Fuzziness , Requisite Compatibility and System Design

1 . IN T R O D U C T IO N Ergonomics, which focuses on the design of human–machine systems with respect to requisite compatibility between the users, products, systems, and environments, is often faced with the complex and uncertain relationships between human characteristics, various artifacts, and human activity requirements (Karwowski 1991). Investigation of such relationships must take into consideration the natural fuzziness in human and system performance, which can be expressed in terms of degrees of vagueness, and which formally can be modeled through gradation in categories (Z adeh 1965 ). U ncertainty due to fuzziness is inherent to any complex system and to the human thought and perception processes (Smithson 1982). It should be noted that fuzziness, which measures the degree to which an event occurs, and not whether it occurs, differs from randomness, which describes the uncertainty of event occurrence. (Kosko 1992). Furthermore, fuzziness, i.e. a type of deterministic uncertainty, also models ambiguity as a property of physical phenomena. In order to study complex human–machine systems it is necessary to use modeling approaches that are approximate in nature (Z adeh 1973 ; Karwowski 1983 ). Fuzzy systems methodologies allow accounting for human and human–artifact fuzziness, and, therefore, provide the necessary framework for successful modeling efforts in the ergonomics (Karwowski 1991; Karwowski and Mital 1986). As fuzziness occurs at all levels of human interactions with the outside environments, ranging from physical to cognitive tasks, it can be used as the model for human– artifact interactions. It can also help to explain the complex phenomena of human sensation, information processing, decision-making and communication and functioning (Karwowski 1991, 1992; Karwowski and Salvendy 1992).