Lateralized power spectra of the EEG as an index of visuospatial attention

The electroencephalogram (EEG) was measured in an endogenous orienting paradigmwhere symbolic cues indicated the likely side of to-be-discriminated targets.Combined results of event-related lateralizations (ERLs) and a newly derivedmeasure from wavelet analyses that we applied on the raw EEG and individualevent-related potentials (ERPs), the lateralized power spectra (LPS) and theLPS-ERP, respectively, confirmed the common view that endogenous orientingoperates by anterior processes, probably originating from the frontal eyefields, modulating processing in parietal and occipital areas. The LPS dataindicated that modulation takes place by increased inhibition of the irrelevantvisual field and/or disinhibition of the relevant to-be-attended visual field.Combined use of ERLs, the LPS, and the LPS-ERP indicated that most of theinvolved processes can be characterized as externally evoked, either or not withclear individual differences as some evoked effects were only visible in theLPS-ERERP, whereas few processes seemed to have an internally induced nature.Use of the LPS and the LPS-ERP may be advantageous as it enables to determinethe involvement of internally generated lateralized processes that are notstrictly bound to an event like stimulus onset.