Speech and Language Development 5 Years Post-Implantation:- The Value of Continuity of Auditory Verbal Therapy

Abstract

Cochlear implants (CIs) are a well-established treatment for severe to profound hearing loss, particularly in young children. The success of CIs is influenced by various factors, including the age of implantation and the quality and duration of post-operative rehabilitation, such as Auditory Verbal Therapy (AVT). AVT plays a crucial role in developing listening and spoken language skills in children with CIs. However, the impact of AVT duration on long-term outcomes remains unclear. This study aimed to investigate the impact of AVT duration on the long-term auditory and speech outcomes of children who received CIs between 9 and 12 months of age. Specifically, we compared the outcomes of children who received AVT for one year, one and a half years, and two years after implantation. This descriptive cohort study included 45 children diagnosed with severe to profound hearing loss who received unilateral CIs and completed at least one year of AVT. Participants were divided into three groups based on AVT duration (Group A: 1 year, Group B: 1.5 years, Group C: 2 years). Their auditory perception, speech intelligibility, receptive and expressive language, and speech production skills were assessed using standardized tests five years post-implantation.. Children who received AVT for two years (Group C) demonstrated significantly better outcomes in auditory perception and speech intelligibility compared to those who received AVT for one year (Group A). Group C also exhibited higher scores in expressive language and speech production, while both groups achieved similar results in receptive language. These findings suggest a positive correlation between AVT duration and long-term language and speech development. Early cochlear implantation, coupled with continuous AVT for at least two years, significantly enhances auditory and speech abilities in children with severe to profound hearing loss. This study underscores the importance of extended AVT duration to maximize the long-term benefits of cochlear implants and enable children to reach their full communication potential.

Introduction

Cochlear implants (CIs) are now the most successful of all prostheses of the nervous system. CIs are used in individuals with severe to profound hearing loss caused by loss of cochlear hair cells, and there is no significant improvement after using a conventional hearing aid for 3–6 months [1]. The outcome of CI is affected by various factors, so it is mandatory to study these factors influencing the outcome. Many studies have assessed the effect of CI age on auditory and speech rehabilitation outcomes [2, 3]. The principle behind early implantation is to provide adequate and appropriate auditory stimulus to these subjects during the critical/sensitive period of nerve connection development [4]. Thompson et al. reported that among 48 children who underwent CI treatment, the auditory and speech abilities of those who underwent CI treatment within the first 12 months of age were better than those who underwent the procedure within the first 18 months [5]. The auditory and speech development of children who underwent CI treatment at 18 months of age lagged behind that of children of the same age with normal hearing, while children who underwent CI treatment within the first 12 months of age could reach the standard levels of auditory and speech development [6]. Other studies have shown that children who undergo CI treatment younger than four years of age show better auditory and speech development than older children [7, 8]. Such findings have prompted a reduction in the earliest age of approved cochlear implantation by the US Food and Drug Administration from 24 months in 1990 to 18 months in 1998 to less than 12 months in 2000.

Literature proves that cochlear implantation alone will not suffice, but adequate and timely Auditory Verbal Therapy (AVT) post-implantation can help patients make the greatest use of their implanted device. AVT is a rehabilitation programme that includes structured exercises designed to help the patient understand and recognize sound signals. It begins with simply detecting the sound, then distinguishing different sounds, and thence to recognize spoken words. It is a parent-centred approach programme that encourages the use of naturalistic conversation and spoken language to communicate [9]. Auditory verbal therapists are trained to provide therapy sessions to the implantees and also train the parents of the implantees. The ultimate goal is to develop hearing as an active sense so that listening becomes an integral part of the child’s development. Much of the literature regarding cochlear implantation outcomes has focused on speech development, and less is known about language acquisition. Speech is the oral production of sounds, whereas total language development consists of comprehension, verbal reasoning, narrative ability and spontaneous language production and is the basis for communication [10]. Improvements in speech perception and production post-implantation have been well documented. However, gains in speech skills do not necessarily correlate with language competence [11–13].

Longitudinal studies on the effectiveness of AVT in terms of listening and linguistic performance of children with cochlear implants are scarce. No fixed categorized protocols have been used so far to document the linguistic performance of implantees, so it becomes all the more important that a structured protocol using established tools should be conceptualized concerning listening and linguistic performance for overall outcome and parent satisfaction from AVT. So, the current study aims to evaluate the effectiveness of AVT in terms of Receptive language, expressive language, speech, auditory perception and Speech Intelligibility Rating Scale after 5 years of cochlear implantation age and compare the variability of outcome with terms of the therapeutic continuity.

Materials and Methods

This descriptive and cohort research design study was approved by the Ethical Committee of the Institute and was conducted in the Department of Audiology and Speech-Language Pathology in collaboration with the Department of ENT of a tertiary care centre in North India. The study duration was between April 2021 to July 2022.

A total of 45 children with bilateral severe to profound hearing loss and with no benefit of a hearing aid who underwent unilateral cochlear implantation at 9–12 months of age and had a minimum of 5 years of listening experience were included in this study. Thus, the chronological age of all implantees at the time of assessment was approximately six years.

Bilaterally severe to profound hearing loss children of age group 9–12 months were included in the study who had no benefit from a hearing aid and had no other known conditions that interfered with speech/language development. They were implanted unilaterally and there were no surgical complications. They received 45-minute sessions of AVT thrice a week and completed at least one year of AVT.

Procedure

The implant switch-on programming session was conducted by an experienced audiologist three weeks after CI surgery. All subjects underwent regular mapping. The following mapping protocol was used:

1st mapping (Initial activation) was typically done 21 days post-operatively. 2nd, 3rd, 4th, 5th, 6th and 7th mappings were done one week, two months, 3 months, 6 months, 9 months and 12 months post-initial activation respectively.

The average dynamic range between T and C Levels was 35 to 40 amperes. The aided thresholds were obtained by the audiologist during the visit for AVT in all subjects after every routine mapping. After 5–6 months of mapping, the child’s aided responses were under the speech banana curve and aided responses were also checked after 5 years of implantation age.

Follow-up intensive rehabilitation was conducted for each child thrice a week and the duration of each session was approximately 45 min over 1–5 years All AVT providers had a minimum qualification of BASLP degree with one year or more experience in AVT in cochlear implant children. Ling’s six sound tests were done on every visit and documented.

After five years of implantation age, all children were called and were reassessed by the revised Categories of Auditory Performance (CAP) score described by The Shepherd Centre based on the Nottingham CI program, 1995 [14]. CAP test tool is specially developed to assess auditory performance in hearing-impaired children using cochlear implants or hearing aids. The tool is given in Table 1.

Table 1.

Revised categories of auditory performance (CAP) score: the Shepherd Centre (based on Nottingham CI program,1995)

Category	Criteria
Level 0	Unaware of environmental sounds
Level 1	Detects some environmental sounds
Level 2	Responds to some speech sounds
Level 3	Can identify some environmental sounds
Level 4	Understands some spoken words with additional performatives, e.g. ' Where is the duck that says quack quack’, ‘Give me the car brmm’
Level 5	Understands common phrases, e.g. pick it up; it’s bath time
Level 6	Understands some spoken words without performatives. e.g. give me the duck’/ ‘go get the car’
Level 7	Responds appropriately to simple questions, e.g. what is it?
Level 8	Understands conversations with familiar speakers
Level 9	Understands conversations with unfamiliar speakers
Level 10	Follows recorded stories
Level 11	Uses the telephone with familiar speakers
Level 12	Uses the telephone with unfamiliar speakers

Speech intelligibility was assessed by the Speech Intelligibility Rating (SIR) [15] (Table 2). Receptive language, expressive language and speech levels were assessed using integrated scales of development (ISD) [16]. ISD scale assesses language skills in six domains: receptive language, expressive language, speech, audition, cognition, and pragmatics. The age range is 0 to 48 months.

Table 2.

Speech intelligibility rating (SIR) (O’Donoghue et al.)

Category	Criteria
5	Connected speech is intelligible to all listeners. The child is understood easily in everyday contexts
4	Connected speech is intelligible to a listener who has little experience of a deaf person’s speech
3	Connected speech is intelligible to a listener who concentrates and lip reads
2	Connected speech is unintelligible. Intelligible speech is developing in single words when context and lip-reading clues are available
1	Connected speech is unintelligible. Pre-recognizable words in spoken language; primary mode of communication may be manual

Based on the therapeutic continuity after Cochlear implantation, all 45 participants were divided into three (03) groups.

Group A – The duration of AVT received was one year.

Group B – The duration of AVT received was one and a half years.

Group C – The duration of AVT received was two years.

It was observed that none of the implantees in the present study completed the AVT till five years of implantation age, the reasons being access to rehabilitation provided by hospitals is limited for many hearing-impaired patients due to time constraints, expense, and the proximity of patients to the rehabilitation site which is even more serious for children under two years old [17]. The duration of free AVT sessions with mapping is also limited to two years under the central government-funded ADIP scheme.

Before implantation, the CAP score was category 0, the SIR score was category one, while receptive language, expressive language, and speech levels were 0 months for all implantees.

Statistical Analysis

Data was systematically collected, compiled in Microsoft Excel and statistically analyzed using the statistical package of Social Sciences (SPSS) version [26] to draw relevant conclusions. The present study outcomes are mentioned in number and percentage and data is minimal/ordinal so mean has been mentioned instead of SD. To draw the relevant conclusion, data was analyzed using ANOVA for parametric data and the Chi-square test for categorical data. The level of significance was determined as p < 0.05 as significant and p ≤ 0.001 as highly significant. All the groups were compared using the nonparametric ANOVA test.

Results

A total of 45 participants with a mean age and hearing age of 6 years and implantation age of 5 years participated in the present study. Among 45 participants, 22 were males and 23 were females. The participants were divided into three groups based on the duration of rehabilitation (AVT) received.

CAP Scores 5 years after CI (Tables 3and4). The mean CAP score of group A was 9.2 (p < 0.001), while in groups B and C, it was 9.7 (p > 0.05) and 10.06(p < 0.001), respectively. Maximum patients in group A (i.e. 11 out of 15) and in group B (8 out of 15) could achieve a CAP score of 9, and the maximum score achieved in both these groups was 11, while in group C, the maximum score achieved was 12 (the maximum limit).

Table 3.

Association of outcomes with AVT duration

Variable		AVT Duration						1 year vs. 1.5 yrs	1 year vs. 2 yrs	1.5 yrs vs. 2 yr
		1 yr		1.5 yrs		2 yrs
		N	%	N	%	N	%	P value	P value	P value
Gender	F	9	60.0	9	60.0	5	33.3	1.000	0.143	0.143
	M	6	40.0	6	40.0	10	66.7
CAP Score	8	1	6.7	-	-	1	6.7	0.040*	0.005*	0.449
	9	11	73.3	8	53.3	5	33.3
	10	1	6.7	3	20.0	3	20.0
	11	2	13.3	4	26.7	4	26.7
	12	-	-	-	-	2	13.3
SIR Score	3	6	40.0	2	13.3	3	20.0	0.060	0.035*	0.881
	4	9	60.0	10	66.7	9	60.0
	5	-	-	3	20.0	3	20.0
RL	Above 48 Mon	15	100.0	15	100.0	15	100.0	-	-	-
EL	31-36 M	5	33.3	-	-	-	-	< 0.001**	< 0.001**	-
	37-42 M	6	40.0	-	-	-	-
	42-48 M	2	13.3	-	-	-	-
	> 48 M	2	13.3	15	100.0	15	100.0
Sp. Level	16-18 M	1	6.7	-	-	-	-	< 0.001**	< 0.001**	0.048*
	19-24 M	12	80.0	-	-	1	6.7
	25-30 M	2	13.3	8	53.3	2	13.3
	31-36 M	-	-	4	26.7	4	26.7
	37-42 M	-	-	3	20.0	4	26.7
	43-48 M	-	-	-	-	4	26.7

Chi-Square Test: **p < 0.001;Highly significant; *p < 0.05: significant

Table 4.

Auditory verbal therapy duration and mean value of its outcome

	Group A		Group B		Group C
	Mean	p-value	Mean	p-value	Mean	p-value
CAP	9.2	*** P < 0.001	9.7	ns P > 0.05	10.06	*** P < 0.001
SIR	3.6	P < 0.05	4	ns P > 0.05	4	ns P > 0.05
RL	Above 48	*** P < 0.001	Above 48	*** P < 0.001	Above 48	*** P < 0.001
EL	37–42 months	** P < 0.01	Above 48	*** P < 0.001	Above 48	*** P < 0.001
Speech Level	19–24 months	** P < 0.01	25–30 months	*** P < 0.001	43–48 months	*** P < 0.001

Chi-Square Test: **p < 0.001;Highly significant; *p < 0.05: significant

SIR Scores 5 years after CI (Tables 3and4). The mean SIR score of group A was 3.6 (p < 0.05), while in groups B and C, it was 4 (p > 0.05). The maximum number of patients in groups A and C (i.e. 9 out of 15) and in group B (10 out of 15) could achieve an SIR score of 4. A maximum SIR score of 5 was achieved in groups B and C in 3 out of 15 CI implantees. In group A, SIR mean score was 3.6 and in group B and C SIR mean score was 4 each, indicating that speech therapy continuity and early implantation (less than 1year) gives good outcome. According to literature, AVT continuity does influence SIR score but in the present study, there was no significant variation in the duration of AVT amongst the groups which is the reason for the same SIR scores of 4 each.

Receptive language five years after CI (Tables 3and4). The RL was above 48 months in all the groups A, B and C(p < 0.001).

Expressive language five years after CI (Tables 3and4). The mean EL of group A was 37–42 months (p < 0.01), while in groups B and C, it was > 48 months (p < 0.001). All the implantees in groups B and C could achieve EL of > 48 months after AVT of 1.5 and 2 years, respectively.

Speech levels five years after CI (Tables 3and4). The mean Sp. L of group A was 19–24 months (p < 0.01), while in groups B and C, it was 25–30 months (p < 0.001) and 43–48 months (p < 0.001), respectively. 12 out of 15 implantees in group A could achieve Sp. L of up to upto19-24 months. In group B, 8 out of 15 achieved Sp. L of up to 25–30 months, while 4 achieved Sp. L of up to 31–36 months, and three implantees achieved Sp. L of up to 37–42 months. In group C, 4 out of 15 achieved Sp. L of up to 31–36 months, while 4 achieved Sp. L of up to 37–42 months, and 4 of the implantees achieved Sp. L of up to 43–48 months.

Association of the outcomes among different groups with AVT Duration: As shown in Table 3, the CAP score was significant when Group A was compared with both Group B (p = 0.04) and C (p = 0.005), but it was not significant when Group B was compared with Group C (p = 0.449). The SIR score was only significant when Group A was compared with Group C (p = 0.035), but it was not significant when Group A was compared with Group B (p = 0.06), and Group B was compared with Group C (p = 0.881): the EL and Sp. L outcomes were highly significant when each group was compared to the other (p < 0.001), indicating a strong correlation of both EL and Sp. L with AVT duration.

Fig. 1.

Graphical representation of outcome of CAP and SIR across the groups

Discussion

Hearing loss is the most prevalent newborn congenital disorder, with 3 out of 1000 children born with hearing loss. The early months of life are crucial for central auditory development, and it is the period when neural plasticity is highest due to increased synaptogenesis [18–20]. Lack of auditory stimulation leads to degeneration across the auditory system. Thus, temporal patterns that are important for developing neurocognitive skills, such as pattern detection, sequential memory, and sustained attention, could be affected [21]. These detrimental effects of auditory deprivation could be prevented by early identification of infants with profound hearing loss and early CI, which can stimulate and preserve central auditory development at a time of maximal plasticity. On-time identification is only the first step. The quality of the intervention services following the early identification will affect the communication outcomes of such infants. One of the goals of pediatric cochlear implantation is the development of communication skills sufficient to allow these children to function independently at school and in the community. The habilitation programs after CI include timely and adequate AVT, and its focus is for the implantees to function similarly to their normal hearing peers.

AVT is a listening and spoken language instructional approach that aims to use hearing as the main sensory modality in developing speech production skills since these CI implantees manage the listening experiences created by AVT [22]. Another aim of AVT is to achieve full integration into mainstream society following an array of 10 principles of clinical practice. These ten principles aim to trigger the auditory cortex of these infants and help communication partners benefit their children’s receptive and expressive language skills [23].

In the present study, it was observed that none of the implantees continued the AVT protocol till five years of implantation age. The maximum duration of AVT received was two years post-CI. (15 out of a total of 45 implantees). The mean CAP score of 9.2 was achieved in just one year of AVT post-CI, and it increased to a mean of 10.06 in 2 years of AVT. A mean SIR score of 3.6 was achieved by the end of 1 year of AVT and increased to 4 by the end of just two years of AVT. By the end of 1 year of AVT, the mean Receptive Language Age was above 48 months while the mean Expressive Language Age and Speech level of above 48 months was achieved by the end of 1.5 years of AVT, which was highly significant. In Group C (n = 15), two implantees achieved a CAP score of 12, three implantees achieved a SIR score of 5, 100% of implantees achieved Receptive Language Age and Expressive Language Age above 48 months, and 4 out of 15 achieved Speech Levels above 48 months. In the present study, explanations for improved scores in our subject population involve earlier intervention and intensity of AVT.

In literature, many factors have been found to affect the outcome of implantation, such as duration of deafness [24], age at onset of deafness and age at implantation [25, 26], duration of implant use, length of daily device use [27], and preoperative level of residual hearing [28]. Studies have proved that earlier implantation produces better outcomes [29]. Most children implanted before the age of 2 years can develop speech and language at a rate equal to similarly aged children with normal hearing [30]. More and more children have received cochlear implants before two and even at one year of age to obtain better results, as is seen in our study, as most of the children who received AVT for 2yrs were at par with their normal hearing peers.

Tomblin et al. reported that younger age at implantation was a significant predictor of improved language scores [31]. Studies stress the effectiveness of AVT in association with early identification of HL and intervention revealing language capabilities within normal limits (WNL) among children with CI who attain this combination. Of children who started AVT before six months, 90.5% had “normal” language development, while the percentages of “normal” language development were 77.4% and 75% for children who started AVT between 6 and 12 and between 12 and 18 months, respectively. The rate of “delay” in development was found to be increasing as the starting age of training was delayed [31].

A recent study conducted by Nandurkar and Susmitha to see the progress in the listening skills of cochlear implant children suggests the development of auditory skills triggers in the first three months of cochlear implantation [32]. Another study suggested that within nine months of AVT, CI children’s linguistic skills are significantly boosted, and age-appropriate linguistic skills can be achieved within 24 months [33].

In the present study, the intergroup outcome comparison revealed a significant difference was found on CAP scores when Group A was compared with Group B and C, and a significant difference was found with the duration of AVT of one versus two years on SIR scores. A highly significant difference was found in the Expressive Language Age and Speech Levels when Group A was compared to Group B and C but there was no significant difference between Group B and Group C.

The results suggest that the duration of therapeutic continuity positively affected the later outcomes of the child’s speech and language skills. Dornan et al. suggested that within nine months of auditory verbal therapy, there is a significant boost in linguistic skills of CI children, and age-appropriate linguistic skills can be achieved within 24 months of this rapid increase in auditory skills, which allows young CI users to attain aural skills that can come close to their normal hearing peers as is seen in the present study [33]. Fulcher et al. suggested that in early implantees (< 12 months) receiving AVT up to 3 years of age, 93% of all participants scored within normal limits for speech, 90% for understanding vocabulary, and 95% for receptive and expressive language [34]. Sahli investigated the development of 169 children who received a single-sided CI and concluded that children diagnosed before six months, instrumented in less than 12 months, and started with immediate AVT revealed normal skills in their language capabilities (Expressive Language and Receptive Language) as their normal hearing peers [35].

The present study is one of few endeavours to assess outcomes of continuity of AVT after early cochlear implantation. The results show that the scores are within one standard deviation of the scores of normal-hearing children. In our view, the current study is the first to study the effect of continuation of AVT on the later development of receptive, expressive language and speech levels of children with cochlear implants.

The strengths of this study are the use of validated, objective instruments to assess CAP, SIR scores, Expressive Language, Receptive Language and Speech Level performance in children after cochlear implantation. To minimize selection bias, strict inclusion and exclusion criteria were also identified at the beginning of this endeavour. All children in this study followed strict AVT protocols and used oral communication.

There are a few limitations of the study. First, our sample size was too small to be replicated in a larger population, and a more frequent and longer duration encounter with CI implantees is needed to document the efficacy of the therapeutic continuity of long-term CI outcomes. Second, the study has only focused on the effect of early implantation age (especially under one year) and continuity of AVT. There are other factors also that affect the outcome of CI in the long term.

Conclusion

Early CI, along with strict continued AVT, provides satisfactory hearing and speech abilities to congenitally deaf children. Regular follow-up and active participation by parents are necessary to maximize the outcomes. Duration of AVT received post-CI has an impact on the hearing and speech development of a child. These findings underscore the importance of extended AVT duration in maximizing the long-term benefits of cochlear implants and enabling children to achieve their full communication potential.

Funding

None.

Declarations

Research Involving Human

This study was performed in line with the principles of the Declaration of Helsinki. Approval was granted by the Institute Ethics Committee of SGRD Medical College, Amritsar. A written consent was obtained from the caregivers of all the subjects.

Conflicts of Interest

All authors declare no conflicts of interest.