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Based on electrophysiological and functional imaging data, Friederici (1995; 1999; 2002) proposed a neurocognitive model of auditory sentence processing. According to the model, sentence processing passes through three distinct phases (after the input was phonologically analyzed) (Figure 3.1).

Phase 1 Phase 2 Phase 3

initial structure building on the basis of word category information

lexical integration reanalysis or repair

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early left anterior negativity (150-200 ms)

negativity (300-500 ms)

late positivity (~ 600 ms)

ELAN left-anterior: LAN

centro-parietal: N400

P600

Figure 3.1 A neurocognitive model of sentence comprehension, after Friederici (1999).

Phase 1. During the first phase, the parser evaluates word category information

to build an initial syntactic structure. This assumption is based on the ELAN effect, which is elicited by local phrase structure violations induced by word category errors.

Phase 2. In the second phase, lexical integration takes place. On the one hand,

lexical-semantic information is processed. This is reflected in the N400 component, which is enhanced if semantic integration is difficult. On the other

hand, morpho-syntactic information is processed. This is reflected in the LAN component, which is enhanced if, for example, agreement errors are encoun- tered.

Phase 3. During the last phase, the semantic and structural representations estab-

lished in Phase 2 are mapped onto each other. This may require syntactic re- analysis in the case of dispreferred sentence structures, or repair in the case of ungrammatical sentences. Such processes are reflected in the P600 compo- nent.

This sentence processing model was extended in the Argument Dependency Model (ADM) (Bornkessel, 2002; Schlesewsky & Bornkessel, 2004; Bornkessel & Schlesewsky, to appear). The focal point of the ADM is the establishment of hierarchical dependencies between the arguments of a sentence. This is achieved during Phase 2 of Friederici's model. Essentially, the ADM assumes a subdivi- sion of Phase 2 into two separate processing pathways for the establishment of hierarchical relations between arguments (Figure 3.2). One pathway establishes dependencies on the basis of morphological information, while the other estab- lishes dependencies on the basis of positional information. Which of the two pathways determines sentence interpretation depends on the morphological case information on the arguments. The abstract representation that is derived via the respective pathway is language specific. In German, the parser applies the fol- lowing procedure. If no unambiguous case information is available, syntactic dependencies are built on the basis of word order information. If the arguments are unambiguously case marked, thematic dependencies are built on the basis of case information, overriding word order information.

The necessary morphological analysis of the constituents is supposed to take place at the end of Phase 1 of the ADM. The results of the two pathways are in- tegrated at the end of Phase 2. Lexical semantic information or general knowl- edge cannot influence the syntactic and thematic processing in Phase 2. Finally, a general mapping of all information types takes place in Phase 3. The two path- ways of Phase 2 will be further described in the following.

Figure 3.2 Argument Dependency Model (ADM) (Bornkessel & Schlesewsky, to appear).

Morphological Pathway

On the Morphological Pathway, the morphological case information on the ar- guments is evaluated. In German, morphological case information is used to es- tablish the thematic relationship between the arguments of a sentence. Thus, a thematic hierarchy is built up, which determines the relative thematic ranking of two or more arguments. This is thought of in the sense of generalized thematic roles (Kibrik, 1997; Primus, 1999; Van Valin & La Polla, 1997). For instance, one argument receives the generalized role Proto-Agent and is thus ranked higher than the argument receiving the generalized role Proto-Patient. However, no spe- cific role assignment (like GOAL or EXPERIENCER) takes place yet.

The basis of the thematic ranking is the morphological case marking of the ar- guments. Thus, an argument unambiguously case marked with nominative will be ranked higher than an argument case marked with accusative or dative. Im- portantly, this is independent of word order. Evidence in favor of the Morpho- logical Pathway stems from ERP experiments involving active and object-ex- periencer verbs (Bornkessel et al., 2002; 2003). With active verbs, the thematic ranking that can be established via case markings works well. However, with dative object-experiencer verbs, the ranking has to be reversed. This reversal or reranking of the thematic hierarchy was reflected in an early positivity on sen-

tence final object-experiencer verbs, which was independent of word order. By contrast, no such positivity was observed in sentences with ambiguous argu- ments.

Positional Pathway

On the Positional Pathway, the sequential ordering of the arguments is evalu- tated. In German, positional information is used to establish the syntactic rela- tionship between the arguments of a sentence. The Positional Pathway only de- termines the outcome of relational argument processing in Phase 2 if the argu- ments of a sentence are case ambiguous. Syntactic dependencies are established on the basis of word order information. Thus, the first ambiguous argument will be assigned the syntactic function 'subject', whereas the second ambiguous argu- ment will be assigned 'object'.

Evidence in favor of the Positional Pathway stems from a number of behavioral studies reporting a strong subject-first preference in the processing of ambiguous arguments (e.g. Schriefers et al., 1995; Bader & Meng, 1999; Schlesewsky et al., 2000). In addition, ERP experiments provided evidence for the exclusive use of the Positional Pathway by ambiguous arguments. As reported above, Bornkessel et al. (2004) investigated the processing of subject- and object-initial sentences. Crucially, the disambiguation towards an object-initial structure was associated with higher processing costs only if the arguments were case ambiguous. This was reflected in an N400 for dative verbs, and in a P600 for accusative verbs. No such word order related effects emerged in the processing of sentences with unambiguously case marked arguments. Hence, only with case ambiguous arguments, word order is used to establish a syntactic representation.

In sum, sentence processing takes place in an incremental manner. Each incom- ing lexical item is integrated into the structure to the highest possible degree. The way the arguments of a sentence are interpreted depends on the degree of mor- phological informativeness. If the arguments are case ambiguous, their sequential ordering leads to a syntactic analysis, the first argument being analyzed as the subject of the sentence. However, if the arguments are unambiguously case marked, word order information is overridden. Morphological case information leads to a thematic interpretation of the arguments, such that they are ranked relatively to each other according to the case hierarchy.

Chapter 4

Sentence Comprehension in Children

Given the immense complexity of linguistic knowledge each native speaker has, and given the astonishing speed with which the complex speech signal is accu- rately processed, the question arises: How do we arrive at such highly specialized and efficient language processing mechanisms? Of particular interest in this thesis is the acquisition of the relationship between morphological case and the- matic role information, as well as the role of word order in German sentence processing. In the following, previous behavioral experiments will be presented that investigated how children use case markings and word order in sentence comprehension. Moreover, selected language acquisition accounts on the acqui- sition and development of sentence processing mechanisms will be introduced.