Regina Bernhaupt
email: r.bernhaupt@tue.nl

Dimitri Drouet
email: dimitri.drouet@ruwido.com

Michael Pirker
email: michael.pirker@ruwido.com

Absolute Indirect Touch Interaction: Impact of Haptic Marks and Animated Visual Feedback on Usability and User Experience

Keywords: user experience, absolute touch input element, usability, automotive, interactive TV, remote control;

Goal of this paper is to investigate usability and user experience (UX) of a touch-based control of user interfaces that the user can not directly interact with. An example is a user controlling the television screen via a touch interaction on the remote control, or the driver of a car using touch to control the input on the steering wheel for the middle-console screen. Based on a controlled within subject experiment investigating touch based interaction with and without a haptic mark we replicate findings on usability that it is significantly faster to complete a task with haptic marks on the touch area than without haptic marks. For user experience the dimensions of pragmatic quality and attractiveness were rated higher for touch input with a haptic landmark. The variation of user interface animations for target selection did not have a significant impact on user experience, showing that the tactile feedback is the most prominent factor to determine user experience. The contribution concludes with a discussion how replication of studies must become part of user-centered design and development processes to handle the threat of outdated research due to technology change.

Introduction

Figure 1 shows an example of absolute indirect touch interaction: When changing the TV channel on the remote control, the area the user touches corresponds to the area on the user interface: if the finger is in the upper left corner, the upper left corner on the screen is selected. Once the finger is moved to the right one step, the corre-sponding element in the grid is selected. Using a haptic mark on the touch area allows the user to feel the position, without the need to look at the touch area. The finger position in this interaction is absolute, as moving one step to the right, moves one step to the right on the screen. The interaction itself is indirect as, evidently, the user is not touching directly the user interface, but touches the touch area of the control grid, to have an effect in the user interface. If the finger is positioned on the orange area, the related element on the screen (right, green arrow) is highlighted. When pushing the area, the item in the user interface is selected.

The problem is that as touch technologies are changing and improving, it is important to verify if enhancements in the technology as well as the material still lead to the same impact on usability and how such novel touch concepts are perceived in terms of user experience (UX).

Main research question was to understand if usability effects like improvement of time taken for the completion of the task still holds, and what type of user experience is associated to such an interaction. In terms of UX enhancement a set of animations was investigating looking for possible improvements of UX. A controlled experiment was performed to answer these questions.

In the following, the article shows the current state of the art on touch interaction (that is indirect and/or absolute) in terms of usability. Then the method is described, followed by results and a discussion of the results. The article concludes by a more general discussion on how to change user-centered design and development processes to take into account the replication of findings based on technology change.

2

Related Work

Using Touch for Controlling User Interfaces via a Distance

Direct touch interaction on a screen is becoming a de-facto standard for interactive systems like mobile phones or tablets. While touch interaction with direct and immediate feedback on the area you touched is taken up quickly, the usage of touch to control elements on a distant screen is perceived as less usable [START_REF] Kim | Comparing relative and absolute touch input for remote controls[END_REF]. While usability seems to be lower, industry [START_REF] Pirker | Investigating usability and user experience as possible entry barriers for touch interaction in the living room[END_REF] claims that using touch elements as control elements for interaction on a distant screen enhances user experience. Such elements of (technological novel) touch input for distant screens is currently considered for in-car systems for secondary driving tasks, for in-home applications like interactive TV and even for aircraft cockpits.

The traditional solution for any task including navigation, selection, or in general interaction with a visual display from a distance are buttons, knobs or sliders [START_REF] Pirker | Investigating usability and user experience as possible entry barriers for touch interaction in the living room[END_REF]. A recent trend is the incorporation of touch as means of interaction, ranging from using tablets to interact with large displays [START_REF] Avellino | Accuracy of Deictic Gestures to Support Telepresence on Wall-sized Displays[END_REF] to incorporating touch elements in cars, especially for secondary tasks while driving [START_REF] Sheik-Nainar | Force-Enabled TouchPad in Cars: Improving Target Selection Using Absolut Input[END_REF]. Touch interaction for distant screens or displays is different from the direct touch interaction known from mobile phones, tablets or touch screens, as the touch input is performed on an area dissociated from the output area, typically a distant screen.

For touch interaction on a distant screen there are in general two ways to map the user input to the movement on the distant screen: absolute and relative. Absolute mapping is defined as a homothetic correspondence between the position of a contact on the input surface and the position of an object on the output display [START_REF] Gilliot | Impact of Form Factors and Input Conditions on Absoute Indirect-Touch Tasks[END_REF]. In other words, it is a position-to-position and velocity-to-velocity mapping between the input and output device [START_REF] König | Adaptive pointing design and evaluation of a precision enhancing technique for absolute pointing devices[END_REF]. In contrast, relative mapping/pointing is the correspondence of the displacement on the input surface and the displacement of an object on the output display. It generally involves a non-linear transfer function to support fast movements over large distances and precise interactions with small objects [START_REF] Gilliot | Impact of Form Factors and Input Conditions on Absoute Indirect-Touch Tasks[END_REF]. Absolute pointing is claimed to be easier to learn [START_REF] König | Adaptive pointing design and evaluation of a precision enhancing technique for absolute pointing devices[END_REF], and to be more natural and convenient; however, absolute pointing also has disadvantages.

Absolute pointing could lead to parallax error [START_REF] Bieber | Screen Coverage: A Pen-Interaction Problem for PDA's And Touch Screen Computers[END_REF], or perception error due the apparent shift of the interaction area against a background when the observer position is not aligned with the device. It could also lead to occlusion effects -when interacting, the finger, hand and/or arm can hide a part of the output device and can even totally occlude small targets [START_REF] Roudaut | TapTap and MagStick: Improving One-Handed Target Acquisition on Small Touch-screens[END_REF]. Forlines et al. [START_REF] Forlines | HybridPointing: Fluid Switching Between Absolute and Relative Pointing with a Direct Input Device[END_REF] report that absolute touch interaction is uncomfortable on large displays and/or during long use. Relative pointing is said to be less natural than absolute pointing and more difficult to learn, but on the contrary it allows speeding up the interaction as different transfer functions can support movement over longer distances [START_REF] Gilliot | Impact of Form Factors and Input Conditions on Absoute Indirect-Touch Tasks[END_REF].

Touch as interaction technique to interact with user interfaces on distant screens has been discussed controversially for different application domains, including the television [START_REF] Pirker | Investigating usability and user experience as possible entry barriers for touch interaction in the living room[END_REF], automotive [START_REF] Pfeiffer | A multi-touch enabled steering wheel: exploring the design space[END_REF] or aeronautic [START_REF] Hamon | Multi-Touch interactions for control and display in interactive cockpits: issues and a proposal[END_REF] domains.

Compared to other types of interactions, e.g. input elements like knobs, sliders or other forms with haptic feedback, a set of disadvantages is reported for touch interactions:

 Touch misses the dimension of immediate haptic feedback [START_REF] Zimmermann | I feel it in my fingers: haptic guidance on touch surfaces[END_REF].

 Touch was reported to the less efficient [START_REF] Pirker | Investigating usability and user experience as possible entry barriers for touch interaction in the living room[END_REF] for selection and navigation tasks.  Touch was reported to be less effective [START_REF] Pirker | Investigating usability and user experience as possible entry barriers for touch interaction in the living room[END_REF] for selection and navigation tasks.

On the other hand, touch interaction is increasing user experience, especially the overall hedonic quality and the user's need for novelty in a product or novelty of an interaction technique, compared to standard interactions like buttons [START_REF] Pirker | Investigating usability and user experience as possible entry barriers for touch interaction in the living room[END_REF].

2.2

Absolute indirect touch.

Absolute indirect touch is the use of one-to-one mapping between a separated touch input device and a distant display.

Norman & Norman [START_REF] Norman | Comparison of Relative Versus Absolute Pointing Devices[END_REF] compared the use of a Nintendo Wii Remote for a selection task in three different conditions. The first condition was absolute pointing using an infrared camera to detect the movement, the second one was stabilized absolute pointing using the camera coupled with a 6-axis accelerometer, and the last one was relative pointing using only the gyroscope. They conclude that the advantage of absolute pointing compared to relative pointing is its intuitiveness. However, in their study relative pointing showed better performance and users preferred relative pointing to absolute pointing. The intuitiveness stems from the direct mapping users learn during all their live. König et al. [START_REF] König | Adaptive pointing design and evaluation of a precision enhancing technique for absolute pointing devices[END_REF], who proposed a precision enhancing technique for absolute pointing devices, confirm the hypothesis that absolute pointing is a more natural and more convenient pointing experience, as it provides easier hand-eye coordination compared to relative pointing. However, König et al. pointed out the common problem shared by all absolute indirect pointing approaches, which is the missing precision -especially when using high resolution displays.

Gilliot et al. [START_REF] Gilliot | Impact of Form Factors and Input Conditions on Absoute Indirect-Touch Tasks[END_REF] investigated the influence of form factors on absolute indirecttouch pointing performance in two studies. In the first one, they compared two different screen sizes (196 x 147 mm, 66 x 50 mm) and two visual conditions (looking at the input device, not looking at the input device). They found that users get better performances when they can look at the input surface, and that scale does not affect user performance. In the second experiment, they compared several aspect ratios between the input and the output device, and they conclude that the same aspect ratio leads to better performance.

Pietrosek and Lank [START_REF] Pietroszek | Clicking Blindly: Using Spatial Correspondence to Select Targets in Multi-Device Environments[END_REF] investigated spatial correspondence between a smartphone screen and a projection screen to select targets. They investigated two different conditions. In the first one, the desired target was displayed on the projection screen and on the smartphone screen, while in the other condition the desired target was only displayed on the projection screen. They found out that error rate was 3.5% (of screen width) when the target was mirrored on the smartphone screen, while it doubled to around 6% when the target was only displayed on the distant screen.

Palleis and Hussmann [START_REF] Palleis | Indirect 2D Touch Panning: How Does It Affect Spatial Memory and Navigation Performance[END_REF] explored the effect of touch indirectness on spatial memory and navigation performance in a 2D panning task. Comparing direct absolute touch to indirect absolute touch, they found out that spatial memory performance is not decreased by a spatial separation of touch input gesture and visual display, and also that decreasing the size of the input surface increases navigation efficiency.

For the automotive domain, Sheik-Nainar et al. [START_REF] Sheik-Nainar | Force-Enabled TouchPad in Cars: Improving Target Selection Using Absolut Input[END_REF] compared three different touch interaction techniques for target selection for drivers in cars: direct absolute pointing, indirect absolute pointing and indirect relative pointing. Their study revealed comparable performance for absolute indirect touch and absolute direct touch in terms of efficiency, effectiveness, distraction, and user preferences. Compared to relative indirect input, absolute indirect input showed better performances, lower distraction and higher user ratings.

For interaction with large displays the ARC-Pad [START_REF] Mccallum | ARC-Pad : Absolute+Relative Cursor Positioning for Large Displays with a Mobile Touchscreen[END_REF] is an indirect interaction technique for interacting with large displays using a mobile phone's touchscreen. It combines absolute and relative pointer positioning. Tapping with ARC-Pad roughly positions the cursor to the corresponding location on the distant screen, using an absolute mapping. Then the user can adjust the cursor location by sliding her finger on the touchscreen, using a relative mapping. This technique reduces clutching by half compared to a cursor acceleration technique.

Tactile and Visual Feedback in Touch Interaction

Bruke et al. [START_REF] Bruke | Comparing the Effects of Visual-Auditory and Visual-Tactile Feedback on User Performance: a Meta-Analysis[END_REF] compared the effect of visual-auditory and visual-tactile feedback on user performance in a meta-analysis of 43 studies. They selected studies that reported at least one comparison between single modes and multimodal combinations, and that reported a measure of error rate, reaction time, and/or performance score outcome. They found that visual-tactile feedback provides a significant advantage over using a visual-only feedback system, and that visual-tactile feedback is particularly effective when multiple tasks are being performed, and under normal workload condition. Another finding of this meta-analysis is that while multimodal feedback seems to enhance performance, improving performance scores and reducing reaction times, it has little or no effect on error rate.

Pasquero and Hayward [START_REF] Pasquero | Tactile Feedback Can Assist Vision During Mobile Interactions[END_REF] investigated the use of tactile feedback in the task of scrolling through a long list of items. They conducted a study with two different conditions -in the control condition, no tactile feedback was provided, while in the experimental condition, a short tactile feedback was provided when the user moves from an item to another, and a longer tactile feedback was provided every 10 items. They measured the frequency at which users needed to look at the screen. They observed an average reduction of 28% in the number of glances that the users required to complete a task with tactile feedback compared to the number of glances that the users required to complete a task without tactile feedback.

Treskunov et al. [START_REF] Treskunov | Active Haptic Feedback for Touch Enabled TV Remote[END_REF] investigate how haptic feedback affects the user experience of a touchpad-based television remote. They conducted two user studies with two haptic prototypes. A pilot study with eight users, employing smartphones to simulate a directional touchpad, revealed that users preferred enabled haptic feedback. Encour-aged by the results, they conducted a second study. In this study they use a touch remote control coupled with a Linear Resonant Actuator on the back of the remote. They compared three haptic conditions (5ms, 25ms, No Haptic). They did not find significant effects on time, error, or ratings. However, at the end of the study users were asked to choose which haptic condition they preferred, and although some participant did not make any distinction between the 5ms and the 25ms conditions, eight of the nine participants preferred haptic feedback over no haptic feedback.

HaptiCase [START_REF] Corsten | HaptiCase: Back-of-Device Tactile Marks for Eyes-Free Absolute Indirect Touch[END_REF] is an interaction technique for smartphones that provides back-ofdevice tactile marks that users sense to estimate the position of her finger in relation to the touchscreen. By pinching the thumb to a finger at the back, the finger location is transferred to the front as the thumb touches the touch screen. The study revealed that users were more accurate for eyes-free indirect typing with HaptiCase compared to having no tactile marks. The second study investigated the impact of tactile targeting on visual targeting, when both targeting strategies are combined. Users where both faster and had a lower offset to the target when being able to look at the input device compared to when they could not look at the input device. Guerreiro et al. [START_REF] Guerreiro | Exploring the Non-Visual Acquisition of Targets on Touch Phones and Tablets[END_REF] attached tactile marks on mobile devices' touch screens to guide blind people's interactions. It showed positive effects on the acquisition of targets on screen, and it was perceived as helpful by users.

Animations

Early work by Disney [START_REF] Thomas | Disney Animation: The Illusion of Life[END_REF] shows that Animations affect user experience in general. Chevalier et al. [START_REF] Chevalier | Animations 25 Years Later: New Roles and Opportunities[END_REF] revisited the pioneer work of Baecker and Small [START_REF] Baeker | Animation at the interface[END_REF] about the place of animation in interfaces. They concluded that user experience is the most important aspect for using animations. Merz et al. [START_REF] Merz | Perceived User Experience of Animated Transitions in Mobile User Interfaces[END_REF] investigated how different animation principles for animated transitions in mobile application influence the perceived user experience. They conducted a pilot study in which they compared three different animation styles: slow in and slow out, exaggeration, and linear. The results of this pilot study showed a tendency that animation style could affect the perception of UX.

Research Overview

Table 1 gives an overview on current literate related to the dimensions absolute and relative mapping, direct and indirect mapping and is complemented by the categories visual feedback, tactile feedback and animation. As highlighted with checkmarks, the contribution of this article is to understand how a combination of absolute indirect touch input with visual feedback and/or haptic feedback influences usability, and especially the overall user experience, as this dimension is not explored in the current literature.

The Problem of Touch Interaction with Haptic Marks

To support absolute touch interaction in situations where the screen is out of reach for the user, we developed a touch interaction element with haptic marks that can be applied in various contexts and domains, e.g. as an interaction element in the car to control secondary tasks while driving, in a cockpit for tasks where the pilot cannot reach the screen, or for standard applications like TV to be included in a remote control. Figure 1 shows some possible usages of such an absolute touch interaction element with haptic feedback. Contrary to absolute touch elements mapping the touch input to the user interface one to one (1:1), this touch interaction element has a number of fixed areas that can be varied depending on the constraints and necessities for the different domains, mapping the area on the touch input field absolute to the fixed area on the user interface. The number of elements on the touch input depends on the application area. For tasks with high cognitive load and risk, like in cars [START_REF] Sheik-Nainar | Force-Enabled TouchPad in Cars: Improving Target Selection Using Absolut Input[END_REF], there are only 3x3 fields, while for areas with less cognitive load, or more entertainment oriented applications like the TV or interactions on large screens, there are more fields (e.g., 4x3, 3x4, or larger), see also Figure 1.

The haptic marks support the user in achieving their goals by offering the opportunity to use them without having to look at them, as the haptic marks can easily be felt with the fingertips. As opposed to a flat touch area where the user has to evaluate the position of the pointer on the distant screen constantly, the haptic marks support ease of use, efficiency, and effectiveness by providing unobtrusive haptic feedback on the touchpad and simplify target acquisition on the distant screen. General goal of this research is to focus on touch interaction as an input for distant displays, such as television screens, car displays or aircraft displays. Put simply, we aimed to investigate whether haptic feedback ("to feel"), visual feedback ("to see"), or a combination of both are more important to the user, and how this affects usability and UX.

Research Question and Hypothesis

The research questions were the following: (1) How does the presence or the absence of haptic marks influence usability of the system and affect user experience? And (2) How does the presence or absence of animated visual feedback influence the usability and the overall user experience?

Hypothesis 1 (flat vs haptic marks):

There is a significant difference in terms of usability (efficiency, effectiveness, satisfaction) and user experience (naturalness, aesthetics, hedonic and pragmatic qualities) when using the flat touch interaction input element compared to using the touch interaction element with haptic marks.

Hypothesis 2a (visual feedback/no feedback):

There is a significant difference in terms of usability (efficiency, effectiveness, satisfaction and naturalness) and user experience (naturalness, aesthetics, hedonic and pragmatic qualities) when using a system with animated visual feedback compared to using a system without visual feedback.

Hypothesis 2b (visual feedback with three different curves):

There are significant differences in terms of user experience (naturalness, aesthetics, hedonic and pragmatic qualities) when using a system with animated visual feedback that uses ease in combined with easy out, a linear curve or only easy out.

Method, Participants and Procedure

A within-subject design was performed with 16 participants. The experiment consisted of two parts: in the first part of the experiment, the independent variables are the remote control and the feedback condition, while in the second part of the experiment, the independent variable consists of the type of animation used (cf. Tables 2 and3). Both parts of the experiment collected data about usability and user experience metrics using measures through observation and logging, standard questionnaires, short semi-structured interviews upon completion of conditions, as well as short interviews at the end of the experiment.

Sixteen participants (14 male and 2 female), aged from 21 to 25 years (mean = 23, SD = 1.41) took part in the study. The sample was a convenience sample recruited via Facebook, mailing lists and personal contacts. In order to avoid biases caused by a missing familiarity with touch interaction, we recruited young people, as they are more likely familiar with touch interaction. All participants use a touch device at least several times a week, and own either a smartphone or use a tablet at home. All of the participants were right handed, with normal or corrected to normal vision, and no participant indicated to be color blind. Daily TV consumption ranged from no TV usage to up to 4 hours -2 participants indicated to never watch TV (12.5%), 6 participants watch less than 30 minutes a day (37.5%), one participant up to an hour (6.3%), 4 participants up to two hours (25%), one participant up to 3 hours (6.3%), and 2 participants up to 4 hours (12.5%).

Independent Variable

Values Descriptions

Animation Curve

Ease In / Ease Out animation is slowed down at the beginning and the end, and sped up in-between Linear speed of the animation is constant the entire time Ease Out animation will speed up at the beginning and slow down at the end The daily smartphone usage ranged from no usage to more than 4 hours a dayone participants stated to not use a smartphone (6.3%), 2 participants use it up to an hour (12.5%), 4 persons use it up to 1.5 hours a day (25%), another four persons use it up to 3 hours (25%), while one person uses it up to 4 hours (6.3%). Finally, 4 persons indicated that they use their smartphone for more than 4 hours every day (25%).

System Information

In order to evaluate the touch element with haptic marks, two remote controls where produced: one included a standard touch interaction pad, while the other included haptic marks. Figure 2 shows the two remote controls used in the experimentation.

The driver software for both remote controls is identical, and both touch areas, regardless of the haptic marks, send information in a 12 byte array (for a 3 times 4 grid).

Each byte indicates how close the finger of the user is to the sensor on a scale from 0 to 255 for the given area -this allows interpolating the position of the user's finger on the touch grid. The only difference between the two remote controls is that the sensors of the flat touch area are slightly more sensitive to account for the differences in the height of the touch area without the recessed haptic marks: this implies the same sensor sensitivity for both remote controls. The user interface prototype consists of a page with 12 tiles (4 columns, 3 rows). During the experimentation dots appear pseudo randomized on the tiles. Users have to click on the corresponding area of the remote to select the indicated tile. Correct selections are indicated with a green checkmark, incorrect selection with a red cross on the item. Figure 3 shows the user interface for the different conditions. For the second part of the experiment, the user interface (UI) consisted simply of twelve areas with a set of TV channels (see Figure 4 below) and images simulating a TV channel displayed in the background.

Material

In the first part of the experiment, two versions of the prototypical UI were tested in order to provide two different feedback types for the condition that offers visual feedback within the user interface. The condition with feedback offered two visual clues for the interaction, which were a highlight of the corresponding tile in the UI when an area of the remote control was touched, as well as a temporary downscaling of the corresponding tile in the UI when an area of the remote control was pressed. The condition without feedback did not offer this visual feedback. The tiles in the UI have a square shape and occupy the maximum space on the screen, taking into account the gaps at the border and between two tiles (see Fig. 3).

The background of the prototype is medium gray, the tiles are black with a different opacity whether they are highlighted or not, and the dots are white. This choice of color was made to avoid any biases related any types to color blindness. The contrast between the dot and a tile is important (above 50%) even if the tile is selected.

For the second part of the study, the UI only changed in terms of animations used (see Table 3). A variation of the remote control with haptic marks was used, enhanced by two buttons (left/right) that allowed changing pages within the grid.

The experiment was conducted in a usability lab that resembles a living room. The room is equipped with a 40 inch TV with 4k resolution, two sofas, and a coffee table. Two cameras recorded each session, one behind the user to have an 'over-theshoulder' view of the interaction with the remote control and capture the use of the remote control, and the second one below the TV in front of the user to capture the facial expressions and posture of the user. The prototypical user interfaces used in the study were running on a small form factor computer behind the television to give the participants the impression that they are using a normal TV with a set-top box.

The experiment started with an introduction about the general goal of the study, followed by a demographic questionnaire that investigated the media consumption habits of the participants and a short pre-interview. Subsequently, participants were introduced to the user interface, and were asked to perform tasksthe selection of dots on the tiles of the UI for the four experimental conditions in the first part of the experiment, and the selection of specific channels in the UI for the three experimental conditions in the second part of the experiment. The experiment used a withinsubjects design, where each participant evaluated all four conditions for remote control and feedback in the first part of the study, and the three different conditions for the animations in the second part of the study. Condition order was randomized and counterbalanced within the sample, and each evaluation sessions lasted about 45 minutes.

For each task in each condition, task completion rate, task completion time, and number of errors were collected. After each condition, participants were asked for ratings regarding the ease of use of the system, how comfortable it is to use the system, how natural the use of the system was perceived by the user, how accurate the remote control was perceived, how smooth the interaction with the system was, how responsive the system was, and how pertinent and suitable the animations were for the given tasks. Additionally, the participants were filling in the SUS [START_REF] Brooke | SUS: a 'quick and dirty' usability scale[END_REF] questionnaire and the AttrakDiff questionnaire [START_REF] Hassenzahl | The interplay of beauty, goodness, and usability in interactive products[END_REF] after having completed the tasks for each condition.

After the two parts of the experiment, participants were asked which remote controls they preferred in terms of usage and in terms of design, as well as which one they perceived as more accurate in a closing interview. Test subjects did not receive any compensation for their participation.

Tasks

The selection task in the first part of the experiment consisted of a sequence of 24 dots that were randomly appearing on one of the 12 tiles of the user interface (two dots per tile per condition) that the participants needed to select as fast and as precise as possible. The procedure was repeated for each of the four experimental conditions (without visual feedback, and without haptic feedback (1); without visual feedback, and with haptic feedback (2); with visual feedback, and without haptic feedback (3); and with visual feedback, and with haptic feedback (4)).

The selection task in the second part of the experiment consisted of a sequence of eight channels that the user needed to select one after the other, again as fast and as precise as possible. The procedure was repeated for each of the three experimental conditions of the second part of the experiment (Ease In and Ease Out animation; Linear animation; Ease Out animation only).

Results

The data of the two parts of the experiment was analyzed with respect to the experimental conditions and the underlying research hypotheses.

Impact of Haptic Marks and Visual Feedback on Usability

Usability: Task Completion Time.

Haptic marks on the remote control have a significant influence on users' performance: when using the remote control with haptic marks, users were faster in terms of task completion (flat: mean = 00:02.29; haptic marks: mean = 00:01.30) which is statistically significant: a Mann-Whitney test indicated that task time was significantly faster for the remote control with haptic marks (Mdn = 00:01.00) than for the flat remote control (Mdn = 00:01.30; U = 194823,5 p = .000).

Providing visual feedback increases the task completion time from 00:01.55 to 00:02.03. A Mann-Whitney test indicated that task time was significantly faster for the No-Feedback condition (Mdn = 00:01.00) than for the Feedback condition (Mdn = 00:01.30;U = 206449, p = .000). This is in line with previous findings that people tend to wait until the visual feedback is over, but feedback is important for such types of tasks in case of interruptions [START_REF] Bruke | Comparing the Effects of Visual-Auditory and Visual-Tactile Feedback on User Performance: a Meta-Analysis[END_REF]. Usability: User Ratings of the Interaction.

Haptic marks do furthermore significantly influence users' ratings and perceptions on the following dimensions: perceived speed, perceived likelihood for errors, perceived difficulty, comfort, naturalness, accuracy, smoothness and responsiveness. Table 4 gives an overview on these results. Usability: Impact of Visual Feedback.

The Feedback/No Feedback condition yielded significant results for perceived comfort (Mdn: 3 for no-feedback; Mdn: 2 for feedback), perceived naturalness (Mdn: 2 for no-feedback; Mdn: 1.5 for feedback), as well as pertinence of the animation (Mdn: 2.5 for no-feedback; Mdn: 1.0 for feedback), where the scale was ranging from 1 being best to 5 being worst. Additionally, also attractiveness scored significant results (Mdn:.71 for no-feedback; Mdn: 1.0 for feedback) on a scale from -3 (worst) to +3 (best). The Feedback/No Feedback condition did not yield significant results for speed feeling, error rate feeling, perceived difficulty, perceived accuracy, perceived smoothness, perceived responsiveness, success percentage, and both hedonic quality identification as well as stimulation.

Interaction Effects.

There was no statistically significant interaction effect between the feedback condition and the type of remote control used on the combined dependent variables, F(14, 47) = 1.390, p = .196; Wilks' Λ = .707. A Kruskal-Wallis H test showed that there was a statistically significant difference in pragmatic quality as well as attractiveness between the different study conditions. No difference has been observed in the variables for perceived smoothness, perceived responsiveness, hedonic qualityidentification, as well as hedonic qualitystimulation between the different study conditions (see Figure 5 for AttrakDiff metrics for the different study conditions).

Impact of Animation Type

Statistical analysis compared usability and user experience metrics of the different animation conditions of the second part of the study. There were no significant differences in the scores for the usability and user experience metrics between the conditions 'Ease In / Ease Out', 'Linear', and 'Ease Out', except for error count between the 'Linear' and the 'Ease Out' condition which was significantly higher for the 'Linear' condition -Mann Whitney U = 88, N = 32, Z = -2.104, p = .035, r = .37. These results might also be biased by channel logos unfamiliar for the user, as most of the time, errors were related to confusing channel logos.

Final Interview

In the closing final interview, twelve of the sixteen participants stated they preferred the remote control with the haptic marks (75%), while four participants stated to prefer the flat remote control (25%). Users were also asked whether they have perceived a difference between the test sessions of the second part of the experiment, where only the animation types changed between the tasks. The majority of participants (10 persons) indicated that they did not recognize differences, while 6 persons stated they perceived differences. The differences that the users observed were related to the speed (4 persons), the fluidity (1 person), and the change of the page on the UI (1 person).

Finally, participants were asked if they preferred one session over the others in the second part of the study. Seven of the 16 participants did not state any preferences four participants preferred the Ease In / Ease Out session, three persons preferred the Ease Out session, while two persons stated to prefer the Linear animation session.

Summary

Our study shows that using haptic marks significantly improves usability and some aspects of user experience. Usability indicators showed significantly better scores for the haptic landmark remote control (faster for task completion; higher perceived speed, lower perceived likelihood for error, lower perceived difficulty, more accurate, more responsive). These findings were supported by the ratings for pragmatic quality in the AttrakDiff questionnaire which were significantly better.

In terms of user experience the haptic marks influence the users' perceptions on comfort, naturalness and attractiveness. The sub-dimension hedonic quality of the At-trakDiff questionnaire with its sub-dimensions stimulation and identification did not yield significant results. A possible explanation is that the type of task is too narrow and the prototype user interface to limited in terms of functionality to allow the investigation of UX. In similar studies of interactive TV systems using a broader range of tasks we were able to show influences on UX by manipulation type of interaction technique [START_REF] Pirker | Investigating usability and user experience as possible entry barriers for touch interaction in the living room[END_REF].

Our second hypothesis regarding the influence of visual feedback on usability and user experience was limited verified. For the usability metrics, we did not observe significant differences between the feedback/no-feedback conditions except for the task time, which was significantly slower with feedback than without it, which is in line with previous findings that people tend to wait for animations to finish. Pragmatic quality in the AttrakDiff was close to being significant (.052), but not within the 95% confidence interval.

Concerning user experience, the visual feedback conditions did not yield significant differences regarding the hedonic quality dimension, which could be again explained by the fact that the type of task is too narrow and the prototype user interface to limited in terms of functionality to allow the investigation of UX, but we observed significant results for perceived comfort, perceived naturalness, as well as attractiveness. This indicates that visual feedback has a positive impact on some aspects of UX.

Variations in terms of animation speed curves during the second part of the experiment did not show significant differences in terms of usability or user experience. This could be explained by a selective perception bias. Users were asked to find channels without any information about changes in terms of animation. The majority of them were likely so focused on finding the right channels, that they did not realize the change of animation. This assumption is consistent with the final interviews, where the majority of participants stated that they did not observe differences between the three sessions, and also no clear favorite was noticeable when the participants were asked for their preferred session.

The results of our experiment suggest that touchpads enhanced with haptic marks are a possible solution to overcome current limitations of touch. It also indicates that even if visual feedback was not as significant as tactile feedback, it still has an impact on UX, and should be taken into account when it comes to absolute indirect touch interaction design.

We acknowledge that the mean age of our sample is quite young. This was chosen on purpose, as we were aiming for a high familiarity with touch devices and smartphones.

6

Discussion and Future Work

In Software engineering, processes have been tuned and adapted to take into account specific software qualities such as safety [START_REF] Basnyat | Formal socio-technical barrier modelling for safety-critical interactive systems design[END_REF], reliability [START_REF] Martinie | A development process for usable large scale interactive critical systems: application to satellite ground segments[END_REF], learnability [START_REF] Martinie | Model-based training: an approach supporting operability of critical interactive systems[END_REF] or usability [START_REF] Palanque | A model-based approach for supporting engineering usability evaluation of interaction techniques[END_REF]. One issue with these contributions is that focusing on improving a specific property might damage other ones are they are usually conflicting [START_REF] Fayollas | FORMEDICIS. QBP Notation for Explicit Representation of Properties, Their Refinement and Their Potential Conflicts: Application to Interactive Systems Pages[END_REF]. Beyond, what is missing in all of these processes are clear indications of when and how to re-evaluate scientific findings, due to technology changes. For instance, while the process presented in [START_REF] Navarre | A Tool Suite for Integrating Task and System Models through Scenarios[END_REF] allows integrating evaluation results (through scenarios) into task models, the integration of a pure repetition of evaluations is not considered. This missing re-confirmation and replication of knowledge can be a threat for the scientific community. As user centered design and development (UCD) approaches require iterative design and detailed evaluation at each iteration step [START_REF] Gulliksen | Usability Design: Integrating User Centered System Design in the Software Development Process[END_REF], it means that evaluators' work is not well supported as it is difficult to compare evaluation results from different UCD stages.

In this particular case it became clear that conflicting software properties like users judgment on usability and user experience were aligned, but that traditional approaches for enhancing the user experience (animations) did not impact the judgment of the users. Thus, an advancement in this field should look more on the haptic feedback, than on any type of visual feedback, which is outside of the mainstream approaches currently applied in the field.

For the indirect absolute touch interaction itself, future work will focus on the investigation of the technology with a larger set of users that includes a broader variety of tasks to better address the UX dimension. In terms of technology the haptic touch remote control will be enhanced with different elements, like a relative touch element, in order to enrich the interaction technique by combining the advantages of both mappings.

On a longer term we intent to investigate an automotive application of the haptic touch element. We will adapt our solution to this different context e.g. using less fields. And we will conduct a secondary-task experiment and investigate the effect of the haptic marks on user attention, cognitive load, and usability. Based on the current results, we expect that haptic marks will reduce distraction and provide a more eyesfree experience than other touch-based user interface that are currently on the market.

Concerning the integration of replication studies and continuous evaluation of upcoming technologies a series of investigation in industrial (design) oriented context is underway to develop enhanced user-centered design and development processes that will be able to integrated a set of software qualities, including usability, user experience, reliability, safety and security. This work will conclude efforts that are on the way for more than 10 years [START_REF] Palanque | Beyond usability for safety critical systems: how to be sure (safe, usable, reliable, and evolvable)[END_REF].

Fig. 1 .

 1 Fig. 1. The touch interaction element on a remote control (left) or on a driving wheel (middle).If the finger is positioned on the orange area, the related element on the screen (right, green arrow) is highlighted. When pushing the area, the item in the user interface is selected.

Fig. 2 .

 2 Fig. 2. Touch interaction element with haptic marks integrated in a remote control (left) and without haptic marks (right)

Fig. 3 .

 3 Fig. 3. User Interface with correct selection (left) and incorrect selection (right)

Fig. 4 .

 4 Fig. 4. User interface with twelve areas showing TV channels

Fig. 5 .

 5 Fig. 5. Means of UX metrics (for study conditions)

Table 1 .

 1 Overview on the state of the art summarizing contribution on touch research for usability and user experience. The highlight marks the contribution area of this article

		Effectiveness Efficiency	Satisfaction UX	Naturalness
	Absolute mapping	[9, 12, 13, 18, 22, 25, 28, 29, 31, 34, 36]	[9, 12, 13, 18, 22, 25, 36] 28, 29, 34,	[13, 18, 22, 34, 36] 25, 28, 29,	[36]	[18]
	Relative mapping	[22, 25, 34]	[22, 25, 34] [22, 25, 34] [36]
	Direct	[9, 13, 28,	[9, 13, 28,	[9, 13, 28,
	pointing	29]	29]	29]
	Indirect pointing	[9, 12, 18, 22, 25, 28, 31, 34, 36]	[9, 12, 18, 22, 25, 28]	[9, 18, 22, 36] 25, 28, 34,	[28]	Missing
	Visual feedback	[6, 9, 12, 31] [6, 9, 12]		Missing	Missing
	Tactile feedback	[6, 9, 13, 29, 36]	[6, 9, 13, 29, 36]	[9, 11, 36].	Missing	Missing
	Animation [19]	[19]	[8, 19]	[8, 19, 23]	[7, 19]

Table 2 .

 2 Conditions for the first part of the experiment based on the two independent variables

	Independ-	Values	Descriptions
	entVariables
		With haptic marks	12 distinct debossed areas
	Type of
	touchpad	Flat	No distinction between the areas, flat touch area
			Highlighting of tiles on
		With visual feedback	touch. Downscaling of tiles
	Visual feedback		on press.
		Without visual feedback	Control Condition

Table 3 .

 3 Second system's independent variables & values for the second part of the experiment

Table 4 .

 4 User ratings: mean value with/without haptic marks and description of the performed test. Mean on scale 1 to 5, 1 being best.

		Haptic,	Non-Haptic,	Mann-Whitney U,
		Mean (SD),	Mean (SD),	p (2-tailed)
		N=32	N=32
	perceived speed	1.59 (.134)	2.69 (.176)	U = 210 p = .000
	perceived likelihood for	1.34 (.085)	3.06 (.185)	U = 97,5 p = .000
	errors
	perceived difficulty	1.47 (.090)	2.75 (.191)	U = 177,5 p = .000
	comfort	2.06 (.155)	2.91 (.192)	U = 292 p = .002
	naturalness	1.50 (.110)	2.69 (.187)	U = 196 p = .000
	accuracy	1.72 (.157)	3.28 (.181)	U = 132,5 p = .000
	smoothness	1.75 (.156)	1.94 (.195)	U = 477 p = .613
	responsiveness	1.47 (.142)	1.81 (.158)	U = 389 p = .065
	4.2

Impact of Haptic Marks/Visual Feedback on User Experience User Experience:


José Luís Silva
email: jose.l.silva@m-iti.org

J C Silva
email: jcsilva@ipca.pt

Graphical User Interface Redefinition Addressing Users' Diversity

Keywords: Engineering Interactive Computing Systems, Graphical User Interface redefinition, Diversity Inclusion, Design Guidelines, Affective Computing

Improvements can still be made in the development of Interactive Computing Systems (ICSs) aiming to ease their use. This is particularly true when trying to address users' diversity. Most ICSs do not adjust themselves to the user nor consider user's particularities. However, some provide solutions to address better specificities of expert and novice users. Others adjust themselves based on user's interaction history, but this does not always lead to improvements in use. An aspect that prevents to address users' diversity broadly is the fact that most of existing ICSs do not provide source code access. This means that only owners can introduce improvements on them. This paper proposes an approach (based on both affective computing and computer vision) to broadly improve design for diversity (without source code access) for both existing and to be developed ICSs. The results are twofold: i) example of an initial set of design guidelines; ii) opens the way to runtime Graphical User Interface (GUI) redefinition and adjustment based on both user's features and emotions reducing therefore designers' restrictions when addressing users' diversity.

Introduction

User interfaces (UIs) are a central aspect in any ICSs and critical for user's acceptance. According to the life cycle of a technology presented by Norman [START_REF] Norman | The invisible computer: Why Good Products Can Fail, the Personal Computer Is So Complex, and Information Appliances Are the Solution[END_REF] there is a transition point where technology satisfies basic needs and customers are much more interested in efficiency, pleasure, and convenience. Therefore, UIs associated with a technology should be adjusted along time to meet user's expectations. Adjustment along time is also important while designing UIs because user's specificities are not always static, they change over time.

Even with the advances of user-centered approaches, design (e.g. universal design [START_REF] Law | A systematic examination of universal design resources: part 1, heuristic evaluation[END_REF]) and usability (e.g. universal usability [START_REF] Huh | Designing for all users: including the odd users[END_REF][START_REF] Shneiderman | Universal usability[END_REF]) issues persist [START_REF] Ruzic | Universal Design Mobile Interface Guidelines (UDMIG) for an Aging Population[END_REF]. According to Meiselwitz et al. [START_REF] Meiselwitz | Universal usability: Past, present, and future[END_REF] the challenges to achieve universal usability are associated to gap in users' knowledge and both technological and user diversity. Several approaches have been developed to take diversity into account when developing ICSs. Some consider that universal solutions should be considered while others ponder the use of specific designs targeted to specific user profiles as a way of embracing users' diversity. Both approaches have advantages and disadvantages. In one hand, designing for all users pose several challenges. One of the biggest challenges pointed out by Huh et al. [START_REF] Huh | Designing for all users: including the odd users[END_REF] is finding the right balance between supporting all users and bringing enough profit to the designers. This is related to the fact that extreme users tend to be easily ignored due to their small number or simply because their existence is not always known. In the other hand, design for specific users or situations might deal better with extreme users but usually at the expense of compromised universality/globality. This paper outlines a generic approach that allows the application of specific design guidelines to any individual or set of ICSs at runtime. The approach is based on the analysis of the graphical user interface (GUI) using both computer vision-based (Sikuli-based [START_REF] Yeh | Sikuli: using GUI screenshots for search and automation[END_REF]) and affective computing-based approaches. Therefore, this allows the approach to be generic and without the need for ICS(s)' source code access. This enables developers and designers to improve the use of existing ICSs by empowering them to redefine existing GUIs and, consequently providing support for a wider diversity design inclusion. GUI adaptation without source code access poses several challenges as the information access and interaction should be made using computer vision-based techniques. In addition, the addressed GUI should be hidden or augmented to cope with the introduced modifications.

The article is structured as follows. Section 2 describes background concepts and presents some related research. Section 3 presents the proposed approach illustrated with an example in Section 4. Finally, discussion and conclusions are presented in Sections 5 and 6.

Related Work

Developing ICSs that address diversity of users pose several challenges. The term "universal design" describes the concept of designing all products to be ideally usable by everyone. Universal usability [START_REF] Shneiderman | Universal usability[END_REF] was introduced with the goal of facilitating the use of interfaces. From those concepts several principles, guidelines, heuristics and standards were developed [START_REF] Shneiderman | Shneiderman's eight golden rules of interface design[END_REF][START_REF]Ergonomics of human system interaction-Part 110: Dialogue principles[END_REF][START_REF] Iso | Ergonomics of Human-system Interaction: Principles and requirements for physical input devices[END_REF]. However, those approaches are sometimes not sufficiently complete to meet usability needs of specific users [START_REF] Ruzic | Universal Design Mobile Interface Guidelines (UDMIG) for an Aging Population[END_REF]. They might even be contradictory [START_REF] Pak | Designing displays for older adults[END_REF].

Those challenges lead to the proposal of a new set of solutions to support diversity mostly based on computer vision. The ISI (Interactive Systems Integration) tool [START_REF] Silva | Make it ISI: interactive systems integration tool[END_REF] enables the integration of several GUIs of different ICSs into one new GUI adapted to user's characteristics. However, features such as collecting the state of the original GUIs are still primitive. The work of Dixon et al. enables the identification of some GUI widgets [START_REF] Dixon | Content and Hierarchy in Pixel-Based Methods for Reverse Engineering Interface Structure[END_REF][START_REF] Morgan Dixon | Prefab Layers and Prefab Annotations: Extensible Pixel-Based Interpretation of Graphical Interfaces[END_REF]. From this identification it is possible to build GUI pixel-based enhancements [START_REF] Dixon | Content and Hierarchy in Pixel-Based Methods for Reverse Engineering Interface Structure[END_REF]. One example presented by the authors is the automatic translation of a GUI using Prefab, a tool using computer vision algorithms. The approach provides GUI pixel-based enhancements (to a set of GUI widgets) but not its redefinition. We argue that supporting attentive real-time GUI redefinition is of major importance to foster design for diversity. Other works [START_REF] Krzysztof | Automatically generating personalized user interfaces with Supple[END_REF][START_REF] Krzysztof | Improving the performance of motor-impaired users with automatically-generated, ability-based interfaces[END_REF] like SUPPLE [START_REF] Gajos | SUPPLE: automatically generating user interfaces[END_REF] enable automatic GUI generation adapted to a person's specificities but it does not enable GUI redefinition of existing ones.

Several solutions from the computer vision field provide basis for GUI's widgets identification (e.g. OpenCV1 , CVIPtools 2 ). For example, neural networks YOLO [START_REF] Redmon | YOLO9000: better, faster, stronger[END_REF] is a real-time object detection solution that can detect over 9000 object categories from an image or video. Unfortunately, it was not applied to GUI widgets. We believe that this approach can be successfully applied to support GUI redefinition, but we are unware of any work with this purpose or any annotated GUI widgets database essential for this purpose.

Emotion has gain importance in Human-Computer Interaction. Affective Computing [START_REF] Picard | Affective computing[END_REF] in particular addresses several challenges concerning with computers and emotions (e.g. ability to recognize and express emotions). The work of Tao et al. [START_REF] Tao | Affective computing: A review[END_REF] and Poria et al. [START_REF] Poria | A review of affective computing: From unimodal analysis to multimodal fusion[END_REF] provide an adequate review. Works in the area of affective interfaces consider emotion in the design (e.g. [START_REF] Cyr | Emotion and web site design[END_REF]). For example, the work of Mori et al. [START_REF] Mori | Design Criteria for Stimulating Emotions in Web Applications[END_REF] reports results that aim to improve the understanding about what design techniques are more important to stimulate an emotion on the user. Alexander et al. [START_REF] Alexander | Interfaces that adapt like humans[END_REF] outlined the plan for an interface that adapt like humans to the non-verbal behavior of users. The idea has similarities with our approach however our focus is on GUI redefinition based on user's emotions but also based on other user's features (e.g. disease, experience).

GUI Redefinition and Design Guidelines

Prior work done by Gaganpreet et al. [START_REF] Singh | Physiologically Attentive User Interface for Robot Teleoperation -Real Time Emotional State Estimation and Interface Modification using Physiology, Facial Expressions and Eye Movements[END_REF] developed an emotional state estimator that provides input for runtime GUI redefinition in the context of life critical robot teleoperation. This work is a complement to the Prefab's approach because users' emotions can be considered. However, the GUI redefinition is done manually case by case and without any guidelines.

Complementing those works enables a generic GUI redefinition for all approach fed by the user emotional state. This is beneficial because it enables designers and developers to keep existing design and source code but without preventing them to redefine the GUI to the diversity at runtime. Those advances might be further improved if user's specificities are considered. In addition, the development of a Design Guideline Provider (see Figure 1) suggesting automatic GUI redefinitions based on both emotional user's states and specificities represent also an improvement.

Figure 1 presents the architecture of our GUI redefinition approach. It is composed by three main components that enable the proposed redefinition. They are:

1.

Emotional State Estimator that identifies user's emotional states from their physical monitorization (e.g. via affectiva 3 and imotions 4 ); 2.

User's Specificities Identifier that identifies the user's profile and personality (Myers-Briggs Type Indicator 5 ) from the answers provided to the questionnaire and from results of the test task performed; 3.

Design Guidelines Provider that suggests design guidelines for the GUI redefinition based on the identified emotional states and user's specificities.

The output of the Design Guidelines Provider supports an automatic GUI redefinition at runtime. The old GUI is hidden running in a virtual machine and only the new GUI is presented to the user. We follow the approach made by Silva et al. [START_REF] Silva | Make it ISI: interactive systems integration tool[END_REF] to enable a transparent GUI redefinition for the user. Silva et al. developed ISI, a tool that enables the creation of a new UI abstraction layer integrating different ICSs without accessing their source code. The proposed integration aims to improve end user interaction. The tool uses enriched ConcurTaskTree models and selected scenarios to generate Sikuli scripts. Each script is then associated to a widget of the new GUI. The interaction with a widget of the new GUI triggers the execution of the associated Sikuli script that will perform the task on existing ICSs. This work enables an innovative approach that address diversity more effectively. For this an example of an initial set of guidelines (mapping between user's specificities / emotional state and redefinition rules) for the Design Guidelines provider are presented below.

Design Guidelines for some detected user's specificities:

1.

Novice: step by step with tutorial; 2.

Expert: automation; 3.

Parkinson: selection via gaze, increase size; 4.

Blind: translation rules; 5.

Deaf: augmented captions.

Design Guidelines for some detected user's emotional states:

1.

Frustrated: more effective interaction; 2.

Confused: clarification, more feedback; 3.

Stressed: use additional communication channels (e.g. scent, relaxing music) to appease the user; 4.

Overload: split information into different communication channels (e.g. visual, audio, haptic). This is only an example of initial set of guidelines. Machine learning algorithms will be developed to identify better guidelines based on the combination of the set of inputs detected (user's specificities and emotional states) and users' reaction. The resulting guidelines will be used as a basis for better automatic GUI redefinition.

We aim at enriching GUIs with emotional intelligence. This means that in the same way a person usually adapts to its interlocutor while interacting with him/her. Our approach enables a GUI to automatically adapt at runtime to the user that is interacting with it.

Example

This section as the purpose of illustrating the value of the approach with a concrete example where the opening for user diversity is made clearer.

Consider an application running on a tablet while its user is travelling by train. Due to the vibrations of the train the user becomes frustrated because he can't always hit the desired widget at the first attempt. In addition, the analysis of the interaction made revealed that the user has motor difficulties. Therefore, the input provided to our Design Guidelines provider (frustrated mental state and motor difficulties) lead to design guidelines suggestions such as:

• increase the size of icons;

• associate wrong clicks to the closer widget;

• enable gaze interaction. Those guidelines are then automatically applied at runtime for the GUI redefinition. The GUI is updated when user emotional state changes are detected.

Discussion

Most contributions tend to develop models, applications or technologies to improve the design and development of new and better ICSs. This work aims to facilitate the improvement of existing ones without accessing their source code. One can argue that (old) existing ICSs tend to disappear being replaced by new versions. The fact is that several systems or old versions are still in use today. Some of them will eventually be updated in the future but the remaining ones will not. This might be explained by two reasons: i) absence of updated versions; ii) the user does not update it.

Several ICSs do not enable personalization nor were designed to consider diversity. Furthermore, as integration is also considered, this approach enables the application of specific or universal solutions to the set of GUIs to be integrated. Ultimately, this can lead to a new way of designing and developing ICSs where they are used, as a whole, in task and user centered design approaches. For instance, several pieces of existing software with different purposes can be merged together into a new GUI where the goal is not to expose the functionalities of the system but rather use them to empower the user to accomplish easier tasks execution.

The design of GUIs to be run on top of existing ICSs raise implementation challenges but we believe that the advantages are strong:

1.

GUIs enhanced with emotional intelligence adjusting themselves to the user who is interacting with it; 2.

Enable design for diversity to be automatically applied at runtime to new and existing GUIs. Challenges of using computer vision-based techniques such as disambiguation in the identification of widgets can be reduced with anchors (UiPath6 software follow this method). Theme variations (e.g. color, text font, size) might introduce difficulties while running the Sikuli scripts. These can be reduced by introducing transparencies in the figures provided to the scripts.

It is important to note that, although some parts are already implemented, the presented approach is an ongoing work. The solution and guidelines must be evaluated with user studies. For instance, GUI runtime modifications in one direction can be fast when detecting user confusion but should be slow when the user emotional state is going back to user "normal" state. The identification of an adequate delay to be used in this case is an example of the importance that the user studies will have.

Conclusions

This paper presents an approach that aims at enabling developers and designers to change any existing GUI at runtime based on both user's specificities and emotional state. This will ultimately enable designing for diversity to be broadly applied. In addition, an example of a set of design guidelines based in this innovative approach is presented.

Fig. 1 .

 1 Fig. 1. GUI redefinition approach.

  3 affectiva.com (last accessed June 4, 2018).

  4 imotions.com (last accessed June 4, 2018). 5 psycnet.apa.org/record/2013-29682-000 (last accessed June 4, 2018).

opencv.org (last accessed June 4,

2018). 2 cviptools.ece.siue.edu (last accessed June 4, 2018).

uipath.com (last accessed July 4, 2018).

Acknowledgments

This work was supported from Fundação para a Ciência e a Tecnologia (FCT, Portugal), through project UID/EEA/50009/2013 and by ISTAR-IUL through project UID/MULTI/0446/2013.


T Richeton

Mechanical derivation of elastic constants of ε-martensite 1

Keywords: martensitic phase transformation, elastic behavior, micromechanical modeling, austenitic steels, anisotropic elasticity

This work presents direct formulas to compute the HCP elastic constants of ε-martensite from the FCC ones of austenite. The derivation is performed thanks to mechanical compatibility arguments while considering ε-martensite as a laminate structure of twinned and untwinned FCC phases. The formulas are applied to predict the elastic constants of several alloys and very good agreement with measurements is found. According to these relations, directional Young moduli of ε-martensite are most of the time stiffer than the austenite ones and the (0001) shear modulus is always greater than the (111) one, which hardens dislocation glide parallel to the interfaces.

The martensitic transformation γ (FCC) -→ ε (HCP) may occur in several crystalline materials during deformation or cooling. It can be observed in low stacking fault energy austenitic steels [GPH05, IRV + 09, BAS + 11], in Febased shape memory alloys [ST74, YW92, BGE97, NBL + 10] or in Co alloys [FD67, [START_REF] Weston | Cubic and hexagonal singlecrystal elastic constants of a cobalt-nickel alloy[END_REF][START_REF] Kaita | Plastic deformation mechanisms of biomedical cocrmo alloy single crystals with hexagonal close-packed structure[END_REF] for instance. The part of ε-martensite can be significant [START_REF] Gey | Electron backscattered diffraction study of ε/α' martensitic variants induced by plastic deformation in 304 stainless steel[END_REF], and the size and the distribution of martensitic constituents are primordial issues for the material in-use properties.

Elastic constants of ε-martensite are generally badly known for most materials, in particular in high manganese austenitic steels [BAS + 11, GMK + 11, PNM + 13]. Due to its lower ductility, a good understanding of the elastic behavior of ε-martensitic phase is actually even more important. The difficulty to measure accurately anisotropic elastic constants of a specific phase of an alloy arises typically from the impossibility to produce a single crystal with exactly the same composition. On the other hand, direct measurements on multiphase alloys involve the use of inverse methods, such as the self-consistent scheme, and suffer from the non-uniqueness of the solutions. However, the knowledge of elastic constants may be of prime importance for mechanical modeling of internal stresses through mean-field elasto-(visco)plastic approaches (e.g. [LBG + 18]), full-field crystal plasticity simulations (e.g. [REH + 10]) or investigations at the dislocation scale like evaluation of image forces on dislocations due to elastic mismatch between phases [PK94, JD18, CRCS19]. Furthermore, anisotropic elastic constants are also needed if one wants to estimate accurately local stresses from elastic strain measurements by diffraction (e.g. [KMRM94, WMD06, BBP + 14]). In particular, the load transfers between austenite and ε-martensite, generally stronger and harder [NBL + 10, BAS + 11], depend closely on the values of the elastic stiffnesses of each phase. The correct estimation of these load transfers is especially crucial to control damage resistance in steels.

The martensitic transformation γ (FCC) -→ ε (HCP) is reported to be due to the glide of a/6 11 2 Shockley partial dislocations on every second closepacked (111) γ plane, which corresponds to the introduction of a stacking fault in each second (111) γ plane (see Figure 1a) [IRV + 09]. As a result, the εmartensitic phase has the following crystallographic relationship with the γphase:

(111) γ (0001) ε , 11 2 γ 01 10 ε , 1 10 γ 2 11 0 ε (1)
which is known as the Shoji-Nishiyama orientation relationship [START_REF] Nishiyama | MartensiticTransformation[END_REF]. This process is actually very similar to the mechanism of Σ3(111) twin formation in FCC crystals which also occurs by glide of Shockley partials but on each successive (111) γ plane, resulting in the introduction of a stacking fault in each (111) γ plane (see Figure 1b). In Figure 1, it is seen that the crossing from an untwinned to a twinned FCC crystal is described by a sequence ABA which is also present in the HCP stacking sequence. As a consequence, it may be possible to consider the HCP ε-martensitic phase as a periodic laminate structure made of alternating twinned and untwinned FCC phases with equal volume fractions as pictured in Figure 2. Accordingly, the idea of the present work is to compute the elasticity tensor of ε-martensite as the effective elasticity tensor of a laminate composed of alternating twinned and untwinned FCC phases.

To perform this derivation, let first consider a general infinite periodic lam- Through consideration of strains compatibility and balance of linear momentum without body force, it can be shown that the Cauchy stresses σ I,II i are uniform in crystals I and II and that their expressions can be analytically derived [START_REF] Gemperlova | Compatibility stresses in deformed bicrystals[END_REF][START_REF] Richeton | Effects of heterogeneous elasticity coupled to plasticity on stresses and lattice rotations in bicrystals: a Field Dislocation Mechanics viewpoint[END_REF]. Denoting s ij the components of the elastic compliance tensor and using the contracted Voigt notation [START_REF] Voigt | Lehrbuch Der Kristallphysik[END_REF]

(11 → 1, 22 → 2, 33 → 3, 23 → 4, 31 → 5, 12 → 6) along with the notations [[s ij ]] = s II ij -s I ij and sij = f II s I ij + f I s II ij
, they may be written as [RB13, RTBB15, TRM + 15, Ric17]:

σ I i = Σ i + f II G ik [[s kj ]]Σ j σ II i = Σ i -f I G ik [[s kj ]]Σ j (2)
where the Einstein summation convention over repeated indices is used, indices range from 1 to 6 and the non-zero components of the symmetric tensor G ij read:

G 11 = s2 26 -s22 s66 /D , G 22 = s2 16 -s11 s66 /D , G 66 = s2 12 -s11 s22 /D , G 12 = (s 12 s66 -s16 s26 ) /D , G 16 = (s 22 s16 -s12 s26 ) /D , G 26 = (s 11 s26 -s12 s16 ) /D , with D = s22 s2 16 + s11 s2 26 + s66 s2 12 -s11 s22 s66 -2s 12 s16 s26 . (3)
By definition, the effective compliance tensor s ef f ij of the laminate structure satisfies ε i = s ef f ij Σ j where denotes a volume average. Hence, from relation 2, we have:

ε i = s il -f I f II [[s ij ]]G jk [[s kl ]] Σ l (4)
and then by identification, the effective compliance tensor may be expressed as:

s ef f ij = s ij -f I f II [[s ik ]]G kl [[s lj ]]. (5)
In order to retrieve the structure of ε-martensite as described in Figure 2, it is thereafter considered that the crystals have a FCC structure and that the interfaces correspond to Σ3(111) twin boundaries with I the parent phase and II the twin phase. The Zener anisotropy ratio A is then introduced in order to express the elastic compliance tensors of crystals I and II, s I,II ij , in the frame e 1 , e 2 , e 3 of Figure 2. By definition, A = 2 (s * 11 -s * 12 ) /s * 44 where s * ij designate the elastic compliances in the orthonormal axis system aligned with respect to the 100 directions of the cubic crystal. Without loss of generalization, it is supposed that e 1 is collinear to the twinning shear direction which corresponds to a 112 crystallographic direction, whereas e 3 is taken as the normal of (111) planes. Accordingly, s I ij is deduced from s * ij by the appropriate rotation and s II ij by a 180˚rotation of s I ij around e 3 [START_REF] Richeton | Analytical expressions of incompatibility stresses at Σ3(111) twin boundaries and consequences on single-slip promotion parallel to twin plane[END_REF]. As a result, the non-zero components of the symmetric tensor s I ij can be related to A as follows:

s I 11 = s I 22 = s * 11 - A -1 4 s * 44 s I 12 = s * 12 + A -1 12 s * 44 s I 13 = s I 23 = s * 12 + A -1 6 s * 44 s I 14 = -s I 24 = 1 2 s I 56 = √ 2 6 (A -1)s * 44 s I 33 = s * 11 - A -1 3 s * 44 s I 44 = 2(A + 1) 3 s * 44 s I 66 = A + 2 3 s * 44 (6)
whereas s II ij is identical to s I ij , except for the following components which have opposite signs:

s II 14 = -s II 24 = 1 2 s II 56 = -s I 14 (7)
Hence, many components of [[s ij ]] and s ij are zero, especially in the case of equal volume fractions which corresponds to the description of the ε-martensite structure made in Figure 2 where twinned and untiwnned phases have same volume. In this particular case, s ef f ij can be easily derived from Eq.5:

s ef f ij =         s * 11 -A-1 4 s * 44 s * 12 + A-1 12 s * 44 s * 12 + A-1 6 s * 44 0 0 0 s * 12 + A-1 12 s * 44 s * 11 -A-1 4 s * 44 s * 12 + A-1 6 s * 44 0 0 0 s * 12 + A-1 6 s * 44 s * 12 + A-1 6 s * 44 s * 11 -A-1 3 s * 44 0 0 0 0 0 0 3A A+2 s * 44 0 0 0 0 0 0 3A A+2 s * 44 0 0 0 0 0 0 A+2 3 s * 44         (8)
It is observed that s ef f ij is symmetric with respect to a rotation about e 3 , i.e. the effective medium is transversely isotropic for equal volume fractions. From the previous developed arguments, it seems relevant to use this transversely isotropic tensor to obtain a good estimation of the HCP elastic compliance tensor of ε-martensite, although such a procedure ignores of course the chemical processes at stake during the martensitic transformation, like diffusion of solutes or segregation of chemical elements.

The stiffness tensor is simply the inverse of s ef f ij . As a result, very simple and direct formulas that allow to get from the FCC elastic constants of austenite to the five independent HCP elastic constants of ε-martensite are obtained:

c HCP 11 = c * 11 + A 2 + 7A -8 3A(A + 2) c * 44 c HCP 12 = c * 12 + A 2 -5A + 4 3A(A + 2) c * 44 c HCP 13 = c * 12 - 2(A -1) 3A c * 44 c HCP 33 = c * 11 + 4(A -1) 3A c * 44 c HCP 44 = A + 2 3A c * 44 (9)
where c * 11 , c * 12 and c * 44 are taken in the orthonormal axis system aligned with respect to the 100 directions of the cubic crystal.

It is noteworthy that a previous procedure relating the elasticity tensors of HCP and FCC structures already existed. It was developed by Martin [START_REF] Martin | Relation between elastic tensors of wurtzite and zinc-blende structure materials[END_REF] for wurtzite (HCP) and zinc-blende (FCC) structure materials and then applied by Fuller and Weston to metallic structures [START_REF] Fuller | Relation between elastic-constant tensors of hexagonal and cubic structures[END_REF]. The starting point of their method is the construction of wurtzite and zinc-blende structures from tetrahedral building blocks whose corners lie along 111 directions [START_REF] Robinson | Relations between the components of the nonlinear polarisability tensor in cubic and hexagonal iivi compounds[END_REF]: for zinc-blende structure, tetrahedra are aligned in equivalent orientations and for wurtzite structure, tetrahedra are alternatively aligned in two mirror orientations [START_REF] Martin | Relation between elastic tensors of wurtzite and zinc-blende structure materials[END_REF][START_REF] Fuller | Relation between elastic-constant tensors of hexagonal and cubic structures[END_REF] which can be related to the frame e 1 , e 2 , e 3 and the associated twinned phase previously defined. Then, according to the procedure of Martin [START_REF] Martin | Relation between elastic tensors of wurtzite and zinc-blende structure materials[END_REF], the elastic constants of the wurtzite structure are deduced from the minimization of its elastic strain energy density U (computed as the average density of the two trigonal orientations) with respect to the difference of strains in the two trigonal orientations

[[ε i ]]: ∂U ∂[[ε i ]] = 0 (10)
As a result of this minimization, the following transformation formulas are obtained [START_REF] Martin | Relation between elastic tensors of wurtzite and zinc-blende structure materials[END_REF][START_REF] Fuller | Relation between elastic-constant tensors of hexagonal and cubic structures[END_REF]:

c HCP ij = c ij -[[c ik ]] c kl -1 [[c lj ]] (11)
The first term of the sum in Eq.11 is a simple average of elastic stiffnesses whereas the last term is called an internal strain contribution [START_REF] Martin | Relation between elastic tensors of wurtzite and zinc-blende structure materials[END_REF][START_REF] Fuller | Relation between elastic-constant tensors of hexagonal and cubic structures[END_REF]. This expression shares some similarities with the one of the effective compliance tensor (Eq.5), which is also composed of a first average term and a second one that depends on differences. It is nevertheless not strictly equivalent. It must be underlined for instance that in general s ij -1 = c ij . Actually, among the five independent elastic constants, the internal strain contribution of Eq.11 is non-zero for c HCP It can be easily checked that the results provided by Eq.11 are the same as the ones given by Eq.9, with the notable exception of c HCP 44 for which Eq.9 actually translates into c HCP 44 = c 44 . Precisely about c HCP 44 , Fuller and Weston [START_REF] Fuller | Relation between elastic-constant tensors of hexagonal and cubic structures[END_REF] noticed that the computed elastic constants are in better agreement with experimental measurements without considering the internal strain contribution and wrote "there is no basis for this except that it gives the correct pattern for the internal strain contributions". It is therefore worth underlying that the present work offers a rigorous mechanical justification and presents the formulas in a very simple form that allows straightforward applications. Furthermore, it is interesting to resume the different comparisons with measured constants performed by Martin [START_REF] Martin | Relation between elastic tensors of wurtzite and zinc-blende structure materials[END_REF] and Fuller and Weston [WG75] using Eq.9. Four materials, ZnS, Co-32wt.%Ni, Co and Tl, exhibiting the ε-martensitic transformation are thus considered in Table 1. HCP elastic constants are computed from Eq.9 considering experimentally measured values for the FCC constants and are compared with experimental values. It must be noticed however that the presented HCP and FCC experimental values refer to the exact same compound only for ZnS and Co-32wt.%Ni alloys. For pure cobalt and pure thallium, the HCP values are extrapolations derived from measurements of alloys of different compositions.

It can be observed that the agreement between the computed and the experimental values is pretty good. In all the cases, the differences between constants are always smaller than 10 GPa. For the two most reliable cases, ZnS and Co-32wt.%Ni, the relative errors are less than 7%, which can be considered within experimental errors.

From Eq.9, the elastic heterogeneity of a multiphase alloy composed of both γ-austenite and ε-martensite can be evaluated. Considering for instance typical values of elastic constants for austenitic steels, Fig. 3 displays the magnitude of the directional Young modulus of both phases in all the space directions. In Fig. 3, the anisotropy of the FCC phase is significant with A = 3.36 but it is seen that it is much less pronounced in the HCP phase. Along the normal to the γ/ε phase boundary which is parallel to 111 γ and 0001 ε , the value of the Young modulus is actually maximal and equal with E max F CC = E max HCP = 288 GPa. However, strong differences of Young modulus can be observed along other directions and it was checked that ε-martensite is much stiffer along a set of crystallographic directions representing a predominant part of the orientation space. In particular, the minimal value is much higher in ε-martensite, E min HCP = 172 GPa, than in austenite, E min F CC = 101 GPa. The fact that the Young modulus should be for most directions higher in ε-martensite is consistent with some local nanoindentation measurements in a Fe-based shape memory alloy which showed greater values of Young modulus and hardness in ε-martensitic grains compared to austenitic ones [NBL + 10].

Besides, it is noteworthy that ε-martensite variants can form lamellar structures within grains where γ/ε phase boundaries may act as obstacles to dislocation motion [YW92, GPH05, BAS + 11]. In such confined environment, dislocation glide parallel to interfaces is promoted due to less slip resistance (e.g. [DDR + 12]). As dislocation glide is also controlled by the value of the shear modulus of the slip plane, it is therefore worth comparing the values of the shear modulus in the (111) γ and (0001) ε planes. From Eqs.6 and 9, it is deduced that these shear moduli are isotropic within their planes and that they can be expressed as:

µ (111) γ = 3 2A + 1 c * 44 µ (0001) ε = A + 2 3A c * 44 (12)
Accordingly, their ratio can be written in an original manner only with re- Fig. 4 shows then that the variation of this ratio with A is symmetric around 1 in a log-log scale. From Eq.13 and Fig. 4, it is noticed that both shear moduli are equal for A = 1 but that µ (0001) ε is always greater than µ (111) γ otherwise. The increase of the shear modulus becomes significant as soon as A departs from unity. For instance, an increase of 37% is obtained for A = 3.36. Apart from other considerations, this finding indicates that it should be much more difficult to make dislocations glide along (0001) ε planes than along (111) γ ones, which is consistent with the observed pronounced hardening in presence of εmartensite variants [NBL + 10, BAS + 11]. Finally, and as already sated in the introduction, it is worth underlying that the elastic mismatch between austenite and ε-martensite could generate non-negligible incompatility stresses and image forces on dislocations.

Figure 1 :

 1 Figure 1: (a) FCC and HCP stacking sequences. (b) FCC stacking sequences for a perfect crystal and one with a twin plane (mirror symmetry). The red lines represent stacking faults in the FCC sequence. The common sequence ABA of the HCP and parent/twin structures is surrounded in orange.

Figure 2 :

 2 Figure 2: HCP stacking sequence seen as a periodic alternating structure of twinned and untwinned FCC phases and model of an infinite periodic laminate structure composed of two alternating crystals with different volume fractions.

  hand-side member of Eq.5 is non-zero only for s HCP 44 .

Figure 3 :Figure 4 :

 34 Figure 3: On the left, magnitude of the directional Young modulus of the FCC phase of an austenitic steel in all the space directions considering c * 11 = 197.5 GPa, c * 12 = 125 GPa and c * 44 = 122 GPa [Sau06]. On the right, magnitude of the directional Young modulus of the corresponding HCP phase computed from Eq.9. The vertical axis is aligned with the 111 γ and 0001 ε crystallographic directions, respectively.

Scripta Materialia 169 (2019) 14 -18, https://doi.org/10.1016/j.scriptamat.2019.04.042

Corresponding author. Tel.:+33

72 74 78 02, thiebaud.richeton@univ-lorraine.fr

Acknowledgements

This work was supported by the French State through the program "Investment in the future" operated by the National Research Agency (ANR) and referenced by ANR-11-LABX-0008-01 (LabEx DAMAS).