“…More recently, L2 complexity, and its development over time, have also been studied for their own sake (i.e. as primary research foci), particularly by studies couched in usage-based theories of SLA or those adopting a dynamic systems theory (DST) approach (Larsen-Freeman, 2006;Spoelman & Verspoor, 2010;Verspoor, Lowie, & van Dijk, 2008;Verspoor, Schmidt, & Xu, 2012;Verspoor & Van Dijk, 2012;Vyatkina, 2012Vyatkina, , 2013Vyatkina, Hirschmann, & Golcher, 2015). These studies suggest that although the complexity of L2 learners' performance increases along with their overall L2 proficiency as time and L2 development proceed, linguistic complexity and proficiency do not always increase in parallel and the increase in complexity is neither linear, constant nor guaranteed for all layers (lexical, morphological, syntactic) and sub-dimensions (e.g.…”