“ground occupied..” meaning

Question

I cannot figure out the meaning of this sentence:

There is a ground in between the voluntary and the involuntary occupied by expressions that were once learned but come to operate automatically without choice, or even despite choice, and typically without awareness.

For me as a non-native speaker it is kinda complicated. I guess the "ground" goes together with "occupied". However, it does not make any sense to me.

Could you help me with synonyms here to understand the first part of the sentence?

Answer 1

In this context, I  believe "ground" to be synonymous with "territory" or "place"

There is a [territory] or [place] in between the voluntary and the involuntary [where] expressions that were once learned but come to operate automatically without choice, or even despote choice, and typically without awareness.

(from this definition of "ground" from the Merriam-Webster Online Dictionary:

4e: an area of knowledge or special interest