A visual evoked potential study of spatial noise

Since evoked potentials have the highest temporal resolution of any noninvasive measurement of brain activity, this technique is an invaluable tool for investigating human brain function. In this study, we examined the visual evoked potential (VEP) to a square-wave grating pattern embedded in different degrees of spatial noise. The five basic patterns used as visual stimuli were selected as a representative sample from convergent sequence of images generated by the ALOPEX optimization algorithm. All stimulus patterns were rectangular grayscale images of the same size and average luminance. In addition, the stimulus content of each pattern was quantified using a number of image processing algorithms including space-averaged global contrast, image entropy, central moments, 2D Fourier transform, and 2D wavelet transform. The results presented demonstrate the affects of spatial noise on both the time and frequency components of the visual evoked potential recorded from different lobes of the brain.