EPENTHESIS in CHILDREN's CONSONANT CLUSTER PRODUCTIONS: a PERCEPTUAL and ACOUSTICAL STUDY by MARTA KELCEY EVESON B.Sc, the Unive
EPENTHESIS IN CHILDREN'S CONSONANT
CLUSTER PRODUCTIONS: A PERCEPTUAL
AND ACOUSTICAL STUDY
\ by
MARTA KELCEY EVESON
B.Sc, The University of Victoria, 1991
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE
in
THE FACULTY OF GRADUATE STUDIES
(School of Audiology and Speech Sciences)
We accept this thesis as conforming to the required standard
THE UNIVERSITY OF BRITISH COLUMBIA
April 1996
© Marta Kelcey Eveson, 1996 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.
Department of Aud^nq^ qp A ^Sy^fj^V) Soe^ceS
The University of British Columbia Vancouver, Canada
DE-6 (2/88) ABSTRACT
The purpose of the present study was to examine epenthesis in children's consonant cluster productions from phonological and phonetic perspectives. The following questions were investigated: (1) Do consonant clusters produced with an epenthetic vowel differ in duration from those without? (2) Is the epenthetic vowel in the consonant cluster consistent in length and quality, or do co-articulatory effects occur?
(3) Is the epenthetic vowel dependent in terms of duration on the phrasal context or the duration of the syllable nucleus? The subjects, S_i (Charles) and S2 (Blair), were two of six subjects in a doctoral research study investigating the application of a nonlinear phonological framework to the assessment and remediation of phonological disorders.
Consonant cluster data were transcribed from the original data. Acoustic measurements included the duration of consonant clusters with and without epenthesis and the duration of the epenthetic vowel. Results of the investigation show that consonant clusters with an epenthetic vowel are significantly longer in duration than those without. No coarticulatory effects were seen between the epenthetic vowel and the syllable nucleus suggesting that the epenthetic vowel is part of the consonant cluster unit which is governed by its own timing system. Prosodically, ^syllabification of the word occurs as a result of epenthesis in the consonant cluster. The implication of these results appears to be that the consonant cluster containing the epenthetic vowel needs to be considered as a separate timing unit and representationally attributed unitary status.
ii TABLE OF CONTENTS
ABSTRACT II
TABLE OF CONTENTS HI
LIST OF TABLES VI
LIST OF FIGURES VH
ACKNOWLEDGEMENT VIII
CHAPTER ONE INTRODUCTION 1
OVERVIEW 1
PHONOLOGY VERSUS PHONETICS 2 Phonology 3 Implications of phonological environment 4 Phonemes 4 Allophones 5 Phonetics 5
GENERAL IMPLICATIONS OF PHONOLOGICAL THEORY 6
NONLINEAR PHONOLOGY 7 Representation Versus Rules 7 Underlying Representation of Syllable Structure 8 Ffierarchical Representation of the Prosodic Tier 8 Theories of the Structure of the Prosodic Hierarchy 10 Tier Association 11 The Segmental Tier 11 Markedness 11 Developmental Implications of a Feature Hierarchy 12
CONSONANT CLUSTER DEVELOPMENT 13 Delay Versus Deviation 15 Pattern of Acquisition 16
IMPACT OF DIFFERENT METHODOLOGIES: UR VERSUS REALIZATIONS
iii UNDERLYING REPRESENTATION OF CONSONANT CLUSTERS 18
TEMPORAL CO-ORDINATION IN CONSONANT CLUSTER PRODUCTION 21
COARTICULATION 22
METHODOLOGICAL IMPLICATIONS 23
TIMING CONSTRAINTS 24 Duration and Temporal Variability 25
IMPLICATIONS OF THEORETICAL MODELS 26
MODELS OF LANGUAGE PROCESSING 27 Serial Model 27 Parallel Interactive Model 28 Theoretical Assumptions 28
SUMMARY 29
CHAPTER TWO METHOD 32
SUBJECTS 32 51 Summary 33 52 Summary 34
APPARATUS AND PROCEDURES 34
MEASUREMENTS 36 Measurement Reliability 38
CHAPTER THREE RESULTS AND DISCUSSION 40
SUMMARY OF RESULTS 41 Occurrence of Epenthesis 41 Consonant Cluster Duration 42 Epenthesis as a Strategy for Overcoming Timing Demands 44 Effect of Phonological Context on the Epenthetic Vowel 44 Coarticulatory Effects 45 Epenthetic Vowel Duration 46
IMPACT OF EPENTHESIS ON PROSODIC STRUCTURE 48 Representation of Consonant Clusters 48
iv APPLICATION OF NONLINEAR PHONOLOGICAL FRAMEWORK 50 Epenthesis in a Serial Model of Language Processing 51 Epenthesis in a Parallel Interactive Model 52
STUDY LIMITATIONS 54
FUTURE RESEARCH 55
CONCLUSION 56
REFERENCES 58
APPENDIX ONE SI DATA 62
APPENDIX TWO S2 DATA 67
v LIST OF TABLES
TABLE 1: Summary of Mam-Whitney test for difference in duration between consonant clusters without and with epenthesis 42
vi LIST OF FIGURES
FIGURE 1: Hierarchical representation of prosodic structure 9
FIGURE 2: Alternative representation of CV syllables in onset-rime
and moraic theories 10
FIGURE 3: Specified feature geometry for English 12
FIGURE 4: Representation of epenthesis and deletion processes 15 FIGURE 5: Duration of consonant clusters without and with epenthesis for Subjects 1 and 2 43
FIGURE 6: Relationship between syllable nucleus duration and epenthetic
vowel duration for Subjects 1 and 2 47
FIGURE 7: Representation of epenthesis in moraic and onset-rime theories" 49
FIGURE 8: Representation of ClVeC2 as one unit 49
vii ACKNOWLEDGEMENT
I would like to express my sincere gratitude to my supervisors, Dr. John H. V.
Gilbert and Dr. Barbara Bernhardt, for their guidance and patience as I have made my way through this process and for the large amount of time that they have spent reading and revising numerous copies of my drafts. Thank you for the encouragement when it was needed the most.
I would also like to thank my Mom and Dad for their endless support and encouragement throughout this endeavor. I could not have gotten to where I am without you. Special thanks need to go to my sister, Paige, for her statistical knowledge and help and for putting up with me during the final stages.
Lastly, I would like to acknowledge the support and encouragement of all my friends and colleagues. Thanks to Eva Major for her time, resources and crisis management skills (coffee and a sense of humour) as I neared the end. Special thanks to
NJG, MM, NT, ST, and CM as they were there along the way.
viii CHAPTER ONE
INTRODUCTION
OVERVIEW
When examining children's productions of initial consonant clusters it is frequently observed that correct production of clusters occurs at a late stage in phonological development. Factors such as timing and lack of neuromotor maturation contribute to a
child's difficulties in combining consonants into clusters. To overcome these difficulties
children use a variety of transformation processes. It has been reported (Ingram, 1976;
Stoel-Gammon and Dunn, 1985) that one of these processes, epenthesis, does not occur
as frequently as others (e.g. deletion of one consonant). Therefore, little attention has been paid to the effect of epenthesis on the consonant cluster unit. However, because
epenthesis affects timing of the word and the cluster unit itself, it raises questions with respect to representation and syllable structure. This paper will focus on epenthesis in
consonant cluster development from phonological and phonetic perspectives. To do this, it is necessary to discuss current theories of consonant cluster representation in the underlying phonology and to examine acoustic aspects of them. This paper will examine
how consonant clusters are represented using a nonlinear phonological framework. A
review of literature on consonant cluster development will provide the necessary
background information to discuss the relevant timing issues. In addition, two current
models of language processing (Serial Model, Garrett, 1994; Parallel Interactive Model,
Stemberger, 1985a and b) will be reviewed to examine how they might deal with the issue
1 of epenthesis and the relationship between the underlying representation and phonetic level
of these consonant clusters.
Children's consonant cluster productions have been examined at the surface or realization level. Detailed explanations exist of the varying processes (e.g. deletion of one
consonant, substitutions) that seem to occur before a child's consonant cluster productions match an adult model. However, very few studies have looked at consonant cluster
acquisition while considering the underlying representation level of a child's phonology. In recent years, emphasis has shifted to investigating child phonological development with respect to a specific phonological theory, allowing for the consideration of the relationship between the underlying phonology and the output (i.e. the surface level).
In one of the few studies which considered an underlying representation of a child's phonological system, Chin and Dinnsen (1992), using a two-level generative phonology framework, found that a systematic relationship could be described between adult representations and children's underlying representations as well as between children's underlying and phonetic representations of consonant clusters. Since then, more advanced versions of nonlinear frameworks have evolved which have been shown to account better for many phonological occurrences (Bernhardt, 1992). One major purpose of this paper is to examine the consonant cluster productions of two children using a current nonlinear phonology framework.
PHONOLOGY VERSUS PHONETICS
In the fieldo f speech/language pathology, it is the practice of many to distinguish between "phonological" disorders and "phonetic" disorders. This application of linguistics
2 to the fieldo f speech/language pathology has proven useful but has led to some confusion
and oversirnplification (Grunwell, 1985; Hewlett, 1985). Therefore, when differentiating between levels of analysis of speech production, it is necessary to define the concepts
discussed.
Phonology
In his discussion of the relationship between phonetics and phonology, Laver
(1994) outlined that the function of phonology is to relate the phonetic events of speech to
other areas such as the morphological, lexical, syntactic and semantic levels. Thus,
phonology is directly tied to phonetics. Laver states, "at the phonological level of
analysis, two utterances are held to be different if the phonetic differences between them
serve to identify the two utterances as representing different grammatical units of a given
language" (1994, p.30). Further to this, a phonological system can be defined as a set of
consonants which exist in potential distinctive opposition to each other. More simply,
phonology involves the manner in which speech sounds function to contrast or distinguish
different words (e.g. /p/ in 'pan' versus /k/ in 'can' versus Iml in 'man'), (Hewlett, 1985;
Laver, 1994). The presence or absence of such a contrast can be used as the criterion for
assigning a given sound to a specific phonological category. It is also frequently used as
the criterion for distinguishing between phonological and phonetic disorders. If a
phonological contrast is lost it is considered a phonological disorder, whereas if the
contrast is maintained, the disorder is phonetic or at least, lower-level (Hewlett, 1985).
Lower-level refers to a late occurring process as defined with respect to models of
language processing. Such models assume that language is composed of a hierarchical set
of interconnected levels of processes (Stemberger, 1985a; Stemberger, 1985b).
3 Implications of phonological environment
It is important, when examining the characteristics of mdividual phonological units,
to consider the specific phonological structure and phonological context in which the unit
is found. Phonological structure can be defined as the sequence of consonants
(represented as C) and vowels (represented as V) that constitute syllables and feet (e.g.
the structural formula for the word 'cup' > /kAp/ is CVC, or a strong monosyllabic foot
[see Figure 1]). This type of sequencing formula is commonly used to describe syllable
structure (Laver, 1994). Related to this, the phonological context refers to the actual
identity of the C's and Vs adjacent to the given phonological unit. The relevance of
considering phonological context lies in the influence that it exerts on the phonetic
realization of the individual phonological unit being examined.
Phonemes
In considering the notions of contrastiveness, structure, and context, it is important
to discuss a widely used phonological concept, the phoneme. Laver (1994) states that the
notion of the phoneme is based on the alphabetic tradition of writing and is not theoretically strict. In the simplest of terms, each individual segment represented in an underlying form is called a phoneme (Sloat, Taylor and Hoard, 1978). More explicitly,
two speech sounds are to be considered as different phonemes in a given language when they act in contrastive opposition to distinguish two words with identical phonological
structure. That is, in the context in question, the two speech sounds must exhibit parallel
distribution by having the potential to occupy the same place in a given phonological
structure and form a minimal pair (Laver, 1994).
4 Allophones
Each given phoneme can include a set of members called allophones. Two speech
sounds are classed as allophones of a specific phoneme if they are found to occur "in
complementary distribution, and if they display sufficient phonetic similarity to make it
plausible to class them together as members of a common set" (Laver, 1994, p.42). The
concept of an allophone is an abstract description and should not be confused with the
definition of a phone which will be discussed later.
In summary, a distinct phoneme is identified when a given speech sound occurs in
contrastive distribution to other speech sounds in words with identical phonological
structure. Different pronunciations of a speech sound which show phonetic similarity are
said to be allophones of a given phoneme when they are complementary in distribution and
their phonetic differences are a result of the phonological structure or environmental
context (Laver, 1994).
Phonetics
This then leads us to the area of phonetics. Whereas phonology deals with
underlying representations of individual units, phonetics deals with speech sounds as
physical entities (Hewlett, 1985). Phonetics is the description of the "learnable aspects of
use of the vocal apparatus" (Laver, 1994, p. 28). Individuals acquire the specific phonetic
behaviours common to the language in their environments in a social context. The
phonetic level of description is considered to be abstract. Therefore, a statement of
phonetic sameness is based on the comparison of abstract features, not acoustic identity.
This is based on the assumption that two different speakers should be capable of
producing phonetically identical utterances (although acoustically different). A speech
event which is considered phonetically equivalent between speakers is called a phone
5 (Laver, 1994). Phonetic description is theoretically held as independent of phonological description in that knowledge of the linguistic value that the speech event may have as a communicative element in a given language is not required. A phonetic "distortion" occurs when the underlying representation is correct but the phoneme is incorrectly realized. For example, if a person is trying to produce the word 'gum' (/gAm/), the fg/ could be "distorted" as a result of loss of some of its voicing during actual articulation. In the most extreme case /g/ may be retrieved from storage but the loss of voicing is complete and /g/ is produced as Ikl (Hewlett, 1985).
GENERAL IMPLICATIONS OF PHONOLOGICAL THEORY
In the past, the assessment and intervention of speech disorders was strictly constrained to description at the phonetic level (Grunwell, 1985). In the past 25 years, researchers have presented different theories of phonology and have applied them in the assessment and intervention of speech disorders (Edwards and Shriberg, 1983; Hewlett,
1985; Bernhardt, 1992). The application of phonological theory has had direct impact on the fieldo f speech/language pathology by allowing generalizations and descriptions to be made about a child's speech output with reference to an underlying phonological system.
Nonlinear phonological frameworks have been shown capable of describing and explaining observed phonological events of a given language (Bernhardt, 1992).
6 NONLINEAR PHONOLOGY
Major purposes of this paper are to examine epenthetic vowel insertion in consonant cluster productions from phonetic and phonological (nonlinear) perspectives. It is necessary to outline first the major aspects of nonlinear phonology. (For a more complete overview of nonlinear phonology, please refer to Bernhardt, 1992.)
Nonlinear phonology has risen from generative phonology and is based on many of the same tenets (Bernhardt, 1992). Two main assumptions of generative phonology which also act as the basis of a nonlinear phonological theory are as follows:
1. Each linguistic component, although interactive for language processing, can
be studied as an independent system.
2. Within a linguistic component, there exists an 'unmarked' versus 'marked'
parameter option where it is usually assumed that the 'unmarked' value of a
variable is the one available innately from the 'universal grammar' (UG).
Representation Versus Rules
One major difference between nonlinear and classical generative phonology is the
emphasis that nonlinear phonology places on representation. As a result, within a nonlinear phonological framework, rules and processes become more limited and generalized. Rather than being sequential, as in classical generative phonology, the nonlinear representation is multi-tiered and involves prosodic information. The limited set
of phonological rules or processes results fromassociatio n between the separate tiers and is restricted in function. Phonological processes either add content, through information linking ('spreading') or 'insertion' of new information, or subtract content, through information delinking between domains.
7 Traditionally, as a child's phonological system develops, comparisons are made with an adult system. Any differences between the child and adult systems have been described in terms of rules and processes. Bernhardt (1992) outlines two basic theoretical weaknesses with this approach:
1. It may suggest more 'neurological activity" than is actually happening.
2. It explains acquisition in terms of a negative 'progression' whereby the child has
to learn to undo a specific process (e.g. un-front or un-delete).
If it is assumed that children have an intact representational framework which acts more as a passive 'filter' when they begin to learn language, as it might be assumed with nonlinear phonology, phonological development can be seen more as a building process.
If the information from the adult form matches the child's present perceptual and production level, it will pass through and be accepted. Any mismatched information will be ignored until the child's system matures and incorporates it or until the mismatched information is received enough times to cause recognition and change (Bernhardt, 1992).
Underlying Representation of Syllable Structure
In addition to assuming that a child comes to the language learning process with an underlying segmental feature inventory, a nonlinear phonological approach assumes that the child also comes with an expected underlying framework for syllable structure. Thus, although parameters need to be set for both features and for syllable structure, tier autonomy implies independence in phonological learning for each tier.
Hierarchical Representation of the Prosodic Tier
In a nonlinear framework,representatio n occurs as a hierarchically linked set of tiers rather than as a sequential string with little internal structure (Chin and Dinnsen,
8 1992). Therefore, prominent units of the system dominate other more embedded units. In looking at the prosodic level, the word dominates feet which in turn dominate syllables
(see Figure 1). By incorporating prosodic information in the hierarchical representations, several differing conditions can be accounted for including stress patterns, segmental processes involving feature-spreading, and the phonotactics of a language (Bernhardt,
1992). This then implies developmentally, that if a child comes to the language learning process with a determined underlying phonological framework, that child also comes with an expected prosodic structure.
WORD (CV.CV)
FOOT
ONSET RIME ONSET RIME
C V C V
Figure 1: Hierarchical Representation of Prosodic Structure
9 Theories of the Structure of the Prosodic Hierarchy
Two major theories of the structure of the prosodic hierarchy are onset-rime theory and moraic theory. With onset-rime theory, in the hierarchical structure, the onset node (O) dominates the prevocalic consonants and the rime (R) dominates the nucleus (N)
(see Figure 2). The nucleus is a node which dominates the most sonorant segment
(usually a V). As the hierarchy is represented with a branching tree structure, more complex syllable shapes (e.g. those containing consonant clusters) have more branches. In addition to complexity being related to branching, in many languages, stress assignment is related to branching in the rime (Bernhardt, 1992).
In moraic theory, it is suggested that prosodic 'weight units' or 'morae' (M) are the important components of syllables for stress assignment. Moras are realized through vowels (see Figure 2). Prevocalic and postvocalic consonants not contributing to syllable weight are adjoined to the mora or syllable node and have no particular structural function. Moras combine together to form syllables, (usually a maximum of two moras per syllable), which are grouped into feet. In moraic theory, onsets by representation do not affect stress assignment whereas in onset-rime theory, onsets although branching, by stipulation are assumed not to attract stress (Bernhardt, 1992).
O R a
N M
V C V
Onset-rime Moraic
Figure 2: Alternative representations of CV syllables in onset-rime and moraic theories.
10 Tier Association
Although tier autonomy allows for independent phonological learning at the prosodic level, the prosodic tier is linked to the segmental tier. Linking of tiers occurs according to principles of association (Bernhardt, 1992). Bernhardt and Stemberger (in preparation), state that association lines can be present in the underlying representation, created by a mapping rule, or added by an assimilation rule.
The Segmental Tier
By representing segments as geometrically organized sets of features, a single feature in a dominating node can be shown as affecting other segments within a set domain. Each feature is autonomous (i.e. on its own tier), but can be influenced by its dominating features (see Figure 3). The dominating node may only influence neighbouring segments, or may involve the entire word (Bernhardt, 1992; Chin and
Dinnsen, 1992). Segments exist as distinct phonological entities but in reality, are co- articulated to such an extent that information from several phonological segments is perceived at any given time (Bernhardt and Stemberger, in preparation).
Markedness
A hierarchical representation of features also allows for the notion of markedness
('unmarked' versus 'marked' features) in that higher level or dominating features could be seen as being more 'marked' than lower level, deeply embedded features (Bernhardt,
1992). Different proposals exist as to a set of universal features and their relative markedness.
11 ROOT
LARYNGEAL
[+voice] [+spread glottis]
PLACE
LABIAL CORONAL DORSAL
[+distributed] [-anterior]
Figure 3: Specified feature geometry for English
Developmental Implications of a Feature Hierarchy
The developmental implications of this type of a feature hierarchy include the notion of developmental progression. Features which appear more deeply embedded may appear later developmentally that those features which are found higher in the hierarchy
(Bernhardt, 1992).
12 CONSONANT CLUSTER DEVELOPMENT
As stated earlier, the main objective of this paper is to look at the development of consonant clusters in child phonology with reference to the nonlinear phonology framework just outlined. More specifically, epenthetic vowel insertion in consonant clusters will be examined. Therefore, it is now necessary to review what is known about consonant cluster development.
One of the major controversies that still exists among researchers interested in the study of phonology is the twofold issue of how children acquire the necessary phonemes of their language and how they learn to combine these sound segments into speech.
Children do not simply need to learn the specified features of their language. They are also required to learn the complex patterns of sound combinations for their language.
Research shows that this process begins with children's earliest babblings of a labial consonant plus a vowel (e.g. /ba/) and continues until approximately the age of six when children finally become adept at producing word-final consonant clusters (Stoel-Gammon and Cooper, 1984; Stoel-Gammon and Dunn, 1985).
As discussed earlier, one major difference between nonlinear and classical generative phonology is that nonlinear phonology places emphasis on representation, thus limiting the number of rules and processes that need to be applied. However, many prior studies into consonant cluster development used a process or rules-based approach.
Therefore, to look at the findingso f these studies, it is necessary to discuss the types of processes to which they refer. Regardless of the chosen theory, it has been recognized that children use phonological strategies to help them organize and simplify the processes of acquiring and combining speech sounds, especially with consonant clusters. It is also evident that children exhibit great variability in the use of these processes and strategies.
13 There are three general categories into which these processes can be grouped: syllabic structure processes, substitution processes and assimilation processes. Syllabic structure processes involve modification of the syllable structure of the target word by means such as deleting an unstressed syllable (e.g. "telephone" /tolafoun/ > /telfoun/), final consonant deletion, or cluster reduction. Substitution processes allow for the replacement of one sound with another that the child has already mastered (e.g. using a stop /p/ for a fricative
/f/). Assimilation processes are identified as occurring when one sound becomes more similar to another (e.g. fronting: "cat" /kaet/ > /taet/) (Roach, 1983; Stoel-Gammon and
Dunn, 1985). It is important to note that there is large individual variation in the use of such strategies and processes as well as in their outcomes. While some children may never use a certain strategy, others may rely solely on that same strategy and apply it to all utterances that they produce. In addition, target words can be affected by different processes simultaneously which can account for some of the odd productions made by children (e.g. /kik/ for "stick" involves consonant cluster reduction and assimilation).
Children usually do not apply these strategies or processes randomly. Rather, each child has an internal system or filter which helps them to work towards adult-like speech sound combinations. According to Stemberger (1985a) a given rule is represented in two parts:
1) a structural condition, a pattern governing where the rule applies, and 2) a structural change, a pattern signifying what changes occur to the underlying representation. Each rule is filtered through to see if the information matches with the child's current representation. As stated earlier, according to nonlinear phonology, any mismatched information will simply be ignored until the child's system is ready to incorporate it
(Bernhardt, 1992). Figure 4 illustrates an example of how representationally the effect of different processes on syllable structure can be shown.
14 Adult Epenthesis Deletion Representation
onset onset nucleus onset onset A
C C Ve C C
t r tar
Figure 4: Representation of epenthesis and deletion processes
Delay Versus Deviation
When examining child speech, it is necessary to have a thorough understanding of the basic sound modification possibilities. Understanding these basic processes has led to the reanalysis of the nature of functional (i.e. nonorganic in nature) speech disorders
(Ingram, 1976; Dinnsen, Chin, Elbert and Powell, 1990). In examining data from children with functional speech disorders, it is necessary to consider the properties of such disordered systems. If it is accepted that functional speech disorders represent a delay in speech acquisition, then the information gained can also be applied to normal language development. However, if functional speech disorders represent a deviation from the normal pattern of acquisition, the information cannot be applied in the same manner.
In an attempt to clarify this issue, Dinnsen, Chin, Elbert, and Powell (1990) looked at the phonological systems of 40 children with functional speech disorders and identified the different properties and constraints which appeared to be acting. One of the
15 difficulties with this type of characterization is that although there are fundamental acquisition processes which occur, as mentioned earlier, there also appear to be widespread individual differences in the properties and in the specific order of the normal acquisition of the different speech sounds. For the purpose of their study, a variety of language tests were administered to each child and a single-word spontaneous speech sample was elicited. According to the researchers, analyses indicated that the properties of the speech systems of the children with functional speech disorders closely paralleled the principles applied during normal language acquisition. Therefore, it would seem that these speech disorders could be classified as delays rather than deviations: the children with phonological disorders appeared to be using the same processes as the children with
'normal' speech but applying them at a different rate.
Pattern of Acquisition
Although children use a variety of different processes in learning speech, a general pattern of sound acquisition can still be outlined. Furthermore, a general pattern of acquisition can be described within individual speech sound categories. For example, children tend to acquire front stops before back ones (labials and alveolars before velars).
As stated earlier, children firstbegi n producing words by combining these early acquired consonants with vowels in a simple CV syllabic shape. As they acquire more phonemes, the variety of syllabic shapes that they are able to produce concurrently increases.
However, there is much evidence to support the claim that children do not seem to be able to combine consonants in the form of a consonant cluster (as required for a more complex
CCV syllabic unit) until quite late. Even if a child has mastered the two single phonemes, it cannot be assumed that s/he will be able to combine them to produce the form of a consonant cluster. Templin (1957) found that children did not produce initial consonant
16 clusters correctly until approximately age 4. She claimed that final nasal clusters were mastered at the same time but [liquid + stop], [liquid + fricative], and [fricative + stop] clusters in final position did not appear until between the ages of 6 and 7. At this stage, phonological development is very transitional. Much of the child's early development is set and the use of processes begins to occur less frequently (Ingram, 1976).
IMPACT OF DIFFERENT METHODOLOGIES: UR VERSUS REALIZATION
Although early research has provided some answers about the acquisition of consonant clusters into children's phonologies, there are still many questions to be answered. Two different approaches have been taken in studying consonant clusters: 1) from the perspective of normal, non-disordered acquisition, and 2) within the scope of treatment studies with speech-disordered children. Chin and Dinnsen (1990) point out that although different, both approaches mainly focus solely on the realization level. Thus, the representational level, or the underlying segment representation, has not been thoroughly investigated, especially with regard to a specific theoretical framework.
"There seems to be no principled, structural explanation available of why target clusters come out the way they do in children's productions, either normal or disordered" (Chin and Dinnsen, 1990, p.2).
17 UNDERLYING REPRESENTATION OF CONSONANT CLUSTERS
In the few earlier studies done which examine children's underlying representation
of clusters, it has been hypothesized that clusters may first be represented in children's
repertoire as a single unit which later is separated into its distinct components. This
hypothesis has been supported by acoustic evidence reported by Menyuk (1972), which
indicated that consonant clusters may be represented as a single consonant in some
children's underlying phonology. Further evidence can be found in a study conducted by
Barton, Miller, and Macken (1980), in which 24 children between the ages of 4;0 and 5;0
completed three experimental tasks which examined their ability to segment initial
consonant clusters into distinct phones. The data support the theory that children treat
clusters as a single phonological unit before they are capable of distmguishing separate
segments. As children acquire the metalinguistic skills (i.e. the explicit awareness and
understanding of language forms or structures) necessary to separate a sound into its
distinct phoneme components, different processes, such as deletion of one component, or
weakening or substitution of one consonant in the cluster are seen in their cluster
realizations. Other processes such as apparent epenthesis (inserting a vowel or consonant)
or apparent metathesis (a reversal of adjacent segments) are also seen although most
researchers claim that they are much more uncommon (Ingram, 1976; Stoel-Gammon and
Dunn, 1985).
Other researchers (Stemberger and Treiman, 1986) have upheld the claim that
children use specific strategies as evidence that consonant clusters are not first represented
as a single unit. They believe that the fact that a child uses epenthesis may support the hypothesis that both consonants are represented. Furthermore, although children often use reduction to avoid producing the actual consonant cluster, a general pattern of
18 deletion does exist (/s/ deletion in /s/-clusters and liquid deletion in liquid clusters) and is somewhat predictable, depending on the target cluster. The one-unit stage, hypothesized by Greenlee (1974), can be viewed as a lower-level application of the process of reduction on a two-element adult-like underlying representation (Chin and Dinnsen, 1992).
In support of this notion that children have a two-element underlying representation for consonant clusters, some researchers (Menyuk and Klatt, 1975;
Kornfeld, 1976) claim that although in early stages of cluster acquisition adults perceive children's consonant clusters as a singleton consonant, these children are making acoustic distinctions between singleton consonants and clusters. It has been suggested that in the early stages of cluster development, specific consonants (i.e. phonemes) may be less accessible to children for their consonant cluster productions, even though both consonant slots are present in the underlying representation (Stemberger and Treiman, 1986).
Stemberger and Treiman (1986) looked at whether word-initial consonants are more accessible, by examining loss, addition and substitution errors made in cluster productions, occurring naturally and induced experimentally. Both sets of data indicated that the position of a consonant in an initial cluster affects the rate of error occurrence. For example, for addition, shift and loss errors, far more errors occur involving C2 than CI.
Stemberger and Treiman state that to account for their data, CI and C2 must be present in the underlying representation but are represented differently, with CI having a greater level of activation. Additional evidence supporting the hypothesis that both consonants are represented in the underlying representation is that, in speech errors, consonant clusters do not act like single phonemes. Rather, individual segments are affected
(Stemberger and Treiman, 1986).
As stated above, even after children are able to differentiate perceptually between the component parts of a consonant cluster, their cluster realizations may not accurately
19 reflect this knowledge. Research has shown that although children are able to perceive and produce acoustic distinctions between single consonants and consonant clusters reliably, these differences are not necessarily noticed by adult listeners. Evidence supporting the claim that children make acoustic distinctions between a consonant as a singleton and in a cluster can be seen when studying voice onset time (VOT) characteristics. Menyuk and Klatt (1975) examined spectrograms of words in isolation and in sentences produced by eleven children and two adults and measured VOT. The results showed that when the average VOT of singleton stops and stops in clusters were compared, the VOT values were longer for stops in clusters for both children and adults.
Menyuk and Klatt noted that even though the VOT values of stops produced by the children did not match those of the adults, few of the children's cluster productions were perceived as incorrect in the sentence context. SHghtly more of the consonants in the children's consonant cluster productions were perceived as incorrect when produced in isolation. The most common errors involved the incorrect production of a liquid in a cluster and substitutions of stops in clusters. Another error which was noted involved the introduction of a schwa between the consonants in [stop + liquid] clusters. This epenthesis occurred most frequently with labial and dental stops and occasionally with velar stops. According to Kornfeld (1976), these findings theoretically suggest that children may use principles different from adults for classifying and representing their underlying phonology. In other words, children may be responding to different acoustic cues and relying more on phonetic information for speech recognition than adults do.
Evidence to support this can be seen in that children, both normal and language disordered, can produce a consonant correctly as a singleton but distort it in the context of a reduced consonant cluster. Furthermore, children frequently can differentiate more
20 phonetic contrasts than they can produce, and will not accept adult imitations of then- productions as correct (Kornfeld, 1976).
TEMPORAL CO-ORDINATION IN CONSONANT CLUSTER PRODUCTION
Further to Menyuk and Klatt's (1975) study, Gilbert and Purves (1977) examined several hypotheses regarding the development of temporal coordination involved in the production of consonant clusters. Typically most research that has looked into temporal organization in children's speech has narrowly focused on variability in durations.
Comparatively, the main issue in studies of temporal organization of adult speech has been to identify what triggers the initiation of speech gestures. The question that has been asked is, is speech sound initiation governed by a higher level timing programme over a given unit or is each individual phone produced separately, i.e. does the completion of one phone trigger the production of the next. In exarnining this issue, Kozhevnikov and
Chistovich (1965) concluded that some type of higher order timing programme seems to be in effect. According to Ohala (1970), this is the result of a timing dominant system, which he distinguished from an articulation dominant system. In a tirning dominant system, the speaker must perform the necessary specified articulatory gestures within a limited and rigid time requirement. In contrast, in an articulatory dominant system, cluster production is governed by a chain reaction of articulatory gestures.
Evidence supporting an articulation dominant system can be found by examining the results of coarticulation studies. Coarticulation is defined as the influence of one speech segment upon a neighbouring segment (Daniloff and Hammarberg, 1973).
Although it is assumed that at some level, for example, in the underlying representation, speech sounds exist in invariant uncoarticulated forms, in running speech, sounds seem to overlap and there is a "spreading of features." It has been hypothesized that the uncoarticulated forms in the underlying representation are encoded when entered into the articulatory mechanism. However, controversy exists because it is impossible to identify the encoding unit and the contribution of the encoding mechanism. The question also arises whether coarticulation is a deliberately applied process or whether it is a result of the articulatory mechanism. Ohman's (1967) study of the coarticulation of [+voiced] stops in VCV type utterances provides evidence which is suggestive of some degree of articulatory preprograrmning. Some degree of preparation for the following speech gesture appeared to occur simultaneously with production of the preceding segment.
Peterson and Lehiste (1960) examined the influence of preceding and following consonants on the duration of stressed vowel and diphthongs. They point out that changes in the duration of a sound may be related to or determined by the linguistic environment. These durational changes may become cues for the identification of associated phonemes (i.e. the preceding or following segmental sounds). Peterson and
Lehiste determined that the influence of an initial consonant on the syllable nucleus duration appeared negligible. Rather, the duration of the syllable nucleus was significantly affected by the nature of the following consonants. As Peterson and Lehiste only used words containing a singleton word-initial consonant, direct conclusions cannot be made
22 about consonant clusters. However, the study raises the idea that if it is the following consonant that has the effect on the duration of the syllable nucleus, the consonant cluster unit may be separate from the word in its timing. In addition, if the syllable nucleus is subject to anticipatory lengthening, can this also be expected in the epenthetic vowel?
Ohala (1970) does not completely support the notion of an exclusive tirning dominant system. Rather, he proposed that a co-occurrence of the two systems could exist with each operating on separate levels. Allen (1973) furthered this idea by proposing a model which involves the notion of three separate factors interacting to deteirnine the phonetic duration of a given segment. The three factors he outlined are: 1) the speaker's intended speech rate; 2) the underlying phonological length of the segment; and 3) the peripheral effects of transmission time. According to Purves (1976), although Allen's
(1973) model "clarifies the role of various factors in determining segment durations, it does not provide any information about the way in which speech gestures may be integrated into higher-level units with a cohesive temporal program" (p. 10).
In summary, the phenomenon of coarticulation and the process of consonant cluster reduction are upheld as evidence of preprograrriming of higher level temporally organized speech units. It is also accepted that many factors such as speech rate and the nature of the underlying segment and its neighbouring segments interact to determine the produced duration of a given segment within an utterance.
METHODOLOGICAL IMPLICATIONS
However, Purves(1976) notes that different methodological approaches can be suggestive of differing results and need to be further evaluated before stronger claims can
23 be made. A primary example can be found in the fact that differences in durational aspects of clusters can be seen by examining results from child data rather than adult data.
Hawkins (1973) found that children tend to lengthen fricatives in the CI position of a cluster. Furthermore, in child speech, Is/ + stop + prevocalic Ixl clusters were lengthened.
The data indicated that specific aspects of the timing relationship within a cluster differ fairly consistently between children's and adults' speech. Hawkins (1973) suggests these differences may reflect specific articulatory difficulties on the part of the children.
However, she does note that specific methodological aspects also need to be taken into consideration. Primarily, a consistent criterion for the segmentation of an acoustic waveform needs to be determined.
If the durational differences discussed by Hawkins (1973) were significant, it could be concluded that the control of segmental duration in clusters is mastered over time. In support of this, Tingley and Allen (1974) examined the extent to which control of timing improves over time and found that timing accuracy increased with age. This finding is consistent with the fact that a child's motor skill development continues to improve as the child grows older.
TIMING CONSTRAINTS
According to Gilbert and Purves (1977), findings which suggest that children's timing control may be less accurate than that of adults', could also indicate the presence of timing constraints in child speech production. Many different factors, including the effects of surrounding phonological segments, are involved in controlling duration of given speech segments and need to be taken into consideration. The results of the Gilbert and
24 Purves (1977) experiment indicated that consonant cluster productions of young children can be differentiated from those of older children and adults on the basis of absolute duration of consonants. In addition, it was found that children use strategies of reduction and sphtting (schwa insertion) during the acquisition of consonant clusters. They suggest that the splitting process may be a means for a child to overcome rigid timing demands and to attempt to match the adult model. That is, during the earlier stages of consonant cluster acquisition, the child's timing control has not yet sufficiently developed to allow the correct production of both consonants within the restricted time frame. Thus, at first, the child omits specific features and produces reduced consonant clusters. Then later, the child establishes an individual timing system and applies the process of sphtting where segmentation allows for the individual phonemes to be accurately articulated. Over time, the child's consonant cluster productions become more refined and the overall absolute duration becomes less until eventually it matches that of adult speakers. This description of how children overcome timing constraints to approximate consonant clusters is suggestive of more frequent use of epenthesis than most studies report. This may be the result of the epenthetic vowel being considered as part of the following consonant and measured as such.
Duration and Temporal Variability
As noted from the above studies, it is generally accepted that duration and temporal variability tend to decrease as children grow older and become better speakers.
Researchers are interested in these two parameters because they are generally viewed as indicators of neuromotor maturation of speech skills. As there is an observed tendency for duration and variability to decrease with increased age, many researchers assume that these two measures are closely related. However, Smith, Sugarman and Long (1983)
25 observed that although children speaking at an increased rate had durations similar to adults, variability was still greater. The question arises whether these two measures can be viewed as separate indicators of neuromotor maturation or whether variability is a by• product of duration. In an attempt to address this, Smith (1992) examined temporal data from children ranging between 2;6 and 9;6 and found that duration and variability were not closely correlated. Thus similar conclusions cannot be drawn about speech motor control. Therefore, it is necessary to consider carefully which variable is being discussed when examining children's speech productions. Smith concluded that it can generally be assumed that duration and variability will decrease with increased age but that conclusions cannot be made as to how these measures pertain to mdividual children. Duration and variability do not appear to be congruent indicators of individual speech maturation. From
Smith's data, it appears that measures of duration become more adult-like earlier than measures of variability. Smith also noted that his results indicated that variability should not be considered a function of duration. He suggested that one of the measures (perhaps duration) may be a better reflection of lower-level articulation skills whereas variability may be associated more with higher-level organizational skills.
IMPLICATIONS OF THEORETICAL MODELS
Although different theories exist, it is clear that the exact relationship between children's early consonant cluster productions and those of adults is still not completely understood. There is no convincing explanation detailing the process and stages by which children learn to coordinate consonants into clusters. This is complicated by the fact that concrete and accurate knowledge regarding the nature of the underlying representation of
26 the phonological system is not available. Different methodologies lend themselves to distinct theories and measures of the processes or levels that are applied to the underlying representation before it is perceived by a listener. That is, without an existing model of the nature of the underlying representation, it is virtually impossible to measure the effect of the hypothesized processing levels.
MODELS OF LANGUAGE PROCESSING
Serial Model
One current model of language processing is Garrett's (1980, 1984) model which consists of three distinct processing levels: a message level, a linguistic sentence level
(consisting of functional, positional and phonetic levels of representation) and a motor articulatory level. If the different processing levels are serial and are affected separately, as Garrett suggests, then it would be possible to hypothesize that differences in the breakdown of speech may also be seen. In this model, the message level is where the general concept is first processed into an approximate sentence construction. Then at the sentence level, the general concept undergoes the application of logical and phonological rules and is represented with specific linguistic structures. That is, the phonological form of the lexical item is retrieved. Finally, at the articulatory level, the initial representation of the signal undergoes phonetic and prosodic encoding and is then translated into the correct instructions necessary for articulatory sequencing. This is the finaloutpu t form.
There has been some criticism of Garrett's proposed model, however, because of its rigid linear nature. Some researchers claim that although there do seem to be different levels involved in the encoding and processing of language, they do not act entirely
27 independently of each other. Rather, the possibility of interaction exists between levels of processing.
Parallel Interactive Model
In a parallel interactive model "several levels of the language system are being processed at a given moment and are interacting" (Stemberger, 1985b, p. 148). A speaker accesses language production when an intent to speak is formulated and pragmatic and semantic information leads to the partial activation of all words that represent that irrformation. The activation of these units causes a cascade of activation to all associated units. In addition, lower-level units that are associated, such as phonemes, are also activated. Lower-level activation then spreads back up to cause activation of other words with those particular phonemes. Eventually, the word that is most highly activated will be articulated (Stemberger, 1985a; Stemberger, 1985b). Any given unit is not considered to be on or off but rather, on a continuum of activation. The unit's activation threshold needs to be exceeded for it to be selected. According to Bates and MacWhinney (1989), this type of competition model assumes the dynamic control of the mapping of form onto function for comprehension and of function onto form for production. It is not to be assumed the relationship between form and function is one to one. Rather, it is a many to many relationship. It is understood that this mapping is governed by parallel activation with strength level resolution.
Theoretical Assumptions
For this paper, the premise was made that children typically have a two-element adult-like underlying representation of consonant clusters as discussed by Chin and
Dinnsen (1992). Therefore, any discrepancies between the child's production of a
28 consonant cluster and the adult version can be explained as the application of transformation processes at lower levels. For example, as outlined earlier, the one- element stage in consonant cluster production would be viewed as a lower-level application of a reduction process on the two-element underlying representation. In
Garrett's model, this would occur at the articulatory level. In an interactionist model, the reduction process could occur at different points, although it would still be a lower-level application.
In summary, this uncertainty about the underlying representation is only one of many unanswered questions about consonant cluster development. There is no concrete explanation about the relationship between the underlying representation and the output and why the different stages of consonant cluster development occur. It is accepted that timing constraints and neuromotor maturation may play a role. However, even this idea is complicated by the fact that the measures of duration and variability are not correlated.
As stated earlier, it is unclear how these two measures are related and how they pertain to individual children.
SUMMARY
Although children seem to follow a normal developmental sequence in the acquisition of consonant clusters, it is known that as a result of such factors as timing and lack of neuromotor maturation, children have difficulty combining consonants into clusters. To help deal with these difficulties, they often use a variety of transformation processes. However, not all children use the same processes in mastering consonant cluster production. Some researchers claim that one of these processes, sphtting or
29 insertion of an epenthetic vowel, does not seem to occur as frequently as the other processes discussed (e.g. reduction, assimilation) (Ingram, 1976; Stoel-Gammon and
Dunn, 1985). However, in an intervention study performed by Bernhardt (1990), epenthetic vowel insertion was seen in consonant cluster productions of four of six subjects. The objective of this paper is to examine the consonant cluster productions of two of these subjects and compare the clusters with and without an epenthetic vowel in order to determine further information about phonology and phonetics of cluster development. The following questions will be investigated:
1. Do consonant clusters with an epenthetic vowel differ in duration than those
without? This is related to the issue of timing constraints: if as Gilbert and
Purves (1977) suggest, epenthesis is a means of overcoming the tirning
demands of consonant cluster production, clusters without an epenthetic vowel
should be shorter in duration.
2. In consonant clusters with an epenthetic vowel, is the epenthetic vowel
consistent in length and quality or is it affected by the surrounding consonants
of the cluster? In other words, is the epenthetic vowel a constant or are there
coarticulafion effects?
3. Where an epenthetic vowel exists within a consonant cluster, is it dependent in
terms of length on the phrasal context or the duration of the syllable nucleus?
If such outside factors influence the epenthetic vowel, then the epenthesis
needs to occur at a higher processing level because these factors are
determined prior to the final articulatory level.
Whether epenthetic vowel insertion is a late or low-level process will also be discussed. It is proposed that children have an existing adult-like underlying representation of consonant clusters which is altered by the application of a lower-level
30 process. Following the theoretical models outlined earlier, the last level of transformation of the underlying representation would be the pronunciation of the consonant cluster. If children were purely having articulatory difficulty in producing consonant clusters, it would seem that epenthesis would occur frequently. For instance, adult speakers of languages which prohibit initial consonant clusters often insert an epenthetic vowel between adjacent consonants of clusters in their second language or in 'borrowed' words from languages with clusters, even though they perceive and spell it as a cluster (Greenlee,
1974). This therefore raises the question of whether or not the epenthetic vowel is part of the consonant cluster itself (i.e. does the consonant cluster have its own timing rules independent of the word) or whether it is a separate entity. In an attempt to look at some of these issues, the focus of this paper will be restricted to epenthesis in consonant clusters and how it relates to timing issues. The nonlinear phonology framework outlined will be used to discuss the theoretical underlying representation. The relationship between the underlying representation and the output will also be examined with reference to the language processing models discussed.
31 CHAPTER TWO
METHOD
In order to examine epenthetic vowel insertion in children's consonant cluster productions, consonant cluster data produced by two children in Bernhardt's (1990) study were examined acoustically.
SUBJECTS
For this study, consonant cluster data were examined from Sl (Charles) and S2
(Blair) from Bernhardt's (1990) study of six children with phonological disorders. In the original study, all subjects were children who had moderately severe or severe phonological disorders. Criteria for inclusion were as follows: 1) Subjects were between the ages of 3 and 7 years. 2) English was the only input language. 3) There was an absence of any other major impairment excluding a language production disorder, mild impairment of language comprehension, cognition, or motor development, or controlled otitis media. 4) Parents participated over the course of therapy. The subjects took part in therapy sessions three times per week for 18 weeks. An initial assessment consisted of an audio-recorded phonological and language sample, a battery of standardized tests of language comprehension and production (Preschool Language Scale. Revised
(Zimmerman et al., 1979), Peabody Picture Vocabulary Test. Revised. Form M (Dunn and
Dunn, 1981)), a hearing screening, oral mechanism examination and case history.
32 SI Summary
Over the period of the original study, SI was 5;10 to 6;4. During the initial assessment it was noted that he had a tongue thrust during speech and swallowing, and a finger sucking habit. SJ_ also had mild phonemic discrimination difficulties. SJ_ had received varying dialectal input as a result of differences in parental dialect (Mother -
English, Father - Australian) and changing residency (Vancouver and Australia). S_l was the middle of three boys, with the youngest having a mild phonological disorder. Hearing was screened within normal limits at the beginning of the original project.
SI was initially assessed at the age of 2;9 for phonological difficulties. He received intermittent therapy in Vancouver and Australia between the ages of 2;9 and 5;0.
Consonant clusters were not targeted during this time. At the beginning of Bernhardt's
(1990) study, SI evidenced frequent consonant cluster reduction. As word length increased, the frequency of reduction increased. Consonant cluster matches for 'skeletal slots' ranged from 42% for monosyllabic words to 0% for four syllable words. In cases where a cluster match occurred for 'skeletal slots' for word-initial consonant clusters, no segment matches were recorded for both consonants (i.e. there were no instances where both phones were produced correctly). In several instances where two consonant elements were realized (in terms of skeletal slots), an epenthetic vowel was transcribed.
33 S2 Summary
During the original study, S2 was 4;2 to 4;6 years of age. Facts associated with his phonological disorder include: 1) a history of chronic otitis media from age 1 year with a myringotomy for "glue ear" three months before the study (Hearing was screened regularly throughout the study and was consistently found to be within normal limits.), 2) a mild language production delay evidenced by copula/auxiliary BE omissions, pronominal case errors and sibilant morphophonemes, and 3) a mild attention deficit which was possibly related to his middle ear history.
S2 had partaken in three months of a group articulation therapy program prior to the study. The main goal of these sessions had been stimulation of fricatives.
During the initial assessment for Bernhardt's (1990) study, S2's consonant cluster development was not yet established at the syllabic level. Most consonant clusters were realized as one element only. Those clusters produced with two elements in syllable initial position included reduced or full epenthetic vowels.
APPARATUS AND PROCEDURES
For the original study, the children underwent an initial assessment protocol, outlined above. The experimenter (E) used a standard set of objects and pictures as stimuli for phonological sampling. Most responses were spontaneous single-word elicitations. General conversation was also recorded during the session to provide other words, some in connected speech contexts. Sarnpling probes were administered at the end of each of the three six-week therapy cycles. The subjects' responses were recorded using
34 a Nagra IV reel-to-reel tape recorder and Ampex 631 tapes with an AKG D202 microphone in a speech/language therapy clinic.
The assessment and major probes were then transcribed phonetically (International
Phonetic Alphabet, 1979, plus diacritics) and orthographically by Bernhardt using a Revox taperecorder and Videoconcepts F700 dynamic earphones.
For this study, the experimenter (E) transcribed stimulus words containing consonant clusters from the original data of SI and S2. For SI, data was used from probes administered at ages 5;10, 6;0, 6;2, and 6;4. Probes for S2 were administered at the ages 4;2, 4;4, 4;6, and 4;9. Transcription was done independently by the E using a
Revox taperecorder and AKG K240 earphones. This transcription was then compared to
Bernhardt's (1990) original transcription. Discrepancies were resolved by E and
Bernhardt jointly hstening to the tape. Solely exarnining the consonant cluster unit, the two transcribers were in agreement 88% prior to discussion and 98% after. Overall, discrepancies in transcription were related to differences in the narrowness of transcription, involving voicelessness and aspiration.
The consonant cluster data was then dubbed onto a Fuji FR-LlxPro60 audiocassette tape using a quality stereo audiocassette recorder (Marantz PMD 420) from the original reel-to-reel tapes and a Revox taperecorder. When a stimulus word was embedded in running speech, the entire utterance was dubbed onto the audiocassette tape.
The data were then converted from analog to digital. This high quality audio bandwidth analog-to-digital signal conversion was done by hooking the audiocassette recorder
(Marantz PMD 420) up to a stereo audio/DSP port interface (Proport Model 656 dual- channel analog 1/0 module) which was connected to a NeXT station monochrome computer. The speech stimuli were recorded onto the NeXT station computer using
Soundworks 3.0 (version 2) application at a sampling rate of 22 kHz. Several stimulus
35 words were saved into one file. In total, there were 171 stimulus words for Sl and 119 stimulus words for S2. For both subjects, data from all four probes were pooled due to the limited number of words containing word-initial consonant clusters in each sample. As only one trend was observed over time for S2, (which was the beginning of a coarticulatory effect between the glide (C2) and the epenthetic vowel), it was felt that the decision to pool the stimuli was justified. During analysis, four words for Sl and eight words for S2 were discarded because of distortion.
MEASUREMENTS
Using the visual and auditory playback of the digital signal in Soundworks 3.0
(version 2), (off the NeXT station computer), three separate measurements of duration were made for each stimulus word: 1) the consonant cluster and syllable nucleus (CCV),
2) the consonant cluster (CC), and 3) the epenthetic vowel, when it occurred. Visual playback included a signal waveform and a sound spectrum of the stimulus word. A sound spectrum involves a description of the different frequencies found in a given sound and is represented graphically with the vertical axis representing the amplitude of the sound signal and the horizontal axis representing the component frequencies (Fry, 1979;
Borden and Harris, 1984).
As most of the stimulus words were in isolation, the onset of the CCV and CC units was taken as the beginning of the speech waveform. Occasionally, during the initial auditory and visual playback, extraneous noise was observed to precede the stimulus word
(e.g. click of the taperecorder being activated). The noise was represented as an aperiodic, low amplitude waveform. In these few cases, onset of measurement was taken
36 to be where a marked rise in waveform amplitude occurred. When the stimulus word was
embedded in running speech, and the initial consonant of the cluster (Cl) was a voiceless
fricative, the onset of measurement was placed where a rise in ampHtude occurred in
conjunction with an marked increase in intensity of the waveform. When C1 was a
plosive, onset of measurement was placed at the point where the waveform rose in
amplitude, with the second wave peak being sUghtly higher than the first.
For the CCV unit, the offset of measurement was taken at the point where the
periodicity of the waveform changed fromtha t of the vowel to the following consonant.
For the consonant cluster, C2 was either a semivowel (/r,l,w/), or a voiceless plosive. In
cases with a semivowel, the offset of measurement was signaled by a rise in amplitude and
a change in the periodicity or shape of the waveform. In instances where C2 was a voiceless plosive, the measurement offset was placed at the end of the plosive release.
In cases where the consonant cluster was judged auditorily to contain an
epenthetic vowel, the vowel duration was measured. In general, the signal waveform of
the epenthetic vowel was distinct from the signal representation of the surrounding
consonants. When Cl was a voiceless fricative, onset of the epenthetic vowel was marked
at the point where the waveform amplitude began to rise after decreasing at the end of
ffication. When Cl was a stop, the onset of measurement was set at the end of the plosive
release. Determining the offset of measurement for the epenthetic vowel was the most
difficult. If the waveform was magnified, a distinct change in the character (amplitude, intensity and periodicity) of the waveform could be observed. Offset of measurement was placed at the point where the change occurred. It was observed that determining the transition between the back rounded vowel (lul) and /w/ was the most difficult. These
criteria for measurement are consistent with those described elsewhere by Haggard (1973)
and Hawkins (1973).
37 While analyzing the data, E checked the accuracy of each of the duration measurements made on the signal waveform by measuring the given segment on the produced sound spectrum. E also checked the accuracy of duration measurements by producing spectrograms of the consonant cluster and syllable nucleus portion of the stimulus words using Sonogram 0.9, on the NeXT station computer. A spectrogram is a graphic display of a speech event with frequency represented on the vertical axis and time on the horizontal axis. Intensity is represented as relative darkness of the display (Fry,
1979; Borden and Harris, 1984). After launching Sonogram 0.9, a spectrogram of poor quality was first produced, based on the program's default options. To produce spectrograms of good quality with the same scales throughout the study, the spectrogram parameters were consistently set each time Sonogram 0.9 was run. First, analysis method was set to FFT, window shape was set to Hanning and peak picking was set to sideband
1000 Hz. Next, for the analysis resolution, window size was set at 128 points
(corresponding to a frequency resolution of 172.26 kHz), time increment was set to 62 points (corresponding to a time resolution of 2.90ms), and sampling frequency indicated
22.05 kHz. Occasionally, window size was set at 512 points so that a narrow band spectrograph was produced. A narrow bandwidth produces a more sharply tuned spectrogram. Generally, wide band spectrographic analysis is more useful than narrow band analysis when studying speech, as a result of the short durations of many speech events (Fry, 1979). For the display options, the upper limit of the frequency range was set at 5 kHz and the dynamic range was set at -7.777dB to -40.806dB.
Measurement Reliability
To ensure that measurement criteria did not change over time, E remeasured the segment durations of the first thirty-five stimulus words once data measurements were
38 complete, and found measurements to be in agreement within 5ms. In addition, random measurements were made independently by a second person on fifteen percent of Si's stimulus words, with measurements in agreement within 5ms.
39 CHAPTER THREE
RESULTS AND DISCUSSION
As discussed in Chapter One, there is no definite description or explanation of the relationship between the underlying phonological representation and the final phonetic representation of children's consonant clusters. The purpose of this paper has been to look at one transformational process, epenthesis, and to examine its use in children's consonant clusters fromphonologica l and phonetic perspectives. Little information exists on the effect of epenthesis on a consonant cluster unit. It is generally accepted that timing constraints and neuromotor maturation may play a role in consonant cluster development and impact on the occurrence of epenthesis (Gilbert and Purves, 1977; Smith, 1992).
However, because epenthesis affects the timing of the word and the consonant cluster unit, it raises some interesting questions with respect to representation and syllable structure. This study investigated the following questions:
1. Do consonant clusters produced with an epenthetic vowel differ in duration
from those without?
2. Is the epenthetic vowel in the consonant cluster consistent in length and
quality, or do co-articulatory effects occur?
3. Is the epenthetic vowel dependent in terms of duration on the phrasal context
or the duration of the syllable nucleus?
In an attempt to answer these questions, this study examined how consonant clusters are represented using a nonlinear phonological framework and how two models of language processing (Serial Model, Garrett, 1984; Parallel Interactive Model, Stemberger,
40 1985a and b) may account for the relationship between the underlying representation and the final output.
The results of measurements of consonant cluster duration, epenthetic vowel duration, and syllable nucleus duration will be reported. Their significance and what they tell us about the relationship between the underlying phonology and the phonetic level will be discussed below.
SUMMARY OF RESULTS
Occurrence of Epenthesis
During Bernhardt's original study, it was found that Sl used epenthesis in 77/166
(46.4%) of his consonant cluster productions while S2 used epenthesis in 67/111 (60.%) of his consonant cluster productions. Bernhardt notes that prior to participating in the original phonological intervention study, both subjects used epenthesis as a strategy for producing consonant clusters. When consonant clusters were set as an intervention target,
Bernhardt (1990) used epenthesis as a means to create pronounceable onset conditions
(i.e. CVC for CC) which resulted in an increase in the use of epenthesis in consonant cluster productions for both subjects.
41 Consonant Cluster Duration
Do consonant clusters with an epenthetic vowel differ in duration from those without?
One aim of this study was to look at epenthesis in consonant cluster productions to see how it related to the timing of the consonant cluster unit. The duration of consonant cluster units with and without an epenthetic vowel was measured. For Si, the duration of consonant clusters without epenthesis ranged from46m s to 696ms (x =223ms, 5=145ms) while the duration of consonant clusters with an epenthetic vowel ranged from61m s to
1017ms ( x =332ms, s=163ms). For S2, the duration of consonant clusters without epenthesis ranged from 300ms to 2704ms (x =712ms, 5=611ms) while the duration of consonant clusters with an epenthetic vowel ranged from 190ms to 1040ms ( x =348ms, s= 129ms) (see Figure 5). It must be noted that S2 had few consonant clusters without an epenthetic vowel where both elements were realized. A Mann-Whitney test was used to determine that a significant difference in duration exists between those consonant clusters with an epenthetic vowel and those without for both subjects. Test results are summarized in Table 1.
Table 1: Summary of Mann-Whitney test for difference in duration between consonant clusters without and with epenthesis
Subject Mann-Whitney Number of CC Number of CC p-value Statistic (U) without epenthesis with epenthesis
1 1475.5 72 77 .0000
2 193.0 18 67 .0000
42 S1: consonant clusters S1: consonant clusters without epenthesis with epenthesis
0 I 1 1 1 1 1 1 1 1 1 1 1
0 200 400 600 800 1000 0 200 400 600 800 1000
duration (ms) duration (ms)
S2: consonant clusters S2: consonant clusters without epenthesis with epenthesis
00 -
I 1 1 1 1 1 ° 1 1 1 1 1 1
0 200 400 600 800 1000 0 200 400 600 800 1000
duration (ms) duration (ms)
Figure 5: Duration of consonant clusters without and with epenthesis for Subjects 1 and 2
(Note: For "S2: consonant clusters without epenthesis", two outlying durations of 1844ms and 2704ms, where S2 purposefully lengthened the CC, were omitted to improve scale comparison.)
43 Epenthesis as a Strategy for Overcoming Timing Demands
If, as Gilbert and Purves (1977) suggest, epenthesis is used as a strategy for applying appropriate segmentation and overcoming timing demands, those consonant clusters containing an epenthetic vowel should be longer in duration, (assuming that both consonants are represented at the underlying level). As reported above, in the case of Sl and S2, clusters containing an epenthetic vowel were longer in duration than consonant clusters produced without epenthesis. Thus, epenthesis appears to allow for the exaggeration of clustered features, so that both phonemes can be realized at the production stage. Gilbert and Purves (1977) suggest that at this stage, Ohala's (1970) articulation dorninant system might better explain consonant cluster production. An alternate explanation would be if the timing system and articulatory system were co- occurring at separate levels of production (Ohala, 1970). Sl and S2 could be using epenthesis as a strategy to achieve correct articulatory segmentation while working within the constraints of their own timing systems (i.e. the timing systems may not yet match that of the adult model). Although one system may be more dominant than the other, at differing stages of the consonant cluster development, the second system is still active.
Effect of Phonological Context on the Epenthetic Vowel
In consonant clusters with an epenthetic vowel, is the epenthetic vowel consistent in length and quality or is it affected by the surrounding consonants of the cluster?
When discussing the relevance of the application of phonological theory in the first chapter, the importance of exarnining the phonological structure and context of a given unit was raised. It was stated that when examining a specific phonological unit it is
44 necessary to consider the influence that the phonological context may have on the unit's
phonetic realization. In looking at consonant cluster productions of both subjects, it was
noted that epenthesis occurred only with consonant clusters where C2 was either /Lwj/.
However, in looking closely at the data, an interesting difference was seen between the
two subjects. For SI, when epenthesis occurred, if C2 was HI, the epenthetic vowel was
usually IQI, if C2 was /w/, it was /u/, and if C2 was /j/, it was usually /i/. For S2, when
epenthesis occurred, the vowel was almost always lal regardless of what C2 was.
Occasionally, when C2 was /w/, S2 inserted lul between the consonant elements. These
instances were found on the last probe when S2 was 4;6.
Coarticulatory Effects
In the discussion of timing dominant and articulation dominant systems, it was
stated that evidence of an articulation dominant system can be found in co-articulation
studies. It appears that for SI, there is a co-articulatory effect between the epenthetic
vowel and C2 which may suggest that the articulation system may be more highly
activated (i.e. there appears to be some linking of articulatory gestures as the epenthetic
vowel seems to function as a transition between CI and C2). It is interesting to note that
at the beginning of the original study, SJ. was observed to have mild oral motor difficulties
(a tongue thrust during speech).
For S2, his timing system may have more influence because the epenthetic vowel
appears to be functioning more as a neutral marker to help overcome timing demands.
Support for the hypothesis that S2 may be attending more to timing demands may also be
seen by examining some of his single element realizations of consonant clusters. It was
occasionally observed that S2 lengthened the duration of the singleton consonant to match perceptually that of similar two-element consonant cluster realizations. It may be that S2
45 was attaching both tirning units to the single segment. In later consonant cluster development where some co-articulation was noted between C2 and the epenthetic vowel, the articulation system may be becoming more active.
Epenthetic Vowel Duration
Where an epenthetic vowel exists within a consonant cluster, is it dependent in terms of length on the phrasal context or the duration of the syllable nucleus?
In considering epenthesis in consonant clusters, the duration of the epenthetic vowel was also measured. In addition to the variations in the quality of the epenthetic vowel that have been discussed, differences were seen in vowel length. For SI, the duration of the epenthetic vowel ranged from 27ms to 264ms. For S2, the epenthetic vowel duration ranged from 26ms to 237ms. In order to examine the possible influence of the duration of the syllable nucleus on the duration of the epenthetic vowel, correlations were calculated. Correlation coefficients were not significant. For SI, r = 0.293 and for
S2, r = 0.178. No correspondence was seen between the length (see Figure 6) or quality of the underlying syllable nucleus and the length of the epenthetic vowel. It would seem then that the epenthetic vowel is independent of the underlying word structure and is part of the consonant cluster unit itself. Further, the consonant cluster appears to be governed by its own timing system or constraints, separate from the timing of the word.
46 S1: Scatterplot of epenthetic vowel duration vs. syllable nucleus duration (r = 0.293)
5 I ID o
8
0.4 0.6
syllable nucleus duration (ms)
S2: Scatterplot of epenthetic vowel duration vs. syllable nucleus duration (r=0.178)
•E
0.2 0.4 0.6 0.8 1.0
syllable nucleus duration (ms)
Figure 6: Relationship between syllable nucleus duration and epenthetic vowel duration for Subjects 1 and 2.
47 IMPACT OF EPENTHESIS ON PROSODIC STRUCTURE
It is important to look farther at the change in the prosodic tier representation of a word containing a consonant cluster when epenthesis occurs. As stated in the earlier discussion of nonlinear phonology, information about prosodic structure is included in the underlying representation. The prosodic tier is linked to the segmental tier according to principles of association (Bernhardt, 1992). At the prosodic level, the word dorninates feet which in turn dominate syllables. Different theories about the prosodic hierarchy exist with regard to the status of the syllable as a constituent and its components.
Representation of Consonant Clusters
When looking at consonant clusters from the perspective of onset-rime theory, both consonants branch from the onset and the vowel makes up the nucleus which branches from the rime. In moraic representation, the two consonants are adjoined to the mora (the actual point of joining is controversial) and the vowel is dominated by the mora.
If epenthesis occurs during consonant cluster production, the consonant cluster unit is split, altering the syllable structure of the word (i.e. resyllabification occurs). In onset- rime terms, the consonants are separated into two onset-rime units which are dominated by a branching foot. In moraic terms, an extra weight unit (mora) is created. The two moras create two syllables which are dominated by a branching foot (see Figure 7). In both cases, the prosodic structure of the word is altered to allow the child to cope with the articulatory and timing demands of consonant cluster production. However, as previously discussed, the data suggest that the consonant cluster is governed by its own timing constraints separate from the timing of the word. With these current theories, as shown in
Figure 7, there is no way representationalfy to attribute unitary status to C1 VeC2, unless
48 Moraic O-R
a A A A A C M C M O R O R
C Ve C V
Figure 7: Representation of epenthesis in moraic and onset-rime theories
Word
A, C,0 M,R C M,R
Figure 8: Representation of Cl VeC2 as one unit
C2 is represented as both a coda of the weak syllable and an onset to the strong (see
Figure 8). Although this is unusual, there are examples in English where intervocalic
consonants may be ambisyllabic (e.g. Dd in 'bucket' ^Ak^t/) (Bernhardt and Stemberge:
49 in preparation), although not usually in weak-strong syllable sequences (e.g. /behxa/, IM is an onset). Furthermore, in English, weak syllables can have a coda. It is important to note that even though it is unusual to think of glides as codas (i.e. /kaw/ = CVC), it is one way to describe diphthongs ([aw], [ay] rather than [au ], [ai]). This issue needs to be examined in much further detail before it can be resolved.
APPLICATION OF NONLINEAR PHONOLOGICAL FRAMEWORK
The impact of examining consonant cluster productions using a nonlinear phonological frameworki s that it allows for reference to the underlying phonological system. The main purpose of this paper was to look at epenthesis in consonant clusters from phonological and phonetic perspectives. As stated, by applying the nonlinear phonological theory to describe the underlying representation of consonant clusters, an opportunity arises for describing how the underlying representation changes before reaching the production stage.
In Chapter One, evidence was discussed to support the claim that both elements of a consonant cluster are present in the underlying representation. It was shown earlier in this chapter how this would be represented using a nonlinear phonological framework.
The next step then is to look at how the two-element consonant cluster in the underlying representation is transformed into its phonetic form, especially when it includes an epenthetic vowel. To look further at this, it is necessary to refer to the language processing models described in Chapter One.
50 Epenthesis in a Serial Model of Language Processing
In Garrett's (1980, 1984) model of language processing, three distinct levels of processing are described: the message level, the linguistic sentence level, and a motor articulatory model. According to Garrett, information is passed linearly from one level to the next. The first level where an epenthesis rule could be applied would be at the sentence level where the general concept of the message undergoes the application of logical and phonological rules. The other option would be for an epenthesis rule to be applied at the final level, the articulatory level, where the signal undergoes phonetic and prosodic encoding before being translated into instructions for the correct articulatory sequencing.
If the epenthetic rule was applied at the sentence level, it means that it is a higher- level process and thus associated closely with the underlying representation of the consonant cluster. As stated in Chapter One, if this is the case, it would be expected that phrasal context or the duration of the syllable nucleus would exert some influence on the epenthetic vowel. As discussed, no evidence of this was seen in the consonant cluster productions of the two subjects. Neither the length or quality of the syllable nucleus had any effect on the duration or quality of the epenthetic vowel. Support for this is found in the study by Peterson and Lebiste (1960) which looked at the effect of preceding and following consonants on the duration of the syllable nucleus. They found that the syllable nucleus was only influenced by the nature of the following consonants. This suggests that if it is the following consonant that has the effect on duration of the syllable nucleus, the consonant cluster may be separate from the word in its timing. Therefore, no anticipatory lengthening would be expected in the epenthetic vowel.
It seems more likely that the epenthesis is occurring at the articulatory level when the underlying signal undergoes phonetic encoding and articulatory sequencing. This is
51 supported by evidence from adults who pronounce foreign words with unfarniliar consonant cluster combinations with an epenthetic vowel (Greenlee, 1974). However, as discussed in Chapter One, it appears that the application of epenthesis cannot simply be occurring at the time of the actual articulatory sequencing; otherwise it should be seen more frequentlyi n children's consonant cluster productions.
It is important to remember that according to Garrett's model, the occurrence of the different processing levels and application of rules is a fixed,seria l process. Therefore, the epenthesis rule would always be applied at the same level during phonetic encoding and should produce consistent results. However, an interesting difference was seen in the use of epenthesis by the two subjects that cannot easily be account for by a linear model.
Epenthesis in a Parallel Interactive Model
In Chapter One, the possibility of a more interactive model of language processing was introduced. Proponents of a parallel interactive model suggest that varying levels of processing can be active at any given moment in time and that information interacts top down and bottom up (Stemberger, 1985b). Initial processing begins when the speaker forms an intent to talk thus activating pragmatic and semantic information. Each time a new unit or level of processing is activated, a cascading effect of activation occurs.
Although phonemes are still considered lower-level units, as in Garrett's model, they are not restricted to a finalstag e of processing. Once associated phonemes have been activated, there can be a spreading of activation back up the processing levels (e.g. other words containing the particular phonemes activated may then be partially activated).
Eventually the units that are most highly activated will be chosen and the correct articulatory sequencing will occur.
52 When looking at how epenthesis in consonant cluster productions would be accounted for in terms of a parallel interactive model, several factors need to be considered. First, although an assumption of the model is that language is made up of interconnected levels which are processed in parallel, this does not imply that processing begins simultaneously at all levels. Second, within the parallel interactive model, rules can be viewed as being units similar to any other unit. Stemberger states "structural conditions on a rule are simply the set of input lines from other language units, as those other units become activated they send activation to the phonological rule, and it also begins to rise in activation level" (1985a, p.9). This means that the model assumes that phonological information leads directly to the accessing of relevant rules. If the activation level of a rule is high enough, the underlying information or representation is inhibited before its activation level can become high enough for it to be accessed. Stemberger
(1985a) points out that this type of model was not developed to describe phonological rule order. As phonological rules are equated with other units, they are treated as such and therefore, said to be accessed and applied in the same manner as other units (e.g. words, segments).
Since epenthesis is a phonological rule, it can be assumed that it occurs in the mapping fromsegment s to features (Stemberger, 1985a) which occurs at a lower processing level. However, in contrast to a linear model, with a parallel interactive model, the possibility exists that the application of a rule does not occur at the exact same point of processing for different speakers. That is, the threshold point of activation which causes the rule to be accessed may be reached more quickly in some speakers than in others.
Therefore, although the application of epenthesis, a phonological rule, will occur at a low- level of processing, there may be varying points of application.
53 It was noted earlier that an interesting difference was seen in the surface realization
of the epenthetic vowel in the consonant cluster productions of the two subjects. Greater
coarticulatory effects were seen between the epenthetic vowel and C2 for Sl than for S2.
For S2, the epenthetic vowel appeared to function more as a neutral place marker.
In looking at Garrett's model of language processing, it was seen that due to its
linear nature, rule application occurs in a fixed serial process when specific requirement
conditions are met. Therefore, the application of epenthesis should be consistent between
speakers (i.e. the surface realizations should be phonetically similar) This does not mean
that a serial model would not be able to account for the differences between the two
subjects. However, it appears that detailed conditions would need to be outlined in order
to explain the production differences. In contrast, in a parallel interactive model of
language processing, rules function like any other unit and can, therefore, be activated at
various points in the language production process. The possibility exists that for Sl, the
application of epenthesis is activated just before articulatory sequencing but after feature
activation for C2 (hence the coarticulatory effects) whereas for S2, activation of
epenthesis may occur slightly earlier (for example, at the stage of mapping phonemes to
the CC prosodic structure).
STUDY LIMITATIONS
It is clear that this study has a number of limitations in terms of sample size, data
quality and measurement techniques. The small number of subjects limits generalizations that can be made across children. Furthermore, only a relatively small sample of words
containing word-initial consonant clusters existed for both subjects. The sample size of
54 consonant clusters was particularly restricted for S2 since many of his consonant clusters were realized as one element. Another limitation was that the data were not originally collected for purposes of this study. This project arose from observations made during
Bernhardt's (1990) study. In terms of data quality, all measurements were made from data which was transferred from original reel-to-reel tapes to audiocassette. Several stimulus words needed to be discarded because of poor tape quality. Lastly, an essential limitation in the measurement of segment durations was that of segmentation.
Historically, segmentation has been a major problem in speech analysis. Although there are instances where cues signaling the onset and offset of a segment are relatively unambiguous, there are many cases where it is difficult to determine accurately the segmentation point. This was particularly true when determining the segmentation point between an epenthetic vowel and C2 glide. It must be pointed out that although segmentation criteria, as outlined in Chapter Two, were applied consistently, and reUabihty calculated, measurement was still dependent on human judgment of speech characteristics.
FUTURE RESEARCH
The present study shows that epenthesis does occur in some children's productions of consonant clusters and that these consonant cluster units differ in terms of length from consonant clusters without an epenthetic vowel. Due to the small number of subjects considered, it should serve as a preliminary effort in examining epenthesis in children's consonant cluster productions. Further research is warranted to examine how widely occurring epenthesis is in children's productions and what the acoustic and perceptual characteristics of epenthesis are. Further acoustical analysis needs to be done to determine
55 if the frequencyo f epenthesis is being under-reported as a result of the epenthetic vowel being considered as part of the following consonant.
Theory development is necessary in order to account better for the representation of consonant cluster units containing an epenthetic vowel in terms of syllable structure.
Neither of the current theories, onset-rime or moraic, can satisfactorily account for a consonant cluster with an epenthetic vowel as one unit, unless the second consonant is considered ambisyllabic (not an optimum solution in a weak-strong syllable sequence).
CONCLUSION
This paper has investigated the occurrence of epenthesis in consonant cluster productions of two subjects from both phonological and phonetic perspectives. In
Chapter One, previous research was examined and evidence supporting the hypothesis that children have a two-element underlying representation for consonant clusters was discussed. A current nonlinear phonological framework and two current models of language processing were also reviewed.
Results of this study showed that consonant clusters produced with an epenthetic vowel were significantly longer in duration than those produced without. This supports the hypothesis presented by Gilbert and Purves (1970) that epenthesis is used as a strategy for applying appropriate segmentation and overcoming timing demands. It was also found that coarticulation occurred between the epenthetic vowel and C2 but not between the epenthetic vowel and the syllable nucleus which suggests that the epenthetic vowel is part of the consonant cluster unit and governed by its own timing system.
56 Another aspect of epenthesis in consonant clusters that was examined was the effect of the epenthetic vowel on the prosodic structure of the word. It was shown, using the nonlinear phonological framework discussed, how epenthesis in a consonant cluster unit would be represented. Two current theories of the structure of the prosodic hierarchy, onset-rime and moraic, were presented and it was shown that resyUabification of the word occurs as a result of epenthesis in the consonant cluster. However, it is important to note that the results of the study indicated that the consonant cluster unit is governed by its own timing constraints, separate fromth e timing of the word. Taking this into consideration, it was shown that in terms of both onset-rime theory and moraic
theory, there is no way to attribute unitary status to ClVeC2 unless C2 is ambisyllabic.
Further research will need to be conducted in this area to find a more optimum solution.
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61 APPENDIX ONE
Sl DATA
TestList ccv/cv duration cc duration v duration j c duration ep. v duration sleeping f(w)ipin 0.254 0.155 0.1 oj 0.000 no epenthesis bread bwAd(9}__ 0.335 0.205 0.13] OJpTjOjn o epenthesis snowman no(3)m£en(s) 0.306 0.000 0.31 0.112 no epenthesis snowing nowen 0.447 0.000 0.45 0.202 no epenthesis brush VWA8 0.305 0.105 0.20 0.000 no epenthesis airplane eupein 0.361 0.000 0.36 0.112 no epenthesis broken b(w^oukm 0.274 0.118 0.16 0.000 no epenthesis glove 0.207 0.115 0.09 0.000 no epenthesis glovey gAvi(?) 0.232 0.000 0.23 0.090 no epenthesis grey gawei(j) 0.000 0.000 0.00 o.ooot plum p/bAm 0.166 0.000 0.17 0.085 no epenthesis brushing bA(s)9m 0.000 0.000 0.00 0.000 snake (s)n:eik 0.783 0.452 0.33 0.000 no epenthesis truck fWAk 0.777 0.394 0.38 0.000 no_epenthesis trailer vweiio 0.274 0.129 0.14 0.000 no epenthesis soring fvwin 0.386 0.249 0.14 o.ooo'n o epenthesis clown q(i)aun 0.531 0.133 0.40 0.000 no epenthesis sleep _^ fwip 0.287 0.077 0.21 0.000 no epenthesis three fwi(i) 0.470 0.086 0.38 0.000 noepenthesis flower 0.386 0.000 0.39 0.016 no epenthesis crayra__ kuweijo£g)n 0.389 0.288 0.10 °5go " 108 crayon keiwAn 0.250 0.000 0.25 0.033 no epenthesis screwdriver f/f(w)uv(w)aiVA 0.279 0.049 0.23 0.000 no epenthesis crayons fweipnQ 0.284 0.153 0.13 0.000 n^epjnthesis black bask 0.452 0.000 0.45 0.027 no epenthesis twenty fwenti(i) 0.193 0.150 0.04 0.000 no epanrthesis cry fwai 0.516 0.060 0.46 0.000 no epenthesis tried vwaU 0.425 0.148 0.28 0.000 Ino epenthesis train dswem(9) 0617 0.270 0.35 0.000! 0.138 brothers b(w)ASa9 0.180 0.100 0.08 0.000 no epenthesis twin dswm 0.415 0.241 0.17 0.000 0.120 blue b(i)iu 0.465 0.046 0.42 0.000 no epenthesis blue fbwu I 0.334 0.0861 0.25 I 0.000 no epenthesis
62 twins t(a)wmz 0.556 0.229 0.33 O.OOOl 0.035 obstacle obsOika 0.407 0.217 0.19 O.OOOmo epenthesis quiet k(a)waiAt 0.725 0.343 0.38 O.OOO) 0.060 glove q(i)JAf 0.476 0.153 0.32 O.OOOl 0.042 gloves g(j)Avz 0.355 0.088 0.27 O.OOOjno epenthesis glove _ gAy 0.207 0.000 0.21 0.021 \no epenthesis dress fweG 0.316 0.162 0.15 0.000|no epenthesis string t(u)wm 0.449 0.193 0.26 0.000 0.052 spring pwerj 0.378 0.228 0.15 0.000 no epenthesis play_ pwei 0.410 0.206 0.20 0.000 no epenthesis break bwei 0.614 0.117 0.50 0.000 no epenthesis screwdriver f(w)uvwaiv(w)a(a; 0.585 0.300 0.29 0.000 no epenthesis green gwin 0.478 0.192 0.29 0.000 no epenthesis bring vwirj 0.266 0.110 0.16 0.000 no epenthesis plane pwecn 0.600 0.2071 0.39 0.000 no epenthesis airplane e(o)pwei:n 0.636 0.298 0.34 0.000 no epenthesis truck dowAk 0.774 0.427 0.35 0.000 0.231 plum p/bwAm 0.579 0.217 0.36 0.000 no eg«nthesis twenty fwenti 0.295 0.165 0.13 0.000 nojgpenthesis black b(3)wak 0.441 0.224 0.22 0.000 0.042 queen k/g(a)w:in 0.946 0.392 0.55 0.000 0.047 broke bwok 0.304 0.110 0.19 O.OOOjno epenthesis crown kwaun 0.469 0.29 O.OOOfno epenthesis quick k/g(u)wik 0.372 0.157 0.22 0.000 0.050 flower fauwa 0.507 0.000 0.51 0.102 no epenthesis
3wel 0.33 0.000 0.146 grape 9 L______- 0.555 0.230 brush bWAS 0.439 0.224 0.21 0.000 no^erjenthesis brush DO:WA9 0.615 0.409 0.21 0.000 0.238 sleeping Gajipen 0.636 0.250 0.39 0.000 0.104 sleep (e)tjip 0.745 0.532 0.21 0.000 no epenthesis snowman snoiwmsn 1.162 0.476 0.69 0.000 no epenthesis snowing snoiwin 1.207 0.440 0.77 0.000 no epenthesis squirrel f.oijau 0.333 0.000 0.33 0.060 no epenthesis snake 0.703 0.256 0.45 0.000 no epenthesis dropped fwopt 0.175 0.000 0.17 0.046 no epenthesis growl qwau:(w) 1.170 0.251 0.92 0.000 no epenthesis cry k/gwec 1.334 0.249 1.09 0.000 no epenthesis cry kwei 1.064 0.126 0.94 0.000 no epenthesis throw fwo 0.558 0.285 0.27 0.000 no epenthesis throwing fowin 0.268 0.000 0.27 0.081 no epenthesis twins t(u)win5 0.489 0.321 0.17 0.000 0.061 gross guwos: 0.711 0.390 0.32 0.0001 0.168 elovev aiAvi 0.385 0.250 0.13 O.OOOlno enenthesis
63 brow b£u)wais 1.075 0.304 0.77 O.OOOl 0.091 sis. g(s)wm 0.306 0.189 0.12 O.OOOl __Pi>±3 sweater th(u)weio(?) 0.371 0.269 0.10 o.oool 0.065 sweater 0t(u)weJa 0.523 0.387 0.14 O.OOOl 0.045 sweater tuweJo(s) 0.445 0.341 0.10 O.OOOs 0.111 sweater 6t(u)web(3) 0.520 0.297 0.22 0.000 0.068 sweater GweJo/a 0.490 0.369 0.12 0.000 0.048 sweater 0uweJo(3) 0.486 0.364 (J 1 J 0.000 0.114 plane plein 0.287 0.087 0.20 0.000 no ep^nti^esis airplane 0.824 0.401 0.42 0.000 0.037 crayon k(u)weijan 0.454 0.254 0.20 0.000 0.076 clock kh(u)bkh 0.645 0.337 0.31 0.000 0.027 brush bWA0 0.204 0.125 0.08 0.000 no epenthesis brush D(U)WAJ 0.433 0.241 0.19 0.000 0.079 brush D(OJWA8 0.345 0.160 0.19 0.000 0.048 brush MU)WA| 0.269 0.146 0.12 0.000 0.043 clock k(u)bkh 0.345 0.180 0.16 0.000 0.034 three fuwi: 1.403 0.498 0.91 0.000 0.239 transformer twsenSfoms 0.172 0.074 0.10 0.000 no epenthesis microscope mAkw30kouph 0.111 0.048 0.06 0.000 no epenthesis bread buwed(s) 0.721 0.458 0.26 0.000 0.194 bread 0.488 0.223 0.27 0.000 0.075 quarter khozdo(a) 1.171 o.ow 1.17 0.076 n^pe^thesis black balak 0.628 0.331 0.30 0.000 0.219 throwing fuwo(w)m 0.779 0.601 0.18 0.000 0.264 throwing fuwowm 0.000 0.000 0.00 0.000 throw f(u)wo 0.603 0.438 0.16 0.000 0 054 play p(9)lei 0.524 0.281 0.24 0.000 0.045 dressed duwest 0.428 0.324 0.10 0.000 0.150 plum pgUm 0.526 0.294 0.23 0.000 O.044 grows gwouS 0.861 0.432 0.43 0.000 no epenthesis quick khuwik 0.597 0.331 0.27' 0.000 0.175 broke bwok 0.624 0.255 0.37 0.000 no epjenthesis crown k(u)waun 0.556 0.224 0.33 0.000 0.044 queen kwin 0.698 0.221 0.48 0.000 no epenthesis great gweit 0.205 0.109 0.10 0.000 no epenthesis trample th(3)waempy 0.478 0.252 0.23 0.0001 0.041 glove q(3)lAV 0.353 0.195 0.16 0.000 0.051 glove g(3)Uv 0.306 0.164 0.14 0.000 0.061 glove g(3)Uv 0.356 0.195 0.16 0.000 0.045 dress d(ojwe0 0.368 0.223 0.15 0.000 0.053 dress d(u)wa9 0.485 0.273 0.21 0.000 0.093 truck dru")WAkh 0.423 0.266 0.16 0.000 0.062
64 screwdriver |t/d(u)wudwaivo(a) 0.610 0.297 0.31 o.oogj drive |d(a)waiv 0.441 0.170 0.27 0.0001 0.050 screw t(s)wu 0.677 0.261 0.42 0.000 0.044 brush b(u)wAj 0.460 0.318 0.14 0.000 0.045 green guwi:n 1.211 0.553 0.66 0.000 0.211 0.000 0.179 green ffijwjn___ 0.835 0.629 0.21 flower f(9)lawo(s) 0.523 0.178 0.34 0.000 0.037 snowman t(s)nomaen 0.892 0.384 0.51 0.000 noepenthesis snowing s:nowen 0.842 6.696I 0.1? 0.000 no epenthesis broom b^wj^n^ 0.795 0.349 0.45. 0.000 0.037 sleeping 03liphen 0.807 0.479 0.33! 0.000 0.064 sleep Oslip 0.000 0.000 0.00* 0.000 snake sneik 0.715 0.408 0.31: 0.000 no epenthesis black blaek 0.267 0.106 0.161 0.000 no epenthesis black b(a/u)laek 0.248 0.061 0.1 gl o.ooo 0.019 stuck s(9)Ak 0.463 0.292 0.17f 0.000 no epenthesis 0.187 0.36 0.000 0.029 E^i£!L____ p(a)lei6 0.542 monster manGu 0.190 0.000 0.19 0.083 no epenthesis crew k(u)wu(u) 0.266 0.114 0.15 O.OOOl 0.027 tricked thwikt 0.267 0.195 0.07 0.000 no epenthesis dressing dwesGin 0.219 0.154 0.06 0.000 no epenthesis monster manGu 0.287 0.000 0.29 0.127 no_epenthesis stuck GAk 0.244 0.000, 0.24 0.138 no epenthesis crying k(u}waKJm 1.223 0.603 0.62 0.000 i 0.061 broke b(u)wok 0.393 0.228 0.17 0.000 0.063 three a Guwija 1.041 0.644 0.40 0.000 0.190 three a Gwija 0.965 0.687 0.28 _aooo nojggenthesis string Guwirj 1.816 1.017 0.80 0.000 0.176 black b(u)lsek 0.531 0.292 0.24 O.OOOl 0.034 gloves qalAVZ 0.714 0.395 0.32 O-OOOJ 0.167 throw fwou 0.232 0.149 0.08 O.OOOjno epenthesis tree th(u)wi(i) 0.853 0.348 0.50 0.000 0.065 skate skeit 1.088 0.547 0.54 0.000 no egejn^hesis bridge b^]wic^ 0.599 0.319 0.28 0.000 0.049 thread Gswed 1.141 0.813 0.33 0.000t""~ ai?2 treasure th(u)wed50 0.479 0.315 0.16 0.000 0.057 snowman snoumae(3)n 0.598 0.254 0.34 0.000 no epenthesis plum pUm 0.236 0.110 0.13 0.000 no epenthesis plum pUm 0.312 0.120 0.19 0.000 no epenthesis clock k(Y)bkh 1.090 0.671 0.42 0.000 clock k(u)lak 0.394 0.191 0.20 0.000 0.049 strucked thWAkt 0.375 0.273 0.10 0.000 no epenthesis airolane eod)l£in 0.404 0.244 0.16 0.000 no eoenthesis
65 sleep s(s)lip 0.884 0.461 0.42 0.000 0.037 sleeping 63lip(?)m 0.669 0.380 0.29 0.000 0.060 truck tWAk 0.381 0.195 0.19 0.000 noepenthesis spring spuwirj 1.101 0.619 0.48 0.000 0.189 throw fwou 0.272 0.154 0.12 0.000 no_epenthesis grows 0.567 0.318 0.25 0.000 0.037 squirrel skwab3 0.591 "O4801 0.11 0.000 no epenthesis cry kw:ai 1.200 0.321 0.88 0.000 no epenthesis screwdriver tCu^wudCuWaivu
66 APPENDIX TWO
S2 DATA
Test List | ccv/cv duration cc duration v duration c duration ep. v duration snowman noum(w)aen 0.606 0 0.61 0.09 no epenthesis snowing snowin 0.359 0 0.36 0.089 no epenthesis snake reei(?) 0.657 0 0.66 0.282 no epenthesis snakey 1 n:ei?i 0.729 0 0.73 0.531 noj^enthesjs green din 0.22 0 0.22 0.038 no epenthesis black balas? 0.506 0.283 0.22 0 0.117 crayon theijan 0 0.00 0 0 glasses dslasiz 0 0.00 0 0 S3 .... , _ clothes taloQ 0.696 0.322 0.37 0 0.131 glove daUd 0.572 0.314 0.26 0 0.12 glovey dsLvblit?) 0.47 0.299 0.17 0 0.13 string dm 0 0.00 0 0 screwdriver tudaUa 0.322 0 0.32 0.033 jnojpeiujiesis airplane e:p(3)lein 0.6 0.293 0.31 0 0.037 truck dA(3?) 0.149 0 0.15 0.015 jiojspenthesis sgoon pun 0.777 i 0.78 0.092J no_egenthesis sleeping lip?in 0.327 0 0.33 0.101 no epenthesis black bala/as? 0.49 0.24 0.25 0 0.095 squirrel thewsl 0.313 0 0.31 0.029 no epenthesis plum p/baUm 0.53? 0.285 0.25 0 0.107 srjring lphm 0.263 0 0.26 0.027 no epenthesis clouds Jslaudz 0.831 0.318 0.51 0 0.117 airplane e(3)palein 0.858 0.403 0.46 0 0.132 glowing t/dowin 0.287 0 029 0.02 no epenthesis dress dswAG 0.699 0.48 0.22 0 0.181 screwdriver thu?h(3)od9waidA 0.418 0 0.42 0.042 no epenthesis driver dawaidA 1.314 0.534 0.78 0 0.237 snake s::nei? 2.24 1.844 j 0.40 0 noepenthesis snakey s:nei?i 1.066 0.809 0.26 0 no epenthesis snakey s:nei?i 1.144 0.956 0.19 0 no epenthesis snake n:ei? 0.686 0.69 0.537 no epenthesis snake snrela 3.247 2.704 0.54 0 noepenthesis snake rnei(?) 0.566 0 0.57 0.314 no epenthesis sauirrel n^ewaCu') 0.423 0 0.42 0.036 no eoenthesis
67 flower laA(u)we(a) 0.979 0 0.98 0.159 no epenthesis sleeping tilip?in 0 0.00 0 0 snowman nomae(a)n 0.138 0 0.14 0.043 no epenthesis snowing no(r)wjn. 0.747 0 0.75 0.327 no epenthesis broom th-w(i)um 0.365 0 0.36 0.015 jic^ejgerrthesis broom b£(?)wum 0.785 0.584 0.20 0 no epenthesis spider phaide(3) 0.551 0 0.55 0.096 no epenthesis plum 0.515 0.279 0.24' _! 0.128 0.13 0 0.144 §E22S_ pewirL 0.367 0.239 try thai 0 0.00 2 0 green dswjm^ 0 apoj 0 0
h 0.204 glove dslAb 0.735 0.431 0.30 0 spoon pu(u)n 0.468 0 0.47 0.034jiojerjentihiesi s black 0.64 0.237 0.40 0 0.102 0.218 string theWEn^____ 0.622 0.411 0.21 0 crayons theijan(t) 0.224 0 0.22 0.036 no epenthesis stream din 0.411 0 0.4_,1 0.018 no epenthesis blue bslu 0.657 0.332 0 0.173 glovey dalAvi 0.669 0.259 0.41 0 0.112 no epenthesis sleeping slipin 0.875 0.482| 0.39 , 0 airplane e(o)pslein 0.664 0.409 0.26 0 0.228 broke biwoot 1.09 0.40? 0.69 0 0.219 spoon spi(u)n 0.92 0.691 0.23 0 no epenthesis driving dAwaivin 0.896 0.357 0.54 0 0.182 snoring i[chcjc}nawjn_ 0.823 0.407 0.42 b no epenthesis squirrel t3Wl(0)WA(u) 0.687 0.319 0.37 0 0.121 snake s:nei(?) 0.888 0.593 0.29 0 no epenthesis Pjum_ pUm 0.632 0.358 0.27 0 0.144 fly f(s)lai 0.885 0.32 0.56 0 no epenthesis spider spaide(a) 0.902 0.489 0.41 0 no epenthesis crown th3waun 0.68 0.274 0.41 0 0.12 queen _ tswin 0.785 0.38 0.41 0 0.217 spring spswin 0.838 0.609 0.23 0 0.195 0 try tawai 0 0.00^ , 0 blue b£(A)luju^ 0.727 0.33rz _o.4o 0 0.139 black bolae(?) 0.551 0.274 0.28I 0 0.079 string tuwm 0.69 0.471 0.22 0 0.217 pjay phslei 0.825 0.411 0.41 0 0.127 crayons daweijant 0.781 0.448 0.33I 0 0.105 stream dawin 0.881 0.352 0.53 0 0.175 breaking buwei?in 0.727 0.439 0.291 o 0.183 break buwei(?) 0.679 0.47 0.21 0 0.186 brush bu\VA0 0.481 0.329 0.15 0 0.143
68 i screwdriver 0.739 0.374 0.37 0.237 t3w(i)uduwaiv(j)5 green dawin 0.673 0.378 0.30 0.111 flower flaup(3) 0.738 0.3 0.44 Oj no e^gnthesis drawing dowawin 0.536 0.298 0.24 0.079 snowman snoumae(3)n 0.734 0.416 0.32 no epenthesis snowing snowin 0.644 0.372 0.27 Olnoepenthesis splashing pula;tin 1.088 0.402 0.69 Of 0.107 splashing pulaetin 0.477 0.221 0.26 0 0.102 glove dalAv(3) 0.807 0.474 0.33 0 0.212 spring sp(A)wm 0.779 0.587 0.19 0 0.158 plum paUm 0.644 0.338 0.31 0 0.176 spoon sph(i)u:n 0.771 0.571 0.20 0 no epenthesis clock kala? 0.525 0.268 0.26 0 0.079 crown kuwaum 0.555 0.29 0.27 0.103 broom bsyy^fjOom 0.514 0.293 0.22 0 0.114 snowing onowin 0.495 0 0.50 0.213 no epenthesis glasses 0.461 0.279 0.18 0.096 draw d(u)wa(3^ 0.885 0.198 0.69 0 0.068 snake s(s)neik 0.707 0.513 0.19 0 0.026 snakey sneiki: 0.754 0.451 0.30 0 no epenthesis squirrel guwia5 0.109 0 0.11 0.031 no epenthesis brush bWA(3)0 0.684 0.496 0.19 0 noepenthesis brushing buwAGin 0.45 0.306 0.14 0 0.162 broke buwout | __ 0.414 0.62 0 0.162 crying kuwaijin 0.658 0.257 0.40 0 0.095 cry k(3)wai 0.876 0.481 0.39 0 0.063 cjuack k9Wffi(3)kh 0.504 0.223 0.28 0 0096 flower 0.648 0.328 0.32 0 no epenthesis string sPtawin 1.243 1.04 0.20 L 0 0.092 dress dswas 0.509 0.275 0.23 0 0.139 flipping f(9)lup?in 0.453 0.327 0.13 0 0.057 sleepy (t)6(a)lipi 0.364 0.207 0.16 0 O.041 screwdriver ski - tudswaive 0 0.00 L _o 0 truck tawAk 0.479 0.248 0.23 0 0.097 sleep 9(3)lip 0.417 0.199 0.22 0 H.048 green dawin 0.44 0.263 0.18 0 __JM47 black balse: 1.259 0.215 1.04 0 0.108 black bslaek11 0.883 0.341 0.54 0 0.158 crayons 0.557 0.225 0.33 0 0.162 airpj^ane e^pslein 0.388 0.25 0.14 0 0.102 glove aj_l_\y_ 0.624 0.338 0.29 0 0.138 dressing duwA0in 0.318 0.19 0.13 0 0.086
69