As architects usually decide on the shape and look of windows during the design of buildings, opportunities for interactive windows have not been systematically explored yet. In this work, we extend the vision of sustainable and comfortable adaptive buildings using interactive smart windows. We systematically explore the design space of interactive windows to chart requirements, constraints, and challenges. To that end, we built proof-of-concept prototypes of smart windows with fine-grained control of transparency. In two studies, we explored user attitudes towards interactive windows and elicited control methods. We found that users understand and see potential for interactive windows at home. We provide specific usage contexts and specify interactions that may facilitate domestic applications. Our work illustrates the concept of interactive smart windows and provides insights regarding their design, development, and user controls for adaptive walls. We identify design dimensions and challenges to stimulate further development in the domain of adaptive buildings.

Touchscreens are the most successful input method for smartphones. Despite their flexibility, touch input is limited to the location of taps and gestures. We present PalmTouch, an additional input modality that differentiates between touches of fingers and the palm. Touching the display with the palm can be a natural gesture since moving the thumb towards the device's top edge implicitly places the palm on the touchscreen. We present different use cases for PalmTouch, including the use as a shortcut and for improving reachability. To evaluate these use cases, we have developed a model that differentiates between finger and palm touch with an accuracy of 99.53% in realistic scenarios. Results of the evaluation show that participants perceive the input modality as intuitive and natural to perform. Moreover, they appreciate PalmTouch as an easy and fast solution to address the reachability issue during one-handed smartphone interaction compared to thumb stretching or grip changes.

Previous research and recent smartphone development presented a wide range of input controls beyond the touchscreen. Fingerprint scanners, silent switches, and Back-of-Device (BoD) touch panels offer additional ways to perform input. However, with the increasing amount of input controls on the device, unintentional input or limited reachability can hinder interaction. In a one-handed scenario, we conducted a study to investigate the areas that can be reached without losing grip stability (comfortable area), and with stretched fingers (maximum range) using four different phone sizes. We describe the characteristics of the comfortable area and maximum range for different phone sizes and derive four design implications for the placement of input controls to support one-handed BoD and edge interaction. Amongst others, we show that the index and middle finger are the most suited fingers for BoD interaction and that the grip shifts towards the top edge with increasing phone sizes.

Smartphones, wearables, and other mobile devices often use tactile feedback for notifying users. This feedback type proved to be beneficial since it does not occupy the visual or auditory channel. However, it still can be distracting in other situations such as when users are already stressed. To investigate tactile feedback patterns which do not increase the user's stress level, we developed two wrist-worn prototypes capable of providing tactile feedback (i.e., vibrotactile and pressure-based feedback). Further, we conducted a user-study with 14 participants comparing both feedback types. The results suggest that vibrotactile feedback increases the user's stress level more, compared to pressure-based feedback particularly applied when the user currently has a low stress level. Consequently, we present implications for designing notifications for mobile and wearable devices.

Previous research proposed a wide range of interaction methods and use cases based on the previously unused back side and edge of a smartphone. Common approaches to implementing Back-of-Device (BoD) interaction include attaching two smartphones back to back and building a prototype completely from scratch. Changes in the device's form factor can influence hand grip and input performance as shown in previous work. Further, the lack of an established operating system and SDK requires more effort to implement novel interaction methods. In this work, we present a smartphone prototype that runs Android and has a form factor nearly identical to an off-the-shelf smartphone. It further provides capacitive images of the hand holding the device for use cases such as grip-pattern recognition. We describe technical details and share source files so that others can re-build our prototype. We evaluated the prototype with 8 participants to demonstrate the data that can be retrieved for an exemplary grip classification.

Our eyes use multiple cues to perceive depth. Current 3D displays do not support all depth cues humans can perceive. While they support binocular disparity and convergence, no commercially available 3D display supports focus cues. To use them requires accommodation, i.e. stretching the eye lens when focusing on an individual distance. Previous work proposed multilayer and light field displays that require the eye to accommodate. Such displays enable the user to focus on different depths and blur out content that is out of focus. Thereby, they might ease the separation of content displayed on different depth layers. In this paper we investigate the effect of focus cues by comparing 3D shutter glasses with a multilayer display. We show that recognizing content displayed on a multilayer display takes less time and results in fewer errors compared to shutter glasses. We further show that separating overlapping content on multilayer displays again takes less time, results in fewer errors, and is less demanding. Hence, we argue that multilayer displays are superior to standard 3D displays if layered 3D content is displayed, and they have the potential to extend the design space of standard GUI.