Detection of Evoked Potentials

Abstract

In biosignal processing it is exceedingly difficult to detect evoked potentials in an objective way. The main problem is that neither the biosignal nor the surrounding EEG fulfils any necessary condition concerning the properties of signal and noise known from the detection theory. Further, there is a strong nonlinear and time-variant relation between the stimulation sequence and the evoked response. Thus, for a reliable detection, optimization of both the stimulating series and the stimulus response is necessary. Although evoked responses to standard stimuli are well known in healthy subjects and can be found easily, responses of ill subjects are possibly completely different if present at all. Thus, correlation detector or matching filter will not work in pathological cases. The only way for detection is the energy detector and related methods. This chapter will show exemplarily on visual evoked potentials (VEP) how the stimulation and the detection can be combined suitably for detection. Several methods for an efficient enhancement of the SNR¹ are presented. One of the main tasks is to show how the signal properties of signal and noise can be improved in the sense of detection theory.