Control

Engineering definition

Engineers generally think of an artificial electronic controller when they hear the word “control.” PID control (proportional, integral, derivative) often comes to mind. Parameters of the control system are defined by the engineer, and performance is observed. Control parameters are “tuned” until adequate performance is achieved. The control parameters are easily manipulated, and the controller can be turned off to observe and measure the uncontrolled natural system behavior. Many other types on control exist, including optimal control (LQR), fuzzy logic, and sliding mode control to name a few.

Medical definition

Control is generally associated with a patient’s ability to voluntarily regulate the movement of body segments such as the arms, hands, fingers, or toes. It may also be used to describe the ability to regulate bodily organs such as the bladder. Control may be characterized by a clinician as good, bad, full, or partial, depending on the level of disability.

In neuroscience, however, medical practitioners may refer to the control of various organs or functions, through the nervous system. Similar to some engineering systems, electronic signals are sent to various receptors in the human body to initiate activity or responses to various stimuli. This field is quite complex, but it is a branch of medical science that is perhaps closest to the electronic controllers of the engineering world.

Confusion

For engineers, a control system is something that is well defined and can be easily manipulated. But in medicine, it is not possible to “turn off” a person’s natural body control to observe uncontrolled system behavior. Even when a patient is unconscious, reflexes are still present. This can make obtaining information about the human control system very difficult. Moreover, the human control system is not as simple as a PID controller. A second order differential equation is only an approximation to the overall controller capability. Anticipation and preparation for stimuli affect the system response. Motivation also affects performance and dramatic difference are observed between people who are energetically encouraged and those who are not.