Motivated or unmotivated words?

The verbal sign conscious of linguists, defined by the duality meant / significant excludes the indicated object, the referent, who would have no link either with the significant, or with the meant. It is what is still taught in 2012 in the cours of Linguistics of our Faculties of literature.
The spirit of these rationalist linguists, locked into their ivory towers, is not interested in the relationship)of the sign in the reality which it reflects or to the individual who is originally, but in the relationship of the sign in another sign inside a closed system there, when he was adopted and admitted. As expresses it, Strap ( 1993 ): " in simple terms, the arbitrary power of the sign implies that the shape of the word has no natural relationship with its sense: to indicate a tree (i.e. the referent), no matter that we pronounce tree, tree, Baum or derevo. " The corollary of this postulate, this hypothesis raised to the rank of founding dogma, is that the language is an abstraction, without any natural foundation, no physical link with the referent.
But this split enters the conscious linguistic world where reigns the duality significant / mean cut by the referent does it respect the neurosensory physiology? Is not it obvious that this vision of the linguistics excluding the referent, and thus all the biological neurosensory processes which allow the human brain to have a representation of this referent, can be considered very reducing? The human language is really an object abstracts, virgin of any influence and any track of the multisensory perception.

Lacan nevertheless asserts that the significant preexists before the meant and the contents of this site will demonstrate that the conscious language is only the part) emerged from the Language, the unconscious base of which is the immense block immersed in waters until then dark and deep.

Why the saussurienne linguistics is established on a conventional sign and built itself on the exclusion from the referent? In front of the image of the tree, named(appointed) a referent by the linguists, we associate, according to her language, significant sound arbre in French, Baum in German or tree in English.
So in front of an object x, the referent tree for example, every language(tongue) would use(wear out) to indicate(appoint) him(it) of a continuation(suite) of sounds, of a significant one clean(appropriate), by pure agreement(convention), without any motivation for the linguists