Situation awareness (SA) has been a topic of interest for more that two decades in human factors and ergonomics. This paper proposes a critical account on this useful concept for human-centered design. First and foremost, it proposes various meanings of the concept of situation, ranging from the real, available, perceived, expected, to desired situations. In addition, a situation is not a snapshot; it should be investigated as a dynamic set of states. This paper proposes two perspectives of situation models: extrinsic and intrinsic. The extrinsic-intrinsic distinction is interesting because it can support deeper analysis of SA complexity. In particular, human operator's expertise and experience is central to the concepts of SA and associated mental models, especially in safety-critical systems and environments. For example, aircraft pilot's mental models are incrementally formed by training and extensive experience. This is the intrinsic account of SA complexity. In addition, aeronautical operational situations can be very complex (e.g., high density traffic or bad weather conditions). This kind of "external" situation cannot be represented by a set of states only, but requires multi-agent models. This is the extrinsic account of SA complexity. Human-systems integration cannot be done correctly if both intrinsic and extrinsic SA complexities are not properly taken into account.< Leer menos