The influence of referential processing on sentence complexity

This paper reports the results of five experiments designed to investigate the effects of referential processing on sentence complexity. Gibson (Cognition, 68 (1998) 1) suggested that sentence complexity is related to the locality of integrations between dependent syntactic heads, and that an appropriate measure of locality is the number of new discourse referents intervening between the endpoints of those integrations. The experiments in this paper test, modify and extend Gibson's (1998) claims. Each experiment manipulated noun phrases (NPs) in the subject positions of object-extracted relative clauses in order to determine how different types of NPs affected sentence complexity. Experiments 1, 2 and 3 used questionnaires to gauge sentence complexity, whereas Experiments 4 and 5 used self-paced reading. The results from Experiments 1, 2, 4 and 5 suggest that the complexity of the experimental items was more closely related to the Givenness status of the embedded subject in the Givenness Hierarchy than to whether the embedded subject was old or new to the discourse. Experiment 3 compared materials in which a quantifier was rotated through subject positions of a nested relative clause structure. The results of this experiment support a discourse-processing-based distance metric for computing locality and provide evidence against a pure similarity-based account of structural complexity such as proposed by Bever (Bever, T. G. (1970). The cognitive basis of linguistic structures. In J. R. Hayes (Ed.), Cognition and the development of language (pp. 279-362). New York: Wiley).     

The processing of extraposed structures in English

In most languages, most of the syntactic dependency relations found in any given sentence are projective: the word-word dependencies in the sentence do not cross each other. Some syntactic dependency relations, however, are non-projective: some of their word-word dependencies cross each other. Non-projective dependencies are both rarer and more computationally complex than projective dependencies; hence, it is of natural interest to investigate whether there are any processing costs specific to non-projective dependencies, and whether factors known to influence processing of projective dependencies also affect non-projective dependency processing. We report three self-paced reading studies, together with corpus and sentence completion studies, investigating the comprehension difficulty associated with the non-projective dependencies created by the extraposition of relative clauses in English. We find that extraposition over either verbs or prepositional phrases creates comprehension difficulty, and that this difficulty is consistent with probabilistic syntactic expectations estimated from corpora. Furthermore, we find that manipulating the expectation that a given noun will have a postmodifying relative clause can modulate and even neutralize the difficulty associated with extraposition. Our experiments rule out accounts based purely on derivational complexity and/or dependency locality in terms of linear positioning. Our results demonstrate that comprehenders maintain probabilistic syntactic expectations that persist beyond projective-dependency structures, and suggest that it may be possible to explain observed patterns of comprehension difficulty associated with extraposition entirely through probabilistic expectations.     

Data from eye-tracking corpora as evidence for theories of syntactic processing complexity

We evaluate the predictions of two theories of syntactic processing complexity, dependency locality theory (DLT) and surprisal, against the Dundee Corpus, which contains the eye-tracking record of 10 participants reading 51,000 words of newspaper text. Our results show that DLT integration cost is not a significant predictor of reading times for arbitrary words in the corpus. However, DLT successfully predicts reading times for nouns. We also find evidence for integration cost effects at auxiliaries, not predicted by DLT. For surprisal, we demonstrate that an unlexicalized formulation of surprisal can predict reading times for arbitrary words in the corpus. Comparing DLT integration cost and surprisal, we find that the two measures are uncorrelated, which suggests that a complete theory will need to incorporate both aspects of processing complexity. We conclude that eye-tracking corpora, which provide reading time data for naturally occurring, contextualized sentences, can complement experimental evidence as a basis for theories of processing complexity.     

The Dependency Structure of Coordinate Phrases: A Corpus Approach

Hudson (1990) proposes that each conjunct in a coordinate phrase forms dependency relations with heads or dependents outside the coordinate phrase (the “multi-head” view). This proposal is tested through corpus analysis of Wall Street Journal text. For right-branching constituents (such as direct-object NPs), a short-long preference for conjunct ordering is observed; this is predicted by the multi-head view, under the assumption that structures resulting in shorter dependencies are preferred. A short-long preference is also observed for left-branching constituents (such as subject NPs), which is less obviously accommodated by the multi-head view but not incompatible with it. The repetition of determiners was also examined (the dog and cat versus the dog and the cat), and a stronger preference was found for repetition with singular count nouns as opposed to mass or plural nouns; this accords well with the multi-head view, under the reasoning that single-determiner constructions require crossing dependencies with count nouns but not with plural or mass nouns.     

Syntactic Complexity Effects in Sentence Production

Syntactic complexity effects have been investigated extensively with respect to comprehension (e.g., Demberg & Keller, 2008; Gibson, 1998, 2000; Gordon et al., 2001, 2004; Grodner & Gibson, 2005; King & Just, 1991; Lewis & Vasishth, 2005; Lewis et al., 2006; McElree et al., 2003; Wanner & Maratsos, 1978). According to one prominent class of accounts (experience‐based accounts; e.g., Hale, 2001; Levy, 2008; Gennari & MacDonald, 2008, 2009; Wells et al., 2009), certain structures cause comprehension difficulty due to their scarcity in the language. But why are some structures less frequent than others? In two elicited‐production experiments we investigated syntactic complexity effects in relative clauses (Experiment 1) and wh‐questions (Experiment 2) varying in whether or not they contained non‐local dependencies. In both experiments, we found reliable durational differences between subject‐extracted structures (which only contain local dependencies) and object‐extracted structures (which contain nonlocal dependencies): Participants took longer to begin and produce object‐extractions. Furthermore, participants were more likely to be disfluent in the object‐extracted constructions. These results suggest that there is a cost associated with planning and uttering the more syntactically complex, object‐extracted structures, and that this cost manifests in the form of longer durations and disfluencies. Although the precise nature of this cost remains to be determined, these effects provide one plausible explanation for the relative rarity of object‐extractions: They are more costly to produce.     

Cross-serial dependencies in dutch: Testing the influence of NP type on processing load

We tested the cross-linguistic generalizability of three models of sentence processing complexity--Lewis (1996), Gibson (1998, 2000), and Gordon (Gordon, Hendrick, & Johnson, 2001; Gordon, Hendrick, & Levine, 2002)--by investigating the on-line processing of cross-serial dependencies in Dutch. The number of subject-verb relations in a clause was manipulated, as well as type of noun phrase (indexical pronouns vs. proper names or full definite NPs). Several of our findings diverged from Gibson's model: Processing difficulty at the verbs was not affected by the use of proper names versus first- and second-person pronouns; an increase at the first verb was seen for full NPs versus pronouns in 3-verb constructions, which was predicted by the Gibson model, but is in contrast to Lewis's model. These findings are best explained within the framework of similarity-based inference models (Gordon et al., 2001; Gordon et al., 2002), according to which the number of similar NPs affects processing difficulty at the point of retrieval, and not specifically their discourse status or syntactic function.     

Rare Constructions Are More Often Sentence‐Initial

Main clause phenomena (MCPs) are syntactic constructions that occur predominantly or exclusively in main clauses. I propose a processing explanation for MCPs. Sentence processing is easiest at the beginning of the sentence (requiring less search); this follows naturally from widely held assumptions about sentence processing. Because of this, a wider variety of constructions can be allowed at the beginning of the sentence without overwhelming the sentence‐processing mechanism. Unlike pragmatic and grammatical accounts of MCPs, the processing account predicts avoidance of MCPs in non‐initial main clauses (non‐initial coordinate clauses and premodified clauses). A corpus study supports these predictions, but it is somewhat inconclusive. A further corpus study examines another type of syntactic construction, premodifying adjunct phrases (“openers”); the prediction here is that less common types of opener will be especially avoided in non‐initial contexts. The prediction is confirmed, supporting the processing view of rare constructions.     

Case Matching and Relative Clause Attachment

Two accounts of relative clause attachment will be discussed, the case-matching hypothesis proposed by Sauerland and Gibson (1998) and the attachment-binding dualism (Hemforth et al., in press a, b). While the case-matching hypothesis predicts that relative clauses are preferentially attached to NPs whose case matches that of the relative pronoun, attachment binding predicts that NPs are preferentially attached to the most salient host, that is NP1 in constructions with two NPs. We conducted two off-line studies, one sentence completion task and one magnitude estimation experiment using subject (nominative pronoun) and object (accusative pronoun) relative clauses that can be attached to either of the two nouns in a complex subject (NP1 = nominative, NP2 = genitive) or object NP (NP1 = accusative, NP2 = genitive). While attachment binding predicts an across-the-board NP1 preference, the case-matching hypothesis predicts an NP1 prefence only in the case of subject (object) NPs followed by subject (object) relative clauses. The results of both experiments provide evidence for attachment binding and against case matching.     

Word Order Variation is Partially Constrained by Syntactic Complexity

Previous work suggests that when speakers linearize syntactic structures, they place longer and more complex dependents further away from the head word to which they belong than shorter and simpler dependents, and that they do so with increasing rigidity the longer expressions get, for example, longer objects tend to be placed further away from their verb, and with less variation. Current theories of sentence processing furthermore make competing predictions on whether longer expressions are preferentially placed as early or as late as possible. Here we test these predictions using hierarchical distributional regression models that allow estimates of word order and word order variation at the level of individual dependencies in corpora from 71 languages, while controlling for confounding effects from the type of dependency (e.g., subject vs. object), and the type of clause (main vs. subordinate) involved as well as from trends that are characteristic of individual languages, language families, and language contact areas. Our results show the expected correlations of length with position and variation only for two out of six dependency types (obliques and nominal modifiers) and no difference between clause types. These findings challenge received theories of across-the-board effects of complexity on word order and word order variation and call for theoretical models that relativize effects to specific kinds of syntactic structures and dependencies.     

Syntactic structure assembly in human parsing: a computational model based on competitive inhibition and a lexicalist grammar

We present the design, implementation and simulation results of a psycholinguistic model of human syntactic processing that meets major empirical criteria. The parser operates in conjunction with a lexicalist grammar and is driven by syntactic information associated with heads of phrases. The dynamics of the model are based on competition by lateral inhibition ('competitive inhibition'). Input words activate lexical frames (i.e. elementary trees anchored to input words) in the mental lexicon, and a network of candidate 'unification links' is set up between frame nodes. These links represent tentative attachments that are graded rather than all-or-none. Candidate links that, due to grammatical or 'treehood' constraints, are incompatible, compete for inclusion in the final syntactic tree by sending each other inhibitory signals that reduce the competitor's attachment strength. The outcome of these local and simultaneous competitions is controlled by dynamic parameters, in particular by the Entry Activation and the Activation Decay rate of syntactic nodes, and by the Strength and Strength Build-up rate of Unification links. In case of a successful parse, a single syntactic tree is returned that covers the whole input string and consists of lexical frames connected by winning Unification links. Simulations are reported of a significant range of psycholinguistic parsing phenomena in both normal and aphasic speakers of English: (i) various effects of linguistic complexity (single versus double, center versus right-hand self-embeddings of relative clauses; the difference between relative clauses with subject and object extraction; the contrast between a complement clause embedded within a relative clause versus a relative clause embedded within a complement clause); (ii) effects of local and global ambiguity, and of word-class and syntactic ambiguity (including recency and length effects); (iii) certain difficulty-of-reanalysis effects (contrasts between local ambiguities that are easy to resolve versus ones that lead to serious garden-path effects); (iv) effects of agrammatism on parsing performance, in particular the performance of various groups of aphasic patients on several sentence types.     

Sentence Complexity and Working Memory Effects in Ambiguity Resolution

Two self-paced reading experiments using a paraphrase decision task paradigm were performed to investigate how sentence complexity contributed to the relative clause (RC) attachment preferences of speakers of different working memory capacities (WMCs). Experiment 1 (English) showed working memory effects on relative clause processing in both offline RC attachment preferences and in online reading time measures, but no effects of syntactic complexity. In Experiment 2 (Korean), syntactic complexity due to greater distance between integrating heads, as measured by the dependency locality theory (Gibson in Cognition 68:1–76, 1998), significantly increased the proportion of attachment to NP1. However, no effects of working memory were found. The difference in results between English and Korean is proposed to be due to head-directionality effects. The results of our study support the conclusion that working memory-based accounts provide a better explanation than previous language-dependent accounts for differences in RC attachment preferences. We propose that previous language dependent-accounts of cross-linguistic differences in RC processing have overlooked the interaction between individual WMC and a language’s general structure, which is a central factor in RC attachment.     

Subject relative clauses are not universally easier to process: Evidence from Basque

Studies from many languages consistently report that subject relative clauses (SR) are easier to process than object relatives (OR). However, Hsiao and Gibson (2003) report an OR preference for Chinese, a finding that has been contested. Here we report faster OR versus SR processing in Basque, an ergative, head-final language with pre-nominal relative clauses. A self-paced reading task was used in Experiments 1 and 2, while ERPs were recorded in Experiment 3. We used relative clauses that were ambiguous between an object or subject-gap interpretation and disambiguated later in the sentence. The results of Experiments 1 and 2 showed that SR took longer to read than OR in the critical disambiguating region. In addition, Experiment 3 showed that SR produced larger amplitudes than OR in the P600 window immediately after reading the critical disambiguating word. Our results suggest that SR are not universally easier to process. They cast doubts on universal hypotheses and suggest that processing complexity may depend on language-specific aspects of grammar.     

Syntactic Complexity Effects in Sentence Production: A Reply to MacDonald,Montag, and Gennari (2016)

In our article, “Syntactic complexity effects in sentence production” (Scontras, Badecker, Shank, Lim, & Fedorenko, 2015 ), we reported two elicited production experiments and argued that there is a cost associated with planning and uttering syntactically complex, object‐extracted structures that contain a non‐local syntactic dependency. MacDonald et al. ( 2016 ) have argued that the results of our investigation provide little new information on the topic. We disagree. Examining the production of subject versus object extractions in two constructions across two experimental paradigms—relative clauses in Experiment 1 and wh‐questions in Experiment 2—we found a strikingly similar pattern: reliable differences in latency and word durations, as well as in rates of disfluencies, signaling a greater cost associated with planning and uttering the syntactically more complex object extractions. MacDonald et al. reject that interpretation, namely that the differences we observed in the production of subject versus object extractions demonstrate asymmetric production difficulties. Here we address the concerns they raise by clarifying confusion and presenting novel experimental evidence in support of our original claims.     

Processing relative clauses in Chinese

This paper reports results from a self-paced reading study in Chinese that demonstrates that object-extracted relative clause structures are less complex than corresponding subject-extracted structures. These results contrast with results from processing other Subject-Verb-Object languages like English, in which object-extracted structures are more complex than subject-extracted structures. A key word-order difference between Chinese and other Subject-Verb-Object languages is that Chinese relative clauses precede their head nouns. Because of this word order difference, the results follow from a resource-based theory of sentence complexity, according to which there is a storage cost associated with predicting syntactic heads in order to form a grammatical sentence. The results are also consistent with a theory according to which people have less difficulty processing embedded clauses whose word order matches the word order in main clauses. Some corpus analyses of Chinese texts provide results that constrain the classes of possible frequency-based theories. Critically, these results demonstrate that there is nothing intrinsically easy about extracting from subject position: depending on the word order in the main clause and in a relative clause, extraction from object position can be easier to process in some circumstances.     

Plausibility and Verb Subcategorization in Temporarily Ambiguous Sentences: Evidence from Self-Paced Reading

A self-paced reading experiment investigated processing of sentences containing a noun-phrase that could temporarily be mistaken as the direct-object argument of a verb in a subordinate clause but actually constituted the syntactic subject of the main clause (often referred to as an early vs. late closure ambiguity). Subcategorization preference of the subordinate verb and plausibility of the syntactic misanalysis were manipulated. Elevated reading times occurred during processing of the temporarily ambiguous noun-phrase for those sentences where the noun-phrase was an implausible direct-object of the preceding verb, regardless of the verbs subcategorization preferences. Elevated reading times were observed for all sentence types following syntactic disambiguation. Subsequent correlational analyses showed that the verbs individual subcategorization preferences affected processing time on the critical noun-phrase and the syntactically disambiguating main verb.     

Processing complexity and sentence memory: evidence from amnesia.

This study examines sentence memory as a function of linguistic processing complexity in amnesic patients. Sentence length as well as lexical and syntactic complexity were manipulated in two sentence repetition experiments. It was found that the amnesic patients performed considerably worse than the control subjects and that performance decreased: (1) when sentence length was increased by the addition of adjuncts compared to arguments of the verb; (2) when the verb selected more thematic frames; and (3) when sentences involved "empty" argument positions that must be linked to antecedents, particularly across clausal boundaries. These data showed how linguistic complexity affects sentence memory and implied that the amnesic deficit did not involve a generalized difficulty for materials of similar length, rather, the deficit was specific to certain representational types and processing routines.     

In search of on-line locality effects in sentence comprehension

Many comprehension theories assert that increasing the distance between elements participating in a linguistic relation (e.g., a verb and a noun phrase argument) increases the difficulty of establishing that relation during on-line comprehension. Such locality effects are expected to increase reading times and are thought to reveal properties and limitations of the short-term memory system that supports comprehension. Despite their theoretical importance and putative ubiquity, however, evidence for on-line locality effects is quite narrow linguistically and methodologically: It is restricted almost exclusively to self-paced reading of complex structures involving a particular class of syntactic relation. We present 4 experiments (2 self-paced reading and 2 eyetracking experiments) that demonstrate locality effects in the course of establishing subject-verb dependencies; locality effects are seen even in materials that can be read quickly and easily. These locality effects are observable in the earliest possible eye-movement measures and are of much shorter duration than previously reported effects. To account for the observed empirical patterns, we outline a processing model of the adaptive control of button pressing and eye movements. This model makes progress toward the goal of eliminating linking assumptions between memory constructs and empirical measures in favor of explicit theories of the coordinated control of motor responses and parsing.     

Neural correlates of Dutch Verb Second in speech production

Dutch speakers with agrammatic Broca's aphasia are known to have problems with the production of finite verbs in main clauses. This performance pattern has been accounted for in terms of the specific syntactic complexity of the Dutch main clause structure, which requires an extra syntactic operation (Verb Second), relative to the basic Subject-Object-Verb order surfacing in Dutch subordinate clauses. We report an fMRI study into the question whether this syntactic complexity is reflected in increased brain activation correlated with the production of Dutch main clause word order, in speakers without language impairment. Nineteen healthy subjects performed a covert sentence completion task, during which main and subordinate clauses were alternately elicited in a block design. Results show a left middle to superior frontal cluster of activation correlated to production of Verb-Second over Verb-Final clauses, with no activation in the opposite contrast. This activation pattern is counter to what might be expected from the frequency distribution of main and subordinate clauses. We conclude that the Verb-Second deviation from the basic Dutch SOV word order costs extra neural resources and that this also underlies the agrammatic problems with the production of finite verbs in Dutch main clauses.     

句法加工中的预测现象及实验证据

句法加工是读者通过整合输入的言语信息来理解句子的过程。句法加工的存在,使得读者能够提前预测文本的信息,提高阅读效率。由于阅读离不开信息整合,研究者提出两类不同的句法理论:句法预测的模块局域性理论和句法预测的互动分析性观点。这两类理论的争论点在于句法加工是单独模块化的自上而下加工,还是自下而上-自上而下的互动分析加工过程。其区别表现为句法预测的作用——前者认为句法预测对句子加工有抑制作用,后者认为句法预测对句子加工起促进作用。来自眼动、ERP等研究的数据佐证了句法预测的存在。未来研究应围绕其差异进行深入探讨,以揭示句法加工的实质。