use cards or tangible elements with attached fiducial markers to share objects (e.g., documents, game elements) or trigger reactive behaviors in a target surface on the table. The built-in camera in each device is used for the marker detection; therefore no additional hardware infrastructure is required. In this kind of setting, several interactive surfaces can be placed on a table at different distances, rotations, etc. Thus, the entry point at which users approach each surface can dramatically change, and so can the conditions surrounding the interaction itself. As such, before designing any complex ADI for these settings, the fundamental issue that must be addressed is the acqu isition of the marker [START_REF] Tuddenham | Graspables revisited: M ulti-touch vs. tangible input for tabletop displays in acquisition and manipulation tasks[END_REF] (i.e., the initial step at which the fiducial marker is placed in the camera's field of view for it to be detected), and evaluating how usable this is under different conditions. The main aim of this paper then is to present an ADI technique that uses fiducial markers and to obtain the ground knowledge that will enable us to design a table-based MDE that uses it effectively. Specifically, we evaluate the usability of the acquisition phase of the proposed ADI through an in-lab study, focusing on the ergonomic conditions that are perceived as facilitators of this interaction .

Related Work

There are a number of different ADI techniques with varying degrees of flexibility and hardware complexity. For example, Hasan et al. [START_REF] Hasan | Ad-binning: Leveraging around device space for storing, browsing and retrieving mobile device content[END_REF] present AD-Binning, an ADI used to extend the workspace given by the small screen of a smartphone by in cluding their surroundings. Users then interact with the smartphone by using a ring-shaped band on their fingers, and store/retrieve items to/from the extended space. Both the device and the ring are tracked by a complex hardware setup formed by eight external cameras. While this may be precise, it is not available to the common user and requires previous assembly and calibration. Avrahami et al. [START_REF] Avrahami | Portico: Tangible interaction on and around a tablet[END_REF] also explore ADI by using cameras mounted on both sides of the tablets to track distinct objects and c apture interactions in the space near the device. While this approach allows mobility and the possibility of forming groups of users virtually anywhere in an improvised way, it still requires a careful installation of external hardware. A simpler approach is by Kratz et al. [START_REF] Kratz | Expanding the design space of around-device interaction[END_REF], who attach external IR sensors on a smartphone screen, and allow ADI using hands. Their main purpose is to reduce the occlusion produced by touch contacts, which is a form of interference. Other works reduce the hardware complexity even further by making use of the integrated sensors in the tablets. Ketabdar et al. [START_REF] Ketabdar | Interaction with mobile devices based on compass (magnetic) sensor[END_REF], for instance, exploit the magnetic (compass) sensor of the device, and interact around it using magnets. Unlike optical approaches, this solution is more robust to occlusion. They also can shape the magnets in different forms, though the system is not capable of differentiating between different magnets since they do not have an encoded ID. This prevents its use in applications with multiple collocated users.

Although the previous examples enable ADI by augmenting tablets with external sensors, they are designed to be used by a single user and on one device. Probably for this reason most of them [START_REF] Avrahami | Portico: Tangible interaction on and around a tablet[END_REF][START_REF] Ketabdar | Interaction with mobile devices based on compass (magnetic) sensor[END_REF][START_REF] Kratz | Expanding the design space of around-device interaction[END_REF] require the interactions to take place close to the device. In a table-based MDE, this restriction could require that users lean over the table or even move towards the target device, which could be cumbersome and cause interference with interaction on the other devices.

Finally, Nacenta et al. [START_REF] Nacenta | The effects of interaction technique on coordination in tabletop groupware[END_REF] compare several interaction techniques, including ADI, in tabletop groupware in terms of how they enhance coordination. They include a spects like lack of interference, ease of transference of elements, and easy access to out-of-reach zones as important factors. Our work complements this previous work by considering other forms of interaction based on fiducial markers and studies the erg onomic, visual feedback, and marker size factors.

User Evaluation

In its simplest form, the proposed interaction consists of taking a card with the marker and bringing it close to a selected tablet for recognition. To study the usability of this, we identified seven ergonomic factors that may have an effect on this initial interaction phase: the user posture (sitting vs. standing), the active hand (non-dominant vs. dominant), the marker size (small vs. big, as shown in Fig. 2), the tablet position with respect to the users (whether it is at their non-dominant vs. dominant side), the tablet distance to the users (near vs. far, depending on whether it is within arm's reach or not), the presence of a visual feedback on the tablet that allows the us ers to see what the camera sees (missing vs. present), and the users' gender (male vs. female). In presenting the results (see Fig. 3), the first condition listed is represented as "level -" and the second as "level +", e.g., sitting is the "-" level and standing is the "+" level for the user posture factor.

Apparatus

The experiment was conducted with a 120x80cm table 75cm high in an environment with ambient light intensity ~150-200lx, and without any direct light source above the table. The surface's table was visually divided across both horizontal and vertical axes, resulting in four identical rectangular sectors to account for near/far tablet distances and non-dominant/dominant tablet positions. When required, the users sat on a chair 47cm high. The marker detection application was running on a Samsung Galaxy Note 10.1 tablet using the computer vision algorithms provided by Vuforia TM for Android devices. Visual feedback about the position of the marker with respect to the camera was given by video on the display. The size of this video region was 1/9 the screen size, and it was located in the lower-left corner. The size of the big and small markers was 50x50mm and 17x17mm respectively, and both were printed on a cardboard card of dimensions 63x91mm and situated near the top (see Fig. 2).

Participants

Thirty-two volunteers, 16 male and 16 female, participated in this study. Ages ranged from 24 to 48 (M = 32.28, SD = 6.3). The average height of males was 180.88cm (SD = 7.27), and females' was 167.38cm (SD = 7.14). Four of them were left-handed and the rest, right-handed.

Design

Since the number of factors considered is high and it would be impractic al to have each user perform every combination of their levels, the experiment follows a mixed fractional factorial design 2 𝐼𝑉 7-3 , for which only 16 different treatments are needed; Fig. 2. Cards with the fiducial frame markers used in the experiment and, since gender is a between-subjects factor, each user only had to conduct 8 treatments. A total of 1536 interactions were performed across factors and treatments. To avoid order and carryover effects during the performance of the 8 treatments by a given subject, the order in which the treatments were presented follows an 8x8 ba lanced Latin squares design for each gender.

Procedure

Firstly, the users were given some time to train with the system in order to minimize posterior learning effects. During this training, they practiced the experimental task which consisted of taking the card with the marker and bringing it closer to the tablet's camera for it to be recognized. Once they felt familiar with the interaction, the proper experiment began, where one user at a time had to repeat the previous interaction but following the instructions given by the different factor treatments (i.e., being seated or standing, holding the marker with their dominant or non -dominant hand, having the tablet near or far, etc.). Each treatment was repeated six times, and subjects were encouraged to perform this interaction as quickly as possible. For each treatment, the average elapsed time to the detection of the marker was measured, and the users filled a NASA-RTLX questionnaire [START_REF] Byers | Traditional and raw task load index (tlx) correlations: Are paired comparisons necessary? Advances in Industrial Ergonomics and Safety[END_REF] to assess subjective task load. Once all treatments were complete, a System Usability Scale (SUS) questionnaire [START_REF] Brooke | A "quick and dirty" usability scale[END_REF] was administered to evaluate the usability of the technique. Users were also asked about their experiences in a short post-task interview.

Results

Regarding quantitative differences, Fig. 3 depicts the mean completion times by each factor. A repeated measures ANOVA (with an α = 0.05) revealed only two factors having a significant effect on the response variable: the marker size (F 1,243 = 19.514, p < 0.001) and the visual feedback (F 1,243 = 11.555, p = 0.001). No double or triple interactions were found significant. The shorter times correspond to performing the interaction with the big marker and having visual feedback, respectiv ely. NASA-RTLX scores for workload were analyzed using Friedman's χ2 tests for ranks (df = 1). Subjects reported relatively low levels of mental, physical, and temporal demand for all conditions, as well as low levels of effort and frustration. All of the above were rated between 20 and 30 approx., with 0 meaning "very low", and 100 "very high". However, some aspects show significant differences b etween the levels of factors in some conditions. Participants reported a significant lower degree of workload in general using the big marker and having the tablet near. Concretely, these two conditions received significantly (p < 0.05) lower scores of mental/temporal demand, effort, and frustration. Subjects also made less effort (p = 0.034) when the visual feedback via video was shown. No significant differences were found between postures, but subjects perceived using their dominant hand as less physical (p = 0.009) and time demanding (p = 0.009). As for differences between gender, women reported significantly (p < 0.05) lower levels of workload in general than men. Concretely, they reported lower levels of mental demand, effort, and frustration, and they showed more confidence regarding performance than men, whose scores were more neutral.

The perceived general usability of the ADI technique was studied via a SUS questionnaire. The analysis using Mann-Whitney U tests revealed no significant differences between genders (U = 90.5, p = 0.156). The SUS total score (calculated as it is explained in [START_REF] Brooke | A "quick and dirty" usability scale[END_REF]) is, on average, 73.13 (SD = 11.46) for men, and 75.63 (SD = 20.18) for women, which, according to Sauro's guidelines [START_REF] Sauro | M easuring usability with the system usability scale (sus)[END_REF] is above average (68). In Sauro's letter-grade system (from A+ to F), the overall usability of our technique would receive a B.

Discussion

The results show that the proposed interaction technique is usable in general (obtaining a B grade from the SUS questionnaires). This was also confirmed by some subjects' comments regarding the good performance of the system and their suspicions about whether this was a real working prototype. Further, the quantitative analysis has not found any statistically significant effects related to the posture of the users (sitting vs. standing), the side at which the device is located (dominant vs. non-dominant) and its distance from the user (near vs. far). This proves that the technique is usable under a wide spectrum of ergonomic situations. Moreover, the fact that subjects reported low levels of mental, physical, and temporal demand for all conditions means that the analyzed interaction is intuitive and potentially applicable to more demanding scenarios with subjects having cognitive or motor disabilities. However, the analysis of the qualitative results shows some implications for future applications using the interaction technique considered in this work. Several participants reported having difficulties with the visibility of the video feedback when they were seated and the tablet was not located within arm's reach. This issue disappeared when they were standing up. Hence, this suggests that activities designed for situations where the users are seated should either keep the devices within arm's reach for all participants or avoid video feedback.

Subjects also reported using their dominant hand was less physically and time demanding. However, this did not have a significant impact on the time to perform the gesture and some participants even commented they preferred to use one hand or the other depending on which side the tablet was on. This observation provides initial clues about the feasible use of both hands to allow bi-manual aerial interactions in the design of future ADI systems . Visual feedback and marker size had a greater impact on the interaction. The small marker was harder to recognize by the application, and the users needed to put it very close to the camera, which made them "lean too much" on the table when the tablet was distant. In a real application, this could cause inte rference with others' actions and lead to much more frustration. Therefore, the results suggest that big markers are more suited for this sort of interaction. They can be attached to cards and, because the proper marker is a frame, they can be filled with application-specific content. Taking advantage of markers ' IDs, a potential use for these cards could be using them as information containers and also for the transfer of elements/documents in a co-located group, which many subjects of our experiment showed great excitement about. According to Nacenta et al. [START_REF] Nacenta | The effects of interaction technique on coordination in tabletop groupware[END_REF], an interaction like this one, using the card as an information container, presents intrinsic benefits in terms of awareness since the system does not need to present any action points to the user (e.g., via a cursor), and because any user can easily identify which colleague performed a given gesture with the card because of the visibility of such actions. On the other hand, having visual feedback in a small region of the screen was perceived as a very useful feature for allowing users to adjust and correct their actions . Similar benefits from visual feedback are reported by Nacenta et al. [START_REF] Nacenta | The effects of interaction technique on coordination in tabletop groupware[END_REF]. Nevertheless, some subjects pointed out that it might not be convenient to integrate this feature, since it would reduce the display work area.

Limitations and Future Work

It is important to note that, as Nacenta et al. [START_REF] Nacenta | The effects of interaction technique on coordination in tabletop groupware[END_REF] remark, the choice of a given interaction technique affects coordination, preference, and performance. Hence, the results reported in this paper are only conclusive for this particular interaction. There are also several limitations to our work. Firstly, the experiments were performed with the same tablet brand and model, and the resolution of the camera could have an effect on the recognition. Secondly, the study only refers to the initial acquisition phase of the interaction. However, analyzing the feasibility of this initial phase and obtaining first user impressions is a necessary step forward before designing and considering more complex scenarios based on ADI. Regarding this, the results obtained provide useful information for future designers of ADI-based environments using frame markers. As a next step, we plan to perform a full study of different types of ADI marker-based manipulations to obtain a full set of feasible interactions with this technique. Another limitation is that the controlled interaction was performed in isolation by a single user and, therefore, no interference issues that could happen in a collaborative scenario were evaluated. This is certainly an interesting area of future research to evaluate the full potential of the proposed technology to support MDE collaboration. Despite these limitations, the relatively good usability results obtained encourage us to delve into the ADI proposed in this paper, and conduct further experiments that test its suitability in actual collaborative environments. Regarding future uses, we consider this interaction to be promising in meeting environments where users c ould easily exchange documents attached to marker cards. Another potential application domain is gaming, where, for instance, the tablets could be used in consonance with a physical gaming board offering digital augmentation, whereas the cards could encode abilities or objects to be transferred to the other participants. Physical games could also be implemented in which participants would exercise by moving around a big table with their cards obtaining and depositing items from the tablets scattered on it. This ADI could also be interesting in rehabilitation tasks for people with acquired brain injuries. In this case, markers could be attached to tangible elements that represent objects in real life and the patients should have to reach the tablet (among several others) that shows some digital content related to the element they are holding.

Fig. 1 .

 1 Fig. 1. Hypothetical collaborative scenario with ADI using fiducial markers

Fig. 3 .

 3 Fig. 3. M ean completion times (in milliseconds) for each considered factor

Acknowledgements

This work received financial support from Spanish MINECO (projects TIN2010-20488 and TIN2014-60077-R), from Universitat Politècnica de València (UPV-FE-2014-24), and from GVA (APOSTD/2013/013 and ACIF/2014/214).


Naveed Ahmed
email: ahmed.naveed@yahoo.co.in

Wayfinding Behavior in India

Keywords: Navigation, wayfinding, India, culture, behavior 1

India is highly heterogeneous in the way cities are laid out; the way people use landmarks and how certain cultural aspects affect wayfinding. These factors influence the design of maps and navigation systems. Users from Mumbai and Rajasthan were interviewed to explore such implications and find design opportunities. These users had low education levels and needed to find addresses on a regular basis. The study was centered on the Indian context. People in India rarely use maps for navigation. They rely primarily on asking around and navigate using landmarks. The landmarks people use during this are prominent but sometimes highly volatile and ad hoc like cows and people sitting on street corners. Some of these landmarks may not necessarily always be popular. While inquiring about the route, people repeatedly seek reliable sources en route, to validate the information they have. Other findings during the study include people's preferences in using maps and concerns while seeking directions. Mental models of people also affect the way people navigate and exchange the wayfinding information. Some of these are very specific to the Indian context. In the end, we also discuss how these findings will affect the design of navigation and (culture-centric) wayfinding systems.

Introduction

Navigation and wayfinding are an integral part of modern lives. Wayfinding is the process of gathering required information and making decisions about the direction of travel. This includes determining one's location in comparison to the destination or a nearby location.

According to Golledge, wayfinding is concerned principally with how the route is structured rather than the environment through which the path passes [START_REF] Golledge | Wayfinding Behavior: Cognitive Mapping and Other Spatial Processes[END_REF], but in a modern city where life is affected by factors like traffic congestion, multitasking, etc., the path and the environment equally impact wayfinding and navigation.

The process of wayfinding is affected by a person's physical, intellectual abilities, socio-cultural background, gender, etc. [START_REF] Arthur | Wayfinding: People, Signs, and Architecture[END_REF] [START_REF] Lawton | Gender Differences in Wayfinding Strategies and Anxiety About Wayfinding: A Cross-Cultural Comparison[END_REF] and in turn adversely affects the design of wayfinding systems. In India, where people rely primarily on asking around, these factors even determine if the information conveyed is right or wrong. People have apprehensions and preferences in asking around. People take time to decide whom to ask, when to ask and how often to ask.

Along with these, mental models and perceptions of a particular place determine how people store information about routes and how they are conveyed to other people. As navigation is a spatiotemporal process, these perceptions change based on the stimuli the traveler receives at the moment [START_REF] Montello | Human Factors of Wayfinding in Navigation[END_REF]. This results in creation of newer wayfinding strategies and routes, than that already exist [START_REF] Hunter | Spatial Orientation, Environmental Perception and Wayfinding[END_REF].

India as a country is highly heterogeneous in the way cities are laid out and the way people use landmarks in the absence of proper road signage. Cultural aspects specific to this country determine how wayfinding instructions are exchanged. These affect the way maps and navigation systems are designed. The studies reported in this paper are an attempt to explore such implications and find design opportunities.

In a map, landmarks like buildings, trees, statues, etc. and topographical features like hills and elevations act as referential points to know one's position or to orient oneself. These are marked on a physical map to aid navigation. But in India, where very few people use printed maps, landmarks play a pivotal role and wayfinding is done by asking around for these landmarks en route. Added to these are many biases of how people provide these instructions that affects the process of wayfinding.

The findings of user studies have been presented further and possible implications that affect the design of wayfinding systems in a country like India are discussed.

Methodology

As part of a Master's project, we tried to understand people's wayfinding habits, how people use existing solutions and conditions under which these have failed. The findings in this paper are the result of user studies conducted during the project.

To understand the process of wayfinding, users who did this on a regular basis were interviewed. This included delivery personnel, intra-& inter-city drivers and repair technicians. Most of the users had low education levels and needed to find addresses on a frequent basis. People who used existing solutions regularly were also interviewed to understand their usage behavior.

Users were chosen based on their vocation and availability. In all, 15 people were interviewed and most of them were in the age group of 25-35 and have lived in city suburbs most of their lives. Of these, 10 were men and 5 women. Finding unique users was time-consuming as these cohorts operate within fixed areas in the city. The users had low familiarity with using a computer but used smartphones regularly.

The project also took into account and extended the outcome of a study on wayfinding by design students at IIT Bombay, which involved interviews with 47 people in towns near Mumbai.

Indian cities are structured differently and hence users were chosen from geographically different regions to obtain diversity in inputs-two of which were inter-city drivers from Jaipur (Rajasthan) and the rest from Mumbai and its suburbs.

Contextual inquiries were conducted with the users to know their working processes, how they find addresses, their recent journeys and the hurdles they face. As part of unstructured studies, something similar to the master-apprentice model was followed. We chose a few destinations and asked random people (en route) for ways to reach the place. In both the cases, the responses were recorded and later analyzed through affinity mapping.

Towards the end of the primary studies, a separate set of 5 people were interviewed to understand mental models of sketching and representation of familiar routes.

The project resulted in the conceptualization of a navigation mechanism using schematic maps and photographs of landmarks. This has not been discussed in this paper.

Findings

The findings of the user studies, discussed below, affect the way maps are designed, particularly in the Indian context.

Landmark Information

As India is not a very map-savvy culture, landmarks have always played an important role in wayfinding. In our studies, even users of online maps mentioned that they checked major landmarks on their route before starting the journey.

Prominent physical structures like buildings and trees are commonly used as landmarks. Sometimes the color of a building is more important than the building itself. But this is mainly in case of larger roads.

In smaller streets, the choice of landmarks changes completely. People use garbage bins, broken walls, nullahs and even volatile entities like road-side vendors, people sitting on street corners, potholes and cows as reference points. Here, religious structures like minarets and nishan sahib which are specific to an area are also used.

Some landmarks from user studies (specific to India): Mother dairy outlets (milk booths), trees, color of buildings, slums, electric poles, banyan trees, fish markets, post-boxes, tiny temples and dargahs under trees, rickshaw stands, road-side shops (like ironing store, cobblers, cycle shop, betel nut & cigarette shops), street vendors, drainages, broken walls, garbage bins, chabutras, political party offices, police outposts, policemen, gated communities (like chawls), minarets, electric transformers, religious flagpoles (e.g. nishan sahib), prominent cultural residences (like pols in Ahmedabad), public toilets, grocery stores, flyover pier numbers are amongst other prominent locations.

This list is not exhaustive and is in no specific order.

3.2

Whom to ask?

Though people rely heavily on asking around to find the address right, they are often not sure about whom to ask for directions. People solve this problem by relying on 'seemingly-trusted' persons and 'possible' providers of information.

Well-dressed and older people are presumed to be more trustworthy than others. Autowallahs and panwallahs1 are considered more reliable as they are usually local to an area and might know the place better. But some users said that autowallahs often refused or provided wrong information.

A user also mentioned a case where school students misguided him and he had to find his route all over again.

Women prefer asking other women. This striking feature was noticed more than once in our studies. According to Lawton and Kallai, women are more likely to experience wayfinding anxiety than men. This could be due to the cultural upbringing resulting in a feeling of insecurity and vulnerability, especially in unfamiliar areas. Studies have also shown that women use different wayfinding strategies than men [START_REF] Lawton | Gender Differences in Wayfinding Strategies and Anxiety About Wayfinding: A Cross-Cultural Comparison[END_REF].

People also seek multiple sources (en route) to verify and validate the information they have been provided with. But this may sometimes cause more harm than good, as people have their own perceptions and understanding of a route and excessive verification by the information seekers (info-seekers) might lead them astray.

Mental Models

People create mental models and have perceptions in navigation and wayfinding too. Users construe a route without any turns as a straight road. They do not perceive a curve unless it is at a sharp angle. Users subconsciously perform rectilinear correction of the path by ignoring the minor bends and curves.

When asked to draw the route between two points they travel regularly, users usually did a correction in the path. If the route had no major turns, it was drawn as a straight road. Bends were ignored. People mentioned details only when the path involved too many turns. They sketched finer details only when they got closer to the destination.

High-speed parts of the road were drawn straighter than the low-speed ones. However, the nature of sketch might change depending upon how familiar the route is to the person. Regular commuters, infrequent travelers and first-time travelers will have a different perception of the same route. Understanding the difference in their mental models will require further study and inquiry into this subject.

Kevin Lynch in his book, The Image of the City, talks about how landmarks should be created in a city so that people can create easy mental maps of the city they live in and of the routes they traverse (called imageability and visibility) [START_REF] Lynch | The Image of the City[END_REF]. So, these mental models are also affected by the layout and structure of the city.

For example, cities like Chandigarh in India follow a grid (also called gridiron) structure, while New Delhi has a radial structure and places like Hyderabad which have evolved organically, do not follow any fixed structure. As grid cities are organized in rectilinear roads, referring to and recalling routes is easier, than in case of an organic or non-grid layouts.

Roads look different at different times of the day. Landmarks also appear different because of traffic and light conditions which vary greatly depending on the time of the day. The perception of a route, hence, also depends on several natural and manmade variables.

Progressive Discovery

People find their way through progressive discovery. Progressive discovery is like progressive disclosure which is an interaction design technique where only the important and primary information is disclosed initially and the rest of it is provided on demand [START_REF] Nielsen | Progressive Disclosure[END_REF]. Similarly, users divide their journey into shorter milestones and once they reach each of these, they inquire for further directions.

Depending upon proximity to the destination, information providers (infoproviders) also provide directions progressively. They advise the info-seekers to reach a certain point ahead and then ask further. Certain info-seekers and even infoproviders felt that verbal directions are complex and confusing. Hence, they followed progressive disclosure of information intuitively. In short, both info-seekers and infoproviders first search for larger information and get into finer details only when they are closer to the destination. This is true even in case of some Google Maps users who obtained the approximate route to their destination online and got into micro details of reaching their destination by asking around.

Size of the road

People feel it is easier to ask for directions on larger roads than in the inner streets. This may be because of progressive discovery. People seek major landmarks while on the larger roads and get into intricate details only when they get closer to their destination. Intricate details mean specificity and finding them is more difficult.

Info-providers would generally know the bigger picture better than the finer details, compared to inner streets where the volatile landmarks are known only to those who know the area well.

Measuring Distance

People use several indigenous and ingenious methods to measure distance. Locally available data such as the number of buildings, telephone poles, traffic signals and trees are often used. In some cases, the distance is measured by the amount of fare charged by the bus or any available mode of public transport. In rural areas, people also use the number of villages between the starting point and the destination as a measure of distance.

The number of route options to reach the destination depends directly on the distance between the source and the destination. The layout of the city also affects the number of routes available. A grid structure has lesser route options to complete a journey compared to a radial or organic layout [START_REF] Walker | The power and pleasure of grids[END_REF]. One user mentioned that grid meant more travel whereas it was easier for him to find shortcuts in a city with a nongrid layout. As a result, he perceived travel times to be lower in such (non-grid) cities.

People do not prefer online maps

Being a society where maps are sparsely used for wayfinding, online aerial maps are something that users in India find difficult to adapt to. Traditional GPS-based solutions evolved from aerial perspective of locations. But in India where use of traditional maps is low, digital solutions based on aerial perspectives may not always work.

Users mentioned that online maps do not contain adequate information for wayfinding. People in India usually find their way using landmarks and by asking around. This information is not readily available to them on the maps or easily accessible. Even if they find the right route, they could not backtrack or travel again on the same route without assistance. This created a negative bias towards online maps.

Landmark information was something they wanted maps to provide, so that they can remember the route even if they are not using maps during subsequent travel. Some users were not comfortable using software for navigation, as they could not operate them easily. Anxiety during travel and unfamiliarity with the place and the use of software may contribute to this behavior.

Users were not very keen on continuously using mobile phones for maps as it was perceived as 'talking on the phone' by others. A user was once booked by traffic police for using mobile phone while the vehicle was waiting at a traffic signal. Also, solutions like Google Maps did provide audio feedback but it was difficult to listen to instructions in noisy traffic conditions.

Usage of existing solutions

Of all the users interviewed, five of them had used print maps and online solutions like Google Maps and Nokia HERE earlier.

One user (a European citizen) who used print maps extensively found it difficult to use them in India as they were not detailed and finding street names was not easy. This is due to improper and insufficient signage. He later resorted to asking around.

A user felt that Google Maps provided information that was not completely reliable. He used the application primarily to know his current position and if the taxi was taking him on the correct route. But the app always re-routed based on the current position. There was no direct way to confirm the authenticity of his route.

Due to the shortest path strategy, the map applications sometime route user via smaller streets and villages, instead of the main roads or the highways. This confused users about the authenticity of the route provided. Users in such cases had to go back to asking people around to make sure they are on the right path. It leads to further anxiety when the app re-routes to a new route in an already unfamiliar path.

One user was gifted a dashboard console for his car a year back, but had stopped using it within a month. He did not find it useful as most of the travel was intra-city and it was too cumbersome to input data to find a route.

Design Implications

All the entities that form part of the wayfinding process seem to have some sort of uncertainty associated with them-may it be the mental models, the way people exchange information or the kind of landmarks that are used. In spite of all this, the seemingly-chaotic process works successfully, and for many users most of the navigation information becomes expendable after they cross a milestone during the journey.

In the findings so far, we also see that existing solutions failed due to various internal or external reasons like interface issues, poor infrastructure or specific requirements by users. Sometimes, as the profile of the user changed, so did their requirements.

Landmarks, big or small, are the key elements in the wayfinding process especially in absence of proper signage. And for a culture that navigates primarily on verbal onthe-go basis, a solution must seamlessly integrate landmark data and provide it along the route being traversed. Instead of an aerial view, the solution must be completely landmark-based that shows a ground-level view to the user.

Also in a country like India, where topographical changes are very frequent, care must be taken that landmark data is valid and correct at any given point of time. The solution must be flexible enough to accommodate the volatility of the landmarks. This will help in making the system more reliable.

People seek trustable sources and they will look for 'trust' in any solution. This has been clearly noticed in the user studies where people tried to seek reliable sources repeatedly. Creating trust into a non-human entity is something that would make or break the solution. As Progressive Discovery is an almost accepted behavior, it is not required that complete information is provided to the user in one go. Necessary information can be provided to the user to take him to the next intermediate point in his journey and he can take further decisions thereafter. The solution can have smaller milestones for people to achieve, like a game, leading to the final destination. This will help the user be assured that he is on the right path and also get a feeling of accomplishment.

The kind of landmark information people use also has a major impact on the way data is collected for the solution. It would be easier to find data in the bigger context than the intricate street-level details. The details from the last mile of journey are the most important and if the solution fails at this stage it would render the whole exercise of wayfinding useless. The main aim is to create a solution that works for first-time users, as people would remember the route (even if vaguely) on subsequent travel.

There is also an opportunity to create solutions, which cater to different times of the day-mainly lighting conditions-to provide a seamless experience.

Human mind ignores minor bends and curves to create unique mental models. This feature can be incorporated in a map to provide the simplest of information, similar to a schematic map. Schematic maps are closest to mental models in terms of simplicity and have been used over the years for representing transit routes. E.g. the London Tube. Major turns and prominent topological features can be reproduced for guidance and to prevent errors. Users can concentrate on their route instead of the other details, if they are provided with simplest and only the necessary information.

It may not always be possible to create an ultimate solution. But these findings might lead to a solution for certain target groups like people with low-education levels or those unfamiliar with using maps, who amount to a fairly large and untapped part of the population in India.

5

Future Work

In the past few years, India has seen the emergence of professions like delivery, courier, cab and related door-to-door services. These require searching and finding addresses on a daily basis. Most of these professions do not require very high educational levels and hence people employed in these are not highly educated. (Low education levels here does not imply low literacy.) People in these professions often possess smartphones but never use them beyond the employer-specified application. Cohorts like these, who underuse accessible technology, can be the primary focus to create a solution. This must also be done by keeping in mind the bottom of the pyramid to facilitate easy adoption amongst users with very less or no exposure to technology.

Further research would include making such applications more usable through newer technologies like text-less and aural interfaces.

Fig. 1 .

 1 Fig. 1. On the left are sketches by people and on the right are screenshots from Google Maps.

An autorickshaw driver is a autowallah and a panwallah is a betel nut seller. Both of these can be found in most of the street corners in India.

Acknowledgements. I would like to thank my project guide Prof. Anirudha Joshi of Industrial Design Centre (IDC), IIT Bombay, for his critical feedback throughout. Faculty at IDC for their inputs during the project. Participants and friends who assisted me during the user studies. Anshumali Baruah and Ishneet Grover for the initial reviews. Umme Hani for the thorough proof-reading and suggestions during the making of this document.


Ivan Burmistrov

Tatiana Zlokazova
email: t.zlokazova@gmail.com

Anna Izmalkova

Anna Leonova
email: ableonova@gmail.com

Flat Design vs Traditional Design: Comparative Experimental Study

Keywords: flat design, usability, visual search, cognitive load, eye-tracking

In the past few years flat user interface design has become the predominating visual style of operating systems, websites and mobile apps. Although flat design has been widely criticized by HCI and usability experts, empirical research on flat design is still scarce. We present the results of an experimental comparative study of visual search effectiveness on traditional and flat designs. The following types of visual search tasks were examined: (1) search for a target word in text; (2) search for a target icon in a matrix of icons; (3) search for clickable objects on webpages. Time and accuracy parameters of the visual search, as well as oculomotor activity, were measured. The results show that a search in flat text mode (compared with the traditional mode) is associated with higher cognitive load. A search for flat icons takes twice as long as for realistic icons and is also characterized by higher cognitive load. Identifying clickable objects on flat web pages requires more time and is characterised by a significantly greater number of errors. Our results suggest replacing the flat style user interfaces with interfaces based on the design principles developed over decades of research and practice of HCI and usability engineering.

Introduction

In 2012-2014 the design of user interfaces for the operating systems (OS) of desktop computers, mobile OS and mobile applications, as well as for websites, saw cardinal changes relating to the appearance of so-called flat user interface design. The first flat design appeared in the mobile OS Windows Phone 7 in 2010. It came to prominence two years later with the OS Windows 8 for personal computers. This new approach to the design of user interfaces was enthusiastically received by the graphic design community as well as by many users, as a result of which it was adopted by two other leading software vendors, Apple and Google. The basic flat design principle means that the computer screen represents a selfcontained two-dimensional digital environment in which there is no place for an ything replicating three-dimensional objects of the real world [START_REF] Banga | Essential M obile Interaction Design: Perfecting Interface Design in M obile Apps[END_REF]. The user interface elements are simplified: abstract graphic forms are used and spaces are filled with bold colours. Text and font are especially important in flat design. In particular, this leads to a wide use of condensed, light and ultralight variations o f typefaces. The density of screen information is often extraordinarily low [START_REF] Nielsen | Windows 8 -Disappointing Usability for Both Novice and Power Users[END_REF].

Shortly after its introduction, flat design became subject to criticism by HCI and usability experts [START_REF] Belveal | Where Have All the Affordances Gone?[END_REF], [START_REF] Enders | Flat UI and Forms[END_REF], [START_REF] Nielsen | Windows 8 -Disappointing Usability for Both Novice and Power Users[END_REF], [START_REF] Noessel | Your Flat Design Is Convenient for Exactly One of Us[END_REF], [START_REF] Page | Skeuomorphism or Flat Design: Future Directions in M obile Device User Interface (UI) Design Education[END_REF], [START_REF] Walker | The ABCs of Website User Experience[END_REF]. The main criticism was that flat design ignores the three-dimensional nature of the human brain, which is extremely sensitive to visual cues linking interfaces to the real world. The removal of affordances from interactive interface objects means that users regularly perceive interactive elemen ts as non-interactive, and non-interactive elements as interactive.

Despite these limitations flat design is becoming more and more common, and criticism of experts in HCI and usability is generally ignored by the software industry and graphic designers. Unlike these expert assessments (from 2012 onwards) the results of empirical research into flat design are still not numerous, so it is important to conduct more comparative experimental studies of flat and traditional design.

Background and Related Work

Recent empirical research has mostly considered a quantitative comparison of the performance measures by users of both traditional and flat style interfaces, and users' emotional reactions and preferences for realistic and flat icons.

A comparative usability study of Windows 8 (flat interface) and its predecessor Windows 7 (traditional interface) showed that Windows 7 was superior to Windows 8 in each of three aspects of usability: effectiveness, efficiency and satisfaction [START_REF] Schneidermeier | Changing Paradigm -Changing Experience? Comparative Usability Evaluation of Windows 7 and Windows 8[END_REF].

In research carried out by Idler [START_REF] Idler | Flat Web Design Is Here to Stay[END_REF] 100 web professionals completed tasks relating to the clickability of objects on four flat websites, and also assessed the advantages and disadvantages of flat design. The results showed that the number of 'false alarm' errors when working on flat sites varied from 16% to 38% (average 29%). The authors concluded that despite the apparent clarity and simplicity of flat design, achie ving an acceptable level of website usability is not easy.

Comparative research of the aesthetic perception by users of pairs of realistic and flat icons of applications for desktop computers and mobile devices indicated that the users preferred realistic icons to flat icons by a proportion of 75:25 [START_REF] Hou | A Preliminary Study on Aesthetic of Apps Icon Design[END_REF]. In another study, flat icons scored higher on semantic scales such as "timeliness" and "simplicity", but they fared worse than realistic icons in "identity", "interest" and "familiarity" aspects [START_REF] Li | Two Typical Symbols in Human-M achine Interactive Interface[END_REF]. A semiotic inspection of icons of standard applications for iOS 6 (realistic icons) and iOS 7 (flat icons) showed that the uns uccessful transformation from realistic to flat icons is often related to the loss of semantically important attributes during the "simplification" process inherent to flat design [START_REF] Stickel | Cutting Edge Design or a Beginner's M istake? -A Semiotic Inspection of iOS7 Icon Design Changes[END_REF].

Method

As can be seen from the above-mentioned studies, an empirical analysis of flat design is still at an early stage. In our experiment we tried both to build on previous research, but also to include in our analysis several new aspects. In order to conduct an accurate comparative study of traditional and flat interfaces we chose the following design elements: fonts, icons and webpages. In addition to the classical performance measures like time on task and number of errors, we also included an analysis of oc ulomotor indicators of cognitive load.

The experiment consisted of two series: traditional and flat. In each series of the experiment participants carried out three types of task:

(1) A search for a target word on a page comprising three paragraphs, all type d using the same font (Fig. 1).

Fig. 1. Examples of traditional and flat text stimuli

For the traditional series we used three similar typefaces: Helvetica Neue, Arial and Tahoma (these are fonts used in older versions of OS Windows and pre -flat era websites); for flat series we used three variations of Helvetica Neue font: Condensed Normal, Light and UltraLight (condensed fonts are popular on modern websites, while Helvetica UltraLight and Light were system fonts in iOS 7, beta and final ve rsions respectively) (Table 1). The target word (e. g. "structure") was placed randomly in the first, second or third paragraph. The participants were instructed to click the target word.

Table. 1. Typefaces used in the experiment

(2) A search for an icon depicting a specific object (e. g. "ice-cream") in a matrix of 9х9 icons presented on the screen (Fig. 2). The position of the target icon was ra ndomly distributed between the nine quadrants of the matrix. The participants were instructed to click the target icon.

Fig. 2. Examples of realistic and flat icons stimuli

(3) A search for clickable objects (i. e. objects which change something on the screen after a click) on screenshots of existing websites (Fig. 3). The participants were instructed to click all screen objects that look clickable (buttons, links, menus, ima ges, banners etc.).

Fig. 3. Examples of traditional and flat web page stimuli

In each series of the experiment the participant was given 9 slides with text, 9 slides with icons and 9 webpage screenshots. The order of tasks in each series was the following: first the participant was given one text search task (each of the typesets appeared three times within a series), then one icon search task, then one screenshot search task. This pattern was then repeated until all 27 tasks had been completed. The order of the different series of the experiment (first traditional, then flator the other way round) was counterbalanced. Before the experiment began, the participants were given instruction and training.

The stimuli were presented on a 19 inch LCD monitor with 4:3 aspect ratio. To measure the participant's eye movements an EyeLink 1000 eye-tracker was used. All screen events and mouse movements were recorded using the TechSmith Morae 3.2 data logging application.

For the search of target words and icons the performance time was measured. For the screenshot task we measured the average time taken to click all clickable objects on a slide, and also registered the number of 'miss' and 'false alarm' errors.

For each task type the mean eye-tracking indicators were analysed, including fixation and saccade parameters. These parameters are considered in t he literature as indicators of the cognitive load and show the following dynamics when the cognitive load increases: an increase in fixation duration [START_REF] Crosby | Visual Search and Background Complexity: Does the Forest Hide the Trees?[END_REF], [START_REF] Renshaw | Designing for Visual Influence: An Eye Tracking Study of the Usability of Graphical M anagement Information[END_REF], a decrease in saccadic amplitude [START_REF] Pomplun | Investigating the Visual Span in Comparative Search: The Effects of Task Difficulty and Divided Attention[END_REF], [START_REF] Zelinsky | Eye M ovements During Parallel-Serial Visual Search[END_REF], and a decrease in saccadic peak velocity [START_REF] App | Saccadic Velocity and Activation: Development of a Diagnostic Tool for Assessing Energy Regulation[END_REF], [START_REF] Di Stasi | M ain Sequence: An Index for Detecting M ental Workload Variation Complex Tasks[END_REF].

Participants were: 19 female and 1 male university student from Moscow, aged 18-28 (mean -21.2), experienced web, smartphone and tablet users . The experimental sessions were conducted in November 2014. By that time flat style already predominated on desktops and mobiles, and so was familiar to all the participants.

Results and Discussion

Fonts. Mean values of performance time and oculomotor measures for the text search task are shown in Table 2. Statistical analysis did not reveal any significant difference in performance time. At the same time, oculomotor indicators of increased cognitive loadincrease in fixation duration, decrease in saccadic amplitude and saccadic peak velocityshowed statistically significant differences in the traditional and flat series. This type of co mbination of measures (long fixations and short saccades) is characteristic of focal visual information processing: i. e. a conscious analysis of information, precise identification of objects and events, which are implemented when the visual search tasks increase in complexity [START_REF] Velichkovsky | Heterarchy of Cognition: The Depths and the Highs of a Framework for M emory Research[END_REF]. In the text search with traditional fonts, subjects had more opportunities to switch to "semi-automatic" information processing associated with a lower cognitive load (which is indicated by shorter fixations and longer sa ccades). Also the lower values of saccadic peak velocity provide evidence in favour of associating the text search in the flat series with a higher cognitive load.

Icons. Mean values of performance time and oculomotor measures for the icon search task are shown in Table 3. A significant difference was found in the mean values of the icon search time: a lmost twice as high for flat as for realistic icons. Unlike in the previous task, a compa rison of oculomotor activity in the graphic objects search did not reveal any significant difference in mean fixation duration. Nevertheless, a difference in mean saccadic amplitude and saccadic peak velocity remained, just as in the text search task. Values were less in the flat series, which may indicate the higher complexity of the task and a higher cognitive load in the flat icon search.

Monitoring the performance process of this task allowed us to assume that many participants in the flat series could not find the target icon during the initial "fast" slide scanning. Later in the search these participants tended to show more care in scanning the images, enabling them to find the target object. This, however, led to a significant increase in search time.

Websites. Mean values of performance time and oculomotor measures, as well as rates of 'miss' and 'false alarm' errors are shown in Table 4. As expected, total task performance time on traditional sites was higher, as info rmation density on the screen was considerably higher than on flat screenshots. On traditional sites there were 110 clickable and 64 unclickable screen areas (total: 174), while on flat sites there were 78 clickable and 54 unclickable screen areas (total: 132). For this reason, the mean performance time for a single screen area was calculated (for both traditional and flat sites). The results demonstrated that the average pro-cessing time for a screen area (including making a decision on the objects' clickability and clicking the clickable objects) was significantly higher for flat websites.

An analysis of 'miss' and 'false alarm' error types revealed a significant difference between traditional and flat sites: errors of both types were significantly more frequent on flat sites. It is noteworthy that the percentage of false alarms on flat sites in our experiment (28%) almost exactly corresponds with the figure for false alarms (29%) in the research conducted by Idler [START_REF] Idler | Flat Web Design Is Here to Stay[END_REF].

It should be noted that in the web search task oculomotor effects were revealed, which were the reverse of those found in the text and icon searches: a search for clickable objects on the page with flat design was characterized by a higher saccadic amplitude and saccadic peak velocity. However, we are not inclined to in terpret these results as evidence in favour of a higher cognitive load when working with traditional sites. In our opinion, a key role here is played by the difference in the characteristics of the stimulus material. These effects may be associated with fu ndamental differences in the design of traditional and flat sites, which force subjects to use different scanning strategies. Thus, in our experiment on sites with traditional design the nu mber and density of graphic objects was higher and interface contro l tools were more distinct. After initial orientation this allowed the user to develop a systematic search strategyseen in the combination of longer fixations and shorter saccadic duration. By contrast, the flat design sites initially contained less graphic and text information, which normally facilitate the search for interface control tools. This made subjects repeatedly perform search activity and return to viewing certain areas of web pages several times, shown by a decrease in fixation duration and increase in the amplitude and velocity characteristics of saccades. Thus, the search on flat sites was more "ch aotic", which had a negative impact on time and accuracy parameters of task perfo rmance.

Conclusions

Our study has shown that flat design is inferior to traditional design in most of the aspects we analysed. Text search, where fonts popular in flat design were used, leads to higher cognitive load than search in texts with traditional fonts, although there was no significant difference in the objective measuresearch time. A flat icons search is performed almost twice as slowly as a realistic icons search, and is characterized by a higher cognitive load. Analysis and processing of user interface objects on webpages with flat design takes more time than on traditional websites (calculated per screen area), and is accompanied by a significantly higher error rate; the difference in oc ulomotor activity reflects the specificity of traditional and flat webpage design. Our experimental study supports the opinion expressed by many HCI and usability experts that flat design is a harmful tendency in area of user interfaces, and should be replaced by interfaces based on the design principles developed over decades of research and practice of HCI and usability engineering.

The research was supported by a grant from the Russian Foundation for Basic Research (14-06-00371).

Table 2 .

 2 Results for the text search

	Measure	Traditional series Mean (σ)	Flat series Mean (σ)	Student t-value	p
	Performance time (sec)	46.0 (16.7)	42.7 (12.3)	1.258	0.215
	Fixation duration (msec)	256 (34.6)	266 (32.9)	3.462	0.001
	Saccadic amplitude (deg)	3.7 (0.81)	3.3 (0.74)	3.967	0.001
	Saccadic peak velocity (deg/sec)	138 (18.7)	128 (18.6)	3.919	0.001

Table 3 .

 3 Results for the icon search

	Measure	Traditional series Mean (σ)	Flat series Mean (σ)	Student t-value	p
	Performance time (sec)	8.0 (2.2)	15.4 (4.6)	5.611	0.000
	Fixation duration (msec)	284 (70.4)	264 (58.4)	0.857	0.403
	Saccadic amplitude (deg)	4.6 (1.11)	3.2 (0.93)	8.728	0.000
	Saccadic peak velocity (deg/sec)	174 (25.2)	137 (22.5)	8.810	0.000

Table 4 .

 4 Results for the clickable objects search

	Measure	Traditional series Mean (σ)	Flat series Mean (σ)	Student t-value	p
	Performance time (sec)	28.0 (5.5)	24.2 (6.7)	4.081	0.001
	Time per screen area (sec)	1.45 (0.28)	1.65 (0.46)	-3.622	0.002
	Errors: misses (%)	26.0 (9.6)	35.8 (13.3)	-5.498	0.000
	Errors: false alarms (%)	16.6 (9.4)	28.0 (16.1)	-4.688	0.000
	Fixation duration (msec)	342 (43.6)	351 (44.0)	-0.915	0.373
	Saccadic amplitude (deg)	3.63 (0.42)	3.91 (0.48)	-3.282	0.004
	Saccadic peak velocity (deg/sec)	141 (11.6)	146 (16.0)	-2.646	0.017