The properties of nonlinear spatial filters as a major part of the peripheral nervous system are investigated with respect to processing of two types of signals: a deterministic stepfunction and Graussian noise. The nonlinearity of the nerve cell is treated as a threshold element. It is shown that certain unfavorable characteristics of linear filters do not occur in such nonlinear filters. The basic nonlinear effects of combined space-time-filtering are demonstrated by using bandpass filters. Time-and space-dependent noise is applied to the nonlinear bandpass. The two subsystems formed by linear bandpass section and the threshold are treated separately. Two examples for the application of nonlinear spatial filtering are given.