A dynamic interaction model of topic interest and written language fluency: an empirical study

Drawing on dynamic systems theory (CDST), this study aims to explore how topic interest dynamically interacts with written language fluency among first-year Chinese university students majoring in Spanish. Using the moving correlation coefficient method, it investigates the evolving relationship between topic interest and lexical and syntactic fluency indicators across 18 essays per participant. A four-component analytical framework was applied, including (1) regression smoothing for trend identification, (2) correlation distribution analysis for significant associations, (3) fluctuation curve examination for temporal dynamics, and (4) change point detection for critical transitions. The findings reveal that the influence of topic interest on fluency is stage-dependent, with both positive and negative correlations coexisting. Notably, a high level of interest does not necessarily lead to fluent writing, and clear differences were found between lexical and syntactic fluency subsystems-lexical fluency tended to correlate positively with topic interest, while syntactic fluency showed negative correlations, reflecting uneven resource allocation between subsystems. This study extends CDST-based research in applied linguistics and psycholinguistics by revealing the nonlinear and multifaceted influence of affective factors on L2 writing. Pedagogically, the findings suggest that enhancing students' topic engagement and balancing attention between lexical and syntactic fluency can foster more sustainable development in L2 writing.