Mathematical model for the filling-in of illusory contour.

It is demonstrated that illusory contour in the shape of a square is perceived lighter when abutted by black horizontal lines and white vertical lines, darker when abutted by white horizontal lines and black vertical lines. These differences in perceived brightness and the spread of brightness, or a filling-in phenomenon, can be modeled by the major product of a column vector and a row unit vector where the order of each vector corresponds to extent and the value of each entry in the column vector corresponds to brightness.