Applying the TC-unit-based measures proposed and validated in Chapter  2 , this chapter investigates how Chinese syntactic complexity may be affected by cognitive task complexity in terms of the varied demands for attentional resources imposed on learners as they perform tasks. Considering resource-directing variables such as more involved elements, longer performing time, and higher cognitive reasoning demands, L1 and L2 Chinese speakers (N = 115) spoke with higher syntactic complexity in more cognitively complex tasks. Considering resource-dispersing variables such as longer and more in-depth task planning, participants did not demonstrate statistically significant difference in their Chinese complexity performance, but held overall positive perceptions of their own performance and language strategies in the repetition regardless of their actual performance. Rather than confirming the Limited Attentional Capacity Model or the Multiple Resources Attentional Model, the findings are inconclusive and further research is needed to understand how cognitive task complexity affects language performance. In order to generate comparable results for synthesis, this chapter calls for a comprehensive scale that accurately measures the complexity degree of all tasks across studies rather than general differentiation of more and less complex tasks. For better precision in measurement application, this chapter also adds discussions on the ambiguity or difficulty involved in applying the TC-unit-based measures, and how the issues may be resolved.