We present StringTouch, a user interface design exploration translating the expressive resource of string instruments to a new interface morphology. StringTouch transfers the string as a tactile element of interaction to the touch surface, resulting in a tactilely experienceable interface. In this paper we discuss our research through design centered approach, which focused on the exploration of musical string instruments and their translation to the UI context. To investigate this specific design space, we analyzed the systematic and handling of string instruments as well as common HCI principles to develop the interaction concept. The resulting experience prototype demonstrates the idea’s potential for haptic UI design and provides insights into the prototyping process. We present: (1) the investigation of string instruments as a resource for TUI design and (2) the transfer to a generic UI context to inform new hybrid interface morphologies that combine features of tangible, touch, and flexible interaction.

Various on-the-road situations can make additional demands on the driver that go beyond the basic demands of driving. Thereby, they influence the appropriateness of in-vehicle input modalities to operate secondary tasks in the car. In this work, we assess the specific impacts of situational demands on gaze, gesture and speech input regarding driving performance, interaction efficiency and subjective ratings. An experiment with 29 participants in a driving simulator revealed significant interactions between situational demands and the input modality on secondary task completion times, perceived suitability and cognitive workload. Impairments were greatest when the situational demand addressed the same sensory channel as the used input modality. This was reflected differently in objective and subjective data depending on the used input modality. With this work, we explore the performance of natural input modalities across different situations and thereby support interaction designers that plan to integrate these modalities in automotive interaction concepts.

Gestural interfaces are increasingly integrated in human-machine interfaces, but they often rely on visual and auditory feedback and neglect the haptic channel. With technologies providing tactile feedback in midair becoming more mature, it is important to investigate their specific properties. In this paper, we focus on pointing gestures and the combination with floating displays, more precisely tapping buttons. We report the results of a user study investigating in detail different parameters of feedback created through ultrasonic transducers. The results show that the feedback is perceived as most suitable when a modulation frequency of about 150--200Hz is used, which confirms the findings on sensitivity for vibro-tactile stimuli on surfaces. The duration of the signal of either 50 or 130ms did not have a significant effect. Moreover, we present a questionnaire consisting of word pairs to rate the subjective perception of haptic characteristics, to provide a basis for future research.

Touch screens are on the rise and replace traditional knobs and buttons at a fast pace. However, their lack of tangible guidance and feedback can become a problem in scenarios where visual attention is scarce. Besides dynamic tactile feedback by vibrations, the usability of touch screens can be improved by static haptic structures such as shaped or structured surfaces. In this paper we describe the prototype of an in-vehicle application using unimanual four-finger interaction and haptic guidance in order to avoid visual distraction from the primary task of driving. We built a low fidelity prototype with static haptics using an Android tablet and silicone foil. A user study showed that flexible positioning of touch buttons mapped to the user's fingers was more convenient and produced fewer errors than fixed positioning. A curved haptic border provided the user with orientation and allowed a new selection mode: dragging buttons over the edge resulted in a reduced interaction time when compared to double tapping. We present several different variants for unimanual multifinger interaction on planar and non-planar surfaces. Our results can support the development of future concepts for blind interaction.

Large touch screens are recently appearing in the automotive market, yet their usability while driving is still controversial. Flat screens do not provide haptic guidance and thus require visual attention to locate interactive elements that are displayed. Thus, we need to think about new concepts to minimize the visual attention needed for interaction, to keep the driver's focus on the road and ensure safety.

In this paper, we investigate pointing as a lightweight form of gestural interaction in cars. In a pre-study, we show the technical feasibility of reliable pointing detection with a depth camera by achieving a recognition rate of 96% in the lab. In a subsequent in-situ study, we let drivers point to objects inside and outside of the car while driving through a city. In three usage scenarios, we studied how this influenced their driving objectively, as well as subjectively. Distraction from the driving task was compensated by a regulation of driving speed and did not have a negative influence on driving behaviour. Our participants considered pointing a desirable interaction technique in comparison to current controller-based interaction and identified a number of additional promising use cases for pointing in the car.

Tangible user interfaces utilize our ability to interact with everyday objects in order to manipulate virtual data. Designers and engineers usually follow the rule "form follows function", they support an existing interaction with a purpose-built interface. Still, we do not fully exploit the expressiveness of forms, materials and shapes of the nondigital objects we interact with. Therefore, we propose to invert the design process: we empower materiality to inspire the implementation of tangible interactions. Glass objects were chosen as an example of culturally and structurally rich objects: in a three-month workshop, these glass objects were transformed into interactive artefacts. In the paper, we present three resulting contributions: First, we describe our inverted design process as a tool for the stimulation of multidisciplinary development. Second, we derive a list of material-induced interactions. Third, we suggest form-related interactions as a means of designing future tangible interfaces.

We introduce NaviRadar: an interaction technique for mobile phones that uses a radar metaphor in order to communicate the user's correct direction for crossings along a desired route. A radar sweep rotates clockwise and tactile feedback is provided where each sweep distinctly conveys the user's current direction and the direction in which the user must travel. In a first study, we evaluated the overall concept and tested five different tactile patterns to communicate the two different directions via a single tactor. The results show that people are able to easily understand the NaviRadar concept and can identify the correct direction with a mean deviation of 37° out of the full 360° provided. A second study shows that NaviRadar achieves similar results in terms of perceived usability and navigation performance when compared with spoken instructions. By using only tactile feedback, NaviRadar provides distinct advantages over current systems. In particular, no visual attention is required to navigate; thus, it can be spent on providing greater awareness of one's surroundings. Moreover, the lack of audio attention enables it to be used in noisy environments or this attention can be better spent on talking with others during navigation.