e.g., mood (Federmeier et al 2001), schizotypy (Kiang & Kutas 2005), etc. – as well as task demands and goals may change activity levels in semantic memory, at the global or more local levels, if not both. In all of these cases, to the extent that some information represented in LTM is already partially or wholly active by the time semantic access for a given input stimulus is initiated, that information will not need to become active in response to the input. Thus, preactivation of semantic information, by any means, will tend to reduce baseline N400s to a stimulus that would normally activate that information. As a consequence, in an experimental context the N400 response to a given input can be used as a tool to assess semantic memory states, with the amount of N400 reduction (relative to a control condition) revealing how much of the information normally elicited by that stimulus is already active.
