Niels Henze

My App is an Experiment: Experience from User Studies in Mobile App Stores

Experiments are a cornerstone of HCI research. Mobile distribution channels such as Apples App Store and Googles Android Market have created the opportunity to bring experiments to the end user. Hardly any experience exists on how to conduct such experiments successfully. This article reports on five experiments that were conducted by publishing Apps in the Android Market. The Apps are freely available and have been installed more than 30,000 times. The outcomes of the experiments range from failure to valuable insights. Based on these outcomes, the authors identified factors that account for the success of experiments using mobile application stores. When generalizing findings it must be considered that smartphone users are a non-representative sample of the worlds population. Most participants can be obtained by informing users about the study when the App had been started for the first time. Because Apps are often used for a short time only, data should be collected as early as possible. To collect valuable qualitative feedback other channels than user comments and email have to be used. Finally, the interpretation of collected data has to consider unpredicted usage patterns to provide valid conclusions.

Text Entry on Tiny QWERTY Soft Keyboards

The advent of wearables (e.g., smartwatches, smartglasses, and digital jewelry) anticipates the need for text entry methods on very small devices. We conduct fundamental research on this topic using 3 qwerty-based soft keyboards for 3 different screen sizes, motivated by the extensive training that users have with qwerty keyboards. In addition to ZoomBoard (a soft keyboard for diminutive screens), we propose a callout-based soft keyboard and ZShift, a novel extension of the Shift pointing technique. We conducted a comprehensive user study followed by extensive analyses on performance, usability, and short-term learning. Our results show that different small screen sizes demand different types of assistance. In general, manufacturers can benefit from these findings by selecting an appropriate qwerty soft keyboard for their devices. Ultimately, this work provides designers, researchers, and practitioners with new understanding of qwerty soft keyboard design space and its scalability for tiny touchscreens.

Visualization of off-screen objects in mobile augmented reality

An emerging technology for tourism information systems is mobile Augmented Reality using the position and orientation sensors of recent smartphones. State-of-the-art mobile Augmented Reality application accompanies the Augmented Reality visualization with a small mini-map to provide an overview of nearby points of interest (POIs). In this paper we develop an alternative visualization for nearby POIs based on off-screen visualization techniques for digital maps. The off-screen visualization uses arrows directly embedded into the Augmented Reality scene which point at the POIs. In the conducted study 26 participants explored nearby POIs and had to interpret their position. We show that participants are faster and can interpret the position of POIs more precisely with the developed visualization technique.

FlashLight: optical communication between mobile phones and interactive tabletops

Mobile phones can be used as mediators between users and interactive tabletops in several scenarios, including authentication and the sharing of information. Existing radio-based methods such as WiFi or Bluetooth offer a high-speed communication channel, but have serious limitations regarding the tabletop-phone-human interaction. They are not able to locate mobile phones placed on the surface, often require fairly complex coupling procedures for establishing connections, and are potentially vulnerable to eavesdropping attacks. In this paper, we present a method for establishing a bidirectional communication channel between mobile phones and vision-based interactive surfaces utilizing the built-in flash-light and camera of mobile phones and the screen and camera of vision-based tabletops. We establish an entirely visual, secure and bidirectional communication channel at a speed superior to previous vision-based approaches, enabling users to establish connections and transfer data to and from interactive surfaces using ordinary out-of-the-box hardware.

Smart Textiles: From Niche to Mainstream

Current technology supports only special-purpose, low-volume textiles, garments, and electronics. Moreover, the textile, electronic, and software industries have different product cycles, cultures, and price models, creating scores of practical problems for smart textiles. Mass producing smart cloth will require decoupling the textile production from concrete sensing apps and moving the complexity to generic electronics and software--creating wearable sensing as an app.

Insights into layout patterns of mobile user interfaces by an automatic analysis of android apps

Mobile phones recently evolved into smartphones that provide a wide range of services. One aspect that differentiates smartphones from their predecessor is the app model. Users can easily install third party applications from central mobile application stores. In this paper we present a process to gain insights into mobile user interfaces on a large scale. Using the developed process we automatically disassemble and analyze the 400 most popular free Android applications. The results suggest that the complexity of the user interface differs between application categories. Further, we analyze interface layouts to determine the most frequent interface elements and identify combinations of interface widgets. The most common combination that consists of three nested elements covers 5.43% of all interface elements. It is more frequent than progress bars and checkboxes. The ten most frequent patterns together cover 21.13% of all interface elements. They are all more frequent than common widget including radio buttons and spinner. We argue that the combinations identified not only provide insights about current mobile interfaces, but also enable the development of new optimized widgets.

Exploiting thermal reflection for interactive systems

Thermal cameras have recently drawn the attention of HCI researchers as a new sensory system enabling novel interactive systems. They are robust to illumination changes and make it easy to separate human bodies from the image background. Far-infrared radiation, however, has another characteristic that distinguishes thermal cameras from their RGB or depth counterparts, namely thermal reflection. Common surfaces reflect thermal radiation differently than visual light and can be perfect thermal mirrors. In this paper, we show that through thermal reflection, thermal cameras can sense the space beyond their direct field-of-view. A thermal camera can sense areas besides and even behind its field-of-view through thermal reflection. We investigate how thermal reflection can increase the interaction space of projected surfaces using camera-projection systems. We moreover discuss the reflection characteristics of common surfaces in our vicinity in both the visual and thermal radiation bands. Using a proof-of-concept prototype, we demonstrate the increased interaction space for hand-held camera-projection system. Furthermore, we depict a number of promising application examples that can benefit from the thermal reflection characteristics of surfaces.

Understanding shortcut gestures on mobile touch devices

Touch gestures become steadily more important with the ongoing success of touch screen devices. Compared to traditional user interfaces, gestures have the potential to lower cognitive load and the need for visual attention. However, nowadays gestures are defined by designers and developers and it is questionable if these meet all user requirements. In this paper, we present two exploratory studies that investigate how users would use unistroke touch gestures for shortcut access to a mobile phones key functionalities. We study the functions that users want to access, the preferred activators for gesture execution, and the shapes of the user-invented gestures. We found that most gestures trigger applications, letter-shaped gestures are preferred, and the gestures should be accessible from the lock screen, the wallpaper, and the notification bar. We conclude with a coherent, unambiguous set of gestures for the 20 most frequently accessed functions, which can inform the design of future gesture-controlled applications.

Perceiving layered information on 3D displays using binocular disparity

3D displays are hitting the mass market. They are integrated in consumer TVs, notebooks, and mobile phones and are mainly used for virtual reality as well as video content. We see large potential in using depth also for structuring information. Our specific use case is 3D displays integrated in cars. The capabilities of such displays could be used to present relevant information to the driver in a fast and easy-to-understand way, e.g., by functionality-based clustering. However, excessive parallaxes can cause discomfort and in turn negatively influence the primary driving task. This requires a reasonable choice of parallax boundaries. The contribution of this paper is twofold. First, we identify the comfort zone when perceiving 3D content. Second, we determine a minimum depth distance between objects that still enables users to quickly and accurately separate the two depth planes. The results yield that in terms of task completion time the optimum distance from screen level is up to 35.9 arc-min angular disparity behind the screen plane. A distance of at least 2.7 arc-min difference in angular disparity between the objects significantly decreases time for layer separation. Based on the results we derive design implications.

Modeling Distant Pointing for Compensating Systematic Displacements

Distant pointing at objects and persons is a highly expressive gesture that is widely used in human communication. Pointing is also used to control a range of interactive systems. For determining where a user is pointing at, different ray casting methods have been proposed. In this paper we assess how accurately humans point over distance and how to improve it. Participants pointed at projected targets from 2m and 3m while standing and sitting. Testing three common ray casting methods, we found that even with the most accurate one the average error is 61.3cm. We found that all tested ray casting methods are affected by systematic displacements. Therefore, we trained a polynomial to compensate this displacement. We show that using a user-, pose-, and distant-independent quartic polynomial can reduce the average error by 37.3%