Syntactic complexity: wh-questions and relative clauses

2.1.2.1 The Derivational Complexity Hypothesis

As mentioned in Section 1.1.1.1, it is a well-documented finding that both the comprehension and production of structures that move an object are problematic for young children, with several proposals having been put forward in an attempt to pinpoint what it is about these structures that makes them complex. According to Jakubowicz’s (2011) Derivational Complexity Hypothesis (DCH, 1.1.3.1), complexity can be described in terms of the number and nature of syntactic operations to be performed in order to arrive at the derived structure and the DCH links the mastery of computationally complex structures to cognitive constraints.

More specifically, according to the DCH framework, the operation of moving a syntactic element from its base position and remerging it in one that is higher in the hierarchy is computationally complex and is bound by WM capacity. That movement operations, in particular those that front an object, are difficult for children has been empirically illustrated by acquisition studies of object questions in French, whose production data show that initially, children preferentially produce in situ (1) rather than ex situ structures (2) (Hamann, 2006;

Jakubowicz, 2011; Jakubowicz & Strik, 2008; van Kampen, 1997; Zuckerman & Hulk 2001).

In other words, children start by producing wh-questions that avoid movement and thus maintain the canonical subject-verb-object word order, but with age adopt the more computationally complex noncanonical structure that contains wh-fronting. The DCH interprets these findings as evidence that complex syntax emerges as WM capacity grows with maturation.

20 (1) Tu as poussé qui?

2ps have pushed who (2) Qui tu as poussé ?

who 2ps have pushed

2.1.2.2 Featural Relativized Minimality

While movement operations increase complexity, movement alone does not render a structure complex as computationally comparable structures have been shown to generate different processing patterns. For example, object-extracted which questions (5) are associated with poorer comprehension than object-extracted who questions (6) (Avrutin, 2000; De Vincenzi, 1991; Donkers & Stowe, 2006; Friedmann & Novogrodsky, 2011; Sheppard, Walenski, Love,

& Shapiro, 2015) despite the fact that both structures are derived via movement that fronts a wh-element. Grammatical approaches explain this asymmetry in terms of an intervention effect that stems from theories of locality, namely featural Relativized Minimality (fRM) (Friedmann et al., 2009; Rizzi, 2004; Starke, 2001), which is formulated as follows:

(3) In the configuration …X…Z…Y,

a local relation cannot hold between X and Y when a. Z intervenes between X and Y, and

b. Z fully matches the specification in morphosyntactic features of X

According to fRM, the facility with which a syntactic structure can be computed is determined by the nature of the featural match between a moved element X and an intervening Z. The various configurations of feature identity are summarized in (4). In the case of (4a), where +A and +B represent morphosyntactic features, an identity configuration is described in which there is complete featural overlap between the moved element X and the intervening element Z, which results in an ungrammatical structure as it is impossible to establish a relationship between X and Y. In (4b), the feature match is only partial and computation is thus possible within this inclusion configuration. In the final configuration in (4c), the moved element X and the intervener Z do not share any features, which leads to a disjunction configuration.

(4) X Z Y

a. Identity: +A +A +A

b. Inclusion: +A, +B +A +A, +B

c. Disjunction: +A +B +A

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Within an fRM framework, the difficulty associated with which object questions is due to the fact that it represents an inclusion configuration in which a lexically-headed object crosses over an intervening lexical subject and the two elements share a +noun phrase (+NP) feature. The inclusion of the +NP feature in the intervening (c-commanding) lexical subject creates a filler-gap dependency that is costly to parse for the computational system as the relation, which is sensitive to distance, must be established across the embedded subject despite its featural similarity to the target head. In the case of object-extracted who questions, the featural specifications of the fronted wh-operator and the embedded lexical subject over which it crosses are distinct, thus creating a disjunction configuration for which the syntactic analysis is more easily realized¹⁴.

(5) Which mailman did the fireman pull _____?

[+Wh +NP] [+NP]

(6) Who did the fireman pull _____?

[+Wh] [+NP]

Evidence for an intervention effect as described by fRM has been found across different age groups, different cognitive profiles and different languages (see Friedmann et al., 2009 for young typically-developing [TD] children, Friedmann & Novogrodsky, 2011 for children with developmental language disorder [DLD], and Garraffa & Grillo, 2008 and Sheppard, Walenski, Love, & Shapiro, 2015 for individuals with aphasia). One thing these populations all have in common is known limitations in WM (see Gathercole, Pickering, Ambridge, & Wearing, 2004 for TD children, Archibald & Gathercole, 2006 for children with DLD, and Majerus, Attout, Artielle, & van der Kaa, 2015 for aphasia). Comprehension difficulties related to lexically-headed object structures may be due to the need to move a determiner phrase (DP) specified with a +NP feature over another DP with the same featural specifications, and to temporarily store both DPs in WM while computing the filler-gap dependency. In this case, the embedded lexical subject would behave as a memory distractor that competes with the displaced element for retrieval at the position of the gap as they share a similar retrieval cue. This is in line with models of cue-based retrieval parsing, in which memory retrieval of the filler at the position of the gap involves comparing a set of retrieval cues against other items in memory in parallel.

14 It should be pointed out that not all features play a role in the computation of similarity. Belletti, Friedmann, Brunato, and Rizzi (2012) showed that only features that incite syntactic movement are relevant for intervention effects, and that a particular feature, such as gender, can have a different status cross-linguistically. The effect of featural mismatch on comprehension is outside of the scope of this work but see Belletti and colleagues (2012) for a detailed explanation of this phenomenon.

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Thus an item that partially matches the retrieval cues of the target may be activated and erroneously retrieved. Formal linguistic principles such as fRM make explicit what can be considered a cue in parsing, namely features, such as the +NP feature, that trigger movement.

Differentiating the two DPs conceivably taxes WM, as computing a dependency in the presence of intervention would consume more processing resources than computing a dependency in which intervention is absent. For the still-developing or atypically-developing child system that lacks the necessary WM capacity to perform the syntactic computation, the processing mechanism would break down, impeding comprehension. It thus seems legitimate to hypothesize that syntactic computation is directly linked to processing, which is assumed to be at least partly sustained by WM, as formulated by Jakubowicz (2011).