By observing forms in action, Leonardo became increasingly aware of certain errors of “recognition”. He noticed the pseudo-transparency of objects observed in rapid motion, such as the vibrating chords of a musical instrument. But how was he to incorporate the impression of movement into his paintings?

Rather than risking making forms incomprehensible, he reverted to the conventional methods of flowing draperies and dynamic poses to suggest the speed of figures in motion. However, a variety of graphic techniques in his drawings capture a remarkable range of visual effects.

In this preparatory drawing for the Sforza Monument Leonardo seems to be portraying the movements of the horse and rider. To the modern eye accustomed to cinematography the multiple contours seem to convey the frantic motions of a cavalryman engaged in battle. But what Leonardo was trying to do was simply establish the best single position for his sculpture! Given that the multiple lines work so effectively with our own perceptual system, it is possible that Leonardo did “see” the motion implicit in his drawing, even if it lay outside the parameters of a static sculpture.

In Leonardo's words
Actual motion made with rapid impetus will never obstruct from the eye the object which is behind the body that is moving, providing it is near to the eye and not too much larger than the eye - as happens with the motion of certain instruments worked by women, made for the purpose of gathering their threads together…