The Link between Cognition and the Complexity of Engineering Systems Design

This paper focuses on the role of human cognition in the design of large complex systems. It contrasts the physical system that is the product of the design with the cognitive model that is used by the designer to “understand” the system. The complexity of the system relevant to the designer is a function not only of the physical system, but also of the cognitive model that the designer holds in his mind. Furthermore, the level of cognitive model available to an experienced designer depends on the state of domain knowledge. To be useful in answering the question, “How complex is this system to design?” the state of the domain knowledge available to the designer must be assessed with respect to the level at which the design problem is posed. The concept of conceptual distance is introduced that depends on the disparity between the present level of integrated knowledge and the conceptual level of the design problem. This “distance” is a measure of the complexity of the design task and is called the cognitive complexity of the design. To investigate the concept of cognitive complexity a model of human knowledge is proposed along with a set of graphical abstractions. It is concluded that the cognitive complexity of the design task is neither wholly intrinsic (a property of the system) nor wholly subjective (a property of the mind) but requires an objective evaluation of the engineering problem with respect to present knowledge. It is noted that the structure of knowledge in a specific domain can be mapped and therefore a research program can be launched to systematically determine the difficulty of various engineering endeavors. 1 Associate Professor, Engineering Systems Division and Civil and Environmental Engineering Department, Massachusetts Institute of Technology, Cambridge, MA 02139