by presenting a series of Surface Structures which we then subjected to

A serious Surface Strutures are finally arriving at the full linguistic representatin. Correct?

Correction: A series Surface Structures are .... representation.

Sorry for my typos.

In my opinion, the subject of "finally arriving at the full linguistic representation" seems to be "we."

Compare:

"WE then subjected a series of surface structures to the well-formed-in-therapy conditions, so that WE finally arrived at the full linguistic representation."

IMO

The phrase answers "how" or "when" - good adverb qualifiers - and modifies subjected.

Similar to:
We drove home, finally arriving at midnight.

Thank you both for your help.

Would any of you explain the function of which I highlight in red? I think "which" refer to "Surface Structures", and "which" is the object in the following clause, correct?

we then subjected Surface Structures (or which) to the well-formed-in-therapy conditions

"She began by presenting a series of surface structures, WHICH WE THEN SUBJECTED TO THE WELL-FORMED-IN-THERAPY CONDITIONS."

In my opinion:

a. "which we then subjected to the well-formed-in-therapy conditions" is a non-defining (optional) adjective clause. (I believe a comma is necessary in front of "which.")

b. I agree with you that "which" is a relative pronoun that refers to "a series of surface structures" and is the object of "subjected."

i . She began by presenting a series of surface structures. We then subjected this series of surface structures to the well-formed-in-therapy conditions.

Thank you very much!