A Voice User Interface (VUI) or Interactive Voice Response (IVR) system
utilizes three levels of navigation (e.g. Main Menu, Services, and Helper
Commands) in presenting information units arranged in sets. The units are
"spoken" by a system in a group to a human user and the group of
information at each level is preceded by a tone that is unique to the
level. When navigating the levels, the tones of the levels are in a
musical progression, e.g. the three-note blues progression I, IV, V, for
preceding the groups of information, respectively. The musical
progression returns to the tonic of the musical key when the navigation
returns to the level one of the first group of information.