volume 105(2), 151-173 production accuracy in ayoung

Volta Review, Volume 105(2), 151-173

Production Accuracy in aYoungCochlear Implant RecipientAndrea D. Warner-Czyz. M.A., Barbara L Davis, Ph.D., andHelen M. Morrison, Ph.D.

The availability of cochlear implants in younger children has provided the opportunity to evalu-ate the relative impact of the production system, or the sounds young children can say, and the audi-tory system, or the sounds children can hear, on early vocal communication. Limited access to theacoustic properties of speech results in differences in vocal dei^elopment related to emergence of lex-ical accuracy. Understanding this aspect of speech acquisition can form an important aspect ofassessment and intervention protocols for the emerging population of young cochlear implant recip-ients. One child who received a cochlear implant at 24 months was follcnved longitudinally toexplore the impact of the production system and audition on changes in phonetic inventory, lexicaltarget characteristics and early word accuracy. Over time, she diversified lier phonetic inventoryand improved accuracy, particularly for vowels. Segments and syllables produced most frequentlywere most accurate.

Production Accuracy in aYoung Cochlear Implant Recipient

Young children undergoing early cochlear implantation have been noted toexhibit differences in early vocal acquisition (e.g., Blamey, Barry, & Jacq, 2001;McCaffrey, Davis, MacNeilage, & von Hapsburg, 1999; von Hapsburg, 2003).Although inventories of consonants, vowels and syllable patterns have beenfrequently studied, early emergence of accuracy has not been a focus in thisgrow ing population. Studying these children is important for evaluating therelative roles of the production system and auditory input in achieving earlyword accuracy as well as developing clinically valid assessment and inter-vention protocols.

The onset of first words marks a young child's earliest deliberate attempt tolink concepts with sounds and sequences. To communicate intelligibly, chil-dren must achieve lexical accuracy by matching sounds they can actually pro-duce with word target characteristics. The role of the production system inachieving accuracy can be understood through analysis of consonant, vowel

Andrea D. Warner-Czyz, M.A., is a doctoral candidate in the department of communicationsciences and disorders at The University of Texas at Austin. Barbara L. Davis, Ph.D., is a pro-fessor at The University of Texas at Austin in the department of communication sciences anddisorders. Helen M. Morrison, Ph.D., is an associate professor in the the department of com-munication and sciences and disorders at Texas Christian University.

Early Production Accuracy 151

and syllable pattems relative to word targets attempted. However, auditoryfactors also influence accuracy; children must be able to hear to understandthe nature of words they are attempting to say. Young children receivingcochlear implants (CIs) enable a unique view of the importance of auditoryinput on both emergence of phonetic characteristics and on accuracy in devel-opment of intelligible speech and language.

Understanding the nature of early speech acquisition in young childrenwith typical hearing at the same developmental level provides a backgroundfor understanding early word accuracy in infants and toddlers who receiveCIs. Phonetic inventories of consonant and vowel types and frequenciesproduced during the early word period have been widely reported for chil-dren with typical hearing (e.g., Boysson-Bardies & Vihman, 1991; Davis,MacNeilage, and Matyear, 2002; Kent & Bauer, 1985; Stoel-Gammon, 1985).Infants and toddlers with typical hearing produce more oral stop (i.e., /b, d, g/)and nasal (/m, n/) manners of articulation. They also show preferences forplace of articulation, with more labial (i.e., /b, m/) and coronal (i.e., /d, n/)than dorsal (i.e., /g, k/) consonants (Boysson-Bardies & Vihman, 1991; Daviset al., 2002; Kent & Bauer, 1985, Stoel-Gammon, 1985). Preferred vowel qual-ities include front and central, low and mid vowels (e.g., / a / , /A/ , / a / , /ae/)(Davis & MacNeilage, 1990; Davis et al., 2002). Syllable shapes include mainlyCV (me), CVC (bat), and CVCV (baby).

Fewer studies have examined consonant and/or vow el accuracy in earlywords (e.g. Davis & MacNeilage, 1990; Ferguson & Farwell, 1975; Hare, 1983;Paschall, 1983; Shibamoto & Olmsted, 1978). For children with typical hear-ing, consonants and vowels that are most often produced correctly mirror themost frequently produced segments. Labial, nasal, glide and stop consonants,especially /b, m, w/, are most accurately produced (Hare, 1983; Paschall,1983). Vowel accuracy is greatest for front and central dimensions, particu-larly I'll and /a / , before the age of 24 months (Davis & MacNeilage, 1990;Hare, 1983; Paschall, 1983). Children are better able to match consonants andvowels in the first syllable than the second syllable (Davis & MacNeilage,1990; Shibamoto & Olmsted, 1978).

Although several studies have reported phonetic distribution and accuracyfor individual consonants and vowels, the Frame/Content Theory(MacNeilage & Davis, 1990) posits a connection between elements within syl-lables. MacNeilage and Davis propose that early speech-like vocal patternsresult from rhythmic jaw movements accompanied by phonation, with littleindependent movement of other components of the speech production sys-tem. Rather than consonant-vowel (CV) sequences requiring an additionaltongue movement, consonants and vowels share the same tongue location, orarticulatory compatibility, which results in three predicted CV sequenceswithin syllables. Moving from a closed to open jaw position with a neutraltongue results in a labial consonant-central vowel pairing (e.g., "bottle" or"mama"). If the tongue is in the front of the mouth, opening the jaw results

152 ]Namer-Czyz, Davis, & Morrison

in a coronal consonant-front vowel co-occurrence (e.g., "daddy" or "sit"). Abacked tongue position results in dorsal consonants with back vowels (e.g.,"cookie" or "go"). Although children can produce a variety of CV combina-tions, they produce the CV pairings predicted by the Frame/Content Theoryat levels above chance in babbling (Davis & MacNeilage, 1995; Oiler &Steffans, 1993), first words (Davis, et al., 2002; Stoel-Gammon, 1985) and indiverse languages (see Davis & MacNeilage, 2002 for a review).

Within syllables, children are accurate more often when words contain CVpatterns they favored during babbling (i.e., labial-central, coronal-front anddorsal-back). These patterns are based on articulatory compatibility ratherthan tongue movement independent of the jaw within syllables (Davis,MacNeilage, & Matyear, 2003). This type of result suggests that when theyare accurate in early words, children with typical hearing use their availablemovement patterns from babbling. However, they are not always accurate,mainly because the lexical target characteristics of the words childrenattempt contain diverse CV patterns (Davis et al., 2003), indicating that chil-dren are not selecting only words they are capable of producing during thisperiod.

Relative to hearing peers, children with severe-to-profound hearing loss(SPHL) receive compromised acoustic information for speech sounds andexhibit difficulties developing intelligible speech patterns. Words not onlyrequire a link between concepts and production patterns, but also a connec-tion with audition to hear the unique speech spectrum (Wallace, Menn, &Yoshinaga-Itano, 1999). With the advent of CIs, children with SPHL canaccess frequency, intensity and durational characteristics of speech via acoded signal (Skinner et al., 1994; Wilson et al., 1991). This signal is transmit-ted to an electrode array that is surgically inserted into the cochlea to stimu-late remaining basal ganglion cells of the auditory nerve fibers. With earlyimplantation, children with SPHL can receive consistent auditory input of thespeech frequency range, albeit different from the auditory input affordedchildren with typical hearing, potentially resulting in development of intelli-gible oral communication comparable with children with typical hearing(Blamey, et al., 2001; Gillis, Schauwers, & Govaerts, 2002; McCaffrey et al.,1999; Moore & Bass-Ringdahl, 2002).

Children with SPHL who receive a CI have been observed to developspeech differently than children with typical hearing. They often producemore visible consonants (i.e., labials versus coronals or dorsals) (Blamey, etal., 2001; Ertmer & Mellon, 2001; McCaffrey et al., 1999; Tobey, Pancamo,Staller, Brimacombe, & Beiter, 1991). In contrast, children with typical hearingproduce more coronal consonants, consistent with distribution in ambient lan-guage (Davis & MacNeilage, 1995; Yoshinaga-Itano, Stredler-Brown, &Jancosek, 1992). Nasals outnumber oral vocalizations (Tobey et al., 1991) andvowel patterns are dominated by central and front qualities (Blamey et al.,2001; Ertmer, 2001; McCaffrey et al., 1999).


Like hearing children, children with CIs produce labial place, nasal andglide manners with greatest accuracy; fricative and stop manners are pro-duced least accurately. Ertmer, Kirk, Sehgal, Riley, & Osberger (1997)reported the highest vowel accuracy for high and back categories in animitation condition. However, available research on accuracy has focused onchronologically older children who are past the early word period, whichmay not necessarily apply to very young CI recipients (McDermott & Jones,1984).

Children with SPHL often produce more single-appearing consonants andvowels than CV syllables (Davis, Morrison, von Hapsburg, & Warner-Czyz,2005; McCaffrey et al., 1999). When syllables are present, patterns tend toreflect Frame/Content Theory predictions of consonant-vowel pairings witharticulatory compatibility (i.e., labial-central, coronal-front and dorsal-back),similar to infants with typical hearing. McCaffrey et al. (1999) examined pro-duction patterns in a young CI recipient to evaluate within-syllable organiza-tion relative to auditory access over time. Prior to CI activation at 24 monthsof age, two-thirds of this child's limited monosyllables followed theFrame/Content Theory prediction of labial-central CVs. As coronal conso-nants emerged and frequency of syllable-like vocalizations increased post-implant, she added coronal-front syllables to her repertoire. AlthoughMcCaffrey and colleagues detailed phonetic inventories and serial organiza-tion patterns in this child's speech output, they did not analyze lexical targetcharacteristics or accuracy. Very few studies to date have investigated serialpatterns in the production repertoire, lexical target characteristics, or accu-racy of very young CI recipients.

Rationale for the Study

Consonants, vowels and syllable inventories in early words in ir\fants withtypical hearing and young CI recipients have been described. However, thereis little available information that details the connections between children'searly phonetic repertoire and either lexical accuracy or characteristics ofwords they are attempting. This study examined longitudinal change in pro-duction accuracy in a child with SPHL who received a CI at 24 months.Characteristics of consonants, vowels and CV pairings were analyzed pre-and post-implant. The following questions were posed. (1) Do sounds andsyllable patterns that children produce most frequently coincide with thosethey produce most accurately? (2) Do children attempt word targets with thesame sound sequences they produce most frequently? This information couldsupport understanding of how accuracy emerges in children with SPHL fol-lowed by early implantation. The course of developing accuracy is crucial tounderstanding the path to intelligible speech in children implanted early andcan potentially contribute to assessment and intervention protocols for thispopulation.

154 Warner-Czyz, Davis, & Morrison

Method

Participant

One female child (F), identified at 12 months with bilateral profound sen-sorineural hearing loss of unknown etiology, participated. This child has beendescribed previously in McCaffrey et al. (1999). With the exception of speech,language, and hearing, F's parents reported no concerns regarding achieve-ment of other developmental milestones. She was an only child reared in amonolingual, English-speaking family. She participated in twice weeklyAuditory-Verbal therapy sessions from 13 months throughout the study.

The Rossetti Infant-Toddler Language Scale (Rossetti, 1990) was employed toevaluate speech and language. At each evaluation, results fell within the chrono-logical age level for assessment categories in interaction-attachment, gestureand play. At 22 and 28 months of age, restilts indicated a 12 month delay in lan-guage comprehension and expression. The final assessment at 32 monthsshowed a 7 month delay in language comprehension and a 10 month delay inlanguage expression. Parent diaries of utterances produced and word targetsattempted were also supplied to provide confirmation of observations madeeach recording session.

Pre-implant amplification descriptions can be found in McCaffrey et al.(1999). At 24 months, F was implanted with the Cochlear SPECTRA-22 CI inher right ear, and all 22 electrodes were successfully implanted. Initial stimu-lation with the implant occurred at age 25 months, with 19 electrodes receiv-ing stimulation via the SPEAK strategy in common ground mode. Post-implant, she discontinued hearing aid use in her left ear. Unaided, aided andimplanted auditory responses are shown in Table 1. Aided and unaidedresponses were obtained at 23 months just prior to surgery and are consistentwith responses obtained over the previous year, demonstrating that F hadlimited access to the acoustic properties of speech sounds pre-implant.Implanted responses were obtained 5 months after implant surgery.

Data Collection

Videotape samples were collected over a 14-month period in five one-hourrecording sessions: at 3 months and 1 month pre-implant and at 2, 7 and9 months post-implant (chronological ages of 22, 24, 27, 32 and 34 months,respectively). During recording sessions, an observer was always present andinteracted with the parent and child. Recordings were made of ordinaryhousehold activities and play routines between mother and child.

Vocal productions were audiotaped using a Sony TCM-5000 portable cas-sette tape recorder with a Telex ProStar FM remote microphone clipped to thechild's shoulder to maintain a consistent mouth-to-microphone distance. The


Table I. Unaided, Aided and Implanted Auditory Thresholds (American NationalStandards Institute, 1989)

ConditionSpeech

Detection 250 Hz 500 Hz WOO Hz 2000 Hz 4000 Hz

Unaided right *NR *NR 105 dB HL **NR **NR **NRUnaided left *NR *NR **NR **NR **NR **NRAided right 65 dB HL 55 dB HL 85 dB HL **NR **NR **NRImplanted 30 dB HL 30 dB HL 40 dB HL 40dBHL 35 dB HL 45 dB HL

Note. Unaided responses were obtained under headphones. Aided and implanted responses were obtained ina soundfield. Soundfield frequency specific thresholds were obtained to warbled pure tones. 'NR = no responseat 100 dB HL; "NR = no response at 120 dB HL.

FM transmitter was placed in a fanny pack at her waist. After a few minutesof orientation to the recording equipment in each session, she ignored themicrophone and transmitter. Sessions were also videotaped to disambiguateintent and content of productions during transcription.

One of the primary observers transcribed all speech-like utterances occur-ring during the one-hour sessions, utilizing broad phonetic transcription.Tokens selected as single utterance strings were bound by one second ofsilence, noise, or adult vocalization. Utterances were classified as wordattempts if there was an agreement between parent and observer that thechild was exhibiting a consistent sound-meaning correspondence, though notnecessarily comparable to the lexical target.

Data Analysis

Consonants and Vowels

Consonants were categorized according to place and manner. The placedimension included labials (/b, p, m, f, v, w/), coronals (/d, t, n, s, J, 6, 6, 3,j , 1, r, tj", d3/), and dorsals (/g, k, 0/). Manner groupings were comprised oforal stops (/b, p, d, t, g, k ?/), nasals (/m, n, g), affricates/fricatives (/f, v, s,J, 6, d, 3, tj, d3, h/), glides (/w, j / ) and liquids (/L r/). Voicing distinctionswere not considered due to the limits of phonetic transcription when appliedto infant vocalizations (Vihman & McCune, 1994).

Vowels were sorted by front-back (i.e., front, central, back) and height (i.e.,high, mid and low) dimensions, resulting in seven possibilities: high front (/i,I/), mid front (/e, e/), low front ( /«/) , mid central (/A, a/), low central(/a/), high back (/u, o/) and mid back (/o, o/).

CV syllables

Child realizations of CV syllables in word targets were grouped into fourcategories: (1) correct CV, a match of all consonant and vowel characteristics;(2) correct CV category, a match of consonant place and vowel front-back


categories to evaluate Frame/Content Theory predictions based on articula-tory compatibility; (3) incorrect CV, the production of a CV excluded from thetwo previous categories; and (4) non-CV or omitted, omission of the conso-nant, vowel or both aspects of the CV syllable.

Phonetic inventories, lexical target characteristics and accuracy of conso-nants, vowels, and CV syllables in word-based utterances are described.Frequency of occurrence was calculated for both phonetic inventory and lex-ical target characteristics. The phonetic inventory details child productionsregardless of the connection to the lexical target. Lexical target characteristicsspecify sound and sound-sequence properties of the intended target word.F's actual productions were compared to her word targets to determine accu-racy, or how frequently productions matched lexical target characteristics.Accuracy was calculated by dividing the number of correct productions bythe number of attempts in each word position. Category accuracy was calcu-lated by dividing the number of productions in the correct category (i.e.,place or manner for consonants, front-back or height for vowels) by totalattempts and includes the completely correct productions as a subset.Omissions were counted separately. Various levels of accuracy were calcu-lated to accommodate phonetic variability as a hallmark of early speechdevelopment in lexical acquisition and at this chronological age (for a review,see Vihman, 1996).

Calculations of all measures are shown in Table 2. During the first pre-implant session, F attempted the word "no" 12 times, including one attempteach for /jse, n:a, n e. A/, two attempts each for /n, n A/ and four attemptsfor / E / . F'S phonetic inventory includes various consonant, vowel, and CVpairings in her attempts to reproduce "no." Lexical target characteristics for"no" include a coronal nasal consonant-mid back vowel pairing. Consonantattempts at the coronal nasal / n / are split between correct / n / and omittedclassifications. Vowel accuracy is 0%, although she matched the mid height ofthe vowel 8 of 12 times. Attempts at the CV syllable were never correct, withfive incorrect CVs and seven isolated vowels counting as non-CVs. Overallword accuracy was 0%.

In addition to characterizing accuracy in terms of consonants, vowels andCV syllables, measures of lexical accuracy and diversity were computed.Lexical accuracy required a correct match of all consonant and vowel charac-teristics present in the target word (e.g., /kset/ for "cat"). To measure lexicaldiversity, a Type-Token Ratio (TTR) was calculated by dividing the total num-ber of different words (i.e., types) by the total number of words (i.e., tokens)(Templin, 1957). Results range from 0 to 1, with a high value indicating highlexical diversity and a low value indicating low lexical diversity. Producing10 words the same way 10 times would result in a TTR of 10 types/10 tokens= 1.0. Producing 1 word differently 10 times would result in a TTR of 1type/10 tokens = 0.1. Children with typical hearing between the ages of 3 and8 years maintain a TTR of 0.5 across the time span, although both types andtokens increase over time (Templin, 1957).


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Results for phonetic inventory, lexical target characteristics and accuracyare described chronologically within consonant, vowel and CV syllable sub-sections to emphasize longitudinal change relative to auditory access. All fivesessions were analyzed individually.

Consonants

Total consonant attempts increased from 51 pre-implant to 377 at 9 monthspost-implant. Most consonant targets occurred in initial position (M=46%,range 39% to 49%) in all sessions. Table 3 summarizes consonant results col-lapsed across word position.

Phonetic Inventory

Phonetic inventory was dominated throughout by labial place (52% to94%), particularly in initial and medial positions. Consonant place distribu-tion remained stable throughout the course of the study, although coronalsemerged more consistently across word positions in later sessions.Distribution of manner characteristics showed a similar change. Nasal conso-nants were most frequent in earlier sessions (65% to 72%), especially initialposition. At 7 months her repertoire expanded to include oral stops (64%) ininitial and medial positions in addition to glides and nasals (13% each). By 9months post-implant, stop consonants comprised 60% of productions in allpositions.

Lexical Target Characteristics

Distribution of consonant place in lexical targets followed a pattem similarto the phonetic inventory. Initial labials dominated lexical targets pre-implantin words such as "more" {n=\2), "where" {n=6) and "want" (fj=6). Of 57words produced during the 2 month session, targets with initial labials dom-inated (66%) and initial coronals (e.g., "down" and "night-night") emerged(23%). By 9 months post-implant, lexical targets showed equal attempts at ini-tial labial and coronal consonants, but more medial coronals than labials. Themost frequent lexical targets in the final session, in descending order ofappearance, were "walking," "daddy," "yellow" and "bye-bye."

Contrary to the prevalence of nasals in her phonetic inventory, F's lexical tar-gets revealed varied manners, with nasals exceeding 30% only at 2 months post-implant. Pre-implant, fricatives, liquids and stops accounted for at least 50% ofconsonants types attempted. At 7 months post-implant, stops emerged as themost frequent lexical type (64%), a trend persisting at 9 months (53%). Mannerdistribution differed by word position. Though initial fricatives (e.g., "hi") wereobserved pre-implant (66%), most irutial consonant targets in later sessions werestops (40% to 55%) in "bye-bye," "baby" and "daddy." Pre-implant, the medial


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position was dominated by the glide in "away" (58%) and stops in later ses-sions (55% to 73%). Across sessions, stops were most frequent in final position.

Accuracy

Until 7 months post-implant, F exhibited low accuraq' for either place ormanner. In all sessions, initial / m / (e.g., "more," "moo" and "mommy") wasproduced with 86% to 100% accuracy in=5 to 14 occurrences per session).Medial / w / in "away" (n=3) emerged with 100% accuracy at 2 months post-implant. After 7 months of CI use, she mastered (i.e., greater than 75% accuracy[Templin, 1957]) / b / in both initial {n=58) and medial («=48) positions. Samplewords included (in descending order of appearance) "bye-bye," "baby," "buck-buck," "ball" and "big." At 9 months post-implant, mastery of initial / d / (e.g.,"daddy," "down" and "doggie") began to emerge with 68% accuracy (n=22).

Category Accuracy

Consonant place analysis revealed greatest accuracy for labial consonantsthroughout the study, as shown in Table 3. F produced initial labials most cor-rectly (17% to 70%) in earlier sessions, a tendency sustained at 7 months post-implant. Coronal and dorsal accuracy never exceeded 30% correct. Accuracyby manner was highest for initial nasal consonants pre-implant (27% to 37%)and at 2 months post-implant (26%), primarily due to correct productions of/m/ . Glides emerged at 2 months post-implant (31%). At 7 and 9 monthspost-implant, F accurately produced stops (21 % to 29%), particularly in initialposition; nasals (16% to 21%), particularly in initial position; and glides (35%to 40%), particularly in medial position.

Although individual consonant accuracy was relatively low, F often substi-tuted consonants from the correct category. This trend was evident in labialplace accuracy, where she matched consonant place 4% to 16% more oftenthan when manner was also required.

SpecificaUy, accuracy improved from 17% for place and manner to 31% cat-egory accuracy for place only at 3 months pre-implant and from 62% accuracyto 76% category accuracy in the final session. This trend extended to manner,where stop consonant accuracy did not exceed 75% in initial or medial posi-tion, but category accuracy reached 90% to 96% during the last two sessions.

Level of accuracy showed little progress over time and did not fully revealthe nature of changes in F's production patterns. When omissions were con-sidered, F did exhibit improvement over time. Although most omissionsoccurred in final position, omissions across word position decreased fromgreater than 70% in earlier sessions to 38% to 50% in later sessions. As the pro-portion of consonant omissions decreased, category accuracy increased. Forexample, correct production of initial coronal consonants ranged from 15% at 2months to 36% at 9 months post-implant. Although accuracy remained wellbelow 50%, omissions decreased from 44% pre-implant to 23% at 9 months post-implant, and she was able to better match either place or manner characteristics.This trend was evident in all places of articulation in all word positions.


Vowels

Phonetic volubility increased from 65 vowels overall pre-implant to 334 inlater post-implant sessions. Vowels in the first syllable comprised more than70% of vowels across sessions. Table 4 details vowel results compiled acrossword positions.

Phonetic Inventory

Mid central vowels constituted the largest proportion of F's phonetic inven-tory before and 2 months after CI activation (45% to 48%). After 7 months ofCI experience, vowel types diversified to include low central (23%) as well asmid central (19%) categories. Further expansion occurred at 9 months withthe addition of high front (18%), mid back (13%) and low front (13%) vowels.Central vowels were produced most frequently except at 9 months post-implant, when front vowels comprised 35% of monophthongs. Vowel heightpatterns mainly included mid vowels until the last two sessions, when thedistribution became more balanced across height dimensions. Although in-dividual diphthongs accounted for less than 10% of vocalizations in earliersessions, the proportion of non-standard vowel qualities increased as hervowel repertoire broadened. Specifically, / a l / and /aU/ together accountedfor 15% to 22% of productions in later sessions, mostly due to correct pro-duction of the word "bye-bye" (w=42).


Mid (23% to 46%) and central (21% to 26%) vowels were attempted mostfrequently until the final sessions, when front vowels emerged (31% to 49%)and the vowel heights balanced. The most common vowels in F's lexical tar-gets varied by word position. Pre-implant through 7 months post-implant,the initial syllable of targets primarily contained mid central vowels in wordslike "away" and "buck-buck" and diphthongs beginning with a low centralvowel (i.e., / a l / in "hi", /aU/ in "down"). This pattern changed at 9 months,when low front vowels (i.e., "daddy" and "glasses") and central vowels (i.e..Baa) became most frequent. Second syllable patterns exhibited a lexical effectwith more mid front vowels (i.e., "away") in earlier sessions and more highfront vowels (i.e., "daddy" and "mommy") in later sessions.

Accuracy

Vowel accuracy surpassed consonant accuracy in all sessions. In contrast toconsonants, where omissions accounted for the majority of target attempts, Fomitted only 6% of monophthong vowel targets. Thus, omissions will not bereported. Syllable accuracy pre-implant was highest for low front (66%, «=3)and mid central vowels (69%, «-29) in the words "hat" and "away," respec-tively. By 7 months post-implant, 11 of 15 high front vowels (e.g., "green,"


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"sleep," "big" and "please") were produced correctly in the first syllable. At9 months, F achieved the correct vowel category at least 50% for six differentcells: high back, high front, low central, low front, mid back, and mid central.No accurate vowels were transcribed in the second syllable until later ses-sions, when F matched 11% to 83% of mid back targets (n=32) in words like"yellow" and "uh-oh" and 59% to 62% of high front vowels (M=45) in wordslike "daddy," "kitty" and "piggy"

Category Accuracy

Front-back analysis revealed central vowel accuracy above 70% comparedto front (29% to 69%) and back vowels (0% to 86%). Height analysis showedhigher accuracy for mid vowels in earlier sessions but comparable accuracyfor all three heights in later sessions.

Consonant-Vowel (CV) Syllables

F's attempts at syllable-based CVs in words increased dramaticallybetween the pre-implant sessions (n=56-59 CVs) and 9 months post-implant(»=286 CVs). Table 5 describes the proportion of CV syllables in lexical targetcharacteristics and accuracy.

Phonetic Inventory

The Frame/Content Theory prediction for child productions is that CVpairings based on articulatory compatibihty (i.e., labial-central, coronal-frontand dorsal-back) will be produced more often than those requiring an addi-tional tongue movement. Labial-central pairings accounted for 36% to 89% ofproductions across sessions.


In contrast, CV patterns in lexical targets were diverse relative to patternsfound in F's productions. Diverse CV types exceeded CVs characterized byarticulatory compatibility by more than 60% in earher sessions, when coronal-back (19% to 26%) (e.g., "more" [n=32] and "no" [n=13]) and labial front (e.g.,"away" [n=22]) combinations comprised the majority of her lexicon. In the 7month session, she more frequently attempted predicted CVs (i.e., labial-central,coronal-front and dorsal-back) in lexical targets (61% vs. 39%), particularly "bye-bye" (tt=32), "daddy" (M=11), "red" in=9) and "go" («=5). The CV syllables inlexical targets became more evenly distributed at 9 months post-implant as sheexpanded her vocabulary over time.

Accuracy and Category Accuracy

Table 5 displays F's ability to achieve correct productions of specific CV syl-lables, and Figure 1 depicts levels of accuracy for CV syllables overall. Any


Table 5. Accuracy and Error Patterns in Consonant-Vowel (CV) Syllables in Targets

r u- 1 cLa b la 1-r ron t(e.g., "baby")

L,aDla l-K^k^TyiTai

(e.g., ''mommy")

(e.g., "push")

n 1 c ILoronai-rtont(e.g., "daddy")

Coronal-Central(e.g., "yuck")

„ 1 D 1L. oronal- oa CK(e.g., "no")

p . 1 c ,

L/orsa 1- r ront(e.g., "kitty")

p. I r- 4. ^U o r s a l - ^ w e n t r a l

(e.g., "guppy")

n 1 n 1LJorsai-DacK

n

Proportion of attemptsCorrect CV

Correct CV categoryIncorrect CV

Non-CV or omitted

Proportion of AttemptsCorrect CV


Non-CV or omitted



Non-CV or omitted



Non-CV or omitted



Non-CV or omitted



Non-CV or omitted



Non-CV or omitted



Non-CV or omitted



Non-CV or omitted

Months re: Cochlear Implant Activation

-3 (Prel) -1

59

0.440.000.050.090.82

0.180.000.330.000.67

0.100.600.000.000.40

0.000.000.000.000.00

0.020.000.001.000.00

0.260.000.000.000.62

0.000.000.000.000.00

0.000.000.000.000.00

0.000.000.000.000.00

(Pre2)

56

0,390.070.000.000.86

0.000.000.000.000.00

0.310.000.000.000.18

0.000.000.000.000.00

o.n0.00O.DO0.000.50

0.190.000.000.000.71

0.000.000.000.000.00

0.000.000.000.000.00

0.000.000.000.000.00

2m

74

0.210.000.070.000.67

0.100.140.140.140.57

0.340.040.000.160.16

0.030.000.000.001.00

0.230.000.180.120.65

0.030.000.000.000.50

0.070.000,000,001.00

0.000.000.000.000.00

0.000.000.000.000,00

7m

273

0.160.220.070,000.27

0,410.570.270.010.06

0.070.220.170.060,00

0,180.100.040.290.39

0.110.260.290.060.10

0.040.250.500.080.42

0.000.000.000.000.00

0.000.000.000.001.00

0.020.200.000.000.20

9m

286

0.170.340.120.000.32

0.170.580.210.000.08

0.090.120.000.120.54

0.190.150.080.110.38

0.090.190.040.190.22

0.120.450.030,030.36

0.160.020.000.040.42

0.010.000.000.001.00

0.001,000,000.000.00

Note. Totals may not sum to 100% due to omissions of the CV syllable. Abbreviation: NA, not attempted.

Early Production Accuracy

Ita.

100%

75%

50%

25%

0%

CI Activation

Pre 1 Pre2 2 (n-74) 7 (n-273) 9 (n-286)(n-56)

Months re: Cochlear Implant Activation

I Correct C VI Incorrect CV

^Correct CV CategoryD Non-CV or Omitted

Figure 1. Accuracy and category accuracy of consonant-vowel syllables.

statement about CV syllable accuracy pre-implant and 2 months post-implantmust be made cautiously due to low occurrence of CV targets in these ses-sions. F rarely achieved the correct CV in earlier sessions though she obtained100% accuracy in "more" (n=3) in the first pre-implant session and 33% CVcategory accuracy for "Baa" {n=3), the name of her toy sheep. Before CI acti-vation, most CVs in lexical targets were realized as non-CV or omitted utter-ances {M=79%, range: 18% to 86%). Complete omission of the CV syllablecomprised less than 15% of total attempts in any session because F oftenmarked a syllable with a single vowel.

After 7 months of CI use, the proportion of non-CV vocalizations decreasedto 18% (range: 6% to 100%), suggesting a positive effect of auditory experi-ence on her ability to produce a CV in lieu of a vocalic singleton. Overall CVaccuracy improved to 35% (range: 10% to 57%), with an additional 20% CVcategory accuracy (range: 4% to 50%). In later sessions, 49 labial-central syl-lables, a pattern predicted by the Frame/Content Theory, were producedmost correctly with 57% to 58% CV accuracy and 79% to 84% CV categoryaccuracy. The high level of accuracy relates to her correct renditions of "bye-bye" (w=12), bunny {n=5) and mommy (n=4). All other CV syllables were pro-duced correctly less than 50% of the time.

Worrfs

Throughout the study, F exhibited poor word-level accuracy, whichrequires a correct match of all consonant and vowel characteristics of the lex-

166 Yiamer-Czyz, Davis, & Morrison

ical target. In the first three sessions, she demonstrated an overall word accu-racy of 0%. She achieved 6% accuracy for words in the 7 month post-implantsession, with greater than 75% accuracy for "bye" (H=3) and "like" {n=\). At9 months post-implant, her overall word accuracy improved to 14%. She wasat least 75% correct for the following words: "Baa" («=8), "two" {n=4),"wash" (H=4), "eye" {n-3), "pee" (n=3) and "up" (n=l).

In addition to word accuracy, we measured the variety of word attempts.F's lexical diversity, as assessed via TTR, remained steady between 0.25 and0.32 throughout the study. Rather than suggesting a lack of improvement indiversity, TTR stability may reflect an increase in sample size such that as thenumber of utterances increases, words tend to repeat, and TTR subsequentlydecreases. Watkins, Kelly, Harbers, and Hollis (1995) proposed using thenumber of different words as a more sensitive and informative index of worddiversity. Examining the number of different words revealed a more strikingpattern, with 18, 15, 27, 60 and 85 different words at 3- and 1-month pre-implant and 2, 7 and 9 months post-implant, respectively.

Discussion

This young CI recipient expanded her phonetic inventory, attempted morediversified lexical targets and improved target accuracy, particularly for vow-els, as she gained auditory experience with speech cues. Consonant andvowel qualities produced did not necessarily influence lexical targets sheattempted. However, her most frequently produced segments (i.e., labialplace, nasal manner and central vowels) were generally most accurate. CVsyllables she produced conformed to Frame/Content Theory predictionsbased on articulatory compatibility between the consonant and vowel,although her lexical targets did not. CV syllables produced most accurately atnine months post-implant (i.e. labial central) also reflect Frame/ContentTheory predictions.

Phonetic Inventories

Results for consonant, vowel and CV inventories were congruent in generalwith data on children with typical hearing in the early word period (Davis etal., 2002; Kent & Bauer, 1985). Labial place dominated her consonant reper-toire in all sessions whereas stop and glide manners emerged in later ses-sions. Front, central, low and mid vowels were produced most frequentlyacross sessions. CV production patterns reflected Frame/Content Theorypredictions of labial-central pairings, supporting prominence of vocaliza-tions based on articulatory compatibility. Because the sound and syllablepreferences in canonical babbling and early words exhibit continuity (e.g.Davis & MacNeilage, 2002; Vihman, 1996), F's production patterns also par-alleled the vocal output of infants with the same auditory experience, orhearing age, of seven to nine months. The resemblance between F and her


hearing age-matched peers helps to shed light on how the addition of audi-tory information via a cochlear implant impacted her speech production.

Aside from these consistencies, important differences exist relative to chil-dren with typical hearing. F preferred nasals in earlier sessions, a qualityoften described for children with SPHL (Tobey et al., 1991). As she gainedauditory access to ambient language patterns, the proportion of nasals dimin-ished from 70% at 2 months to 13% at 7 months post-implant to more closelyreflect data on infants with typical hearing (Davis et al., 2002) and ambientlanguage patterns (Davis & MacNeilage, 1995). A second dissimilarityinvolved change in inventories over time. Although F's consonant distribu-tion remained stable across the study, Boysson-Bardies and Vihman (1991)reported a concurrent decrease in labials and increase in coronal and dorsalconsonants over time in the early words of children with typical hearing. Apossible explanation for this difference is that the length of the study did notallow observation of change in place distribution. Without enough auditoryexperience and with limited visual information on lingual consonants, con-sistent integration of coronals and dorsals into her repertoire might not haveoccurred by 9 months post-implant.


Consonants and vowels attempted in lexical targets mirrored those mostfrequently produced for place (Ferguson & Farwell, 1975; Vihman, Kay,Boysson-Bardies, Durand, & Sundberg, 1994). However, consideration ofphonetic context within syllables pointed to a different interpretation. CVs inword targets were more diverse throughout, indicating no evidence for selec-tion or avoidance relative to the early lexicon, as has been explored for chil-dren with typical hearing (e.g., Schwartz & Leonard, 1982). Differences inword characteristics may also reflect factors such as maturation related tochronological age and training related to targets in therapy.

Accuracy

An overall pattern for the development of accuracy emerged. For dimen-sions analyzed, available production system characteristics guided earlyaccuracy results. F produced labial consonants and central vowels both mostfrequently and most accurately. She mainly produced labial-central CVsalthough the lexical target characteristics did not always contain labial-central patterns. Also, F was most accurate for labial-central CVs, supportingthe proposal that early speech is guided by closed-open jaw oscillations withlittle or no additional articulatory movement within syllables (MacNeilage &Davis, 1990). Viewed together, these findings reflect use of production systemcapacities as a means to bootstrap to intelligible speech in early words.

Early accuracy patterns coincide with those of infants at the same develop-mental level (i.e., early word period), but the question arises as to how F'sabilities compared with those of her hearing peers. Several studies have


shown that children achieve labial consonant accuracy early (Hare, 1983;Prather, Hedrick, & Kern, 1975), a pattern also seen in F's productions.However, comparison of F's results with children who have typical hearingat the same chronological age revealed a dramatic difference in degree ofaccuracy (see Table 2). At age 21-24 months, the accuracy of children withtypical hearing (Hare, 1983) far surpassed F's pre-implant results in all cate-gories by 20% to 84%. The gap begins to close for labials in later sessions (13%to 22% difference), but not for any other consonant place. The most noticeabledifference for manner of articulation is that F's overall accuracy for consonantmanner never exceeded 50%. This differs from her age-matched hearingcounterparts, who achieved at least 50% accuracy for all manners in all timeperiods except for liquids at 21-24 months (Hare, 1983) and nasals at 36months (Prather et al., 1975).

Vowel accuracy has received little attention in children above the chronolog-ical age of 24 months, primarily because children attain high accuracy for vow-els early on (Stoel-Gammon & Herrington, 1990). Templin (1957) reported that3 year olds accomplished a mean percentage of 93.3% correct for vowels, sug-gesting that major development for vowels occurs prior to 36 months, Stoel-Gammon and Herrington (1990) divided vowels into two categories based onprevious research: early mastery/high accuracy (i.e., /i, u, o a. A/) and latemastery/low accuracy (/I, e, E/) using a 75% criterion for mastery. F's voweldevelopment follows a similar order: she mastered early central vowels like /A/and mid vowels like /A, o/, but the level of accuracy for back vowels seemedconsiderably lower than those reported for children with typical hearing.

Overall, the growth in F's production output and accuracy reflects the inputreceived from the production and auditory systems over time. Pre-implant datashows the combination of experience with the production and visual percep-tual systems with little auditory input, which evolved limited phonetic inven-tories typified by visible labial consonants and neutral vowel qualities with fewCV syllables. These results are consistent with heightened visual processing abil-ities in individuals with congenital deafness (Neville, Schmidt, & Kutas, 1983).

The introduction of audition via CI changed the stable platform on whichvocal patterns were based pre-implant. At 7 months post-implant, F diversi-fied consonant, vowel and CV syllable types, albeit with little accuracy.Greater accuracy emerged after 9 months of CI experience, particularly forvowels. Ertmer (2001) found similar improvement in vowel accuracy, whichhe attributed to the perceptual salience of vowels due to longer duration andsteady state parameters. This relative access in the auditory signal may alsoexplain why vowel accuracy exceeded consonant accuracy across sessions.

In addition, the length of exposure to auditory input prior to differentiatedinventories and improved accuracy might reflect the process of multimodalintegration, or the interaction between visual and auditory perception(Lewkowicz, 2000; Massaro, Thompson, Barron & Laren, 1986). Lewkowiczvaried place, manner and voicing of a stimulus and presented the informa-tion both unimodally (i.e., audition only or vision only) and bimodally (i.e..


audition and vision). Results indicated that all featural characteristics (i.e.,place, manner and voicing) of the bimodal syllable were salient by 8 monthsof age. Likewise, this child required seven to nine months of auditory experi-ence before substantial differences were apparent in phonetic inventory orproduction accuracy. Although the amount of time needed for multimodalintegration may differ based on age at onset of hearing loss, age at implanta-tion, and therapeutic strategies, these results suggest that incorporation ofnew sensory input (e.g., audition) requires time before the system can achievemultimodal integration.

This young CI recipient increased volubility, expanded her phonetic inven-tory, diversified target attempts and improved accuracy as she gained audi-tory experience. Future research should focus on interaction of phonetic andlexical factors through lexical selectivity and avoidance in a larger cohort ofchildren with CIs. As the age at which children are implanted decreases, lon-gitudinal analysis of the phonetic repertoire in words relative to accuracy willbecome an important factor in documenting potential benefits to earlierimplantation in larger groups of children.

Acknowledgements

Portions of these data were presented at the Early Lexical AcquisitionConference, Lyon, France, in December 2001 and at the American Speech-Language-Hearing Association Annual Convention, Atlanta, Georgia, inNovember 2002.

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