This paper describes a battery of tests used to clinically assess the hearing performance of adolescent, Mandarin-speaking, experienced cochlear implant users upgraded to a new fine structure coding strategy. The battery of tests include speech in quiet conditions, speech in noisy conditions, lexical tone, and music perception.
Cochlear implant (CI) provision is the most effective clinical treatment to restore hearing performance in individuals with profound sensorineural hearing loss (SNHL). It has been successful in providing improved speech perception outcomes, especially in quiet environments. However, speech perception performance within complex environments, lexical tone recognition, and music perception have been shown to only improve with newer fine structure coding strategies or related techniques. Therefore, the methods used to assess hearing performance in noisy environments, lexical tone recognition, and music perception are of vital importance. These assessments must reflect the postoperative outcomes and also provide guidance for the programming, rehabilitation, and application of new coding strategies. In this study, hearing performance in simple and complex situations was evaluated before and after upgrading to a fine structure strategy. The participants were a cohort of Mandarin-speaking adolescents, who were experienced CI users. The comprehensive clinical workflow involved assessments of speech in quiet conditions, speech in noisy conditions, lexical tone recognition, and music perception. This battery of tests is explained in detail, from the coding strategy to the test methods, including the test process, environment, device, material, and order. The details that require special attention are discussed, such as the position of the participants, the angle of the loudspeaker, the intensity of the sound, the noise type, the practice test, and the way of answering questions. Each test step, method, and material for speech, lexical tone, and music perception is presented in detail. Finally, the clinical results are discussed.
Technological improvements in cochlear implants (CIs) have given users increasingly greater benefits, particularly in speech understanding in quiet and noisy environments, but also through tinnitus reduction and increased quality of life1,2,3,4. It is common and necessary to evaluate how technological upgrades potentially alter postoperative outcomes. Therefore, establishing a strict battery of tests is of benefit, as it can better enable the direct comparison of results of different types of hearing implant users from different clinics. This can enable the pooling of data and provide more robust results that can better inform patients and health care providers in the decision-making process. The sound coding strategy of a CI audio processor is one of the core technologies that affects a CI user's hearing performance5,6,7. Coding strategies have progressed from the previous envelope-based continuous interleaved sampling (CIS) strategy to the newer FS4, a temporal fine structure strategy8,9,10,11,12.
Sound coding strategies are responsible for processing sound signals into electrical pulses that are sent to the implant's electrode channels. In CIS, all electrode contacts on the array are stimulated with envelope-modulated strains of pulses at a constant rate (i.e., there is no temporal coding). In fine structure coding, the apical region (low frequencies) is stimulated at a variable rate so as to mimic the phase-locking of the inner hair cells in normal (acoustic) hearing, and thereby mimic the perception of normal hearing as closely as possible. Channels in the basal and middle regions are stimulated at a constant rate, as in CIS8,9,10,11,12,13.
In this study, a strict battery of tests was used to evaluate performance with the FS4 coding strategy. Tonal languages, such as Mandarin and Cantonese, use pitch cues to provide lexical meaning14. Apart from the frequently used speech tests, the battery of tests can carefully consider the pitch cues used in most tonal languages. Mandarin contains four lexical tones, characterized by variations in the fundamental frequency (F0 or pitch) in speech. Therefore, it is of key importance when evaluating Mandarinspeaking CI users to be able to identify these variations in frequency and speech15,16,17,18,19.
Throughout the years, there has been a considerable lack of tests which evaluate music perception in young Mandarinspeaking CI users. However, fine structure coding strategies must help tonal-speaking CI users discriminate pitch contours and lexical tones20. So far, only two studies have investigated coding strategies on speech and tone perception in adult CI users who are Mandarin speakers21,22. To the best of our knowledge, no investigation has assessed the hearing performance of adolescent Mandarin-speaking CI users when upgraded to the FS4 coding strategy. Therefore, the current study aimed to establish a battery of tests to evaluate the performance of adolescent Mandarin-speaking CI users, following an upgrade from an audio processor using the CIS+ coding strategy to one using the FS4 coding strategy.
This study was approved by the Medical Ethics Committee of Shandong Provincial ENT Hospital (approval No. XYK20211201). Informed consent was obtained from all study participants.
1. Instrumentation
2. Participant preparation
NOTE: A total of 10 participants (seven males, three females) volunteered for this study, two of whom volunteered to film the protocol. The participants were unilateral CI users with a mean age of 10.4 ± 1.2 years (range: 9-14 years), who were implanted at a mean age of 2.8 ± 1.2 years (range: 1-4 years) and had at least 5 years of experience using the CIS+ coding strategy (Table 1). All the participants were fluent in Mandarin and were willing to comply with all planned study procedures.
3. Experimental protocol
4. Data analysis
The speech test results indicate speech recognition ability both in quiet and in noisy conditions. The tone test results indicate the lexical tone discrimination for Mandarin lexical tones. The pitch results indicate musical discrimination ability. For speech and tone test results, all results are presented as percentages. A higher percentage score indicates a better test result. For speech tests, the results for words and sentences are presented separately. This enables the results to be analyzed and compared separately. The result for the pitch test is displayed as a visualized resolution threshold. Lower limens indicate better results. These data are easy to analyze and compare.
Spondee recognition in quiet conditions
Spondee recognition in quiet conditions significantly improved from pre-upgrade to 3 months post-upgrade (on average 16.1% better; z = 2.497; p = 0.013). The improvement was not significant from pre-upgrade to 6 weeks post-upgrade (on average 9.4% better; z = 1.735; p = 0.083) or from pre-upgrade to immediately post-upgrade (on average 5.8% better; z = 1.429; p = 0.153; Table 2 and Figure 1).
Monosyllable recognitionin quiet conditions
Monosyllable recognition in quiet conditions significantly improved from pre-upgrade to immediately post-upgrade (on average 8.2% better; z = 2.494; p = 0.013), from pre-upgrade to 6 weeks post-upgrade (on average 11.8% better; z = 2.570; p = 0.010), and from pre-upgrade to 3 months post-upgrade (on average 22.5% better; z = 2.810; p = 0.005; Table 2 and Figure 2).
Sentence recognition in quietconditions
Sentence recognition rate in quiet conditions significantly improved from pre-upgrade to 3 months post-upgrade (on average 17.8% better; z = 2.670; p = 0.008). No significant improvement was observed from pre-upgrade to 6 weeks post-upgrade (on average 13.0% better; z = 2.314; p = 0.021) or from pre-upgrade to immediate post-upgrade (on average 0.8% better; z = 0.255; p = 0.798; Table 2 and Figure 3).
Sentence recognition in noisy conditions
The pairwise comparisons from pre-upgrade to each of the post-upgrade sessions confirmed the non-significant differences in sentence recognition in noisy conditions (Wilcoxon signed-rank test: z = 1.355; p = 0.176 to z = 0.674; p = 0.500). However, sentence recognition in noisy conditions did increase on average 26% from pre-upgrade to 3 months post-upgrade (Table 2).
Tone recognition
Tone recognition significantly improved from pre-upgrade to 6 weeks post-upgrade (on average 5.0% better; t = 11.180; p < 0.001) and from pre-upgrade to 3 months post-upgrade (on average 9% better; t = 4.803; p = 0.001). No significant improvement was found from pre-upgrade to immediately post-upgrade (on average 1.6% better; t = 1.652; p = 0.133; Table 2 and Figure 4).
Musical pitch perception
Musical pitch perception significantly improved from pre-upgrade to 4 months post-upgrade (on average, 12.7 limen better; z = 2.371; p = 0.018). A non-significant improvement was observed from pre-upgrade to 6 weeks post-upgrade (on average 5.5 limen better; z = 0.840; p = 0.401), and a non-significant deterioration was observed from pre-upgrade to immediately post-upgrade (on average 7.2 limen worse; z = 0.491; p = 0.623; Table 2).
ID | Gender | Ear implanted | Age at time of surgery (years) | Age at time of evaluation (years) | Implant type |
S01 | M | R | 2.0 | 14.2 | COMBI 40+ |
S02 | F | L | 1.5 | 10.3 | COMBI 40+ |
S03 | M | L | 4.4 | 12.2 | COMBI 40+ |
S04 | F | R | 1.6 | 9.4 | COMBI 40+ |
S05 | M | R | 3.8 | 10.6 | COMBI 40+ |
S06 | M | R | 4.2 | 11.1 | COMBI 40+ |
S07 | F | R | 4.2 | 11.7 | COMBI 40+ |
S08 | M | R | 2.3 | 9.8 | COMBI 40+ |
S09 | M | R | 4.3 | 9.4 | COMBI 40+ |
S10 | M | R | 3.7 | 9.3 | COMBI 40+ |
Table 1: Demographic data of all participants. Abbreviations: M = male; F = female; R = right; L = left.
Tests | Pre-upgrade | Immediately post | 6-weeks post | 3-months post |
Monosyllables (quiet; %) | 59.6 (±14.3) | 67.8 (±17.6) | 71.4 (±13.3) | 82.1 (±12.2) |
Spondees (quiet; %) | 69.2 (±16.1) | 75.0 (±14.5) | 78.6 (±14.1) | 85.3 (±10.0) |
Sentence (quiet; %) | 78.0 (±19.4) | 78.8 (±19.2) | 91.0 (±7.8) | 95.8 (±7.9) |
Sentence (noise; %) | 59.8 (±33.78) | 70.2 (±13.5) | 80.0 (±12.9) | 85.8 (±10.7) |
Tone recognition (%) | 75.4 (±13.3) | 77.0 (±14.8) | 80.4 (±13.1) | 84.4 (±12.3) |
Musical pitch (quartertone) | 16.5 (±11.5) | 23.7 (±20.4) | 11.0 (±13.2) | 3.8 (±3.4) |
Table 2: Hearing performance on each test at each interval. All data are presented as mean values (± standard deviation). There are significant differences in spondee, monosyllable, and sentence recognition in quiet conditions in favor of the FS4 coding strategy (p ≤ 0.017). However, no significant differences can be found in the sentence recognitions in noisy conditions test (p > 0.05).
Figure 1: Spondee recognition results for each interval. Spondee recognition in quiet conditions significantly improved from pre-upgrade to 3 months post-upgrade (p = 0.013). Data are presented as mean values (± standard deviation). *p < 0.05. Circles, squares, and triangles indicate individual participant's results. Please click here to view a larger version of this figure.
Figure 2: Monosyllable recognition results for each interval. Monosyllable recognition in quiet conditions significantly improved from pre-upgrade to immediately post-upgrade (p = 0.013), from pre-upgrade to 6 weeks post-upgrade (p = 0.010), and from pre-upgrade to 3 months post-upgrade (p = 0.005). Data are presented as mean values (± standard deviation). *p < 0.05. Circles, squares, and triangles indicate individual participant's results. Please click here to view a larger version of this figure.
Figure 3: Sentence recognition in quiet conditions results for each interval. Sentence recognition rate in quiet conditions significantly improved from pre-upgrade to 3 months post-upgrade (p = 0.008). Data are presented as mean values (± standard deviation). *p < 0.05. Circles, squares, and triangles indicate individual participant's results. Please click here to view a larger version of this figure.
Figure 4: Tone recognition results for each interval. Tone recognition significantly improved from pre-upgrade to 6 weeks post-upgrade (p < 0.001) and from pre-upgrade to 3 months post-upgrade (p = 0.001). Data are presented as mean values (± standard deviation). *p < 0.05. Circles, squares, and triangles indicate individual participant's results. Please click here to view a larger version of this figure.
In the present study, the hearing performance of adolescent Mandarin-speaking CI users were systematically evaluated. The results showed significant improvements in speech recognition in quiet conditions, tone recognition, and musical pitch recognition after upgrading from the CIS+ to the FS4 coding strategy. This approach can help establish guidance for exploring clinical evaluation tools to evaluate the comprehensive effects with the new fine structure coding strategy in young Mandarin-speaking CI users.
Within the current study, the primary outcome measure was speech performance, especially speech performance in noisy conditions. Due to the difficulty of the test materials for young participants, the tests were presented in the order of easiest to hardest: spondee speech recognition in quiet conditions, monosyllable recognition in quiet conditions, sentence recognition in quiet conditions, and sentence recognition in noisy conditions. Throughout the sentence recognition in noisy conditions test, participants were asked to focus on the speech rather than the babble noise. All participants performed adequately on the sentence recognition in noisy conditions. Recognition of monosyllables in quiet conditions significantly improved at each of the three sessions compared to pre-upgrade. Similarly, the spondee and the sentence recognition in quiet conditions significantly improved between pre-upgrade and 3 months post-upgrade. These results are consistent with the previous findings in adult Mandarin-speaking CI users21,22. Although the results in the present study were not statistically significant for the sentence recognition in noisy conditions test, mean scores did increase from 59.8% at pre-upgrade to 85.8% after 3 months of use. This was in accordance with the previous report21. This test procedure and the results shown here verify the effective use of a newer speech processor for adolescent Mandarin-speaking CI users and demonstrated the usefulness of the proposed testing method.
After the speech performance tests, the tone test was conducted. In contrast to speech recognition in noisy conditions, the tone test appeared to be more interesting than speech tests for participants, with shorter test times. All participants understood the testing method after one practice session and performed well. As previously stated, recognition of tone is a crucial aspect of hearing and communication for Mandarin speakers. Normal hearing children can discriminate lexical tones in a domain-general fashion as early as 12 months17; however, this is certainly not the case in children with pre-lingual bilateral deafness. Previous studies have shown that pediatric CI users with pre-lingual deafness have marked deficits in tone recognition compared to their normal-hearing counterparts14,17. Studies on adult Mandarin-speaking CI users have shown that tone perception significantly improves over time with the FS4 coding strategy22. Similarly, the present study demonstrated that tone recognition significantly improves after both 6weeks and 3 months of using FS4.
The music software was chosen because it takes less time and thus helps keep the overall test time short. As indicated earlier, pitch perception, especially musical pitch perception, alongside tone recognition, is important for CI users. However, this is the most difficult and tedious portion of the battery of tests. Due to the difficult nature of the testing, four participants needed more than one practice session, six needed one practice round, three needed two practice rounds, and one needed multiple rounds. Due to the practice sessions, all the participants had a clear understanding of the test protocols and were able to perform the tests. The results showed significant improvements in pitch perception after 3 months of using FS4. These results were in accordance with previous literature in adult Mandarin-speaking CI users9. This validates the importance of fine structure information for music recognition in pediatric, Mandarin-speaking CI users, and the suitability of this method for evaluating young, non-Mandarin-speaking CI users of any language.
In the present study, assessing the utility of upgrading to the new coding strategy in the short term can be fully validated and tested by this battery of tests. Mandarin-speaking CI users demonstrated significantly better scores in all tests except the sentence recognition in noisy conditions test. In addition to the test methods being applicable to participants, all the tests were convenient and intuitive for the evaluation of the effect. Other than the results of musical pitch perception, all results are presented as percentages. The higher the percentage score, the better the result. For musical pitch, the lower the result, the better the effect. Researchers should ensure that all the test software have strict pre-experimental and formal test tables and the content is not repeated.
Therefore, the present study, for the first time, explored a battery of tests that could be used for clinically evaluating hearing performance in young Mandarin-speaking CI users after upgrading to the FS4 coding strategy. The approach presents valid test material, appropriate preparation, a strict test sequence, and a rigorous test procedure. However, the current study was not without limitations. Firstly, the sample size makes it difficult to extrapolate these findings to larger populations. Future studies must benefit from having a greater number of participants. Secondly, future studies must test timings, to determine how long completing each part of the test battery takes, thus being more useful for younger populations, especially those with a limited attention span. An easier methodology that shortens the overall testing time can be of clinical benefit.
Overall, the present study demonstrates that fine structure information plays a crucial role in the discrimination of speech in quiet conditions, pitch contours, and lexical tone recognition amongst adolescent Mandarin-speaking unilateral CI users. This battery of tests provides guidance for both CI users and candidates and doctors to choose different technologies, as well as to steer their clinical rehabilitation.
The authors have nothing to disclose.
This work was supported by the National Natural Science Foundation of China under grants (number 81670932, 81600803, 82071053). Michael Todd (MED-EL) edited a version of this manuscript.
INVENTIS PIANO audiometer | Russia | This audiometer is mainly used for the behavioural audiometry in this study. | |
HOPE software | Chinese PLA General Hospital | This software is used for testing the speech performance including adequate test lists for testing the monosyllable recognition in quiet, spondee (disyllable) speech recognition in quiet, sentence recognition in quiet, and sentence recognition in noise | |
JAMO Loudspeaker | China | these loudspeakerw are used for all the tests in the sound booth. | |
Lenovo computers | China | They are used for mapping and manipulating all the test softwares. | |
MAESTRO mapping device | MED-EL | These devices include the MAX box and programming cable used for connecting the processor to the mapping software. | |
MAESTRO software | MED-EL | This software is used for mapping | |
Mandarin Tone Identification in Noise Test (MTINT) | Beijing Tongren Hospital | This software is used to measure tone recognition. A 4-alternative forced-choice (4AFC) Mandarin lexical tone task is used. The test material consists of 25 monosyllabic words spoken with the four Mandarin lexical tones to create 100 different words for each talker. | |
Musical Sounds in Cochlear Implants (MuSIC) | MED-EL | The MuSIC test battery consists of six objective subtests assessing several areas of music perception. This software is chosen as it takes less time and thus helps keep the overall test time rather short. The battery contains approximately 2800 sound files recorded at the Royal Scottish Academy of Music and Drama by prefessional musicians playing natural instruments. |