Assessing the evolution of the evoked potential average: a new color display method.

A new method to control the averaging process and to check the stability of evoked potential (EP) components is described. The principle of the method is based on the display of the consecutive averages of the EP after each stimulus in a color-coded picture. In this way the evolution of the process is visualised instead of only the last average. The colors are assigned according to the amplitudes. The resulting picture initially consists of erratic colors. However, with increasing numbers of stimuli, tracks of one color soon emerge, indicating stable components. The number of stimuli necessary to generate a stable peak and the duration of stability can easily be quantified. Details with regard to the methods of extraction of essential data and data compression to record the picture are described. The color display method was evaluated with the analysis of 18 somatosensory evoked potentials and 17 visual evoked potentials of controls and 33 EPs of 18 patients. It is shown that this method preserves essential information about the averaging process: the stability of the EP components can be quantified and consequently the optimum number of stimuli to be applied. Furthermore, 14 of the 33 patient recordings showed artifacts, which could be traced with the average-evolution method, but not from the final average alone.