The previous review of ERP studies on L1 and L2 semantic and syntactic processing indicate that L2 semantic processing patterns are less different from L1 processing patterns than are L2 syntactic processing patterns. Up to date, within SLA research, there is no sufficient answer to why some linguistic phenomena (predominantly
2. ERPs as Response to L1 and L2 Processing
syntactic ones) produce differences between L1 and L2 processing and others (e.g. lexical-semantically related ones) do not.41 One promising approach that may contribute
to the discrepancy between lexical-semantic and syntactic processing and the above mentioned differences between L1 and L2 processing is the dual mechanism approach to language processing suggested by Clahsen & Felser (2006a, b). The authors postulate the “shallow structure hypothesis”. This account attributes to the dissociation between semantic and syntactic processing. Likewise, the shallow structure hypothesis is based on the idea that for successful sentence comprehension the processing system has to follow a lexical-semantic processing route on the one hand and a grammatical-syntactic processing route on the other hand.42 The former is based on strategies that are
retrieved by lexical-semantic processing heuristics. The latter involves mechanisms of full grammatical parsing and structural analysis.
Figure 2.3: Adopted from Clahsen & Felser (2006b, p.119) illustrating the model of L2 processing according to the shallow structure hypothesis. Original citation: “Figure 1. Of the two routes to interpretation available in principle, full parsing is restricted in L2 sentence processing because of inadequacies of the L2 grammar.”
41 Within SLA research there is the long enduring debate whether L1 and L2 acquisition are fundamentally different or not. However, this question will not be focussed in the present thesis.
42 The model accounts for differences between morphological and syntactic L2 processing as the former reveals more native like results than the latter. It additionally puts forward possible explanations of differences between child and adult processing. Since the present thesis does not intend to test the model, these implications will not be focussed any further.
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2. ERPs as Response to L1 and L2 Processing
Clahsen & Felser claim that L2 processing is predominantly shallow. This means that L2 learners process their L2 via the lexical-semantic route whereas deep parsing is not (fully) applied in L2 processing. Figure 2.3 above is adapted by Clahsen & Felser (2006b, p. 119) and presents their illustration of the model. Among other suggestions, the authors’ propose that L2 processing might be shallow because full syntactic parsing is constrained due to the incomplete L2 grammar (again, see Figure 2.3 above).43
Accordingly, (adult) L2 learners rely on shallower and less detailed syntactic representations than native speakers. They still are able to comprehend L2 input on the basis of lexical-semantic information since these are sufficient to chunk a sentence into meaningful units and to coordinate their semantic relationships (cf. ibid. pp.116). Consequently, this approach may account for the observation that ERPs as response to the L2 processing of semantic violations (as discussed in 2.2.1) are less different from native speakers’ ERPs than those as response to syntactic violations (see 2.2.2).
Further, the model may put forward some implications about the influence of AoA and proficiency. Consider the processing of double nominative violations as described in 2.2.2: If shallow processing restricts the full activation and retrieval of syntactic processing mechanisms this would account for the different ERP patterns revealed by L1 and L2 processing. Further, if this restriction is due to incomplete L2 grammar, proficiency may show an influence in that ERPs elicited by high proficient L2 learners should be less different from L1 ERP patterns than those of low proficient L2 learners. In other words, ERPs of L2 learners as response to the processing of a syntactic anomaly should converge that of native speakers as proficiency improves. This is consistent with the idea of Steinhauer et al.’s model of temporal dynamics (see 2.2.2.4 above). However, if full parsing routines are not available to L2 processing due to
43 Note that the authors give an extensive cross-linguistic review on the processing data of native speakers and L2 learners for numerous morphological and syntactic structures including off-line and on-line measures. They further provide a detailed description of the different demands as to the language processing system made by various linguistic structures and elaborate explanations why L2 shallow processing is sufficient for some structures but not others. Further, a great amount of their evidence does not involve results from the processing of (syntactic) violations but rather the resolution of ambiguities and long-dependencies. Since none of their reviewed data corresponds to the structures investigated in the present thesis the above interpretation of shallow processing shall be sufficient.
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2. ERPs as Response to L1 and L2 Processing
maturational restrictions this would indicate AoA influence, irrespective of L2 proficiency. Clahsen & Felser acknowledge potential influence of AoA and proficiency. However, they do not make any predictions on their own concerning possible proficiency influence due to improving L2 grammar and, hence, increasing automatization of according processing mechanisms (as e.g. Steinhauer et al. do). This might be due to the designs of their own studies, where L2 learners showed little variation with respect to AoA and proficiency and, further, were compared to native speakers categorically (i.e. group design). Moreover, the authors recognize that the determination of whether and to what degree a specific structure is “shallow” needs further investigations.
2.4 Summary
Chapter 2 has dealt with the differences of ERP responses between native speakers and L2 learners. Further, it was outlined that the specific linguistic structure determines the activation of neural resources and retrieval of the subsequent processing mechanisms. Studies carried out so far have shown that both AoA and proficiency of L2 learners are accountable for differences across L1 and L2 processing patterns. Furthermore, previous outcomes suggest that their influence appears rather gradual than discontinuous not only when factors were treated as continuous variables but also when they were part of a categorical design (e.g., L2 learner groups with different mean levels of proficiency or AoA). With respect to isolated semantic and syntactic L2 processing and to subsequent ERP data, previous results suggest that the semantic processing appears robustly and differences are rather small when compared with the outcomes of L1 processing patterns. Nevertheless, the relatively slight differences and explanations in the light of AoA and proficiency influence are not uniform. Syntactic processing patterns elicited by L2 learners show greater differences when compared with native speakers’ ERPs. Furthermore, relative to the differences between L1 and L2 semantic processing, the reported AoA and / or proficiency influences on the observed differences reflected by ERPs as response to syntactic violations are more consistent.
2. ERPs as Response to L1 and L2 Processing
The shallow structure hypothesis as proposed by Clahsen & Felser provides a good way to account for the observed differences between L1 and L2 semantic and syntactic processing. They argue that L2 processing is shallow, which is satisfactory to activate and retrieve lexical-semantic processing mechanisms but does not or to a much lesser degree suffice to process (more) complex syntactic structures. In their view, L2 processing predominantly relies on lexical-semantic cues.
The following studies do not intend to test the shallow structure hypothesis although it may be interesting to see whether e.g. proficiency has an impact on shallow processing and / or whether results provide an indication that the processing of an unlicensed NPI are different than the processing of a double nominative violation in terms of “shallow structure” determination (see above). Rather, the upcoming experiments aim to contribute more insights into the observed inconsistency of AoA and proficiency influence as a source of differences between the activation and retrieval of L1 and L2 processing mechanisms reflected by ERPs. Moreover, the following designs aim to disentangle the correlation between both factors (i.e., the older the AoA, the lower the proficiency) by including them as fixed variables into statistical analysis. Thereby, the target will be to unfold potential differences of their weighting with respect to their impact on L2 processing mechanisms. Firstly, this will be observed for isolated semantic and syntactic processing mechanisms. Hereby the ERP components N400 and P600 will be focussed, respectively. Secondly, structures that require the enhanced activation of both semantic and syntactic processing mechanisms (N400-P600 processing pattern) will be investigated in light of the formerly observed influences of AoA and proficiency. Accordingly, the present study will also address the questions whether the influences of AoA and proficiency and their weighting could also occur with the combined processing demands and whether they are similar or different. A continuity approach is assumed concerning this matter. The present design intends to trigger evidence on potentially gradual influence of AoA and proficiency. In the remainder of this thesis the methodological and procedural aspects of the conducted experiments (Chapter. 3) and their results (Chapter. 4) are presented.
3. Participants, Materials and Experimental Procedures