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Breaking down complexity
(2015)
The unbounded expressive capacity of human language cannot boil down to an infinite list of sentences stored in a finite brain. Our linguistic knowledge is rather grounded around a rule-based universal syntactic computation—called Merge—which takes categorized units in input (e.g. this and ship), and generates structures by binding words recursively into more complex hierarchies of any length (e.g. this ship; this ship sinks…). Here we present data from different fMRI datasets probing the cortical implementation of this fundamental process. We first pushed complexity down to a three-word level, to explore how Merge creates minimally hierarchical phrases and sentences. We then moved to the most fundamental two-word level, to directly assess the universal invariant nature of Merge, when no additive mechanisms are involved. Our most general finding is that Merge as the basic syntactic operation is primarily performed by confined area, namely BA 44 in the IFG. Activity reduces to its most ventral-anterior portion at the most fundamental level, following fine-grained sub-anatomical parcellation proposed for the region. The deep frontal operculum/anterior-dorsal insula (FOP/adINS), a phylogenetically older and less specialized region, rather appears to support word-accumulation processing in which the categorical information of the word is first accessed based on its lexical status, and then maintained on hold before further processing takes place. The present data confirm the general notion of BA 44 being activated as a function of complex structural hierarchy, but they go beyond this view by proposing that structural sensitivity in BA 44 is already appreciated at the lowest levels of complexity during which minimal phrase-structures are build up, and syntactic Merge is assessed. Further, they call for a redefinition of BA 44 from multimodal area to a macro-region with internal localizable functional profiles
Cleft exhaustivity
(2020)
In this dissertation a series of experimental studies are presented which demonstrate that the exhaustive inference of focus-background it-clefts in English and their cross-linguistic counterparts in Akan, French, and German is neither robust nor systematic. The inter-speaker and cross-linguistic variability is accounted for with a discourse-pragmatic approach to cleft exhaustivity, in which -- following Pollard & Yasavul 2016 -- the exhaustive inference is derived from an interaction with another layer of meaning, namely, the existence presupposition encoded in clefts.
The present dissertation investigates changes in lingual coarticulation across childhood in German-speaking children from three to nine years of age and adults. Coarticulation refers to the mismatch between the abstract phonological units and their seemingly commingled realization in continuous speech. Being a process at the intersection of phonology and phonetics, addressing its changes across childhood allows for insights in speech motor as well as phonological developments. Because specific predictions for changes in coarticulation across childhood can be derived from existing speech production models, investigating children’s coarticulatory patterns can help us model human speech production.
While coarticulatory changes may shed light on some of the central questions of speech production development, previous studies on the topic were sparse and presented a puzzling picture of conflicting findings. One of the reasons for this lack is the difficulty in articulatory data acquisition in a young population. Within the research program this dissertation is embedded in, we accepted this challenge and successfully set up the hitherto largest corpus of articulatory data from children using ultrasound tongue imaging. In contrast to earlier studies, a high number of participants in tight age cohorts across a wide age range and a thoroughly controlled set of pseudowords allowed for statistically powerful investigations of a process known as variable and complicated to track.
The specific focus of my studies is on lingual vocalic coarticulation as measured in the horizontal position of the highest point of the tongue dorsum. Based on three studies on a) anticipatory coarticulation towards the left, b) carryover coarticulation towards the right side of the utterance, and c) anticipatory coarticulatory extent in repeated versus read aloud speech, I deduct the following main theses:
1. Maturing speech motor control is responsible for some developmental changes in coarticulation.
2. Coarticulation can be modeled as the coproduction of articulatory gestures.
3. The developmental change in coarticulation results from a decrease of vocalic activation width.
Discourse production is crucial for communicative success and is in the core of aphasia assessment and treatment. Coherence differentiates discourse from a series of utterances/sentences; it is internal unity and connectedness, and, as such, perhaps the most inherent property of discourse. It is unclear whether people with aphasia, who experience various language production difficulties, preserve the ability to produce coherent discourse. A more general question of how coherence is established and represented linguistically has been addressed in the literature, yet remains unanswered. This dissertation presents an investigation of discourse production in aphasia and the linguistic mechanisms of establishing coherence.
Previous studies on the acquisition of verb inflection in normally developing children have revealed an astonishing pattern: children use correctly inflected verbs in their own speech but fail to make use of verb inflections when comprehending sentences uttered by others. Thus, a three-year old might well be able to say something like ‘The cat sleeps on the bed’, but fails to understand that the same sentence, when uttered by another person, refers to only one sleeping cat but not more than one. The previous studies that have examined children's comprehension of verb inflections have employed a variant of a picture selection task in which the child was asked to explicitly indicate (via pointing) what semantic meaning she had inferred from the test sentence. Recent research on other linguistic structures, such as pronouns or focus particles, has indicated that earlier comprehension abilities can be found when methods are used that do not require an explicit reaction, like preferential looking tasks. This dissertation aimed to examine whether children are truly not able to understand the connection the the verb form and the meaning of the sentence subject until the age of five years or whether earlier comprehension can be found when a different measure, preferential looking, is used. Additionally, children's processing of subject-verb agreement violations was examined. The three experiments of this thesis that examined children's comprehension of verb inflections revealed the following: German-speaking three- to four-year old children looked more to a picture showing one actor when hearing a sentence with a singular inflected verb but only when their eye gaze was tracked and they did not have to perform a picture selection task. When they were asked to point to the matching picture, they performed at chance-level. This pattern indicates asymmetries in children's language performance even within the receptive modality. The fourth experiment examined sensitivity to subject-verb agreement violations and did not reveal evidence for sensitivity toward agreement violations in three- and four-year old children, but only found that children's looking patterns were influenced by the grammatical violations at the age of five. The results from these experiments are discussed in relation to the existence of a production-comprehension asymmetry in the use of verb inflections and children's underlying grammatical knowledge.
Connective ties in discourse: Three ERP studies on causal, temporal and concessive connective ties and their influence on language processing. Questions In four experiments the influence of lexical connectives such as " darum", therefore, " danach", afterwards, and " trotzdem", nevertheless, on the processing of short two-sentence discourses was examined and compared to the processing of deictical sentential adverbs such as " gestern", yesterday, and " lieber", rather. These latter words do not have the property of signaling a certain discourse relation between two sentences, as connective ties do. Three questions were central to the work: * Do the processing contrasts found between connective and non-connective elements extend to connective ties and deictical sentential adverbs (experiments 2 and 3)? * Does the semantic content of the connective ties play the primary role, i.e is the major distinction to be made indeed between connective and non-connective or instead between causal, temporal and concessive? * When precisely is the information provided by connective ties used? There is some evidence that connective ties can have an immediate influence on the integration of subsequent elements, but the end of the second sentences appears to play an important role as well: experiments 2, 3, and 4. Conclusions First of all, the theoretical distinction between connective and non-connective elements does indeed have " cognitive reality" . This has already been shown in previous studies. The present studies do however show, that there is also a difference between one-place discourse elements (deictical sentential adverbs) and two-place discourse elements, namely connective ties, since all experiments examining this contrast found evidence for qualitatively and quantitatively different processing (experiments 1, 2, and 3). Secondly, the semantic type of the connective ties also plays a role. This was not shown for the LAN, found for all connective ties when compared to non-connective elements, and consequently interpreted as a more abstract reflection of the integration of connective ties. There was also no difference between causal and temporal connective ties before the end of the discourses in experiment 3. However, the N400 found for incoherent discourses in experiment 2, larger for connective incoherent than non-connective incoherent discourses, as well as the P3b found for concessive connective ties in the comparison between causal and concessive connective ties gave reason to assume that the semantic content of connective ties is made use of in incremental processing, and that the relation signaled by the connective tie is the one that readers attempt to construct. Concerning when the information provided by connective ties is used, it appears as if connectivity is generally and obligatorily taken at face value. As long as the meaning of a connective tie did not conflict with a preferred canonical discourse relation, there were no differences found for varying connective discourses (experiment 3). However, the fact that concessive connective ties announce the need for a more complex text representation was recognized and made use of immediately (experiment 4). Additionally, a violation of the discourse relation resulted in more difficult semantic integration if a connective tie was present (experiment 2). It is therefore concluded here that connective ties influence processing immediately. This claim has to be modified somewhat, since the sentence-final elements suggested that connective ties trigger different integration processes than non-connective elements. It seems as if the answer to the question of when connective ties are processed is neither exclusively immediately nor exclusively afterwards, but that both viewpoints are correct. It is suggested here that before the end of a discourse economy plays a central role in that a canonical relation is assumed unless there is evidence to the contrary. A connective tie could have the function of reducing the dimensions evaluated in a discourse to the one signaled by the connective tie. At the end of the discourse the representation is evaluated and verified, and an integrated situation model constructed. Here, the complexity of the different discourse relations that connective ties can signal, is expressed.
My thesis focused on the predictions of the activation-based model of Lewis and Vasishth (2005) to investigate the evidence for the use of the memory system in the formation of non-local dependencies in sentence comprehension.
The activation-based model, which follows the Adaptive Control of Thought-Rational framework (ACT-R; Anderson et al., 2004), has been used to explain locality effects and similarity-based interference by assuming that dependencies are resolved by a cue-based retrieval mechanism, and that the retrieval mechanism is affected by decay and interference.
Both locality effects and (inhibitory) similarity-based interference cause increased difficulty (e.g., longer reading times) at the site of the dependency completion where a retrieval is assumed: (I) Locality effects are attributed to the increased difficulty in the retrieval of a dependent when the distance from its retrieval site is increased. (II) Similarity-based interference is attributed to the retrieval being affected by the presence of items which have similar features as the dependent that needs to be retrieved.
In this dissertation, I investigated some findings problematic to the activation-based model, namely, facilitation where locality effects are expected (e.g., Levy, 2008), and the lack of similarity-based interference from the number feature in grammatical sentences (e.g., Wagers et al., 2009). In addition, I used individual differences in working memory capacity and reading fluency as a way to validate the theories investigated (Underwood, 1975), and computational modeling to achieve a more precise account of the phenomena.
Regarding locality effects, by using self-paced reading and eye-tracking-while reading methods with Spanish and German data, this dissertation yielded two main findings: (I) Locality effects seem to be modulated by working memory capacity, with high-capacity participants showing expectation-driven facilitation. (II) Once expectations and other potential confounds are controlled using baselines, with increased distance, high-capacity readers can show a slow-down (i.e., locality effects) and low-capacity readers can show a speedup. While the locality effects are compatible with the activation-based model, simulations show that the speedup of low-capacity readers can only be accounted for by changing some of the assumptions of the activation-based model.
Regarding similarity-based interference, two relatively high-powered self-paced reading experiments in German using grammatical sentences yielded a slowdown at the verb as predicted by the activation-based model. This provides evidence in favor of dependency creation via cue-based retrieval, and in contrast with the view that cue-based retrieval is a reanalysis mechanism (Wagers et al., 2009).
Finally, the same experimental results that showed inhibitory interference from the number feature are used for a finer grain evaluation of the retrieval process. Besides Lewis and Vasishth’s (2005) activation-based model, also McElree’s (2000) direct-access model can account for inhibitory interference. These two models assume a cue-based retrieval mechanism to build dependencies, but they are based on different assumptions. I present a computational evaluation of the predictions of these two theories of retrieval. The models were compared by implementing them in a Bayesian hierarchical framework. The evaluation of the models reveals that some aspects of the data fit better under the direct access model than under the activation-based model. However, a simple extension of the activation-based model provides a comparable fit to the direct access model. This serves as a proof of concept showing potential ways to improve the original activation-based model.
In conclusion, this thesis adds to the body of evidence that argues for the use of the general memory system in dependency resolution, and in particular for a cue-based retrieval mechanism. However, it also shows that some of the default assumptions inherited from ACT-R in the activation-based model need to be revised.