Visually evoked potentials evoked by moving unidimensional noise stimuli: Effects of contrast, spatial frequency, active electrode location, reference electrode location, and stimulus type

We determined the relative importance of electrode derivation, stimulus typ e, spatial frequency and contrast in determining the relative size of the l ate negative and early positive responses of motion elicited VEPs. Seven su bjects aged 22-48 years with normal vision were tested binocularly. Motion onset and motion reversal were employed as modes of stimulus presentation. For both, pseudo-random one-dimensional noise patterns whose peak power was at 5.2, 2.6, 1.3, 0.325 and 0.1625 cycles per degree (cpd) were stimuli. C ontrasts were 70% and 5%. Active electrodes were placed at Oz, 5 cm to the left of Oz, 5 cm to the right of Oz and a frontal midline position (Fpz) an d referenced to linked mastoids. Transient motion reversal elicited a promi nent positive response present in all subjects and at low contrasts. Motion onset VEPs have a complex waveform which may be either predominantly posit ive or negative. The most important variables in determining whether a p ro minent positivity or negativity is present in the motion onset VEP are the contrast and the spatial frequencies. Data such as these are first efforts in developing recommendations for the motion VEP.