On the Boundaries of Phonology and Phonetics
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3.2.Demuth & Fee (1995)Demuth & Fee propose a more abstract approach which, although primarily based on data of English acquiring children, aims to capture the prosodic development universally. The basic assumption in Demuth & Fee’s model is that prosodic development goes along the prosodic hierarchy (see Figure 1). In contrast to Fikkert, Demuth & Fee avoid the notion of prosodic circumscription and trochaic template mapping. According to them, sensitivity to the moraic structure of the mother tongue is already there from the onset of word production on. They distinguish between the following stages: Stage 1The first stage is characterized by sub-minimal (monomoraic) words. The productions consist of a single CV-syllable and there are no vowel length distinctions yet. Thus, the phonological representation of the words also is CV. Stage 2At stage 2, children realize words of foot-size (Minimal Words). Stage 2 is characterized by three successional sub-stages: at the beginning, the foot is disyllabic as for example in ‘papa’. Second, as soon as the child is able to produce coda consonants the foot can also have a monosyllabic form, e.g. ‘duck’. Third, the vowel length distinction becomes phonemic. The child is now aware of the fact that the stressed syllable of Dutch ‘banana’ has to be realized with a long vowel , while in ‘giraffe’ the second vowel remains short (examples from Robin, see Fikkert, 1994). Demuth & Fee assume a direct relationship between distinctive vowel length and the appearance of coda consonants. Thus, a CVV structure counts as sub-minimal, and a CVVCVV structure as minimal as long as the child does not produce coda consonants. Stage 3Beyond the minimal word stage, syllable structure can be more complex and words can have a larger size than a single foot. This is also the stage where the largest progress in the development of the word stress is predicted. The child seems to become aware that feet have to be stressed and that there are language-specific stress rules. Demuth & Fee do not assume a trochaic template. However, they adopt Fikkert’s assumption of an obligatory intermediate stage of level stress where two feet are produced with primary stress. At the end of stage 3, children acquire stress at the word level and they realize one primary stress per word. Stage 4At the final stage, extrametrical (i.e. unfooted) syllables are permitted. Children at this stage operate at the level of the prosodic word. 4.Discussion of the modelsAlthough both models can explain a number of frequently observed patterns like syllable deletions and word size restrictions, there are a number of empirical and theoretical problems related with the models. First, Fikkert and Demuth & Fee assume that the prosodic development proceeds bottom-up, i.e. from a lower level of representation (the foot or the mora) to the top of the prosodic hierarchy (the prosodic word). Children invariably have to pass trough one stage before they can go to the next. For example, multisyllabic words like ‘elephant’ or ‘crocodile’ have to show a level stress pattern before they can be produced adult-like. Fikkert explicitly points to that fact. Missing evidence in her data is explained by the recording modalities or is due to the fact that a given stage took a very short time. Demuth & Fee, in contrast, are not explicit with respect to the ordering of the stages. However, they claim that prosodic development proceeds along the prosodic hierarchy. Since in the prosodic hierarchy one constituent strictly dominates the constituent below, stages cannot vary with respect to their temporal order. According to the models, the following realizations for / ‘crocodile’ of Jule, a girl acquiring German, should be chronologically impossible (data from my own corpus):
As the examples illustrate, level stress can occur after a finally stressed variant of the target word was produced, contrary to the predictions of the models. Such an acquisition order provides empirical evidence against level stress as an obligatory component of prosodic development. Additional empirical support comes from the data of English acquiring children examined by Kehoe & Stoel-Gammon (1997) who also could not find a systematic emergence of level stress. Level stress as assumed in the models above is problematic also from a grammatical point of view: the representation intended to create level stress (see Figure 4 above) essentially violates the strict layer hypothesis because the two feet are not correctly bounded into the prosodic word. The problem is that the strict layer hypothesis never can be kept by such a representation because there is no gradation in prominence at the word level. According to prosodic theory, two equally stressed feet must not occur within a single prosodic word:
Figure 8. The ill-formed representation of the prosodic hierarchy as implied by Fikkert (1994) and Demuth & Fee (1995) Both models remain vague with respect to the source of level stress: it is unclear how the stages of level stress fit to the assumption that prosodic development is directed by universal prosodic principles. Since they do not discuss the possibility of a child-specific representation, the representation according to the prosodic hierarchy should look like illustrated in Figure 6: Wd Wd
  FS FS
Another problem is that the models described above are primarily based on truncation patterns in multisyllabic words. This is critical from a methodological point of view because it is presupposed that the truncation of syllables is exclusively triggered by prosodic size restrictions. Recent evidence, however, suggests that segmental properties of syllables can also affect the truncation rate. For example, syllables with sonorant onsets seem to be more prone to truncation than syllables with obstruent onsets (Kehoe & Stoel-Gammon 1997). A comparison of both models suggests that the predictions of the template mapping model of Fikkert (1994) are sometimes too strong. Thus, the prosodic hierarchy model of Demuth & Fee (1995) seems to be superior because of its greater flexibility. First of all, it prevents Fikkert’s circular process of assigning a trochaic structure via prosodic circumscription that actually should be created by the foot template. Furthermore, the prosodic hierarchy model allows for more variability in the productions of children. For example, it allows for the co-occurrence of monosyllabic and disyllabic feet in contrast to Fikkert’s model that only proposes disyllabic trochees for a very long period of time. As the data of children acquiring English suggest, there are doubts on Fikkert’s view that the disyllabic trochee is the unique representation at the early stages (Kehoe & Stoel-Gammon, 1997; Salidis & Johnson, 1997). Moreover, Fikkert predicts a systematic stress shift to the left in disyllabic iambs, a pattern that still needs empirical evaluation. It is also possible that stress shift is rather the result of a complex interplay of factors like edge preferences, weight sensitivity and segmental factors than of a simple template mapping mechanism. If this is true, stress shift can be bidirectional to the left or to the right, depending on the relative importance of the factors involved. Fikkert’s model is more detailed than the model of Demuth & Fee. It is at best elaborated for stage 1 and 2. With respect to the later stages she remains somewhat inconsistent. For example, she strongly argues for the foot as the relevant prosodic unit, but already at stage 2 the syllable, not the foot, becomes the target of circumscription: “[...] the child realises both syllables of the target word. However, stress falls on the first syllable. The segmental material of both syllables of the adult word is taken out and mapped onto the child’s trochaic template [...]” (p. 210).
‘elephant’ ‘pelican’ ‘locomotive’ ‘farm’
Demuth & Fee, in contrast, have problems to explain the stress shift to the first syllable in the examples above for two reasons: first, recent evidence suggests that the relationship between distinctive vowel length and the emergence of coda consonants is not as categorial as they claim. In an examination of Fikkert’s data, Salidis & Johnson (1997) found that, contrary to their English acquiring child, the vowel length was not controlled by the Dutch children even if they correctly produced coda consonants. If in turn, children cannot control vowel length appropriately, they cannot assign two moras to a long vowel. The authors relate the divergence between the languages to the impact of vowel quantity on the stress pattern: in English, the long vowels in (C)VV(C) syllables count as heavy and thus attract stress, contrary to Dutch which rather relies on the open-closed distinction. In Dutch, a (C)VC syllable counts as heavy, while a (C)VV does not. Thus, a learner of Dutch presumably does not rely on vowel length as an indicator for stress, while it is crucial for a learner of English to identify the relationship between vowel quantity and stress. Second, given that the absence of the vowel length distinction is an artifact of the investigation and children have mastered the vowel length distinctions if they produce bimoraic feet. Then neither universal nor language-specific constraints could account for the fact that the superheavy finals lose their primary stress in favor of the less heavy ultimates because Dutch follows the universal generalization that a (C)VCC (e.g. //) or a (C)VVC (e.g. //) syllable is heavier than a (C)VV syllable (//,//). The observation that Dutch children need more time to acquire vowel length distinctions indicates that language-specific properties may influence the prosodic representation in a more detailed way than assumed so far. Thus, further empirical work is needed to shed light on the interplay of universal principles and language-specific conditions in prosodic development.
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