Four behavioural priming experiments investigated the access and representation of alternating and non-alternating vowels in the present tense stem of strong, weak and mixed German verbs. All four experiments supported the view of the FUL model (Lahiri and Reetz, 2002b), according to which lexical architecture does not have a dual structure, as proponents of traditional dual route approaches would propose. Rather, the results provided evidence for morphemic, partially underspecified stem representations to which both alternating and non-alternating forms can be mapped in accordance with the ternary matching logic, distinguishing between (full) matches, nomismatches and mismatches.
From an architectural point of view, then, strong and weak verbs were not expected to differ in priming, independent of whether the vowel alternation in the corresponding 2ND SG PRES involved raising or umlaut, and independent of whether the inflected form was used as prime or as target. This prediction was borne out by the experimental data: In all four experiments, the amount of priming did not depend on the verb class of the target. Neither did it depend on the prime-target direction (2ND SG PRESÆINFINITIVE versus INFINITIVEÆ2ND SG PRES). The latter result posed a challenge for the specific dual route model developed by Clahsen and colleagues, who would have predicted priming asymmetries based on whether the morphosyntactically more specific form is the prime or the target. No such verb class based asymmetries were found in the experiments reported here.
Clearly, then, the results of the experiments strongly support a monophonemic and monomorphemic stem representation for all verb classes. There is no evidence for structural differences between strong and weak PRESENT TENSE stems, although it is quite likely that PRETERIT and PAST PARTICIPLE stems of strong verbs are stored separately (cf. Figure 14, p. 101). Traditional dual route models which would store irregular (strong) verb forms as wholes do not justice to the very productive and transparent affixation of the 2ND SG PRES suffix –st. This suffix attaches to verbs of all verb classes across all tenses. Hence, it is never necessary to store 2ND SG PRES as whole forms or as subnodes in
hierarchically structured lexical entries. There are however differences in the stems of strong, weak, and mixed verbs. Weak verbs have only one stem for all tense and person/number realisations. Strong verbs may have different stems for specific tense realisations (PRETERIT, PAST PARTICIPLE), but not for productive alternations within a tense (PRESENT TENSE 2ND/3RD SG, SUBJUNCTIVE cf. Table 16, p. 53).
Here, two different surface forms relate to one underlying representation. The experiments showed that the umlauted or raised surface forms of the strong verbs primed their (underlying) infinitives as much as the nonumlauted or unraised surface forms of the weak verbs primed their respective infinitives.
On the other hand, the nominal amount of priming did differ between [a]- and [e]-stems in the weak verbs: Weak [a]-verbs generally had a priming advantage compared to all other conditions, however, this effect was only significant in experiment 2. Nevertheless, the trend is explicable in the framework of FUL: While overall, no contrasts between root vowels are predicted, in the weak verbs, [a]-stems are characterised by full matches between 2ND SG forms and INFINITIVES, while [e]-stems involve nomismatches. Thus, for the former, the matching score is better than for the latter. In fact, experiment 2 showed a significant correlation between the amount of priming and the matching score. Clearly, more research is necessary to precisely investigate the correlation of priming and featural full- versus nomismatches. The experiments in this dissertation were not designed for this specific purpose, though.
Furthermore, the comparison of mixed [a]- and [e]-verbs in experiment 1 showed that although the average priming was the same across all verb classes, mixed [a]-verbs did not yield significant priming since the coronal surface feature of the umlauted 2ND SG PRES primes mismatched with the stem alternative comprising a dorsal root vowel. This effect did not show up in experiment 2 where there was full priming for the mixed [a]-verbs. It is quite likely that the concomitant semantic priming in the immediate priming design of experiment 2 overrode the subtle morphological effect of experiment 1.
Altogether, it could thus be shown that priming asymmetries in German verbs did not arise as a consequence of the morphological verb class and alleged structural organisation of the relevant targets or as a consequence of the prime-target direction. Rather, priming asymmetries reflected asymmetries in the featural matching between the signal and the lexical representation. These asymmetries were dependend on the root vowel quality. Crucially, a difference was assumed between the root vowels [a]
and [e]. The former vowel is underspecified for its place of articulation if it occurs in stems of which the inflectional surface forms show umlaut. The latter vowel is a priori underspecified for its place of articulation since it is a front vowel (cf. chapter 1). It is underspecified for its height since it is a mid vowel. Hence, raised as well as unraised 2ND SG PRES involve a nomismatching vowel with regard to the root vowel [e].
The opposition of crossmodal immediate and unimodal delayed experiments allowed to disentangle genuine morphological from „morphological plus semantic‰ effects. In this respect, the results of the four experiments are not at odds with recent findings in the psycholinguistic literature. The work of Feldman and colleagues (Feldman, 2000; Feldman and Prostko, 2002) showed that semantic priming effects only occur at short lags between primes and targets. In fact, facilitation of semantically related prime-target pairs was absent in experiment 1 and 3 of this study involving an average lag of 6 items (17 seconds). Genuine morphological effects, on the other hand, develop over time and can be teased apart from semantic priming only in delayed, i.e. in long lag priming designs. According to Feldman (Feldman, 2000; Feldman and Prostko, 2002; Feldman et al., 2004), morphological priming is complex
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and interacts with the morphological family size of the target57. Elsewhere, it has been shown that the recognition of spoken words depends on the density of a targetÊs phonological neighbourhood (Dell and Gordon, 2003; Goldinger et al., 1989; Luce and Pisoni, 1998). Finally, Stockall and Marantz, 2006, propose that any competition or interference effects between particular stem allomorphs only show up at later stages of processing. Taken together, the three aspects are compatible with the findings that subtle morphophonological effects, based on competition and interference only occurred in experiment 1 and 3.58 Crucially, these two experiments involved a delayed repetition priming and revealed genuine morphological relations. Second, the delay between prime and target possibly enabled the emergence of later processing effects, as applicable in the mixed [a]-verb competition effect based on the differential root vowel representations. Here, it was assumed that mixed [a]-verbs have two phonologically different root vowel representations, one of which has dorsality specified (non-alternating) while the other one is underspecified for that feature (alternating). Hearing a 2ND SG PRES with an umlauted root vowel mismatches with the root vowel specified for dorsality, whereby the facilitation effect is reduced. Thus, the featural mismatch caused interference in the priming of mixed [a]-verbs. In fact, compared to all other conditions, priming in these verbs was not significant in experiment 1, despite the sparsity of alternative 2ND SG forms for such verbs in German.
Altogether, the results of experiment 1-4 support a speech recognition model with featurally organised lexical core representations, onto which speech inputs from both the auditory and the visual modality are mapped and evaluated. This evaluation corresponds to the calculation of the goodness-of-fit between the input and the lexical representation and is entirely based on phonological features. The features may match, mismatch or not mismatch. Lexical access is possible if a word form matches or does not mismatch with the corresponding features specified in the lexicon. In a priming design, a word can facilitate the recognition of another word if the second word is in the cohort of the first word. The particular emphasis in this study was on the representation of alternating vowels. How are the vowels of verbs with alternating present tense stems represented feature-wise? The experimental data provided evidence that the prerequisite for a vowel to participate in a vowel alternation is directly encoded in its lexical representation: Both in the height and articulator place dimensions, a vowel must be underlyingly underspecified for its respective alternating features. Based on this underspecification, the present tense stem representation determines the verbÊs class membership: If surfacing back vowels are lexically underspecified in German verbs, these verbs are strong. If they are fully specified, the verbs are weak. Mixed verbs have both underspecified and specified variants. Their usage appears to be determined by syntactic and semantic contexts. As can be learnt from DUDEN (Drosdowski, 1995), strongly inflected verb forms of mixed verbs are preferably used in inchoative senses and intransitive constructions, while weakly inflected forms appear in transitive sentences with a causative sense. This correlation was investigated in chapter 1 (p. 59: Motivation for two representations in mixed verbs).
How would other theories fare if they had to explain the outcome of experiments 1-4?
57 Note that this was not a problem for the stimuli in experiment 1-4, since the morphological family size did not differ between verb classes.
58 It is important to note that the differential effects found in experiment 1 (no mixed [a]-verb priming) were subtle: Comparisons between the two experiments within these conditions did not yield significant differences in the amount of priming. However, in each experiment, priming was absent in the respective conditions.
Furthermore, FUL is capable of answering the question why it were that just these verb types showed the particular priming pattern.
Most of the results would also be explicable in full listing theories (e.g. Butterworth, 1983; 1989).
However, such theories could not readily explain the asymmetry in the mixed [a]-verbs. Furthermore, they could not account for the trend of weak [a]-verbs towards the greatest amount of piming in all experiments. In general, full listing theories would not allow for vowel-specific priming effects since the representations in these approaches is based on whole forms and not on „atomic‰ units such as phonological features. Furthermore, a possible problem for full listing approaches has to do with the relation of full forms in the lexicon. If this relation is (partly) based on semantic associations (such as in connectionist models, c.f. McClelland and Elman, 1986), then there should be priming differences between experiments which are sensitive to semantic (associative) effects (experiment 2 & 4) and experiments which are not (experiment 1 & 3). No such differences have been found in the experiments reported here. The lack of such differences is a challenge for traditional dual route models which assume associative connections between strongly inflected verb forms, while weakly inflected verb forms are derived by symbolic rules.59 Thus, these models are challenged by the lack of priming differences between strong and weak verbs. But also the more recent dual route approaches (Clahsen et al., 2002;
Pinker and Prince, 1994; Pinker and Ullman, 2002) would have difficulties to account for the data presented here: If, at best, the strong present tense stems of German verbs would be considered
„subregular‰ with respect to the vowel alternation in the 2ND and 3RD SG,priming within the present tense should be reduced compared to weak verbs without such alternations.
One of the strongest arguments for FUL and against a hierarchically structuring of lexical entries of strong verbs (Clahsen et al., 2001a; Sonnenstuhl et al., 1999) was provided by the reversal of the prime-target directions (2ND SG PRESÆINFINITIVE) in experiment 3 and 4: Within the strong verbs, this reversal did not affect the amount of priming. This result cannot be explained in terms of lexical hierarchical structures, which are solely based on the fact that vowels do alternate. More precisely, the reason to assume that the 2ND/3RD SG PRES formsof strong [a]- and [e]-verbs in German are morphosyntactically more specific than their infinitives must have been entirely based on the stem alternations. Otherwise, one could equally claim that the 2ND/3RD SG PRES of weak [a]- and [e]-verbs are more specific than their infinitives (which is in fact true, restricted to a morphosyntactic point of view).
On the other hand, vowel specifications seem to have morphosyntactic repercussions. However, these are not based on hierarchical lexical entries but on featural underspecification. Crucially, the strong present tense stem alternation in German [a]-verbs is claimed to be directly rooted in the lexical and featural representation of the corresponding root vowels. If these vowels are not specified for dorsality in the mental lexicon, stem alternations in the appropriate person/number realisations are possible. Mixed [a]-verbs are assumed to involve two stem representations of which the underspecified stem patterns with the strong present tense conjugation, while the place-specified stem is used for the weak conjugation.
Exemplar-models of the type proposed by Warren and colleagues (Warren and Hay, 2006; Warren et al., to appear, cf. chapter 5) would predict that the amount of priming reflects the acoustic distance of the vowel in the prime to the vowel in the target. Thus, the general expectation would be that a prime-target pair like machst-machen (make.2ND SG PRES-INFINITIVE)ought to yield more priming than a pair in which the vowels differ, as in schläfst-schlafen (sleep.2ND SG PRES-INFINITIVE).This effect was clearly
59 Note that FUL assumes rule-based decomposition for both regular and irregular (i.e. weak and strong) affix-based verb inflection.
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not present in the actual data. Furthermore, exemplar-models would also not predict vowel-specific asymmetries, as long as they do not correlate with acoustic distances.
Altogether, the results of experiment 1-4 support the view that the present tense stem representation is monomorphemic, even if 2ND and 3RD SG PRES surface forms involve vowel alternations as seen in the strong and mixed verbs. The retrieval of the appropriate meaning of schlafen upon hearing the altered vowel in schläfst is possible through a relation between the 2ND SG PRES signal and the lexical representation of the verb in which no phonological feature mismatches occur. The representation of mixed verbs (in the specific sense) is such that they involve two lexical representations, but they may be identical in their phonological underlying representation ([e]-verbs).
The phonological makeup of verb stems is a necessary condition for the identification of the inflectional class a given verb belongs to. Morphosyntactic and semantic repercussions of underspecification have been sketched and two judgement studies provided evidence for an interaction between morphophonology and syntax/semantics (chapter 1).
While there are still many open questions – for instance, regarding the hypothesis of the PRETERIT
root vowel underspecification – the results of this study may be suggestive in which direction future research can go. A starting point for this is provided in the next chapter, which deals with the representation of root vowels in German umlauting and non-umlauting nouns. Experimental support is drawn from two neurolinguistic studies, indicating the cerebral reality of phonological underspecification in vowel alternations (chapter 4).
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4 Neurolinguistic evidence from nominal paradigms
4.1 Introduction
The last two chapters presented the Featurally Underspecified Lexicon (FUL) as a model of lexical representations and lexical access which bridges two sides of foci in the psycholinguistic research. One side, most prominently represented by dual route approaches (e.g. Pinker, 1998), assumes specific lexical organisations as a consequence of regular versus irregular morphology. The other side, exemplified by exemplar models (e.g. Johnson, 1997), tries to achieve a one-to-one mapping between the speech signal and lexical representations since as many phonetic details as possible are located in the individual exemplars. Lexical access in the dual route approach distinguishes between qualitatively distinct access routes for regular versus irregular word forms, while lexical access in the exemplar approaches is guided by probabilistic knowledge of the best-fitting exemplar, irrespective of morphological regularity.
FUL shares neither of these two main assumptions regarding lexical access and lexical representation. The claim of FUL is that lexical access only uses one route and involves the ternary matching algorithm introduced in chapter 2. The other claim is that lexical representations are abstract and feature-based. Front vowels are always underspecified for their place of articulation, while back vowels are underspecified for their place of articulation if they participate in productive alternations such as umlaut. Thus, FUL pays tribute to both the phonology and the morphology of umlaut. In this respect, chapter 1 argued for an apparent oddity regarding the mental representation of the acoustically identical vowels [] in Stock (stick) versus [] in Stoff (cloth). The crucial assumption was that if a noun umlauts its root vowel in inflectional paradigms (e.g. in the plural, Stock~Stöcke Âstick.SG~PLÊ), this vowel does not have an articulator place specification in the mental lexicon. Umlauted surface forms derive from one phoneme via the specific rule ordering which ensures that the coronal default rule is applied before the dorsal markedness rule. Accordingly, in perception, umlauted and non-umlauted surface forms (i.e. Stock and Stöcke) can activate the stem entry which contains a place-underspecified root vowel: Neither dorsality from Stock nor coronality from Stöcke mismatches with this root vowel representation. The vowel in Stoff, in contrast, was claimed to be fully specified (i.e. dorsal) since it does not umlaut its root vowel in the plural (*Stöffe).
While it is assumed that plural and singular forms derive from one morpheme, diminutives with either the –chen or the –lein suffix represent a different lexeme. This was motivated by the observation that diminutive formation in German is not as transparent as, for instance, in Dutch. As mentioned before, Brötchen (bun) is not just a „little bread‰, but a specific kind of pastries. Furthermore, there are many cases in which German native speakers are not confident as to whether the umlauted or non-umlauted stem is the „correct‰ stem for the diminutive formation. If diminutives involve a stem with an umlauted vowel on the surface, this vowel is not specified for dorsality, hence place-underspecified in the mental lexicon. For Brot (bread) or Stoff (cloth), this means that there exist separate stem entries surfacing as Bröt- or Stöff- respectively. These particular stems (cf. chapter 1) are phonologically different to their corresponding inflectional stems, which contain dorsal, i.e. place-specified vowels,
since the plural forms Brote and Stoffe do not show umlaut. For Stock, on the other hand, the derivational stem which is used for the diminutive, and the inflectional stem which accounts for the umlauted plural Stöcke, are phonologically identical. This is illustrated in Figure 27.
[LAB]
Figure 27: Proposed lexical representations of German Stock (stick) and Stoff (cloth). The place-underspecified [o] is given as a capital letter.
In speech perception, the diminutive form Stöckchen can activate its corresponding inflectional and derivational stem: The vowel in Stöckchen does neither mismatch with the vowel of the base stem nor with the vowel of the diminutive stem (cf. Figure 27). This is different for Stöffchen: Here, coronality from the surface vowel would mismatch with dorsality specified in the root vowel of the inflectional base. Hence, Stöffchen cannot activate Stoff via a phonological relation.
Words with surfacing coronal vowels remain constant in all nominal paradigms. These lexical entries comprise the additional rule order information which derives the coronal surface vowel independent of the morphosyntactic context. Nevertheless, the diminutive forms of these words also use different stems, which are phonologically identical to the inflectional stems. Crucially, both contain vowels not specified for their articulator place feature. The stem selection for words with coronal, dorsal
Words with surfacing coronal vowels remain constant in all nominal paradigms. These lexical entries comprise the additional rule order information which derives the coronal surface vowel independent of the morphosyntactic context. Nevertheless, the diminutive forms of these words also use different stems, which are phonologically identical to the inflectional stems. Crucially, both contain vowels not specified for their articulator place feature. The stem selection for words with coronal, dorsal