On the continuity of thought and the representation of knowledge: Electrophysiological and behavioral time-course measures reveal levels of structure in semantic memory

Abstract

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...

Temporal dynamics of verbal object comprehension

“…This result agrees with several previous estimates of the onset of semantic processing derived from scalp and intracranial ERP techniques (e.g., 150-300 msec from ERP, 230 msec in the left inferior frontal region) (10,45). Others have suggested that cognitive processing during naming occurs in the lateral posterior temporal lobe at 700-1,200 msec, as assessed by change of spectral density of the ECoG (46).…”

A Rose by Any Other Name: Long-Term Memory Structure and Sentence Processing

“…It has therefore proven difficult to draw unequivocal conclusions from such studies. How can we be sure that the category-based effects arise because individuals tap into existing structured representations and not because individuals create structure as needed by the categorization task itself (for review, see Kounios, 1996)?…”

“…Both groups found that a final word that was not a category member generated more N400 activity than did a category member. Category effects on the N400 have also been observed during the performance of sentence verification tasks (in which individuals are asked to judge the truth of statements of the form "An X is a Y "-for example, "A robin is a bird") (e.g., Fischler, Bloom, Childers, Roucos, & Perry, 1983;Kounios, 1996;Kounios & Holcomb, 1992). In these tasks, an enlarged N400 response is observed to the final word of false statements such as "A carrot is a fruit."…”

On the locus of the semantic satiation effect: Evidence from event-related brain potentials

“…Specifically, N400 is typically oflarger amplitude to words (or pictures) that do not fit their semantic context (e.g., "He put cream and sugar in his dog/coffee," where dog elicits a larger N400 than does coffees. Although a definitive theory ofthe N400 does not yet exist, a number of researchers have argued that this component reflects a mechanism that attempts to integrate a piece of information into its semantic context (e.g., Kounios, 1996;Osterhout & Holcomb, I995)-hence, the larger amplitude in response to a word such as dog that does not fit well. Frenck-Mestre et al (1997) reasoned that if semantic satiation were truly semantic, satiation should diminish the magnitude of the N400 effect (defined as the difference in N400 amplitude to words that fit and do not fit their context).…”

“…Frenck-Mestre et al (1997) focused on the N400 component, a negative deflection in the ERP waveform that typically peaks approximately 400 msec after stimulus onset (Kutas & Hillyard, 1980). The N400 component, likely a complex of related subcomponents (see e.g., Holcomb, Kounios, Anderson, & West, 1999;Kounios, 1996;Kounios & Holcomb, 1994), was of particular interest to these investigators, because it has been shown to be sensitive to semantic factors in a variety of tasks (for reviews, see Kounios, 1996;Kutas & van Petten, 1994;Osterhout & Holcomb, 1995). Specifically, N400 is typically oflarger amplitude to words (or pictures) that do not fit their semantic context (e.g., "He put cream and sugar in his dog/coffee," where dog elicits a larger N400 than does coffees.…”