Title: Evaluation of Core Vocabulary Therapy for Deaf Children: Four Treatment Case
Rosalind Herman*, Katie Ford+, Jane Thomas+, Natalie Oyebade*,
Danita Bennett* & Barbara Dodd*
*City University London
Language & Communication Science Division,
Northampton Square, London EC1V 0HB
+Oxleas NHS Foundation Trust
Memorial Hospital, Shooters Hill, London SE18 3RG
Dr. R. Herman email@example.com
Language & Communication Science Division,
London EC1V 0HB
This study evaluated whether core vocabulary intervention (CVT) improved single
word speech accuracy, consistency and intelligibility in four 9-11 year-old children
with profound sensori-neural deafness fitted with cochlear implants and/or digital
hearing aids. Their speech was characterised by inconsistent production of different
error forms for the same lexical item. The children received twice weekly therapy
sessions for eight weeks. Fifty target words were drilled and changes in production
assessed for accuracy and consistency. Generalisation of consistency and accuracy was
assessed on non-targeted words. There were four assessment points: six weeks pre-
therapy; immediately before therapy; immediately following therapy and six weeks
post-therapy. In addition, ten unfamiliar listeners judged the intelligibility of audio
recordings of the children’s speech before and after therapy. The children’s consistency
and accuracy of single word production improved following CVT. Consistency
generalised to untreated words. Sentence intelligibility ratings improved and more
target words were identified after therapy. These case studies suggest that CVT merits
further investigation as an effective intervention approach for deaf children, enhancing
consistency, accuracy and intelligibility of speech.
KEY WORDS: Core vocabulary therapy, hearing-impaired, deaf, speech
intelligibility, speech consistency, listener feedback, intervention
Deaf students’ speech intelligibility is crucial for oral communicative competence
(Marschark, & Spencer, 2006) and social development (Most, 2007). However, few
studies have evaluated specific interventions to enhance the speech intelligibility of
children with prelingual, profound deafness. Some intervention approaches target
impaired articulation at a phonetic level (e.g., electropalatography, Pantelemidou,
Herman & Thomas, 2003; ultrasound, Bacsfalvi, 2010). Other studies focus on
phonological knowledge that underpins the acquisition of both speech intelligibility and
literacy (Thomson & Goswami, 2010; Leybaert 2005). Core vocabulary therapy (CVT),
designed for hearing children making inconsistent speech errors, targets both
articulatory and phonological aspects of word production (Dodd, Holm, Crosbie, &
McIntosh, 2010). The case studies reported here evaluated whether the poor speech
intelligibility of four children with cochlear implants and/or hearing aids would be
enhanced by CVT.
Characteristics of deaf children’s speech production skills
Since the days of early research characterising the effects of deafness on speech (e.g.,
Hudgins & Numbers, 1942), technological advances such as cochlear implants have
lead to significant improvements in the intelligibility and language of deaf speakers
(Marschark & Spencer, 2006). For example, Blamey et al. (2001) monitored the
conversational speech of nine children from when they received their implants between
2-5 years until aged 6-11 years. The final assessment revealed that the number of
intelligible words per utterance had increased from 3.6% to 80.8%, despite an increase
in sentence complexity, reflecting great accuracy in the production of monophthongs,
diphthongs and consonants. Although speech acquisition was incomplete six years post-
insertion, indicating slow development, there was no evidence of a plateau in
performance (ibid). Tobey, Geers, Sundarrajan and Shin (2011) assessed 110
adolescents with cochlear implants at 8-9 years and again at 15-18 years to identify
factors influencing speech intelligibility. Participant, family, and performance measures
at the first assessment predicted improvements in speech accuracy at the second
assessment. The most important influences on adolescents’ speech intelligibility were
the extent to which participants’ relied on oral communication and their use of shorter
sentences (Tobey et al., 2011). A similar finding emerged from an investigation of the
speech intelligibility of 17 children with cochlear implants, aged 4-11 years (Khwaileh
& Flipsen, 2010). Single word and sentence level intelligibility were linked to the
extent of cochlear implant use rather than age at implantation.
In contrast, De Raeve (2010) reported that the intelligibility of connected speech was
related to age of cochlear implantation. Children receiving implants after 23 months
had lower intelligibility than those implanted before 18 months. Marschark and
Spencer’s (2003) review concluded that receiving a cochlear implant at a younger age
leads to higher levels of communication skills while a late age of implantation is
associated with negative long-term speech and language outcomes.
Despite the benefits of cochlear implants for profoundly deaf children, Ouellet and
Cohen’s (1999) review emphasised great variability in post-implant performance for
speech intelligibility, vocabulary and sentence structure. Factors affecting outcomes
included age of onset, degree of hearing loss, extent of amplification experience and
type of intervention (Khwaileh & Flipsen, 2010; Ouellet & Cohen, 1999). The data
reviewed suggests that speech intelligibility remains an issue for some children with
cochlear implants. The proportion of children having poorer outcomes after cochlear
implantation, however, depends on the population studied. Children fitted with hearing
aids alone also have a range of speech intelligibility outcomes, although these are
typically less positive than those of children with cochlear implants (Lejeune &
Interventions targeting speech
Traditional interventions to establish spoken language focus on the phonetic level, i.e.
the articulation of single sounds, then on phonology, i.e. use of sounds contrastively in
meaningful words (Ling, 1984). For example, four adolescents with moderate to severe
deafness received 14 weekly, 30 minute, individual sessions using instrumental
feedback. Treated consonant accuracy improved by 36% compared to 15% for
untreated sounds. Speech intelligibility was not measured and no long-term follow-up
data on maintenance of gains was reported (Bernhadt, Gick, Bacsfalvi & Ashdown,
2003). A single case study of an 18 year-old deaf client used electropalatography to
target accurate alveolar plosive production (Martin, Hirson, Herman, Thomas & Pring,
2007). The statistically significant gains made, measured perceptually and
instrumentally following six bi-weekly hour-long intervention sessions, were
maintained and generalised to untaught words. A review of intervention focusing on
phonetic targets using electropalatography and/or ultrasound, however, found the
evidence base to be limited (Vuckovich, 2007).
An intervention targeting phonology (Massaro & Light, 2004) trained eight 6-10 year
old deaf children to identify and produce 24 vocabulary items using residual hearing
and lip-read cues presented by a computerised ‘talking head’. Students also read and
wrote the words. The students received 18 twice weekly 30 minute sessions. Children
learned 72% of the words receptively and 64% expressively, with learning retained four
weeks after therapy ended. No measures of generalisation to speech intelligibility were
made.Core vocabulary therapy (CVT) combines both phonological and articulatory
cues to teach the intelligible production of words of high functional importance for
children, their families and school classrooms. Clinical intervention trials indicate that
CVT successfully targets inconsistent phonological disorder in hearing children. A
review of the evidence for CVT with hearing children (Dodd, et al., 2010) included
case studies, group comparison of children with different types of speech disorder
(consistent and inconsistent errors) receiving different intervention programmes (CVT
and phonological contrast) and a randomised control trial. The results indicate that an
approach targeting both phonetic and phonological aspects of word production achieves
intelligible speech, usually after eight hours of intervention (twice weekly, 16, 30-
minute sessions). The long-term goal of therapy is to teach children to plan consistent
production of the sequence of phonemes for specific lexical items. Children are taught a
set of 50-70 target words selected for their functional value to the child, their family
and school. Clinical research suggests that once a threshold level of words has been
taught, consistency and accuracy of production generalises to untaught words (Crosbie,
Holm & Dodd, 2005). The methods section details the components of CVT.
Experimental studies comparing hearing children who make inconsistent errors with
those who make consistent errors indicated different profiles of speech processing
strengths and weaknesses (Dodd, 2014). Children whose speech is characterised by
non-developmental consistent errors do poorly on cognitive-linguistic tasks (e.g.,
phonological rule derivation, phonological awareness, literacy). In contrast, children
making inconsistent errors appear to have a phonological assembly difficulty, i.e. in
consistently selecting and sequencing the phonemes that make up a word. While the
nature of inconsistency has been well described, both theoretically and clinically, little
is yet known about the nature of inconsistency in children who are hearing impaired.
The trigger for the current study was provided by Speech and Language Therapists
(SLTs) working in schools with provision for deaf students. They reported CVT was
useful when working with children whose speech intelligibility had plateaued following
therapy that adopted traditional approaches in targeting specific phonemes in isolation
and in words (Martin, 2009, personal communication). The theoretical rationale for
using CVT for this study is that prelingual deafness might lead to internal phonological
representations of words that are incomplete or inaccurate. In addition, the ability to
implement the phonetic plan for a word from an intact representation may be limited by
poor self-monitoring of speech output. Inconsistent and/or erroneous word production
would arise from both deficits. CVT targets the underlying phonological representation
of words, ensuring that the client is aware of and can articulate all speech sounds in a
specific word in the correct sequence, consistently. Once a word’s best production has
been elicited, it is drilled in single words, carrier phrases and sentences, developing the
ability to assemble phonology and plan the phonetic program from a word’s intact
mental representation (e.g., Dodd et al., 2010). The importance of practice to
automaticity has previously been emphasised by Perigoe and Ling (1986).
The research questions concern whether CVT can increase the accuracy of sounds in
words in order to enhance the speech intelligibility of four deaf children. While the
children attended the same school, they had different hearing histories, language
exposure, communication methods and motivation.
It was hypothesised that there would be a significant increase from pre-therapy to post-
therapy measures after CVT:
In Percentage Consonants Correct (PCC) and Percentage Vowels Correct (PVC)
for words targeted in CVT therapy, and
For PCC and PVC in non-targeted therapy words in the Diagnostic Evaluation
of Articulation and Phonology Inconsistency Subtest (DEAP: Dodd, Hua, Crosbie,
Holm, & Ozanne, 2002);
In consistency of production of single words targeted in therapy and a set of
control words not targeted in therapy
In the intelligibility of the children’s speech, measured by listeners’
identification of single word targets and listeners’ comprehension of spoken sentences.
Table 1 presents individual participant data. The children attended a mainstream
primary school with a resource centre for deaf pupils. Total Communication (Sign
Supported English and British Sign Language) was used consistently. Each child
received weekly specialist speech and language therapy.
Insert Table 1 here.
Ten listeners rated the participants’ speech intelligibility. Three were male and seven
were female with an average age of 22 years (range 13-29 years). None of the listeners
knew the participants or had any training in phonetics or experience with deaf speakers.
1. All children were initially assessed on the Diagnostic Evaluation of Articulation and
Phonology (Dodd, et al., 2002), administered and scored according the assessment's
manual. Participants completed the diagnostic screen, which indicated whether they
should receive the consistency and oro-motor subtests. All children had inconsistency
scores of greater than 40% at that initial assessment. If a child’s inconsistency score is
40% or more, they are diagnosed with inconsistent speech disorder based on
inconsistency data from typically developing and undifferentiated speech disordered
children. None of the participants performed poorly on the oro-motor assessment,
indicating that no apraxic or dysarthric characteristics were present. Subsequent
assessments included the consistency and phonology subtests from the DEAP to gain
measures of both consistency and accuracy (PCC, PVC and percent phonemes correct
(PPC). The four assessment points were: 1) six weeks prior to therapy, 2) immediately
before therapy, 3) immediately following therapy and 4) six weeks post-therapy.
2. Therapy Resources. Each participant received a CVT homework book that listed
current target words, represented in written words and pictures. The parents and class
teachers were provided with their child’s best production of each word, e.g. MA’s best
production of /rules/ was [ɹu], therefore the English spelling ‘roo’ was provided for
ease of interpretation. A board game with dice, a counter and letter cards was used
during the drilling sessions to encourage repetition of target vocabulary.
Parents and teachers completed a post-therapy questionnaire rating their experience of
CVT including the amount of practice they had offered the children and the progress
Before the start of intervention, according to CVT protocol, approximately 85 words
were collected from each child, their parents and teachers. Fifty were selected for
targeting in therapy, ensuring inclusion of educationally and socially important
vocabulary as well as words the children wanted to say better, enhancing motivation.
The taught vocabulary contained a variety of phonemes, syllable shapes (CV, VC,
CCVC, CVCC) and words of more than one syllable. Ten untreated probe words were
matched to target words for syllable length and complexity to monitor consistency
during intervention. Probe words were elicited three times in separate trials every
second session. Children were presented with pictures of the probe words and had to
name them. This occurred three times within the session, each occasion separated by
another activity. Video recordings were made to ensure accurate transcription. These
data were only analysed for consistency, not accuracy, to detect when generalisation of
Participants were offered 16 twice weekly 45 minute therapy sessions during the course
of the study. In the first weekly session, each child randomly selected 10 target words
for that week from a box containing all 50 targets. The child’s best production was
elicited for each of these 10 words by breaking the word down into separate syllables,
and syllables into separate sounds. The aim was not the accurate adult production of
each word but the child’s best possible production. When the correct production could
not be elicited for a sound, a developmental error used by typically developing children
was accepted, e.g. [t] for /k/; [b] for /bl/; [w] for /r/. Cued Articulation (Passy, 1990)
was sometimes used to elicit participants’ best productions of words as it had been used
in previous therapy with these participants. CVT allows the use of any cues (e.g.
Prompt, finger spelling, written letter sequences, cued articulation) to elicit a child's
best production, irrespective of whether a child is hearing or hearing impaired. Best
productions were identified and transcribed, then practised in games to establish
consistency. This is a crucial component of CVT. When the best production is not used,
listeners (clinician, parent, teachers) say “That is not the way we say it. Remember?” If
it is still not produced, then cues are given about the phonological structure of the word
(e.g. number of syllables, the sounds in the first syllable, and other syllables. When a
child uses their best production, they should receive positive feedback, that is, specific
about the word's structure, e.g., “You said that word just right. It had a 's' at the
beginning and a 'n' at the end. People would understand you when you said it.” There
was an emphasis on the child actively remembering the production pattern, rather than
In the second weekly session, selected words were drilled in games. Children
consistently produced their ‘best production’ of each target word at least 20 times.
Once they could produce a particular word consistently (tested at different points
throughout the session), the word was allocated to a “Words I can say well” pile on a
visual chart. Words produced inconsistently were allocated to a “Words I need to
practise” pile. Words that had been drilled were revisited the following week to review
their consistency: any words that children struggled to say consistently were placed
back into the ‘word box’ to be targeted another week. At the start of therapy, children
were asked what they wanted to receive as a reward and were reminded of this during
therapy. Children received their reward once therapy was completed.
The implementation of CVT with deaf participants presented a number of challenges.
The student therapists carrying out the intervention used basic SSE to support the
children’s understanding of the presented activities. In addition, visual explanations
using pictures demonstrated what was expected. Due to limitations in staff availability
it was not possible to have an experienced signer or Teacher of the Deaf (TOD) attend
Homework carried out by parents and teachers
Homework sheets and class-work sheets were used to liaise with families and teachers.
It was essential for children to practise their words outside the therapy sessions to
develop consistency of word productions and promote generalisation. Traditional CVT
has included the parent/carer being present at every session. However, in the current
study, this was not possible for parents. The homework sheets provided a detailed
breakdown about how to carry out CVT homework practice with their child. Parents
were advised to help children practise for at least 10 minutes every day. The sheets also
provided a checklist for parents to mark off when they had finished practising each
week and they were encouraged to provide feedback or make comments on their child’s
production of the target words. Where parents were unable to support their child,
another family member was enlisted.
Teachers were familiar with the use of Cued Articulation and had received training
from the SLT in its implementation. The class sheets contained information on the
specific cues used in the session and advised teaching staff to encourage the child by
using cues that helped to elicit their best production of the target words. Children
practised their words at least three times a week during literacy lessons with support
For the purposes of listener intelligibility ratings, a 30 minute audio recording was
presented individually to 10 unfamiliar listeners. It comprised 80 sentences, 10 spoken
by each of the four participants on two occasions, before and after CVT. The last word
of each carrier sentence was a word targeted in therapy (see Table 2). The order of
sentences and of the children producing them was randomised. The listeners could only
hear the children speaking; no visual clues (signs or lip patterns) were provided. All
recordings were made in a quiet room using identical recording conditions. Each
sentence was presented twice and listeners could request a third presentation. The
listeners were asked to a) identify and write down the last word in each sentence (1 =
correct identification of whole word, 0 = incorrect), and b) rate the overall intelligibility
of each sentence on a four point scale of understanding (1= nothing; 2= part; 3= most;
4= entire sentence).
Insert Table 2 here
Reliability of coding was assessed by two raters independently phonemically
transcribing the 50 words from video of the DEAP phonology assessment for each
participant. If the phonetic variation was within the phonemic category of the target
phoneme, the realisation was counted as correct. The transcriptions were compared for
number of correct consonants and vowels present in relation to the target word.
Transcriptions were highly correlated (0.939, p<0.001) indicating high inter-rater
The quantitative and qualitative data collected were used to evaluate the effectiveness
of CVT for the children’s speech intelligibility, consistency and generalisation of
therapy. Below we present the study findings at each of the four assessment points.
Table 3 presents the scores obtained for the two DEAP assessments carried out at the
two pre-therapy assessment points. All children had more accurate vowel than
consonant production and exhibited inconsistency at a level indicative of inconsistent
speech disorder. SI and DB had the highest levels of inconsistency while SI and MA
made more consonant and vowel errors. DK achieved the highest PCC and PVC scores
and also had the lowest level of inconsistency. All children showed small positive
changes at the second assessment point, with the mean difference scores for consonants
being +6%; for vowels +3.5%; and for inconsistency -15%. These changes probably
reflect increased familiarity with assessors, procedure and stimulus items.
Insert Table 3 here
Comparing pre and post-therapy scores
To investigate whether or not therapy was effective, the mean of the two DEAP pre-
therapy scores for each of PCC, PVC and inconsistency were compared to the
immediate post-therapy scores (see Table 4). All children showed positive changes
post-therapy, with the mean difference scores for consonants being +10.3%; vowels
+10.8%; and inconsistency -19%.
Insert Table 4 here
Individual differences were apparent. SI increased consistency of word production by
28% but accuracy changed little. MA improved his vowel accuracy by 20% and
consistency by 24%. DK’s consistency increased by 20% but accuracy gain was
limited. DB gained only 14% in consistency but accuracy improved for both consonants
(17.5%) and vowels (17%). Given that core vocabulary primarily targets consistency of
production, it is not surprising that all four children showed gains post-therapy that
exceeded their pre-therapy change.
Maintenance of therapy
To explore whether benefits from therapy were maintained after therapy had ceased, a
comparison was made of the immediate post-therapy DEAP scores and those obtained
6 weeks later (see Table 5). By the maintenance assessment point, the mean positive
difference score for consonants was +4.2% and for vowels +5.5, indicating that speech
accuracy was maintained. Change in inconsistency varied: one child became 8% less
consistent, one made no change, one improved consistency by 12% and one by 32%.
Two of the children had consistency below the diagnostic criterion of 40% of the
DEAP (Dodd, et al., 2002). For the group the mean decrease in inconsistency between
the combined pre-therapy assessments and the final follow-up assessment was 30.5%
(range 20-46%). Although statistical analyses should be treated with caution for such a
small clinical sample, a paired t-test was significant (t (2) = 7.1813, p < 0.02).
Insert Table 5 here
Generalisation to untaught words during therapy
Every second week, children named ten untaught words matched for phonological
complexity to ten of their target words. There was a 30% decrease in inconsistency
between sessions three and seven for two of the children: SI from 80% to 50%; MA
from 70% to 40%. Consistency data for the other two children were unavailable as one
student mislaid her data. PCC accuracy improved between sessions three and seven for
three of the four children: MA 25%; DK 31%; DB 15%, but there was no change for SI
with a 3% gain.
Results of listener ratings of sentence intelligibility and listener identification of target
words are presented in Table 6. Paired t tests showed that sentence intelligibility ratings
(t(9)= 8.44, p=<0.001) and word identification (t(9)=5.10, p=0.001) were significantly
Insert Table 6 here
Parent and teacher questionnaires
All four class teachers reported that they had practised three times per week with each
child. They noted that children showed benefits by becoming more intelligible in class
and more confident when speaking or reading aloud at school. One teacher mentioned
that she now felt more confident in her ability to correct children’s speech errors
appropriately following the intervention.
Parental feedback questionnaires were returned by two of the four children’s parents.
One mother reported that she had practised three times per week with her child. The
other parent had only practised at weekends. Both reported satisfaction with the therapy
their child had received and felt that there were noticeable improvements in their
children’s speech. One parent requested that further CVT therapy should be offered.
For another child (DB), it was evident from speaking to him that although he had
practised his target words regularly at school, practice at home had been sporadic.
Clinical trials indicate that CVT is an effective intervention for hearing children who
make inconsistent speech errors (Dodd et al., 2010). The evidence base includes case
and group studies, as well as a randomised control trial. This paper presents the first
evaluation of CVT with a small group of deaf children, the first step of the development
of an evidence base for a particular approach to intervention (Robey & Shultz, 1998).
All children made significant improvements in their speech intelligibility post-therapy.
In addition, change was evident when measured by listener ratings of intelligibility and
word identification and more informally from parent and teacher report.
Importantly, there was evidence of generalisation to untaught words and gains made
were maintained six weeks after therapy had ended. The CVT described in this study
specifically targeted single word speech accuracy. Nevertheless, the higher ratings of
sentence intelligibility post-therapy using listeners who were unfamiliar with deaf
speech are indicative of gains extending beyond the single word level.
Speech characteristics prior to therapy
Initial DEAP assessment results indicated that all children made inconsistent speech
errors. They had been referred specifically because they had reached a plateau in their
speech development with traditional therapy, suggesting their speech was resistant to
change. The four children’s inconsistency scores were surprisingly high (range 40-
80%) for a group of children with hearing impairment who had received intervention
over many years. Although the second pre-therapy assessment showed some decrease
in inconsistency, all four children’s scores met criteria for a diagnosis of inconsistent
speech disorder (Dodd et al., 2002).
It is surprising that inconsistent speech production of the same lexical item has not
previously been reported in the literature for deaf children (e.g., Tobey, et al., 2011).
Indeed, descriptive studies usually report deaf children’s speech errors to be systematic
(Parker & Rose, 1990) and to respond best to phonological rather than phonetic
intervention approaches when these have been compared (Paatsch, Blamey & Sarant,
2001). The current results indicate that even at the single word level, many lexical
items were pronounced differently on repeated production, affecting listeners’ ability to
learn how a child says a particular word. It may be that the inconsistent speech of these
children is atypical of primary school deaf children fitted with cochlear implants.
Alternatively, given that most speech assessments only require children to say each test
item once, consistency of word production is not often tested and may have been
overlooked due to the use of assessment measures that focus on phonetic repertoires
and severity measured by counting errors.
Vowels were less prone to error than consonants, reflecting previous research on
phonological acquisition of deaf children (e.g. Hudgins & Numbers, 1942). The
percentage of consonant errors made by the four children studied varied: two were in
the severe range with fewer than 50% correct consonants, one moderate – severe (50-
64%), and one moderate (65-85%) according to Bowen’s (2013) criteria. The wide
variation shown in only four children probably reflects variation in factors such as age,
language learning background (two were bilingual), age at implantation, means of
communication at home and school, and support in the use of hearing aids and cochlear
implants (Marschark & Spencer, 2006).
Response to CVT
The results indicated a reduction in inconsistency with three children attaining scores at
or below the threshold of 40% criterion for diagnosis of inconsistent speech disorder.
One child, who continued to show 56% inconsistency, may benefit from further therapy
focusing on consistency of production given that he was absent for three sessions. CVT
not only reduced inconsistency in the participating deaf children's word production, but
also led to improvement in consonant accuracy although the mean improvement
between the combined pre-therapy assessments and the final follow-up assessment was
limited (15%) compared to that of three hearing children (33%) (McIntosh & Dodd,
2009). Nevertheless, by the final assessment, one child could be classed as mild and
one as moderate and even the two whose accuracy remained in the severe category
showed improvements of 14% and 15% in PCC. Vowel accuracy remained relatively
constant across assessments, with severity of impairment in the mild to moderate range.
The improved intelligibility ratings and identification of target words in sentences
suggest that the impact of CVT on communication was greater than might be predicted
by consistency and accuracy scores. Perhaps the acceptance and reinforcement of
developmental speech errors aided listener comprehension despite words not being
accurate. This intervention strategy might have contributed to maintenance and a trend
for continuing improvements at the final follow-up assessment.
CVT is inherently motivating because children, their parents and teachers play an active
role in selecting the target vocabulary and in practising outside of therapy sessions. All
children practised their target words regularly in school and enjoyed the therapy
sessions, particularly when they became aware of the improvements in their speech and
when others commented on their progress. However, outside school, regular practice
was only confirmed for 1 child, was occasional for 2 children and information was
missing for the fourth child, whose parents spoke little English. Nevertheless,
observable progress was made by all participants. By drilling a substantial number of
words intensively to achieve each child’s best production, children’s phonological
representations were stabilised and their intelligibility improved. The progress made,
then, might be considered clinically significant. Even in the absence of large gains in
consonant accuracy, consistency of word production allows listeners to learn how
children say particular words, enhancing communication (Bernstein-Ratner, 2006).
In hearing children, inconsistent speech errors in the absence of childhood apraxia of
speech are attributed to an impaired ability to assemble a phonological plan (the
sequence of phonemes to be uttered) from an intact mental phonological representation
of a word (Dodd et al., 2011). The cause of inconsistent errors in deaf children may
differ. Should future research indicate that inconsistent production of the same lexical
item is prevalent in this population, it would need to be explained. One plausible
account would be that children learning to use information provided by a cochlear
implant take time to build complete and accurate underlying phonological
representations for words. These representations are thought to underpin both speech
intelligibility and literacy (Leybaert 2005). An incomplete representation (e.g. /m-æ-
plosive/ for ‘mat’) would result in a variety of different spoken realisations ([mæt];
[mæp]; [mæk]; [mæs]; [mæd], etc.) as well as an impaired ability to map between
written words, phonology and meaning, affecting literacy.
The identification of inconsistent speech errors among a small group of deaf
participants with persistently poor intelligibility suggests that clinicians need to
consider the impact of inconsistency on speech and literacy and the implications for
intervention. CVT was successful in achieving significant speech improvement.
Nevertheless, there is a need for the intervention to be better adapted for this
population. Future research might establish the prevalence and nature of inconsistency
in the speech of deaf children to better inform the development of CVT for deaf
Research has noted the variability in outcomes following cochlear implantation
(Marschark & Spencer, 2006). Of the four children referred, three used cochlear
implants either alone or in addition to a digital hearing aid. In view of their poor speech
intelligibility, they may be considered to be relatively unsuccessful implant users. One
explanation for this may be the timing of implantation. In all cases, implantation or
activation of the implant occurred between the ages of 3 and 5 years, which is
considered late by current standards (Marschark & Spencer, 2006). Interestingly it was
the participant who used only digital hearing aids (DK) who presented with the best
speech. A further participant (SI) presented with additional difficulties, having been
diagnosed with autism and a speech-language disorder. Nonetheless, he made
significant improvement. Further research is needed to evaluate the usefulness of CVT
therapy for children with impaired hearing whose speech is characterised by
inconsistent errors. Case studies would build evidence concerning which children
respond positively to CVT. Experimental studies exploring the intactness of
phonological representations and phonological assembly skills would allow better
understanding of how CVT affects the speech processing skills of hearing impaired
This study has identified a small group of deaf children who made inconsistent speech
errors. For these children, CVT was an effective intervention approach, enhancing
consistency, accuracy and intelligibility of speech. Clearly caution is needed in drawing
conclusions from four individuals. Nevertheless, despite widely differing profiles and
differences in initial speech ability, the results indicated the usefulness of CVT for all
children. Further research is needed on larger numbers of participants, at different ages
and from different language learning contexts. That research might explore ways in
which CVT can be better adapted for deaf children, to determine the potential of CVT
to enhance real world communication.
We would like to thank the children, their families and teachers who participated so
enthusiastically in this research.
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Table 1. Participant information
Speech production /
ASD (at 5
activated at 3
at school and
Parents & SI
using SSE +
Highly inconsistent on
Not stimulable for
production of velar
consonants [g, k, ŋ]
Imitated a range of
syllable structures and
away ill for
activated at 5
at school and
Parents & MA
using SSE +
vowels & consonants
Consonants /v, n, ŋ/
were not stimulable
Poor discrimination of
on left /
at school and
except for one
of her three
Parents & DK
using SSE +
contrasts and many
discriminate: /t, k/, /d,
g/, /ʃ, tʃ/ and /z, d/
Often omitted WFC
activated at 4
at school but
except for DB’s
spoken at home
Parents & DB
structures and vowel
contrasts by listening
PBSNHL: profound bilateral sensori-neural hearing loss; ASD: autistic spectrum disorder; SLD: speech
and language disorder; CI: cochlear implant; HA: hearing aid; WFC: word final consonants.
Table 2. Treated words included in pre- and post-therapy sentences for listener ratings
Table 3. DEAP assessment scores at pre-therapy assessment points 1 and 2: PCC and
PVC and percentage inconsistency scores
Table 4. DEAP pre and post-therapy assessment scores: PCC and PVC and percentage
Table 5. DEAP assessment scores at two post-therapy assessment points: PCC and
PVC and percentage inconsistency scores.
Table 6. Mean listener sentence intelligibility ratings (N=10) and word identifications
pre- and post-therapy