A user input to a system is processed by receiving reflections of signals from a moving input object. Information relating to the direction of movement of the input object and information relating to the speed of the input object are determined from the reflections. Continual sensory feedback is provided to the user, controlled by a parameter that is repeatedly updated based on the direction and speed of the input object. When no new determination of information relating to the speed or direction of the input object has been made since a previous update, a time-dependent change is made to the parameter.