Dynamic hierarchical cognition: Music and language demand further types of abstracta.

Hierarchical structures are rapidly and flexibly built up in the domains of human language and music. These domains require a tree-building capacity - "dendrophilia" - to dynamically infer hierarchical structures from sensory input (or to hierarchically structure output), based on subunits stored in a lexicon. This dynamic process involves a crucial class of abstracta overlooked in the target article.