The reign of typicality in semantic memory.

This paper begins with a brief description of a theoretical framework for semantic memory, in which processing is inherently sensitive to the varying typicality of its representations. The approach is then elaborated with particular regard to evidence from semantic dementia, a disorder resulting in relatively selective deterioration of conceptual knowledge, in which cognitive performance reveals ubiquitous effects of typicality. This applies to frankly semantic tasks (like object naming), where typicality can be gauged by the extent to which an object or concept is characterized by shared features in its category. It also applies in tasks apparently requiring only access to a 'surface' representation (such as lexical decision) or translation from one surface representation to another (like reading words aloud), where typicality is defined in terms of the structure of the surface domain(s). The effects of surface-domain typicality also appear early in the time course of word and object processing by normal participants, as revealed in event-related potential studies. These results suggest that perceptual and conceptual processing form an interactive continuum rather than distinct stages, and that typicality effects reign throughout this continuum.