1. A neural stimulation method, comprising: generating a first stimulation pattern by stimulating neural tissue of a patient with a series of impulsive electrical signals; generating a second stimulation pattern by stimulating neural tissue of a patient with a series of impulsive electrical signals, wherein said second stimulation pattern alters at least one of amplitude, pulse width, and inter pulse duration; and determining how visual perception depends on the generated stimulation pattern by observing perceptual threshold as a function of features of the impulsive electrical signals.