On the Boundaries of Phonology and Phonetics
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2.The prosodic hierarchy of wordsThe prosodic hierarchy up to the word level consists of four constituents. The lowest element of the prosodic hierarchy is the mora (). Since there are often no segmental slots in moraic models, the mora has a double function as the unit of syllable weight and as the unique sub-syllabic constituent. The moraic level is dominated by the syllabic level (), and syllables are parsed into feet (F) at the foot level above. The highest unit is the prosodic word (Wd) which directly dominates the foot level (see Figure 1): Prosodic word (Wd) 
Foot (F)
Syllable ()
Mora ()
Figure 4. The prosodic hierarchy (Selkirk, 1980) Syllables differ with respect to the number of moras they contain. Light syllables contain one mora, while heavy syllables contain at least two. The tendency of languages to assign stress to heavy syllables is expressed by the Weight-to-Stress-Principle (WSP). In a parametric approach to word stress (cf. Hayes, 1995), languages either respect this principle (quantity-sensitive languages) or do not (quantity-insensitive languages). The next constituent of the prosodic organization above the syllable level is the foot. Ideally, the foot is binary branching which implies that it should consist of two moras or of two syllables. Thus, a binary foot can be monosyllabic if it contains two moras (e.g. ‘duck’) or it can be disyllabic if it consists of two syllables or two moras (e.g. ‘papa’). The head constituent of the foot receives stress. The prosodic word is the domain of stress application. It can also coincide with a single foot. Because the foot size is the smallest shape a prosodic word can have, it is called Minimal Word. Many languages have restrictions such that content words must not be smaller than the minimal word. There is ample evidence that the minimal word restriction also governs the shape of the early words in language acquisition (Demuth & Fee, 1995; Demuth, 1996; Fikkert, 1994; Ota, 2001). A very important principle of the prosodic hierarchy is the Strict Layer Hypothesis (Selkirk, 1984) which demands that layers must not be skipped, i.e. that a given prosodic constituent(n-1) is contained in the constituent(n) immediately above. Furthermore, it requires that constituents have one and only one head, which implies that there is always a difference in prominence among the elements forming a given prosodic unit. 3.The acquisition of word stress: two current models3.1. Fikkert (1994)Fikkert’s study of Dutch children is the most detailed research on stress acquisition to date. Fikkert mainly focused on disyllabic words and argued for the foot as the basic unit of development. Although Fikkert’s model is based on Dutch, she claims that the trochaic template is universal in child language since it is the only quantity-insensitive foot in the typology of Hayes (1991). Thus, children should not show sensitivity to syllable weight at the earliest stages of prosodic acquisition. The postulation of a universal foot template implies that the child always makes reference to the foot level in the word productions. Consequently, it is a foot, not a syllable that is being truncated in forms like below: Example 1.
Fikkert assumes that the output a child produces is directed by the mapping of a melody template onto a trochaic template via prosodic circumscription. Based on phenomena such as truncation, stress shift and epenthesis, four different stages of prosodic development are postulated. Stage 1According to Fikkert, the child circumscribes the stressed syllable of the adult form together with its segmental material and maps it onto a trochaic template. The presumed representation of the child is given in Figure 2 (‘S’ denotes the prominent position and ‘W’ the non-prominent position within the foot): Wd
F
S W
Figure 5. The prosodic representation at stage 1 Prosodic circumscription forces the child to divide the input into two parts, the kernel (i.e. the stressed syllable) and the residue. In the mapping process, the kernel () is mapped onto the strong position in the prosodic template. The residue (//) becomes truncated because there are no empty positions in the template. The mapping onto the trochaic template accounts for the fact that, if the result of prosodic circumscription is a monosyllabic foot, sometimes a syllable is added to receive a disyllabic output, for example instead of . Stage 2At stage 2, the child circumscribes a trochaic foot. Thus, if the prosodic circumscription already results in a trochee as in / ‘holiday’, the trochee remains unchanged in the output and appears as . Words consisting of more than a single foot are circumscribed differently. Fikkert argues that the child selects the next stressed syllable to the left in addition to the stressed final syllable. For instance, Dutch / ‘crocodile’ should be realized as because the ultimate, main stressed syllable and the antepenultimate, secondary stressed syllable are kept. The disyllabic representation is then mapped onto the trochaic template resulting in a trochaic pattern. Since the production template still consists of one single trochaic foot, stress shifts to the initial syllable. The representation of the child is depicted in Figure 3: Wd
F
 S W
Stage 3At stage 3, the productions are extended to two feet. According to Fikkert, the children have noticed that the target words can consist of more than a single foot. She claims that her subjects realized two syllables of the target word with equal prominence (level stress). However, her argument for the level stress stage is rather weak: she stipulates that the children have to produce two equally stressed feet because they are unable to realize stress at word level. The prosodic representation at stage 3 is depicted in Figure 4 below: Wd  
  F F
S W S W
Figure 7. The prosodic representation at stage 3 Since the trochaic foot still governs the productions, weak positions in the template can be filled with extra syllables. Stage 4The representations are now adult-like. The word level stress has been acquired and the child is able to operate at the level of the prosodic word. |
