<?xml version="1.0" standalone="yes"?>
<Paper uid="W04-1306">
  <Title>On the Acquisition of Phonological Representations</Title>
  <Section position="3" start_page="42" end_page="43" type="metho">
    <SectionTitle>
2 Representations of stress
</SectionTitle>
    <Paragraph position="0"> Phonetic representations are not simply bundles of features. Consider stress, for example.</Paragraph>
    <Paragraph position="1"> Depending on the language, stress may be indicated phonetically by pitch, duration, loudness, or by some combination of these dimensions. So even language learners gifted with phonetic feature detectors will have to sort out what the specific correlates of stress are in their language. For purposes of the ensuing discussion, I will assume that this much can be acquired prior to further acquisition of the phonology.</Paragraph>
    <Paragraph position="2"> But simply deciding which syllables have stress does not yield a surface representation of the stress contour of a word. According to metrical theory (Liberman and Prince 1977, Halle and Idsardi 1995, Hayes 1995), stress results from grouping syllables into feet; the strongest foot is assigned the main stress, the other feet are associated with secondary stress. Moreover, some syllables at the edges of the stress domain may be designated as extrametrical, and not included in feet.</Paragraph>
    <Paragraph position="3"> For example, I assume that learners who have sorted out which acoustic cues signal stress can at some point assign the stress contours depicted in (1) to English words.</Paragraph>
    <Paragraph position="4"> The height of the column over each syllable, S, indicates how much relative stress it has.</Paragraph>
    <Paragraph position="5"> However, these are not the surface representations. They indicate levels of stress, but no  metrical organization.</Paragraph>
    <Paragraph position="6"> (1) Representations of stress contours before setting metrical parameters a. AmOrica b. M nit ba  English stress, the metrical structures assigned to these words are as in (2).</Paragraph>
    <Paragraph position="7"> (2) Acquired representations a. AmOrica b. M nit ba</Paragraph>
    <Paragraph position="9"> Looking at the word America, these representations indicate that the first syllable A is unfooted, that the next two syllables meri constitute a trochaic foot, and that the final syllable ca is extrametrical. Manitoba has two feet, hence two stresses, of which the second is stronger than the first. The Ls and Hs under the first line of the metrical grid designate light and heavy syllables, respectively. The distinction is important in English: The syllable to: in Manitoba is heavy, hence capable of making up a foot by itself, and it receives the stress. If it were light, then Manitoba would have stress on the antepenultimate syllable, as in America.</Paragraph>
    <Paragraph position="10"> How does a learner know to assign these surface structures? Not just from the acoustic signal, or from the schematic stress contours in (1). Observe that an unstressed syllable can have several metrical representations: it can be footed, like the first syllable in America; it can be the weak position of a foot, like the second syllable of Manitoba; or it can be extrametrical, like the final syllables in both words. One cannot tell from the sound which of these representations to assign. The only way to know this is to acquire the grammar of stress, based on evidence drawn from the observed contours in (1).</Paragraph>
    <Paragraph position="11"> Similar remarks hold for determining syllable quantity. English divides syllables into light and heavy: a light syllable ends in a short vowel, and a heavy syllable contains either a long vowel or is closed by a consonant. In many other languages, though, a closed syllable containing a short vowel is considered to be light, contrary to the English categorization. Learners must decide how to  classify such syllables, and the decision cannot be made on phonetic grounds alone.</Paragraph>
  </Section>
  <Section position="4" start_page="43" end_page="44" type="metho">
    <SectionTitle>
3 Acquisition of metrical structure
</SectionTitle>
    <Paragraph position="0"> How, then, are these aspects of phonological structure acquired? Following Chomsky (1981), I will suppose that metrical structures are governed by a finite number of parameters, whose value is to be set on the basis of experience. The possible values of a parameter are limited and given in advance.1 Parameter setting models must overcome a basic problem: the relation between a parameter and what it does is indirect, due to the fact that there are many parameters, and they interact in complex ways (Dresher and Kaye, 1990). For example, in English main stress is tied to the right edge of the word. But that does not mean that stress is always on the last syllable: it could be on the penultimate syllable, as in Manitoba, or on the antepenultimate, as in America. What is consistent in these examples is that main stress devolves onto the strong syllable of the rightmost foot.</Paragraph>
    <Paragraph position="1"> Where this syllable and foot is in any given word depends on how a variety of parameters are set. Some surprising consequences follow from the nontransparent relationship between a parameter and its effects.</Paragraph>
    <Paragraph position="2"> The first one is that a learner who has some incorrectly set parameters might know that something is wrong, but might not know which parameter is the source of the problem. This is known as the Credit Problem (cf. Clark 1989, 1992, who calls this the Selection Problem): a learner cannot reliably assign credit or blame to individual parameters when something is wrong.</Paragraph>
    <Paragraph position="3"> There is a second way in which parameters can pose problems to a learner. Some parameters are stated in terms of abstract entities and theory-internal concepts that the learner may not initially be able to identify. For example, the theory of stress is couched in 1For some other approaches to the acquisition of stress see (Daelemans Gillis and Durieux, 1994), (Gupta and Touretzky, 1994), (Tesar, 1998, 2004), and (Tesar and Smolensky, 1998).</Paragraph>
    <Paragraph position="4"> terms of concepts such as heavy syllables, heads, feet, and so on. In syntax, various parameters have been posited that refer specifically to anaphors, or to functional projections of various types. These entities do not come labelled as such in the input, but must themselves be constructed by the learner. So, to echo the title character in Plato s dialogue The Meno, how can learners determine if main stress falls on the first or last foot if they do not know what a foot is, or how to identify one? This can be called the Epistemological Problem: in this case we know about something in the abstract, but we do not recognize that thing when it is front of us. Because of the Credit Problem and the Epistemological Problem, parameter setting is not like learning to hit a target, where one can correct one s aim by observing where previous shots land. The relation between number of parameters correct and apparent closeness to the target is not smooth (Turkel, 1996): one parameter wrong may result in forms that appear to be way off the target, whereas many parameters wrong may produce results that appear to be better (Dresher, 1999). This discrepancy between grammar and outputs defeats learning models that blindly try to match output forms (Gibson and Wexler, 1994), or that are based on a notion of goodness-of-fit (Clark and Roberts, 1993). In terms of Fodor (1998), there are no unambiguous triggers: thus, learning models that seek them in individual target forms are unlikely to be successful.</Paragraph>
    <Paragraph position="5"> I have argued (Dresher, 1999) that Plato s solution a series of questions posed in a specified order is the best approach we have. One version of this approach is the cue-based learner of (Dresher and Kaye, 1990). In this model, not only are the principles and parameters of Universal Grammar innate, but learners must be born with some kind of a road map that guides them in setting the parameters. Some ingredients of this road map are the following: First, Universal Grammar associates every parameter with a cue, something in the data  that signals the learner how that parameter is to be set. The cue might be a pattern that the learner must look for, or simply the presence of some element in a particular context.</Paragraph>
    <Paragraph position="6"> Second, parameter setting proceeds in a (partial) order set by Universal Grammar: this ordering specifies a learning path (Lightfoot 1989). The setting of a parameter later on the learning path depends on the results of earlier ones.</Paragraph>
    <Paragraph position="7"> Hence, cues can become increasingly abstract and grammar-internal the further along the learning path they are. As learners acquire more of the system, their representations become more sophisticated, and they are able to build on what they have already learned to set more parameters.2 If this approach is correct, there is no parameter-independent learning algorithm.</Paragraph>
    <Paragraph position="8"> This is because the learning path is dependent on the particular parameters. Also, the cues must be discovered for each parameter.</Paragraph>
    <Paragraph position="9"> Thus, a learning algorithm for one part of the grammar cannot be applied to another part of the grammar in an automatic way.3</Paragraph>
  </Section>
  <Section position="5" start_page="44" end_page="46" type="metho">
    <SectionTitle>
4. Segmental representations
</SectionTitle>
    <Paragraph position="0"> Up to now we have been looking at an aspect of phonological representation above the level of the segment. I have argued that acquisition of this aspect of surface phonological representation cannot simply be based on attending to the acoustic signal, but requires a more elaborate learning model.</Paragraph>
    <Paragraph position="1"> But what about acquisition of the phonemic inventory of a language? One might suppose that this be achieved prior to the acquisition of the phonology itself.</Paragraph>
    <Paragraph position="2"> Since the pioneering work of Trubetzkoy and Jakobson, phonological theory has posited that phonemes are characterized in terms of a limited set of distinctive features. There- null models see (Nyberg, 1991), (Gillis Durieux and Daelemans, 1995), (Bertolo et al. 1997), and (Tesar, 2004). fore, to identify a phoneme one must be able to assign to it a representation in terms of feature specifications. What are these representations? Since Saussure, it has been a central assumption of much linguistic theory that a unit is defined not only in terms of its substance, but also in negative terms, with respect to the units it contrasts with. On this way of thinking, an /i/ that is part of a three-vowel system /i a u/ is not necessarily the same thing as an /i/ that is part of a seven-vowel system /i e a o u/. In a three-vowel system, no more than two features are required to distinguish each vowel from all the others; in a seven-vowel system, at least one more feature is required.</Paragraph>
    <Paragraph position="3"> Jakobson and Halle (1956) suggested that distinctive features are necessarily binary because of how they are acquired, through a series of binary fissions . They propose that the order of these contrastive splits, which form what I will call a contrastive hierarchy (Dresher 2003a, b) is partially fixed, thereby allowing for certain developmental sequences and ruling out others. This idea has been fruitfully applied in acquisition studies, where it is a natural way of describing developing phonological inventories (Pye Ingram and List, 1987), (Ingram, 1989), (Levelt, 1989), (Dinnsen et al., 1990), (Dinnsen, 1992), and (Rice and Avery, 1995).</Paragraph>
    <Paragraph position="4"> Consider, for example, the development of segment types in onset position in Dutch  At first there are no contrasts. The value of the consonant defaults to the least marked (u) onset, namely an obstruent plosive, desig- null nated here as /P/. The first contrast is between obstruent and sonorant. The former remains the unmarked (u), or default, option; the marked (m) sonorant defaults to nasal, /N/. At this point children differ. Some expand the obstruent branch first, bringing in marked fricatives, /F/, in contrast with plosives. Others expand the sonorant branch, introducing marked sonorants, which may be either liquids, /L/, or glides, /J/. Continuing in this way we will eventually have a tree that gives all and only the contrasting features in the language.</Paragraph>
    <Paragraph position="5"> 5. Acquiring segmental representations Let us consider how such representations might be acquired. To illustrate, we will look at the vowel system of Classical Manchu (Zhang, 1996), which nicely illustrates the types of problems a learning model will have to overcome. Zhang (1996) proposes the contrastive hierarchy in (4) for Classical Manchu, where the order of the features is [low]&gt; [coronal]&gt;[labial]&gt;[ATR].</Paragraph>
    <Paragraph position="6">  (4) Classical Manchu vowel system (Zhang</Paragraph>
    <Paragraph position="8"> Part of the evidence for these specifications comes from the following observations: (5) Evidence for the specifications in (4) a. /u/ and / / trigger ATR harmony, but /i/ does not, though /i/ is phonetically [+ATR], suggesting that /i/ lacks a phonological specification for [ATR].</Paragraph>
    <Paragraph position="9"> 4Zhang (1996) assumes privative features: [F] vs. the absence of [F], rather than [+F] vs. [ F]. The distinction between privative and binary features is not crucial to the matters under discussion here.</Paragraph>
    <Paragraph position="10"> b. / / triggers labial harmony, but /u/ and / / do not. Though phonetically [+labial], there is no evidence that /u/ and / / are specified for this feature.</Paragraph>
    <Paragraph position="11"> Acquiring phonological specifications is not the same as identifying phonetic features.</Paragraph>
    <Paragraph position="12"> Surface phonetics do not determine the phonological specifications of a segment. Manchu /i/ is phonetically [+ATR], but does not bear the feature phonologically; /u/ and / / are phonetically [+labial], but are not specified for that feature. How does a learner deduce phonological (contrastive) specifications from surface phonetics?5 It must be the case that phoneme acquisition requires learners to take into account phonological processes, and not just the local phonetics of individual segments (Dresher and van der Hulst, 1995). Thus, the phonological status of Manchu vowels is demonstrated most clearly by attending to the effects of the vowel on neighbouring segments.</Paragraph>
    <Paragraph position="13"> This conclusion is strengthened when we consider that the distinction between /u/ and /U/ in Classical Manchu is phonetically evident only after back consonants; elsewhere, they merge to [u]. To determine the underlying identity of a surface [u], therefore, a language learner must observe its patterning with other vowels: if it co-occurs with [+ATR] vowels, it is /u/; otherwise, it is /U/.</Paragraph>
    <Paragraph position="14"> The nonlocal and diverse character of the evidence bearing on the feature specifications of segments poses a challenge to learning models.</Paragraph>
    <Paragraph position="15"> Finally, let us consider the acquisition of the hierarchy of contrastive features in each language. Examples such as the acquisition of Dutch onsets given above appear to accord well with the notion of a learning path, whereby learners proceed to master individual feature contrasts in order. If this order were the same for all languages, then this 5Phonological contrasts that play a role in phonological representations are thus different from their phonetic manifestations, the subject of studies such as (Flemming, 1995).</Paragraph>
    <Paragraph position="16">  much would not have to be acquired. However, it appears that the feature hierarchies vary somewhat across languages (Dresher, 2003a, b). The existence of variation raises the question of how learners determine the order for their language. The problem is difficult, because establishing the correct ordering, as shown by the active contrasts in a language, appears to involve different kinds of potentially conflicting evidence. In the case of metrical parameters, the relevant evidence could be reduced to particular cues, or so it appears. Whether the setting of feature hierarchies can be parameterized in a similar way remains to be demonstrated.</Paragraph>
  </Section>
class="xml-element"></Paper>