publications: representative articles (including unpublished work)

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.

This paper presents the results of an experimental study on multiple focus configurations, that is, structures containing two nested focus-sensitive operators plus two foci supposed to associate with those operators. There has been controversial discussion in the semantic literature regarding whether or not an interpretation is acceptable that corresponds to this association. While the data are unclear, the issue is of considerable theoretical significance, as it distinguishes between the available theories of focus interpretation. Some theories (e.g. Rooth’s 1992) predict such a pattern of association with focus to be impossible, while others (such as Wold’s 1996) predict it to be acceptable. The results of our study show the data to be unacceptable rather than acceptable, favouring important aspects of the theory of focus interpretation developed by Rooth.

Eye fixation durations during normal reading correlate with processing difficulty, but the specific cognitive mechanisms reflected in these measures are not well understood. This study finds support in German readers’ eye fixations for two distinct difficulty metrics: surprisal, which reflects the change in probabilities across syntactic analyses as new words are integrated; and retrieval, which quantifies comprehension difficulty in terms of working memory constraints.We examine the predictions of both metrics using a family of dependency parsers indexed by an upper limit on the number of candidate syntactic analyses they retain at successive words. Surprisal models all fixation measures and regression probability. By contrast, retrieval does not model any measure in serial processing. As more candidate analyses are considered in parallel at each word, retrieval can account for the same measures as surprisal. This pattern suggests an important role for ranked parallelism in theories of sentence comprehension.

The surprisal of a word on a probabilistic grammar constitutes a promising complexity metric for human sentence comprehension difficulty. Using two different grammar types, surprisal is shown to have an effect on fixation durations and regression probabilities in a sample of German readers’ eye movements, the Potsdam Sentence Corpus. A linear mixed-effects model was used to quantify the effect of surprisal while taking into account unigram frequency and bigram frequency (transitional probability), word length, and empirically-derived word predictability; the so-called “early” and “late” measures of processing difficulty both showed an effect of surprisal. Surprisal is also shown to have a small but statistically non-significant effect on empirically-derived predictability itself. This work thus demonstrates the importance of including parsing costs as a predictor of comprehension difficulty in models of reading, and suggests that a simple identification of syntactic parsing costs with early measures and late measures with durations of post-syntactic events may be difficult to uphold.

Cross-linguistically, subject relative clauses are generally easier to process than object relative clauses. Hsiao & Gibson 2003 present surprising evidence that object relatives in Chinese are easier to process than subject relatives. We present a series of self-paced reading experiments which consistently show that the subject-preference tendency holds for Chinese relative clauses as well. The results suggest that neither the storage cost hypothesis nor the integration cost hypothesis of the Dependency Locality Theory (Gibson 2000) can explain the reading time patterns for subject versus object relative clauses. We argue that the higher frequency of subject relative clauses furnishes a better explanation for Chinese relative clause processing.

While it is widely acknowledged in the formal semantic literature that both the truth-functional focus particle only and it-clefts convey exhaustiveness, the nature and source of exhaustiveness effects with it-clefts remain contested. Based on an event-related brain potentials (ERPs) study on only-foci and it-clefts, we provide experimental evidence that the violation or cancelation of exhaustive readings involve different underlying processes in the two structural environments.

Background: In addition to the canonical subject-verb-object (SVO) word order, German also allows for non-canonical order (OVS), and the case-marking system supports thematic role interpretation. Previous eye-tracking studies (Kamide et al., 2003; Knoeferle, 2007) have shown that unambiguous case information in non-canonical sentences is processed incrementally. For individuals with agrammatic aphasia, comprehension of non-canonical sentences is at chance level (Burchert et al., 2003). The trace deletion hypothesis (Grodzinsky 1995, 2000) claims that this is due to structural impairments in syntactic representations, which force the individual with aphasia (IWA) to apply a guessing strategy. However, recent studies investigating online sentence processing in aphasia (Caplan et al., 2007; Dickey et al., 2007) found that divergences exist in IWAs' sentence-processing routines depending on whether they comprehended non-canonical sentences correctly or not, pointing rather to a processing deficit explanation. Aims: The aim of the current study was to investigate agrammatic IWAs' online and offline sentence comprehension simultaneously in order to reveal what online sentence-processing strategies they rely on and how these differ from controls' processing routines. We further asked whether IWAs' offline chance performance for non-canonical sentences does indeed result from guessing. Methods & Procedures: We used the visual-world paradigm and measured eye movements (as an index of online sentence processing) of controls (N = 8) and individuals with aphasia (N = 7) during a sentence-picture matching task. Additional offline measures were accuracy and reaction times. Outcomes & Results: While the offline accuracy results corresponded to the pattern predicted by the TDH, IWAs' eye movements revealed systematic differences depending on the response accuracy. Conclusions: These findings constitute evidence against attributing IWAs' chance performance for non-canonical structures to mere guessing. Instead, our results support processing deficit explanations and characterise the agrammatic parser as deterministic and inefficient: it is slowed down, affected by intermittent deficiencies in performing syntactic operations, and fails to compute reanalysis even when one is detected.

We present a detailed process theory of the moment-by-moment working-memory retrievals and associated control structure that subserve sentence comprehension. The theory is derived from the application of independently motivated principles of memory and cognitive skill to the specialized task of sentence parsing. The resulting theory construes sentence processing as a series of skilled associative memory retrievals modulated by similarity-based interference and fluctuating activation. The cognitive principles are formalized in computational form in the Adaptive Control of Thought–Rational (ACT–R) architecture, and our process model is realized inACT–R.We present the results of 6 sets of simulations: 5 simulation sets provide quantitative accounts of the effects of length and structural interference on both unambiguous and garden-path structures. A final simulation set provides a graded taxonomy of double center embeddings ranging from relatively easy to extremely difficult. The explanation of center- embedding difficulty is a novel one that derives from the model’s complete reliance on discriminating retrieval cues in the absence of an explicit representation of serial order information. All fits were obtained with only 1 free scaling parameter fixed across the simulations; all other parameters were ACT–R defaults. The modeling results support the hypothesis that fluctuating activation and similarity-based interference are the key factors shaping working memory in sentence processing. We contrast the theory and empirical predictions with several related accounts of sentence-processing complexity.

Understanding a sentence requires a working memory of the partial products of comprehension, so that linguistic relations between temporally distal parts of the sentence can be rapidly computed. We describe an emerging theoretical framework for this working memory system that incorporates several independently motivated principles of memory: a sharply limited attentional focus, rapid retrieval of item (but not order) information subject to interference from similar items, and activation decay (forgetting over time). A computational model embodying these principles provides an explanation of the functional capacities and severe limitations of human processing, as well as accounts of reading times. The broad implication is that the detailed nature of crosslinguistic sentence processing emerges from the interaction of general principles of human memory with the specialized task of language comprehension.

A production study is presented that investigates the effects of word order and information structural context on the prosodic realization of declarative sentences in Hindi. Previous work on Hindi intonation has shown that: (i) non-final content words bear rising pitch accents (Moore 1965, Dyrud 2001, Nair 1999); (ii) focused constituents show greater pitch excursion and longer duration and that post-focal material undergoes pitch range reduction (Moore 1965, Harnsberger 1994, Harnsberger and Judge 1996); and (iii) focused constituents may be followed by a phrase break (Moore 1965). By means of a controlled experiment, we investigated the effect of focus in relation to word order variation using 1200 utterances produced by 20 speakers. Fundamental frequency (F0) and duration of constituents were measured in Subject-Object-Verb (SOV) and Object-Subject-Verb (OSV) sentences in different information structural conditions (wide focus, subject focus and object focus). The analyses indicate that (i) regardless of word order and focus, the constituents are in a strict downstep relationship; (ii) focus is mainly characterized by post-focal pitch range reduction rather than pitch raising of the element in focus; (iii) given expressions that occur pre-focally appear to undergo no reduction; (iv) pitch excursion and duration of the constituents is higher in OSV compared to SOV sentences. A phonological analysis suggests that focus affects pitch scaling and that word order influences prosodic phrasing of the constituents.

Discourse context has been argued to be the main factor responsible for increased processing difficulty in non-canonical order sentences: if appropriate discourse context is provided (the argument goes) both canonical and non-canonical order sentences are equally easy to process. This research suggests that this generalization may not be true across languages: the distance between arguments and verbs could affect the ease with which the for- mer can be integrated with the latter, and sufficiently increasing this distance makes processing difficult, regardless of discourse context.

A central question in online human sentence comprehension is: how are linguistic relations established between different parts of a sentence? Previous work has shown that this dependency resolution process can be computationally expensive, but the underlying reasons for this are still unclear. We argue that dependency resolution is mediated by cue-based retrieval, constrained by independently motivated working memory principles defined in a cognitive architecture (ACT-R). To demonstrate this, we investigate an unusual instance of dependency resolution, the processing of negative and positive polarity items, and confirm a surprising prediction of the cue-based retrieval model: partial cue-matches—which constitute a kind of similarity-based interference—can give rise to the intrusion of ungrammatical retrieval candidates, leading to both processing slow-downs and even errors of judgment that take the form of illusions of grammaticality in patently ungrammatical structures. A notable achievement is that good quantitative fits are achieved without adjusting the key model parameters.

Seven experiments using self-paced reading and eyetracking suggest that omitting the middle verb in a double centre embedding leads to easier processing in English but leads to greater difficulty in German. One commonly accepted explanation for the English pattern—based on data from offline acceptability ratings and due to Gibson and Thomas (1999)—is that working-memory overload leads the comprehender to forget the prediction of the upcoming verb phrase (VP), which reduces working-memory load. We show that this VP-forgetting hypothesis does an excellent job of explaining the English data, but cannot account for the German results. We argue that the English and German results can be explained by the parser's adaptation to the grammatical properties of the languages; in contrast to English, German subordinate clauses always have the verb in clause-final position, and this property of German may lead the German parser to maintain predictions of upcoming VPs more robustly compared to English. The evidence thus argues against language-independent forgetting effects in online sentence processing; working-memory constraints can be conditioned by countervailing influences deriving from grammatical properties of the language under study.

In Hindi certain word order possibilities that are grammatical in non-negative sentences become ungrammatical in the presence of sentential negation. In movement-based accounts of such negation-induced word order constraints, the restricted word order has been argued to provide evidence that negative polarity items (NPIs) in Hindi are licensed at LF and S-structure while in English NPI licensing occurs at S-structure. I argue for a non-movement-based, uniformly monostratal (S-structure) account for the word order facts in Hindi, cast in the multimodal categorial grammar framework. The NPI licensing issue is dealt with independently following Dowty’s monotonicity marking analysis.

Three experiments (self-paced reading, eyetracking and an ERP study) show that in relative clauses, increasing the distance be tween the relativized noun and the relative-clause verb makes it more difficult to process the relative-clause verb (the so-called locality effect). This result is consistent with the predictions of several theories (Gibson 2000, Lewis and Vasishth 2005), and contradicts the recent claim (Levy 2008) that in relative-clause structures increasing argument-verb distance makes processing easier at the verb. Levy's expectation-based account predicts that the expectation for a verb becomes sharper as dis- tance is increased and therefore processing becomes easier at the verb. We argue that, in addition to expectation effects (which are seen in the eyetracking study in first-pass regression probability), processing load also increases with increasing distance. This contradicts Levy's claim that heightened expectation leads to lower processing cost. Dependency- resolution cost and expectation-based facilitation are jointly responsible for determining processing cost.

Although proximity between arguments and verbs (locality) is a relatively robust determinant of sentence-processing difficulty (Hawkins 1998, 2001, Gibson 2000), increasing argument-verb distance can also facilitate processing (Konieczny 2000). We present two self-paced reading (SPR) experiments involving Hindi that provide further evidence of antilocality, and a third SPR experiment which suggests that similarity-based interference can attenuate this distance-based facilitation. A unified explanation of interference, locality, and antilocality effects is proposed via an independently motivated theory of activation decay and retrieval interference (Anderson et al. 2004).

Two Hindi eyetracking studies show that clefting a noun results in greater processing difficulty initially, due to the extra processing steps involved in encoding a clefted noun (e.g., for computing the exhaustiveness interpretation). However, this extra difficulty in encoding a clefted noun results in a processing advantage when the clefted noun needs to be retrieved later on in the sentence - the clefted noun is retrieved faster in subsequent processing compared to its non-clefted counterpart. This effect is short-lived, however; it does not last beyond the current sentence. We also show that given-new ordering yields a processing advantage over new-given order, but this is only seen after the whole sentence is processed, i.e., it is a late effect that occurs after syntactic processing is completed. Finally, following up on work on German by Hoernig et al. (2005), we present evidence that non-canonical order can be processed more easily than canonical order given appropriate context.

What theories best characterize the parsing processes triggered upon encountering ambiguity, and what effects do these processes have on eye movement patterns? An eye-tracking study involving adjunct attachment ambiguities in Spanish showed that although conventional dependent measures favored the unrestricted race model, when we additionally took eye-movement patterns into account, the evidence was consistent only with the good-enough theory of parsing.A scanpath analysis further showed that rereading occurred more often in high working-memory capacity participants, which verifies a surprising prediction of the good-enough parsing account: high-capacity participants tend to commit to a parse more often than low-capacity participants, leading to more errors and a greater need to reanalyze. These findings also have broader implications for models of reading processes: Late regressive eye movements triggered in response to disambiguation suggest that the coupling of the eye and parser may not be as tight as assumed in current computational models of reading.

Which repair strategy does the language system deploy when it gets garden-pathed and what can regressive eye movements in reading tell us about reanalysis strategies? Several influential eye-tracking studies on syntactic reanalysis (Frazier & Rayner 1982, Meseguer et al 2002, Mitchell et al 2008) have examined scanpaths-sequences of eye fixations-to answer this question. However, in the absence of a suitable method for analyzing scanpaths, these studies relied on simplified dependent measures that are arguably ambiguous and hard to interpret. We address the theoretical question of repair strategy by developing a new method that quantifies scanpath similarity. Our method reveals several distinct fixation strategies associated with reanalysis that went undetected in a previously published data set (Meseguer et al 2002). One prevalent pattern suggests re-parsing of the sentence, a strategy that has been proposed in the literature (Frazier & Rayner 1982); however, readers differed tremendously in how they orchestrated the various fixation strategies. Our results raise the possibility that the human parsing system non-deterministically adopts different strategies when confronted with the need to reanalyze.