Using electropalatographic feedback to treat the speech of a child with severe-to-profound hearing loss.

Abstract

The speech production of a 7-year-old child with severe-to-profound hearing loss and severe speech disorder was treated using visual feedback via electropalatography (EPG). The child's productions of /k/ and /t/ were treated in consonant-vowel syllables in three vowel contexts. A single-subject multiple-baseline design was used to document treatment effects and generalization. Visual inspection and multiple time-series analyses were used to assess the data. The child demonstrated a treatment effect for /k/ as measured by lingual-palatal placement and perceptual adequacy of the productions. A treatment effect for /t/ also was suggested. Generalization was observed for the production of /g/ at the syllable level, and /g/ and /k/ in monosyllabic words in the word-initial position. Generalization to other sounds and word-final positions was not evidenced. Of note was the extreme performance variability associated with the treatment.

Key Words: Electropalatography, Speech Treatment, Hearing Loss, Children.

Introduction

The ability to develop the motor and linguistic skills for the normal production of speech typically requires a relatively intact auditory system. Audition is critical for the development of a linguistic system with its phonological performance rules and associated acoustic goals (Tye-Murray, 1992). Furthermore, recent auditory-based models of speech development and production argue that a multi-dimensional auditory perceptual space emerges during infancy and provides the basis for the development and maintenance of speech (Callan, Kent, Guenther, & Vorperian, 2000; Guenther, 1995; Perkell et al., 1995, 1997). Speech production is learned by mapping the orosensory information to acoustic-based targets (or regions) within this auditory space. So, speech impairment and reduced speech intelligibility are expected consequences of prelingual hearing loss if early and substantive intervention does not occur (Hudgins & Numbers, 1942; Smith, 1975; Yoshinaga-Itano & Sedey, 1998).

Most children with hearing loss require some type of intervention if they are to speak intelligibly and in a manner acceptable to normal hearing listeners, even though the character and severity of the speech impairments vary greatly across children. Much of the variability relates to the severity of their hearing impairment, but even children with mild-to-moderate hearing loss are at risk for resonance and segmental speech problems (Elfenbein, Hardin-Jones, & Davis, 1994; Oller & Kelly, 1974; West & Weber, 1973). The speech differences of children with mild-to-moderate hearing loss typically are treated in the same manner as the speech of hearing children, but children with more severe hearing loss tend to require more aggressive and long-term treatment to become effective oral-aural communicators. Despite the acknowledged long-term need, well-controlled studies documenting speech treatment effectiveness and efficacy is limited for this population. Even in the growing cochlear implant literature, little has been reported on what behavioral treatment approaches work best with the various types of speech impairments that occur secondary to hearing loss in children. Nearly all treatment approaches applied to children with hearing loss try to stimulate optimal use of residual hearing and/or compensate for the hearing loss by developing alternate routes for input and feedback (see Pratt, 2005 and Pratt & Tye-Murray, 1997 for reviews). Implementing speech treatment through the auditory modality typically is preferred if the auditory system itself can be treated (i.e., sensory devices and auditory training) so that sufficient sensory input and feedback are accessible. However, if hearing is limited and children are unable to form or interface with a complete internal auditory mapping of the auditory space, speech production will be restricted. Furthermore, there remain a substantive number of children with hearing loss who fail to develop normal speech production and phonology skills despite appropriate and early fitting of sensory devices and adequate behavioral intervention (Blamey et al., 2001; Serry & Blamey, 1999, 2001; Uchanski & Geers, 2003). Augmentation or stimulation through other sensory modalities may be required for speech skill acquisition or correction to take place. Although not without controversy, the visual modality frequently is used to provide sensory input and feedback during speech treatment.

Visual Feedback

Using visual and other non-auditory forms of sensory feedback is a critical distinction between the major therapeutic approaches for treating speech impairment in children with hearing loss. The relevance of non-auditory and artificial forms of feedback to the speech sensory-motor system is the primary issue. So too, is whether these forms of feedback interfere with the development of the auditory system and it's linkage with speech production. The traditional multisensory treatment approaches accept the use of non-auditory modalities, and the inclusion of artificial input and feedback to train speech skills (Carhart, 1947, 1963; Ertmer & Maki, 2000: Magner, 1979; Silverman, 1971). In contrast, proponents of auditory-verbal approaches have been more cautious in the use of visual feedback, particularly artificial or augmented visual feedback (Estabrooks, 1994; Ling, 1976, 2002; Pollack, 1985). They have argued that the focus of therapy should be to improve residual hearing and auditory function, and that other types of sensory feedback interfere with the development of the auditory skills that are needed to promote and sustain speech production. The intent of instruction is to strengthen the auditory system or force strategy formations through the training of auditory perception and feedback. The goal is better utilization of speech-acoustic information by the impaired ear so that speech develops more naturally. In some respects, strict adherence to the auditory-verbal approaches can be viewed as a form of constraint-based therapy; a therapeutic approach that restricts the use of the more intact parts of a system in an effort to isolate and focus training on the more impaired part of the system (Pratt, 2003). In auditory-verbal approaches, visual speech cues typically are restricted with even naturally occurring visual speech eliminated at some levels of training. Constraint-based (or constraint-induced) therapeutic approaches were initially developed for the treatment of motor impairments (Mark & Taub, 2002; Schaechter et al., 2002; Taub, Crago, & Uswatte, 1998), but they also have been successfully applied to other clinical populations, such as persons with aphasia and those with cognitive impairments (Jennings & Jacoby, 2003; Lillie & Mateer, 2006; Pulvermuller et al., 2001). Nonetheless, empirical evidence is lacking in the application of constraint-based speech treatment approaches with children with hearing loss, irrespective of severity and type.

Despite the concerns raised about the use of artificial or augmented forms of feedback such as visual feedback provided by computer-based speech feedback systems, Ling (1976, 2002) acknowledged that visual and other forms of non-auditory feedback (artificial and naturally occurring) may be beneficial when some children are initially learning to produce particular sounds. However, because children might become dependent on the feedback, Ling warned that visual and other non-auditory forms of feedback should be withdrawn as quickly as possible. Although not tested in children with hearing loss, his concerns have been supported in the motor-learning literature. For example, Puttemans, Vangheluwe, Wenderoth and Swinnen (2004) found that artificially augmented visual feedback interfered with the learning of a bimanual motor task in which the participants simultaneously learned independent spatial trajectories with the upper limbs. Similarly, Lintern, Roscoe, and Sivier (1990) argued that skill learning of motor tasks can be hindered by artificial and augmented feedback when intrinsic feedback (feedback inherently associated with the task, such as muscle tension) is minimal or difficult to interpret. A dependency results from the feedback becoming a part of the motor memory during practice, and when it is withdrawn the weaker intrinsic feedback is not sufficient to support the skill (Proteau & Cournoyer, 1990; Proteau, Marteniuk, Girouard, & Dugas, 1987). Dependence on augmented feedback and feedback that is not intrinsic to the task is particularly problematic when the task and feedback are simple and feedback is provided on every trial (Weinstein & Schmidt, 1990; Wulf, Shea, & Matschiner, 1998). However, behaviors that are complex and have multiple characteristics, such as speech, may be less affected by the frequency of the feedback. So, the 100% feedback schedule that commonly is used by clinicians and most computer-based speech feedback systems might not be detrimental to skill acquisition and generalization.

The lack of consensus on the application of visual feedback when treating speech production in speakers who have hearing loss leads to the question of how and when visual and artificial forms of feedback are most effectively applied. Furthermore, questions exist about which types of speech impairments and clinical groups are most amenable to treatment with visual feedback. These questions are relevant to computer-based feedback systems because most depend on some form of visual feedback. A further complication is that visual feedback is artificial, and typically transformed and restricted to a limited number of features (typically one) for ease of understanding (Bernstein, 1989; Pratt & Hricisak, 1994). As a result, the feedback characteristics are many steps removed from the act of producing speech. For example, moving an object on a screen to a graphic target by producing acoustically adequate vowels is many steps removed from the coordinated movements of the speech mechanism that produced the vowels.

Effectiveness of Computer-based Speech Feedback

Computer-based speech feedback systems have been proposed for over two decades as a way to improve speech production in children with hearing loss due to the visual nature of the feedback (Bernstein, 1989; Watson & Kewley-Port, 1989). Computer-based feedback systems have been developed to train speech skill acquisition and to modify existing speech behaviors. The ultimate goal is that computer-based feedback systems will be developed in such a way that children can use them independently; potentially increasing the amount of time that children can be involved in therapy without substantially increasing clinician contact and cost (Watson & Kewley-Port, 1989; Osberger, Moeller, Kroese, & Lippmann, 1981). Independent use is a critical matter for children with hearing loss because, as stated previously, they frequently require long-term treatment and extensive practice. Moreover, many speech-language pathologists have limited experience working with children who have hearing loss. So to address these issues, the visual feedback provided by computer training programs must be easily understood by children and effective at producing appropriate change (Bernstein, 1989; Pratt & Hricisak, 1994; Watson & Kewley-Port, 1989). Most of the commercially available computer-based feedback systems include a number of independent modules, and target a range of acoustic parameters of speech such as voicing, vocal pitch and vocal intensity (Pratt & Hricisak, 1994). In most systems the modules vary in the type and complexity of feedback provided (e.g., modifying pitch represented on a frequency scale vs. maneuvering a maze by adjusting voice-onset-time). Hence, each module needs to be assessed relative to the types of speech impairments that match the particular foci of the modules, the cognitive demands of the feedback, and the interest level of the activities and feedback.

Only a limited number of studies have documented the effectiveness of commercially available visual feedback systems with children who have hearing loss. In a study using single-subject design with replication, Pratt, Heintzelman, and Deming (1993) observed that the Vowel Accuracy Module of the IBM SpeechViewer effectively promoted correct vowel production in five preschool-aged children who had hearing loss, although clinician involvement was critical when using the module with youngest of the children. These younger children needed additional instruction and encouragement from a clinician to benefit from the computer-based feedback. Spaai, Derksen, Hermes, and Kaufholz (1996) similarly found that visual feedback for pitch contour production was more meaningful for children 9 to 11 years of age than it was for children 6 through 7 years. The implication from both studies was that development and cognitive skills should be a considered when selecting feedback systems or the modules within systems.

It has long been argued that many spectral displays are too complex for use as feedback during speech training, but Ertmer, Stark, and Karlan (1996) found that spectographic feedback with the first and second formants highlighted was effective in treating vowel production in two nine-year-old deaf children. However, clinician instruction and encouragement was an integral component of the treatment protocol, and generalization to untreated vowels was limited. Later, Ertmer and Maki (2000) compared the efficacy of traditional behavioral instruction (multisensory approach with clinician feedback) against behavioral instruction in conjunction with visual feedback from a spectrographic display. The /m/ and /t/ productions of four teenage deaf children were treated at the monosyllabic word level and both approaches resulted in improvement. Yet, the relative differences between approaches were child and speech-sound dependent, making it difficult to ascertain the direct influence of the spectrographic display.

A synthesized three-dimensional head (Baldi) that allows visual access to the oral articulators has been developed for the study and treatment of speech and language (Massaro, 2004). The feedback provided by Baldi is visually complex but more directly related to actual speech production than many other feedback displays. Massaro and Light (2004) recently used Baldi to treat the speech perception and production skills of a small group of school-aged children with hearing loss. Positive treatment changes were observed from pre to post-treatment, but it was difficult to determine the direct impact of the visual feedback and whether the visual feedback was the source of the changes due to the multifaceted nature of the treatment program. Moreover, a control-group was not used, and treatment design-controls were not implemented.

The limited number of studies in which computer-based feedback has been applied to the treatment of speech production in children with hearing loss have demonstrated benefits (Bernhardt, Gick, Bacsfalvi, & Ashdown, 2003; Dagenais, Critz-Corsby, Fletcher & McCutcheon, 1994; Ertmer & Maki, 2000; Ertmer et al., 1996; Fletcher & Hasegawa, 1983; Osberger, Moeller, Kroese, & Lippman, 1981; Pratt et al., 1993; Ryalls, Michallet, & Le Dorze, 1994; Spaai et al., 1996). As indicated above, the benefits are influenced by developmental status of the children, and the nature of the training task and the feedback provided. Younger children are less able than older children to use these systems independently and generally need a clinician present to provide supplementary instruction and feedback. As such, computer-based feedback systems should be considered therapy tools rather than treatment approaches when used with young children, although, even with older children the nature of the feedback should correspond with the skills and disorders presented by each individual child.

The expectation is that the selection, applicability and the effectiveness of computer-based visual feedback will be dependent on the speech characteristic being treated. Visual feedback may be particularly helpful with speech features that are susceptible to hearing loss, as well as speech gestures associated with limited visibility and proprioceptive feedback. For example, the articulation of velar sounds like /k/ and /g/ are not easily viewed. Consequently, they often are poorly articulated or omitted by speakers with severe-to-profound prelingual hearing loss (Geffner, 1980; Tye-Murray & Kirk, 1993). If children are unable to adequately hear these sounds even with appropriately fitted sensory devices and auditory training, the use of computer-based visual feedback may be a reasonable treatment alternative. The electropalatometer (or electropalatograph or palatograph) is a computer-based system that provides artificial visual feedback that is particularly illustrative of sounds requiring lingual contact with the palate, such as /k/ and /g/.

Electropalatometric (EPG) Feedback

Electropalatometers consist of a pseudopalate that is worn against the palate and in which electrodes are embedded, although efforts have been made to use pressure transducers rather than electrodes (Murdock, Goozee, Veidt, Scott, & Meyers, 2004). The electrode leads are fed out of the mouth to a computer and when a region of the pseudopalate is contacted by the tongue, circuits are completed between the electrodes in that region and read by the computer. The computer monitor displays the area of the contact on a cartoon of the palate and electrode array. The feedback is direct and online, although articulation cannot be immediately linked to acoustics because the pseudopalate and extruding electrode leads distort the sounds produced. Therefore, any connections between articulation, speech acoustics and audition need to be accomplished offline. So too, tactile and proprioceptive feedback associated with lingual contact with the pseudopalate differ somewhat from that produced with the pseudopalate removed. In order to benefit from EPG feedback patients need to be able to generalize from the artificial feedback condition to more natural speaking situations.

Although most EPG systems do not provide direct information about movement or contact pressure, EPG has been used to describe the lingual-palatal contact patterns for a range of speaking tasks, and to explain the speech articulation of disordered populations, such as speakers with dysarthria, cleft palate, and articulation/phonological disorders (Gibbon, 2002; Gibbon, Ellis, & Crampin, 2004; Hartelius, Theodoros, & Murdoch, 2005; McAuliffe, Ward, & Murdoch, 2006; McLeod, Roberts, & Sita, 2006). It similarly has been applied to speakers with hearing impairment. For example, Dagenais and Critz-Crosby (1991) identified five patterns commonly associated consonants produced by children with profound hearing loss. The patterns included an open configuration with little or no contact, a closed configuration with full lingual-palatal contact, front occlusion with lingual contact around the entire alveolar ridge, back occlusion with contact only toward that back of the palate, and a grooved configuration with contact at the extreme lateral sides of the palate. The open configuration was the most common pattern observed, especially with lingual stops. Dagenais and Critz-Crosby (1992) also found that vowels produced by children with profound hearing loss were characterized by a flatter tongue posture and less vertical movement than those produce by children with normal hearing. Dagenais and Critz-Crosby (1991; 1992) further observed that these patterns often were used idiosyncratically by children with profound hearing loss, particularly those with poor intelligibility.

Although most studies using EPG have used it to characterize the articulatory patterns of different speaker populations or to characterize differences across speech segments, articulatory contexts and languages; a number of studies have been conducted looking at the effectiveness of the feedback provided by EPG when treating speech impairment in speakers with normal hearing. For example, EPG has been used to effectively treat speech production in patients with apraxia of speech (Howard & Varley, 1995), various forms of dysarthria (Gibbon & Wood, 2003; Hartelius, Theodoros, & Murdoch, 2005) cleft palate (Scobbie, Wood, & Wrench, 2004) Down's syndrome (Gibbon, McNeill, Wood, & Watson, 2003) and school-aged children who stutter (Craig et al., 1996).

A restricted number of EPG treatment studies have been reported with children with hearing loss. Pantelemidou, Herman and Thomas (2003) reported a case study in which EPG was used to treat the /k/ and /g/ productions of a child who wore a cochlear implant. Pre to post-treatment comparisons of lingual to velar placement suggested improvement; although the perceptual assessment of the target productions were not error-free and experimental control was limited. Similarly, Bernhardt et al. (2003) used EPG in conjunction with ultrasound-based visual feedback with four deaf adolescents. Pre to post-test comparisons of their participants' productions were consistent with improvement but this study also suffered from inadequate controls, too few subjects, and an under-specification of the treatment. In contrast, Dagenais et al. (1994) conducted a group treatment study that compared Ling's (1976) treatment approach (a commonly used auditory-verbal treatment approach) to speech treatment with EPG feedback. They enrolled two groups of nine school-aged children with profound hearing loss and observed positive outcomes with both approaches. When comparing the target-sound productions, treatment with EPG was more effective than the Ling approach, but intelligibility was similar across the two approaches when tested at the single-word level. It could be argued that noninstrumental training approaches, such as the Ling approach, may be preferable to treatment with EPG feedback for children who are able to acquire speech skills through audition given the lack of a substantial difference between treatment approaches, and the hardware requirements and cost associated with EPG. However, treatment data have not been reported for children for whom these more traditional auditory-verbal approaches have failed. The following describes a single-subject treatment study in which EPG was used with a child who was unable to develop functional speech through an auditory-verbal training program.

Methods

Participant Description

The participant was a seven-year-old boy with a severe-to-profound bilateral sensorineural hearing loss that was presumed congenital. He had been fitted with appropriate binaural amplification as a toddler and consistently wore his hearing aids. His aided and unaided thresholds are illustrated in Figure 1. Despite residual hearing up through 4000 Hz, the child exhibited poor functional auditory skills, although his performance on the Test of Auditory Comprehension (Office of the Los Angeles County Superintendent of School, 1980) was appropriate for his age and hearing loss severity. His performance on the Early Speech Perception Test for Profoundly Hearing Impaired Children (Moog & Geers, 1990) was consistent with the test's category 2, indicating that he could discriminate simple patterns and words of dissimilar syllable number and stress, but had difficulty discriminating words of similar stress and syllable number. However, speechreading performance was 97% correct when augmented with audible speech as tested at the word level with The Craig Lipreading Inventory (Craig, 1964/1990). It should be noted that at the time of this treatment study the child's parents were not interested in him receiving a cochlear implant.

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The child's speech production was severely impaired. At the beginning of the study he was 35% intelligible at the single-word level as measured by the CID Picture SPINE (Monsen, Moog, & Geers, 1988). He also had a severely restricted sound inventory and limited vocal control as tested with the Goldman Fristoe Test of Articulation (Goldman & Fristoe, 1986) and the Phonologic Level Speech Inventory (Ling, 1976). He had a functional set of vowels although most non-central vowels were distorted. His consonants at the syllable level were limited to frontal sounds, mostly labial sounds. Many of the correct productions were vowel-context specific, with /a/ being the easiest context; /i/ and /u/ the most difficult. He could repeat vowels but had difficulty repeating CV syllables and was unable to alternate dissimilar syllables. At the word and phrase levels, consonants were typically omitted.

When first fitted with his pseudopalate the child consistently produced an open configuration with little if any lingual contact with the palate during speech production (Dagenais & Critz-Crosby, 1991). His oral mechanism examination (St. Louis & Ruscello, 1987) indicated that his oral structures were intact and there was no indication of dysarthria or apraxia of speech, although apraxia of speech could not be completely ruled out due to the limited number of sounds that the child was able to produce. He had been enrolled in an oral school for children with hearing loss for approximately four years. He had received treatment for speech via an auditory-verbal approach in which auditory stimulation and training was the primary treatment avenue. He was referred for the treatment study by his speech-language pathologist because he was not making the expected gains.

Treatment Design

Treatment. An ABA single-subject treatment design was employed using multiple baselines to document treatment and generalization effects. A Kay Palatometer (Kay Elemetrics, 1993) was used to provide the visual feedback. The /k/ sound was treated initially because the child was unable to produce posterior consonants. The sound /t/ was later treated to provide an oppositional placement to the /k/ and to document any generalization to anterior-articulated sounds. The two consonants were trained in consonant-vowel (CV) syllables with three vowel contexts, /i/, /a/, and /u/. These vowels were chosen because they require lingual positions that are distinct from one another, and as such, encourage variation in the articulation between the consonants and vowels. This type of variation is believed to promote learning and generalization. The treatment criterion was 80% correct placement within all three vowel context for two consecutive sessions.

Treatment occurred twice a week with at least two days between sessions. It consisted of the examiner showing the child an orthographic representation of the target syllables while also producing it. Each syllable combination was presented in blocks of ten with the order of the blocks randomized across sessions. The target region on the computer display of the child's pseudopalate was highlighted, and the child attempted to produce the syllable by matching the visual target. Each vowel context had a slightly different contact region based on normal contact patterns and was used to encourage appropriate coarticulation. After each production, the child indicated if he had matched the target. This was done to document that the he was attending to the feedback and evaluating the results. He also was given feedback from the examiner relative to his judgments. That is, the child received feedback from the display, knowledge through the generation of a judgment, and confirmation from the examiner. The child's judgments were correct over 96% of the trials.

Acquisition was measured at the beginning of each subsequent session. It was assessed by testing the child's production of the CVs without feedback from the EPG. The child's CV productions were judged for placement with the pseudopalate in place. The pseudopalate was then removed and the CVs were repeated and judged perceptually for acceptability by the examiner. The examiner judged the perceptual acceptability of the entire syllable, not just the target sound.

Generalization. The /t/ baseline was used to assess generalization during the treatment of /k/. In addition, the production of /g/ and /r/ in CV syllables, the production of /k/ and /g/ in words, and single-word intelligibility were assessed to document generalization. The /t/ and /g/ productions in CVs were assessed perceptually and for placement. The remaining measures only were assessed perceptually.

The /t/ was monitored to determine if the treatment of /k/ generalized across place of articulation. The /g/ was selected to document generalization because the child had difficulty coordinating voicing and lingual placement simultaneously. When he was able to achieve adequate lingual placement for /g/ voicing often deteriorated. The /r/ production in CV syllables was monitored in order to establish that any changes in /k/ production were not attributable to uncontrolled factors, such as development and classroom activities. The /r/ was chosen because it differed from the target sounds in place and manner of production, and was not likely to change in response to the treatment but could reflect changes due to uncontrolled development or training factors. The generalization of the treatment to /k/ and /g/ production in CVC words was assessed to document generalization from the syllable to the word level (initial and final word position). Also, pre and post-tests of single word intelligibility was completed with the CID Picture SPINE.

To document the perceptual reliability of the examiner, samples of the child's speech productions were judged independently for acceptability by the examiner and two graduate students in Audiology. The students had two years experience working with deaf children. They listened to 30 randomly selected CV syllables of each targeted consonant. Agreement ranged from 87 to 97% between the three listeners, and between the listeners and the online judgment of the examiner recorded during the sessions.

Results

The results, relative to placement, are illustrated in Figures 2 and 3. Those that were evaluated perceptually are shown in Figures 4 through 6. Three judges familiar with single-subject treatment data independently evaluated the placement and perceptual figures for treatment and generalization effects. The judgments were made for overall effects for the target consonants and for each vowel context. An effect was considered present if there was consensus across the three judges (Brossart, Parker, Olson, & Mahadevan, 2006; Jayaratne, Tripodi, & Talsma, 1988).

Judgments of Treatment Effect

The judges agreed that there were treatment effects for /k/ (overall and in all vowel contexts) when assessed for placement and perceptual changes in CV syllables. Treatment effects for /t/ were not present for the placement data but were observed for the perceptual data overall and in the contexts of /i/ and /a/. It is acknowledged that the judges were cautious about over-interpreting the /t/ treatment data because of the limited number of sessions in the treatment phase. The /t/ treatment was terminated early, before reaching criterion, because the child outgrew his pseudopalate and his parents were reluctant to have a new one fitted.

Judgments of Generalization

The judges indicated a generalization of the treatment of /k/ to /g/ overall for both placement and perception, but only within the /i/ and /a/ contexts for placement, and the /a/ context when judged from the perceptual data. Generalization to /k/ and /g/ at the word-level was observed in the initial position only. A lack of generalization to /t/ was observed, which increased the likelihood that the gains in /k/ production were a result of the treatment alone. Furthermore, no generalization was observed for /r/, which also suggested that the observed treatment and generalization effects were due to the treatment and not other factors such as developmental gains. Single-word speech intelligibility increased only minimally from 35 to 43% suggesting that the treatment resulted in limited overall gain in speech performance.

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Statistical Analysis of Treatment and Generalization

Time series analyses were implemented with the C statistic to supplement the judges' evaluations of the treatment data (Jones, 2003; Suen & Ary, 1989; Tyron, 1982). The C statistic is less affected by autocorrelation than many other parametric tests and considered a reasonable statistic when testing for changes in clinical single-subject data (Jones, 2003). For the comparisons tested, the alpha was set at .05 and controlled only at the contrast level because of the preliminary nature of the treatment study and because the C statistic was used to supplement the results of the expert judges.

The functions for all of the sounds and contexts were tested according the pre-treatment (A1), treatment (B) and post-treatment (A2) phases established during the treatment of /k/ to assess treatment effects and generalization. The A1 baselines were compared independently to the B and the A2 data for both placement and perception. The pretreatment and treatment phases for /t/ also were tested but were limited to documenting the treatment effects for /t/. The results of all of these tests are shown in Tables 1 and 2.

The C statistics agreed with the judges with regard to the presence of /k/ treatment effects, generalization to word-initial /k/ and /g/ productions, and the lack of generalization to word-final /k/ and /g/ productions, and /r/ in CV syllables. In contrast, the C statistics did not confirm the judges' determination that a treatment effect was lacking in the /t/ placement data (overall and all three vowels) and for the /ta/ perceptual data. In these instances the judges were more conservative than the statistics. The statistics largely confirmed a generalization of the treatment of /k/ to the /g/ productions in CV syllables when evaluated perceptually. The placement data were less consistent, however, with the judges being less conservative than the statistics particularly with the /ga/ placement results. These inconsistencies likely were due to the substantial variability in the /g/ data across sessions.

Discussion

The results of the analyses confirmed a treatment effect for the treatment of /k/ in CV syllables with the EPG feedback. The treatment effect was observed in all three vowel contexts and evidenced by lingual-palatal placement and perceptually with the pseudopalate removed. The treatment of /k/ generalized to /g/ in CV syllables and to /k/ and /g/ in word-initial CVC words but it did not generalize to /t/ or /r/ in CV syllables. Of note, however, were the delays between the onset of the /k/ treatment and the resulting effects. Similarly, the number of sessions needed to meet criterion was substantial. It took 4 to 5 sessions before the child started to shift from his neutral lingual placement for /k/, and it took 22 sessions to reach criterion. Although large, when comparing the total number of trials it was within the range observed by McReynolds (1984) who treated VC syllables in hard-of-hearing children. Another concern is that once change began, performance variability became extreme across sessions and vowel contexts, particularly in the perceptual data. There was a general improvement in /k/ and /g/ productions, but /k/ placement accuracy cycled substantively across sessions with perceptual accuracy even more variable across sessions and vowel contexts. Eventually the /k/ stabilized and then it maintained after the direct treatment of /k/ was withdrawn and the treatment of /t/ was initiated. However, the placement and production of /g/ did not stabilize at the syllable level and may have needed direct intervention or a modification of the treatment protocol to stabilize.

Not evident in the treatment figures was that the child's productions were highly volatile within treatment sessions. Before the /k/ productions stabilized, it was common for the child to abruptly switch between an accurate placements and being unable to even approximate a correct placement. His productions were correct for a number of trials and then he would suddenly lose the skill, so that he performed in a near binary fashion. These abrupt changes within sessions might reflect the difficulty of learning speech through vision with limited access to auditory feedback, whereas the variability across sessions probably reflected destabilization and reorganization (or self-organization) associated with learning a new speech task.

When treatment began with /t/, it too was characterized by increased variability, although the increased variability was more directly linked to the onset of treatment. As indicated previously, the pretreatment baselines for /t/ did not illustrate direct generalization of the /k/ treatment, but prior experience with the EPG likely facilitated this early onset of variability. Moreover, during the /k/ treatment phase the child's /t/ placement shifted from a non-palatal fricative production (similar to /h/) to a velar placement. So, although his production of /t/ was incorrect the child was applying skills he had acquired while learning to produce /k/. It also is possible that more generalization might have occurred if /t/ had been treated first since it is more visible than the /k/. McReynolds (1984) observed that children with hearing loss demonstrated more generalization when trained with visual sounds than when training occurs with sounds made towards the back of the mouth. It also is possible that the blocked training and 100% feedback may have hampered generalization.

The general patterns of acquisition illustrated by this child likely reflected motor learning but also learning acquired largely independent of audition. Increased variability commonly is associated with the learning new motor skills, followed by a decrease in variability as the skill becomes more automated. Similar patterns have been observed with language, cognitive and perceptual learning and development, and may be followed by a series of fluctuations in variability (see van Geert, P. & van Dijk, 2002, for review). From a dynamical systems approach, it has been argued that variability represents instability and is a precursor of change (Thelen & Smith, 1994; van Geert, P. & van Dijk, 2002; van Geert, Savelsbergh, & van der Maas, 1997). It allows for the self-organization of systems and corresponds with acquisition and subsequent stabilization of the new skills (Thelen & Smith, 1994; van Geert, Savelsbergh, & van der Maas, 1997). In other words, variability is not necessarily error but represents flexibility allowing for, or even promoting change. As such, the variability observed in the speech of typically developing children need not be viewed as a negative phenomenon. Furthermore, the lack of variability in the pretreatment baselines of the child treated in this study might well have been a manifestation of his speech disorder. It is reasonable to assert that the extreme swings in performance during the treatment phases were a consequence of his not being able to use his auditory system to modulate productions through establishment of, and comparisons to, the auditory map that feeds into the speech motor system (Guenther, 1995). It could be argued that the child had to rely primarily on the visual feedback provided by the EPG and the internal orosensory feedback that may have been hampered by the presence of the pseudopalate.

Variability in children's speech production has been documented across numerous studies, and accounted for in various ways (DiSimoni, 1974; Eguchi & Hirsh, 1969; Kent & Forner, 1988; Sharkey & Folkins, 1985; Smith, 1994; Smith & Goffman, 1998: Also see Stathopoulos, 1995 and Clark, Robin, McCullagh & Schmidt for differing accounts). The variability could simply reflect neural immaturity with slower and less accurate neural commands producing slower and more variable articulation (Smith & Goffman, 1998; Tingley & Allen, 1975). It also could be a sign of plasticity or parameter adjustments in the face of changing anatomical and linguistic mechanisms (Shumway-Cook & Woolcott, 1985). In addition, the changes in variability with development might well be a function of practice and experience as a speaker (Salmoni, Schmidt & Walter, 1984; Schmidt & Lee, 1999). This later explanation is consistent with the results of Schulz, Stein and Micallef (2001) who found that speech kinematics initially were variable when adults were asked to produce nonsense words, but it does not account for the greater variability observed in the speech of older adults when compared to younger adults on these same tasks. Nor are the fluctuations in variability across tasks and speech structures observed with different pediatric age groups (Stathopoulos, 1995). Practice and experience is, however, directly reflected in most speech production intervention protocols; that is, speech treatment typically consists of focused practice occurring within a restricted context.

Future studies in the treatment of speakers with hearing loss need to investigate various protocol combinations to determine which combinations produce optimal levels of variability so that positive change occurs with minimal intervention time and maximum acquisition and generalization. The data obtained in this study did not directly address whether the treatment approach was optimal for this child or if it was better or worse than other approaches. The treatment effects observed with the /k/ and /t/ sounds reflected effective treatment, since the child had not made gains previously with a more traditional treatment approach. Furthermore, the treatment results obtained might reflect the best results possible given the child's hearing and speech production skills, but the limited generalization does suggest that treatment efficiency was less than optimal. It is possible that adjustments of the treatment protocol (e.g., number and schedule of trials and sessions, sound combinations, syllable structure and feedback schedule) could have produced more extensive generalization. Further investigation would require a larger set of children to determine the type and scope of modifications that would produce optimal results in this child and other children with hearing loss.

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Author Information

Sheila R. Pratt, Ph.D.

Department of Communication Science & Disorders

4033 Forbes Avenue 

University of Pittsburgh

Pittsburgh, PA 15260

[phone] (voice)

[phone] (fax)

[e-mail]

Table 1. Comparisons across treatment
phases for the placement analyses

Stimulus      Comparisons Across Treatment: Phases

                  Phase [A.sub.1] vs. B
                   (re: /k/ treatment)

                  C         z         P
              Statistic   Score

/k/ Overall     .638      3.502    .001 **
/ki/            .552      3.033    .001 **
/ka/            .615      3.378    .001 **
/ku/            .368      2.024    .021 *
/g/ Overall     .126      0.693    .243
/gi/            .340      1.866    .031 *
/ga/            .061       .337    .368
/gu/           -.002      -.014    .505
/t/ Overall   -0.088      -.484    .686
/ti/           -.076      -.422    .663
/ta/           -.037      -.203    .580
/tu/           -.076      -.422    .663

Stimulus      Comparisons Across Treatment: Phases

               Phase [A.sub.1] vs. [A.sub.1]
                    (re: /k/ treatment)

                  C         z         P
              Statistic   Score

/k/ Overall     .715      2.517    .005 **
/ki/            .694      2.44     .007 *
/ka/            .769      2.706    .003 *
/ku/            .605      2.129    .016 **
/g/ Overall     .549      1.934    .026 **
/gi/            .752      2.648    .004 **
/ga/            .229       .809    .209
/gu/           -.143      -.506    .693
/t/ Overall     .200       .704    .240
/ti/            .444      1.563    .059
/ta/            .169       .596    .275
/tu/            .120       .424    .335

Stimulus      Comparisons Across Treatment: Phases

                 Phase [A.sub.1] vs. B
                  (re: /k/ treatment)

                  C         z         P
              Statistic   Score

/k/ Overall      --         --       --
/ki/             --         --       --
/ka/             --         --       --
/ku/             --         --       --
/g/ Overall      --         --       --
/gi/             --         --       --
/ga/             --         --       --
/gu/             --         --       --
/t/ Overall     .282      .1650    .049 *
/ti/            .327     1.910     .028 *
/ta/            .276     1.609     .053
/tu/            .220     1.286     .099

Note: p [less than or equal to] .05 *

Note: p [less than or equal to] .005 **

Table 2. Comparisons across treatment
phases for the perceptual analyses

Stimuli            Comparisons Across Treatment Phases

                       Phases [A.sub.1] vs. B
                         (re: /k/ treatment)

                      C           z         p
                   Statistic   Score

/k/ Overall        .638        3.502     .001 **
/ki/               .201        1.105     .134
/ka/               .615        3.378     .001 **
/ku/               .368        2.024     .021 *
/g/ Overall        .299        1.641     .050 *
/gi/              -.039        -.218     .586
/ga/               .319        1.754     .039 *
/gu/               .314        1.725     .942
/t/ Overall       -.019        -.108     .543
/ti/              -.136         .747     .772
/ta/               .221        1.215     .112
/tu/               .109         .598     .274
/r/ Overall        .045         .250     .401
/ri/               .358        1.968     .024 *
/ra/              -.068        -.377     .646
/ru/               .199        1.094     .136
Word-initial /k/   .590        3.074     .001 **
Word-final /k/     .000         .000     .500
Word-initial /g/   .691        3.601     .001 **
Word-final /g/     .000         .000     .500

Stimuli            Comparisons Across Treatment Phases

                    Phases [A.sub.1] vs. [A.sub.2]
                           (re: /k/ treatment)

                      C           z         p
                   Statistic    Score

/k/ Overall         .715        2.517     .005 **
/ki/                .721        2.539     .005 **
/ka/                .769        2.706     .003 **
/ku/                .605        2.129     .016 *
/g/ Overall         .554        1.952     .025 *
/gi/                .640        2.252     .012 *
/ga/                .509        1.793     .036 *
/gu/                .024         .087     .465
/t/ Overall         .819        2.881     .002 **
/ti/                .519        1.827     .003 **
/ta/                .757        2.663     .003 **
/tu/               -.243        -.857     .804
/r/ Overall        -.288       -1.013     .884
/ri/               -.076        -.270     .606
/ra/               -.250        -.879     .810
/ru/               -.111        -.390     .652
Word-initial /k/    .713        2.410     .008 *
Word-final /k/      .437        1.479     .069
Word-initial /g/    .726        2.555     .005 **
Word-final /g/      .000         .000     .500

Stimuli            Comparisons Across Treatment Phases

                      Phases [A.sub.1] vs. B
                        (re: /k/ treatment)

                       C         z         p
                   Statistic   Score

/k/ Overall           --         --        --
/ki/                  --         --        --
/ka/                  --         --        --
/ku/                  --         --        --
/g/ Overall           --         --        --
/gi/                  --         --        --
/ga/                  --         --        --
/gu/                  --         --        --
/t/ Overall         .694       4.057     .001 **
/ti/                .429       2.508     .006 *
/ta/                .689       4.028     .001 **
/tu/               -.052       -.144     .557
/r/ Overall           --         --        --
/ri/                  --         --        --
/ra/                  --         --        --
/ru/                  --         --        --
Word-initial /k/      --         --        --
Word-final /k/        --         --        --
Word-initial /g/      --         --        --
Word-final /g/        --         --        --

Note: p [less than or equal to] .05 *

p [less than or equal to] .005 **