the Pattern Maker application, each input device displays a single shape, color, or scale. A shape can also be modified on a cube by rearranging these different shapes, colors, and scales. Shape cubes can be manipulated independently but also modified with color or scale cubes to create new design patterns. Concurrency is achieved through simultaneous access to multiple physical devices where each one displays its own shape, color, or scale.
2) Tangible Models
Tangible Models provides a similar experience, but with each tangible object assuming the geometric properties of a 3D object. The spatial rearrangement of the 3D models is directly correlated with the 3D composition. Concurrency is achieved through simultaneous access to multiple 3D models, each on a separate physical object. A protocol study of designers using Tangible Models, described in Kim and Maher (2008), showed that users were more focused on the spatial and functional relationships among the individual 3D objects than on the properties of each object when compared to an interaction design that was time-multiplexed (keyboard and mouse). With the direct, naïve manipulability of physical objects and rapid visualization, designers in the TUI environment produced more cognitive actions and completed the design tasks faster.
2.2.3 STRONG SPECIFIC DEVICES
TUIs provide strong specific devices for interacting with the system. This offers more efficiency because the tangible objects are designed to be more specialized and tailored for working on a given task in order to increase the directness and intuitiveness of interactions (Le Goc et al., 2015; Hornecker, 2005). The design of appropriate physical representations is a very important aspect of tangible interface design (Ullmer and Ishii, 2000). To create strong specific devices, the most common approach is to utilize existing objects into which position sensors or ID tags are inserted. Alternatively, strong specific devices are achieved with Augmented Reality (AR), where each physical device is associated with a virtual object. The user interacts with a virtual object by manipulating the corresponding physical object (Waldner et al., 2006). While seeing virtual imagery superimposed on physical objects, the user perceives interaction with the digital object. These specialized interactive objects may lack generality and therefore may not be effective for some tasks. This loss of generality may be overcome by the advantages provided by task-specific physical tools (Fitzmaurice, 1996). Tangible user interaction with physical objects that have a specialized form and appearance offer affordances normally associated only with the physical object.
1) Tangible Keyboard
In the case of the Tangible Keyboard, the form is constant (cube-like objects with a display) and the appearance (display) is variable. The image on the display is designed to fit the context of the tasks supported by the application. The affordances of these specific devices are those associated with the shape of the object and the content on the display. In the Pattern Maker application, shape cubes are rearranged to form patterns and color cubes are tilted to pour a new color on a shape. These strong specific devices do not have the generality of the mouse for selecting any function, but provide strong feedback on the functions enabled by the application.
2) Tangible Models
With Tangible Models, simple 3D blocks as tangible devices are rearranged on a tabletop system with a vertical display of the 3D scene. Each block is associated with a single 3D model, providing a strong specific device for creating a composition of a scene or spatial design. With static mappings and multiple input objects, 3D blocks as tangible input elements can be expressive and provide affordances specific to the object they represent. The visualization of each 3D block directly indicates its meaning or function while the user is moving the pieces and making a composition.
2.2.4 SPATIALLY AWARE COMPUTATIONAL DEVICES
Spatially aware computational devices and spatial configurations are important concepts in embodied interaction. A physical object in TUIs is typically aware of its spatial position and is registered with a central processing unit. Both position and orientation are critical pieces of information to be sensed (Fitzmaurice, 1996; Valdes et al., 2014). Proximity information is possible through communication to a central processing unit or independent sensors on each device. Applications that are more graphic than alphanumeric benefit from having spatially aware input devices, as graphical tasks are inherently spatial in nature (Fitzmaurice, 1996). Spatially aware computational devices allow users to interact with complex information spaces in a physical way by changing the spatial position and orientation of tangible devices.
1) Tangible Keyboard
Tangible Keyboard is built on the hardware/software platform of Sifteo cubes™ and the sensors include adjacency awareness and accelerometers. These sensors allow the cubes to be aware of other cubes and the movements of each cube, such as shaking, tilting, and turning over. By communicating with a central processor, the rearrangement and movements of the cubes can be mapped onto input events related to the composition task. For the Pattern Maker application, spatial awareness of the individual devices allows the user to form compositions and to modify the shape, color, and scale of elements of the composition.
2) Tangible Models
Tangible Models is built on the software platform of the ARToolkit, in which spatial awareness is achieved by a camera that senses the location of predefined markers (Kato et al., 2001). The assignment of each marker to a 3D model allows the superposition of the visualization of the 3D model on the block. The identification of a marker in the physical space sensed by the camera allows the movement of the block in the physical space to be tracked and visualized in the digital space and displayed on the tabletop for the plan view and on the vertical screen for the perspective view.
2.2.5 SPATIAL RECONFIGURABILITY OF DEVICES
Tangible objects are discrete, spatially reconfigurable physical objects that represent and control digital information. Tangible objects enable reconfiguration, which provides the feeling that users are actually holding and rearranging the information itself. According to Fitzmaurice (1996), the spatial reconfiguration of physical elements such as placement, removal, orientation, and translation are the modes of interaction with tangible interfaces. Those physical controls generally communicate with the surrounding environment and contribute to its overall function and use. The value of discrete, spatially reconfigurable interactive devices goes beyond the value in grasping and rearranging the devices because the physicality of the device serves as a cognitive aid by providing an external cue for a particular function or data item. Users can rapidly reconfigure and rearrange the devices in a workspace and customize their space to suit their own needs in task workflows and task switching (Fitzmaurice, 1996). While this can be achieved in some WIMP interfaces, the use of tangible devices makes this reconfiguration as simple as holding the device and moving it to a new location.
1) Tangible Keyboard
Tangible Keyboard enables configuration of elements within an application or across applications. In the Pattern Maker application, each cube can represent a shape, color, or scale. Within that application, the display and meaning of a specific cube can be changed from a shape to a color to a scale. Across applications, when, for example, comparing the Pattern Maker application to the Silly Poems application, the display on a cube can be changed from a shape to a word. Seeing the Tangible Keyboard, even when it is not being used, conveys an interaction design of physical manipulation and spatial configuration of the physical elements within the interaction design.
2) Tangible Models
Tangible Models enables configuration of models within or across applications. Within an application, the 3D model associated with each block can be changed by selecting another object from the library to assign to a specific block. Across
