This is the shortest explanation I could make within 30 minutes, which was not enough time to say everything I wanted. There may be some typos, but here is what I am theorizing in a nutshell.
1. Socionics derives judgement and perception from the instance of the preferance of the base function. Rational functions are logical and ethical. If the base function is a rational function, then a type has an emphasis on judgement. Irrational functions are sensible and intuitive. If the base function is an irrational function, then a type has an emphasis on perception.
2.)Everyone has a base portion of their brain that they perfer to use more often than the other; just as a person has a dominant left or right hand, people have prefrences in right and left brained usage. The right side of the brain has a prefrence for perception, and the left side of the brain has a preference for judging.
3.)Since socionics does not hold judgement or perception preferences according to brain dominance issues, a person's base function may or may not be located in the dominant portion of a persons brain; because of this, diffrent people may display slightly diffrent behaviours with the same type, and must be subtyped. If a person's base function is rational and located in the rational left portion of the brain, he or she is a logical and ethical subtype. If a person's base function is irrational and located in the irration right portion of the brain, he or she is a sensory or intuitive subtype. And vice versa if the base function is not located within the same portion of the brain of its own prefrence.
4.) There are views that purportedly conflict with the J/P braintype hemisphere theory. One such view is that purposed by J. Newnam, who has been considered by some to have disproved the J/P brain theory through various means of brain imagining and scanning. However, upon close examination of the theory, one would note that technically there is no diffrent in what the J/P brain dominance theory proposed and his theory other than a supposed reorganization of the functions within the various brain hemispheres. His theory reveals that actually the right frontal lobes were primarily responsible for judging prefrences and the peripheral and posterior lobes were responible for perceptive prefrences. In result, his general conclusion was that the left hemisphere was actually responsible for feeling and sensing prefrences, and the right hemisphere for thinking and intuition.
However, while there is much truth to the fact that most SF types and most NT types do in fact generally share differing hemispheres, there is no conclusive and irrefutable scientific evidence to show that all SF types must have dominant left brain hemispheres and all NT types must have dominant right brain hemispheres. Even so, the theory porported by J. Newman may hold truth in an entirly diffrent context, and should not be thrown out or considered insignifigant. All scientific data, no matter how biased or conflicting, should be considered important in this regards.