The effects of task demand on the contingent negative variation during working memory
Abara, Jose Antonio Paulino
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Electroencephalography (EEG) provides an objective measure of electrical brain activity. Event-related potentials (ERP) represent brain electrical activity generally elicited by identifiable stimuli and have been of particular interest in the study of human cognition. The Contingent Negative Variation (CNV) is another electrophysiological component used to study the relationship between brain electrical activity and human cognition. The CNV consists of a slow negative potential that depends upon the association or contingency of preparatory and imperative stimuli (e.g., S1-S2) during a warned reaction task requiring a response. The CNV is classified into early and late components. The early CNV (eCNV) relates to orientation to the preparatory stimulus and expectancy associated with the imperative stimulus; whereas, the late CNV (lCNV) relates to the anticipation of processing the imperative stimulus and preparation for a motor response. The amplitudes of the eCNV and lCNV are positively related to the degree of orientation, expectation, and preparation for the paired preparatory and imperative stimuli. The more neural resources allocated for cognitive and motor processing required for a task, the greater the negativity of the CNV. This study examined the effects of working memory (WM) and task-demand on the CNV using a unique n-back continuous performance task, the sequenced WM paradigm (SWMP). There were two task-demand conditions (lower demand and higher demand) in the SWMP. The participants were required to remember the spatial location of a preparatory stimulus (S1) and make a judgment on an imperative stimulus (S2) as to whether it was in the same location as the preparatory stimulus. The participants were asked to make a button press for a match of the location and to withhold their response for nonmatch. The first set of hypotheses examined the eCNV and lCNV for the Preparatory, Distractor, and Imperative stimuli for each of the two conditions. The second set of hypotheses examined the effects of task demand on the CNV. The results supported the involvement of the eCNV and lCNV with the cognitive processes engaged during WM. The eCNV was found to be sensitive to orientation and expectancy for the upcoming stimulus. The lCNV was found to be sensitive to preparation to evaluate and preparation to make a motor response to the Imperative stimulus. The effects of demand on the WM system due to stimulus relevancy were shown to affect the CNV. Furthermore, the effects of the NonTarget stimulus on the CNV suggest that the NonTarget was a relevant stimulus within the context of working memory paradigm used in this investigation.