Speech Intelligibility and Psychosocial Functioning in Deaf Children and Teens with Cochlear Implants

Abstract

Deaf children with cochlear implants (CIs) are at risk for psychosocial adjustment problems, possibly due to delayed speech–language skills. This study investigated associations between a core component of spoken-language ability—speech intelligibility—and the psychosocial development of prelingually deaf CI users. Audio-transcription measures of speech intelligibility and parent reports of psychosocial behaviors were obtained for two age groups (preschool, school-age/teen). CI users in both age groups scored more poorly than typically hearing peers on speech intelligibility and several psychosocial scales. Among preschool CI users, five scales were correlated with speech intelligibility: functional communication, attention problems, atypicality, withdrawal, and adaptability. These scales and four additional scales were correlated with speech intelligibility among school-age/teen CI users: leadership, activities of daily living, anxiety, and depression. Results suggest that speech intelligibility may be an important contributing factor underlying several domains of psychosocial functioning in children and teens with CIs, particularly involving socialization, communication, and emotional adjustment.

The auditory input provided by a cochlear implant (CI) dramatically improves the speech perception and spoken language skills of prelingually deaf children, especially when implantation occurs at an early age (e.g., Geers & Nicholas, 2013; Geers, Nicholas, & Sedey, 2003; Nicholas & Geers, 2007; Svirsky, Chin, & Jester, 2007; Svirsky, Teoh, & Neuburger, 2004). Many young children with CIs are able to perceive and produce spoken language well enough to attend mainstream schools and interact using spoken language with hearing peers, family, and strangers. However, even with speech and language habilitation, many young CI users still experience delays in language development, and enormous variability in speech, language, and literacy outcomes is routinely reported at CI centers around the world (e.g., Ertmer, 2007; Geers & Hayes, 2011; Geers, 2002; Niparko et al., 2010; Pisoni et al., 2008; Sarant, Blamey, Dowell, Clark, & Gibson, 2001; Svirsky et al., 2007).

One important speech–language outcome measure is speech intelligibility—how well the deaf child's speech is recognized by others. (Note that here, intelligibility reflects on the talker's speech production as measured by listeners’ correct recognition of the talker's words. This should not be confused with another common use of the term “intelligibility” as referring to the receptive skills of the listener to recognize other's words. In the work discussed here, talkers are intelligible if listeners recognize their words correctly.) Good speech intelligibility is often viewed as an important benchmark of expressive speech–language development because it requires all core components of speech perception, cognitive processing, linguistic knowledge, and articulation to be mastered (Chin & Svirsky, 2006; Chin, Bergeson, & Phan, 2012; Ertmer, 2011; Monsen, 1978; Montag, AuBuchon, Pisoni, & Kronenberger, 2014). Furthermore, speech intelligibility has high face validity because it is instantly judged by any interlocutor without reference to less apparent language components like vocabulary size, syntax, or comprehension (Svirsky et al., 2007; Svirsky, Chin, Miyamoto, Sloan, & Caldwell, 2000). Thus, when speech intelligibility is less than optimal, other areas of development, daily living, and social functioning may be affected. Relations between speech intelligibility and several areas of psychosocial adjustment in young CI users are the focus of the work presented here.

Background and Problem

Studies by Most et al. have found links between speech intelligibility in children with mild to profound hearing loss who use CIs or hearing aids and their loneliness, sense of coherence, and social competence. Speech intelligibility also influences how peers and teachers view the personalities, abilities, and intelligence of children with hearing loss (Most, 2007; Most, Ingber, & Heled-Ariam, 2012; Most, Weisel, & Lev-Matezky, 1996; Most, Weisel, & Tur-Kaspa, 1999). Using teacher ratings, peer ratings, and self-reports, Most et al. reported difficulties in these domains for children with hearing loss from kindergarten through high school, with better psychosocial outcomes related to better ratings of speech intelligibility, among other factors. Importantly, hearing peers’ attitudes about deaf children's personal qualities (e.g., likeability, intelligence, confidence, extroversion) were closely related to deaf children's speech intelligibility: as intelligibility improved, so did peers’ attitudes, particularly those of peers with little experience with deaf speakers (Most et al., 1999). These findings establish the importance of speech intelligibility as an integral link between linguistic and psychosocial abilities.

Other studies have found similar links between intelligibility and psychosocial functioning in children with hearing loss. Among children with hearing loss, those with better speech–language skills displayed better psychosocial adjustment on a variety of related dimensions (Dammeyer, 2010) including social competence (Hoffman, Cejas, Quittner, & The CDaCI Investigative Team, 2016; Hoffman, Quittner, & Cejas, 2015; Kronenberger, Ditmars, Henning, Castellanos, & Pisoni, 2016; Wiefferink, Rieffe, Ketelaar, & Frijns, 2012), social development and self-care (Leigh et al., 2015), socialization and social integration with hearing peers (Bat-Chava & Deignan, 2001; Bat-Chava, Martin, & Kosciw, 2005; Stinson, Whitmore, & Kluwin, 1996), social skills and self-esteem (Moog, Geers, Gustus, & Brenner, 2011), social adjustment, self-image, and emotional adjustment (Polat, 2003), and social functioning and behavioral problems (Barker et al., 2009; Netten et al., 2015).

In short, if a child's speech articulation is difficult to understand, frustrated peers may avoid social contact, and with less social interaction, the child has fewer opportunities to learn appropriate social behaviors. In addition, because speech communication is essential to friendship and peer interactions, a poorly intelligible deaf child with few friends or poor-quality social interactions may become lonely and experience other negative emotions that may impact both psychological development and quality of life (Batten, Oakes, & Alexander, 2014; Most et al., 2012; Most, 2007; Xie, Potměšil, & Peters, 2014). Preventing such a situation is important for children, but standardized assessment and appropriate clinical interventions for psychosocial functioning are not always a central component of post-implant assessment and treatment (Hoffman et al., 2016), despite the documented prevalence of psychosocial difficulties in deaf children with and without CIs (for reviews, see Batten et al., 2014; Moeller, 2007; Stevenson, Kreppner, Pimperton, Worsfold, & Kennedy, 2015; Xie et al., 2014).

Rationale, Research Questions, and Hypotheses

The purpose of the two studies reported here was to investigate relations between speech intelligibility and psychosocial–behavioral adjustment in early implanted children and teens with CIs. Understanding these relations is of critical importance for the treatment of children with CIs because both speech intelligibility and psychosocial outcomes have been identified as at-risk areas for CI users (Batten et al., 2014; Chin, Tsai, Gao, 2003; Geers & Nicholas, 2013; Hoffman et al., 2015; Moeller, 2007; Netten et al., 2015; Stevenson et al., 2015; Svirsky, Sloan, Caldwell, & Miyamoto, 2000; Xie et al., 2014). However, outcomes for treatment of speech intelligibility remain highly variable, a consensus has not been reached regarding specific psychosocial areas to target, and widespread behavioral intervention programs have yet to be implemented with this clinical population (Batten et al., 2014; Chin et al., 2003; Dammeyer, 2010; Geers & Nicholas, 2013; Hoffman et al., 2016; Niparko et al., 2010; Peng, Spencer, & Tomblin, 2004; Tobey, Geers, Sundarrajan, & Shin, 2011).

To help address these issues with an approach that is practical for both researchers and clinicians, the present studies combined well-established, easily administered, audio-transcription measures of speech intelligibility—the Beginner's Intelligibility Test (BIT; Osberger, Robbins, Todd, & Riley, 1994) and McGarr Sentence Intelligibility Test (McGarr, 1981)—and parent-reported behavior problems and psychosocial adjustment—the Behavior Assessment System for Children, Second Edition (BASC-2; Reynolds & Kamphaus, 2004). Much of the previous work connecting these two domains has employed a variety of time- or interpretation-intensive methods, such as parent interviews (e.g., Bat-Chava & Deignan, 2001), holistic ratings of speech intelligibility (e.g., Dammeyer, 2010; Most et al., 1996, 2012), or observational evaluations of a specific set of psychosocial behaviors (e.g., Barker et al., 2009; Quittner, Leibach, & Marciel, 2004). The behavioral tests used here are simple to administer, score, and interpret, providing objective scores of speech intelligibility performance and several areas of psychosocial adjustment which can be easily collected by clinicians or researchers multiple times throughout childhood and compared between populations of different ages. We investigated three research questions using this methodology:

• Research Question 1: How does the speech intelligibility and psychosocial functioning of early implanted CI users compare to typically hearing (TH) peers?

• Research Question 2: What are the relations between speech intelligibility and psychosocial outcomes in CI users?

• Research Question 3: Do relations between speech intelligibility and psychosocial outcomes in CI users hold at both early (preschool) and later (school-age and teen) ages?

Consistent with a large body of previous research, we hypothesized lower speech intelligibility, on average, in the CI samples compared to the TH samples (Chin et al., 2003; Peng et al., 2004; Svirsky, Sloan et al., 2000; Tobey et al., 2011), but we also expected a subset of CI users to show good speech intelligibility (Ertmer, 2007; Montag et al., 2014; Osberger et al., 1994; Tobey, Geers, Brenner, Altuna, & Gabbert, 2003). Similarly, we hypothesized poorer psychosocial functioning, on average, in the CI samples compared to the TH samples, particularly on scales related to social, communicative, and executive functioning, in line with previous work which has reported more difficulties among deaf and hard-of-hearing people than TH peers in areas such as social and communicative competence (Hoffman et al., 2015, 2016; Xie et al., 2014), emotional regulation and behavior problems (Barker et al., 2009; Kronenberger et al., 2016; Netten et al., 2015; Stevenson et al., 2015; Wiefferink et al., 2012), and attention and other executive functions (Beer et al., 2014; Castellanos, Kronenberger, & Pisoni, 2016; Kronenberger & Pisoni, 2014; Kronenberger et al., 2016; Quittner et al., 2004). Regarding our second research question, we hypothesized a positive correlation between speech intelligibility and psychosocial adjustment (Barker et al., 2009; Markides, 1989; Most et al., 2012; Most, 2007). In order to address our third research question, we report results from two samples of CI users and TH controls: in Study 1, we examined preschoolers’ BIT and BASC-2 scores from two consecutive years, and in Study 2, we examined McGarr and BASC-2 scores from one time point for school-age children and teens.

Study 1: Preschool Children

This study sought to uncover relations between measures of speech intelligibility and psychosocial–behavioral development collected at two annual testing times from prelingually deaf preschool children with CIs and TH controls.

Method

Participants

The children included in this study were a subset of participants involved in a larger longitudinal investigation of linguistic, behavioral, and neurocognitive development in preschool children with CIs (Beer et al., 2014; Kronenberger & Pisoni, 2014). CI participants were recruited from patient populations receiving services at a large university-hospital-based CI clinic and the surrounding community. Children were recruited for the TH control sample through advertisements in the same hospital and community.

The present CI sample consisted of 27 children with CIs who fit the following criteria: (a) severe-to-profound bilateral hearing loss (>70 dB hearing loss at 500, 1000, and 2000 Hz in the better hearing ear) identified prior to 6 months of age; (b) CI implantation by age 3 years; (c) age at the time of first testing between 3;0 and 6;11 years; (d) consistent use of a multichannel CI with an up-to-date processing system; (e) a primarily English home environment; (f) enrollment in an aural rehabilitative program that encourages the development of speaking and listening skills; (g) no additional developmental or cognitive delays; (h) speech intelligibility and psychosocial behavior scores available from the first testing session (Time 1) and/or the testing session the following year (Time 2). Of the total 27 CI users, 18 had speech intelligibility scores available from both testing times, 6 had scores from Time 1 only, and 3 had scores from Time 2 only, for a total of 24 CI users at Time 1 and 21 at Time 2. Length of CI use at Time 1 ranged from 6 months to 5 years (M = 2.8, SD = 1.1 years).

The TH control sample consisted of 30 children with typical hearing (pure-tone average in the normal range and no history of hearing aid use). They were also between ages 3;0 and 6;11 at time of first testing, reported no developmental or cognitive delays, resided in monolingual English-speaking home environments, and had speech intelligibility scores available for Time 1 and/or Time 2. All 30 had speech intelligibility scores from Time 1, but only 27 had scores from Time 2. Table 1 summarizes demographic and CI device information for the two samples with means, standard deviations, and ranges. Demographic characteristics were comparable, with no significant differences in mean age, nonverbal IQ, or family income between the CI and TH samples (two-tailed Welch's t tests, all p > .05). Nonverbal IQ was assessed by T-scores (M = 50, SD = 10) on the Differential Ability Scales II Picture Similarities subtest (Elliot, 2007); 84% of CI users scored within one standard deviation of the age norm (i.e., scores of 40–60), and only one scored below 40, while 37% of TH controls scored above 60 and none scored below 40. Annual family income was coded on a 10-point scale; 38% of CI users were at the highest point on the scale (>$95,000/year), and 33% were in the lower half of the scale (<$35,000/year), while 23% of TH controls were at the highest point and 10% in the lower half.

Table 1.

Sample descriptions for Study 1 preschool and Study 2 school-age/teen participants

	Study 1		Study 2
Variable	CI	TH	CI	TH
Total N	27	30	51	47
N at Time 1/Time 2	24/21	30/25
Sex (N; male/female)	15/12	16/14	27/24	21/26
Nonverbal IQa at Time 1	53.9 (10.0) (33–81)	59.7 (12.2) (41–81)	54.9 (7.8) (32–68)	55.2 (7.3) (40–70)
Family incomeb at Time 1	6.8 (3.1) (1–10)	7.2 (2.0) (1–10)	7.4 (2.3) (2–10)	7.7 (2.3) (1–10)
Age at Time 1 (years)	4.3 (1.1) (3.1–6.9)	4.2 (0.9) (3.1–7.0)	13.2 (3.1) (7.8–19.1)	13.0 (2.8) (7.1–19.8)
Age at Time 2 (years)	5.2 (1.0) (4.1–7.9)	5.1 (0.8) (4.1–7.2)
Age change Time 1–2 (years)	1.0 (0.2) (0.5–1.4)	1.0 (0.2) (0.6–1.5)
Years of CI use at Time 1	2.8 (1.1) (0.5–5.2)		10.8 (2.5) (7.2–16.0)
Years of CI use at Time 2	3.8 (1.1) (1.5–6.1)
Onset of deafness (months)	0.1 (0.4) (0–2.0)		1.4 (5.0) (0–24.0)
Age at implantation (months)	18.6 (7.6) (8.0–36.6)		31.1 (17.6) (8.3–75.8)
Best pre-implant PTA	101.3 (13.7) (73.3–118.4)		106.9 (11.7) (85.0–118.4)
Communication modec	4.9 (0.6) (2–5)		4.7 (0.8) (2–5)
Bilateral CI (N; Time 1/2)	19/20		23
CI model/processing strategy (N)
CC Nucleus/ACE	23		37
CC Nucleus/SPEAK			5
ABC Clarion/HiRes	3		3
ABC Clarion/MPS			3
ME Opus II/FSP	1		1
ME Opus II/CIS			2

Note. Values are means (SDs) (ranges), unless otherwise indicated. PTA = pure tone average (dB hearing loss); TC = Total Communication (speech + sign); CC = Cochlear Corporation; ACE = Advanced Combination Encoder; SPEAK = Spectral Peak; ABC = Advanced Bionics Corporation; HiRes = High Resolution; MPS = Multiple Pulsatile Stimulation; ME = Med-El Corporation; FSP = Fine Structure Processing; CIS = Continuous Interleaved Sampling.

^aNonverbal IQ in Study 1: T-score from the Differential Ability Scales, II Picture Similarities subtest (Elliot, 2007); in Study 2: T-score from the Wechsler Abbreviated Scale of Intelligence Matrix Reasoning subtest.

^bIncome is coded on a 1–10 scale (<$5,000/year to > $95,000/year).

^cCommunication mode is coded on a 1–6 scale (mostly sign to auditory-oral) (Geers, 2002).

Measures

Beginner's Intelligibility Test

The BIT (Osberger et al., 1994) is a sentence-imitation task that was created for use with young children with hearing loss and that has been used previously with deaf children with CIs (Castellanos et al., 2014; Chin et al., 2003, 2012; Ertmer, 2007, 2011; Miyamoto et al., 1997; Osberger et al., 1994; Svirsky, Sloan et al., 2000). The BIT consists of 4 lists of 10 simple sentences, each with 2–6 words familiar to young children (e.g., “The bear sleeps. My airplane is small.”). One list is used per testing session, during which the examiner reads a sentence aloud and the child repeats the sentence aloud. In our study, the BIT was typically administered about halfway through a 2-hr session including frequent breaks between various linguistic, cognitive, and behavioral tests, with parents observing in the same or an adjoining room. Examiners began with simple instructions (e.g., “I'm going to read some sentences; I want you to listen and repeat them back to me”) and prompted children between sentences as needed (e.g., “You say what I say. Ready?”). BIT sessions were audio recorded in a quiet room directly to a solid-state digital recorder using a table-top microphone set about 18 inches from the child's mouth. The children's sentences were digitally extracted, root-mean-square-normalized to minimize variations in loudness, and stored for later playback, transcription, and scoring.

The intelligibility of each sentence was scored as the mean percentage of words correctly identified via orthographic transcription by five or six naïve TH listeners. All listeners were undergraduate native speakers of American English who reported no prior experience with deaf speakers or CI users and who passed a hearing screening and transcription screening. They received partial course credit or $10 for participation. Seated at a computer with sentences presented over high-quality headphones, listeners orthographically transcribed what they thought the child said after each sentence. Each sentence transcription was scored in terms of the percentage of correctly identified words, and the child's speech intelligibility score for the testing session was calculated as the mean of all sentence scores across all listeners. Because many children did not repeat every word of each modeled sentence, scores were calculated against only the words that the child attempted to produce, not the complete modeled sentence (Ertmer, 2007). For example, it is well known that young children may omit articles, auxiliaries, or inflectional morphemes (e.g., plural –s, third-person singular –s, past tense –ed) during preschool stages of linguistic development, in both everyday productions and in repetition tasks (Slobin & Welsh, 1973), so that a modeled sentence like “The baby cries” may be repeated as “Baby cries” or “Baby cry” (Chin & Ting, 2008). While a broad definition of speech intelligibility may consider every core ability necessary to complete an elicited repetition task (e.g., perceiving and repeating all words and segments accurately), the definition of speech intelligibility used in this paper is narrower, focusing only on audio playback transcription, that is, the number of whole words correctly recognized out of those that were actually produced by the child.

Behavior Assessment System for Children, Second Edition

The BASC-2 (Reynolds & Kamphaus, 2004) is a well-established measure of age-normed psychosocial behavior that has been used in previous studies of various clinical pediatric populations, including deaf children with CIs (Castellanos et al., 2016; Hoffman et al., 2016; Kronenberger et al., 2016). The BASC-2 consists of rating scales of behavior problems and adaptive skills in young people aged 2–21 years, with parent reports for those under 18, teacher reports for all ages, and self-reports for those in later school-age and older. Only parent reports were used in the present studies. For each item, parents rate the child's behavior over the last several months on a 0–3 scale (never, sometimes, often, almost always). Item scores are summed in categories that form several Clinical Scales and several Adaptive Scales. Raw scores are then converted to T-scores (M = 50, SD = 10) using age-based norms. For the Clinical Scales, T-scores above 60 are considered “at-risk,” and scores above 70 are considered “clinically significant” problem areas. For the Adaptive Scales, T-scores below 40 are considered “at-risk,” and scores below 30 are considered “clinically significant.” Table 2 lists the BASC-2 scales on parent-report forms for each age group and key constructs covered by each. (Note that two scales do not appear on the Preschool forms and were therefore only reported for the older children in Study 2..

Table 2.

BASC-2 scales and constructs covered in parent-report forms for each age group

BASC-2 scale	Age	Important constructs covered
Clinical scales
Hyperactivity	P, C, A	Self-control, impatience, fidgeting
Aggression	P, C, A	Bullying, temper, physical outbursts
Conduct problems	C, A	Discipline problems
Anxiety	P, C, A	Worrying, fearfulness, perfectionism
Depression	P, C, A	Moodiness, negativity
Somatization	P, C, A	Illness, physical complaints
Attention problems	P, C, A	Attention span, distractibility
Atypicality	P, C, A	Strange behavior, inappropriate emotions
Withdrawal	P, C, A	Shyness, social avoidance
Adaptive scales
Adaptability	P, C, A	Adjusting to changes, recovering from setbacks
Social skills	P, C, A	Politeness, helpfulness, encouraging others
Leadership	C, A	Decision-making, group participation
Activities of daily living	P, C, A	Daily routines, personal safety, cleanliness
Functional communication	P, C, A	Speaking clearly, communicating appropriately

Note. BASC-2 = Behavior Assessment System for Children, Second Edition. P = preschool (ages 2–5), C = child (ages 6–11), A = adolescent (ages 12–21).

Procedure

Testing was conducted by licensed speech–language pathologists experienced in testing deaf children with CIs. Protocols were approved by the university's institutional review board, and children's parents were consented prior to testing. During testing sessions, parents reported demographic information (see Table 1) and completed checklists of their child's neurocognitive development and psychosocial behavior (including the BASC-2), while children completed several performance tests of neurocognitive abilities and speech–language skills (including the BIT). This report presents BIT and BASC-2 data for the first two annual visits in a larger longitudinal study (Time 1 and Time 2).

Data analysis

In order to address Research Question 1 (comparison of CI and TH samples), BIT speech intelligibility scores and BASC-2 scale T-scores for the preschool CI and TH samples were compared using Welch's t tests, which do not assume equal variances between samples. Pearson correlations were conducted within the CI sample in order to examine influences of demographic or hearing history factors on speech intelligibility. Unless otherwise indicated, t tests and correlations reported in both studies were one-tailed, following the majority of literature on CI users which has found poorer developmental outcomes for CI users compared to TH peers and for CI users with various demographic/hearing traits (lower IQs and incomes, later ages of implantation, greater pre-implant hearing loss, less emphasis on oral communication, etc.).

In order to address Research Question 2 (relations between speech intelligibility and psychosocial outcomes), Pearson correlations were used to identify significant relationships between BIT and BASC-2 scores. Correlations were calculated separately within each sample (CI or TH) and within and between testing times (Time 1 or Time 2). Correlations between BIT and BASC-2 scores at the same time (e.g., Time 1–Time 1) reflect concurrent relations. Correlations at different times reflect predictive relations of speech intelligibility on later psychosocial outcomes (BIT Time 1 on BASC-2 Time 2) or vice versa (BASC-2 Time 1 predicting BIT Time 2).

Results

Comparison of Samples on Speech Intelligibility and Psychosocial Functioning

Speech intelligibility (BIT)

The preschool CI and TH samples differed significantly in speech intelligibility at both testing times (Time 1: t(31.87) = −5.53, Time 2: t(21.59) = −3.76, both p < 0.001). Table 3 summarizes the BIT scores for each sample (means, SDs, ranges). The TH sample displayed high speech intelligibility at both testing times (well above 70%), whereas the CI sample displayed much lower mean scores. Within the CI sample, six hearing/demographic factors were reliably related to speech intelligibility. BIT speech intelligibility at Time 1 was correlated with nonverbal IQ (r(21) = .50, p < .01), family income (r(20) = .49, p < .05), age of implantation (r(22) = .43, p < .05), and length of CI use at Time 1 (r(22) = .39, p < .05), but none of these factors predicted BIT at Time 2. BIT scores at both times were better for CI users with a greater oral communication mode score (Time 1: r(19) = .52, p < .05; Time 2: r(19) = .52, p < .01). BIT scores at Time 2 were better for CI users who had two CIs at Time 1 (r(19) = .50, p < .05; note that four bilateral CI users did not have data for Time 2, and three additional CI users received a second CI between Times 1 and 2). None of the other demographic factors listed in Table 1 reliably predicted BIT scores, including those often associated with speech–language outcomes (e.g., chronological age, length of CI use, age at onset of deafness, residual hearing level), perhaps due to their low variability or uneven distributions in the sample and their involvement in the inclusion criteria.

Table 3.

BIT speech intelligibility scores (in %) for Study 1 preschool CI and TH samples

Variable	CI	TH
N at Time 1/Time 2	24/21	30/25
BIT score at Time 1	50.7 (27.1) (0.8–95.5)	84.1 (13.4) (52.1–99.3)
BIT score at Time 2	67.7 (27.1) (6.1–98.0)	90.4 (5.9) (75.9–98.3)

Note. BIT scores are percent of words correctly transcribed, means (SDs) (ranges). BIT = Beginner's Intelligibility Test.

Within the preschool TH control sample, speech intelligibility scores were consistently high across participants. Figure 1 displays mean BIT speech intelligibility scores for individual preschoolers, with CI users (gray) overlaid on TH participants (white), rank-ordered within each sample and testing time. The majority of the TH sample scored above 70% at Time 1 (left), and all scored above 70% at Time 2 (right; 70% indicated with a reference line). In contrast, CI users varied substantially in speech intelligibility, and individuals improved to differing degrees from Time 1 to Time 2 (range = 1–75% increases).

Figure 1.

Individual BIT speech intelligibility scores, Time 1 (left), Time 2 (right), Study 1 CI users (gray) overlaid on TH preschoolers (white). Reference line at 70% indicates good performance. BIT = Beginner's Intelligibility Test.

Psychosocial adjustment (BASC-2)

Within each preschool sample, two-tailed Welch's t tests revealed no significant differences between mean BASC-2 scale T-scores at Time 1 versus Time 2 (all p > .05), suggesting that psychosocial development proceeded at a pace comparable to that of age norms between annual testing times. Therefore, T-scores from Time 1 and 2 were averaged for each participant before comparing BASC-2 patterns between samples and subgroups. For the few participants who did not have BASC-2 scores at both testing times, the single available T-score was used in place of a mean score. These cases included three CI participants without Time 1 scores and six CI and five TH participants without Time 2 scores. Figure 2 displays the mean T-scores on each scale for the CI and TH samples, with shading to indicate clinically “at-risk” ranges. While both samples had mean T-scores within the normal range (i.e., not “at risk”), the CI sample performed significantly more poorly on eight of the BASC-2 scales (five Clinical, three Adaptive): Hyperactivity (t(44.36) = 1.91, p < .05), Somatization (t(51.87) = 3.39, p < .001), Attention Problems (t(51.04) = 3.16, p < .01), Atypicality (t(48.76) = 2.46, p < .01), Withdrawal (t(53.91) = 1.89, p < .05), Adaptability (t(46.98) = −3.92, p < .001), Social Skills (t(50.66) = −3.51, p < .001), and Functional Communication (t(40.28) = −6.38, p < .001, with these significance levels indicated by stars in Figure 2).

Figure 2.

Mean BASC-2 scores by scale, averaged across Times 1 and 2, Study 1 preschool CI and TH samples. Asterisks indicate scales that differ significantly between samples (*p < .05, **p < .01, ***p <.001, one-tailed Welch's t tests). BASC-2 = Behavior Assessment System for Children, Second Edition.

Relations between speech intelligibility and psychosocial outcomes

To assess the links between speech intelligibility and psychosocial behaviors, Pearson correlations were calculated between BIT and BASC-2 scores at both Times 1 and 2 without averaging across testing times, in order to examine both concurrent and predictive relations. Table 4 lists the correlations within the CI sample. BIT speech intelligibility scores had significant negative correlations with three Clinical Scales and significant positive correlations with two Adaptive Scales, indicating that better speech intelligibility was related to better (less clinical, more adaptive) psychosocial behavior. BIT speech intelligibility scores at Time 1 were significantly related to Atypicality and Adaptability at Time 1, Attention Problems, Atypicality, and Withdrawal at Time 2, and Functional Communication at both Times 1 and 2. BIT scores at Time 2 were significantly related to Atypicality, Withdrawal, and Adaptability at Time 2 and Functional Communication at both times. These scales had some of the most elevated scores for CI users and were among those that differed significantly between the CI and TH samples (see Figure 2). In contrast, for the TH sample, only Aggression at Time 2 was significantly related to BIT (Time 1: r(24) = −.39, p < .05; Time 2: r(23) = −.47, p < .01).

Table 4.

Correlations between BIT speech intelligibility and BASC-2 scale scores within the Study 1 preschool CI sample

BASC-2 scale	BIT T1		BIT T2
	BASC T1 (N = 22)	BASC T2 (N = 20)	BASC T1 (N = 20)	BASC T2 (N = 19)
Clinical scales
Hyperactivity	−0.05	0.15	0.32	0.21
Aggression	−0.25	−0.03	−0.07	0.23
Anxiety	−0.07	−0.10	0.06	0.16
Depression	−0.17	0.01	−0.09	0.18
Somatization	−0.21	−0.03	−0.37	−0.16
Attention problems	−0.33	−0.50*	−0.01	−0.26
Atypicality	−0.42*	−0.39*	−0.28	−0.65**
Withdrawal	−0.24	−0.40*	−0.14	−0.40*
Adaptive scales
Adaptability	0.36*	0.34	0.37	0.43*
Social skills	0.22	0.21	0.21	0.17
Activities of daily living	−0.32	−0.09	−0.20	−0.12
Functional communication	0.72***	0.76***	0.51*	0.67**

Note. BASC-2 = Behavior Assessment System for Children, Second Edition; BIT = Beginner's Intelligibility Test; T1 = Time 1; T2 = Time 2. *p < .05; **p < .01; ***p < .001.

Study 2: School-Age Children and Teens

Study 2 sought to replicate and extend the major findings of Study 1 using an older population of long-term CI users and TH peers. The participants in this study were part of a large project on long-term outcomes for CI users in our laboratory. As part of this project, earlier studies reported on the speech intelligibility (Montag et al., 2014) and psychosocial adjustment (Castellanos et al., 2016) of long-term school-age and teen CI users and TH peers; the current study investigated relations between the two domains for a subset of participants, the 51 CI users and 47 TH controls who had scores available for both measures (McGarr Sentence Intelligibility and BASC-2 parent reports).

Method

Methods were similar to those in Study 1. Differences between the studies are listed in Table 5.

Table 5.

Comparison of methods used in Study 1 and Study 2

Method	Study 1	Study 2
Participant age range	Preschool (age 3–6)	School-age/teen (age 7–20)
Data set origin	Longitudinal project on early implanted CI users and peers	Project on long-term CI users and peers
Testing schedule	Tested annually; data available for first 2 years	Tested once
Intelligibility test	BIT: 10 sentences repeated after live-voice model	McGarr: 36 sentences read and repeated after live-voice model
Intelligibility scoring	Traditional: percentage of words correctly transcribed, averaged across listeners	Perfect-sentence: percentage of sentences perfectly transcribed by all listeners
Psychosocial test	BASC-2 parent report for preschoolers	BASC-2 parent reports for children or teens (including 2 scales not used for preschoolers)

Note. BIT = Beginner's Intelligibility Test. BASC-2 = Behavior Assessment System for Children, Second Edition.

Participants

Participants were enrolled in a larger investigation of long-term outcomes in CI users; the samples for this study were long-term CI users and TH peers age 7–20 years. CI users were recruited from current patient populations, participants in previous studies at the same university-hospital-based clinic as in Study 1, and via professionals and schools in contact with CI users. TH participants were recruited in the same local areas through flyers and emails affiliated with the clinic and university. No participant was enrolled in both Study 1 and Study 2.

The CI sample consisted of 51 school-age children and teens with CIs who fit the same inclusion criteria described for Study 1, with the following exceptions: onset of deafness ranged up to 2 years of age, implantation occurred prior to age 7 years, CIs were used for at least 7 years, and scores for speech intelligibility and psychosocial adjustment were available from the single testing session. The TH control sample consisted of 47 participants with typical hearing (assessed by basic audiometric screening) in the same age range and with both types of scores available. Table 1 includes demographic and device information for these two samples. Demographics for the CI sample were comparable with the TH sample (there were no significant differences in age, nonverbal IQ, or family income via two-tailed Welch's t tests, all p > .05). Nonverbal IQ was assessed with Wechsler Abbreviated Scale of Intelligence Matrix Reasoning subtest T-scores (M = 50, SD = 10); 25% of CI users scored above 60, 6% below 40, while 28% of TH controls scored above 60 and none below 40. Family income was scored on the same 10-point scale as in Study 1; 36% of CI users and 41% of TH controls had family incomes at the highest two points (>$80,000/year), while 11% of CI users 41% of TH controls had incomes in the lower half of the scale (<$35,000/year).

Between studies, the participants in Study 2 were older than those in Study 1 (t(130.34) = −27.11, p < .001), but Study 1 and Study 2 participants did not differ in nonverbal IQ or family income (two-tailed t tests, both p > .1). The CI users in Study 2 had used their CIs longer (t(74.52) = −19.63, p < .001) and were implanted at older ages than the CI users in Study 1 (t(73.89) = −4.35, p < .001), but the CI samples did not differ statistically in age of onset of deafness, communication mode, or hearing level (two-tailed, all p > .05).

Measures

McGarr sentences

The McGarr Sentence Intelligibility Test (McGarr, 1981) is similar to the BIT and has been implemented with CI users in previous work (Dawson et al., 1995; Geers, 2002; Osberger, Maso, & Sam, 1993; Tobey & Hasenstab, 1991; Tobey et al., 2003, 2011). Participants repeat 36 short sentences which are both printed on cards and modeled orally. Because the McGarr sentences were printed, participants in Study 2 did not rely entirely on the examiner's oral model, and they were able to correctly repeat the sentences. Sentence intelligibility was assessed using the same playback-transcription method as in Study 1, with each CI participant transcribed by three naïve listeners and each TH participant by one naïve listener. Using the conventional method of averaging across transcribers to calculate a speech intelligibility score for each participant resulted in very high scores across both samples. All TH participants scored above 89% (M = 96%, SD = 2.3%, range = 89–99%), as did 70% of CI users (M = 89%, SD = 10.2%, range = 44–97%). Due to the small variance in these distributions, a stricter method of calculating participant speech intelligibility was used in Study 2, which we call “perfect-sentence intelligibility”: the proportion of a participant's sentences which were perfectly transcribed by all listeners. This resulted in a wider range of scores which enabled analyses without ceiling effects.

Behavior Assessment System for Children, Second Edition

As in Study 1, BASC-2 parent reports were used for the school-age children and teens in this study. The forms for these age groups (Child: ages 6–11, Adolescent: ages 12–21) include the same scales as the Preschool parent-report form (ages 2–5) used in Study 1, with age-appropriate adjustments (e.g., on the Functional Communication scale, all forms reference communicating clearly, but only the Preschool form includes reciting the alphabet, and only the Adolescent form includes making presentations to a group). The Child and Adolescent forms also include two scales not used for preschoolers, Leadership and Conduct Problems, as noted in Table 2.

Procedure

Procedures were the same as in Study 1. This report presents McGarr speech intelligibility and BASC-2 parent-report data for a single testing session.

Data analysis

As in Study 1, in order to address Research Question 1 (comparison of CI and TH), Welch's t tests were used to compare the CI and TH samples on speech intelligibility and psychosocial adjustment. For Research Question 2 (relations between speech intelligibility and psychosocial adjustment), Pearson correlations were used to identify significant relations between McGarr perfect-sentence scores and BASC-2 scales within each sample. Tests were one-tailed unless otherwise indicated.

Results

Comparison of Samples on Speech Intelligibility and Psychosocial Functioning

Speech intelligibility (McGarr)

Perfect-sentence speech intelligibility in the Study 2 TH sample was high (M = 84%, SD = 6.4%, range = 69%–94%), indicating that the majority of sentences were perfectly recognized by transcribers. Scores for the CI sample were lower and more variable (M = 57%, SD = 19.3, range = 3–81%). The difference between samples was significant (t(61.82) = 9.39, p < .001). Within the CI sample, communication mode was moderately correlated with McGarr perfect-sentence scores (r(49) = .60, p < .001); i.e., CI users who relied more on oral skills had better speech intelligibility than those who also used sign. None of the other hearing/demographic factors listed in Table 1 showed significant correlations with McGarr perfect-sentence speech intelligibility. (However, for other analyses of demographic factors in this population, see Montag et al., 2014.)

Figure 3 displays the McGarr perfect-sentence speech intelligibility scores for individual Study 2 participants, rank-ordered by score with CI users (gray) overlaid on TH participants (white). Similar to Study 1 preschoolers, the Study 2 TH sample showed consistently high speech intelligibility, but CI users varied substantially. Nearly all Study 2 TH participants scored above 70% (indicated with a reference line in Figure 3), while only a third of CI participants reached this level.

Figure 3.

Individual McGarr speech intelligibility scores, Study 2 CI users (gray) overlaid on TH participants (white). Reference line at 70% indicates good performance.

Psychosocial adjustment (BASC-2)

As previously noted, the CI and TH samples in Study 2 were subsets of larger samples for which BASC-2 scores were previously reported (Castellanos et al., 2016). In that report, the larger CI sample scored significantly more poorly than the TH sample on every BASC-2 scale except Anxiety and Somatization (two-tailed t tests, all p < .05). The same pattern was also found for the slightly smaller samples in the current study. Figure 4 displays the mean T-scores on each scale for the Study 2 CI and TH samples, with shading to indicate clinically “at-risk” ranges and stars to indicate the significance levels by which the samples differed on each scale (one-tailed Welch's t tests). Both samples had mean T-scores within the normal range (i.e., not “at-risk”).

Figure 4.

Mean BASC-2 scores by scale, Study 2 CI and TH samples. Asterisks indicate scales that differ significantly between samples (*p < .05, **p < .01, ***p <.001, one-tailed Welch's t tests). BASC-2 = Behavior Assessment System for Children, Second Edition.

Relations between speech intelligibility and psychosocial outcomes

Several significant correlations were uncovered between McGarr perfect-sentence intelligibility scores and BASC-2 psychosocial adjustment scales—9 in the CI sample and 7 in the TH sample, as shown in Table 6. The significant negative correlations with Clinical Scales (Anxiety, Depression, Withdrawal) and significant positive correlations with Adaptive Scales (Adaptability, Activities of Daily Living, Functional Communication) indicate that better speech intelligibility was associated with more positive psychosocial adjustment in these samples. Five scales showed significant correlations only within the CI sample (Anxiety, Withdrawal, Adaptability, Leadership, and Activities of Daily Living), three within only the TH sample (Hyperactivity, Aggression, and Conduct Problems), four within both samples (Depression, Attention Problems, Atypicality, and Functional Communication), and two within neither sample (Somatization and Social Skills).

Table 6.

Correlations between McGarr perfect-sentence intelligibility and BASC-2 scale scores within each Study 2 school-age/teen sample

BASC-2 scale	CI (N = 51)	TH (N = 47)
Clinical scales
Hyperactivity	−0.18	−0.40**
Aggression	−0.20	−0.32*
Conduct problems	−0.03	−0.31*
Anxiety	−0.29*	0.08
Depression	−0.36**	−0.29*
Somatization	−0.17	0.23
Attention problems	−0.34**	−0.26*
Atypicality	−0.32*	−0.52***
Withdrawal	−0.40**	0.02
Adaptive scales
Adaptability	0.26*	0.13
Social skills	0.20	0.07
Leadership	0.38**	0.03
Activities of daily living	0.37**	0.23
Functional communication	0.57***	0.35**

Note. BASC-2 = Behavior Assessment System for Children, Second Edition. *p < .05; **p < .01; ***p < .001.

Discussion

These two studies revealed differences in speech intelligibility and psychosocial functioning between children and teens with CIs and TH peers. Both studies also found relations between speech intelligibility and several domains of psychosocial functioning in samples of CI users at both preschool and later ages (school-age and teen).

Research Question 1: Comparison of Samples on Speech Intelligibility and Psychosocial Functioning

Consistent with our hypotheses, CI users in both studies showed poorer speech intelligibility and psychosocial adjustment than TH peers, but with considerable individual variation in the CI samples, some CI users performed similar to TH peers. Performance among TH preschoolers in Study 1 reached about 70% using the traditional measure of average words correctly transcribed, and all TH and CI participants improved from one testing year to the next, as would be expected for this period of rapid phonological development. By school age, TH performance using the same measure reached about 90%, prompting the implementation of the stricter method of speech intelligibility scoring for Study 2. However, the patterns of performance as high across TH participants and variable across CI users remained within each study regardless of the measure.

Study 1 preschool CI users showed poorer psychosocial adjustment than TH peers in domains most closely related to communication and executive functioning but did not differ from TH peers in other areas. In Study 2, the school-age/teen CI sample's psychosocial adjustment was close to the norm but significantly poorer than TH sample scores on all but two scales. This may reflect difficulties in navigating the increased complexity of social interaction and greater importance of peers in later childhood and teenage years. CI users may be at a disadvantage in group interactions, for example, which pose especially difficult listening environments for CI users, requiring greater concentration and increasing the likelihood of missed social cues needed for learning complex social skills.

Research Questions 2 and 3: Relations between Speech Intelligibility and Psychosocial Outcomes in Preschool and School-Age/Teen CI Users

Study 1 uncovered links between speech intelligibility at two testing time points and psychosocial adjustment. Within the CI sample, five of the BASC-2 scales were correlated with BIT speech intelligibility. Study 2 provided converging evidence in an older sample of long-term CI users, who showed relations between McGarr perfect-sentence speech intelligibility and nine BASC-2 scales, including all five scales that were related to speech intelligibility in the Study 1 preschool CI sample. The inclusion of four additional scales may reflect the cumulative effects of poor speech intelligibility on psychological well-being and independent living skills in children with CIs as they mature. These results establish the first links between audio-transcription measures of speech intelligibility (BIT and McGarr sentences) and psychosocial behaviors (BASC-2 parent reports) in deaf children with CIs.

Most of the BASC-2 scales that were related to speech intelligibility in one or both studies (e.g., Functional Communication, Atypicality, Withdrawal, Adaptability, Activities of Daily Living, Leadership, and Attention Problems) involve a core component of social or communication functioning, which would likely be influenced by speech intelligibility. For example, the relations between speech intelligibility and the BASC-2 Functional Communication scores in both studies are unsurprising, given that several questions on this scale deal specifically with clarity of speech and effective information transmission. This scale also involves pragmatic skills such as responding appropriately to questions, explaining game rules, and relating personal narratives. Previous work has found delays in children with hearing loss in their mastery of pragmatic skills such as maintaining a conversational topic or flow, turn-taking, responding as a listener, and repairing misunderstandings (Jeanes, Nienhuys, & Rickards, 2000; Most, Shina-August, & Meilijson, 2010; Tye-Murray, 2003). While hearing loss may contribute to missing conversational cues, difficulties with speech intelligibility may cause misunderstandings and disrupt conversational flow or narrative clarity. At preschool ages, for example, children with more intelligible speech may have more efficient and effective communication with other children, providing them with more shared experiences of communication, psychological, and emotional functioning. These latter influences on shared psychological and emotional experiences may accumulate over time, explaining some of the relations with emotional functioning (e.g., anxiety and depression) found for long-term CI users in Study 2.

Atypicality was correlated with CI user speech intelligibility in both studies. Like the Functional Communication scale, some items on the Atypicality scale may be impacted by parents’ understanding of the child's linguistic behavior (e.g., babbling to self, nonsensical utterances), and items such as those regarding strange or confused behavior or apparent unawareness of others could reflect a breakdown in the speech-communication chain involving either hearing or interactional components.

Attention problems were also correlated with CI user speech intelligibility in both studies. Some items on the Attention Problems scale (e.g., regarding listening carefully or paying attention when being addressed) may reflect difficulties with another link in the speech chain—hearing and understanding elementary speech cues, which are sparsely encoded by CIs. Previous studies have identified delays in executive functioning—including controlled attention—in children and teens with CIs, and there is evidence that speech and language functioning deficits are significant contributors to these delays (Figueras, Edwards, & Langdon, 2008; Kronenberger, Pisoni, Henning, & Colson, 2013). Thus, a finding that speech intelligibility is related to attention problems is consistent with that prior research, although prior research has focused more on receptive language components rather than intelligibility.

Several BASC-2 scales reflecting social and communication functioning were correlated with CI user speech intelligibility—Withdrawal and Adaptability in both studies and Activities of Daily Living and Leadership in Study 2. Furthermore, some more emotionally focused BASC-2 scales (Anxiety, Depression) were related to speech intelligibility only in the older sample examined in Study 2. It may be that at older ages, language skills and the social benefits of language interactions have a broader impact on a wide range of psychosocial functions, including emotional adjustment and independent living. There may also be a cumulative developmental effect of poor speech intelligibility on emotional well-being that takes time to develop and that becomes apparent only after higher levels of cognitive functioning are attained. School ages and teenage years are developmental periods characterized by demands on emotional coping skills and social competence with increased group social interaction and less support from parents and authorities compared to preschool ages. Thus, effective communication relying on good speech intelligibility may be an important tool for acquiring social support and for engaging in adaptive coping behaviors that promote emotional and social adjustment. In addition, difficulties in these areas may be sources of anxiety and depression, particularly as worries about fitting in and being accepted by peers become more salient during teenage years.

In Study 2, several BASC-2 scales were correlated with speech intelligibility within the TH sample. Three of these scales also showed relations within the Study 2 CI sample (Depression, Withdrawal, Functional Communication), but the three other scales did not show relations among CI users in either study: Hyperactivity, Aggression, and Conduct Problems, although Aggression was related to speech intelligibility among TH preschoolers in Study 1. These three scales constitute an Externalizing Problems composite on the BASC-2 and measure overactive, disruptive, intrusive, and rule-breaking behaviors.

Finally, two BASC-2 psychosocial adjustment scales did not correlate with speech intelligibility in either study: Somatization and Social Skills. Somatization reflects broad physical complaints extending well beyond hearing loss or communication delays related to speech intelligibility. The lack of significant relations with social skills was unexpected given the importance of intelligibility for social interaction. It could be that parents’ views of their children's attempts to be polite and helpful may include nonverbal cues and other behaviors independent of good intelligibility; this scale and its components will be investigated more closely in future research.

Implications and Clinical Relevance

The results of these two studies suggest that several areas of psychosocial development are at elevated risk for young CI users who display poor speech intelligibility, whereas CI users with consistently good speech intelligibility over time, especially during preschool ages, experience more positive psychosocial outcomes. Thus, it is clinically important that deaf children with CIs who display poor speech intelligibility also be evaluated and monitored closely for possible risk and problems in psychosocial development. The measures of speech intelligibility and psychosocial adjustment used in these studies are relatively brief and straightforward to administer and interpret, further enhancing the clinical utility of the present results.

Because the relations identified in this study were correlational in nature, it is unknown if improvements in speech intelligibility positively affect psychosocial behaviors, if better psychosocial skills enable speech intelligibility improvement, or if the two develop together. What is clear, however, is that difficulties in the two domains are related. Because speech intelligibility is considered as an important outcome for CI users, it is often targeted in speech–language therapy, but difficulties with psychosocial behaviors may not receive attention unless they reach clinically significant levels. Based on the current findings, additional attention to psychosocial outcomes is warranted, and psychosocial adjustment should be a focus of evaluation in children who display poor speech intelligibility after cochlear implantation.

Limitations and Future Directions

As with many studies of clinical populations, random sampling is difficult or impossible to achieve, and multiple factors contribute to speech and language outcomes in CI users. By design, the samples in these studies restricted the range of several such variables (age of onset of deafness, age of implantation, residual hearing, etc.) to allow more straightforward comparisons of factors that have not been investigated in the past. However, this may have resulted in smaller sample sizes, especially in Study 1, which were further reduced over time as some participants failed to return each year. In addition, factors that were not evenly matched between samples or studies may impact the results reported here (e.g., age at implantation, length of CI use, nonverbal IQ, family income, communication mode, educational setting). Although age and length of CI use were not correlated with the outcome measures, the ranges of these factors were large and may be a concern for accurate tracking of development or improvement in both speech intelligibility and psychosocial adjustment, especially given the large changes in social and family relationships that occur between early childhood and teenage years. Future work on speech intelligibility and psychosocial outcomes should use larger, more controlled, more diverse samples to systematically evaluate factors that may affect those outcomes and to provide statistical analyses with greater power.

The similarity of the patterns found among the two different age groups using different measures of speech intelligibility supports the generalizability of the present results, but with some limitations. Speech intelligibility was measured from audio recordings only, but many real-life situations have the added benefit of visual speech information to enhance intelligibility, and so CI users may fair better outside research/clinical settings. However, both CI and TH talkers likely experience higher intelligibility in face-to-face communication (in which listener feedback also aids in mutual comprehension), but the least intelligible CI users are likely to remain less intelligible than their peers. Similarly, difficult listening environments (e.g., noisy restaurants, phone conversations with strangers) negatively affect all talkers’ intelligibility, with the least intelligible likely suffering most; these factors should be examined directly in future work. It is also possible that differences in BIT and McGarr test administration (i.e., oral/pictoral versus oral/printed sentence presentation, short versus varying in length and predictability) differentially affected speech intelligibility scores between the two studies. Similarly, items that differ between BASC-2 forms for the different age groups may have an effect, albeit limited, given the use of age-based T-score norms. Finally, because many parents observe and interact with their children far more during preschool than older ages, parent reports may not fully capture aspects of psychosocial behavior that manifest in school settings. For this reason, teacher reports of the BASC-2 are often solicited during clinical evaluations (Reynolds & Kamphaus, 2004).

These studies support a clinical approach of incorporating assessment of psychosocial adjustment into routine evaluation of deaf children with CIs, particularly when speech intelligibility deficits are present. Future work is needed to design and investigate treatment options to improve psychosocial adjustment, possibly through the use of speech–language interventions. Intervention research involving speech intelligibility and psychosocial adjustment will also provide better insight into the causal links between these critical outcomes.

Funding

National Institutes of Health—National Institute on Deafness and Other Communication Disorders (R01 DC009581, T32 DC00012).

Conflicts of Interest

No conflicts of interest are reported.