One limitation with gesture interaction is the scope context in which the gestures can be used. For example, each gesture has only one corresponding command for each application window. Holding down buttons while moving the mouse can be awkward and requires some practice, since the downwards action increases friction for the horizontal motion. An optical mouse would be less susceptible to changes in behavior than a ball mouse with increased friction because the sensor does not rely on mechanical contact to sense movement; a touchpad provides no added friction with all its buttons held down with a thumb. However, it was also argued that muscular tension resulting from holding down buttons could be exploited in user interface design as it gives constant feedback that the user is in a temporary state, or mode (Buxton, 1995).