Heavy NP shift

Heavy NP shift is an operation that involves re-ordering (shifting) a "heavy" noun phrase (NP) to a position to the right of its canonical position under certain circumstances. The heaviness of the NP is determined by its grammatical complexity; whether or not shifting occurs can impact the grammaticality of the sentence. 
Ross (1967) is thought to have been the first to systematically investigate the properties of heavy NP shift. Although the term heavy NP shift derives from the theoretical framework of transformational grammar, which describes the process in terms of movement of the NP, linguists working in other frameworks also use this term. And in approaches to syntax where NP is analyzed as a determiner phrase (DP), heavy NP shift is called heavy DP shift.
Factors contributing to the heaviness of an NP.
Early observations of weight or heaviness have been credited to a rhythmical feel that unconsciously takes shape in languages, that is, the tendency of growth, to go from shorter to longer elements within a phrase. In these early observations, it was noted that when there are two constituents differing in size, the smaller constituent usually precedes the longer one. This observation has been more recently coined as the "principle of end-weight". The literature proposes many different definitions of weight or heaviness such as number of words in the NP (length of NP), number of nodes in the NP, and more generally number of phrasal nodes. Other observations on heaviness include: 
Heavy NP shift in different languages.
Heavy NP shift in English.
Examples 1a, 2a, and 3a all show canonical order whereas 1b, 2b, 3b show the NP shifted to the right of its canonical position:
If a constituent is not considered 'heavy' or 'complex', the shift would not make grammatical sense or would be considered awkward to a native speaker of English, e.g. 
In example 4, the verb "sent" has a personal pronoun as its direct object. Typically, nothing can intervene between a verb and its direct object in most dialects of English, e.g.
In example 5b, the NP "the problem" is not complex enough to be shifted.
Heavy NP shift in Japanese.
Japanese is an SOV (subject, object, verb) language. Particles in Japanese encode syntactic functions, marking the relationship of the subject and object (NP) to the verb. This allows Japanese speakers to 'scramble' the order of particle-marked phrases which is important when considering word ordering biases such as heavy NP shift. In corpus studies and experiments, it has been shown that Japanese-speakers have a long-before-short bias, contrasting English biases of short-before-long in the presence of a heavy NP. 
In an experiment, participants had to create a sentence from a set of phrases that varied in length of the direct object (DO) and indirect object (IO) for dative verbs. In Japanese, the order for dative verbs is; subject (S) -indirect object (IO) -direct object (DO). For example, the 'short' phrase:
In this study, participants chose this order for a short phrase the majority of the time, without rearranging the order of the IO and DO. However, when the DO and IO were lengthened, the participants were more likely to shift the longer phrase before the short phrase even if it switched the order from S-IO-DO to S-DO-IO. For example, the phrase:
was shifted so that the long DO was before the short IO:
If the IO was longer than the DO, the participants were less likely to switch the order, leaving it as S-IO-DO. This suggests that Japanese speakers have a bias towards placing longer phrases before shorter ones.
Heavy NP shift in German.
German word order is variable and flexible and relies on a rich inflectional system. Rearrangements of an NP and PP can take place similar to English i.e. [NP PP V] or [PP NP V]. German does not allow a direct object NP to the right of a final verb. The examples below show the rearrangement of a heavy NP and a PP. Either order is acceptable in German as word order variation is not as strict as it is in other languages such as English. 
Analyses of heavy NP shift.
Movement analyses of heavy NP shift.
For analyses that treat heavy NP shift as movement, there are two kinds of shifts when considering heavy NPs: one involves rightward movement, the involves leftward movement.
Heavy NP shift as rightward movement.
The first, and most traditional, is when a "heavy" object NP is shifted rightward to the end of the utterance. According to one theory a complex NP will be shifted rightward if it does not cross over a verb. Another theory proposes a leftward movement of a "light" indirect object. According to this theory an indirect object is moved leftward independently of verb movement to a higher specifier position, next to the verb and before the direct object, leaving the heavy NP "in situ". 
This syntax tree shows an example of rightward movement of a heavy NP. The entire constituent "my rich uncle from Detroit" has 'shifted' from its position as a complement to the verb to an adjunct of the VP. This tree has been created using a particular style of syntax, mainly X-bar Theory. 
Heavy NP shift as leftward movement.
The syntax tree below shows an example of leftward movement of a 'light' indirect object. The constituent "on the street" has 'shifted' from its position in a small clause environment past the direct object to a higher functional specifier position leaving the 'heavy NP' "in situ". This syntax tree has been created using a particular style of syntax, mainly X-bar Theory. 
Processing analyses of heavy NP shift.
Psycholinguists want to understand when speakers resort to shifting heavy NPs to the end of a phrase. A study of printed corpus material found that different verbs exhibit different word order variation. The study focused on whether speakers and writers produce the word of heavy NP shift for their own benefit, or if they take into account the needs of the listener or reader. In this study, two verb classes were compared to test the choice of early and late commitment (points when the speaker has 'committed' themselves to producing a VP immediately followed by NP and PP constituents). The study examined transitive verbs, which require an NP object (e.g. "bring", "carry", "make", "put", etc.) and prepositional or intransitive verbs that do not require an NP object (e.g. "add", "build", "call", "draw", "leave", etc.).
Example of utterance with transitive verb:
Example of utterance with intransitive verb:
The arrows indicate where the speaker commits to producing a VP with an NP and PP following. They also indicate where the listener is sure the VP will contain a NP and PP. 
After analyzing written and spoken corpus data it was found that heavy NP shift is more common with intransitive verbs. This suggests using heavy NP shift word order with intransitive verbs allows the producer more time to decide whether they will include a direct object or not. This reduces the amount of planning needed and gives the speaker more time to articulate their thoughts. Having this extra time should in turn reduce the chance of the producer having to correct or abort an utterance.