Publikationen von Tim Dünte

Wearables are getting more and more powerful. Tasks like notifications can be delegated to smartwatches. But the output capabilities of wearables seem to be stuck at displays and vibration. Electrotactile feedback may serve as an energy-efficient alternative to standard vibration feedback. We developed prototypes of wristbands and rings and conducted two studies to compare electrotactile and vibrotactile feedback. The prototypes have either four electrodes for electrotactile feedback or four actuators for vibration feedback. In a first study we analyzed the localization characteristics of the created stimuli. The results suggest more strongly localized sensations for electrotactile feedback, compared to vibrotactile feedback, which was more diffuse. In a second study we created notification patterns for both modalities and evaluated recognition rates, verbal associations, and satisfaction. Although the recognition rates were higher with electrotactile feedback, vibrotactile feedback was judged as more comfortable and less stressful. Overall, the results show that electrotactile feedback can be a viable alternative to vibrotactile feedback for wearables, especially for notification rings.

Receiving and reacting to notifications on mobile devices can be cumbersome. We propose MuscleIO, the use of electrical muscle stimulation (EMS) for notification output and electromyography (EMG) for reacting to notifications. Our approach provides a one-handed, eyes-free, and low-effort way of dealing with notifications. We built a prototype that interleaves muscle input and muscle output signals using the same electrodes. EMS and EMG alternate such that the EMG input signal is measured in the gaps of the EMS output signal, so voluntary muscle contraction is measured during muscle stimulation. Notifications are represented as EMS signals and are accepted or refused either by a directional or a time-based EMG response. A lab user study with 12 participants shows that the directional EMG response is superior to the time-based response in terms of reaction time, error rate, and user preference. Furthermore, the directional approach is the fastest and the most intuitive for users compared to a button-based smartwatch interface as a baseline.

Electrical muscle stimulation (EMS) has been used successfully in HCI to generate force feedback and simple movements both in stationary and mobile settings. However, many natural limb movements require the coordinated actuation of multiple muscles. Off-the-shelf EMS devices are typically limited in their ability to generate fine-grained movements, because they only have a low number of channels and do not provide full control over the EMS parameters. More capable medical devices are not designed for mobile use or still have a lower number of channels and less control than is desirable for HCI research. In this paper we present the concept and a prototype of a 20-channel mobile EMS system that offers full control over the EMS parameters. We discuss the requirements of wearable multi-electrode EMS systems and present the design and technical evaluation of our prototype. We further outline several application scenarios and discuss safety and certification issues.

Electrical Muscle Stimulation (EMS) recently received considerable attention in the HCI community. By applying small signals to the user's body, different types of movement can be generated. These movements allow designers to create more meaningful and embodied haptic feedback compared to vibrotactile feedback. This advantage also comes with further technical and practical challenges which need to be tackled. These challenges include a fine grained calibration procedure and a close contact to the user's body at specific on-body locations. This tutorial gives an overview about current research projects, challenges, and opportunities to use EMS for providing rich embodied feedback followed by a hands on experience. The main goal of this tutorial is that participants get a basic understanding of how EMS works and how systems that are using EMS can be developed and evaluated.

Electrical muscle stimulation (EMS) is a promising wearable haptic output technology as it can be miniaturized considerably and delivers a wide range of haptic output. However, prototyping EMS applications is challenging. It requires detailed knowledge and skills about hardware, software, and physiological characteristics. To simplify prototyping with EMS in mobile and wearable situations we present the Let Your Body Move toolkit. It consists of (1) a hardware control module with Bluetooth communication that uses off-the-shelf EMS devices as signal generators, (2) a simple communications protocol to connect mobile devices, and (3) a set of control applications as starting points for EMS prototyping. We describe EMS-specific parameters, electrode placements on the skin, and user calibration. The toolkit was evaluated in a workshop with 10 researchers in haptics. The results show that the toolkit allows to quickly generate non-trivial prototypes. The hardware schematics and software components are available as open source software.

Electromyography (EMG) and electrical muscle stimulation (EMS) are promising technologies for muscle sensing and actuation in wearable interfaces. The required electrodes can be manufactured to form a thin layer on the skin. We discuss requirements and approaches for EMG and EMS as on-skin technologies. In particular, we focus on fine-grained muscle sensing and actuation with an electrode grid on the lower arm. We discuss a prototype, scenarios, and open issues.

Electrical muscle stimulation (EMS) is a promising wearable haptic output technology as it can be miniaturized and delivers a wide range of tactile and force output. However, prototyping EMS applications is currently challenging and requires detailed knowledge about EMS. We present a toolkit that simplifies prototyping with EMS and serves as a starting point for experimentation and user studies. It consists of (1) a hardware control module that uses off-the-shelf EMS devices as safe signal generators, (2) a simple communication protocol, and (3) a set of control applications for prototyping. The interactivity allows hands-on experimentation with our sample control applications.

Pedestrian navigation systems require users to perceive, interpret, and react to navigation information. This can tax cognition as navigation information competes with information from the real world. We propose actuated navigation, a new kind of pedestrian navigation in which the user does not need to attend to the navigation task at all. An actuation signal is directly sent to the human motor system to influence walking direction. To achieve this goal we stimulate the sartorius muscle using electrical muscle stimulation. The rotation occurs during the swing phase of the leg and can easily be counteracted. The user therefore stays in control. We discuss the properties of actuated navigation and present a lab study on identifying basic parameters of the technique as well as an outdoor study in a park. The results show that our approach changes a user's walking direction by about 16 degree/m on average and that the system can successfully steer users in a park with crowded areas, distractions, obstacles, and uneven ground.