1. Introduction

This article introduces the incremental processing mode of English second language spoken sentence production, including three stages of speech production: conceptualization, speech organization, and vocalization. The incremental mode allows the speaker to pass on one unit of information to the next stage after planning, while continuing to plan new information. Increment can be divided into two forms: linear and hierarchical, corresponding to the linear word order and the relationship between sentence structures. The paper analyzes the subject verb agreement errors of native English speakers in specific structures, explores the relationship between incremental processing and the construction process of speech production structures, reviews second language research, and finally conducts experimental research on the incremental processing mechanism of Chinese English learners in producing specific structures.

2. Literature review and research questions

This article summarizes the subject verb agreement errors and their explanations in English native speakers' oral sentence production, and explores whether second language learners adopt the same incremental processing mode as native speakers. Firstly, the incremental processing theory of three types of subject verb agreement errors was analyzed: linear incremental pattern caused by prepositional phrase intervention, hierarchical incremental pattern in relative clause structure, and hierarchical incremental pattern in double modifier structure. Secondly, it points out the gaps in existing second language research, such as research stages, structural differences, incremental processing mechanisms, and the impact of language proficiency. Finally, two research questions were raised: 1) What is the incremental processing mode of Chinese English learners at different levels during the structural construction stage? 2) If it is a hierarchical increase, what is the mechanism?

3. Experiment

Two experiments were conducted to explore the incremental processing mode in the production of English second language spoken sentences. Experiment 1 used sentence completion tasks to study the incremental processing patterns of participants at different levels through prepositional phrases and relative clauses. The experimental design is a mixed factor design of 2 (structural type) x 2 (noun singular and plural consistency) x 2 (English proficiency), with the dependent variable being the number of subject verb agreement errors. The results of Experiment 1 showed that high-level participants used linear increasing processing in prepositional phrases and hierarchical increasing processing in relative clauses; Low level subjects were subjected to linear incremental processing in both structures. Experiment 2 further explored whether the incremental processing mode of high-level subjects conforms to the syntactic distance hypothesis, using an intra subject factor design of 2 (N1 singular and plural) × 2 (N2 singular and plural) × 2 (N3 singular and plural), with the dependent variable being the proportion of subject verb agreement errors. The results of Experiment 2 showed that the incremental processing of high-level subjects did not conform to the syntactic distance hypothesis, but met the prediction of the clause packing hypothesis, indicating that their hierarchical processing mechanism was caused by clause boundary effects.

4. Comprehensive discussion

A comprehensive discussion was conducted on the incremental processing mechanism of Chinese English learners at different levels in the production of second language spoken English sentences. The results of Experiment 1 and Experiment 2 show that high-level learners adopt a hierarchical incremental processing mode during the structural construction stage, while low-level learners adopt a linear incremental processing mode. High level learners use linear progression for prepositional phrases and hierarchical progression for relative clauses, which is caused by clause packing effect rather than syntactic distance effect. This is not entirely consistent with the research results of Jessen et al. (2021), as the differences lie in the study subjects and experimental materials. This study also found that high-level learners adopt different incremental processing modes in different stages of oral sentence production, with linear increment in vocabulary selection stage and hierarchical increment in structural construction stage; Low level learners adopt linear increment at different stages.

5. Conclusion

Two experiments revealed differences in the incremental processing patterns of Chinese English learners in sentence production, with low-level learners using linear increments and high-level learners using linear increments for prepositional phrases and hierarchical increments for relative clauses. The hierarchical progression of high-level learners may differ from that of native speakers, possibly due to differences in syntactic representation. The study suggests that structural difficulty may affect subject verb agreement processing, and suggests future research on controlling structural difficulty to examine the impact of syntactic distance on second language learners.