Abstract
Mobile interfaces should be designed to enable subtle, discreet, and unobtrusive interaction. Biosignals and, in particular, the electromyographic (EMG) signal, can provide a subtle input modality for mobile interfaces. The EMG signal is generated by a muscle contraction and can be used for volitional control; its greatest potential for mobile interfaces is its ability to sense muscle activity not related to movement. An EMG-based wearable input device, the Intimate Communication Armband, is presented in this chapter to demonstrate this subtle interaction concept. The device detects subtle, motionless gestures from the upper arm. Experimental results show that the gestures are reliably recognized without user or machine training, that the system can be used effectively to control a multimodal interface, and that it is very difficult for observers to guess when a trained user is performing subtle gestures, confirming the subtlety of the proposed interaction.
Key Terms in this Chapter
Electrode: Electrically conductive element placed as close as possible to a signal source (the muscle for EMG signals) acting as the interface between the body and the signal recording apparatus
Intimate Communication Armband: Wearable input/output device capable of detecting subtle gestures from the upper arm and of delivering tactile cues
Surface Electrode: Conductive metal plates, typically composed of Ag/AgCl metal, placed on the skin surface and kept in place through adhesive or elastic bands. Sometimes conductive gel is used to improve the electrical conduction between the skin and the electrode.
Subtle Gesture or Motionless Gesture: Voluntary muscle contractions that result in little or no visible movement—based on isometric muscle activity
Electromyographic signal or EMG Signal: An electrical voltage signal generated by muscle activity
Intimate Interfaces: Discrete interfaces that make interaction with mobile devices private and concealed as much as possible, in order to minimize the disruption of colocated individuals
Isometric Muscle Activity: Muscular contraction that does not produce movement; that is, the muscle length is constant; for example, pushing against a wall.