Tangible user interface
A tangible user interface (TUI) is a user interface in which a person interacts with digital information through the physical environment. The initial name was Graspable User Interface, which is no longer used. The purpose of TUI development is to empower collaboration, learning, and design by giving physical forms to digital information, thus taking advantage of the human ability to grasp and manipulate physical objects and materials.
One of the pioneers in tangible user interfaces is Hiroshi Ishii, a professor in the MIT Media Laboratory who heads the Tangible Media Group. His particular vision for tangible UIs, called Tangible Bits, is to give physical form to digital information, making bits directly manipulable and perceptible. Tangible bits pursues the seamless coupling between physical objects and virtual data.
- Physical representations are computationally coupled to underlying digital information.
- Physical representations embody mechanisms for interactive control.
- Physical representations are perceptually coupled to actively mediated digital representations.
- Physical state of tangibles embodies key aspects of the digital state of a system
According to Mi Jeong Kim and Mary Lou Maher, the five basic defining properties of tangible user interfaces are as follows:
- space-multiplex both input and output;
- concurrent access and manipulation of interface components;
- strong specific devices;
- spatially aware computational devices;
- spatial re-configurability of devices.
Differences: Tangible and Graphical user interface
A Tangible user interface must be differentiated by a Graphical user interface (GUI). A Graphical User Interface exists only in the digital world where as the TUI connects the digital with the physical world. For example a screen displays the digital information, where as a mouse allows us to directly interact with this digital information. Moreover a Tangible user interface also represents the input in the physical world, unlike the Graphical user interface, and makes the digital information directly graspable.
A Tangible user interface is usually built for one specific target group, because of the low range of possible application areas. Therefore, the design of the interface must be developed together with the target group to ensure a good user experience.
In comparison with a TUI, the Graphical user interface has a wide range of usages in one interface. Because of that it targets a large group of possible users.
One advantage of the Tangible user interface is the user experience, because it occurs a physical interaction between the user and the interface itself (E.g.: SandScape: Building your own landscape with sand). Another advantage is the usability, because the user knows intuitive how to use the interface by knowing the function of the physical object. So, the user does not need to learn the functionality. That is why the Tangible User interface is often used to make technology more accessible for elderly people. 
|Interface type/Attributes||Tangible user interface||Graphical user interface|
|Amount of possible application areas||Build for one specific application area||Build for many kinds of application areas|
|How the system is driven||physical objects, such as a mouse or a keyboard||Based on graphical bits, such as pixels on the screen|
|Coupling between cognitive bits and the physical output||Unmediated connection||Indirect connection|
|How user experience is driven||The user already knows the function of the interface by knowing the physical objects function||The user explores the functionality of the interface|
|User behavior when approaching the system||Intuition||Recognition|
A simple example of tangible UI is the computer mouse: Dragging the mouse over a flat surface moves a pointer on the screen accordingly. There is a very clear relationship about the behaviors shown by a system with the movements of a mouse. Other examples include:
- Marble Answering Machine by Durrell Bishop (1992). A marble represents a single message left on the answering machine. Dropping a marble into a dish plays back the associated message or calls back the caller.
- The Topobo system. The blocks in Topobo are like LEGO blocks which can be snapped together, but can also move by themselves using motorized components. A person can push, pull, and twist these blocks, and the blocks can memorize these movements and replay them.
- Implementations which allow the user to sketch a picture on the system's table top with a real tangible pen. Using hand gestures, the user can clone the image and stretch it in the X and Y axes just as one would in a paint program. This system would integrate a video camera with a gesture recognition system.
- jive. The implementation of a TUI helped make this product more accessible to elderly users of the product. The 'friend' passes can also be used to activate different interactions with the product.
- On the basis of the TUI, commercial toys are being created, such as Sifteo, which allows playing games in a mixed reality, on the surface of a set of cubes (the development of students of MIT) or WOWCube (the development of the Californian company), which allows playing games in a mixed reality, on the surface a three-dimensional puzzle.
- SandScape: Designing landscape with TUI. This interface lets the user form a landscape out of sand on a table. The sand model represents the terrain, which is projected on the surface. In real-time the model projects the deformations of the sand. 
Several approaches have been made to establish a generic middleware for TUIs. They target toward the independence of application domains as well as flexibility in terms of the deployed sensor technology. For example, Siftables provides an application platform in which small gesture sensitive displays act together to form a human-computer interface.
For collaboration support, TUIs have to allow the spatial distribution, asynchronous activities, and the dynamic modification of the TUI infrastructure, to name the most prominent ones. This approach presents a framework based on the LINDA tuple space concept to meet these requirements. The implemented TUIpist framework deploys arbitrary sensor technology for any type of application and actuators in distributed environments.
State of the art
Interest in tangible user interfaces (TUIs) has grown constantly since the 1990s, and with every year, more tangible systems are showing up. A 2017 white paper outlines the evolution of TUIs for touch table experiences and raises new possibilities for experimentation and development.
In 1999, Gary Zalewski patented a system of moveable children's blocks containing sensors and displays for teaching spelling and sentence composition.
Tangible Engine is a proprietary authoring application used to build object-recognition interfaces for projected-capacitive touch tables. The Tangible Engine Media Creator allows users with little or no coding experience to quickly create TUI-based experiences.
The MIT Tangible Media Group, headed by Hiroshi Ishi is continuously developing and experimenting with TUIs including many tabletop applications.
The Urp and the more advanced Augmented Urban Planning Workbench allows digital simulations of air flow, shadows, reflections, and other data based on the positions and orientations of physical models of buildings, on the table surface.
Newer developments go even one step further and incorporate the third dimension by allowing a user to form landscapes with clay (Illuminating Clay) or sand (Sand Scape). Again different simulations allow the analysis of shadows, height maps, slopes and other characteristics of the interactively formable landmasses.
InfrActables is a back projection collaborative table that allows interaction by using TUIs that incorporate state recognition. Adding different buttons to the TUIs enables additional functions associated to the TUIs. Newer versions of the technology can even be integrated into LC-displays by using infrared sensors behind the LC matrix.
The Tangible Disaster allows the user to analyze disaster measures and simulate different kinds of disasters (fire, flood, tsunami,.) and evacuation scenarios during collaborative planning sessions. Physical objects allow positioning disasters by placing them on the interactive map and additionally tuning parameters (i.e. scale) using dials attached to them.
The commercial potential of TUIs has been identified recently. The repeatedly awarded Reactable, an interactive tangible tabletop instrument, is now distributed commercially by Reactable Systems, a spinoff company of the Pompeu Fabra University, where it was developed. With the Reactable users can set up their own instrument interactively, by physically placing different objects (representing oscillators, filters, modulators...) and parametrise them by rotating and using touch-input.
Microsoft is distributing its novel Windows-based platform Microsoft Surface (now Microsoft PixelSense) since 2009. Beside multi-touch tracking of fingers, the platform supports the recognition of physical objects by their footprints. Several applications, mainly for the use in commercial space, have been presented. Examples range from designing an own individual graphical layout for a snowboard or skateboard to studying the details of a wine in a restaurant by placing it on the table and navigating through menus via touch input. Interactions such as the collaborative browsing of photographs from a handycam or cell phone that connects seamlessly once placed on the table are also supported.
Another notable interactive installation is instant city that combines gaming, music, architecture and collaborative aspects. It allows the user to build three-dimensional structures and set up a city with rectangular building blocks, which simultaneously results in the interactive assembly of musical fragments of different composers.
The development of the Reactable and the subsequent release of its tracking technology reacTIVision under the GNU/GPL as well as the open specifications of the TUIO protocol have triggered an enormous amount of developments based on this technology.
In the last few years, many amateur and semi-professional projects outside of academia and commerce have been started. Due to open source tracking technologies (reacTIVision) and the ever-increasing computational power available to end-consumers, the required infrastructure is now accessible to almost everyone. A standard PC, webcam, and some handicraft work allows individuals to set up tangible systems with a minimal programming and material effort. This opens doors to novel ways of perceiving human-computer interaction and allows for new forms of creativity for the public to experiment with.
It is difficult to keep track and overlook the rapidly growing number of all these systems and tools, but while many of them seem only to utilize the available technologies and are limited to initial experiments and tests with some basic ideas or just reproduce existing systems, a few of them open out into novel interfaces and interactions and are deployed in public space or embedded in art installations.
The Tangible Factory Planning is a tangible table based on reacTIVision that allows to collaboratively plan and visualize production processes in combination with plans of new factory buildings and was developed within a diploma thesis.
Another example of the many reacTIVision-based tabletops is ImpulsBauhaus-Interactive Table and was on exhibition at the Bauhaus-University in Weimar marking the 90th anniversary of the establishment of Bauhaus. Visitors could browse and explore the biographies, complex relations and social networks between members of the movement.
Using principles derived from embodied cognition, cognitive load theory, and embodied design TUIs have been shown to increase learning performance by offering multimodal feedback. However, these benefits for learning require forms of interaction design that leave as much cognitive capacity as possible for learning.
A physical icon, or phicon, is the tangible computing equivalent of an icon in a traditional graphical user interface, or GUI. Phicons hold a reference to some digital object and thereby convey meaning.
Physical icons were first used as tanglible interfaces in the metaDesk project built in 1997 by Professor Hiroshi Ishii's tanglible bits research group at MIT. The metaDesk consisted of a table whose surface showed a rear-projected video image. Placing a phicon on the table triggered sensors that altered the video projection.
- Ishii, Hiroshi (28 October 2017). "Tangible bits". Tangible Bits: Beyond Pixels. ACM. pp. xv–xxv. doi:10.1145/1347390.1347392. ISBN 9781605580043.
- Kim, Mi Jeong; Maher, Mary Lou (2008). "The Impact of Tangible User Interfaces on Designers' Spatial Cognition" (PDF). Human–Computer Interaction. 23 (2): 101–137. doi:10.1080/07370020802016415. ISSN 0737-0024.
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- Urp: a luminous-tangible workbench for urban planning and design John Underkoffler, Hiroshi Ishii May 1999 CHI '99: Proceedings of the SIGCHI conference on Human factors in computing systems
- Augmented Urban Planning Workbench: Overlaying Drawings, Physical Models and Digital Simulation Hiroshi Ishii, Eran Ben-Joseph, John Underkoffler, Luke Yeung, Dan Chak, Zahra Kanji, Ben Piper September 2002 ISMAR '02: Proceedings of the 1st International Symposium on Mixed and Augmented Reality
- Piper, Ben; Ratti, Carlo; Ishii, Hiroshi (28 October 2017). "Illuminating clay". Illuminating Clay: A 3-D Tangible Interface for Landscape Analysis. ACM. pp. 355–362. doi:10.1145/503376.503439. ISBN 978-1581134537.
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- MightyTrace: Multiuser Tracking Technology on LC-displays, R. Hofer, A. Kunz, P. Kaplan, Proceedings of the twenty-sixth annual SIGCHI conference on Human factors in computing systems, 2008, Florence, Italy.
- Tangible user interface for supporting disaster education Kazue Kobayashi, Tatsuhito Kakizaki, Atsunobu Narita, Mitsunori Hirano, Ichiro Kase August 2007 SIGGRAPH '07: SIGGRAPH 2007 posters
- The reacTable: exploring the synergy between live music performance and tabletop tangible interfaces Sergi Jordà, Günter Geiger, Marcos Alonso, Martin Kaltenbrunner February 2007 TEI '07: Proceedings of the 1st international conference on Tangible and embedded interaction
- Demo I Microsoft Surface and the Single View Platform Josh Wall May 2009 CTS '09: Proceedings of the 2009 International Symposium on Collaborative Technologies and Systems
- instant city: a music building game table Sibylle Hauert, Daniel Reichmuth, Volker Böhm June 2007 NIME '07: Proceedings of the 7th international conference on New interfaces for musical expression
- reacTIVision: a computer-vision framework for table-based tangible interaction Martin Kaltenbrunner, Ross Bencina February 2007 TEI '07: Proceedings of the 1st international conference on Tangible and embedded interaction
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- Tangible Factory Planning, Diploma Thesis, Daniel Guse, http://www.danielguse.de/tangibletable.php
- Martin Kaltenbrunner and Ross Bencina. 2007. "reacTIVision: a computer-vision framework for table-based tangible interaction". In Proceedings of the 1st international conference on Tangible and embedded interaction (TEI '07). ACM, New York, NY, USA, 69-74. doi:10.1145/1226969.1226983
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- TUIO open framework for tangible multitouch surfaces at TUIO.org
- Encyclopedia entry on the history of Tangible Interaction and Tangible User Interfaces
- White paper on The Evolution of Tangible User Interfaces on Touch Tables