A visual evoked potential (VEP) component that appears in the power spectrum only during binocular fusion has recently been discovered. When both eyes are stimulated with the same checkerboard but at different pattern reversal rates, this fusional component appears at a frequency intermediate between the two stimulus frequencies. We have proposed a model to explain the appearance of this intermediate component and have tested the model's predictions that the fusional component will remain constant independent of binocular or monocular changes in stimulul contrast As predicted by the model, changes in contrast over the range of 10 to 90% produced no significant change in the power of the fusional component.