Rachel Blagojevic
email: rachel.blagojevic@auckland.ac.nz

Beryl Plimmer

CapTUI: Geometric Drawing with Tangibles on a Capacitive Multi-touch Display

Keywords: TUI, tangible, multi-touch, physical interaction, capacitive, drawing tools

We present CapTUI, an innovative drawing tool that detects tangible drawing instruments on a capacitive multi-touch tablet. There are three core components to the system: the tangible hardware, the recognizer used to identify the tangibles and the drawing software that works in tandem with the tangibles to provide intelligent visual drawing guides. Our recognizable tangible drawing instruments are a ruler, protractor and set square. Users employ these familiar physical instruments to construct digital ink drawings on a tablet in an intuitive and engaging manner. The visual drawing guides enhance the experience by offering the user helpful cues and functionalities to assist them to draw more accurately. A user evaluation comparing CapTUI to an application with passive tools showed that users significantly preferred CapTUI and found that the visual guides provide greater accuracy when drawing.

Introduction

CapTUI is an innovative drawing application for capacitive multi-touch tablets that detects tangible drawing instruments. To develop CapTUI we have designed and constructed tangibles, developed a recognizer to detect the tangibles on a capacitive touch display, and built drawing software that works in tandem with the tangibles to provide intelligent visual drawing guides.

A skill acquired very early in life is the ability to manipulate tangible objects. As a case-in-point, mathematics education has long used manipulatives for introducing young children to mathematical concepts as their intuitive understanding of the physical enables them to transition into the realm of the conceptual [START_REF] Marzola | Using Manipulatives in Math Instruction[END_REF][START_REF] Resnick | Digital manipulatives: new toys to think with[END_REF][START_REF] Uttal | Manipulatives as symbols: A new perspective on the use of concrete objects to teach mathematics[END_REF]. Using tangibles for computing operations takes advantage of this existing skillset: pen-based interaction is a testament to this. Tangibles lower the level of interaction abstraction allowing users to apply their natural tool-based skillset to the digital environment. The use of tangibles on touch displays has been shown to improve interaction with interface objects as they are easier to manipulate, acquire and control in comparison to virtual objects [START_REF] Tuddenham | Graspables revisited: multi-touch vs. tangible input for tabletop displays in acquisition and manipulation tasks[END_REF].

Though the stylus has long been available as a drawing instrument for digital canvases, other instruments have not yet been explored. In addition to stylus input, designers often use passive tools such as rulers or French curves on tablets to guide drawing. Converting these passive tools to active tools seems a promising evolution for drawing based content creation. We have created three recognizable tangible drawing instruments: a ruler, protractor and set square. Through our application, users are able to apply these familiar physical instruments to construct digital ink drawings on multi-touch tablets. Transforming passive instruments into active tools, as we have done here, allows further intelligence to be built into the system. To our knowledge, recognizable tangible drawing tools (other than styli) have not been used on capacitive touch displays for creating electronic content.

Touch surfaces are a well-established technology. Small touch sensitive devices, e.g. phones and tablets, typically have capacitive displays, larger touch devices, such as tabletops, have camera-based detectors. Tangibles on tabletops have been explored for many years e.g. [START_REF] Ullmer | The metaDESK: models and prototypes for tangible user interfaces[END_REF][START_REF] Baudisch | Lumino: tangible blocks for tabletop computers based on glass fiber bundles[END_REF][START_REF] Wellner | The DigitalDesk calculator: tangible manipulation on a desk top display[END_REF][START_REF] Fitzmaurice | Bricks: Laying the Foundations for Graspable User Interfaces[END_REF]. These systems typically use cameras to capture the position of the tangible; this requires specialist equipment and environments. The advantage of capacitive touch is that it is built into many readily available tablets that are portable and require no special environment. Using capacitive touch alters the recognition approach from image processing to gesture processing of the touch points. Touch points may be fingertips or conductive material [START_REF] Yu | TUIC: enabling tangible interaction on capacitive multi-touch displays[END_REF] given that capacitive displays detect touch via the electrical properties of fingertips. As an extension of recent techniques [START_REF] Yu | TUIC: enabling tangible interaction on capacitive multi-touch displays[END_REF] we have devised a novel approach which enables tangible drawing tools to work with capacitive displays (Fig. 1).

To our knowledge tangible geometry drawing tools have not been used in this context before. There are two key contributions of this research: the design and construction of tangible drawing tools for capacitive touch surfaces, and visual drawing guides to enhance the geometric drawing experience. Together, these enhancements have the potential to provide benefits over using passive drawing tools on a screen. In a user evaluation, we explore this idea by comparing our prototype, CapTUI, to drawing with passive tangibles. Possible areas of application for our system include design fields such as architecture and mathematics education.

Related Work

Physical objects are beneficial for learning [START_REF] Inhelder | The early growth of logic in the child[END_REF][START_REF] Piaget | Play, dreams, and imitation in childhood[END_REF]. For example, manipulatives have been used for years to assist in mathematics education [START_REF] Marzola | Using Manipulatives in Math Instruction[END_REF][START_REF] Resnick | Digital manipulatives: new toys to think with[END_REF][START_REF] Uttal | Manipulatives as symbols: A new perspective on the use of concrete objects to teach mathematics[END_REF]. Similarly tangibles are a particularly useful tool for children when interacting with technology because of the Fig. 1. CapTUI added physicality [START_REF] Tuddenham | Graspables revisited: multi-touch vs. tangible input for tabletop displays in acquisition and manipulation tasks[END_REF][START_REF] Fails | Child's play: a comparison of desktop and physical interactive environments[END_REF][START_REF] Sitdhisanguan | Comparative study of WIMP and tangible user interfaces in training shape matching skill for autistic children[END_REF]. Other advantages of tangibles include increasing explorative behaviour [START_REF] Chipman | Paper vs. tablet computers: a comparative study using Tangible Flags[END_REF], reducing conflicts in cooperation [START_REF] Olson | It's just a toolbar!: using tangibles to help children manage conflict around a multi-touch tabletop[END_REF][START_REF] Schneider | Benefits of a Tangible Interface for Collaborative Learning and Interaction[END_REF], encouraging prolonged engagement [START_REF] Druin | Designing PETS: a personal electronic teller of stories[END_REF][START_REF] Karime | Magic stick: a tangible interface for the edutainment of young children[END_REF] and acting as a useful aid to problem solving in comparison to standard graphical user interfaces [START_REF] Xie | Are tangibles more fun?: comparing children's enjoyment and engagement using physical, graphical and tangible user interfaces[END_REF]. Tangibles have been used to enhance physics and mathematics learning [START_REF] Price | Towards a Framework for Investigating Tangible Environments for Learning[END_REF][START_REF] Scarlatos | Tangible Math. Special Issue on Computer Game-Based Learning[END_REF] while other e-learning tools link geometry with algebra in order to augment the learning experience [START_REF] Hohenwarter | Ways of linking geometry and algebra: the case of Geogebra[END_REF][START_REF] Straesser | Cabri-géomètre: Does Dynamic Geometry Software (DGS) Change Geometry and its Teaching and Learning[END_REF]. The use of tangibles on touch surfaces has been shown to improve interaction with interface objects. Tuddenham et al [START_REF] Tuddenham | Graspables revisited: multi-touch vs. tangible input for tabletop displays in acquisition and manipulation tasks[END_REF] compared the use of tangibles and virtual objects on multi-touch interfaces. They found that when using the tangible objects significantly fewer errors were made and significantly less time was taken to acquire and manipulate the objects.

Limited work has been done in the area of tangibles on capacitive touch screens. SmartSkin is an early system that used capacitive sensing with a mesh shaped antenna to detect hands and objects [START_REF] Rekimoto | SmartSkin: an infrastructure for freehand manipulation on interactive surfaces[END_REF]. Conductive materials were attached to blocks in patterns to allow objects to be identified. Yu et al [START_REF] Yu | TUIC: enabling tangible interaction on capacitive multi-touch displays[END_REF] present three tangible technologies for use on capacitive touch surfaces: spatial, frequency and hybrid. Their spatial tangibles employ patterns for object identification, from at least four touch points. Four touch points can be limiting if users have multiple tangibles on touch surfaces that are limited in the number of touch points they are able to detect. Frequency tangibles use a modulation circuit to generate touches of varying frequency. They only require one touch point; however they rely on a power source, are unable to detect object orientation, and are limited in tracking fast movements. The hybrid tangible combines the spatial and frequency technologies to address the aforementioned issues. Our observation is that the tangibles they have presented are quite large in size -particularly thickness, in comparison to our tangibles. They report that the size of the circuit board alone is 2x3x3cm. AppMATes1 are another example of tangible objects, in the form of toy cars that can be used on the Apple iPad. The cars are uniquely identifiable using touch point patterns. More recently [START_REF] Chan | CapStones and ZebraWidgets: sensing stacks of building blocks, dials and sliders on capacitive touch screens[END_REF] stackable tangibles, sliders and dials for capacitive screens have been introduced. The stackable tangibles are able to sense changes in capacitance when blocks are placed on top of them -this in turn modifies the touch point pattern for identification. The dials and sliders are made of conductive zebra rubber and also use unique touch point patterns for identification.

Very few studies have been performed testing the usability of tangibles on capacitive displays. One study compared CapWidgets [START_REF] Kratz | CapWidgets: tangible widgets versus multi-touch controls on mobile devices[END_REF], tangible dials designed for mobile capacitive screens, to touch dials. The results showed that touch was significantly faster and rated higher for usefulness, satisfaction, ease of use, and learnability but there was no significant difference in precision. They identified aspects of the design of the tangibles and the software to be the main hindrance to the usability of their system. Jansen et al [START_REF] Jansen | Tangible remote controllers for wall-size displays[END_REF] designed tangible remote controllers for wall sized displays. The tangibles are manipulated on a capacitive tablet as a way of interacting with a wall sized display. The tangibles were stuck to the tablet to allow mobility and to reduce the need for visual attention. They used various conductive materials including conductive foam and ink to construct the tangible sliders and dials. Their user study compared tangible and touch interaction for a slider. Overall they found that using the tangible slider produced fewer errors, was faster to acquire and did not require as much visual attention as the virtual slider. However, they did comment that their tangible design "still does not measure up to commercial physical controls".

Geometric drawing applications are common. Most rely on mouse and keyboard input [START_REF] Hohenwarter | Ways of linking geometry and algebra: the case of Geogebra[END_REF][START_REF] Straesser | Cabri-géomètre: Does Dynamic Geometry Software (DGS) Change Geometry and its Teaching and Learning[END_REF]. Sketchpad [START_REF] Sutherland | Sketchpad: A man-machine graphical communication system[END_REF] presents the earliest work using a light pen to construct line drawings. It includes the ability to apply geometric constraints to drawings. Balakrishnan et al [START_REF] Balakrishnan | Digital tape drawing[END_REF] introduced the concept of drawing on a large scale with digital tape. Tangible rulers for camera-based systems have been used [START_REF] Tuddenham | Graspables revisited: multi-touch vs. tangible input for tabletop displays in acquisition and manipulation tasks[END_REF][START_REF] Couture | GeoTUI: a tangible user interface for geoscience[END_REF] but their focus has been on investigation of object acquisition or positioning rather than how the tangible might facilitate drawing and precise measurement.

Although the use of tangibles and multi-touch has been investigated in the context of camera-based surface interaction, tangible drawing tools with capacitive screens is yet to be explored. The interaction with drawing tools differs from the dials, blocks and sliders from previous work in tangible user interfaces (TUI's) for capacitive screens. Of the few studies that have been performed it is evident that the tangible's design is the key challenge to success [START_REF] Kratz | CapWidgets: tangible widgets versus multi-touch controls on mobile devices[END_REF][START_REF] Jansen | Tangible remote controllers for wall-size displays[END_REF]. The CapWidgets study [START_REF] Kratz | CapWidgets: tangible widgets versus multi-touch controls on mobile devices[END_REF] suggests that tangible design was a hindrance to the usability of their system, while [START_REF] Jansen | Tangible remote controllers for wall-size displays[END_REF] also allude to the difficulty of constructing good tangibles. The combination of tangible drawing tools with capacitive screens presents significant challenges in the hardware and the interaction design of the applications to ensure a good user experience.

Our Approach

CapTUI combines recognizable tangible drawing tools with an intelligent drawing application. In this section the tangible hardware design is described, followed by the recognition approach used for these tools. Section 3.3 provides details on the drawing application and finally Section 3.4 describes CapTUI's visual drawing guides.

Tangible Hardware

Our goal is to create easily manipulated drawing instruments that are recognizable on a capacitive touch display. Capacitive screens are designed specifically to detect the electrical properties of fingertips. Hence we use conductive materials that act as an extension of the fingertips for the touch point connections between the tangibles and the touch display. These touch points are electrically connected to the user's body via his or her fingers as the user's body is the source of the electrical current.

To discriminate between the tangibles each requires a unique ID. The touch points on the bottom of each tangible are placed so as to form unique patterns. This ID allows differentiation between tangibles, and calculation of a tangible's orientation and location (see Section 3.2 for a full explanation).

There were several iterations in our design process for constructing the tangible hardware. Off-the-shelf standard drawing tools were modified by adding conductive materials to allow detection on the capacitive touch screen. Fig. 2 shows some of our designs using various conductive materials such as: aluminum foil/tape, conductive rubber, conductive foam, steel nuts and bolts, copper wire, and conductive ink [START_REF] Wiethoff | Sketch-a-TUI: low cost prototyping of tangible interactions using cardboard and conductive ink[END_REF].

After preliminary testing of these prototypes, the following factors affecting the detection and use of the objects were identified.

• As a whole, the materials used must ensure a consistent circuit can be maintained, i.e. all circuit components are well connected so that the current from the user's fingertips has an unbroken path to the screen. We found when several materials are used, and therefore more connections required, a significant amount of pressure had to be applied before the touch points were detected. • Tangible stability is important to maintain consistent contact between the screen and the tangible. This means that the touch points must be as flat as possible and positioned such that when the tangible is moved across the screen all points stay in contact with the surface. If the tangible is unstable, and a touch point loses contact with the screen then the tangible is no longer detected. • To maintain tangible to body contact, there must be a clear point of contact for the user's fingertips when the tangible is in use. Our final prototype's top surface is covered with conductive material (Fig. 3). • Usability of the tangible is poor if there is too little friction between the screen and the tangible. Using materials that add friction between the tangible and the screen, reduces unwanted movements when drawing, allowing users to draw along the tangible easily without having to concentrate on keeping it steady. • Designs that require the conductive material to pass over the edge of the tangible block the user from drawing comfortably on the tangible edge (such as the prototypes shown in Fig. 2

    Final design (conductive foam)     
Table 1 shows the performance of each tangible design in terms of the design factors listed above; where performance is based on expert judgement and informal testing. Design (a) was a proof of concept to show that recognition was possible; however it failed to meet most of the design criteria. Design (b) provided a consistent circuit and was a stable design, however its main drawback was that the conductive ink had to be drawn on tape to ensure the circuit was maintained over the edge of the tangible. An experiment using the ink without tape failed as the edge of the tangible was so thin it was difficult to maintain an unbroken circuit. Design (c) and (d) involved too many materials and therefore made it difficult to maintain a consistent circuit. The conductive rubber touch points, while providing a good amount of friction with the screen, were difficult to mould and therefore did not provide a stable base for the tangibles. Design (e) had conductive foam for the touch points which improved stability, as they are easier to cut into shape, and maintained friction with the screen. However it was difficult to maintain good circuits as there were still two conductive materials in use.

Our final design (Fig. 3) was constructed based on the identified design factors; these included a ruler, set square, and protractor. One conductive material was used, conductive foam. This reduces the number of connections that must be made to maintain a circuit from the user's fingers to the screen. The foam covers a large portion of the top surface of the tangible so that there is a clear point of contact for the user's fingers. The foam provides a good amount of friction so that the tangible does not make unwanted movements on the screen. It also provides a stable base for the tangible so that the touch points are consistently in contact with the screen. In addition the conductive foam is easier to work with than other materials as it can be cut into the shape required and does not have to pass over the edge of the tangible.

Tangible Recognition

This section describes how each tangible can be identified and its position computed. The recognition approach is similar to that of SmartSkin [START_REF] Rekimoto | SmartSkin: an infrastructure for freehand manipulation on interactive surfaces[END_REF]. Recognition of the tangible allows for further intelligence to be added to the tangible interaction as described in Section 3.4.

The tangible ID patterns are based on the distance between each pair of points. When constructing a pattern the distances must be distinct; for example, a pattern that forms an isosceles triangle is not allowed because it has two or more identical distances between points. Identical distances make it impossible to determine the correct orientation of the tangible, with the obvious exception of regular shapes (e.g. circle).

There are two main phases for the recognizer: learning and recognition. The learning phase allows users to register and calibrate the tangibles so that they are identified by the system. Several details about each tangible are stored: the location of the touch points, the distances between touch points (i.e. its unique ID), the outline points of the tangible and the type of tangible (ruler, protractor or set square) as specified by the user. This data is used later to identify the tangible and display its outline on the screen.

Tangibles only need to be registered with the system once. To register the tangible (Fig. 4), the user places it on the registration screen and moves the guidelines to delineate a bounding box. The user then specifies the type of tangible (ruler, set square, protractor) from a list.

During the recognition phase, touch input from the tangible currently in use is passed to the recognizer. The recognizer finds its ID by calculating the distances between each touch point detected and comparing these to the previously saved distances for each calibrated tangible. The recognition adds (or subtracts) a degree of error tolerance (e) when comparing the distances between the detected touch points and the saved set of distances. The error tolerance is required as capacitive hardware detects an area of touch but only reports the centre point position. This means the precise position of a touch point can be difficult to determine as we have no way of knowing which part of the tangible's touch point has been detected as the centre. We experimented with different sized touch points and found that a diameter of approximately 7mm is the smallest size that can still be detected on the touch screen for our tangibles. If a match is found between all d i and s j then the tangible ID is identified as s. Our informal experiments showed that a 2mm tolerance level is sufficient for maintaining a good rate of recognition.

The advantage of including a level of tolerance for the patterns is that 100% accuracy can be achieved by the recognizer, resulting in better usability. There is a tradeoff here, as calculating the position and orientation of the tangible is less accurate. To minimize the effect of this tradeoff the user is provided with a visualization of the tangible on the screen; this is described further in Section 3.4.

Drawing Application

The tangible hardware and recognition algorithm were combined together in a drawing application (Fig. 5). Our application allows the tangible ruler, protractor and set square to be used to construct drawings on a capacitive multi-touch screen. It also includes basic functions such as save, erase, undo and redo.

To construct drawings using a tangible drawing tool the user slides a stylus along the edge of the tangible that is placed on the screen (Fig. 1). As the user draws, beautified lines (or curves) are rendered.

The application was developed using the .NET 4.0 framework on a Windows 7 Dell Latitude XT3 tablet, Intel core i7-2640M with 8GB RAM, built in stylus and four available touch points.

Ink beautification

One of the main purposes of having geometric tools in drawing is to use the tangibles as a guide for precise drawing. However, due to the imprecise nature of contact points on the screen, the user's ink may not be rendered where they intend. Therefore we beautify the ink to try to produce what the user intends, in a similar way to many digital ink drawing programs such as [START_REF] Hse | Newton: Recognition and Beautification of Multi-Stroke Symbols in Digital Ink[END_REF]. Our system includes two forms of ink beautification: ink to tangible edge snapping and ink corner snapping. For ink-to-edge snapping, we assume if a user is drawing close to a tangible edge, they intend to draw right on the edge. Therefore ink points are dynamically translated so that they snap to the edge of a tangible's virtualized outline as they are drawn in real time. The result is a beautified straight/curved line drawn along the edge of the tangible (Fig. 6).

Corner snapping beautifies ink to render clean intersections between strokes that are close by. It is automatically enabled in two situations. The first connects the starting point of a stroke to the end of existing strokes when the user first starts drawing a stroke. The second connects the stroke end point to other strokes (at any position) once the stroke is completed. The beautification is applied to the newly added stroke and existing strokes; both strokes are extended or reduced such that they meet exactly at an intersection point (Fig. 7). A corner is snapped if the current stroke end points are close to another stroke -this requires a distance threshold to be set for determining 'closeness'. As this is heuristic-based, corner snapping can be reversed using the undo function. It can also be turned off if the user desires.

Visual Drawing Guides

Our early experiences suggested that drawing guides are essential for an enjoyable experience on current touch technologies [START_REF] Blagojevic | Using tangible drawing tools on a capacitive multi-touch display[END_REF]. The visual drawing guides we developed assist the user in constructing accurate geometric drawings. These guides are directly dependent on the unique identification of the tangibles; therefore making them only possible and relevant with recognizable tangibles.

Tangible Outline

When the tangibles are detected on the screen a visualization of the tangible outline is displayed (the blue line in Fig. 8). The visualization is rendered at the correct location and orientation, using the tangible recognition information, so as to match the tangible itself, though with a small offset such that the outline is visible.

Length visualizations

When drawing straight lines using the ruler or set square, an adjustable line length function is enabled. As a stroke is drawn along the edge of a tangible, its length can be adjusted by moving the stylus up and down the edge. This function has two main advantages: when the user draws the line further than the intended length it can be easily corrected, and having a line dynamically adjustable in length provides a prototyping experience where the user can see how the line will look at various lengths.

To assist in solving occlusion issues caused by the tangible, stylus or hand on the display, the length visualization displays line length in millimetres as the user draws with a ruler or set square (Fig. 6). This visualization is supplementary to the markings on the tangible. The visualization works in tandem with the adjustable length function by providing real time stroke length feedback.

Without recognition of the tangible these visualizations would not be suitable functions as there would be no way of knowing that the user intends to draw a straight line as they are completing the action. When the ruler or set square is recognised we can be sure that straight lines are desired.

Angle visualization

The angle visualization displays the angle between existing strokes and the edges of a tangible ruler to allow a line to be drawn intersecting other lines at specific angles (Fig. 9). It is created by detecting intersections between existing strokes and the ruler edges, calculating the angle between these lines, and displaying the results. This enables the construction of various geometric shapes which consist of connected lines of specific angles, for example, regular polygonal shapes. We have also included an affordance which freezes the angle in place if it reaches multiples of five or ten degrees to assist the user in obtaining common angles. If the angle has been frozen, it is only unfrozen if the tangible is moved approximately 5 degrees away. This threshold was chosen after some informal testing. In essence, this visualization can replicate the protractor for measuring angles. However, it relies on the recognition of the ruler so that the angles between the tangible ruler and existing digital ink can be calculated in real time.

In a similar way to the length visualization, an angle visualization displays the angle in degrees as the user draws an arc with the protractor. This helps to solve occlusion issues and supplements the markings on the tangible itself by providing real time feedback. Again, this visualization relies on the recognition of the protractor to confirm that the user intends to measure angles.

Evaluation

The objective of this evaluation is to determine if CapTUI assists users to easily draw precise geometric drawings. In particular, we are interested in comparing drawing with CapTUI's recognizable tangibles to drawing with standard non-recognizable drawing tools on a screen. For this comparison we have developed another drawing application, referred to as Paint. Paint can be used to construct geometric drawings in much the same manner as CapTUI except that it does not recognize the drawing tools on the screen. To make the comparison as fair as possible it includes the same beautification and corner snapping functions as CapTUI. However, it does not include Cap-TUI's tangible outline, angle and length visualizations, as these functions are dependent on tangible recognition. Using this comparison we can determine if recognizable tangibles and visual guides, that are possible as a result of this recognition, assists users when constructing precise geometric drawings. A within-subject design was used where each participant was given the same tasks to complete using CapTUI and Paint; half used CapTUI first and the other half used Paint first. Participants first completed a pre-questionnaire on their previous experience with touch, stylus and drawing applications. They were then given an introduction to the first system and time to familiarize themselves with the application. When ready, participants completed the tasks required using the first system and filled in a questionnaire on their experience. This process was repeated for the second system.

There were seven tasks designed for the evaluation; the first three tasks served as training tasks (Fig. 10). Each training task aimed at familiarizing the participant with a different drawing function or tangible. They were not told that they were training tasks: this was done to try to encourage them to complete the tasks with the same amount of effort they might apply for the real tasks and therefore get the most out of the training. The remaining four tasks comprised the evaluation tasks, providing data for our analysis (Fig. 11). The focus of task one was on connecting lines of specific length. Task two was aimed at evaluating drawing lines at a specific angle and use of the protractor to connect an arc. Task three focused on drawing angles of specific magnitude. In task four, angle and length measurements were required concurrently.

Quantitative metrics used to analyse the data collected from these tasks included the time taken, and average length and angle errors. Errors were counted as 1mm or 1 degree away from the required measurement. The average length and angle error was calculated for each task using the sum of the errors made / number of lengths or angles in the task. Participants also completed a questionnaire to record their experiences using each system. Questions were presented using a 5 point Likert scale, except for a small number of open ended questions. A Wilcoxon Signed Ranks Test was used to test for significant differences in the results, unless otherwise stated.

After a pilot study with two participants, twelve participants (eight males and four females) were recruited for the final study. They came from a range of backgrounds including computer science, law and health. Seven participants used touch interfaces frequently; the remainder had used such interfaces a few times or occasionally. The majority of participants had experience using stylus input before. Six participants had used a drawing program on a touch device before.

Results

Participants were asked to give an overall rating for each system (using a 5 point Lik ert scale). Seven participants rated CapTUI higher than Paint, one rated Paint higher and four considered them equal. All participants rated CapTUI as good, very good or excellent (m = 3.75, s.d. = 0.62) (see Q1, Table 2). Ratings for Paint were more varied (m = 2.83, s.d. = 1.11). The overall ratings were found to be significantly different (z = -2.157, p = 0.031) where participants rated CapTUI significantly higher than Paint.

The results for the quantitative measures are as follows. A paired t-test showed that there was no statistically significant difference (t = 1.644, p = 0.107) in the time taken to complete the tasks between using Paint (m = 58.30, s.d.= 32.78) and CapTUI (m = 70.36, s.d. = 32.63), Fig. 12. This result is favourable for CapTUI as it shows that even with the time taken for detecting the drawing tools it did not take significantly longer to complete the tasks. There was no significant difference (z = -1.029, p = 0.304) in average length errors per task between using Paint (m = 1.79, s.d.= 2.67) and CapTUI (m = 0.95, s.d. = 0.82), Fig. 13. This shows that both Paint and CapTUI were comparable when creating lines of accurate lengths. On the other hand, average angle errors per task were significantly less (z =-2.861, p = 0.004) when using Cap-TUI (m = 0.96, s.d. = 1.91) than when using Paint (m = 1.68, s.d.= 1.63), Fig. 14. This result confirms that angles drawn using CapTUI were significantly more accurate.

The following are the results obtained from questions answered using a 5 point Likert scale (see Table 2). Participants enjoyed (Q8) using CapTUI (m = 4.33, s.d.= 0.49) significantly more than using Paint (m = 3.25, s.d.=1.06), (z = -2.288, p = 0.010). All participants agreed that the drawing tools were useful (Q3) when completing the tasks for CapTUI (m = 4.33, s.d. = 0.49); however for Paint the results were more varied (m = 3.92, s.d. = 1.16). There was no significant difference found between these results (z= -0.877, p = 0.380). There was no significant difference found for the responses when asked if the drawing tools for each system were easy to use (Q2, z = -0.272, p = 0.785). This indicates that the recognizable drawing tools were just as easy to use as the non-recognizable tools. When asked which system is easier to use overall, five participants chose CapTUI, three chose Paint, and four considered them equal. The main reason for choosing CapTUI was that the visual guides made the system much easier to use than Paint ("the angle and length indicators were really helpful", "easier especially for the more technical drawing due to the ability to easily get exact lengths and fairly easily get precise angles"). The main reason for not choosing CapTUI was due to inconsistent tangible detection ("CapTUI was more accurate and tidy but I had a bit of problem with adjusting the tools").

All but one participant agreed that it was easy to measure line length (Q4) with CapTUI (m = 4.42, s.d. = 0.90) in comparison to seven participants for Paint (m = 3.41, s.d. = 1.24), however this difference was not found to be significant (z = -1.796, p = 0.072). Ten participants agreed that it was easy to measure angles (Q5) with Cap-TUI (m = 4.00, s.d. = 0.85), compared to only six participants for Paint (m = 3.08, s.d. = 1.44); this was also not statistically significant (z = -1.530, p = 0.126). It is possible that with a larger sample size statistically significant differences may be found for these factors given that the majority of participants preferred CapTUI for ease of line and angle measurement.

Eight participants agreed that their drawings were tidy (Q7) when drawn using CapTUI (m = 3.92, s.d. = 0.79), compared with four participants for Paint (m = 2.75, s.d. = 1.22). These differences were statistically significant (z = -2.124, p = 0.034). Only one participant did not believe their drawings were accurate (Q6) with CapTUI (m = 3.67, s.d. = 0.89), compared with half of participants with Paint (m = 2.92, s.d. = 1.24), however this difference was not statistically significant (z = -1.562, p = 0.118). When asked about the overall accuracy of each system, eleven participants considered CapTUI to be the more accurate of the two systems; this was attributed to the visual guide functionalities, in particular the angle indicators ("aids to angles were helpful in making accurate shapes", "accurate and faster to use given the angle/length indicators", "the onscreen angle calibration and tool recognition made it much easier to draw accurate shapes").

Several questions were asked specifically about CapTUI (using a 5 point Likert scale). All but one participant agreed that learning to use the tangibles was easy. Five participants disagreed that the recognition of the tangibles was good. This aspect appears to be CapTUI's primary weakness and will be discussed further in the next section. The majority of participants agreed that the angle visualizations were easy to understand. All participants agreed that the length visualization was easy to understand and that the length and angle visualizations were useful. Ten participants agreed that the visual guides helped them to draw more accurately.

When asked what the best thing about CapTUI was, eleven participants answered that it was the visual guides ("angle and length indicators extremely useful", "It is easy to use and accurate. Also the visual guides are helpful and make the drawings easy"). When asked what the hardest thing about CapTUI was, nine participants mentioned either tangible detection or difficulty with fine adjustments ("detecting the tools was sometimes not accurate", "adjusting the drawing tools was a bit hard").

Overall comments from participants were: "CapTUI is much easier to use and more accurate because of the visual guides", "very good for people who need accurate measurements", "made it easy to draw accurate lines and shapes. Would probably be very useful if integrated into a CAD package", "If the intention is to produce accurate geometric drawings I think CapTUI is superior -however still a little tricky to use in terms of accuracy and fine tuning", "With a little improvement to the localization of the tangibles it will become a very useful tool for precise drawings".

In summary, CapTUI's main strength is in the ability to produce precise geometric constructions using the visual guides. Evidence of CapTUI's accuracy was shown by its significantly lower average angle error. Participants rated CapTUI significantly higher than Paint overall, enjoyed using CapTUI significantly more and found it to produce significantly more tidy drawings than Paint.

Discussion

There is very little work with tangibles for capacitive screens that demand a high level of interaction with precise tracking. In other projects the various blocks, dials and sliders are rotated and tracked, however the CapTUI drawing tools are manipulated in a more fine grained fashion, where a single degree of rotation is significant to the user. The most common feedback received from participants during our study was that they found the visual guides in CapTUI to be extremely useful for drawing precisely; however, making fine grained movements with the tangibles was difficult.

Designing tangibles for ease of use on a capacitive screen is a difficult problem. Of the user studies which feature tangibles on capacitive screens [START_REF] Kratz | CapWidgets: tangible widgets versus multi-touch controls on mobile devices[END_REF][START_REF] Jansen | Tangible remote controllers for wall-size displays[END_REF], both acknowledge tangible design as a challenge; our tangibles are no different. Although our final tangibles were the best of all our designs, there are two remaining issues: consistent detection and accurate positioning.

For consistent detection there must be unbroken body-to-tangible contact and tangible-to-screen contact. A partial solution to this problem is to power the tangibles with their own battery, similar to the work in [START_REF] Yu | TUIC: enabling tangible interaction on capacitive multi-touch displays[END_REF]. This would eliminate the need for the body-to-tangible contact. Maintaining the tangible-to screen contact would require a stable tangible design to ensure all touch points are on the screen at all times. There are also hardware and operating system limitations to consider such as enabling simultaneous touch and stylus input. Although this has been demonstrated in recent research [START_REF] Hinckley | Pen + touch = new tools[END_REF], the ability to use such technology is limited to very few devices. Most devices, including the tablet used in our study, are not able to detect touch and stylus simultaneously. This means that if the stylus is on or in range of the screen (as a stylus can still be detected when it is a short distance away from the screen) then the tangibles cannot be detected via touch. Participants were informed of this limitation; however it still caused some problems when drawing.

A powered tangible is unlikely to solve the issue of accurate positioning. The main limitation here is the hardware. Capacitive hardware is designed to detect a general area of touch from a finger rather than a precise point. Our tangible touch points mimic this area of touch, however in order to calculate an accurate position and orientation of a tangible what is needed is a more precise point of touch. Currently the area of the touch point that is detected is translated to a centre point, but there is no way to know which part of the tangible's touch point is detected as the centre.

To assist in precise drawing it is possible to make more affordances in the software, similar to freezing the angle visualization (Section 3.4). However there is a fine line between tuning affordances to be helpful rather than causing frustration as the users control of the interface with the tangibles lessens. If they are not tuned carefully users may find the tangibles to be unresponsive and hinder them in achieving their goals. For example, we tried using automatic snaps to the horizontal and vertical screen positions of the tangible outline if the tangible came 'close' to these positions. Informal tests showed this to cause frustration when users did not want the tangibles in these positions. For example when tracking the tangible to a new position, if it was horizontal or vertical on the way to its new location, the tangible would seem unresponsive for some time due to the automatic snapping. We also experimented with averaging across three touch point positions to find a single position; however this did not always result in accurate positioning and caused delay in the recognition. Other possibilities would be allowing the user to lock the tangible outline in place or have a degree of stickiness to the movement; however such functions take away from overall goal of controlling the interface with the tangible.

If the above recognition issues can be resolved we believe a tangible drawing system would have great potential. Compared to more complicated drawing programs, tangibles are familiar and intuitive to use, don't require training, don't require the user to look at the tangible markings, therefore providing more flexibility. Our study showed that the main contributor to providing such an environment is the use of visual guides; without these the interaction is cumbersome. They provide essential feedback, such as the tangible outline, and additional information such as length and angle indicators. Users found our visual guides to be helpful and easy to understand; confirming that they enhance the interaction for geometric drawing. In future work we plan to compare tangible drawing systems to pen and paper.

Conclusion

We have presented CapTUI, a tangible drawing application for geometric constructions on a capacitive touch screen. CapTUI is composed of tangible drawing tools, a recogniser to identify each tool, a drawing application and visual drawing guides to augment the drawing experience. Our user evaluation compared CapTUI to Paint, which used non-recognizable drawing tools. Our results show that participants prefer CapTUI significantly more overall. Participants especially found the visual drawing guides to be helpful to drawing more precisely. The main challenges for tangibles on capacitive screens remain in good tangible design and consistent recognition.

  (a) and (b)). a) Aluminium foil and tape. b) Conductive ink. c) Steel nuts and bolts, copper wire and conductive rubber. d) Metal washers, copper wire, conductive rubber and metal handle. e) Conductive foam and aluminum tape.

Fig. 2 .

 2 Fig. 2. Tangible hardware designs

Fig. 3 .Fig. 4 .

 34 Fig. 3. Final tangible drawing tools (conductive foam)

Fig. 5 .

 5 Fig. 5. CapTUI drawing interface. The tangible identification algorithm is as follows: d: detected distances; s: saved distances; e: error tolerance i, j: number of distances For all d i and s j, if: d i -e <= s j <= d i + e; then: d i = s j

Fig. 6 .Fig. 7 .

 67 Fig. 6. Ink-to-edge snapping and length visualization

Fig. 8 . 9 .

 89 Fig. 8. Tangible outline Fig. 9. Angle visualizations

Fig. 10 .Fig. 11 .

 1011 Fig. 10. Training tasks

Fig. 12 .Fig. 13 .Fig. 14 .

 121314 Fig. 12. Time taken to complete tasks (seconds)

Table 1 .

 1 Tangible hardware designs vs design factors

		Consistent circuit	Stable	Clear point of body contact	Friction with screen	Comfortable draw-ing (material does not pass over edge)
	a) Aluminium foil and tape			
	b) Conductive ink		
	c) Steel nuts and bolts,
	copper wire and conductive					
	rubber
	d) Metal washers, copper
	wire, conductive rubber and					
	metal handle
	e) Conductive foam and
	aluminium tape

Table 2 .

 2 Comparative Questionnaire Results (1st row: CapTUI, 2nd row Paint)

	Poor	Fair	Good	Very Good	Excellent
	Q1. Overall rating		4	7	1
	1	4	4	2	1
	SD	D	N	A	SA
	Q2. Drawing tools ease of use	1	5	5	1
	1	1	2	7	1
	Q3. Drawing tools usefulness			8	4
	1		2	5	4
	Q4. Ease of length measurement	1		4	7
	1	2	2	5	2
	Q5. Ease of angle meas-urement	1	1	7	3
	2	3	1	4	2
	Q6. Drawing accuracy	1	4	5	2
	1	5	1	4	1
	Q7. Drawing tidiness		4	5	3
	1	6	1	3	1
	Q8. Enjoyment			8	4
	1	2	2	7

http://www.appmatestoys.com/

Acknowledgements. This project is funded by the Royal Society of New Zealand Rutherford Foundation.


Florian Perteneder

Susann Hahnwald
email: susann.hahnwald@fh-wels.at

Michael Haller

Kurt Gaubinger
email: kurt.gaubinger@fh-wels.at

Systematic Integration of Solution Elements: How Does Digital Creativity Support Change Group Dynamics?

Keywords: Creativity, Design, Creativity Techniques, Interactive Environment, Systematic Integration of Solution Elements, Collaboration

In practice, most creativity techniques are still performed with traditional tools, such as pen and paper, whiteboards, and flipcharts. When transforming these techniques into a digital environment, the reduction of organizational overhead is the main goal to foster accessibility. Still, we do not know if overhead reduction fosters creativity or if it eliminates an important part of the creative process. To get a deeper understanding of these effects, we compare the performance of the creativity technique SIS (Systematic Integration of Solution Elements) in a traditional setting with a setup based on multiple interactive surfaces. By using a mix of diverse evaluation methods, we show how the use of a digital interactive creativity room can really foster creativity and produce better results.

Introduction

Creativity and innovation are predictors of success in our knowledge-based society.

With the increasing availability of digital whiteboards, the development of tools to support creativity has become an emerging field [START_REF] Geyer | Designing Reality-Based Interfaces for Creative Group Work[END_REF][START_REF] Guimbretière | Fluid interaction with high-resolution wall-size displays[END_REF][START_REF] Hailpern | TEAM STORM: Demonstrating an Interaction Model for Working with Multiple Ideas during Creative Group Work[END_REF][START_REF] Hilliges | Designing for collaborative creative problem solving[END_REF]. Since the '70s, psychologists and practitioners have put a lot of effort in developing numerous methods for supporting creativity more effectively [START_REF] Geschka | Modern Techniques for Solving Problems[END_REF][START_REF] Rohrbach | Kreativ nach Regeln -Methode 635, eine neue Technik zum Lösen von Problemen[END_REF][START_REF] Schlicksup | Innovation, Kreativität und Ideenfindung[END_REF]. Although there are a lot of creativity techniques for versatile needs and tasks, only a small set of traditional tools and media, such as pen and paper, sticky notes, flipcharts, whiteboards, and pinboards, are used. Due to the limited possibilities to edit and copy content, especially complex creativity techniques often require a huge amount of organizational overhead (e.g. copying content, placing flipchart papers on pinboards). Digital implementations usually aim to limit this overhead and increase the ease of use [START_REF] Clayphan | Firestorm: a brainstorming application for collaborative group work at tabletops[END_REF][START_REF] Liikkanen | Next Step in Electronic Brainstorming: Collaborative Creativity with the Web[END_REF]. However, it is not clear if the efforts of digitizing the creative process lead to the desired effect of decreased task execution time or if they even have negative side effects on creativity and inspiration. New media in creative processes change the balance of power, involvement and satisfaction of participants, as well as the general dynamics of collaborative sessions. To provide a theoretical understanding for developing adequate and practical interaction processes and applications, it is necessary to carefully study the effects of digital solutions and their impact on group creativity.

In this paper, we analyze the impacts of a digital environment on group dynamics and creative outcome when performing a complex creativity method. Therefore, we performed an experiment to compare the traditional paper-based way [START_REF] Eversheim | Innovation Management for Technical Products: Systematic and Integrated Product Development and Production Planning[END_REF][START_REF] Vangundy | Techniques of Structured Problem Solving[END_REF] of performing the creativity technique SIS (Systematic Integration of Solution Elements) [START_REF] Warfield | Academy for Contemporary Problems[END_REF] to its implementation in a digital, interactive environment (cf. Fig. 1). We use a combination of different evaluation approaches to get a deeper understanding of the emerging side effects that come with overhead reduction. Finally, we present the results of our analysis and discuss their implications on environments that are supposed to support collaborative creativity, and on creative tasks in general. Fig. 1. Performing the SIS method in an interactive environment. Participants can discuss and present their ideas using digital paper and a large interactive whiteboard.

2

Related Work

Creativity Techniques

While Osborn's idea of verbal brainstorming [START_REF] Osborn | Applied Imagination: principles and procedures of creative thinking[END_REF] is widely known and used, many studies showed that this collaborative way of idea generation is not the best choice regarding quantity of ideas [START_REF] Paulus | Toward More Creative and Innovative Group Idea Generation: A Cognitive-Social-Motivational Perspective of Brainstorming[END_REF] due to negative social effects (production blocking, evaluation apprehension, and free riding) [START_REF] Diehl | Productivity Loss In Brainstorming Groups: Toward the Solution of the Riddle[END_REF][START_REF] Warr | Understanding Design as a Social Creative Process[END_REF]. Individual idea generation, also known as nominal brainstorming, is a way to overcome these issues and to increase the number of ideas produced [START_REF] Baruah | Effects of training on idea generation in groups[END_REF][START_REF] Taylor | Does Group Participation When Using Brainstorming Facilitate or Inhibit Creative Thinking[END_REF]. Nevertheless, verbal brainstorming is still preferred in many practical situations as it yields diverse perspectives when team members provide complementary skills and expertise [START_REF] Sutton | Brainstorming Groups in Context: Effectiveness in a Product Design Firm[END_REF]. Soon after the introduction of brainstorming, psychologists as well as practitioners developed new and improved creativity techniques [START_REF] Geschka | Modern Techniques for Solving Problems[END_REF][START_REF] Rohrbach | Kreativ nach Regeln -Methode 635, eine neue Technik zum Lösen von Problemen[END_REF][START_REF] Schlicksup | Innovation, Kreativität und Ideenfindung[END_REF][START_REF] Warfield | Academy for Contemporary Problems[END_REF], focusing on different categories of problems. Most of these techniques include aspects of verbal brainstorming (collaborative), nominal brainstorming (individual), or both. The combination is considered as the best solution, especially when dealing with complex problems.

Supporting Creativity Techniques in Interactive Environments

A considerable amount of recent work has explored digital support for creativity, focusing on brainstorming or discussion support. Most systems or tools, however, focus on the implementation of one specific creativity technique. As we identified both individual and collaborative work as crucial parts of creative work, we pay special attention to this aspect when presenting existing work. In addition, we were interested in flexible and open approaches that support a variety of different creativity techniques.

Individual vs. Collaborative Work.

There are multiple concepts that support both individual as well as collaborative aspects of the creative process [START_REF] Clayphan | Firestorm: a brainstorming application for collaborative group work at tabletops[END_REF][START_REF] Geyer | Designing Reality-Based Interfaces for Creative Group Work[END_REF][START_REF] Hailpern | TEAM STORM: Demonstrating an Interaction Model for Working with Multiple Ideas during Creative Group Work[END_REF][START_REF] Hilliges | Designing for collaborative creative problem solving[END_REF]. While some concepts provide shielded, private space for undisturbed, individual work [START_REF] Geyer | Designing Reality-Based Interfaces for Creative Group Work[END_REF][START_REF] Hailpern | TEAM STORM: Demonstrating an Interaction Model for Working with Multiple Ideas during Creative Group Work[END_REF], other implementations provide private, non-shielded space for individual content creation [START_REF] Clayphan | Firestorm: a brainstorming application for collaborative group work at tabletops[END_REF][START_REF] Hilliges | Designing for collaborative creative problem solving[END_REF]. In general it seems as if the need for shielded space rises when tasks become more complex and require e.g. extensive sketching instead of simple input of single words.

Post Brainstorm [START_REF] Guimbretière | Fluid interaction with high-resolution wall-size displays[END_REF] forgoes any dedicated features to support individual phases during the session. Since the system was designed as a substitution for traditional media used within the brainstorming sessions at IDEO, it offers a lot of flexibility regarding the import and arrangement of content, which is important for their creativity method.

Flexibility. Although there is some research about systems supporting very specific creative methods [START_REF] Liikkanen | Next Step in Electronic Brainstorming: Collaborative Creativity with the Web[END_REF] and about providing certain improvements to the ideation process [START_REF] Bao | Momentum: Getting and Staying on Topic during a Brainstorm[END_REF][START_REF] Wang | Idea Expander: Supporting Group Brainstorming with Conversationally Triggered Visual Thinking Stimuli[END_REF], many systems try to provide at least some flexibility to the user. Warr and O'Neill [START_REF] Warr | Tool Support for Creativity using Externalizations[END_REF] recommend providing users with flexible tools, such as free-hand drawing tools. TEAM STORM [START_REF] Hailpern | TEAM STORM: Demonstrating an Interaction Model for Working with Multiple Ideas during Creative Group Work[END_REF] aims not to impose structures by providing flexibility regarding private or public work. However, flexibility regarding a change of the underlying creativity technique is not intended.

Concepts based on the use of virtual sticky notes [START_REF] Geyer | Designing Reality-Based Interfaces for Creative Group Work[END_REF][START_REF] Hilliges | Designing for collaborative creative problem solving[END_REF] or paper strips [START_REF] Clayphan | Firestorm: a brainstorming application for collaborative group work at tabletops[END_REF] can provide a fast way of interaction but have issues with supporting concepts that require more extensive sketching.

Systematic Integration of Solution Elements

The creativity method Systematic Integration of Solution Elements (SIS) or Successive Integration of Problem Elements (Successive Element Integration -SEI)was designed by Schlicksupp for extracting synergies from interdisciplinary teams [START_REF] Warfield | Academy for Contemporary Problems[END_REF].

SIS is a creativity technique to be used on problems that require rather complex solutions and offer only a restricted number of possible solutions, such as industrial or product design tasks. The basic idea of this method is to merge the benefits of individual (cf. nominal brainstorming) solutions to an integrated solution in collaborative work (cf. verbal brainstorming). Due to the integration of all individual solutions and the positive way of analyzing only their benefits (and not their drawbacks), SIS is a technique that leads to high identification of each participant with the final result.

The SIS Process

The SIS creativity technique is designed for 4-8 participants. The attendees develop individual solutions during the first working phase and integrate these ideas collaboratively during the moderated later phases. Usually the individual solutions as well as the integrated solutions consist of sketches with additional explanations.

After the initial problem framing, SIS defines a specific process that consists of three phases (cf. Fig. 2). Fig. 2. Schematic representation of the different phases of the SIS process when used within a group of 4 participants. For our experiment we divided the entire process into three (artificial) stages (at the very right) to perform process-based measurements. Between the stages, we asked participants to complete questionnaires to measure their psychological state. Phase 1 -Individual Solution Finding is characterized by an individual idea generation phase. Each participant comes up with a potential solution for the predefined problem on a sheet of paper. The goal is to get a wide variety of possible solutions by overcoming negative group dynamic effects.

Phase 2 -Solution Analysis consists of two parts. First the solution generated in phase 1 is presented by its creator. Second, beneficial ideas and advantages from the particular solution are extracted collaboratively and written down (on a flipchart or whiteboard) by the moderator.

Phase 3 -Solution Integration describes the process of combining the benefits of different solutions in one integrated solution. As this integration is performed collaboratively, the final solution does not only benefit from diverse ideas during generation, but also from different perspectives and from the expertise of a multidisciplinary team. This helps to consider the pros and cons of certain features in order to find the best solution for the final result.

As depicted in Fig. 2, phase 2 and 3 alternate according to the number of participants.

SIS Implementation for a Digital Environment

In a traditional setup, when performing the SIS method, all individual sketches are drawn by using pen and paper [START_REF] Eversheim | Innovation Management for Technical Products: Systematic and Integrated Product Development and Production Planning[END_REF][START_REF] Vangundy | Techniques of Structured Problem Solving[END_REF]. Due to limited editing possibilities, sketches have to be redone and feature lists have to be copied manually when new solutions are integrated. This causes enormous organizational overhead. Our main goal is to provide a digital environment that minimizes this overhead.

The SIS method involves multiple types of interaction, which also appear in other creativity techniques. Similar to traditional, non-digital tools, the interactive environment as well as the applications were not designed to specifically support SIS but to provide a flexible solution for a variety of creative activities.

Environment

It is essential to adequately support individual and private content creation (phase 1) as well as collaborative, usually moderated work in a group (phase 2 and 3). For this reason, we decided on a twofold solution: We use digital paper (using Anoto pens1 ) to facilitate private content creation in combination with a large-scale interactive whiteboard that offers public space for discussion or collaborative work.

Digital Paper (phase 1). We chose digital paper for individual work for a number of reasons. Primarily, it captures handwriting on paper and enables displaying the content to the public. On the whiteboard, created content can be edited, copied and moved. Second, other than with digital solutions, such as tablets, people are very familiar with paper, so it requires almost no learning to use this technique. Third, paper provides adequate privacy during content generation. In addition, the possibility to take it to another place can be indirectly used for shielding during content creation. Finally, the approach is easily scalable for larger groups.

Interactive Whiteboard (phase 2 and 3). To support collaborative work, we use a large-scale multi-user interactive whiteboard based on the system presented in [START_REF] Haller | The NiCE Discussion Room: Integrating Paper and Digital Media to Support Co-Located Group Meetings[END_REF]. Due to its flexibility, it serves multiple purposes: It can be used for public note taking and to display prepared content, such as presentation slides. In addition, it can be used to display ideas, sketched on the above mentioned digital paper. As it is a digital device, it also offers benefits in terms of editing and space management capabilities compared to traditional media.

Applications

Digital paper is a suitable solution for phase 1 as it enables free-form sketching as well as handwritten content. In contrast, the requirements for the whiteboard software are diverse. First, participants have to be able to present their individual solutions to others. Second, there should be a way to emphasize and mark the benefits of a certain solution. In addition, the creation of integrated solution directly on the whiteboard should be supported. To meet these requirements two different applications were provided.

Paper Application. The first application allows users to display the content written on paper to the entire group (cf. Fig. 3, left).

It is very important to provide smooth and simple transitions of content between different devices and media. The bare possibility of providing ways to move and copy content in a digital system is no guarantee of actual overhead reduction compared to a traditional setting. For this reason, all pages that contain content are displayed per default in a small preview on the whiteboard without any additional interaction necessary. To ensure privacy during the individual content creation, the creator is able to trigger the public visibility by using a printed button directly on the paper sheet. Individual and also groups of pages can be maximized for presentation or comparison (cf. Fig. 3, left). In addition, the application provides the possibility to select and copy content into a free-form sketching application for further editing (cf. Fig. 3, right).

Sketching Application. This application provides the possibility to create and edit content simultaneously for multiple users. Among others, editing includes erasing, selection, transformation and duplication of content. Moreover, the canvas is divided into pages. This way, the application provides effortless spatial navigation. During the SIS sessions, the page navigation was typically used to shift previous solutions and to generate new space (cf. Fig. 4).

Evaluation Methodologies

There are two types of methods that can be used to evaluate the effectiveness and efficiency of creativity techniques. While outcome-based approaches focuses on the final results produced during the process [START_REF] Shah | Metrics for measuring ideation effectiveness[END_REF], process-based approaches focuses on the ideation process itself.

Outcome-based Approach

Outcome-based approaches focus on evaluating the final result of the ideation process. For assessing ideation quality, researchers usually are guided by the following four steps: First, unique ideas from an ideation session are identified; second, a quality score is assigned to each individual idea (usually done by domain experts, who understand and interpret the ideas [START_REF] Liikkanen | Quantitative Evaluation of the Effectivness of Idea Generation in the Wild[END_REF]); third, by using one of the four approaches discussed below, a metric value is computed, which is used, forth, to make statistical comparisons between treatments of every session threshold [START_REF] Reinig | On the Measurement of Ideation Quality[END_REF].

There is a huge variety of criteria to give a score to each individual idea: The creativity of an idea is usually assessed through novelty -how unusual or unexpected an idea is compared to the other ideas [START_REF] Shah | Metrics for measuring ideation effectiveness[END_REF] -and quality (feasibility or the readiness for implementation and the detail of description [START_REF] Diehl | Productivity Loss In Brainstorming Groups: Toward the Solution of the Riddle[END_REF][START_REF] Diehl | Productivity Loss In idea-generation groups: Tracking down the blocking effect[END_REF]) [START_REF] Liikkanen | Quantitative Evaluation of the Effectivness of Idea Generation in the Wild[END_REF]. Other criteria are utility [START_REF] Liikkanen | Quantitative Evaluation of the Effectivness of Idea Generation in the Wild[END_REF], effectiveness [START_REF] Taylor | Does Group Participation When Using Brainstorming Facilitate or Inhibit Creative Thinking[END_REF], the value ideas could create [START_REF] Boehm | Developing groupware for requirements negotiation: Lessons learned[END_REF], the importance of an idea within a specific context [START_REF] Valacich | Idea generation in computer-based groups: A new ending to an old story[END_REF], and the magnitude of impact an idea might have [START_REF] Dennis | An experimental investigation of the effects of group size in an electronic meeting environment[END_REF]. Usually semantic differentials, such as Likert scales, or rubrics that evaluate one or more dimensions are used to measure those criteria [START_REF] Reinig | On the Measurement of Ideation Quality[END_REF].

Process-based Approach

To fully evaluate the effectiveness and efficiency of a creativity technique and to understand the reasons for specific results, the overall process needs to be analyzed. By using process-based approaches, such as the concept of flow, occurrences of cognitive processes inherent to creative thought are evaluated. Other common evaluation methods are, e.g. video analysis and the 'think aloud' technique [START_REF] Shah | Experimental Investigation of Collaborative Techniques for Progressive Idea Generation Techniques in Engineering Design[END_REF].

Concept of Flow.

How does the user feel ideating? How does the user feel at the beginning, the middle and the end of the task? To answer these questions about how participants experience ideation, Csikszentmihalyi's concept of flow [START_REF] Dorta | Signs of Collaborative Ideation and the Hybrid Ideation Space[END_REF] can be used. It describes a complex psychological state that is characterized as a situation of perceiving an optimal and enjoyable experience by engaging in an activity with total involvement, concentration, and enjoyment. This results in intrinsic motivation and a sense of time distortion. Being in the flow contains: Having clear goals, focusing attention, losing self-consciousness, having an altered sense of time, enjoying the sense of control, and a merge of action and awareness. In summary, it describes the perfect balance between one's skills and the situations challenges, leading to an autotelic experience [START_REF] Csikszentmihalyi | Artistic problems and their solution: an exploration of creativity in the arts[END_REF]. Therefore, one way to measure the psychological state of participants is to measure the balance between the skills and challenges, which is divided into eight possible dimensions: apathy, worry, anxiety, arousal, flow, control, boredom, and relaxation [START_REF] Massimini | La selezione psicologica umana tra biologia e cultura[END_REF]. These parameters can be used as a barometer for reflecting the success of the ideation [START_REF] Dorta | Signs of Collaborative Ideation and the Hybrid Ideation Space[END_REF]. The Flow Wheel (cf. Fig. 5) asks participants to relate their amount of skills to the challenge during the recent activity by putting a single dot into one of the eight dimensions [START_REF] Dorta | The Ideation Gap: Hybrid tools, Design flow and Practice[END_REF].

Fig. 5. The Flow Wheel adapted by Dorta [START_REF] Dorta | The Ideation Gap: Hybrid tools, Design flow and Practice[END_REF]. If adequate skills (x-axis) match adequate challenges (y-axis), the user comes into the flow state that is considered most productive.

Open Coding Video Analysis. Video analysis is a popular approach to gather qualitative data of complex processes and to analyze them quantitatively.

The concrete nature of the findings is often uncertain before the analysis. In this case, open coding video analysis is a promising way to get a deeper understanding of the observed process [START_REF] Tang | Collaborative Coupling over Tabletop Displays[END_REF][START_REF] Isenberg | An exploratory study of visual information analysis[END_REF]. In this method, events in the videos are categorized by using codes that are defined during the coding process. This way, the approach is very flexible but also time consuming, as passages of the video have to be recoded as new codes emerge. Consolvo et al. [START_REF] Consolvo | User Study Techniques in the Design and Evaluation of a Ubicomp Environment[END_REF] refer to a similar technique called LSA (Lag Sequential Analysis), as a valuable technique to generate quantitative and statistical data to observe ubicomp environments.

Our Evaluation Approach

Both categories, process-based as well as outcome-based evaluation methods, were used for evaluation. To get a broad insight into the ideation process, we chose to use a variety of process-based evaluation techniques. We used the Flow Wheel to find out about the participants' psychological state during the different stages of SIS. In addition, we used open coding video analyses to investigate overhead reduction and capture effects on group dynamics that might be a result of the changed environment. The evaluations were completed by an expert evaluation. Experts with different backgrounds (design, technic, and marketing) were asked to rate different aspects of the final results. Based on the above mentioned literature about outcome-based methodology we decided to use five criteria: maturity, usability, consumer benefit, level of detail, and novelty.

Experiment

To explore the digital implementation of the SIS method in use and to compare it with a traditional implementation, we conducted an experiment with students from the department of Innovation and Product Management. The main objective of this study was to get insight on how the use of an interactive, digital environment alters creative processes and group dynamics compared to a non-digital solution. Moreover, we wanted to find out how a digital environment fosters creativity and if it helps to get better ideas.

Reasons for Observing SIS

There are multiple reasons why we chose to use the creativity method SIS for our experiment. Most importantly it is a rather complex technique and involves a lot of different components such as individual and moderator guided collaborative work that also occur in other creativity techniques. In addition, the tools used in the traditional setting (flipcharts, pencil and paper) are rather generic and not tightly bound to this creativity method. Moreover, SIS does not limit the input to a specific type, like e.g. Method 635 [START_REF] Rohrbach | Kreativ nach Regeln -Methode 635, eine neue Technik zum Lösen von Problemen[END_REF], as the users can use sketches or handwriting to phrase ideas. Therefore, we believe that it is an appropriate technique to be studied as it is possible to draw conclusions for a variety of other creativity techniques as well.

Participants

32 of first-year students from the local university participated in the study. The participants were divided into eight groups of four, as four is a commonly used number to study various effects on group dynamics in small groups [START_REF] Baruah | Effects of training on idea generation in groups[END_REF][START_REF] Diehl | Productivity Loss In Brainstorming Groups: Toward the Solution of the Riddle[END_REF]. There were seven females and 25 males between the age of 18 and 38 (M = 24.2, SD = 5.1). Participants in a group were either familiar or very familiar with each other. All participants made use of computers on a regular basis and had prior experience with pen-based interactive whiteboards. However, they were neither familiar with the used applications nor with the SIS technique and its digital implementation.

Moderators

As the moderator is a crucial factor in creativity methods alike SIS we decided to use different moderators in the experiment. This way we tried to balance the effects of single persons on the overall results. Overall five moderators (two female, three male) conducted one or two sessions each. The moderators stayed with the group when switching between the classical and the digital condition. They were not selected from the participant pool. The chosen moderators were more advanced students, who had considerable experience in presentation and workshop moderation. All moderators had prior training with the interactive environment and were familiar with SIS.

Apparatus

In the classic condition two flipcharts were used for public note taking and sketching (cf. Fig. 6. left). In addition, sheets of DIN-A3 paper were used by the participants during the Individual Solution Finding phase. Finally, the room was equipped with two pinboards to provide additional space to mount produced content.

The digital condition was conducted on a large (5.2 m × 1.17m) interactive whiteboard, driven by three Hitachi ultra-short-throw projectors with a total resolution of 3,072 × 768 (cf. Fig. 6. right). The whiteboard system was capable of handling simultaneous multi-user input through multiple Anoto pens (ADP-301). In addition, sheets of paper (DIN-A4) were provided to capture handwriting. For this purpose, multiple Anoto pens (ADP-201) equipped with a ball-pen refill were provided.

Tasks

Due to the use of within-subject design, we had to define two different tasks of a similar degree of complexity, the participants were equally familiar with. Therefore, we asked the participants to design an easy-to-handle drip coffee maker in one and a novel vacuum cleaner in the other condition. We chose these tasks due to their medium complexity that enables participants to come up with different solutions but also with the realistic prospect to complete the tasks within one hour.

Procedure

Every group of four completed two tasks (~60 min each) in total, one using the classical and one using the digital environment. This resulted in a two hour session per group with a short break between the two conditions. Each group was assigned to a moderator that were told to keep track of the overall duration. The tasks and also the order of the conditions were counterbalanced. The SIS process and also the ways of analysis were the same for each method. Both tasks were unveiled to the participants one week before the study, so that they had some time to think about possible solutions.

To evaluate the ideation process using the Flow Wheel, the SIS process was divided into three stages (cf. Fig. 2). At the end of each stage, the participants were asked to complete a questionnaire to measure their mental and psychological state. At the end of both sessions, a questionnaire was handed out to the participants and moderation team to compare the experiences during the sessions. It included several questions focusing on problem description and understanding, visualization, further processing of generated ideas, documentation, and interaction. All sessions got videotaped for later analysis.

Results

In the final questionnaire, the digital condition was preferred by far to the classical setting, especially regarding overview, further processing, and fast visualization of the collected concepts. Also the expert evaluation confirms the advantage of the digital condition. To find out more about the causes of these positive results, we carefully analyzed the process using the above mentioned methodologies.

Outcome-based Results Based on Expert Evaluation

All 16 integrated solutions were visually standardized after all sessions had been completed, to avoid mapping of solutions to a specific condition. In addition, a short explanation was added by the moderator. A heterogeneous group of experts (2 senior designers, 2 senior technicians, 2 marketing experts) rated these solutions independently on a 10-point scale by using the five above mentioned criteria (maturity, usability, consumer benefit, level of detail, and novelty). We can make several interim conclusions from the scores in Fig. 7. C l a s s i c a l D i g i t a l Maturity C l a s s i c a l D i g i t a l Novelty C l a s s i c a l D i g i t a l Usability C l a s s i c a l D i g i t a l Consumer Benefit C l a s s i c a l D i g i t a l A Wilcoxon Signed-Rank Test comparing both techniques showed no significant difference in the maturity (z = -0.771, p = .441). The aspect of novelty was rated better in the digital condition ( ̃digital = 6.5) than in the classical condition ( ̃classic = 4), z = -2.524, p = .012. The outcome of the digital condition was also considered superior by the experts in terms of usability ( ̃classic = 5 vs. ̃digital = 6, z = -2.38, p = .017), consumer benefit ( ̃classic = 5 vs. ̃digital = 6, z = -2.521, p = .012), and level of detail ( ̃classic = 5 vs. ̃digital = 6, z = -1.68, p = .039). In the following section we are going to examine the reasons for these results.

Level of Detail

Process-based Results Based on the Flow Wheel

The diagrams in Fig. 8 show that the overall distribution of the psychological states is not entirely different for the two conditions. In both, we can see that most participants went from flow at the beginning (stage 1) towards the control segment at the end (stage 3). As the conditions did not really differ up to this point, this concord is not a surprise. However, it is interesting to see that, when using the classical SIS technique, already in the middle of the session (stage 2) quite a notable number of participants were in a state of boredom. This trend continued in stage 3, as the challenge level continued dropping. In contrast, in the digital condition, participants experienced a better balance between skills and challenges. Therefore they were kept longer and more consistently in the flow and control dimensions. Fig. 9 shows that participants were immediately able to start their task (stage 1) and to get into the state of flow. Stage 2, in contrast, was new to them. In the digital condition, the majority stayed in flow [START_REF] Guimbretière | Fluid interaction with high-resolution wall-size displays[END_REF] and control [START_REF] Diehl | Productivity Loss In idea-generation groups: Tracking down the blocking effect[END_REF] and only one continued to be anxious. Most of the participants stayed in flow [START_REF] Geyer | Designing Reality-Based Interfaces for Creative Group Work[END_REF] or control (8) also in stage 3, only eight participants felt either bored or relaxed. In contrast Fig. 9 shows a much higher drop-off of participants in the flow for the stages 2 and 3 in the classical condition.

Process-based Results Based on Video analysis

The collected video data was subdivided into fragments of five seconds and analyzed by using open coding [START_REF] Tang | Collaborative Coupling over Tabletop Displays[END_REF][START_REF] Isenberg | An exploratory study of visual information analysis[END_REF]. For each fragment the corresponding phase of the SIS technique was determined. Moreover, the physical activity (e.g. sitting, standing, environment adaption) as well as the core activity (e.g. listening, talking, private / public writing, idle) was identified for each participant and the moderator.

Overhead Reduction. Regarding the reduction of overhead, the video analysis gave us the expected clear confirmation. The average amount of overhead decreased from 8:21 min (SD = 1:02 min) in the classical condition to 4:44 min (SD = 0:44 min) in the digital condition (cf. Fig. 10). The measured time includes activities, such as moving flipcharts and pinboards as well as pining sheets of paper and copying content in the classical condition. In the digital condition, navigation and moving, duplicating, and transforming content were activities considered as overhead.

Fig. 10. Overhead Comparison: Idle refers to the time required for organizational tasks that block the creative process. Time needed to complete in-process questionnaires as well as phase 2 was also often used for organizational tasks. Effects on the Overall Process. While the reduction of overall organizational overhead is quite high (43%) in the digital condition, the reduction of the Idle time -the timespan where the creative process has to be stopped to perform tasks considered as overhead -is much smaller (26%). In both conditions, the time to complete questionnaires was used for organization. In addition, in the classical condition phase 2 was heavily used to copy or duplicate content while the participants were busy with presenting. On multiple occasions in the classic conditions, the moderator asked the participants to continue with the discussion, while he/she was still performing organizational tasks. Fig. 11 shows the temporal sequences observed from two sample groups (1, 2) under the digital (D) and classical (C) condition. Although the overall sequence of the phases was more or less the same, certain differences can be observed. 1C and 2D were the first conditions conducted in the selected group. This is why the introduction was a lot longer. It is also noticeable that the illustrated digital conditions (1D, 2D) had a longer overall duration. Although this finding corresponds with the overall, average durations (classic: 54:06 min; digital: 56:47 min), there are too many different influences to identify a clear trend. For instance, the comparatively long problem framing phase in 2D was due to multiple questions of the participants. Furthermore the integration of the third solution in 1C and the forth solution in 2C were extremely short due to large benefit overlaps between individual and combined solutions.

Comparing the idle phases between the classical and digital conditions shows the average number of idle phases per session is exactly the same (M = 18.25; SD digital = 2.6; SD classical = 0.5). The phases, however, last 7.1% longer in the classical condition. This difference seems to be the result of a small number of extraordinary long idle phases that occur when the moderator is no longer able to handle the overhead simultaneously with running the session. These long idle phases appear in nearly all classical conditions (cf. Fig. 11). In contrast, the idle phases' durations are more equal in the digital conditions. Effects on Participants' Performance. Since there are a lot of variables (e.g. personality, involvement) that affect participants' performance, the results in this section have to be handled with care. By all means, the observed sessions in both conditions were very dynamic. Especially when the moderator was busy with writing or organizing, subgroups that actively discussed issues or did something else, unrelated to the actual problem of the session, emerged very fast. Fig. 12 unveils that the communication of the moderators in phase 2 (Benefit Deduction) and phase 3 increases in the digital condition. Most likely this effect occurred due to the reduced amount of overhead performed in these phases. Moreover, increased attention during phase 2 (Presentation) might also affected this result as the moderators had a better understanding of the solutions. Surprisingly the number of the statements of the participants in phase 2 (Benefit Deduction) rose simultaneously. We suppose this is at least partly due to the increased activity of the moderator.

Discussion

In general, the analyses confirm that digital environments are not only capable of substituting the traditional paper-based environment, but also provide additional values reducing the overhead and can lead to better results. Especially the results of the expert evaluation are very convincing.

The results of the flow analysis (cf. Fig. 8 and Fig. 9) shows that participants stayed considerably longer in a state of flow during the digital condition. Excitement about the novelty of the digital approach might be one possible explanation. However, as all participants were already familiar with the interactive environment, the factor of novelty was eased to a great extent. Therefore, we assume that the ability to stay in the flow for a longer period was primarily caused by other reasons, such as changed interaction patterns between the group and the moderator.

In the classical condition, the moderators attempted to keep the creative process alive by doing organizational work during the actual creative phases. Investigating the

Participants

Digital Classical amount of speech (cf. Fig. 12), we can see that this additional work leads to a decreased participation of the moderator especially in the second part of phase 2 and 3. Without a moderator leading the discussion, the results of most discussions between the participants ended quickly or the participants didn't stay focused. The experiment confirmed that a strong moderator is a very important part in the creativity technique. With decreasing his/her workload, which results in a higher participation and availability, the group productivity and process quality can be increased significantly.

In the light of this finding it is even more important to improve both the digital environment and the interaction concepts to decrease the required overhead even further. However, as currently most of the organizational tasks are accomplished by the moderator, also the adaption of the creativity techniques themselves should be considered. Digital environments enable smooth transitions between different private and public media and thus support more dynamic workflows. This could help the group to reduce their dependency from the moderator or to distribute the organizational overhead among all participants. This way, it would be possible to use the observed dynamic creation of subgroups and discussions more productively and sustainably.

Conclusion and Future Work

In this paper, we compared the performance of the creativity technique SIS in a traditional, paper-based setting to a digital environment with focusing on reducing the organizational overhead. Using a set of versatile methodologies, we did not only prove the advantage of a digital environment, but also investigate the negative effects of overhead when performing a creativity technique. Our findings show that the reduction of overhead does not necessarily result in a decrease of the task execution time. It rather leads to a higher participation of the moderator, higher likeliness for the participants to stay in a state of flow, and finally better and more advanced results.

In future work, we think it is important to intensify the research on interface and interaction techniques that support smooth transitions and effortless content management in digital environments to further reduce unnecessary overhead. Moreover, it will be interesting to develop new concepts of creativity techniques that enrich the dynamic possibilities of digital, interactive environments.

Fig. 3 .

 3 Fig. 3. Content written on digital paper is displayed on the whiteboard for presentation (left). Content generated on paper is clipped into the Sketching Application for further usage (right).

Fig. 4 .

 4 Fig. 4. Typical configuration of the digital environment. One third of the whiteboard is used for the paper application (blue) to display the previously created individual solutions; two thirds are used for the sketching application (green) to create combined solutions. In the course of the session the combined solutions are shifted to the right (symbolized by the arrow) to gain new space.

Fig. 6 .

 6 Fig. 6. The classical condition (two flipcharts, two pinboards, paper DIN-A3) (left). The digital condition (one large interactive whiteboard, digital paper DIN-A4) (right).

Fig. 7 .

 7 Fig. 7. Outcome-based expert evaluation of the final, visually standardized results. Each colored section represents one particular value on a 10-point scale (1=very bad, 10=outstanding).

Fig. 8 .

 8 Fig. 8. Psychological state of the participants during the different stages of the session.

Fig. 9 .

 9 Fig. 9. Number of the participants in the flow state during the different stages.

Fig. 11 .

 11 Fig. 11. Four samples of temporal sequences. 1D and 2D represent digital, 2C and 1C classical conditions.

Fig. 12 .

 12 Fig. 12. Percentage of speech in the different phases and conditions. Due to the possibility of simultaneous comments, the combined time for moderators and participants may exceed 100%.

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Acknowledgements. The presented research has received funding from the European Union's Seventh Framework Programme FP7/2007-2001 under grant agreement n° 318552. The experiment was realized in the "sprint>lab" that is supported by the Austrian Research Promotion Agency (FFG) within the research program COIN. The authors would like to thank the participants as well as the moderators, who helped us to realize the extensive study. We would also like to thank our colleagues from the Media Interaction Lab for their support with the implementation and their useful comments.