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.