Cognitive functioning in Deaf children using Cochlear implants

The study sample consisted of thirty-eight children [17 males and 21 females] with congenital bilateral severe to profound sensorineural hearing loss [participants’ socio-demographic characteristics are presented in Tables 1 and 2]. All children were diagnosed with hearing loss during their first year of life. Another battery of audiological evaluation was done prior to the surgery, which included a comprehensive set of behavioral and physiological measurements. All children were prelingual and none of them currently used hearing aids. All participating children with hearing loss were recruited from the Ear, nose, and throat [ENT] at King Abdullah University Hospital (KAUH) in Jordan and were scheduled to receive unilateral cochlear implantation in the year of 2017. All children who matched the inclusion criteria were enrolled in the study. All participants were followed for 16 months period.

Recruitment and baseline testing were performed 1 week prior to the date of the implantation surgery. In addition, a sample of normal hearing [NH] [hearing thresholds on octave frequencies 250–8000 Hz not exceeding15 dB HL] children were recruited from a compiled research project list of typically developing children. The project collected demographic data and tested the cognitive abilities of 434 normally developed children using the Leiter-R scale [Authors, 2017]. From this project sample, fifty-eight children/parents were recruited using a random number table and 48 children/parents agreed to participate.

The sample of normal hearing children included 24 participants aged 4–6 years at first testing and 24 participants aged 7–9 years at first testing. These participants were chosen to be very similar to the deaf group in terms of age and all other important demographic characteristics that have been proven to be related to cognitive functioning. Therefore, there were no statistical differences between groups in term of age and demographic data. The deaf children were divided into two subgroups according to age [chronological age at time of implantations]: ages 4–6 years [N = 22], and 7–9 years [n = 16]. Similarly, the NH children were also divided into two age groups: 4–6-year-old [N = 24], and 7–9-year-old [N = 24]. The normal and deaf participants were similar in all groups by age, gender, area of living, school type, status of living with parents, child’s GPA [Grade Point Average], family yearly income, eating breakfast, sleeping hours and parents’ occupation, level of education and smoking status.

All participants in subject and control groups were between 4 to 9 years of age. All participants were reported to be healthy and free of otological and neurological disorders. Children with learning disabilities, visual impairments, intellectual challenges, developmental delay, or those who were born to deaf parents were excluded from this study. Leiter International Performance Scale-Revised (Leiter-R) [39] was used to evaluate the children’s learning and intellectual abilities. The use of human participants in this study was approved by King Abdullah University Hospital Institutional Review Board and the Deanship of Scientific Research at Jordan University of Science and Technology. Written parental consents and approval from the educational authorities were received before carrying out the study.

Comprehensive audiological evaluation was conducted on all participants prior to CI surgery. Generally, a set of behavioral and physiological measurements were completed prior to surgery. Ear-specific pure tone thresholds were obtained using a standard procedure, visual reinforcement audiometry, or play audiometry depending on child’s age by a licensed audiologist. Specifically, air conduction [AC] hearing thresholds were measured at octave frequencies between .25 to 8 kHz and for bone conduction [BC] at octave frequencies .5–.4 kHz. The average hearing thresholds were in the range of sever to profound sensorineural hearing loss. All testing was done in a sound treated booth that meets noise reduction standards. Calibrated diagnostic audiometer type GSI AudioStar Pro was used to assess hearing thresholds using inserts ER-3A earphones. Bone conduction thresholds were measured using B71 transducer and was placed on mastoid bone. In addition, otologists conducted OAEs (otoacoustic emissions) test to find out how well is the cochlea is working and click ABR (auditory brainstem response) test to measure the way the child’s hearing nerve responds to different sounds.

Postoperative aided warble-tone thresholds were assessed in a sound field and revealed an average of 35 dB HL for the frequencies 250–8000 Hz. Post cochlear implant aided hearing thresholds was done on average of 6 months post the surgery when a stable map was reached for CI children. A total of 22 participants received their CI in the right ear and 16 children in the left ear. All children used the same cochlear implant device.

The audiologist confirmed that optimum cochlear implant fitting was achieved for each participant, cochlear implant was functioning normally, and all cochlear implant channels were activated. The otologist who performed the surgery confirmed, by X-ray that cochlear implant electrode was properly placed in the cochlea.

Speech and language assessments were performed by a licensed speech-language pathologist. Before surgery all participants were classified as prelingual. All participants used lip-reading and sign language for communication. Auditory verbal therapy and total communication therapies were provided once every week post CI for 1 year. Speech therapist noted moderate improvement [few two-word sentences] in speech and language of 8 participants of those who were implanted before 6 years of age. Other participants, including those older than 6 years, had poor speech and language development. Most participants continued to use sign language and lip reading as a mode for communication. Eight participants were able to use short two-word sentences but continued to rely mainly on their sign language abilities to communicate.

Important to note that, the CI team [Surgeons, audiologists and speech pathologists] discussed all cochlear implant candidates to determine eligibility. The criteria were rather loose but emphasize that the participants should have bilateral severe to profound sensorineural hearing loss, prelingual and younger than 10 years old. There was no mandatory rule of hearing aid use before CI. Recently, however, hearing aids use for a minimum of 6 months with no significant benefits was added as a pre-condition for CI eligibility.

The cognitive abilities of visualization, reasoning, memory, and attention were assessed using the Leiter International Performance Scale-Revised (Leiter-R) [39]. The scale was designed specifically for children with impaired hearing, motor function, communicative ability, and those who speak English as a second language. The scale can be used on normal children and adults from age 2 years to age more than 80 years. The Leiter-R composites were chosen because of their psychometric properties and primarily non-verbal nature. They are more conducive to the evaluation of cognitive abilities in individuals from non-Western cultures who do not primarily speak English.

The instrument contains four composites: (1) the visualization composite, with eight subtests of nonverbal intellectual ability, includes figure ground [FG], form completion [FC], matching [M], picture context [PC], classifications [C], design analogies [DA], paper folding [PF], and figure rotation [FR]; (2) the reasoning composite, with two subtests, includes sequential order [SO] and repeated patterns [RP]; (3) the memory composite, with eight subtests, includes associated pairs [AP], delayed pairs [DP], immediate recognition [IR], delayed recognition [DR], forward memory [FM], reverse memory [RM], spatial memory [SM], and visual coding [VC]; and (4) the attention composite, with two subtests, includes attention sustained [AS] and attention divided [AD] [40].

The researchers did not necessarily administer all items of a specific subtest at all ages as suggested by the developer of the Battery. For example, for 6–10 years we can only administered FG, DA, FC, M, SO, RP, PF subtests from the VR battery and AP, IR, FM, AS, RM, VC, SM, DP, DR, and AD subtests from the AM battery. Less number of items can be administered for younger ages and more items for older ages [39].

The Leiter-R composites have internal consistency [Cronbach’s alpha] reliability coefficients ranging from 0.89 to 0.91% for visualization and reasoning and 0.76 to 0.88% for memory and attention [40]. The instrument also shows consistent evidence of validity from content-analysis studies with extensive item analysis data, criterion-related studies with results for classification accuracy in identifying cognitive delay, and in various construct-related study [40]. The psychometric properties of Leiter-R were not investigated in Arabic language because this assessment is administered mainly by gestures and examples/practice. Authors only translated the language of instructions for the battery for Arabic speaking testers/researchers. A raw score for each of the Leiter-R’s four composites was calculated by totaling the scores of the relevant subtests. Raw scores for visualization and reasoning battery were converted to scaled scores as presented in appendix A and for attention and memory battery as presented in Appendix B in the original Leiter-R battery manual [40]. Generally, a higher score indicates better cognitive performance.

The language of instructions for the Leiter-R test battery was translated into Arabic. This translation was for the use of Arabic speaking testers/researchers because the Leiter-R is administered mainly by gestures and examples/practice. The translation was performed by five expert bilingual university professors from Jordan, Saudi Arabia, and the United Arab of Emirates, using a backward-forward translation process [41]. The authors used the same method of translating and standardizing as the Lowenstein Occupational Therapy Cognitive Assessment, Infant /Toddler Sensory Profile and Adolescent/Adult Sensory Profile [References blinded]. Discrepancies in the translation of specific terms were discussed until a consensus was reached. After that, a pilot study with 20 normal hearing children was conducted to evaluate the clarity and readability of the initial versions of the translated subscales; the terms were then modified accordingly, and a revised version was administered to 20 other children. Then, the researchers unanimously agreed that no further modification was required. This translated Arabic version of the language of instructions of the instrument was then translated back into English by a bilingual native English and fluent Arabic speaker, who was unfamiliar with the original versions of the tool.

The process of backward translation was evaluated by ten expert bilingual university professors. The scores of the instrument in evaluating the translation, which is different from the subscales’ scores, ranged from 0 [not similar] to 1 [similar]. A cut score of at least 0.80 was identified to assess the adequacy of the Arabic translation, which implies that 80% or more of the evaluators agreed that the backward translated terms had the same meaning as the original terms. A score below 0.80 suggested a possible problem with the translation. After the translation stage was completed and modifications were attended, all translated terms achieved the cut-off score of 0.80.

All data were collected by two rehabilitation therapists using the Leiter-R scale. For consistency in the administration procedure, both the principal investigator and the two therapists separately assessed and scored a group of 20 children [ten males and ten females aged 4–9 years]. The principal investigator tested 6 children and each therapist tested 7 children. Every testing session was videotaped. Each child was tested once and scored by 3 examiners: the principal investigator and the two therapists. They tested one child after another, scored them separately, and compared their scoring until they reached 98% compatibility/agreement.

All children participating in this study were assessed in a quiet environment, which is the research laboratory of the principal investigator located, and very close to the ENT clinic, where the cochlear implantation surgery was performed. Parents were not present during the testing. All children ate their breakfast before testing. The test was administered between 9 and 11 am to ensure consistency among all participants. The duration of the test ranged from 60 to 90 min [M = 75, SD = 12.4]. All children were offered small incentives such as stickers and smiley faces to keep them attentive and motivated throughout the session. A 15-min break was provided for all children at the middle of the assessment session. The same testing conditions/procedures were used during baseline assessment and re-assessments.

The instructions of the assessment [Leiter-R] were provided pictorially and with visual cues so that children understood the task and were engaged throughout the assessment. Instructions were given in the same way for all participants in all groups. Tests were always administered in the same order, as recommended by the instrument developer, to ensure that the potential effect of the order was the same in both groups. The assessment was administered for the CI group preoperatively [baseline; not more than 1 week before cochlear implant surgery] and then at eight and 16 months post cochlear implant surgery. For the NH participants, a baseline test was administered for each child, and subsequent tests were administered eight and 16 months following the baseline assessment.

As shown in Table 1, almost half of the participants were girls [55.3%] and living in urban areas [52.6%] and more than half of them [60.55%] were enrolled in private schools. There were statistical associations in demographics between CI and NH groups as measured by running Chi-square tests for comparing groups [P > 0.05].

The normal and deaf participants were similar in all groups by age, gender, area of living, school type, status of living with parents, child’s GPA [Grade Point Average], family yearly income, eating breakfast, sleeping hours and parents’ occupation, level of education and smoking status. Authors decided to choose the groups to be similar by these variables because previous research has shown that children’s cognitive abilities are influenced by these factors [1, 4, 6, 8, 9] .

Furthermore, NH group children were not receiving any special educational programs and CI group children were only receiving regular speech therapy sessions at the same center.

Descriptive statistics by Means and Standard Deviations [SD] for Leiter-R subscales by times of testing and child age for NH group and CI group are reported in detail in Table 3 and presented in Fig. 1. Results show that the two age groups of pre-CI children achieved higher scores on the visualization subtest than the NH children; this was true for the 4–6 year and the 7–9 year age groups, across all time- points On the other hand, scores for the reasoning subscales were lower for the 4–6 year and 7–9 year CI children than those for the 4–6 and 7–9 NH children, across all times of testing. Similarly, the two CI groups performed poorer on the memory subscale than the NH children in the 4–6 year and the 7–9-year age groups, across all times of testing. However, the two age groups with CI and normal hearing children performed almost similarly on the attention measure, across all times of testing.

Table 4 shows the results of the factorial repeated measures ANOVA for Leiter-R subscales with interactions by times of testing [baseline, 8 months, 16 months] and child age group [[4-6 years], [7–9 years]] and by times of testing [baseline, 8 months, 16 months] and child hearing status [NH group, CI group]. Visualization scores improved significantly for NH group across times of testing [F = 8.687, P = 0.000], and improved significantly more for [4–6 years] age group [F = 28.530, P = 0.000]. On the other hands, reasoning scores improved significantly across times of testing for CI group [F = 3.278, P = 0.042] and for both age groups; [4–6 years, F = 5.972, P = 0.004] and [7–9 years, F = 4.056, P = 0.019].

Memory scores were improved for both groups across times of testing; however, the scores’ improvements were higher for children in CI group [F = 8.221, P = 0.000] than children in NH group [F = 6.053, P = 0.003] and were the highest in [4‐6] age in CI group [F = 12.721, P = 0.000]. Attention scores were not improved significantly across times of testing in both age groups; see more details on Table 4.

Multiple comparisons using the LSD [Least Significant Difference] test was performed for Leiter-R subscales between times of testing for NH and CI groups. The results showed that performance on visualization [MD = 8.63, 9.13; P = 0.000, 0.000], reasoning [MD = 3.00, 3.78; P = 0.000, 0.000] and memory [MD = 13.42, 16.96; P = 0.001, 0.000] subscales improved significantly for NH and CI groups, respectively, after 16 months when compared to the baseline which is consistent with maturation. However, the mean differences for the CI group were higher than the NH group. Moreover, for 8 to 16 months interval, the only significant differences were seen for CI group in reasoning [MD = 0.73, P = 0.000] and memory [MD = 3.05, P = 0.008] scores, see Table 5 for more details.

The study had some limitations. First, the average age of cochlear implantation in our study is high [6.16] years. It was found that early implanted children [before the age of 27 months] had comparable cognitive skills to those of normal hearing peers [58]. Second, the type and frequency of different interventions that the cochlear implant children are getting in this study are not available. Therefore, the improvement in cognitive abilities may reflect the cumulative effects of other therapies. Third, the study sample size was rather small, not a population-based sample, done only over a period of 16 months and tested only cognitive abilities. Therefore, future research with larger population-based sample size will be necessary to assess the long-term effect of unilateral and bilateral cochlear implantations on cognitive skills as well as other factors such as motor skills, social activity, quality of life, self-esteem, personal autonomy, etc. Fourth, the effect of psychosocial factors [such as the birth order] that could predict the outcomes of cochlear implantations on cognitive abilities were not examined [55].