User interaction concepts, principles and algorithms for gestures involving facial expressions, motion or orientation of body parts, eye gaze, tightening muscles, mental activity, and other user actions are disclosed. User interaction concepts, principles and algorithms for enabling hands-free and voice-free interaction with electronic devices are disclosed. Apparatuses, systems, computer implementable methods, and non-transient computer storage media storing instructions, implementing the disclosed concepts, principles and algorithms are disclosed. Gestures for systems using eye gaze and head tracking that can be used with augmented, mixed or virtual reality, mobile or desktop computing are disclosed. Use of periods of limited activity and consecutive user actions in orthogonal axes is disclosed. Generation of command signals based on start and end triggers is disclosed. Methods for coarse as well as fine modification of objects are disclosed.