Comparison of Oral Diadochokinesis in Two- and Three-Syllable Structures Consisting of Consonants and Vowel /a/ with Two- and Three-Syllable Structures Consisting of Consonants and Vowel /u/ in 7-9-Year-Old Children of Kermanshah, Iran

EXTENDED ABSTRACT

Background

Speech production is a complex motor behavior requiring precise neuromuscular control and coordination across respiratory, phonatory, and articulatory systems [1]. In speech disorders, disruption of this coordination may alter movement rate during both speech and nonspeech tasks [2]. Oral diadochokinesis (DDK) refers to the capacity to perform rapid, repetitive movements of the speech organs and is a traditional component of speech-motor examination used to assess rapid patterned contractions and oral motor coordination [3, 4]. Two common DDK paradigms are alternating motion rate, based on rapid repetition of single syllables, and sequential motion rate, based on rapid repetition of syllable sequences. Sequential tasks are more demanding because they require repeated transitions among bilabial, alveolar, and velar consonants and therefore provide clinically useful information about sequential planning and neuromuscular coordination [5, 6].

DDK performance is influenced by task and speaker characteristics. Fletcher reported faster performance with increasing age in children [7], while work in Thai children indicated effects of age and sex and showed that normative rates vary across languages [8]. In contrast, a study of Persian-speaking children aged 4-6 years did not identify significant age or sex effects, although meaningful words were repeated faster than nonwords [9]. Other investigations have demonstrated effects of phonetic features, neurologic disorder, and task structure on DDK performance [10, 11], and real-word and nonword repetition have also been shown to differ in school-age children [12]. A previous Iranian study evaluated single-syllable DDK in 7-9-year-old children [13], but comparable data for two- and three-syllable sequences contrasting the open vowel /a/ with the closed vowel /u/ were lacking. The present study therefore aimed to provide descriptive sequential-motion benchmarks for healthy 7-9-year-old children in Kermanshah and to determine whether vowel alternation changes production speed in two- and three-syllable structures.

Methods

This descriptive-analytic cross-sectional study was conducted in 2017 among 210 students aged 7-9 years from governmental and non-governmental primary schools in the three educational districts of Kermanshah. Seventy children were included in each age group, with 35 girls and 35 boys at each age, yielding an overall sex ratio of 1:1. Schools were selected by simple random sampling and eligible students were then recruited by cluster sampling from randomly selected classes. Written parental consent and the child's willingness to cooperate were obtained before testing. Eligibility required structurally and functionally normal speech organs, no articulation disorder, no evident speech or language disorder on continuous-speech assessment, and a maximum /a/ phonation duration of at least 12 seconds.

After two practice trials, children were instructed to repeat the two-syllable sequences /pata/, /paka/, /taka/, /putu/, /puku/, and /tuku/ and the three-syllable sequences /pataka/ and /putuku/ as rapidly and accurately as possible. Each two-syllable sequence was repeated 15 times and each three-syllable sequence 10 times. Speech was recorded digitally and transferred to Cool Edit 2000, which allowed waveform-based counting of productions, visualization of brief pauses, and timing to the nearest thousandth of a second [14]. The elapsed time for each required repetition set was recorded. Descriptive statistics were calculated for each task and age group. Simple linear regression and independent-samples t tests were used for inferential analyses. The study was approved by the Ethics Committee of Arak University of Medical Sciences (IR.ARAKMU.REC.1395.175).

Results

All 210 enrolled children completed the protocol: 105 girls and 105 boys, with 35 participants of each sex in every age group. Thus, each of the six age-by-sex strata represented 16.66% of the sample. Across the descriptive data, the time required to complete most DDK tasks decreased as age increased, indicating faster sequential production in older children. For example, mean /pata/ time decreased from 7.65±1.59 seconds at age 7 to 7.34±0.83 seconds at age 8 and 6.97±0.88 seconds at age 9. Mean /pataka/ time similarly decreased from 8.52±2.12 to 7.63±1.14 and 7.29±1.15 seconds across the same age groups.

Figure 1. Distribution of participants by age and sex.

Table 1. Descriptive statistics of time spent (seconds) on diadochokinesis tasks among 7-, 8-, and 9-year-old students.

Sex-related differences were significant for both sequence lengths. For two-syllable tasks, girls had a mean time of 7.86±1.14 seconds and boys 7.39±1.00 seconds (t=-3.13, P=0.000). For three-syllable tasks, the corresponding values were 8.14±1.45 and 7.36±1.37 seconds (t=-4.02, P=0.000). Because shorter completion time represents faster DDK production, boys demonstrated significantly greater production speed for both two- and three-syllable sequences in this sample.

The primary vowel comparison showed a task-specific effect. Mean completion time for /pata/ was 7.32±1.18 seconds versus 7.51±1.29 seconds for /putu/ (t=-3.11, df=209, P=0.002). Likewise, /paka/ was produced in 7.68±1.15 seconds compared with 7.98±1.39 seconds for /puku/ (t=-3.21, df=209, P=0.002). In both comparisons, structures containing /a/ were produced significantly faster than their /u/ counterparts. In contrast, /taka/ and /tuku/ showed no significant difference (7.60±1.15 vs 7.71±1.32 seconds; t=-1.65, df=209, P=0.090), and the three-syllable comparison /pataka/ versus /putuku/ was also nonsignificant (7.81±1.62 vs 7.68±1.52 seconds; t=1.59, df=209, P=0.11). The findings therefore indicate that vowel alternation did not exert a uniform effect across all consonant-vowel combinations.

Table 3. Comparison of mean diadochokinesis time for syllables containing vowel /a/ versus vowel /u/.

The observed age trend is consistent with maturation-related increases in rapid sequential speech-motor performance described in earlier pediatric DDK work [7]. Cross-language studies also indicate that normative DDK values depend on linguistic context [12, 16], supporting the value of Persian-language benchmarks. The present pattern further suggests that consonant context interacts with vowel configuration: the /a/-related advantage was evident for /pata/ and /paka/ but not for /taka/ or the three-syllable sequence. This task dependence is compatible with evidence that speech-motor performance varies substantially with the specific repetition paradigm [11]. The age-related reduction in completion time may also reflect developmental gains in speech sequencing and short-term memory processes that contribute to nonword repetition and speech-rate performance [19, 20], while mature segment durations and oral DDK rates continue to develop through childhood and adolescence [21].

Conclusion

In healthy 7-9-year-old children from Kermanshah, sequential oral diadochokinesis became faster with increasing age, and boys completed both two- and three-syllable repetition tasks faster than girls. Vowel /a/ was associated with significantly faster production than /u/ for /pata/-/putu/ and /paka/-/puku/, whereas no significant difference was observed for /taka/-/tuku/ or /pataka/-/putuku/. These findings provide age-specific descriptive data for Persian-speaking children and show that the effect of vowel configuration on sequential speech-motor speed depends on the accompanying consonant structure.

Keywords: Diadochokinesis, Sequential Motion Rate, Vowel Alternation

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