Comparator Function

Comparator Function

In PCT, the comparator function is not necessarily a place where complex cognitive processes occur. Instead, it is a place where one kind of signal is subtracted from another. In particular, we think of it as a place where a reference signal is subtracted from a perceptual signal. A comparator could very well be a neuron that is excited by neurons carrying perceptual signals and inhibited by neurons carrying reference signals, or the reverse. (In neurophysiology, when some process or event increases the activity of a particular neuron, the process or event is said to excite the neuron. Conversely, when a process or event decreases the activity of the same neuron, it is said to inhibit the neuron.)

The published research in the behavioral and brain sciences is literally filled with discussions and "theories" about excitation and inhibition. For example, many theories that are supposed to explain "ADD/ADHD," or "violent behavior," or "prejudice by older people," all rely on some hypothetical excess or deficiency of excitation or inhibition, from one part of the brain or another. Many Nobel Prizes in medicine and physiology were awarded to people who described the roles of excitation and inhibition in nervous systems. Not one major theory that is widely accepted in the behavioral and brain sciences, or one research program that lead to a Nobel Prize, has ever described the roles of excitation and inhibition the way we describe them in perceptual control theory. In PCT, we say that excitation and inhibition create the necessary comparison between perceptual signals and reference signals, and the comparison is what allows a living system to control its own perceptions, and, consequently, to survive.