Vigilance or availability of processing resources. A study on cognitive energetics
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[S.l. : s.n.]
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RU Radboud Universiteit Nijmegen, 7 december 2004
Promotor : Coenen, A.M.L. Co-promotor : Eling, P.A.T.M.
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The experimental focus of this manuscript was on the exploration of vigilance, which was defined as the energetic condition required for cognitive performance. It was concluded that an increase in theta power in the EEG is a sensitive measure of vigilance lowering. An increase in beta2 power is not only present after mental effort, but also in narcoleptic patients. It was argued that this increase in higher frequencies might reflect compensational effort. Physical effort increases brain activity, but not frontally. Theta and delta power are increased in narcoleptic patients and continuously increase over the day. Hence, narcoleptic patients' vigilance level is vastly decreased and drops even further throughout the day. Performance on tasks requires processing resources. Demanding tasks need high availability of these resources. If performance is sustained, the pool of available resources may be depleted. This depletion is reflected in a performance decline. The availability of resources and the level of vigilance might be conceptually indistinguishable: The level of vigilance may be defined as the availability of processing resources. There appeared to be four separate factors of subjective alertness or fatigue: 'sleepiness', 'tension', 'calmness', and a physical factor. Sleepiness might reflect the degree of general cortical firing. This factor might be most sensitive in determining the availability of processing resources. The physical factor may reflect the activity level of the peripheral nervous system and muscles. EEG, performance and subjective measures of vigilance were all related and thus appear to reflect the level of vigilance in similar ways. A vigilance model was presented that portrays the basic precondition for cognitive performance. The global level of cortical activity might be termed 'arousal', which is not specifically associated with better performance on demanding tasks. Vigilance is not a pure condition of high cortical activity, but it stands for the precondition of cognitive processing, which is reflected in high cortical activity in the frontal lobe, which is required for non-automatic cognitive processing.
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