In following transformations in the family of indo-european languages, Bichakjian noticed that the relationship between subject, object and verb has changed, allowing for a more complex syntactic structure. According to Bichakjian's research, the word order has shifted from head last to head first constructions in which the heads are usually verbs and prepositions and their objects are modifiers such as attributive adjectives. What constitutes head and modifier is not clearly defined, so modified nouns and adnominal complements are modifiers, as in john's BACK or the BACK of the door  where back is the head. This example targets specific language items but the mapping of head and modifiers can be applied to auxiliaries and past participles, comparative adjectives and terms of references, case markers and verb roots, coordinated conjunctions and coordinated nouns and in numerals, tens of units, in which the first element, say twenty is a head and in twenty-five, where five is a modifier.
In using this analysis, Bichakjian has investigated ancestral structure and discovered that there is a shift of the head from an end position to a initial position. His explanation is that head-first constructions are more efficient than head-last. His definition of efficiency is based on how early in life a child can acquire a construction. That is, fewer energy resources are spent to acquire specific language features. Head-first languages are more efficient because psycholinguistic research shows that this kind of structure is acquired earlier in life than left branching. Moreover the shift from last to first position marks the disappearance of inflexional markers which are usually more difficult to learn. Also, head-last constructions are problematic when subordinates are included because they have to be embedded to the left of the sentence, thus head-first constructions offer the possibility for greater complexity in sentence construction.
The advantage in head-first languages are not only measurable in terms of efficiency in learning time but also in real-time decoding of speech. A head-first construction allows the speaker and the hearer to use less processing effort in coding and decoding because the structure of the head-first language fixes the word order such that the sequence of a sentence can be decoded serially as it unfolds and the full sentence does not need to be uttered before the employed syntactic strategy, is inferred. For example, consider the the formally correct sentence:
THE DOG CHASED the cheese eating mouse catching cat, is problematic to utter and to understand. The sentence:
THE DOG CHASED the cat that caught the mouse that was eating the cheese, is far easier to decode than the first one.