Time-coursestudies of semantic verification are reviewed, discussed, and reinterpreted with the aim of drawing general theoretical conclusions about semantic memory structure. These reaction time, speed-accuracy tradeoff, speed-accuracy decomposition, and event-related (brain) potential (ERP) studies suggest that semantic memory is structured on at least three levels. In particular, specific models of the intermediate (macrostructural) level are discussed and compared. ERP investigations of this level suggest that context-independent and context-dependent types of semantic information are potentially isolable and analyzable.Research on semantic memory has been one of the mainstays of cognitive psychology for more than two decades. Since the early papers of Collins and Quillian (1969) and Meyer (1970), the focus of this research has been on exploring how people represent, access, and utilize semantic information about natural categories. Of these interests, the representation of semantic information has been the primary concern. Indeed, the investigations of the 1970s pioneered the use ofa number ofideas that have proved important to the study ofknowledge representation, such as networks, features, exemplars, fuzzy sets, and so on (for reviews, see Chang, 1986; Kintsch, 1980;E. E. Smith, 1978).
Experimental ApproachThe basic experimental approach taken by this body of work is, in principle, simple. Subjects are presented with pairs of terms representing common concepts, usually in the form of a sentence (e.g., "All dogs are animals," or "Some people are trees"). Insuch a sentence verification task, subjects must quickly decide whether the semantic relation given by each sentence is correct or incorrect and respond to each stimulus with a rapid, accurate buttonpress to indicate their decision. Since the sentences are typically rather simple, accuracy is usually high. So, reaction time (RT) has been the dependent variable of primary interest.The preparation of this article was supported by National Institute of Mental Health Grant CEP 1 R29 MH45447-01A3 to 1.K. Thanks go to Jane Anderson, Phillip 1. Holcomb, James Neely, Allen Osman, Richard Schweickert, Roderick Smith, and various anonymous reviewers for helpful discussions, advice, and comments.
RationaleThe logic of this enterprise is straightforward. It was hoped that comparing mean RTs to syntactically similar sentences embodying different semantic relations between the subject and predicate terms would allow inferences to be made about the format and organization of information in semantic memory. This is a different approach from that taken by most researchers in the field of categorization. These researchers have usually adopted a variety of rating andjudgment tasks to study how people form and utilize different types of concepts (for a recent review, see Komatsu, 1992). The latter approach has the advantage of reflecting how people learn and use categories. The drawback is that it is difficult to infer in this way the structure or format of this knowle...