1. A method for recognizing a moving three-dimensional object and for computing a description of motion of the object, said method comprising the steps of: detecting a physical property of the object to produce two-dimensional input image data; applying the input image data to a bi-directional neural network comprising (I) pairs of velocity neurons for respectively obtaining x-and-y components of said optical flow and (ii) edge detecting line processes, each taking a value from a range between a high value and a low value in accordance with a function of the x and y components of optical flow and which is continuous within said range, interposed between said pairs of velocity neurons; and obtaining an optical flow at respective points of said object based on the values taken by the line processes which optical flow provides the description of the motion of the object.