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.
