Publikationen von Max Pfeiffer


  • MuscleIO: Muscle-Based Input and Output for Casual Notifications
    Tim Dünte, Justin Schulte, Max Pfeiffer and Michael Rohs
    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.


  • Zap++: A 20-channel Electrical Muscle Stimulation System for Fine-grained Wearable Force Feedback
    Tim Dünte, Max Pfeiffer and Michael Rohs
    Proceedings of the 19th International Conference on Human-Computer Interaction with Mobile Devices and Services
    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.
  • EMS in HCI: Challenges and Opportunities in Actuating Human Bodies
    Tim Dünte, Stefan Schneegass and Max Pfeiffer
    Proceedings of the 19th International Conference on Human-Computer Interaction with Mobile Devices and Services
    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.
  • Emotion Actuator: Embodied Emotional Feedback through Electroencephalography and Electrical Muscle Stimulation
    Max Pfeiffer, Mariam Hassib, Stefan Schneegass, Michael Rohs and Florian Alt
    The human body reveals emotional and bodily states through measurable signals, such as body language and electroencephalography. However, such manifestations are difficult to communicate to others remotely. We propose EmotionActuator, a proof-of-concept system to investigate the transmission of emotional states in which the recipient performs emotional gestures to understand and interpret the state of the sender.We call this kind of communication embodied emotional feedback, and present a prototype implementation. To realize our concept we chose four emotional states: amused, sad, angry, and neutral. We designed EmotionActuator through a series of studies to assess emotional classification via EEG, and create an EMS gesture set by comparing composed gestures from the literature to sign-language gestures. Through a final study with the end-to-end prototype interviews revealed that participants like implicit sharing of emotions and find the embodied output to be immersive, but want to have control over shared emotions and with whom. This work contributes a proof of concept system and set of design recommendations for designing embodied emotional feedback systems.




  • Let Me Grab This : A Comparison of EMS and Vibration for Haptic Feedback in Free-Hand Interaction
    Max Pfeiffer, Stefan Schneegass, Florian Alt and Michael Rohs
    Free-hand interaction with large displays is getting more common, for example in public settings and exertion games. Adding haptic feedback offers the potential for more realis- tic and immersive experiences. While vibrotactile feedback is well known, electrical muscle stimulation (EMS) has not yet been explored in free-hand interaction with large displays. EMS offers a wide range of different strengths and qualities of haptic feedback. In this paper we first systematically inves- tigate the design space for haptic feedback. Second, we ex- perimentally explore differences between strengths of EMS and vibrotactile feedback. Third, based on the results, we evaluate EMS and vibrotactile feedback with regard to differ- ent virtual objects (soft, hard) and interaction with different gestures (touch, grasp, punch) in front of a large display. The results provide a basis for the design of haptic feedback that is appropriate for the given type of interaction and the material.
  • A Design Space for Electrical Muscle Stimulation Feedback for Free-Hand Interaction
    Max Pfeiffer, Stefan Schneegass, Florian Alt and Michael Rohs
    Workshop on Assistive Augmentation at CHI 2014
    Free-hand interaction becomes a common technique for interacting with large displays. At the same time, providing haptic feedback for free-hand interaction is still a challenge, particularly feedback with different characteristics (i.e., strengths, patterns) to convey particular information. We see electrical muscle stimulation (EMS) as a well-suited technology for providing haptic feedback in this domain. The characteristics of EMS can be used to assist users in learning, manipulating, and perceiving virtual objects. One of the core challenges is to understand these characteristics and how they can be applied. As a step in this direction, this paper presents a design space that identifies different aspects of using EMS for haptic feedback. The design space is meant as a basis for future research investigating how particular characteristics can be exploited to provide specific haptic feedback.