Abstract
This paper deals with some aspects of the difficulties encountered by subjects (students of engineering, industrial apprentices, miners) drawn from traditionally non-pictorial cultures when dealing with technical drawings and their derivatives. It presents a series of experiments involving "impossible" figures as well as a study concerned with interpretation of Geometrical diagrams. The results indicate that the difficulties encountered do not arise from an inability to perceive a pattern of lines as representing a solid object but rather from the inability to arrive at a correct percept of the depicted object.