The electrophysiological measurements of image distortion are based on the model of object's detection in noise which describes quantitatively frequency-contrast characteristics in presence of noise and consist of the several stages including primary filtering, signal match filtering, comparison with threshold, decision, internal and memory noise. The tools for experiments include hardware and software for stimulation and data processing based on interconnection between two computers via RS 232C interface. Hardware for stimulation includes CCD camera, framegrabber, high resolution monitor and device for photometrical control and gamma-correction. Software includes programs for image processing and for test image generation. Hardware for evoked potentials processing includes multiple scalp electrodes, 16-channel amplifier, 12 bit A/D converter. Visual evoked potentials to calibrated natural test images or Gabor gratings from 0.45 to 14.4 cycles/deg with or without superposition of noise were studied. We measured the amplitude of (N1-P1), (N2-P2) components. The noise dispersion imitate the volume of image distortion. Evoked potentials recorded from different areas of the normal subjects cortex. The different reaction in occipital and parietal scalp area to spatial frequency of the test images was obtained. Changes in the form of responses were found when white noise was superimposed to the test images. The early components (N1-P1) of the evoked potentials are not depended from the spatial frequency of the test images with noise, but the late ones (P2-N2) are depended.