Abstract: The paper studies visual lobe by measuring and calculating median successful saceade size (MSSS) in 2-D visual search. The experiment results show that MSSS is a function of Michaelson contrast and the clutter density. During scanning a search scene, saccade eye movement is directed by a combination of global covering plan and moment-to-moment adjustments guided by useful peripheral inforraation. At last, a Gaussian model is given to fit the experiment data. This model captures not only the first order effects of clutter and contrast but also their reciprocal interactions.