International Journal of Speech-Language Pathology

ISSN: 1754-9507 (Print) 1754-9515 (Online) Journal homepage: http://www.tandfonline.com/loi/iasl20

Lexical tone perception in native speakers of Cantonese Kathy Y. S. Lee, Kit T. Y. Chan, Joffee H. S. Lam, C. A. van Hasselt & Michael C. F. Tong To cite this article: Kathy Y. S. Lee, Kit T. Y. Chan, Joffee H. S. Lam, C. A. van Hasselt & Michael C. F. Tong (2015) Lexical tone perception in native speakers of Cantonese, International Journal of Speech-Language Pathology, 17:1, 53-62, DOI: 10.3109/17549507.2014.898096 To link to this article: http://dx.doi.org/10.3109/17549507.2014.898096

Published online: 29 Apr 2014.

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Date: 05 November 2015, At: 14:39

International Journal of Speech-Language Pathology, 2015; 17(1): 53–62

Lexical tone perception in native speakers of Cantonese

KATHY Y. S. LEE, KIT T. Y. CHAN, JOFFEE H. S. LAM, C. A. VAN HASSELT & MICHAEL C. F. TONG

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Institute of Human Communicative Research and Department of Otorhinolaryngology, Head and Neck Surgery, The Chinese University of Hong Kong, HKSAR, PR China

Abstract Purpose. This study aimed at investigating (1) tone perception development among typically-developing Cantonese speakers and (2) the hierarchy of tone perception difficulty among the 15 tone contrasts. Method. Two-hundred typically-developing children aged 3–10 and a group of 25 normal hearing adults were recruited. They were tested on a pool of 75-item calibrated recorded speech signals. Participants responded to each stimulus by pointing at the corresponding picture displayed on a computer screen from a choice of four. Result. There was a gradual increase in tone perception accuracy from children aged 3–6. After age 6, tone perception accuracy was similar to adults with an average error rate of 3–8%. The two tone contrasts that listeners consistently found difficult to distinguish were T2T5 (high-rising vs low-rising) and T3T6 (mid-level vs low-level). In addition, all children groups also showed difficulty in T4T6 identification (low-falling vs low-level). Conclusion. Tone perception is not error-free even among native Cantonese-speaking adults. Overall tone identification performance improved steadily from age 3 to age 6. Based on the participants’ performance, a three-tier set of tone groups, with an increasing level of difficulty for identification, is proposed for rehabilitation purposes. These tone groups are (1) Easy: T1T2, T1T3, T1T4, T1T5, T1T6, and T2T3, (2) Medium: T2T4, T2T6, T3T4, and T4T5, and (3) Hard: T2T5, T3T5, T3T6, T4T6, and T5T6.

Keywords: Tone, lexical tone perception, Cantonese, tone contrast difficulty, three-tier tone groups, ease of tone identification, acquisition.

Introduction Cantonese is a tone language spoken by 62–70 million people worldwide (Lewis, Simons, & Fennig, 2013; Li, Huang, Shi, Mai, & Chen, 1995). There are six distinctive tones in Hong Kong Cantonese based on different fundamental frequency patterns (Gandour, 1981; Matthews & Yip, 1994). In an early perceptual study of Cantonese tones, Fok (1974) stated that pitch variation is the most important clue in tonal perception. Re-analysing the tone confusion data of Fok (1974), Gandour (1981, 1983) further proposed pitch height and contour as the two underlying perceptual dimensions by which to identify Cantonese tones. Pitch height refers to the fundamental frequency level, while contour refers to the fundamental frequency configuration, which can be divided into static, falling, and rising patterns. By using the computer software Dr. Speech (Dr. Speech–software group, Tiger DRS, 1998, Seattle, WA 98175 USA), Figure 1 was constructed to illustrate the different fundamental frequency patterns of the six tones spoken by a female native speaker of

Hong Kong Cantonese. The vertical axis is the fundamental frequency in the unit of Hertz (Hz), while the time duration measured in seconds is represented in the horizontal axis. To facilitate analysis, the tone contours could be viewed sequentially into three parts, namely the onset, the medial, and the offset (Bauer & Benedict, 1997). In brief, tones 1, 3, and 6 are the high-, mid-, and low-level tones, respectively. Tone 2 is a high-rising tone, whereas tone 5 is a low-rising tone. Tone 4 is a low-falling tone. A change in tone equates to a change in the lexical meaning and it is, therefore, important to understand and produce tones correctly. Studies have demonstrated that children can produce all six Cantonese tones by the age of 2 years (Dodd & So, 1994; Tang & Maidment, 1996; To, Cheung, & McLeod, 2013). Tone perception data; however, have revealed that children could only identify all tones at the much older age of 10 (Ching, 1984; Ciocca & Lui, 2003). The first extensive Cantonese tone perception study in adults (n  511) was conducted by Fok in 1974. When recorded male

Correspondence: Kathy Y. S. Lee, Department of Otorhinolaryngology, Head and Neck Surgery, 6/F Clinical Sciences Building, Prince of Wales Hospital, Shatin, N.T., Hong Kong, PR China. Email: [email protected] ISSN 1754-9507 print/ISSN 1754-9515 online © 2015 The Speech Pathology Association of Australia Limited Published by Informa UK, Ltd. DOI: 10.3109/17549507.2014.898096

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Figure 1. The different fundamental frequency patterns of the six Cantonese tones for the vowel /a/.

speech in the natural voice mode was used for the test stimuli, adults identified all tones with over 92% accuracy. Using similar test stimuli, Ciocca and Lui (2003) found a different result in that their adult participants (n  15) achieved only 80% accuracy in T2T5 identification in the eight tone contrast stimuli that were used. Both studies suggested that the tone perception ability of adult Cantonese speakers was not error-free. However, both studies have limitations in that Fok’s study was published about 4 decades ago, while Ciocca and Lui’s did not use a comprehensive set of tone contrast pairs (n  8). With six contrastive tones in Cantonese, there are 15 possible tone pairs. Since Fok’s study in 1974, there have been only two studies which have examined all the 15 tonal contrasts, with normal-hearing children as participants. The one by Barry, Blamey, Martin, Lee, Tang, Ming, et al. (2002) used natural speech of the syllable /wi/ as a stimulus and studied tone discrimination in nine children aged from 3;09–6 years. The other was by Ching (1984), where children aged from 4–10 years were involved in a sixalternative choice procedure of tone identification. There were 10 children each in the age-groups from 7–10 years. The number of participants in the agegroups from 4–6 years was not clearly stated. These studies failed to demonstrate meaningful conclusions because of the small number of participants. In terms of methodological approach, the syllable /ji/, which occurs with all six tones in Cantonese, has commonly been used for tone identification studies (Ching, 1984, 1990; Ciocca & Lui, 2003; Fok, 1984; Yiu & Fok, 1995). Other frequently used syllables, but to a lesser extent, were /si/ and /jɐu/ (Vance, 1976; Wong & Diehl, 2003). However, some stimulus words are not frequently used even by adults. For example, out of the 9933 unique characters in Modern Chinese based on 16 Chinese electronic texts collected between 1997–2003, the words /jɐu2/㞂 pomelo, /jɐu3/ ⸤ thin, and /ji2/㢭 chair did not appear in the 1000 most frequently used characters (Da, 2004). When checking these words against the children’s database (Fletcher, Leung, Stokes, & Weizman, 2000), the word /ji/ occurred only with T2, T5, and T6 (meaning chair, ear, and two, respectively), and /jɐu/ only with T4, T5, and T6 (meaning oil, have, and right, respectively). For the six words with /si/,

none could be found on the database. These findings suggest that the word stimuli which were often used in past studies were beyond most of the children’s listening and speaking experiences. A more appropriate set of stimulus words, using item selection criteria, namely, (1) early acquisition, (2) ready recognizability by speakers of Cantonese, and (3) picturability was used by Varley and So (1995) to compare tonal comprehension between young adults (aged 20–30) and older age-groups (aged 50–69). Unfortunately, the study tested an uneven distribution of tonal contrasts. T1T2 had five test items, whereas there was only one item for each of T3T5, T3T6, and T5T6. Given the problems in using the commonly cited phonemes of /ji/, /si/, and /jɐu/ as test stimuli, Lee, Chiu, and van Hasselt (2002b) used a different methodology to assess the perception of three basic tone contrasts. The test procedures included a word comprehension test to exclude words that were not in the child’s receptive vocabulary. By controlling for linguistic knowledge, the unfamiliar words on examining perception were excluded in the experimental setting. The utilization of a wider range of familiar words when compared with the past studies, where the same six words with different combinations were presented repeatedly, showed a positive effect in capturing young children’s attention. The results showed that (1) children were more successful in perceiving tones related to familiar words than those related to non-words, and (2) the methodology enabled children as young as 3 years of age to be tested reliably. These research procedures were then further refined, using words within a child’s vocabulary inventory as the test stimuli. The number of children recruited included 225 normal 3-year-olds, and 15 children with profound hearing impairment. Both groups of children responded well to the test protocol (Lee, van Hasselt, Chiu, & Cheung, 2002a). This study is the most extensive investigation to date of the youngest children in a Cantonese-speaking population. The inadequacy of the study by Lee et al. (2002a) was that only three tone contrast pairs were included and only the group of 3-year-olds was studied. The present study is an extension of the earlier work (Lee et al., 2002a, b), with the aim of addressing the above limitation in the past research methodology. Using words that are familiar to children as stimuli, the tone perception ability of Cantonese speakers on all the 15 tone contrasts was examined with a more representative sample in this study. The first research objective was to elucidate the developmental pattern of Cantonese tone perception in typically-developing children. The second objective was to investigate the hierarchy of tone perception difficulty among the 15 tone contrasts. The results provided an extensive update to data since Fok’s study in 1974.

Cantonese tone perception

Method

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Participants Stratified random sampling was employed to minimize sampling bias and to optimize a balanced recruitment of students of different ages. The sampling procedure was first by stratification by educational setting (pre-primary vs primary), followed by the random selection of schools among each stratum. Age-appropriate students within each selected school were then invited to join the study. Given that geographical region is unrelated to tone identification performance among Hong Kong students (Lee, 2003; Lee et al., 2002a), students from schools of only one region (the New Territories East) were invited. Participant inclusion criteria were: (1) being from 3;0–10;0 years of age; (2) using spoken Cantonese as their first language; (3) having no abnormalities in overall cognitive development as reported by teachers and parents; and (4) passing both hearing and language screening tests conducted by qualified audiologists and speech-language pathologists. Regarding hearing screening, children needed to demonstrate the ability to detect tone frequencies of 500, 1000, and 2000 Hz at 25 dB hearing level. For language screening, the Cantonese Receptive Vocabulary Test (Lee, Lee, & Cheung, 1996) was used for children below the age of 6, whereas the Grammar Comprehension sub-test of the Hong Kong Cantonese Oral Language Assessments (T’sou, Lee, Tung, Chan, Man, & To, 2006) was used for children older than 6 years of age. Both tests were locally developed norm-reference tests for children, with well-established validity (Cheung, Lee, & Lee, 1997; Klee, Wong, Stokes, Fletcher, & Leonard, 2009). A raw score of not more than 1 SD from the normed mean score of the corresponding age-group was set as the passing criterion. Sending invitations to sampled schools and arranging children for screening were carried out simultaneously. Children were arranged for screening in accordance with the order in which we received their

replies. The sampling and screening procedures continued until we had recruited a total of 200 children who fitted the selection criteria. Out of the total of 1553 children invited, 555 volunteered to join; this was a 35.74% response rate. A pool of 200 children was obtained after 221 students had been screened. Three students were excluded because they failed the hearing screening, while the other 18 students did not pass the language evaluation. The pass rate was 90.49%. Each participant group from the age of 3–10 consisted of 23–27 children, with a total of 101 boys and 99 girls (Table I). A separate group of 25 normal-hearing adults was also included by convenience sampling. They were six males and 19 females with ages ranging from 30–50, and who worked for the Chinese University of Hong Kong. They all use Cantonese as their first language, and their hearing was screened as being normal to detect tone frequencies of 500, 1000, and 2000 Hz at 25 dB hearing level. Stimuli Because the developed test materials are also intended to be used on populations with hearing impairment, the word pool for hearing-impaired children, supplemented with the databases for normal hearing children, formed the basis for selecting appropriate words as stimuli. To be included as a tone word in the test, the word has to exist in either one of the three databases (Fletcher et al., 2000, Lee, 2003; Opper, Chan, Kwong, & Tse, 1999). This is to make sure that the words used in the test stimuli are familiar to young children. The two tone words in each test item had to be: (1) monosyllabic; (2) minimal pairs contrasting in their tones only; and (3) suitable for representation in picture format. The rationale for using monosyllabic words was to avoid the confounding effect of tonal co-articulation (Xu, 1994). In addition to the two tone words which differ only in their lexical tones, two distractors (vowel and consonant distractors) were also constructed in

Table I. Total tone identification scores of the nine participant groups.

Correct tone score Age

n

3 25 4 25 5 24 6 27 7 24 8 27 9 25 10 23 Adult 25 Total 225

55

Error: tone distractor

Error: vowel distractor

Error: consonant distractor

No. of males

No. of females

Mean

SD

Mean

SD

Mean

SD

Mean

SD

10 16 6 12 16 17 12 12 6 107

15 9 18 15 8 10 13 11 19 118

78.93 84.69 88.00 91.70 94.06 96.10 97.49 97.28 97.07 91.70

9.08 15.73 7.44 12.80 5.49 10.78 4.04 7.56 5.49 5.39 3.53 3.70 2.56 2.40 2.68 2.49 3.22 2.51 8.06 7.05

6.37 5.85 5.00 3.88 4.89 3.34 2.43 2.35 2.94 6.35

2.03 1.28 .28 .25 .33 .05 .00 .00 .21 .49

2.08 1.61 .55 .53 .71 .26 .00 .00 .50 1.15

3.25 1.23 .94 .49 .22 .15 .11 .23 .21 .76

3.08 1.72 1.39 .84 .64 .43 .37 .87 .63 1.65

No response Mean SD .05 .00 .00 .00 .00 .00 .00 .00 .00 .01

.27 .00 .00 .00 .00 .00 .00 .00 .00 .09

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each test item. The vowel distractor had the same consonant as the target word but a different vowel and tone, whereas the consonant distractor had the same vowel as the target word but a different consonant and tone. Words used for vowel and consonant distractors were also checked against the three databases (Fletcher et al., 2000; Lee, 2003; Opper et al., 1999). All the words used existed in the databases except two (/thyn5/᪇ break off and /wɐt1/ᒅ bend). The stimulus words were depicted in the form of line drawings. In total, 75 items (five items for each tone contrast) were constructed. An example of a test item is shown, as follows: Tone word 1: book /sy1/ Tone word 2: mouse /sy2/ Vowel distractor: snake /sƐ4/ Consonant distractor: rain /jy5/ The set of picture and sound stimuli was pilottested among a group of 26 typically-hearing children aged from 3–10 (each age-group included three-to-four children) and among a group of nine children with mild-to-profound hearing impairment aged from 6–11. Items with unclear drawings and sound tracks were revised. The 75-item pool was then rated by a panel of 16 experts consisting of university academics, speech therapists, and educators from local institutions. These experts rated the test material as appropriate and representative for testing tone perception in young children. Details of the item construction and the content validity of the items can be found in Lee (2012). Stimuli were recorded in a soundproof booth by using an AKG C420 III PP microphone and a Sony DC 12 V DXC-D35P digital recorder. A male Master of Philosophy student who had received extensive Cantonese phonetics and phonology training in the Department of Linguistics at the Chinese University of Hong Kong, whose voice has an average fundamental frequency of 132 Hz, acted as the stimuli presenter. All stimuli were presented by using a standard framed sentence: /pin1 fuk1 hɐi6 ___ / “Which picture shows ___?”. Using the sound-editing software Adobe Audition 3, a pause of 200 milliseconds was inserted between this introductory phrase and the stimulus word to heighten the saliency of the stimulus word and to minimize the tone co-articulation effect (Xu, 1994). Amplitude equalization was performed digitally so that the peak amplitude of each word was the same across all items. Table II tabulates the average fundamental frequency of the stimulus words and the differences in the fundamental frequency of the 15 tone contrasts at the onset, offset, and dipping, if applicable. A computer program was designed for test administration. The program was equipped with the features of: (1) automatic randomization of item presentation order; (2) automatic randomization of

the placement of the four pictures within each test plate; (3) animated cartoons with visual and auditory effects, to be elicited as reinforcers to capture the attention of children when needed; and (4) automatic storage of all responses of participants. Tester and test environment Eight personnel who were either qualified speechlanguage pathologists or trained research assistants acted as test administrators. Testing was carried out in soundproof booths with a background sound level of less than 25 dB(A). The presentation level was calibrated to 65 dB(A) measured at the ear level of each child with the loudspeaker 1.5 metres away at 0 degrees azimuth from the participant. A laptop computer was put on a low table facing the participants. The test administrator was seated next to the participant, to allow for better control of the computer program and to reduce distractions to the participant.

Procedures Testing was conducted for each individual in a soundproof booth. The participants responded to each stimulus by pointing at the corresponding pictures displayed on the computer screen. One practice trial was conducted, in which the experimenter explained the task to the test taker, presented the sound stimulus, and provided feedback on the accuracy of the response. The test commenced immediately after the practice trial, and during the test no feedback was given on response accuracy. The responses of each child were entered on site by the test administrators, with the computer automatically storing the records. In the case of adult participants, the answers were input by themselves. The proportion of correct responses of the total (n  75) was computed as the total average score, whereas that of correct responses for each tone contrast was computed as the contrast score of a sub-total score of 5. Data analysis The test procedures of 24 children were videotaped for subsequent evaluation of rater reliability. Four raters, which is 50% of the total number of assessors, were required to rate each of the 24 children for two times by video viewing. The interval between the two ratings was within 3–8 weeks. An intra-class correlation coefficient (ICC) with a 95% confidence interval was employed with the models of ICC (2,1) and ICC (3,1), respectively, to assess inter-rater and intra-rater reliability. Overall tone perception scores were examined by analysis of variance (ANOVA), with age as the independent variable. Pair-wise comparisons were

Cantonese tone perception

57

Table II. Average fundamental frequency of the test stimulus words and the difference in fundamental frequency in the 15 tone contrasts. Difference in Hz for each tone contrast

Average value in Hz Tone contrast T1T2 T1T3 T1T4 T1T5 T1T6

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T2T3 T2T4 T2T5 T2T6 T3T4 T3T5 T3T6 T4T5 T4T6 T5T6

Tone

Onset

Offset

Dipping

At onset

At offset

At dipping

T1 T2 T1 T3 T1 T4 T1 T5 T1 T6 T2 T3 T2 T4 T2 T5 T2 T6 T3 T4 T3 T5 T3 T6 T4 T5 T4 T6 T5 T6

188.05 113.54 184.40 146.74 190.88 127.24 179.79 115.42 176.98 135.58 122.42 135.36 122.18 123.54 134.34 126.88 131.06 131.56 149.72 120.90 152.78 116.48 138.76 128.12 128.03 112.36 123.80 132.66 122.64 127.80

169.23 176.27 174.76 138.66 178.60 92.02 172.49 135.68 168.48 125.08 181.94 130.84 188.42 90.81 195.00 166.08 217.71 121.68 138.54 92.91 136.74 129.70 127.75 108.92 93.38 121.59 97.69 120.28 147.88 113.86

NA NA NA NA NA NA NA NA NA NA NA NA NA NA 118.50 109.35 NA NA NA NA NA NA NA NA NA NA NA NA NA NA

74.51

7.04

NA

37.66

36.10

NA

63.64

86.58

NA

64.37

36.81

NA

41.40

43.40

NA

12.94

51.10

NA

1.36

97.60

NA

7.46

28.92

9.15

.50

96.03

NA

28.82

45.63

NA

36.30

7.04

NA

10.64

18.83

NA

15.67

28.21

NA

8.86

22.59

NA

5.16

34.02

NA

run for all nine age-groups by using simple Bonferroni correction for a family-wise error rate of.05. The adjusted alpha level of .00138 (.05 divided by the total number of contrasts, which is 36) was set as achieving significant difference. To examine the performance of Cantonese speakers in distinguishing the individual tone contrasts, separate pair-wise comparisons under each age-group on the 15 tone contrast sub-scores were examined by the Wilcoxon signed-rank tests. Results Rater reliability ICC (2,1) value on the overall tone scoring was .91, indicating good-to-excellent inter-rater reliability. The intra-rater reliability of each of the four raters was assessed by computing four sets of ICC (3,1). The values on the overall tone scores were .84, .92, .93, and .95, thus suggesting satisfactory intra-rater reliability for all raters.

Tone perception scores ANOVA showed a significant main effect of age on tone perception scores F(8, 216)  38.48, p  .001. In

general, the correct tone identification score increases across age, as shown in Table I and Figure 2. Bonferroni post-hoc tests showed that participants from agegroups 3, 4, and 5 scored significantly lower than the older age-groups (all Bonferroni-adjusted p-values  .001). Specifically, 3-year-olds had lower scores than 5-year-olds to adult, 4-year-olds had lower scores than participants aged 6 to adult, and 5-year-olds attained lower scores than those from 8-year-olds to adult. No significant differences were found between the age-groups of 6, 7, 8, 9, 10, and adult, with Bonferroni-adjusted p-values ranged from .004–1.00. The error rates which belong to the vowel and consonant distractors are also shown in Table I. Table III shows the percentage of correct sub-total tone identification scores on the 15 tone contrasts under the different age-groups. Across all tone contrasts, the children scored higher with increasing age in general. A separate pair-wise comparison by using the Wilcoxon signed-rank test on each age-group was employed to examine the performance of Cantonese speakers in distinguishing the individual tone contrasts over time. Because the ANOVA results revealed no significant difference among groups of 6–10-yearolds, the five groups are combined as one in the Wilcoxon tests. In Tables IV–VI, the tone contrasts

58

K. Y. S. Lee et al.

Percentage correct tone identification score

100

90

80

70

60

50

40

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T1T2

T1T3

T1T4

T1T5

T1T6

Aged 3

T2T3

T2T4

Aged 4

T2T5 Aged 5

T2T6

T3T4

T3T5

Aged 6 to 10

T3T6

T4T5

T4T6

T5T6

Adult

Figure 2. The 15 sub-total tone contrast scores achieved by the various age groups.

are listed from highest to lowest, based on the subtotal tone contrast scores. Different age-groups had slightly different orders in the ease of identification over the 15 tone contrasts. In order to capture the results more systematically, the tone pairs with sub-total scores different from at least 10 other tone contrasts at p-value  .05 level were marked in grey. Using this criterion, it is shown that the T2T5 and T3T6 sub-total scores were consistently lower across all groups (z-value ranged from 2.14–7.89, p  .05) from children to adults except two (T3T6 and T4T6 in aged 3 group, z  1.74, p  .05; T2T5 and T4T6 in adult group, z  1.73, p  .05). Tone contrast T4T6 showed significantly lower scores (z-values ranged from 1.98–6.65, p  .05) across all children groups aged from 3–10 except one (T4T6 and T3T6 in aged 3 group, z  1.74, p  .05). Two other tone pairs, namely, T3T5 and T5T6, had significantly lower scores in some children groups. Specifically, age-groups 3, 4, and 6–10 scored T3T5 significantly differently from the other tone pairs (z-values ranged from 2.04–6.51, p  .05), whereas age-group 5 had significantly different scores between T5T6 and other tone contrasts (z-values ranged from 2.00– 3.88, p  .05). Figure 2 shows the sub-total tone contrast scores across the various age-groups.

Discussion Overall tone perception performance The present study found that tone perception is not error-free among native speakers of Cantonese. The overall error rate is ∼ 3% in adults. Using the scores of the adult group as a reference, the performance of children aged from 3–10 was examined. It was found that there was a gradual improvement over age. By the age of 6 years, children have reached a performance similar to adults. The present investigation accords with past studies by demonstrating that tone identification is a difficult area when stimuli are presented in isolation without other linguistic information aiding the listener for message decoding. Unlike the past studies which stated that children can identify all tones by 10 years of age (Ching, 1984; Ciocca & Lui, 2003), we found that children reached an adult-like performance in tone perception by 6 years of age. The use of different test stimuli may have a role to play in the difference. Both Ching (1984) and Ciocca and Lui (2003) used the syllable /ji/ with six tones as their test stimuli. The word /ji/ occurred only with T2, T5, and T6 (meaning chair, ear, and two, respectively) in the two databases (Fletcher et al., 2000; Opper et al., 1999).

Table III. Sub-total tone contrast identification scores of the nine participant groups. Age

T1T2

T1T3

T1T4

T1T5

T1T6

T2T3

T2T4

T2T5

T2T6

T3T4

T3T5

T3T6

T4T5

T4T6

T5T6

3 4 5 6 7 8 9 10 Adult

92.0 92.8 97.6 97.8 98.4 100.0 100.0 100.0 99.2

85.6 92.0 95.0 95.6 95.8 96.2 98.4 100.0 100.0

89.6 96.0 97.6 98.6 99.2 98.6 100.0 99.2 100.0

85.6 92.8 97.6 96.2 97.6 100.0 99.2 100.0 98.4

90.4 96.8 98.4 96.2 99.2 99.2 99.2 99.2 99.2

87.2 96.8 94.2 100.0 100.0 100.0 100.0 100.0 98.4

85.6 89.6 90.8 97.8 98.4 97.0 99.2 99.2 95.2

64.0 64.8 64.2 73.4 78.4 83.8 92.0 88.6 87.2

82.4 90.4 90.0 94.8 95.8 97.8 100.0 99.2 100.0

81.6 84.0 94.2 97.8 97.6 99.2 100.0 100.0 100.0

68.8 81.6 89.2 89.6 90.8 94.0 96.8 94.8 97.6

49.6 56.8 57.6 66.0 74.2 83.0 83.2 83.4 88.8

80.8 88.8 94.2 94.8 95.8 98.6 98.4 98.2 99.2

62.4 64.8 74.2 82.2 92.6 94.8 98.4 99.2 93.6

78.4 82.4 85.8 94.8 97.6 99.2 97.6 98.2 99.2

Cantonese tone perception

59

Table IV. Summary of the results of pair-wise comparison of the 15 tone contrast pairs using the Wilcoxon signed-rank test in the aged-3 and aged-4 participant groups. Aged 3

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T1T2 T1T4 T1T6 T2T3 T1T3 T1T5 T2T4 T2T6 T3T4 T4T5 T5T6 T3T5 T2T5 T4T6 T3T6 Aged 4 T1T2 T1T4 T1T6 T2T3 T1T3 T1T5 T2T4 T2T6 T3T4 T4T5 T5T6 T3T5 T2T5 T4T6 T3T6



2.14*

2.14*

1.8

1.7

— — — 1.89

1.9

2.14* 2.11* 2.83** 2.32* 3.35** 2.95** 3.99** 4.21** 4.14**

2.07* 2.00* 2.68** 2.32* 3.40** 2.82** 4.08** 4.21** 4.15**

2.95** 2.43* 2.16* 1.85 2.08* 2.56* 1.98*

— —

2.00* 2.04* 2.66** 3.72** 3.88** 3.92**

1.9 2.14* 3.03** 2.31* 2.86** 2.88** 4.10** 4.30** 4.05**

— 1.81

2.22*

2.39* 2.24* 3.55** 3.90** 3.98**

2.29* 2.36* 3.90** 3.77** 3.87**

— 1.89



3.69** 3.05** 3.25** 3.34** 2.83** 3.16** 2.81** 2.09* 2.34* 2.58**

— 1.9 — — 2.04* 3.21** 3.71** 3.17** 3.46** 2.61** 2.30* 3.78** 4.06** 2.85** 3.78** 2.64** 2.25* 3.95** 3.94** 3.44** 3.92** 3.46** 3.21** 1.66

3.88** 3.43** 3.89** 3.52** 3.06** 3.42** 3.14** 3.16** 2.75** 2.81** 2.49*

3.76** 3.70** 3.36** 3.45** 3.29** 3.68** 3.35** 3.02** 2.93** 3.04** 1.98*

— —

4.20** 4.04** 4.24** 4.26** 4.26** 4.02** 3.92** 3.64** 3.70** 4.07** 3.85** 2.52* 2.21* 1.74 —

The tone pairs are ordered from highest to lowest (in terms of ease of identification), based on the combined sub-total tone contrast scores of the aged 3 participants. Values in the upper and lower quadrants refer to the Z-statistics reported in the Wilcoxon signed-rank test within aged 3 and aged 4 participants, respectively, when corresponding tone contrasts in the column and row header cells are compared. Omitted cells are those with p  .10, numbers without *denote p  .10; *p  .05, **p  .01.

The frequency ranks of the three words were 102th, 380th, and 63th, respectively, out of the 495 listed words in the database of Fletcher et al. (2000). In the word inventory by Opper et al. (1999), /ji/ in T5 and T6 were found in typically-developing children aged 3, whereas /ji/ in T2 could be found only in the children at the age of 5. In the word pool collected by mother report format, only the word ear (/ji/ in T5) out of the six /ji/ words was found (Lee, 2003). Furthermore, across the three databases, /ji/ in T1 only appeared in the multisyllabic word of /sɐi2 ji1 kei1/ 㲿堋㨇 washing machine, but not in the

form of a monosyllabic word. The familiarity and frequency of occurrence of the six words are found to be low. Young children may fail to show their ability for correct tone perception when the words used in the test were beyond their listening and speaking experience. In the present study, on the other hand, words used are chosen from the inventory of young children. All stimulus words, except two distractors, were evident in the databases of young speakers of Hong Kong Cantonese. The possible confounding variable of word difficulty influencing tone perception is minimized.

Table V. Summary of the results of pair-wise comparison of the 15 tone contrast pairs using the Wilcoxon signed-rank test in the aged-5 and aged 6–10 participant groups. Aged 5 T1T2 T1T4 T1T5 T1T6 T1T3 T3T4 T4T5 T2T3 T2T4 T2T6 T3T5 T5T6 T4T6 T2T5 T3T6 Aged T1T2 6–10 T1T4 T1T5 T1T6 T1T3 T3T4 T4T5 T2T3 T2T4 T2T6 T3T5 T5T6 T4T6 T2T5 T3T6



2.00*

2.13*

2.07*

2.18*

3.30** 3.49** 3.97** 4.25**

1.67

2.31* 2.13* 2.50*

2.50* 2.07* 2.33*

2.00* 1.89 2.46*

3.50** 2.98** 3.42** 2.40* 2.00* 2.49* 2.67**

— — 2.84** 2.68** 1.88 2.60** 2.27* 2.24* 2.45* 2.13* 5.39** 2.13* 4.82** 6.57** 7.89**

— 1.78

2.24* — 2.10*

— 2.02* 2.71** 2.71** 4.03** 2.07*

2.07* 4.97** 4.90** 1.91 4.61** 4.77** 6.52** 6.40** 7.66** 7.69**

— 3.82**

4.41** 3.35** 5.09** 3.54** 4.34** 3.00** 4.25** 3.29** 6.15** 5.90** 6.33** 6.03** 7.57** 7.37** 7.73** 7.41**

— 3.32** 3.42** 5.91** 3.36** 5.42** 6.73** 7.87**

— — 4.43** 3.94** 4.02** 3.71** 6.34** 6.09** 7.57** 7.36**

3.70** 3.57** 3.63** 3.37** 2.94** 3.39** 3.29** 3.10** 2.45* — 2.28* — 3.61** 2.15* — 3.47** 4.38** 6.09** 4.55** 6.51** 7.58** 6.65**

3.87** 3.77** 3.97** 3.69** 3.70** 3.67** 3.98** 3.56** 3.52** 3.57** 3.29** — 2.17*

4.18** 4.18** 4.22** 4.05** 4.03** 3.94** 4.26** 3.68** 3.91** 3.77** 3.88** 2.28* —

The tone pairs are ordered from highest to lowest (in terms of ease of identification), based on the combined sub-total tone contrast scores of the aged 5 participants. Values in the upper and lower quadrants refer to the Z-statistics reported in the Wilcoxon signed-rank test within aged 5 and aged 6–10 participants, respectively, when corresponding tone contrasts in the column and row header cells are compared. Omitted cells are those with p  .10, numbers without *denote p  .10; *p  .05, **p  .01.

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Table VI. Summary of the results of pair-wise comparison of the 15 tone contrast pairs using the Wilcoxon signed-rank test in the adult participant group. Adult

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T1T3 T1T3 T1T4 T2T6 T3T4 T1T2 T1T6 T4T5 T5T6 T1T5 T2T3 T3T5 T2T4 T4T6 T3T6 T2T5

T1T4

T2T6

T3T4

T1T2

T1T6

T4T5

T5T6

T1T5

T2T3

— — — —

T3T5

T2T4

T4T6

T3T6

T2T5

1.73 1.73 1.73 1.73

2.45* 2.45* 2.45* 2.45* 2.24* 1.89 2.24* 1.89

2.53* 2.53* 2.53* 2.53* 2.65** 2.11* 2.65** 2.11* 1.73 1.9 1.89

2.56* 2.56* 2.56* 2.56* 2.57* 2.36* 2.57* 2.36* 2.14* 2.14* 2.15*

2.72** 2.72** 2.72** 2.72** 2.76** 2.51* 2.76** 2.57* 2.29* 2.56* 2.33*

— — — — — — —

— —

1.73 — —

The tone pairs are ordered from highest to lowest (in terms of ease of identification), based on the combined sub-total tone contrast scores of the adult participants. Values in the upper quadrant refer to the Z-statistics reported in the Wilcoxon signed-rank test within the adult participants when corresponding tone contrasts in the column and row header cells are compared. Omitted cells are those with p  .10, numbers without *denote p  .10; *p  .05, **p  .01.

In addition to the argument of a more accurate reflection of listener performance by using words suited to the children’s capability as test stimuli, the difference may also be due to the fact that the present study has included more children at betterdefined yearly intervals than the previous studies. We have included eight groups of participants aged from 3–10, whereas there were only three groups of children (4;00–4;11, 6;00–6;11, and 10;00–10;11) in the study by Ciocca and Lui (2003), with age gaps in-between. As for the number of participants, there were 45 children in the study by Ciocca and Lui (2003). For Ching’s (1984) study, a total of 40 children aged from 7–10 was reported, whereas the number of participants aged from 4–6 was not clearly stated. The 200 children participants in the present study substantially outnumber the ones in the past two studies. The larger sample size with delineated age-groups may, thus, better capture the developmental pattern of tone perception. Performance in identifying individual tone contrasts When viewing tone development from the perspective of individual tone contrast, the general configuration is preserved. In the adult group, participants have more errors on two particular tone contrasts, namely, T2T5 (high-rising vs low-rising) and T3T6 (midlevel vs low-level), where the error rates are ~12%. This result accords with past findings (Ciocca & Lui, 2003) in the way that similar error rates were noted in the T2T5 identification. Having included the comprehensive set of 15 tone contrasts, this study further showed that another tone contrast that adults found difficult was T3T6, which was not demonstrated in Ciocca and Lui’s study of eight tone contrasts.

T2T5 and T3T6 were consistently the pairs among the 15 tone contrasts that received the lowest scores across all age groups. This could be explained by the similarities of the tone patterns of the pairs (Table II). T2T5 are both rising tones with very close values on fundamental frequency onsets. T3T6 are both level tones with a very small difference in terms of fundamental frequency height. The confusion of one with the other is understandable, especially in view of the close proximity of acoustic signals and the fact that no other semantic cues are provided in the present testing conditions. In addition to these two tone pairs, children also showed difficulty in distinguishing T4 from T6. Although the two differ in terms of the pitch direction (T4 is falling whereas T6 is level), they share a very similar pitch height especially during the tone onsets. The fact that both tones have low fundamental frequencies, which are regarded as weaker in power relative to tones with high fundamental frequencies, may also play a role. Young children may find the tones hard to differentiate with the proximity of fundamental frequency and the associated weak power. This speculation gained some support when the pitch levels of the tones involved were examined. Whenever a tone with high pitch level (T1, T2) was involved, the result was always better when compared with contrasts where a tone with low pitch level (T4, T5, and T6) was included. The findings on tone merging in modern Cantonese may also serve to explain the three tone contrasts with lower scores across all age-groups. Bauer, Cheung, and Cheung (2003) proposed that, instead of viewing the confusion of T2T5 production as errors, another way of looking at the tones would be to say some Hong Kong Cantonese speakers merged

Cantonese tone perception

the two tones because the tones are phonetically too similar. The findings by Mok, Zuo, and Wong (2013) further support the claim of tone merging. They identified a group of 16 potential mergers after a total of 129 undergraduate students were screened. They found that the merging tone pairs were T2T5, T3T6, and T4T6, and these are exactly the three tonal contrasts, with significantly lower identification scores in the present study.

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Clinical applications In the field of paediatric speech and language rehabilitation, the ultimate goal is often to assist children to achieve an “adult-like” performance. It is, thus, important to recognize how the adults behave in order to define realistic goals in the therapeutic process. The present findings act as guidance for setting reference points in terms of tone perception rehabilitation. It is suggested that tone training could be set in a sequence in accordance with the acquisition patterns of the children. Based on the present findings on tone identification performance of Cantonese speakers across age, it is proposed that tone pairs could be classified into three categories for perception training. Table VII shows the proposed three groups of Easy, Medium, and Hard tone contrasts for identification. The Easy set consists of six tone contrasts, including all the ones with T1 (T1T2, T1T3, T1T4, T1T5, and T1T6) plus T2T3 contrast. The Hard set includes the pairs that are consistently shown to be difficult for all groups (T2T5, T3T6) or some children groups (T4T6, T3T5, and T5T6). The remaining four tone pairs (T2T4, T2T6, T3T4, and T4T5) constitute the Medium group. The classification of the three tone sets could be justified from two perspectives—from the mean aggregate scores of all age-groups and from the individual mean scores of various age-groups. The overall tone identification accuracy rates were 96.95%, 94.62%, and 83.04%, respectively, for the Easy,

Medium, and Hard sets. These results could be interpreted to mean that Cantonese speakers in general find the tone pairs under the Medium set more difficult to perceive than those under the Easy set. When compared with tone pairs under the Hard set, the Medium set tone pairs are, nevertheless, easier to identify. When viewing the tone group scores by individual age-groups, a developmental pattern could be clearly seen when a 90% acquisition criterion was operationally defined as the child having mastered the tone perception. The age of acquisition of the Easy and Medium sets are ages 4 and 5, respectively. As for the Hard tone group, only the adult group reached the 90% criterion. The tone group scores in the adult participants also rendered support to such a hierarchy of difficulty. The scores decreased from 99.18% to 98.60% and finally to 93.28% when shifting up the hierarchy from Easy to Hard tone groups. One population well documented with tone perception problems is individuals with hearing impairment. Tone perception remains unsatisfactory, despite the assistive devices of hearing aid or cochlear implant (Ching, 1990; Fok, 1984; Lee & van Hasselt, 2005; Lee et al., 2002a; Wong & Wong, 2004). The pitch information essential for tonal languages does not seem to be transmittable through hearing aids, nor does it seem to be explicitly represented in the electrical stimulation via current cochlear implant systems (Lee, van Hasselt, & Tong, 2010). Although the present technology seems to have limitations in accessing the acoustic properties of the Cantonese lexical tones to aid a full spectrum of successful tone perception, individuals with hearing impairment identify some tones more successfully than others. Among the 15 tone contrasts, Lee et al. (2010) found that children with profound hearing impairment showed significantly higher scores in T1T2, T1T4, and T1T5. These three tone pairs fall within the present proposed Easy set. The tone contrast identifications with significantly lower scores were T4T6,

Table VII. Average sub-total tone contrasts identification scores of the proposed Easy, Medium, and Hard sets. Easy (T1T2, T1T3, T1T4, T1T5, T1T6, and T2T3)

Medium (T2T4, T2T6, T3T4, and T4T5)

95% CI Age

n

Mean

SD

3 4 5 6 7 8 9 10 Adult

25 25 24 27 24 27 25 23 25

88.39 94.51 96.65 97.40 99.46 99.70 99.18 99.70 99.18

8.34 5.43 4.06 2.96 1.57 .98 1.48 .98 1.48

LB

UB

Hard (T2T5, T3T5, T3T6, T4T6, and T5T6)

95% CI Mean

61

SD

LB

UB

84.95 91.83 82.60 12.76 77.33 87.87 92.27 96.76 88.20 10.40 83.91 92.49 94.94 98.36 92.29 8.21 88.83 95.76 96.23 98.57 96.30 3.82 94.78 97.81 97.22 99.42 96.88 5.48 94.56 99.19 98.11 99.89 98.15 3.96 96.58 99.71 98.81 100.11 99.40 1.66 98.72 100.08 99.28 100.13 99.13 2.46 98.07 100.19 98.57 99.80 98.60 2.71 97.48 99.72

95% CI Mean

SD

LB

UB

64.64 70.08 74.17 81.19 86.67 90.96 93.60 92.87 93.28

12.47 10.65 9.51 10.51 10.59 8.71 7.02 7.53 8.30

59.49 65.68 70.15 77.03 82.19 87.52 90.70 89.61 89.85

69.79 74.48 78.18 85.34 91.14 94.41 96.50 96.12 96.71

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T2T5, and T3T6, which also fit into the present proposed set of Hard tones. The present proposed tone classification in terms of the level of difficulty receives some support from past studies. It would be interesting to verify the proposed hierarchy of tone training with the future advancement in hearing technology as well as on other clinical populations with impaired tone perception.

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Acknowledgements The work described in this paper was partially supported by a grant from the Research Grant Council of Hong Kong Special Administrative Region, China (Project no. CUHK446207). We sincerely appreciate the participation of the children and parents in the study. We would also like to thank Dr David Wilmshurst for commenting on the draft of this paper. Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

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Lexical tone perception in native speakers of Cantonese.

This study aimed at investigating (1) tone perception development among typically-developing Cantonese speakers and (2) the hierarchy of tone percepti...
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