input

We present HybridPointing, a technique that lets users easily switch between absolute and relative pointing with a direct input device such as a pen. Our design includes a new graphical element, the Trailing Widget, which remains "close at hand" but does not interfere with normal cursor operation. The use of visual feedback to aid the user's understanding of input state is discussed, and several novel visual aids are presented. An experiment conducted on a large, wall-sized display validates the benefits of HybridPointing under certain conditions. We also discuss other situations in which HybridPointing may be useful. Finally, we present an extension to our technique that allows for switching between absolute and relative input in the middle of a single drag-operation.

We present an evaluation of three mouse-based techniques for aligning digital images. We investigate the physical image alignment task and discuss the implications for interacting with virtual images. In a formal evaluation we show that a symmetric bimanual technique outperforms an asymmetric bimanual technique which in turn outperforms a unimanual technique. We show that even after mode switching times are removed, the symmetric technique outperforms the single mouse technique. Subjects also exhibited more parallel interaction using the symmetric technique than when using the asymmetric technique.

We explore the design space of a two-sided interactive touch table, designed to receive touch input from both the top and bottom surfaces of the table. By combining two registered touch surfaces, we are able to offer a new dimension of input for co-located collaborative groupware. This design accomplishes the goal of increasing the relative size of the input area of a touch table while maintaining its direct-touch input paradigm. We describe the interaction properties of this two-sided touch table, report the results of a controlled experiment examining the precision of user touches to the underside of the table, and a series of application scenarios we developed for use on inverted and two-sided tables. Finally, we present a list of design recommendations based on our experiences and observations with inverted and two-sided tables.

Touch is a compelling input modality for interactive devices; however, touch input on the small screen of a mobile device is problematic because a user's fingers occlude the graphical elements he wishes to work with. In this paper, we present LucidTouch, a mobile device that addresses this limitation by allowing the user to control the application by touching the back of the device. The key to making this usable is what we call pseudo-transparency: by overlaying an image of the user's hands onto the screen, we create the illusion of the mobile device itself being semi-transparent. This pseudo-transparency allows users to accurately acquire targets while not occluding the screen with their fingers and hand. Lucid Touch also supports multi-touch input, allowing users to operate the device simultaneously with all 10 fingers. We present initial study results that indicate that many users found touching on the back to be preferable to touching on the front, due to reduced occlusion, higher precision, and the ability to make multi-finger input.

A passive wand tracked in 3D using computer vision techniques is explored as a new input mechanism for interacting with large displays. We demonstrate a variety of interaction techniques that exploit the affordances of the wand, resulting in an effective interface for large scale interaction. The lack of any buttons or other electronics on the wand presents a challenge that we address by developing a set of postures and gestures to track state and enable command input. We also describe the use of multiple wands, and posit designs for more complex wands in the future.

The VideoMouse is a mouse that uses a camera as its input sensor. A real-time vision algorithm determines the six degree-of-freedom mouse posture, consisting of 2D motion, tilt in the forward/back and left/right axes, rotation of the mouse about its vertical axis, and some limited height sensing. Thus, a familiar 2D device can be extended for three-dimensional manipulation, while remaining suitable for standard 2D GUI tasks. We describe techniques for mouse functionality, 3D manipulation, navigating large 2D spaces, and using the camera for lightweight scanning tasks.

A technique for creating a touch-sensitive input device is proposed which allows multiple, simultaneous users to interact in an intuitive fashion. Touch location information is determined independently for each user, allowing each touch on a common surface to be associated with a particular user. The surface generates location dependent, modulated electric fields which are capacitively coupled through the users to receivers installed in the work environment. We describe the design of these systems and their applications. Finally, we present results we have obtained with a small prototype device.

Tracking both hands in free-space with accompanying speech input can augment the user's ability to communicate with computers. This paper discusses the kinds of situations which call for two-handed input and not just the single hand, and reports a prototype in which two-handed gestures serve to input concepts, both static and dynamic, manipulate displayed items, and specify actions to be taken. Future directions include enlargement of the vocabulary of two-handed “coverbal” gestures and the modulation by gaze of gestural intent.

We present a survey of design issues for developing effective free-space three-dimensional (3D) user interfaces. Our survey is based upon previous work in 3D interaction, our experience in developing free-space interfaces, and our informal observations of test users. We illustrate our design issues using examples drawn from instances of 3D interfaces.

For example, our first issue suggests that users have difficulty understanding three-dimensional space. We offer a set of strategies which may help users to better perceive a 3D virtual environment, including the use of spatial references, relative gesture, two-handed interaction, multisensory feedback, physical constraints, and head tracking. We describe interfaces which employ these strategies.

Our major contribution is the synthesis of many scattered results, observations, and examples into a common framework. This framework should serve as a guide to researchers or systems builders who may not be familiar with design issues in spatial input. Where appropriate, we also try to identify areas in free-space 3D interaction which we see as likely candidates for additional research.

An extended and annotated version of the references list for this paper is available on-line through mosaic at address http://uvacs.cs.virginia.edu/~kph2q/.

We present experimental work which explores how the match (or mismatch) between the input space of the hands and the output space of a graphical display influences two-handed input performance. During interaction with computers, a direct correspondence between the input and output spaces is often lacking. Not only are the hands disjoint from the display space, but the reference frames of the hands may in fact be disjoint from one another if two separate input devices (e.g. two mice) are used for two-handed input. In general, we refer to the workspace and origin within which the hands operate as kinesthetic reference frames. Our goal is to better understand how an interface designer's choice of kinesthetic reference frames influences a user's ability to coordinate two-handed movements, and to explore how the answer to this question may depend on the availability of visual feedback. Understanding this issue has implications for the design of two-handed interaction techniques and input devices, as well as for the reference principle of Guiard's Kinematic Chain model of human bimanual action. Our results suggest that the Guiard reference principle is robust with respect to variances in the kinesthetic reference frames as long as appropriate visual feedback is present.

Although cell phones are extremely useful, they can be annoying and distracting to owners and others nearby. We describe sensing techniques intended to help make mobile phones more polite and less distracting. For example, our phone's ringing quiets as soon as the user responds to an incoming call, and the ring mutes if the user glances at the caller ID and decides not to answer. We also eliminate the need to press a TALK button to answer an incoming call by recognizing if the user picks up the phone and listens to it.

High precision parameter manipulation tasks typically require adjustment of the scale of manipulation in addition to the parameter itself. This paper introduces the notion of Zoom Sliding, or Zliding, for fluid integrated manipulation of scale (zooming) via pressure input while parameter manipulation within that scale is achieved via x-y cursor movement (sliding). We also present the Zlider (Figure 1), a widget that instantiates the Zliding concept. We experimentally evaluate three different input techniques for use with the Zlider in conjunction with a stylus for x-y cursor positioning, in a high accuracy zoom and select task. Our results marginally favor the stylus with integrated isometric pressure sensing tip over bimanual techniques which separate zooming and sliding controls over the two hands. We discuss the implications of our results and present further designs that make use of Zliding.

Soap is a pointing device based on hardware found in a mouse, yet works in mid-air. Soap consists of an optical sensor device moving freely inside a hull made of fabric. As the user applies pressure from the outside, the optical sensor moves independent from the hull. The optical sensor perceives this relative motion and reports it as position input. Soap offers many of the benefits of optical mice, such as high-accuracy sensing. We describe the design of a soap prototype and report our experiences with four application scenarios, including a wall display, Windows Media Center, slide presentation, and interactive video games.

Information cannot be found if it is not recorded. Existing rich graphical application approaches interfere with user input in many ways, forcing complex interactions to enter simple information, requiring complex cognition to decide where the data should be stored, and limiting the kind of information that can be entered to what can fit into specific applications' data models. Freeform text entry suffers from none of these limitations but produces data that is hard to retrieve or visualize. We describe the design and implementation of Jourknow, a system that aims to bridge these two modalities, supporting lightweight text entry and weightless context capture that produces enough structure to support rich interactive presentation and retrieval of the arbitrary information entered.

We present SketchREAD, a multi-domain sketch recognition engine capable of recognizing freely hand-drawn diagrammatic sketches. Current computer sketch recognition systems are difficult to construct, and either are fragile or accomplish robustness by severely limiting the designer's drawing freedom. Our system can be applied to a variety of domains by providing structural descriptions of the shapes in that domain; no training data or programming is necessary. Robustness to the ambiguity and uncertainty inherent in complex, freely-drawn sketches is achieved through the use of context. The system uses context to guide the search for possible interpretations and uses a novel form of dynamically constructed Bayesian networks to evaluate these interpretations. This process allows the system to recover from low-level recognition errors (e.g., a line misclassified as an arc) that would otherwise result in domain level recognition errors. We evaluated Sketch-READ on real sketches in two domains--family trees and circuit diagrams--and found that in both domains the use of context to reclassify low-level shapes significantly reduced recognition error over a baseline system that did not reinterpret low-level classifications. We also discuss the system's potential role in sketch based user interfaces.

As technical as we have become, modern computing has not permeated many important areas of our lives, including mathematics education which still involves pencil and paper. In the present study, twenty high school geometry students varying in ability from low to high participated in a comparative assessment of math problem solving using existing pencil and paper work practice (PP), and three different interfaces: an Anoto-based digital stylus and paper interface (DP), pen tablet interface (PT), and graphical tablet interface (GT). Cognitive Load Theory correctly predicted that as interfaces departed more from familiar work practice (GT > PT > DP), students would experience greater cognitive load such that performance would deteriorate in speed, attentional focus, meta-cognitive control, correctness of problem solutions, and memory. In addition, low-performing students experienced elevated cognitive load, with the more challenging interfaces (GT, PT) disrupting their performance disproportionately more than higher performers. The present results indicate that Cognitive Load Theory provides a coherent and powerful basis for predicting the rank ordering of users' performance by type of interface. In the future, new interfaces for areas like education and mobile computing could benefit from designs that minimize users' load so performance is more adequately supported.

This paper describes a testbed and method for characterizing the dynamic response of the type of spatial displacement transducers commonly used in virtual environment (VE) applications. The testbed consists of a motorized rotary swing arm that imparts known displacement inputs to the VE sensor. The experimental method involves a series of tests in which the sensor is displaced back and forth at a number of controlled frequencies that span the bandwidth of volitional human movement. During the tests, actual swing arm angle and reported VE sensor displacements are collected and time stamped. Because of the time stamping technique, the response time of the sensor can be measured directly, independent of latencies in data transmission from the sensor unit and any processing by the interface applications running on the host computer. Analysis of these experimental results allows sensor time delay and gain characteristics to be determined as a function of input frequency. Results from tests of several differnt VE spatial sensors (Ascension, Logitech, and Polhemus) are presented here to demonstrate use of the testbed and method.

The VideoMouse is a mouse that uses a camera as its input sensor. A real-time vision algorithm determines the six degree-of-freedom mouse posture, consisting of 2D motion, tilt in the forward/back and left/right axes, rotation of the mouse about its vertical axis, and some limited height sensing. Thus, a familiar 2D device can be extended for three-dimensional manipulation, while remaining suitable for standard 2D GUI tasks. We describe techniques for mouse functionality, 3D manipulation, navigating large 2D spaces, and using the camera for lightweight scanning tasks.

We introduce an inexpensive position input device called the FieldMouse, with which a computer can tell the position of the device on paper or any flat surface without using special input tablets or position detection devices. A FieldMouse is a combination of an ID recognizer like a barcode reader and a mouse which detects relative movement of the device. Using a FieldMouse, a user first detects an ID on paper by using the barcode reader, and then drags it from the ID using the mouse. If the location of the ID is known, the location of the dragged FieldMouse can also be calculated by adding the amount of movement from the ID to the position of the FieldMouse. Using a FieldMouse in this way, any flat surface can work as a pointing device that supports absolute position input, just by putting an ID tag somewhere on the surface. A FieldMouse can also be used for enabling a graphical user interface (GUI) on paper or on any flat surface by analyzing the direction and the amount of mouse movement after detecting an ID. In this paper, we introduce how a FieldMouse can be used in various situations to enable computing in real-world environments.

Intrabody communication (IBC) is a wireless communications technology that uses a person's body as the transmission medium for imperceptible electrical signals. Because communication is limited to the vicinity of a person's body, ambiguities arising from communication between personal devices and environmental devices when multiple people are present can, in theory, be solved simply. Intrabody communication also potentially allows data to be transferred when a person touches an IBC-enabled device. We have designed and constructed an intrabody communication system, modeled after Zimmerman's original design, and extended it to operate up to 38.4Kbps and to calculate signal strength. In this paper, we present quantitative measurements of data error rates and signal strength while varying hand distance to transceiver plate, electrode location on the body, touch plate size and shape, and several other factors. We find that plate size and shape have only minor effects, but that the distance to plate and the coupling mechanism significantly effect signal strength. We also find that portable devices, with poor ground coupling, suffer more significant signal attenuation. Our goal is to promote design guidelines for this technology and identify the best contexts for its effective deployment.

We present a range of novel interactions enabled by a simple modification in the design of a computer mouse. By converting each mouse button to pop through tactile push-buttons, similar to the focus/shutter-release buttons used in many cameras, users can feel, and the computer can sense, two distinct "clicks" corresponding to pressing lightly and pressing firmly to pop through. Despite the prototypical status of our hardware and software implementations, our current pop through mouse interactions are compelling and warrant further investigation. In particular, we demonstrate that pop through buttons not only yield an additional button activation state that is composable with, or even preferable to, techniques such as double-clicking, but also can endow a qualitatively novel user experience when meaningfully and consistently applied. We propose a number of software guidelines that may provide a consistent, systemic benefit; for example, light pressure may invoke default interaction (short menu), and firm pressure may supply more detail (long menu).

This research explores distributed sensing techniques for mobile devices using synchronous gestures. These are patterns of activity, contributed by multiple users (or one user with multiple devices), which take on a new meaning when they occur together in time, or in a specific sequence in time. To explore this new area of inquiry, this work uses tablet computers augmented with touch sensors and two-axis linear accelerometers (tilt sensors). The devices are connected via an 802.11 wireless network and synchronize their time-stamped sensor data. This paper describes a few practical examples of interaction techniques using synchronous gestures such as dynamically tiling together displays by physically bumping them together, discusses implementation issues, and speculates on further possibilities for synchronous gestures.

A passive wand tracked in 3D using computer vision techniques is explored as a new input mechanism for interacting with large displays. We demonstrate a variety of interaction techniques that exploit the affordances of the wand, resulting in an effective interface for large scale interaction. The lack of any buttons or other electronics on the wand presents a challenge that we address by developing a set of postures and gestures to track state and enable command input. We also describe the use of multiple wands, and posit designs for more complex wands in the future.

Although graphical user interfaces started as imitations of the physical world, many interaction techniques have since been invented that are not available in the real world. This paper focuses on one of these "previewing", and how a sensory enhanced input device called "PreSense Keypad" can provide a preview for users before they actually execute the commands. Preview important in the real world because it is often not possible to undo an action. This previewable feature helps users to see what will occur next. It is also helpful when the command assignment of the keypad dynamically changes, such as for universal commanders. We present several interaction techniques based on this input device, including menu and map browsing systems and a text input system. We also discuss finger gesture recognition for the PreSense Keypad.

Light Emitting Diodes (LEDs) offer long life, low cost, efficiency, brightness, and a full range of colors. Because of these properties, they are widely used for simple displays in electronic devices. A previously characterized, but little known property of LEDs allows them to be used as photo sensors. In this paper, we show how this capability can be used to turn unmodified, off the shelf, LED arrays into touch sensitive input devices (while still remaining capable of producing output). The technique is simple and requires little or no extra hardware - in some cases operating with the same micro-controller based circuitry normally used to produce output, requiring only software changes. We will describe a simple hybrid input/output device prototype implemented with this technique, and discuss the design opportunities that this type of device opens up.

Conventional scrolling methods for small sized display in PDAs or mobile phones are difficult to use when frequent switching of scrolling and editing operations are required, for example, browsing and operating large sized WWW pages.In this paper, we propose a new user-interface method to provide seamless switching between scrolling and other operations such as editing, based on "Paperweight Metaphor". A sheet of paper that has been placed on a slippery table is difficult to draw on. Therefore, in order to write or draw something on the sheet of paper, a person must secure the paper with his/her palm to avoid the paper from moving. This will be a good metaphor to design switching operation of scroll and editing modes.We have made prototype systems by placing a touch sensor under each PDA display where user's palm will be hit. Three application programs - map browser, WWW browser, and photograph browser - that switch between scrolling and other operation modes depending on sensor output have been developed. We have carried out user tests on this mode switching method and have received favorable feedback on the same.

TiltType is a novel text entry technique for mobile devices. To enter a character, the user tilts the device and presses one or more buttons. The character chosen depends on the button pressed, the direction of tilt, and the angle of tilt. TiltType consumes minimal power and requires little board space, making it appropriate for wristwatch-sized devices. But because controlled tilting of one's forearm is fatiguing, a wristwatch using this technique must be easily removable from its wriststrap. Applications include two-way paging, text entry for watch computers, web browsing, numeric entry for calculator watches, and existing applications for PDAs.

We describe the design of and experience with PointRight, a peer-to-peer pointer and keyboard redirection system that operates in multi-machine, multi-user environments. PointRight employs a geometric model for redirecting input across screens driven by multiple independent machines and operating systems. It was created for interactive workspaces that include large, shared displays and individual laptops, but is a general tool that supports many different configurations and modes of use. Although previous systems have provided for re-routing pointer and keyboard control, in this paper we present a more general and flexible system, along with an analysis of the types of re-binding that must be handled by any pointer redirection system This paper describes the system, the ways in which it has been used, and the lessons that have been learned from its use over the last two years.

This paper presents TinyMotion, a pure software approach for detecting a mobile phone user's hand movement in real time by analyzing image sequences captured by the built-in camera. We present the design and implementation of TinyMotion and several interactive applications based on TinyMotion. Through both an informal evaluation and a formal 17-participant user study, we found that 1. TinyMotion can detect camera movement reliably under most background and illumination conditions. 2. Target acquisition tasks based on TinyMotion follow Fitts' law and Fitts law parameters can be used for TinyMotion based pointing performance measurement. 3. The users can use Vision TiltText, a TinyMotion enabled input method, to enter sentences faster than MultiTap with a few minutes of practicing. 4. Using camera phone as a handwriting capture device and performing large vocabulary, multilingual real time handwriting recognition on the cell phone are feasible. 5. TinyMotion based gaming is enjoyable and immediately available for the current generation camera phones. We also report user experiences and problems with TinyMotion based interaction as resources for future design and development of mobile interfaces.

We explore the design space of a two-sided interactive touch table, designed to receive touch input from both the top and bottom surfaces of the table. By combining two registered touch surfaces, we are able to offer a new dimension of input for co-located collaborative groupware. This design accomplishes the goal of increasing the relative size of the input area of a touch table while maintaining its direct-touch input paradigm. We describe the interaction properties of this two-sided touch table, report the results of a controlled experiment examining the precision of user touches to the underside of the table, and a series of application scenarios we developed for use on inverted and two-sided tables. Finally, we present a list of design recommendations based on our experiences and observations with inverted and two-sided tables.

Designing interfaces for interactive handheld projectors is an exiting new area of research that is currently limited by two problems: hand jitter resulting in poor input control, and possible reduction of image resolution due to the needs of image stabilization and warping algorithms. We present the design and evaluation of a new interaction technique, called zoom-and-pick, that addresses both problems by allowing the user to fluidly zoom in on areas of interest and make accurate target selections. Subtle design features of zoom-and-pick enable pixel-accurate pointing, which is not possible in most freehand interaction techniques. Our evaluation results indicate that zoom-and-pick is significantly more accurate than the standard pointing technique described in our previous work.

Information cannot be found if it is not recorded. Existing rich graphical application approaches interfere with user input in many ways, forcing complex interactions to enter simple information, requiring complex cognition to decide where the data should be stored, and limiting the kind of information that can be entered to what can fit into specific applications' data models. Freeform text entry suffers from none of these limitations but produces data that is hard to retrieve or visualize. We describe the design and implementation of Jourknow, a system that aims to bridge these two modalities, supporting lightweight text entry and weightless context capture that produces enough structure to support rich interactive presentation and retrieval of the arbitrary information entered.

Soap is a pointing device based on hardware found in a mouse, yet works in mid-air. Soap consists of an optical sensor device moving freely inside a hull made of fabric. As the user applies pressure from the outside, the optical sensor moves independent from the hull. The optical sensor perceives this relative motion and reports it as position input. Soap offers many of the benefits of optical mice, such as high-accuracy sensing. We describe the design of a soap prototype and report our experiences with four application scenarios, including a wall display, Windows Media Center, slide presentation, and interactive video games.

Recent advances in sensing technology have enabled a new generation of tabletop displays that can sense multiple points of input from several users simultaneously. However, apart from a few demonstration techniques [17], current user interfaces do not take advantage of this increased input bandwidth. We present a variety of multifinger and whole hand gestural interaction techniques for these displays that leverage and extend the types of actions that people perform when interacting on real physical tabletops. Apart from gestural input techniques, we also explore interaction and visualization techniques for supporting shared spaces, awareness, and privacy. These techniques are demonstrated within a prototype room furniture layout application, called RoomPlanner.

The VideoMouse is a mouse that uses a camera as its input sensor. A real-time vision algorithm determines the six degree-of-freedom mouse posture, consisting of 2D motion, tilt in the forward/back and left/right axes, rotation of the mouse about its vertical axis, and some limited height sensing. Thus, a familiar 2D device can be extended for three-dimensional manipulation, while remaining suitable for standard 2D GUI tasks. We describe techniques for mouse functionality, 3D manipulation, navigating large 2D spaces, and using the camera for lightweight scanning tasks.

Volumetric displays provide interesting opportunities and challenges for 3D interaction and visualization, particularly when used in a highly interactive manner. We explore this area through the design and implementation of techniques for interactive direct manipulation of objects with a 3D volumetric display. Motion tracking of the user's fingers provides for direct gestural interaction with the virtual objects, through manipulations on and around the display's hemispheric enclosure. Our techniques leverage the unique features of volumetric displays, including a 360° viewing volume that enables manipulation from any viewpoint around the display, as well as natural and accurate perception of true depth information in the displayed 3D scene. We demonstrate our techniques within a prototype 3D geometric model building application.

Supporting groups of individuals exploring large maps and design diagrams on interactive tabletops is still an open research problem. Today's geospatial, mechanical engineering and CAD design applications are mostly single-user, keyboard and mouse-based desktop applications. In this paper, we present the design of and experience with DTLens, a new zoom-in-context, multi-user, two-handed, multi-lens interaction technique that enables group exploration of spatial data with multiple individual lenses on the same direct-touch interactive tabletop. DTLens provides a set of consistent interactions on lens operations, thus minimizes tool switching by users during spatial data exploration.

The recent trend towards miniaturization of projection technology indicates that handheld devices will soon have the ability to project information onto any surface, thus enabling interfaces that are not possible with current handhelds. We explore the design space of dynamically defining and interacting with multiple virtual information spaces embedded in a physical environment using a handheld projector and a passive pen tracked in 3D. We develop techniques for defining and interacting with these spaces, and explore usage scenarios.

Interaction on digital tables has been restricted to a single layer on the table's active work-surface. We extend the design space of digital tables to include multiple layers of interaction. We leverage 3D position information of a pointing device to support interaction in the space above the active work-surface by creating multiple layers with drift-correction in which the user can interact with an application. We also illustrate through a point-design that designers can use multiple-layers to create a rich and clutter free application. A subjective evaluation showed that users liked the interaction techniques and found that, because of the drift correction we use, they could control the pointer when working in any layer.

We present HybridPointing, a technique that lets users easily switch between absolute and relative pointing with a direct input device such as a pen. Our design includes a new graphical element, the Trailing Widget, which remains "close at hand" but does not interfere with normal cursor operation. The use of visual feedback to aid the user's understanding of input state is discussed, and several novel visual aids are presented. An experiment conducted on a large, wall-sized display validates the benefits of HybridPointing under certain conditions. We also discuss other situations in which HybridPointing may be useful. Finally, we present an extension to our technique that allows for switching between absolute and relative input in the middle of a single drag-operation.

We present a survey of design issues for developing effective free-space three-dimensional (3D) user interfaces. Our survey is based upon previous work in 3D interaction, our experience in developing free-space interfaces, and our informal observations of test users. We illustrate our design issues using examples drawn from instances of 3D interfaces.

For example, our first issue suggests that users have difficulty understanding three-dimensional space. We offer a set of strategies which may help users to better perceive a 3D virtual environment, including the use of spatial references, relative gesture, two-handed interaction, multisensory feedback, physical constraints, and head tracking. We describe interfaces which employ these strategies.

Our major contribution is the synthesis of many scattered results, observations, and examples into a common framework. This framework should serve as a guide to researchers or systems builders who may not be familiar with design issues in spatial input. Where appropriate, we also try to identify areas in free-space 3D interaction which we see as likely candidates for additional research.

An extended and annotated version of the references list for this paper is available on-line through mosaic at address http://uvacs.cs.virginia.edu/~kph2q/.

We present radial scroll, an interface widget to support scrolling particularly on either small or large scale touch displays. Instead of dragging a elevator in a scroll bar, or using repetitive key presses to page up or down, users gesture anywhere on the document surface such that clockwise gestures advance the document; counter clockwise gestures reverse the document. We describe our prototype implementation and discuss the results of an initial user study.

EdgeWrite is a new unistroke text entry method for handheld devices designed to provide high accuracy and stability of motion for people with motor impairments. It is also effective for able-bodied people. An EdgeWrite user enters text by traversing the edges and diagonals of a square hole imposed over the usual text input area. Gesture recognition is accomplished not through pattern recognition but through the sequence of corners that are hit. This means that the full stroke path is unimportant and recognition is highly deterministic, enabling better accuracy than other gestural alphabets such as Graffiti. A study of able-bodied users showed subjects with no prior experience were 18% more accurate during text entry with Edge Write than with Graffiti (p>.05), with no significant difference in speed. A study of 4 subjects with motor impairments revealed that some of them were unable to do Graffiti, but all of them could do Edge Write. Those who could do both methods had dramatically better accuracy with Edge Write.

Zhai and Kristensson (2003) presented a method of speed-writing for pen-based computing which utilizes gesturing on a stylus keyboard for familiar words and tapping for others. In SHARK²:, we eliminated the necessity to alternate between the two modes of writing, allowing any word in a large vocabulary (e.g. 10,000-20,000 words) to be entered as a shorthand gesture. This new paradigm supports a gradual and seamless transition from visually guided tracing to recall-based gesturing. Based on the use characteristics and human performance observations, we designed and implemented the architecture, algorithms and interfaces of a high-capacity multi-channel pen-gesture recognition system. The system's key components and performance are also reported.

We present the design and implementation of a word-level stroking system called Fisch, which is intended to improve the speed of character-level unistrokes. Importantly, Fisch does not alter the way in which character-level unistrokes are made, but allows users to gradually ramp up to word-level unistrokes by extending their letters in minimal ways. Fisch relies on in-stroke word completion, a flexible design for fluidly turning unistroke letters into whole words. Fisch can be memorized at the motor level since word completions always appear at the same positions relative to the strokes being made. Our design for Fisch is suitable for use with any unistroke alphabet. We have implemented Fisch for multiple versions of EdgeWrite, and results show that Fisch reduces the number of strokes during entry by 43.9% while increasing the rate of entry. An informal test of "record speed" with the stylus version resulted in 50-60 wpm with no uncorrected errors.

TiltText, a new technique for entering text into a mobile phone is described. The standard 12-button text entry keypad of a mobile phone forces ambiguity when the 26- letter Roman alphabet is mapped in the traditional manner onto keys 2-9. The TiltText technique uses the orientation of the phone to resolve this ambiguity, by tilting the phone in one of four directions to choose which character on a particular key to enter. We first discuss implementation strategies, and then present the results of a controlled experiment comparing TiltText to MultiTap, the most common text entry technique. The experiment included 10 participants who each entered a total of 640 phrases of text chosen from a standard corpus, over a period of about five hours. The results show that text entry speed including correction for errors using TiltText was 23% faster than MultiTap by the end of the experiment, despite a higher error rate for TiltText. TiltText is thus amongst the fastest known language-independent techniques for entering text into mobile phones.

We present a survey of design issues for developing effective free-space three-dimensional (3D) user interfaces. Our survey is based upon previous work in 3D interaction, our experience in developing free-space interfaces, and our informal observations of test users. We illustrate our design issues using examples drawn from instances of 3D interfaces.

For example, our first issue suggests that users have difficulty understanding three-dimensional space. We offer a set of strategies which may help users to better perceive a 3D virtual environment, including the use of spatial references, relative gesture, two-handed interaction, multisensory feedback, physical constraints, and head tracking. We describe interfaces which employ these strategies.

Our major contribution is the synthesis of many scattered results, observations, and examples into a common framework. This framework should serve as a guide to researchers or systems builders who may not be familiar with design issues in spatial input. Where appropriate, we also try to identify areas in free-space 3D interaction which we see as likely candidates for additional research.

An extended and annotated version of the references list for this paper is available on-line through mosaic at address http://uvacs.cs.virginia.edu/~kph2q/.

Tape drawing is the art of creating sketches on large scale upright surfaces using black photographic tape. Typically used in the automotive industry, it is an important part of the automotive design process that is currently not computerized. We analyze and describe the unique aspects of tape drawing, and use this knowledge to design and implement a digital tape drawing system. Our system retains the fundamental interaction and visual affordances of the traditional media while leveraging the power of the digital media. Aside from the practical aspect of our work, the interaction techniques developed have interesting implications for current theories of human bimanual interaction.

We present experimental work which explores how the match (or mismatch) between the input space of the hands and the output space of a graphical display influences two-handed input performance. During interaction with computers, a direct correspondence between the input and output spaces is often lacking. Not only are the hands disjoint from the display space, but the reference frames of the hands may in fact be disjoint from one another if two separate input devices (e.g. two mice) are used for two-handed input. In general, we refer to the workspace and origin within which the hands operate as kinesthetic reference frames. Our goal is to better understand how an interface designer's choice of kinesthetic reference frames influences a user's ability to coordinate two-handed movements, and to explore how the answer to this question may depend on the availability of visual feedback. Understanding this issue has implications for the design of two-handed interaction techniques and input devices, as well as for the reference principle of Guiard's Kinematic Chain model of human bimanual action. Our results suggest that the Guiard reference principle is robust with respect to variances in the kinesthetic reference frames as long as appropriate visual feedback is present.

This paper presents tangible interaction techniques for fine-tuning one-to-one scale NURBS curves on a large display for automotive design. We developed a new graspable handle with a transparent groove that allows designers to manipulate virtual curves on a display screen directly. The use of the proposed handle leads naturally to a rich vocabulary of terms describing interaction techniques that reflect existing shape styling methods. A user test raised various issues related to the graspable user interface, two-handed input, and large-display interaction.