PROBE EVOKED POTENTIALS AND LATERALIZED COGNITIVE ACTIVITY: EFFECTS OF EXPECTANCY, PROCESSING DEMANDS, AND TIME (MEMORY, STERNBERG, INFORMATION-PROCESSING)

Several previous experiments have suggested that the anticipation and processing of linguistic material are both associated with a left cerebral hemisphere processing advantage, whereas the anticipation and processing of nonlinguistic material are associated a right hemisphere processing advantage. This dissertation critically reviews existing experiments and reports one additional experiment designed to identify some of the mechanisms responsible for producing such advantages.;Subjects were required to execute a manual reaction time response indicating whether or not a visually-presented test item was a member of a set of English or Japanese characters presented 5 sec earlier. A cue stimulus, indicating the number of items comprising the set, and, on one-half of the trials, the linguistic/nonlinguistic nature of these items, occurred 2 sec prior to the memory set. Asymmetries of processing were indexed by shifts in the scalp distribution of ERPs elicited by the cue, memory set, and test (comparison) stimuli, as well as by shifts in the scalp distribution of probe ERPs elicited during the intervals preceding and following the memory set.;The major findings were consistent with the notion that the left and right cerebral hemispheres are relatively more efficient in the encoding and retention of linguistic and nonlinguistic information, respectively, when they are set to do so. Specifically, when the type of characters comprising the memory set was cued, English character memory sets were found to elicit a larger P2 than Japanese character memory sets over the LH, while over the RH, the reverse pattern of results was found. When character type was uncued, no asymmetries in memory set ERP P2 amplitude were found. Evidence suggestive of an asymmetric engagement of retention processes was provided by the finding of a diminished N2-P3 response to RVF probe stimuli when these were preceded by an English character memory set, and a diminished N2-P3 response to LVF probe stimuli when these were preceded by a Japanese character memory set. These findings illustrate the importance of separating stages of processing in ERP studies of cerebral laterality and indicate that cueing can be a major determinant of lateral differences.