Shravan Vasishth

Professor, Dept. of Linguistics, University of Potsdam, 14476 Potsdam
Speaker, Language Cluster, Cognitive Science
Phone: +49-(0)331-977-2950 | Fax: - 2087 | vasishth at uni-potsdam.de




research

My group develops models of human sentence comprehension, in both impaired and unimpaired populations. Statistics is the basis for everything that we do, so we are also interested in statistical theory and practice. My curriculum vitae.

You can watch a somewhat dated film (in German) about about our work here. Two other films describe ongoing research in our department: see here (English) ; and here (German). The Vasishth Lab Blog is here.
Current PhD students: Lena Benz, Felix Engelmann, Sabrina Gerth, Lena Jäger, Carla Kessler, Anna Laurinavichyute, Pavel Logačev, Paul Metzner, Bruno Nicenboim, Dario Paape, Farnoosh Safavi.
Alumni: Sven Brüssow; Katja Suckow; Kate McCurdy; Dr. Titus von der Malsburg, Dr. Umesh Patil.
Postdoctoral researcher: Samar Husain.
Current active collaborations: Frank Burchert, Brian Dillon, Stefan Frank, Sandra Hanne, Philip Hofmeister, Rick Lewis, Charles Lin, Frank Rösler.

teaching

winter 2014-2015

tutorials, lecture notes, code, etc.

research articles

published, accepted, in press
[1]
Samar Husain, Shravan Vasishth, and Narayanan Srinivasan. Strong Expectations Cancel Locality Effects: Evidence from Hindi. PLoS ONE, 9(7):1-14, 2014. [ pdf ]
Expectation-driven facilitation (Hale, 2001; Levy, 2008) and locality-driven retrieval difficulty (Gibson, 1998, 2000; Lewis & Vasishth, 2005) are widely recognized to be two critical factors in incremental sentence processing; there is accumulating evidence that both can influence processing difficulty. However, it is unclear whether and how expectations and memory interact. We first confirm a key prediction of the expectation account: a Hindi self-paced reading study shows that when an expectation for an upcoming part of speech is dashed, building a rarer structure consumes more processing time than building a less rare structure. This is a strong validation of the expectation-based account. In a second study, we show that when expectation is strong, i.e., when a particular verb is predicted, strong facilitation effects are seen when the appearance of the verb is delayed; however, when expectation is weak, i.e., when only the part of speech “verb” is predicted but a particular verb is not predicted, the facilitation disappears and a tendency towards a locality effect is seen. The interaction seen between expectation strength and distance shows that strong expectations cancel locality effects, and that weak expectations allow locality effects to emerge.

[2]
Paul Metzner, Titus von der Malsburg, Shravan Vasishth, and Frank Rösler. Brain responses to world-knowledge violations: A comparison of stimulus- and fixation-triggered event-related potentials and neural oscillations. Journal of Cognitive Neuroscience, 2014. In Press. [ pdf ]
Recent research has shown that brain potentials time-locked to fixations in natural reading can be similar to brain potentials recorded during rapid serial visual presentation (RSVP). We attempted two replications of Hagoort, Hald, Bastiaansen, and Petersson (2004) to determine whether this correspondence also holds for oscillatory brain responses. Hagoort et al. reported an N400 effect and synchronization in the theta and gamma range following world-knowledge violations. Our first experiment (n=32) used RSVP and replicated both the N400 effect in the event-related potentials (ERP) and the power increase in the theta range in the time-frequency domain. In the second experiment (n=49), participants read the same materials freely while their eye movements and their EEG were monitored. First fixation durations, gaze durations, and regression rates were increased, and the ERP showed an N400 effect. An analysis of time-frequency representations showed synchronization in the delta range (1–3 Hz) and desynchronization in the upper alpha range (11–13 Hz) but no theta or gamma effects. The results suggest that oscillatory EEG changes elicited by world-knowledge violations are different in natural reading and RSVP. This may reflect differences in how representations are constructed and retrieved from memory in the two presentation modes.

[3]
Umesh Patil, Sandra Hanne, Frank Burchert, Ria De Bleser, and Shravan Vasishth. A computational evaluation of sentence comprehension deficits in aphasia. 2014. In Press. [ pdf ]
[4]
Titus von der Malsburg, Reinhold Kliegl, and Shravan Vasishth. Determinants of Scanpath Regularity in Reading. Cognitive Science, 2014. In press.
Scanpaths-sequences of fixations of the eyes-have played an important role in the classic research on reading behavior. Nevertheless, they have largely been neglected in later research; this is perhaps due to the lack of suitable tools for analyzing such data. Recently, von der Malsburg and Vasishth proposed a new measure for quantifying the differences between the scanpaths recorded in an experiment. Here, we used the proposed method to conduct the first comprehensive investigation of the determinants of scanpath irregularity in general reading. We derived predictions for scanpath irregularity from the literature on oculo-motor control and sentences processing and tested them using a large corpus of eye movements (N=230). All predictions were confirmed: sentences with short words and syntactically more difficult sentences elicit more irregular scanpaths. Also, older readers produce more irregular scanpaths than younger readers. A result that was not anticipated was that the effects of syntactic difficulty are weaker in older readers. We explain this phenomenon in terms of a shift toward riskier, perhaps less syntax-driven, processing strategies as readers age. Apart from demonstrating that scanpaths provide novel insights into the eye-mind connection, these results establish the scanpath method developed by von der Malsburg and Vasishth as a productive tool for reading research.

[5]
Shravan Vasishth, Zhong Chen, Qiang Li, and Gueilan Guo. Processing Chinese Relative Clauses: Evidence for the Subject-Relative Advantage. PLoS ONE, 8(10):1-14, 10 2013. [ pdf ]
A general fact about language is that subject relative clauses are easier to process than object relative clauses. Recently, several self-paced reading studies have presented surprising evidence that object relatives in Chinese are easier to process than subject relatives. We carried out three self-paced reading experiments that attempted to replicate these results. Two of our three studies found a subject-relative preference, and the third study found an object-relative advantage. Using a random effects Bayesian meta-analysis of fifteen studies (including our own), we show that the overall current evidence for the subject-relative advantage is quite strong (approximate posterior probability of a subject-relative advantage given the data: 78–80%). We argue that retrieval/integration based accounts would have difficulty explaining all three experimental results. These findings are important because they narrow the theoretical space by limiting the role of an important class of explanation—retrieval/integration cost—at least for relative clause processing in Chinese.

[6]
Felix Engelmann, Shravan Vasishth, Ralf Engbert, and Reinhold Kliegl. A framework for modeling the interaction of syntactic processing and eye movement control. Topics in Cognitive Science, 5(3):452-474, 2013. [ pdf ]
We explore the interaction between oculomotor control and language comprehension on the sentence level using two well-tested computational ac- counts of parsing difficulty. Previous work (Boston, Hale, Vasishth, & Kliegl, 2011) has shown that surprisal (Hale, 2001; Levy, 2008) and cue-based mem- ory retrieval (Lewis & Vasishth, 2005) are significant and complementary predictors of reading time in an eyetracking corpus. It remains an open question how the sentence processor interacts with oculomotor control. Using a simple linking hypothesis proposed in Reichle, Warren, and McConnell (2009), we integrated both measures with the eye movement model EMMA (Salvucci, 2001) inside the cognitive architecture ACT-R (Anderson et al., 2004). We built a reading model that could initiate short “Time Out regressions” (Mitchell, Shen, Green, & Hodgson, 2008) that compensate for slow postlexical processing. This simple interaction enabled the model to predict the re-reading of words based on parsing difficulty. The model was evaluated in different configurations on the prediction of frequency effects on the Potsdam Sentence Corpus. The extension of EMMA with postlexical processing improved its predictions and reproduced re-reading rates and durations with a reasonable fit to the data. This demonstration, based on simple and independently motivated assumptions, serves as a foundational step toward a precise investigation of the interaction between high-level language processing and eye movement control.

[7]
Niloofar Keshtiari and Shravan Vasishth. Reactivation of antecedents by overt vs null pronouns: Evidence from Persian. 1(2):243-266, 2013. [ pdf ]
In Persian, a construction exists in which a gap can optionally be replaced by an overt pronoun. A self-paced reading study (110 participants) suggests that the overt pronoun results in deeper encoding (higher activation) of the antecedent noun, presumably because of richer retrieval cue specifications during antecedent retrieval at the pronoun; this higher activation has the consequence that the antecedent is easier to retrieve at a subsequent stage. This provides new evidence for reactivation effects of the type assumed in the cue-based retrieval model of parsing (Lewis and Vasishth, 2005), and shows that dependency resolution is not simply a matter of connecting two co-dependents; the retrieval cue specification has a differential impact on processing.

[8]
Kate McCurdy, Gerrit Kentner, and Shravan Vasishth. Implicit prosody and contextual bias in silent reading. Journal of Eye Movement Research, 6(2):1-17, 2013. [ pdf ]
Eye-movement research on implicit prosody has found effects of lexical stress on syntactic ambiguity resolution, suggesting that metrical well-formedness constraints interact with syntactic category assignment. Building on these findings, the present eyetracking study investigates whether contextual bias can modulate the effects of metrical structure on syntactic ambiguity resolution in silent reading. Contextual bias and potential stress-clash in the ambiguous region were crossed in a 2 × 2 design. Participants read biased context sentences followed by temporarily ambiguous test sentences. In the three-word ambiguous region, main effects of lexical stress were dominant, while early effects of context were absent. Potential stress clash yielded a significant increase in first-pass regressions and re-reading probability across the three words. In the disambiguating region, the disambiguating word itself showed increased processing difficulty (lower skipping and increased re-reading probability) when the disambiguation engendered a stress clash configuration, while the word immediately following showed main effects of context in those same measures. Taken together, effects of lexical stress upon eye movements were swift and pervasive across first-pass and second-pass measures, while effects of context were relatively delayed. These results indicate a strong role for implicit meter in guiding parsing, one that appears insensitive to higher-level constraints. Our findings are problematic for two classes of models, the two-stage garden-path model and the constraint-based competition-integration model, but can be explained by a variation on the two-stage model, the unrestricted race model.

[9]
Titus von der Malsburg and Shravan Vasishth. Scanpaths reveal syntactic underspecification and reanalysis strategies. Language and Cognitive Processes, 28, 2013. [ DOI | pdf ]
What theories best characterize the parsing processes triggered upon encountering ambiguity, and what effects do these processes have on eye movement patterns in reading? The present eye-tracking study, which investigated processing of attachment ambiguities of an adjunct in Spanish, suggests that readers sometimes underspecify attachment to save memory resources, consistent with the good-enough account of parsing. Our results confirm a surprising prediction of the good-enough account: high-capacity readers commit to an attachment decision more often than low-capacity participants, leading to more errors and a greater need to reanalyze in garden-path sentences. These results emerged only when we separated functionally different types of regressive eye movements using a scanpath analysis; conventional eye-tracking measures alone would have led to different conclusions. The scanpath analysis also showed that rereading was the dominant strategy for recovering from garden-pathing. Our results may also have broader implications for models of reading processes: reanalysis effects in eye movements occurred late, which suggests that the coupling of oculo-motor control and the parser may not always be as tight as assumed in current computational models of eye movements control in reading.

[10]
Frank Burchert, Sandra Hanne, and Shravan Vasishth. Sentence comprehension disorders in aphasia: The concept of chance performance revisited. Aphasiology, 2012. [ pdf ]
Background: In behavioural tests of sentence comprehension in aphasia, correct and incorrect responses are often randomly distributed. Such a pattern of chance performance is a typical trait of Broca’s aphasia, but can be found in other aphasic syndromes as well. Many researchers have argued that chance behaviour is the result of a guessing strategy, which is adopted in the face of a syntactic breakdown in sentence processing. Aims: Capitalising on new evidence from recent studies investigating online sentence comprehension in aphasia using the visual world paradigm, the aim of this paper is to review the concept of chance performance as a reflection of a syntactic impairment in sentence processing and to re-examine the conventional interpretation of chance performance as a guessing behaviour. Main Contribution: Based on a review of recent evidence from visual world paradigm studies, we argue that the assumption of chance performance equalling guessing is not necessarily compatible with actual real-time parsing procedures in people with aphasia. We propose a reinterpretation of the concept of chance performance by assuming that there are two distinct processing mechanisms underlying sentence comprehension in aphasia. Correct responses are always the result of normal-like parsing mechanisms, even in those cases where the overall performance pattern is at chance. Incorrect responses, on the other hand, are the result of intermittent deficiencies of the parser. Hence the random guessing behaviour that persons with aphasia often display does not necessarily reflect a syntactic breakdown in sentence comprehension and a random selection between alternatives. Instead it should be regarded as a result of temporal deficient parsing procedures in otherwise normal-like comprehension routines. Conclusion: Our conclusion is that the consideration of behavioural offline data alone may not be sufficient to interpret a performance in language tests and subsequently draw theoretical conclusions about language impairments. Rather it is important to call on additional data from online studies that look at language processing in real time in order to gain a comprehensive picture about syntactic comprehension abilities of people with aphasia and possible underlying deficits.

[11]
Shravan Vasishth, Rukshin Shaher, and Narayanan Srinivasan. The role of clefting, word order and given-new ordering in sentence comprehension: Evidence from Hindi. Journal of South Asian Linguistics, 2012. [ pdf ]
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.

[12]
Shravan Vasishth, Titus von der Malsburg, and Felix Engelmann. What eye movements can tell us about sentence comprehension. Wiley Interdisciplinary Reviews: Cognitive Science, pages 125-134, 2012. [ pdf ]
Eye movement data have proven to be very useful for investigating human sentence processing.Eyetracking research has addressed a wide range of questions, such as recovery mechanisms following garden-pathing, the timing of processes driving comprehension, the role of anticipation and expectation in parsing, the role of semantic, pragmatic, and prosodic information, and so on. However, there are some limitations regarding the inferences that can be made on the basis of eye movements. One relates to the nontrivial interaction between parsing and the eye movement control system which complicates the interpretation of eye movement data. Detailed computational models that integrate parsing with eye movement control theories have the potential to unpack the complexity of eyemovement data and can therefore aid in the interpretation of eye movements. Another limitation is the difficulty of capturing spatiotemporal patterns in eye movements using the traditional word-based eyetracking measures. Recent research has demonstrated the relevance of these patterns and has shown how they can be analyzed. In this review, we focus on reading, and present examples demonstrating how eye movement data reveal what events unfold when the parser runs into difficulty, and how the parsing system interacts with eye movement control

[13]
Brian Bartek, Richard L. Lewis, Shravan Vasishth, and Mason Smith. In Search of On-line Locality Effects in Sentence Comprehension. Journal of Experimental Psychology: Learning, Memory and Cognition, 37(5):1178-1198, 2011. [ pdf ]
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.

[14]
Marisa F. Boston, John T. Hale, Shravan Vasishth, and Reinhold Kliegl. Parallel processing and sentence comprehension difficulty. Language and Cognitive Processes, 26(3):301-349, 2011. [ pdf ]
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.

[15]
H. Drenhaus, M. Zimmermann, and S. Vasishth. Exhaustiveness effects in clefts are not truth-functional. Journal of Neurolinguistics, 24:320-337, 2011. [ pdf ]
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.

[16]
Sandra Hanne, Irina Sekerina, Shravan Vasishth, Frank Burchert, and Ria De Bleser. Chance in agrammatic sentence comprehension: What does it really mean? Evidence from Eye Movements of German Agrammatic Aphasics. Aphasiology, 25:221-244, 2011. [ pdf ]
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.

[17]
Shravan Vasishth and Heiner Drenhaus. Locality in German. Dialogue and Discourse, 1:59-82, 2011. [ pdf ]
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.

[18]
Titus von der Malsburg and Shravan Vasishth. What is the scanpath signature of syntactic reanalysis? Journal of Memory and Language, 65:109-127, 2011. [ pdf ]
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.

[19]
S. Vasishth, K. Suckow, R. L. Lewis, and S. Kern. Short-term forgetting in sentence comprehension: Crosslinguistic evidence from head-final structures. Language and Cognitive Processes, 25(4):533-567, 2010. [ pdf ]
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.

[20]
Sigrid Beck and Shravan Vasishth. Multiple Focus. Journal of Semantics, 2009. [ .pdf ]
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, 1992) predict such a pattern of association with focus to be impossible, while others (such as Wold, 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.

[21]
Umesh Patil, Gerrit Kentner, Anja Gollrad, Frank Kügler, Caroline Féry, and Shravan Vasishth. Focus, word order and intonation in Hindi. Journal of South Asian Linguistics, 1(1):55-72, October 2008. [ .pdf ]
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.

[22]
Marisa Ferrara Boston, John T. Hale, Umesh Patil, Reinhold Kliegl, and Shravan Vasishth. Parsing costs as predictors of reading difficulty: An evaluation using the Potsdam Sentence Corpus. Journal of Eye Movement Research, 2(1):1-12, 2008. [ pdf ]
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.

[23]
Shravan Vasishth, Sven Bruessow, Richard L. Lewis, and Heiner Drenhaus. Processing Polarity: How the ungrammatical intrudes on the grammatical. Cognitive Science, 32(4), 2008. [ pdf ]
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.

[24]
Richard L. Lewis, Shravan Vasishth, and Julie Van Dyke. Computational principles of working memory in sentence comprehension. Trends in Cognitive Sciences, 10(10):447-454, 2006. [ pdf ]
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.

[25]
Shravan Vasishth and Richard L. Lewis. Argument-head distance and processing complexity: Explaining both locality and antilocality effects. Language, 82(4):767-794, 2006. [ pdf ]
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).

[26]
Richard L. Lewis and Shravan Vasishth. An activation-based model of sentence processing as skilled memory retrieval. Cognitive Science, 29:1-45, May 2005. [ pdf ]
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 in ACT-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.

[27]
S. Vasishth. Discourse context and word order preferences in Hindi. Yearbook of South Asian Languages, pages 113-127, 2004. [ .pdf ]
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 former can be integrated with the latter, and sufficiently increasing this distance makes processing difficult, regardless of discourse context.

[28]
Shravan Vasishth. Word order, negation, and negative polarity in Hindi. Research on Language and Computation, 3, 2002. [ .pdf ]
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.

unpublished
[1]
Stefan L. Frank, Thijs Trompenaars, and Shravan Vasishth. Cross-linguistic differences in processing double-embedded relative clauses: Working-memory constraints or language statistics? under review, 2014.
[2]
Sandra Hanne, Frank Burchert, Ria De Bleser, and Shravan Vasishth. Sentence comprehension in aphasia: Eye-tracking reveals delayed morphological cue integration and late parsing commitments. under review, 2014.
[3]
Philip Hofmeister and Shravan Vasishth. Distinctiveness and encoding effects in online sentence comprehension. under review, 2014. [ pdf ]
[4]
Lena Jäger, Zhong Chen, Qiang Li, Charles Lin, and Shravan Vasishth. The subject-relative advantage in Chinese relatives: Evidence for expectation-based processing. MS (submitted), 2014.
[5]
Pavel Logačev and Shravan Vasishth. A Multiple-Channel Model of Task-Dependent Ambiguity Resolution in Sentence Comprehension. Submitted, 2014. [ pdf ]
[6]
Pavel Logačev and Shravan Vasishth. What is underspecification? Submitted, 2014.
[7]
Bruno Nicenboim, Shravan Vasishth, Reinhold Kliegl, Carolina Gattei, and Mariano Sigman. Individual differences in long distance dependency resolution. under review, 2014. [ pdf ]
[8]
Tanner Sorensen and Shravan Vasishth. Fitting linear mixed models using JAGS and Stan: A tutorial. Submitted, 2014. [ pdf ]
[9]
Umesh Patil, Shravan Vasishth, and Richard L. Lewis. Retrieval interference in syntactic processing: The case of reflexive binding in English. unpublished MS, 2012.