Back to the seminar notes for the Sept 2011 Obi Fox event.
There are a lot of neurons in the brain. Motor neurons "fire" (electrical/chemical changes within the cell) in response to a specific stimulus and then cause movements of specific muscles or muscle groups. The type of stimulus depend on the type of neuron. Some only respond to a visual stimulus, some only to touch, some to specific internal changes...etc. AND there are some that respond to two specific types of stimuli, and other to three or more specific types of stimuli.
Quite a few motor neurons respond to visual and tactile stimuli. This means that you are getting the same changes in the brain, the brain is perceiving the same thing... if the individual is touched or if the individual perceives something moving 'within' range. Specific body areas correspond to a part of the 'personal space' field.
By moving into a dog's space, the brain can be responding as if the animal was touched.
Just as important is that those neurons will continue to fire until the 'threat' is removed from the space or when the motor sequence is completed. If someone is too close...those neurons will fire until the dog can move far enough away that the person is out of the dog's 'space'.
That somewhat makes it even harder to think about dogs that are asked to "just get over it," both shy-fearful type dogs, reactive dogs, and super excitable dogs.
The personal space zone can change over time in response to desensitization or sensitization. It can get bigger or smaller.
And that's probably enough to think about for today. Any errors in this post are mine.