Collaborative interactions with many existing digital tabletop systems lack the fluidity of collaborating around a table using traditional media. This paper presents a critical analysis of the current state-of-the-art in digital tabletop systems research, targeted at discovering how user requirements for collaboration are currently being met and uncovering areas requiring further development. By considering research on tabletop displays, collaboration, and communication, several design guidelines for effective colocated collaboration around a tabletop display emerged. These guidelines suggest that technology must support: (1) natural interpersonal interaction, (2) transitions between activities, (3) transitions between personal and group work, (4) transitions between tabletop collaboration and external work, (5) the use of physical objects, (6) accessing shared physical and digital objects, (7) flexible user arrangements, and (8) simultaneous user interactions. The critical analysis also revealed several important directions for future research, including: standardization of methods to evaluate co-located collaboration; comparative studies to determine the impact of existing system configurations on collaboration; and creation of a taxonomy of collaborative tasks to help determine which tasks and activities are suitable for tabletop collaboration.

This paper borrows ideas from social science to inform the design of novel "sensing" user-interfaces for computing technology. Specifically, we present five design challenges inspired by analysis of human-human communication that are mundanely addressed by traditional graphical user interface designs (GUIs). Although classic GUI conventions allow us to finesse these questions, recent research into innovative interaction techniques such as `Ubiquitous Computing' and `Tangible Interfaces' has begun to expose the interaction challenges and problems they pose. By making them explicit we open a discourse on how an approach similar to that used by social scientists in studying human-human interaction might inform the design of novel interaction mechanisms that can be used to handle human-computer communication accomplishments.

We present Audiopad, an interface for musical performance that aims to combine the modularity of knob based controllers with the expressive character of multidimensional tracking interfaces. The performer's manipulations of physical pucks on a tabletop control a real-time synthesis process. The pucks are embedded with LC tags that the system tracks in two dimensions with a series of specially shaped antennae. The system projects graphical information on and around the pucks to give the performer sophisticated control over the synthesis process.

The task of organizing information is typically performed either by physically manipulating note cards or sticky notes or by arranging icons on a computer with a graphical user interface. We present a new tangible interface platform for manipulating discrete pieces of abstract information, which attempts to combine the benefits of each of these two alternatives into a single system. We developed interaction techniques and an example application for organizing conference papers. We assessed the effectiveness of our system by experimentally comparing it to both graphical and paper interfaces. The results suggest that our tangible interface can provide a more effective means of organizing, grouping, and manipulating data than either physical operations or graphical computer interaction alone.

In recent years we have seen a proliferation of musical tables. Believing that this is not just the result of a tabletop trend, in this paper we first discuss several of the reasons for which live music performance and HCI in general, and musical instruments and tabletop interfaces in particular, can lead to a fertile two-way cross-pollination that can equally benefit both fields. After that, we present the reacTable, a musical instrument based on a tabletop interface that exemplifies several of these potential achievements. Author Keywords Tangible interfaces, tabletop interfaces, musical instrument, musical performance, design, interaction techniques. ACM Classification Keywords H.5.2 [User Interfaces]: interaction styles, input devices and strategies J.5: [Arts and Humanities]: performing arts.

If a mobile computing device knows how it is positioned and oriented in relation to other devices nearby, then it can provide enhanced support for multi-device and multi-user interactions. Existing systems that provide position information to mobile computers are reliant on externally deployed infrastructure, such as beacons or sensors in the environment. We introduce the Relate system, which provides fine-grained relative position information to co-located devices on the basis of peer-topeer sensing, thus overcoming dependence on any external infrastructure. The system is realised as a hardware /software plug-in, using ultrasound for peer-to-peer sensing, USB to interface with standard mobile devices, and data abstraction and inferencing to map sensor data to a spatial model that maintains both quantitative and qualitative relationships. We present a set of services and applications to demonstrate the utility of the system. We report experimental results on the accuracy of the relative position and orientation estimates, and other aspects of system performance.

This paper describes how to instrument the physical world so that objects become self-describing, communicating their identity, geometry, and other information such as history or user annotation. The enabling technology is a wireless tag which acts as a radio frequency identity and geometry (RFIG) transponder. We show how addition of a photo-sensor to a wireless tag significantly extends its functionality to allow geometric operations- such as finding the 3D position of a tag, or detecting change in the shape of a tagged object. Tag data is presented to the user by direct projection using a handheld locale-aware mobile projector. We introduce a novel technique that we call interactive projection to allow a user to interact with projected information e.g. to navigate or update the projected information. The ideas are demonstrated using objects with active radio frequency (RF) tags. But the work was motivated by the advent of unpowered passive-RFID, a technology that promises to have significant impact in real-world applications. We discuss how our current prototypes could evolve to passive-RFID in the future.

The Navigational Blocks project demonstrates a tangible user interface that facilitates retrieval of historical stories in a tourist spot. Orientation, movement, and relative positions of physical Blocks support visitor navigation and exploration in a virtual gallery. The Navigational Blocks system provides a physical embodiment of digital information through tactile manipulation and haptic feedback. The simple cubic form of the Blocks is easy to understand and therefore easy to use to manipulate complex digital information. Electromagnets embedded in the Blocks and wireless communication encourage users to quickly rearrange the Blocks to form different database queries.

This paper introduces a new framework for thinking about tangible interfaces in education, with specific focus on abstract problem domains. Manipulatives are physical objects specifically designed to foster learning. We offer a new classification of Manipulatives: “Froebel-inspired Manipulatives ” (FiMs) and “Montessori-inspired Manipulatives ” (MiMs). We argue that FiMs are design materials, fostering modeling of real-world structures. We show that our classification extends to computationally enhanced versions of manipulatives. We present Digital MiMs – computationally enhanced building blocks. We describe two prototypical members of the Digital MiMs class: FlowBlocks and SystemBlocks, physical, modular interactive systems that serve as generalpurpose modeling and simulation tools for dynamic behavior. We present findings from qualitative studies, and conclude that digital MiMs are accessible to young children, engaging, and encourage learning of abstract structures of dynamic behavior through an iterative process of hands-on modeling, simulating, and analogizing. Authors Keywords TUI, Digital manipulatives, Simulation, Education, Toys. ACM Classification H5.2. Information interfaces and presentation (e.g., HCI): User Interfaces. Figure 1: A “normal distribution ” simulation

This system paper reports on some of the advantages tangible interaction can bring to chemistry education. The paper describes the realisation of an in-house designed Tangible User Interface (TUI) called Augmented Chemistry (AC). A set of interactive tools work within this system. Using these tools, elements can be chosen from a booklet menu and composed into 3D molecular models. The tools indicate one way towards realising a seamless integration of the physical and digital realms. Since many tools can be used concurrently, single and multiple users can interact with the system at a time. To use the system in an educational context, it was extended into an educational workbench drawing on haptic and aural augmentation. The design and implementation of the AC system required contributions from optics, mathematics, molecular chemistry, software engineering, and 3D programming, making it a truly interdisciplinary project. Future challenges lie in user acceptance, educational effect, and further system development. Keywords AR educational application, chemistry education, display hardware, haptic and aural augmentation, tangible user interface (TUI) 3D INTERACTION IN AR WORKBENCHES While some TUIs offer planar interaction, such as Tangible Bricks [4], other systems offer 3D interaction, such as Cubes [3][6]. Wireless tracking of interaction handles may be either optical [3][4][5][6] or electromagnetic [7]. This paper reports on an in-house designed TUI performing 3D optical tracking of an interaction cube. Such systems can benefit 3D interaction by offering a more direct form of interaction coming closer to the use of physical artefacts and tools. This offers users a more natural use of hand and body movements. Such movements may hence be integrated into the interaction with digital information, thereby supporting a fluent handling of 3D models [5].