There are six distinctive tones in Cantonese differing according to the fundamental frequency patterns (Gandour, 1981; Matthews & Yip, 1994). While evidences have shown that cochlear implantation facilitates segmental perception including vowels, consonants and word recognition in Cantonese-speaking children (Wei et al., 2000; Wong et al., 2002; Lee & van Hasselt, 2005), their performance on tone perception and production is far from satisfactory.
Cheung, Lee, Chan, Tong & van Hasselt (2000) studied nine children with at least 3 mo of implant experience and documented no major improvement in tone imitation and production. Employing Cantonese lexical tone identification as the outcome measure, other studies included children implanted between 2 yr 6 mo to 8 yr 8 mo with a length of implant experience from 11 to 53 mo (Ciocca, Francis, Aisha & Wong, 2002; Lee, van Hasselt, Chiu & Cheung, 2002; Wong & Wong, 2004). Data have consistently shown that implanted children still presented great difficulties in accurate tone identification irrespective of their age at implantation and duration of implant use.
The unsatisfactory tone performance may be related to the limitations of the past studies. Firstly, the sample sizes of the studies are limited. There were only 9 to 17 subjects in the above mentioned studies. While children in the sample spanned over a wide age range from 2 yr 6 mo to 11 yr 5 mo, none of the subject was younger than 2 yr 6 mo. The cross-sectional data collected also make the generalization of the results implausible.
The objective of the present study is to examine the critical age for satisfactory tone production in Cantonese-speaking children after cochlear implantation by including children younger than 2;06 in a larger subject pool. Instead of employing cross-sectional data, performance of children was evaluated longitudinally over a 5-yr period.
Materials and Methods
Sixty children, implanted at ages from 1 yr 1 mo to 14 yr 9 mo (mean = 5 yr 11 mo), were included. Twenty-seven of them were females, 33 were males. All subjects were profoundly hearing-impaired children with a unilateral cochlear implant for at least 1 yr at the time of data collection.
Pictures depicted in black-and-white line drawings representing words in Cantonese were used as test material. All six Cantonese tones, each with at least five occurrences with different word contexts, were represented in the test stimuli.
Depending on the duration of receiving implant of each individual child, the test was performed at pre-operation, 0.5-, 1-, 2-, 3-, 4- and 5-yr postsurgery whenever possible. Subjects were asked to name each picture presented by experimenters. Pre-operative data on the two youngest age groups were not able to obtain as the picture naming task was beyond these children’s linguistic capability at the time of testing.
Test sessions were recorded with audiotapes. Scoring was expressed as the percentage of tones correctly produced as judged by the experimenter who is accustomed to listening to deaf speech. Linear regression was employed to explore the effect of implant experience (time) and age of implantation on the tone production scores.
Using the mean tone production score as the dependent variable, results of linear regression indicated a significant main effect of time (p < 0.001) and interaction between time and age (p < 0.001). The effect of age at implantation was insignificant (p = 0.28).
In view of the presence of interaction effect which may confound the results obtained, subjects were divided into 10 groups according to their age of receiving implants. Data were reanalyzed with individual linear regression on the tone production scores in each age group.
Table 1 shows the descriptive statistics of the tone production scores of the children implanted at different ages over time while Table 2 is the result of the linear regression.
The effect of time was significant in children implanted at 2, 3, 6 and 8 yr old (p = 0.00, 0.00, 0.05 & 0.04). The parameter estimates, which indicate the increase in tone production score in relation to one unit increase in time, ranged from 0.48 to 8.56.
The positive values of parameter estimates indicated that all children in general benefit from the use of cochlear implant in tone production performance over time. The magnitude of improvement, nevertheless, was different for children implanted at various ages.
For children who received their implants before the age of two, implant experience did not have a significant impact on tone production performance (p = 0.39) and the magnitude of improvement over time is relatively small (parameter estimates = 2.39). The insignificant time effect and small improvement is due to the fact that this group of children had already achieved a reasonably high score (77.2% accuracy) after their first year of implant use. The room for further improvement is thus relatively small. They represent the group of children who achieved a high tone production accuracy within a short time. The satisfactory performance was sustained throughout the 5 yr of postsurgery testing intervals.
For children who had their implants from two to just below 4 yr old, implant experience is highly significant in tone production (p < 0.001). In addition, the magnitude of improvement was the greatest among all subject groups (parameter estimates = 8.56, 6.49). As shown in Figure 1, the two groups of subjects had relatively lower tone scores in the initial testing intervals. The score continued to increase reaching 82.3% and 78.2% accuracy at the 5-yr postimplantation test interval.
Figure 2 depicts the performance of children implanted at age four or older. The values of parameter estimates dropped markedly for these subject groups. The mean tone production scores only ranged from 45.3% to 62.3% even after the implants had been utilized for 4 to 5 yr.
Based on the results obtained, a critical age of receiving implant before 4 yr old for tone acquisition is suggested. Optimally, children should receive their implant before the age of two, when they may then achieve satisfactory tone production after 1 yr of implant use. Children who receive their implant from two to just below 4 yr old also achieved high accuracy of tone production, but after about 4 yr of implant experience.
Results, nevertheless, have to be interpreted with caution in view of two methodological limitations in the present study. Firstly, not all children were tested at all time intervals longitudinally. Secondly, the tone production scores were assessed by a single judge only. The lack of a second judge makes the evaluation of reliability and validity of the scoring impossible. Inclusion of a second judge and recruiting children with longer duration of implant experience who could provide data on every single time interval are suggested for further studies.
Cheung D.M.C., Lee K.Y.S., Chan B.Y.T., Tong M.C.F., van Hasselt, C. A. (2000). Paediatric cochlear implantation: Perspectives in tone reception and production development in the Cantonese Population. Cochlear Implants
, Article 11B, p. 209-210. Edited by Susan B. Waltzman, Noel Cohen: Thieme Medical Publishers, New York.
Ciocca, V., Francis, A., Aisha, R., Wong, L. (2002). The perception of Cantonese lexical tones by prelingually deaf cochlear implantees. Journal of the Acoustical Society of America
Gandour, J. (1981). Perceptual dimensions of tones: evidence from Cantonese. Journal of Chinese Linguistics
Lee, K.Y.S., van Hasselt, C. A. (2005). Spoken word recognition in cochlear implant children: a five-year study on speakers of a tonal language. Ear and Hearing 264
, Suppl, 30S–37S.
Lee, K. Y. S., van Hasselt, C. A., Chiu, S. N., Cheung, D. M. C. (2002). Cantonese tone perception ability of cochlear implant children in comparison with normal-hearing children. International Journal of Pediatric Otolaryngology
Matthews, S., Yip, V. (1994). Cantonese: a Comprehensive Grammar
. London: Routledge.
Wei, W. I., Wong, R., Hui, Y., Au, D. K. K., Wong, B. Y. K., Ho, W. K., Tsang, A, Kung, P., Chung, E. (2000). Chinese tonal language rehabilitation following implantation in children. Acta Otolaryngol
Wong, A. O., Wong, L. L. (2004). Tone perception of Cantonese-speaking prelingually hearing-impaired children with cochlear implants. Otolaryngology – Head & Neck Surgery
© 2007 Lippincott Williams & Wilkins, Inc.
Wong, R. K., Kung, P., Tsang, A., Chung, E., Hui, Y., Wong, B., Au, D., Wei, W. I. (2002). Factors affecting connected speech comprehension in Cantonese-speaking children after cochlear implant. In Kubo, T., Takahashi, Y. & Iwaki, T. (Ed). Cochlear Implants – An Update
, pp.349–352. Kugler, the Hague: the Netherlands.