Hierarchical models in cognition: Do they have psychological reality?

Many theoretical models of cognition are based on the assumption that cogni tive processes and representations are hierarchically structured. The issue of whether these hierarchies are mere constructs or conceptual tools, or w hether they have psychological and neurological reality, is addressed. Theo ries across a range of cognitive domains are reviewed and four kinds of evi dence are considered: behavioural, neuropsychological, ontogenetic, and log ical. Logical constraints are identified in relation to operating principle s of control, access, economy and analogy. The general characteristics of h ierarchical structures and their advantages and disadvantages are discussed .