A comparison of oral diadochokinetic rate in meaningful and non-meaningful word repetition in healthy Turkish-speaking adults

Speech production is a complex behavior involving motor planning and programming processes and is particularly sensitive to these processes in diadochokinetic (DDK) tasks that require rapid and accurate execution of sequential articulatory movements. It has been suggested that meaningful words may facilitate speech motor production through pre-stored phonological and motor representations in the mental lexicon, whereas non-meaningful syllable sequences impose a higher cognitive and motor processing load due to the need for online assembly. Although age-related slowing in processing speed may be expected to accentuate this difference, studies examining the lexical advantage of meaningful words in Turkish remain limited. The aim of this study was to investigate whether repetition of meaningful words facilitates oral DDK performance in healthy Turkish-speaking adults compared to traditional non-meaningful word repetition, and whether this facilitation effect differs across age groups. A total of 120 healthy Turkish-speaking adults participated in the study, with 40 individuals in each of the following age groups: 18–35, 36–55, and 56–75 years. During data collection, participants' language abilities and oral-motor structures were assessed, after which they were asked to repeat sequential DDK tasks containing a meaningful word (/patika/) and a non-meaningful word (/pataka/) in a single breath as quickly and accurately as possible. Analyses focused on DDK production rate, vocal reaction time (VRT), and error rates. The results showed that meaningful words yielded significantly higher DDK production rates compared to non-meaningful words. Motor speech rate decreased significantly with increasing age; however, this decline did not differ as a function of word type, and no statistically significant interaction was found between word type and age group. Although error rates were relatively higher for non-meaningful words, this difference did not reach statistical significance. Overall, the findings indicate that while aging leads to a general slowing of motor speech performance, the lexical facilitation effect based on retrieval from the mental lexicon remains a robust and age-resistant mechanism. These results contribute to the normative and theoretical literature on oral DDK performance in Turkish.