Discussion: Sentence Context experiments

The sentence context experiments examined the neural activity associated with the processing of phonological stem variants of complex words within a section of continuous speech, i.e. in the sentence final position. Critical words in both violation conditions evoked LAN followed by the P600 component in both experimental groups. No N400 effect was observed to either the RD or UD critical items.

We hypothesized that if there was an underlying abstract morpheme for the regular stem allomorphs, e.g. {schwAch} in German and {serIn} in English, then the lexical retrieval of the RD items would be facilitated. This could be possible due to the structural repair mechanisms governed by the morphophonological and morphosyntactic rules that define the surface form of the abstract stem morpheme. The offline application of these rules would therefore result in error-detection mechanisms reflecting morphosyntactic processing. At the same time, the repair of the UD items would be impossible due to the lack of substantial linguistic background that could systematize the manipulation of the stem vowel. The product of manipulation being a purely phonological violation, the UD condition should have been perceived as an irreparable nonword. The results of the present study demonstrated the possibility for both violation conditions to be repaired in the presence of a sentence context. The fact that the N400 effect was not observed in this study provided evidence for the successful lexical retrieval of all experimental stimuli.

The present pattern of results could be explained by a number of factors. We shall first discuss the external ones and then move over to the internal factors.

Figure 13. Bar Plots: German and British Participants

Bar diagrams of mean amplitude values (German group: gray bars, English group: white shaded bars) calculated for groups of three electrodes in the latency range and topography of the LAN component – at FC3, FC5, F5 electrode sites (upper part) and P600 component – at Pz, P1, P2 electrode sites (lower part). Standard error of mean is plotted in both directions.

The first factor that could influence the processing of the linguistic material was the composition of experimental blocks. The first two blocks contained only the RD and UD items in the sentence-final position. After a couple of trials the participants might have already realized that all sentence final words were deviant from the expected standard. While the RD items deviated from the expected stem in the violation of a morphophonological rule, the UD items differed from the standard in a sporadic modification of the stem vowel. The mere phonological overlap with the surface structure of the expected word was in this case equal for the nonword conditions. On hearing both kinds of violations and having subtracted the morphological structure, the participants must have come

up with the strategy of looking up verbal/ trisyllabic shortened stems in the mental lexicon. The occurrence of the LAN effect in both cases demonstrated the repair processes that were running offline in order to reconstruct the original stem.

The sentence context used in the present study was also an additional factor influencing the processing strategy. The sentence frames were not restrictive or high-cloze probability contexts yet they were constructed with a bias towards the critical words. Thus, there was an extensive syntactic context that elicited the pre-activation of a certain grammatical category, i.e. a noun. The homogeneity of the stimulus materials also provided the information about the morphological structure of the sentence final word, i.e. a deverbal noun in German or a trisyllabic shortened abstract noun in English. The semantic context created an additional filter that helped to narrow down the stems to those that met the semantic requirements. The upcoming input was then matched to the pre-activated mental representations rejecting those that did not have the necessary phonological overlap. The violation conditions differed from the real words only in one phoneme, resulting in a minor phonological deviation from the mental representation. Therefore, the candidate that coincided with the input in all constituents but the stem vowel was retrieved, repaired and then integrated into the sentence context.

We expected the character of the stem violation to affect the processing of the nonwords. The morphophonological violation employed in the RD condition was predicted to elicit the morphosyntactic ERP component LAN (Gunter et al., 2000; Kutas & Hillyard, 1983; Münte et al., 1997; Osterhout & Mobley, 1995;

Penke et al., 1997). Although the RD items deviated from the standard in the place of articulation/ the tenseness of the stem vowel, their stems represented one of the steps in the derivation of the critical nouns. The easiest way to reconstruct these nonwords was by the offline application of conversion accompanied by umlaut in German and the TSS in English. The purely phonological violation employed in the UD condition might have induced a number of ERP components. Considering the phonological deviation from the expected input, the PMN component (Connolly & Phillips, 1994; Connolly et al., 1995; Connolly et al., 1992; D'Arcy et al., 2004; Steinhauer & Connolly, 2008) could have been observed. PMN was reported to index the failure of mapping the actual acoustic input onto the expected candidate. However possible in the light of the present experimental conditions, the PMN effect was not observed in either nonword type. We argue here that the product of the stem vowel manipulation resulted in an increased conflict within the sentence context. The gravity of the

conflict thus overrode the PMN effect if that should have been induced. In one of our predictions we mentioned the possibility for the N400 (Kutas & Hillyard, 1980, 1983; M. Kutas & S.A. Hillyard, 1984; van Berkum, Hagoort, & Brown, 1999) effect to be elicited by the UD items. The vowel manipulation was not governed by the non-application of morphophonological rules or by regional pronunciation variants, it was rather sporadic. Without a solid linguistic background behind the violation, the original stem could not be structurally restored and the UD items would be processed as irreparable nonwords yielding a prominent N400 effect.

The last error-detection mechanism that we contemplated was based on a straightforward analysis of the phonological overlap and the structural repair of the stem vowel based on the pre-activation of the possible word candidates. The resulting processing would be indexed by the LAN yet it would not completely correspond to the processing involved in the retrieval of the RD nonwords.

The gravity of both violation types was sufficient to induce a structural and semantic reanalysis reflected in the amplitude of the P600 effect (Gunter et al., 1997; Hagoort et al., 1993; Morris & Holcomb, 2005; Osterhout & Holcomb, 1992;

Osterhout & Holcomb, 1993; Osterhout & Holcomb, 1995). Though the nonwords carried different violation types, they presented comparable impediments for the parsing. According to Zwitserlood (1989), the contextual effects come into play at the point in time when a set of word candidates has already been pre-activated yet the sensory input does not suffice to disambiguate between the pre-activated representations. The lack of disambiguating information, though qualitatively different, had the same quantitative characteristics in the nonword conditions resulting in the elicitation of contextual effects. The increase of the processing demands associated with the reconstruction of the defective phoneme and the consequent integration of the repaired structure into the sentence context yielded a strong conflict. Van de Meerendonk et al. (2008) claimed that a P600 could only be elicited if the gravity of conflict triggered the language monitoring process and structural analysis. Our findings were also in line with the argument advanced by Kolk and colleagues (2003) that growing processing demands were reflected in the magnitude of the P600 effect.

The results of the sentence context experiments showed that a slight phonological deviation from the expected input, whether sporadic or structurally governed, could be morphosyntactically repaired if presented in a biasing context. While structurally different, the TSS and umlaut violations induced similar brain responses in both nationality groups. Considering the homogeneity of the observed effects, a further clarification of the contextual effects is necessary.

Thus, the mentioned external factors could be controlled for if the filler sentences were introduced. This would reduce the proportion of occurrences of violated items. Further, the NC items used in the words list experiments could also be employed in the sentence context studies to control for the degree of deviation from the standard. The difference in processing of the RD and UD items, if it has separate bases, could be investigated by means of functional magnetic resonance imaging (fMRI) providing insight into the structures involved in the repair process. The further investigation of the contextual effects in the processing of regular stem allomorphy should not only be extended via new paradigms and techniques but also via application of new materials, such as tone/tonic in English and stark (strong)/ Stärke (strength) in German.