1. Introduction

The variation in second language development refers to the acquisition and erosion of language behavior by learners at different time points, which is crucial for understanding the overall picture and operational mechanism of SLD. Larsen Freeman introduced the theory of complex dynamic systems into second language acquisition, viewing language as a complex dynamic system that generates variable behavior through adaptive tuning, providing a new perspective for second language oral research.

2. Literature review

The literature review section explores the application of Complex Dynamic Systems Theory (CDST) in the study of second language oral variation, emphasizing the shift from outcome oriented to process oriented variation research. The complexity and dynamism from the perspective of CDST are the core characteristics of the second language system, and variation is a manifestation of the inherent traits of the system. Research has shown that the trajectory of second language oral development reflects the learner's developmental path, and the purpose of variation research is to discover the variations that trigger language development. There are shortcomings in existing research on oral vocabulary and syntactic variations, such as insufficient time sampling, inconsistent measurement indicators, and lack of small sample statistical analysis techniques. This study adopts the CDST perspective and time series analysis method to conduct a two-year longitudinal study on the development and variation of vocabulary and syntax in the second language oral system of Chinese English learners, aiming to reveal the dynamic development patterns of second language oral language and provide a basis for personalized teaching and evaluation. The research questions include: 1) the development and variation of vocabulary; 2) The development and variation of syntax; 3) The path to improving vocabulary and syntax.

3. Research Design

This chapter introduces an empirical research design on vocabulary and syntactic variations in the oral development of Chinese English learners. Based on the CDST perspective, a measurement index system for the dynamic development of second language oral communication was constructed, including TTR, D value, unique word ratio, and LFP of vocabulary, as well as breadth and depth indicators of syntax. The research subjects are four first-year undergraduate students from Chinese universities, divided into two groups: low-level and high-level, and their vocabulary and syntax development trajectories are tracked separately. The data collection period is two years, and a total of 512 historical data values were obtained. Statistical analysis uses resampling techniques and Monte Carlo simulations to determine the type and period of variation.

4. Results and Discussion

This chapter delves into the empirical research results of vocabulary and syntactic variations in the oral development of Chinese English learners. Research has found that the diversity and complexity of vocabulary increase with learners' proficiency, but there are significant variations in the development process. Through TTR index analysis, it was found that four subjects experienced the maximum change in vocabulary use during the mid-term period, and TTR was positively correlated with D value, indicating that the total vocabulary was relatively stable. Gender differences are evident in the use of unique words, with males using more unique words in the early stages and females reaching their peak in the later stages. The syntactic variation shows that the overall trend is from simple to complex, but there are also variations. Low order and high-order learners have different periods of maximum change and peak appearance in MLU, with high-order learners showing earlier periods of maximum change and peak appearance than low order learners. The use of syntactic structures also exhibits different patterns of variation at different stages of learning.

5. Conclusion

This study reveals the dynamics, complexity, and multidimensionality of vocabulary and syntactic variations in the oral development of Chinese English learners. The development of vocabulary shows homogeneity within two years, undergoing a process of variation from moderate to rapid and then to slow; Syntactic development is heterogeneous, with low order indicating free variation and high order indicating developing variation, with different rates of development for males and females. The research results suggest that personalized teaching plans should be developed for oral teaching based on individual differences, and oral evaluation should be combined with long-term and short-term evaluation criteria. This study is an interdisciplinary attempt under the background of the "New Liberal Arts", aiming to improve the scientific and accurate nature of second language research and explore the laws of localized language acquisition.