Speech perception and communication ability over the telephone by Mandarin-speaking children with cochlear implants

Abstract

Objective

(1) To understand speech perception and communication ability through real telephone calls by Mandarin-speaking children with cochlear implants and compare them to live-voice perception, (2) to report the general condition of telephone use of this population, and (3) to investigate the factors that correlate with telephone speech perception performance.

Methods

Fifty-six children with over 4 years of implant use (aged 6.8–13.6 years, mean duration 8.0 years) took three speech perception tests administered using telephone and live voice to examine sentence, monosyllabic-word and Mandarin tone perception. The children also filled out a questionnaire survey investigating everyday telephone use. Wilcoxon signed-rank test was used to compare the scores between live-voice and telephone tests, and Pearson's test to examine the correlation between them.

Results

The mean scores were 86.4%, 69.8% and 70.5% respectively for sentence, word and tone recognition over the telephone. The corresponding live-voice mean scores were 94.3%, 84.0% and 70.8%. Wilcoxon signed-rank test showed the sentence and word scores were significantly different between telephone and live voice test, while the tone recognition scores were not, indicating tone perception was less worsened by telephone transmission than words and sentences. Spearman's test showed that chronological age and duration of implant use were weakly correlated with the perception test scores. The questionnaire survey showed 78% of the children could initiate phone calls and 59% could use the telephone 2 years after implantation.

Conclusion

Implanted children are potentially capable of using the telephone 2 years after implantation, and communication ability over the telephone becomes satisfactory 4 years after implantation.

Introduction

The benefits of cochlear implantation (CI) in speech perception, communication skills as well as language and reading developments have been adequately proved. However, its effects in some difficult tasks such as hearing in noisy environments, telephone use and music perception are less well defined.

The understanding of telephone speech by CI recipients has been investigated by many researchers using different methods, and they have demonstrated that CI users are capable of some degree of telephone communication [1], [2]. Nevertheless, Ito et al. [3] and Milchard and Cullington [4] pointed out that telephone speech was perceived worse by the patients than live voice. Many of the previous studies used simulated telephone speech with limited bandwidth (300–3200 Hz) to test CI users’ telephone speech perception and compared the results with natural broadband speech [4], [5], [6]. Horng et al. [6] tested 15 children with cochlear implants to examine their perception of vowels, consonants, voice gender and Mandarin tones in limited-bandwidth speech, and the results showed that the phonemes (vowels and consonants) and voice gender identification were poorer with the simulated telephone speech than with the broadband one, while the tone recognition did not differ between two types of speech. Fu and Galvin [5] also used simulated band-limiting speech to test ten adult CI users on their capability of perceiving vowels, consonants and sentences over the telephone. They found that identification of consonants and sentences differed significantly between band-limiting and broadband speech, whereas that of vowels did not. These studies all suggest that restricted bandwidth of telephone speech may result in a loss of high-frequency cues, which leads to poorer comprehension.

Questionnaire surveys (telephone profile) on the frequency and experiences of the patients’ telephone use in everyday life are often administered as another way to investigate CI users’ capability of telephone communication. Earlier studies showed that, generally speaking, 56–75% of implanted adults were capable of using landline telephones and 45–75% are able to use cellular phones to communicate with other people [2], [7], [8], [9], [10], [11]. Cray et al.’s [2] study indicated that, of all his patients who were considered telephone users, most were younger and had a longer duration of implantation than non-telephone users. His study showed that 95% of them were able to converse over the telephone with familiar people and 85% with strangers.

Most of the studies on telephone use, however, were conducted on adult populations or even on postlingually deafened adults. Not much data available on prelingually deafened pediatric CI users could be found. Carmel et al. [12] was one of the few studies on the pediatric populations. They used questionnaires and found that 88% of the children with CIs were capable of initiating telephone calls, but only 38% of them had practiced talking on the phone. Tait et al. [13] used telephone profile to monitor the use of telephone of 150 children with up to 5-year experience after implantation. Their results showed a significant progress over time and were highly correlated with tests of speech perception. Nevertheless, Tait et al. [13] pointed out that telephone speech was still more difficult than live speech with the fact that, by three or 4 years after implantation, most children were able to do connected discourse tracking and closed sentence sets in live speech, while on telephone most of them were only capable of identifying single words. The difficulties of telephone speech, as Tait et al. [13] suggested, may come from its lower speech quality due to limited bandwidth as well as from lack of experience.

Mandarin Chinese is a tonal language. Each monosyllable carries one of the four tones or pitch contours that delivers different lexical meanings. The fundamental frequency (F0) patterns during voiced speech characterize the four tones. It has been well known that most of the CI speech processing strategies fail to support tone recognition with sufficient spectral or temporal cues. Fu et al. [14] and Wei et al. [15] showed in their studies that Mandarin-speaking CI patients recognized only 50–70% of Chinese tones with the latest CI technology because F0 and its harmonics were not clearly cued in electric hearing. Earlier research has suggested that Mandarin-speaking CI users chiefly used amplitude contour and periodicity information as cues to decode Mandarin tones [14], [16], [17]. Horng et al. [6] further indicated that these cues may be largely preserved in telephone speech since Mandarin tone recognition was not significantly affected by telephone speech simulation even though the high-frequency information was deprived.

Past literature have shown that, in general, both adult and pediatric CI users are capable of using the telephone to some degree. However, these studies used either a simulated setting or a questionnaire survey to investigate the telephone use by implanted populations. There is hardly any study probing the problem of real telephone use. The present study used a cohort of CI children to examine their perceptual performance on actual telephone speech. By extending the study of Horng et al. [6] which tested phonemes and tones, this study tested the perception of tones, monosyllabic words and sentences, intending a telephone test closer to real telephone use. A questionnaire survey was also conducted as supportive data that helped us have a better view on everyday telephone use by Mandarin-speaking implanted children. The specific aim of this study is (1) to understand recipients of CIs’ speech perception and Mandarin tone recognition over the telephone and compare it with their performance on the same tests using live voice, (2) to report the general condition of telephone use by Mandarin-speaking children with over 4 years of implant experience (mean duration of implant use = 8.0 years), and (3) to investigate the predictive factors that correlate with the perception on the telephone and live-voice speech, such as their age at the detection of hearing loss, age at implantation, chronological age, duration of implant use, duration of post-operative rehabilitation and pre-operative residual hearing.