interaction teaches the child about the world and helps them develop through the cognitive stages, which Piaget neglected to consider. More recent work from a newer dynamic systems approach has strongly challenged some of the basic presumptions of the "core knowledge" school that Piaget suggested. Dynamic systems approaches harken to modern neuroscientific research that was not available to Piaget when he was constructing his theory. This brought new light into research in psychology in which new techniques such as brain imaging provided new understanding to cognitive development. One important finding is that domain-specific knowledge is constructed as children develop and integrate knowledge. This enables the domain to improve the accuracy of the knowledge as well as organization of memories. However, this suggests more of a "smooth integration" of learning and development than either Piaget, or his neo-nativist critics, had envisioned. Additionally, some psychologists, such as Lev Vygotsky and Jerome Bruner, thought differently from Piaget, suggesting that language was more important for cognition development than Piaget implied. Post-Piagetian and neo-Piagetian stages In recent years, several theorists attempted to address concerns with Piaget's theory by developing new theories and models that can accommodate evidence which violates Piagetian predictions and postulates. The neo-Piagetian theories of cognitive development, advanced by Robbie Case, Andreas Demetriou, Graeme S. Halford, Kurt W. Fischer, Michael Lamport Commons, and Juan Pascual-Leone, attempted to integrate Piaget's theory with cognitive and differential theories of cognitive organization and development. Their aim was to better account for the cognitive factors of development and for intra-individual and inter-individual differences in cognitive development. They suggested that development along Piaget's stages is due to increasing working memory capacity and processing efficiency by "biological maturation". Moreover, Demetriou's theory ascribes an important role to hypercognitive processes of "self-monitoring, self-recording, self-evaluation, and self-regulation", and it recognizes the operation of several relatively autonomous domains of thought (Demetriou, 1998; Demetriou, Mouyi, Spanoudis, 2010; Demetriou, 2003, p. 153). Piaget's theory stops at the formal operational stage, but other researchers have observed the thinking of adults is more nuanced than formal operational thought. This fifth stage has been named post formal thought or operation. Post formal stages have been proposed. Michael Commons presented evidence for four post formal stages in the model of hierarchical complexity: systematic, meta-systematic, paradigmatic, and cross-paradigmatic (Commons & Richards, 2003, p. 206–208; Oliver, 2004, p. 31). There are many theorists, however, who have criticized "post formal thinking," because the