Seite - 160 - in Applied Interdisciplinary Theory in Health Informatics - Knowledge Base for Practitioners

1. Introduction of Control Theory Control theory (CT) as espoused by Carver and Scheier [1] is a general approach to understanding the behaviour of self-regulating agents, which could be humans or artefacts. Its conception is usually traced to the publication of Wiener’s seminal book on cybernetics – the science of feedback processes involving control or regulation of certain values within living or artificial systems [2]. Since then, CT has influenced a diverse range of fields including engineering, applied mathematics, economics, medicine, and cognitive and behavioural science. Ammons [3] used feedback processes in the context of human learning, and stated that a person’s knowledge of their own performance, obtained through feedback on that performance, will affect the rate of learning and the competence level ultimately reached by that person. 1.1. Discrepancy-reducing feedback loop The core component of CT is a negative feedback loop (Figure 1), termed negative because its function is to negate, or reduce, discrepancies between a perceived present state and a reference value (such as a goal state or standard). An agent perceives its current condition via an input function, and compares that perception against the reference value through a mechanism termed a comparator. If the agent observes a difference between the two values, it will attempt to reduce the discrepancy by performing a behaviour (termed the output function). The behaviour usually does not counter the discrepancy directly but has an impact on the agent’s environment. This should lead to a different present condition, which in turn is perceived by the input function and compared to the reference value. This arrangement thus constitutes a closed loop of control, the overall purpose of which is to minimise deviations from the standard of comparison. Figure 1. Negative feedback loop (from [1]). Feedback processes like the one described above can occur in diverse physical systems; the best-known example of which is the thermostat. In this system, the input function continuously samples current air temperature from a particular environment W.T.GudeandN.Peek /ControlTheory toDesignandEvaluateAudit andFeedback Interventions160