A tissue stimulation system and computer software and method of operating
the system is provided. An array of electrodes is placed contact with
tissue of a patient (e.g., neural tissue), and electrical current is
conveyed within the electrode array, thereby creating a stimulation
region in the tissue. Electrical current is shifted between cathodes of
the electrode array in incremental steps over a range, thereby causing
displacement of the stimulation region at substantially uniform distances
over the incremental steps. The electrical current may be shifted between
the cathodes in accordance with a sigmoid-like function of a position of
the stimulation region. A navigation table containing a series of states
and corresponding gradually and non-uniformly changing electrical current
values can be accessed, in which case, the electrical current may be
shifted between the cathodes by incrementing through the states of the
navigation table.