This image graphically illustrates the layers of control between a person's body and media content: The boundary that the term 'interface' defines can be interpreted on many levels. In this example, the person acts on a physical control device (the mouse), that acts on a virtual control device (the cusor), that acts on a media control device controller (the scrollbar thumb), that acts on a media control device (the scrollbar), that acts on the media content (a page of text). (See Interaction Device Characteristics: A Functional Anatomy for design options beyond your wildest dreams.)