Feedback dynamics refers to the time-varying behavior of a system that is created by a particular class of causal forces referred to as feedback loops—circular chains of cause and effect among system traits or actors. Such chains create a bidirectional flow of causality: changes or movement at one point influence system behavior in such a way that propagates through the chain to eventually reinforce or mitigate the original change. Feedback comes in two forms: balancing (negative) and reinforcing (positive). As the names imply, balancing feedback balances or mitigates movement away from equilibrium, while reinforcing feedback reinforces and accelerates such movement. The history of feedback thought as an emerging concept in systems theory is documented in references under Historical Roots of Feedback Dynamics. Feedback loops and the dynamic behavior they create are evident at all scales, from the molecular to the global—and they are ubiquitous. Their presence and role in the natural world is discussed under Feedback Dynamics in the Biosphere. Because of limitations in human reasoning and the significant role of feedback dynamics in socio-ecological systems, the presence of feedback poses special problems for exercising judicious management of environmental resources. The literature in Effects of Feedback on Human Decision Making describes the limits of human decision making in the presence of feedback and points to the role of feedback modeling to augment the decision-making process. Building on this thread of reasoning, the literature under Modeling Feedback Dynamics and all its subsections describes both qualitative and quantitative approaches to modeling feedback and discusses the limitations and advantages of each approach. The works in Feedback Dynamics in Socio-ecological Problems provide a summary of several instances of studies involving feedback in socio-ecological systems and highlight that some of the most influential feedback dynamics involve the interacting influences of the natural environment and the humans that depend on that environment for survival. Hence, scientists employing a feedback view of the world and who work on socio-ecological problems have increasingly recognized the need to engage stakeholders in jointly creating models of system feedback dynamics in order to build consensus and a common vision for addressing problems involving human interactions with the environment. Key works describing approaches to engaging stakeholders in feedback modeling are discussed under Group Modeling: Engaging Stakeholders in Feedback Analysis.
Historical Roots of Feedback Dynamics
The sources cited in this section provide a historical perspective on the origins and use of feedback dynamics in complex systems. The recognition of feedback and the dynamic behavior it creates has a rich history that spans a wide range of disciplines, but most notably the fields of engineering, biology, social sciences, business management, mathematics, and environmental sciences. Richardson 1999 demonstrates that the concept of feedback is implicit in the writings of Aristotle and Malthus and is explicit in Wiener 1961 and Bertalanffy 1972, which emerged out of the cybernetics movement and focused almost exclusively on balancing feedback as the source of homeostasis and a means of exercising control over natural and engineered systems. Astrom and Murray 2008 also demonstrates this approach. The authors of Simon 1952 and Forrester 1958 drew on the field of servomechanisms to identify both balancing and reinforcing feedback in economic and business systems. Powers 1990 demonstrates the use of control theory as a closed-loop explanation of human behavior and argues for its superiority over conventional stimulus/response or input/output models. Contrary to the cybernetics school, these authors considered both balancing and reinforcing feedback as fundamental to the emergent and counterintuitive behavior of complex systems. Their focus was first on modeling the feedback structure inherent in a given system in order to explain the behavior of the system, and second on exploiting the insights from that analysis to explore system-wide implications of proposed intervention policies. Research involving this type of analysis is documented in numerous journals across a wide range of disciplines. The System Dynamics Society sponsors the Powers 1990, an interdisciplinary academic journal dedicated to research and applications involving computer simulation of feedback systems in economic, environmental, health, business, and other contexts.
Astrom, Karl Johan, and Richard M. Murray. 2008. Feedback systems: An introduction for scientists and engineers. Princeton, NJ: Princeton Univ. Press.
An upper-level undergraduate or lower-level graduate text in feedback systems. In keeping with the cybernetics thread of feedback thought, the focus here is primarily on recognizing balancing feedback in engineered and natural systems, and developing control feedback structures that maintain the system at a desired state.
Bertalanffy, Ludwig von. 1972. The history and status of general systems theory. Academy of Management Journal 15.4: 407–426.
Aligned more with the cybernetic thread of feedback thought, this work traces the history and origins of general systems theory, identifying the role of feedback as the source of system stability and control.
Forrester, Jay W. 1958. Industrial dynamics: A major breakthrough for decision makers. Harvard Business Review 36.4: 37–66.
This seminal work outlines the core epistemological principles behind system dynamics and computer-based simulation using feedback. This work follows the servomechanisms school of thought and views both balancing and reinforcing feedback as being ubiquitous in all complex systems and as the source of complex system behavior.
Powers, William T. 1990. Control theory: A model of organisms. System Dynamics Review 6.1: 1–20.
Applies control theory to human decision making and behavior and shows how a feedback-based approach can mimic behavior and predict the consequences of that behavior. Conventional stimulus/response or input/output models can mimic behavior but not predict its consequences. This finding is relevant to systems involving human decision making, such as socio-ecological systems.
Richardson, George P. 1999. Feedback thought in social science and systems theory. Waltham, MA: Pegasus Communications.
This text (based on the author’s PhD dissertation at MIT) traces the historical origins of feedback thought as a framework for understanding, modeling, and affecting social phenomena.
Simon, Herbert A. 1952. On the application of servomechanism theory in the study of production control. Econometrica 20.2: 247–268.
Examines the role of feedback dynamics in human decision making and is one of the early papers positing the presence of adaptive feedback in social systems. Simon posits that human decision making is “bounded” to effects and causes that are temporally or causally proximate. This “bounded rationality” has significant implications for evaluating interventions in socio-ecological systems and is an argument for simulation-based exploration of systems involving feedback dynamics.
System Dynamics Review. 1983–.
The official journal of the System Dynamics Society, established in 1983. This group is dedicated to the field of system dynamics, “. . . a computer-aided approach to policy analysis and design [that] applies to dynamic problems arising in complex social, managerial, economic, or ecological systems—literally any dynamic systems characterized by interdependence, mutual interaction, information feedback, and circular causality.”
Wiener, Norbert. 1961. Cybernetics: Or control and communication in the animal and the machine. 2d ed. Cambridge, MA: MIT.
One of the earliest and most influential works explicitly referring to feedback in the context of social systems. Wiener recognized the importance of feedback, but he doubted it could be modeled in social phenomena because of the complexity and limited data on those phenomena. Originally published in 1948. Later work by Forrester (Forrester 1958) in this section and others under Historical Roots of Feedback Dynamics has since demonstrated that Wiener was overly pessimistic. Reprinted by MIT as recently as 2014.
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