We conducted a user study evaluating five selection techniques for augmented reality in optical see-through head-mounted displays (OST-HMDs). The techniques we studied aim at supporting mobile usage scenarios where the devices do not need external tracking tools or special environments, and therefore we selected techniques that rely solely on tracking technologies built into conventional commercially available OST-HMDs [i.e. gesture trackers, gaze tracking and inertial measurement units (IMUs)]. While two techniques are based on raycasting using built-in IMU sensing, three techniques are based on a hand-controlled 3D cursor using gestural tracking. We compared these techniques in an experiment with 12 participants. Our results show that raycasting using head orientation (i.e. IMU on the headset) was the fastest, fatigueless and the most preferable technique to select spatially arranged objects. We discuss the implications of our findings for design of interaction techniques in mobile OST-HMDs.

Users of optical see-through head-mounted displays (OHMD) perceive color as a blend of the display color and the background. Color-blending is a major usability challenge as it leads to loss of color encodings and poor text legibility. Color correction aims at mitigating color blending by producing an alternative color which, when blended with the background, more closely approximates the color originally intended. In this paper we present an end-to-end approach to the color blending problem addressing the distortions introduced by the transparent material of the display efficiently and in real time. We also present a user evaluation of correction efficiency. Finally, we present a graphics library called SmartColor showcasing the use of color correction for different types of display content. SmartColor uses color correction to provide three management strategies: correction, contrast, and show-up-on-contrast. Correction determines the alternate color which best preserves the original color. Contrast determines the color which best supports text legibility while preserving as much of the original hue. Show-up-on-contrast makes a component visible when a related component does not have enough contrast to be legible. We describe SmartColor's architecture and illustrate the color strategies for various types of display content.

As a novel class of mobile devices with rich interaction capabilities we introduce tPads -- transparent display tablets. tPads are the result of a systematic design investigation into the ways and benefits of interacting with transparent mobiles which goes beyond traditional mobile interactions and augmented reality (AR) applications. Through a user-centered design process we explored interaction techniques for transparent-display mobiles and classified them into four categories: overlay, dual display & input, surface capture and model-based interactions. We investigated the technical feasibility of such interactions by designing and building two touch-enabled semi-transparent tablets called tPads and a range of tPad applications. Further, a user study shows that tPad interactions applied to everyday mobile tasks (application switching and image capture) outperform current mobile interactions and were preferred by users. Our hands-on design process and experimental evaluation demonstrate that transparent displays provide valuable interaction opportunities for mobile devices.

Mid-air interactions are prone to fatigue and lead to a feeling of heaviness in the upper limbs, a condition casually termed as the gorilla-arm effect. Designers have often associated limitations of their mid-air interactions with arm fatigue, but do not possess a quantitative method to assess and therefore mitigate it. In this paper we propose a novel metric, Consumed Endurance (CE), derived from the biomechanical structure of the upper arm and aimed at characterizing the gorilla-arm effect. We present a method to capture CE in a non-intrusive manner using an off-the-shelf camera-based skeleton tracking system, and demonstrate that CE correlates strongly with the Borg CR10 scale of perceived exertion. We show how designers can use CE as a complementary metric for evaluating existing and designing novel mid-air interactions, including tasks with repetitive input such as mid-air text-entry. Finally, we propose a series of guidelines for the design of fatigue-efficient mid-air interfaces.

Users of optical see-through head-mounted displays (OHMD) perceive color as a blend of the display color and the background. Color-blending is a major usability challenge as it leads to loss of color encodings and poor text legibility. Color correction aims at mitigating color blending by producing an alternative color which, when blended with the background, more closely approaches the color originally intended. To date, approaches to color correction do not yield optimal results or do not work in real-time. This paper makes two contributions. First, we present QuickCorrection, a realtime color correction algorithm based on display profiles. We describe the algorithm, measure its accuracy and analyze two implementations for the OpenGL graphics pipeline. Second, we present SmartColor, a middleware for color management of userinterface components in OHMD. SmartColor uses color correction to provide three management strategies: correction, contrast, and show-up-on-contrast. Correction determines the alternate color which best preserves the original color. Contrast determines the color which best warranties text legibility while preserving as much of the original hue. Show-up-on-contrast makes a component visible when a related component does not have enough contrast to be legible. We describe the SmartColor's architecture and illustrate the color strategies for various types of display content.

Mobile device use while walking, or eyes-busy mobile interaction, is a leading cause of life-threatening pedestrian collisions. We introduce CrashAlert, a system that augments mobile devices with a depth camera, to provide distance and location visual cues of obstacles on the user's path. In a realistic environment outside the lab, CrashAlert users improve their handling of potential collisions, dodging and slowing down for simple ones while lifting their head in more complex situations. Qualitative results outline the value of extending users' peripheral alertness in eyes-busy mobile interaction through non-intrusive depth cues, as used in CrashAlert. We present the design features of our system and lessons learned from our evaluation.

In optical see-through displays, light coming from background objects mixes with the light originating from the display, causing what is known as the color blending problem. Color blending negatively affects the usability of such displays as it impacts the legibility and color encodings of digital content. Color correction aims at reducing the impact of color blending by finding an alternative display color which, once mixed with the background, results in the color originally intended.

In this paper we present a field trial of the eLabBench, a digital tabletop-based laboratory bench designed to support the exploratory practices of molecular biologists in the laboratory. The eLabBench supports the organization of personal information, capture of experimental work for later access, and the use of a variety of computational resources directly at the lab bench. We deployed the eLabBench in a biology laboratory for 16 weeks, and invited seven molecular biologists to run experiments on it. We report on how they used the bench and how it fitted within their larger experimental process. The main impact of the eLabBench lies in the changes it sparked off in preparing, running, and documenting lab experiments. By supporting computation at the bench and management of physical objects in the office, the eLabBench blurred the separation between office and laboratory work. Based on our observations, we discuss how interactive systems for laboratories such as the eLabBench can support a more exploratory or design-oriented way of 'doing' science.

The success of a volunteer computing infrastructure depends on the contributions of its users. An example of such an infrastructure is the Mini-Grid, a local peer-to-peer system used for computational analysis of DNA. The speed of analysis increases as more users join the Mini-Grid. However, the invisible nature of such an infrastructure hinders adoption, as it is difficult for users to participate in an infrastructure they are not aware of. This paper introduces GridOrbit, a system designed to increase user awareness, fostering contributions to this infrastructure. We designed GridOrbit using a participatory design process with biologists, and subsequently deployed it for use in a biology laboratory. Our results indicate that the number of contributors to the Mini-Grid increased with the use of awareness technologies. In addition, our analysis presents their motives and behaviors. Finally, a characterization of user interaction with GridOrbit emerged, which enabled us to understand how awareness systems can be better designed. We see GridOrbit as an example of a broader class of technologies designed to create "Infrastructure Awareness" as a means to increase the contributions to technological infrastructures.

Interactive surfaces like diffuse illumination tabletops (DIT) identify and track objects using multiple techniques like shape and color recognition, fiducial markers, electronic components, and RFID tags. However, tracking becomes more complex when dealing with multiple small objects of similar form. We propose to use tangible mediators for integrating such objects to tabletops. This paper reports on our initial explorations of mediated tabletop interaction consisting of a mediator prototype and a design space definition. We built a mediator, the Rabbit, a device that translates thevalue of an RFID tag into a visual 2D code. The Rabbit rests on the interactive surface, holds the object, reads its passive RFID tag, and converts the read value into a 2D code that can be read by the DIT's built-in camera. When handling multiple objects, the Rabbit iterates through the generated 2D codes. Through a series of participatory activities with end users (molecular biologists), we collected initial feedback from participants and defined a design space for mediated tabletop interaction.

Workplace collaboration often requires interruptions, which can happen at inopportune times. Sharing availability information can reduce many of these untimely interruptions. However, designing a successful availability-sharing system requires finding the right balance to maximize the benefits and reduce costs for both the interrupter and interruptee. The main challenges for finding such balance lie in the acquisition of availability information from the interruptee and its delivery to the interrupter. In this demonstration, we show how common technical approaches in ubicomp can address some of the problems typically encountered in availability sharing. We present InterruptMe, a novel availability sharing system that uses sensor information to calculate multiple availability measures for each interruptee and that delivers this information in the periphery of the interrupter's attention by using a projected peripheral display and monitoring implicit inputs to the system.

Workplace collaboration often requires interruptions, which can happen at inopportune times. Designing a successful availability-sharing system requires finding the right balance to optimize the benefits and reduce costs for both the interrupter and interruptee. In this paper, we examine the design space of availability-sharing systems and identify six relevant design dimensions: abstraction, presentation, information delivery, symmetry, obtrusiveness and temporal gradient. We describe these dimensions in terms of the tensions between interrupters and interruptees revealed in previous studies of workplace collaboration and deployments of awareness systems. As a demonstration of the utility of our design space, we introduce InterruptMe, a novel availability-sharing system that represents a previously unexplored point in the design space and that balances the tensions between interrupters and interruptees. InterruptMe differs from previous systems in that it displays availability information only when needed by monitoring implicit inputs from the system's users, implements a traceable asymmetry structure, and introduces the notion of per-communications channel availability.

Infrastructure awareness systems reveal invisible aspects of infrastructures to their existing or potential users. Designing such systems is challenging as it requires making visible the hidden activity of infrastructures while providing information of interest to the users. To address this challenge we introduce the AMC technique (for Awareness Model Cards). This technique relies conceptually on awareness model's concepts of nimbus and focus. The main objective is to match the users' interests to the information the infrastructure awareness systems can provide, through the use of card matching. This technique provides three benefits: 1) evaluate how relevant is the information displayed by infrastructure awareness systems; 2) identify which of users' interests infrastructure awareness systems do not take into account; 3) identify elements of re-design in the infrastructures themselves, so to improve their adoption.