Visual information processing: topography of brain electrical activity

Multichannel recordings allow the non-invasive assessment of the electrical fields of the brain. Topographical analysis of EEG and EPs should not be restricted to the qualitative graphical display of maps at many time points instead of time series at many recording points. It is mandatory that quantitative methods are applied to EEG and evoked potential data in order to extract relevant information from such series of maps. For spontaneous EEG data the spatial analysis of frequency bands is of major interest while evoked potential fields are analyzed in terms of latencies and amplitudes of individual components. The computation of global field power, global dissimilarity as well as the location of potential maxima, minima or centroids enable a meaningful data reduction and the statistical evaluation of the effects of different experimental conditions and the comparison of various clinical populations. In a similar way multivariate statistical techniques may be employed in order to detect characteristic potential field configurations. Topographical methods to analyze brain electrical activity are illustrated with multichannel data evoked by localized visual stimuli and by stereoscopic stimulation as well as with evoked potential data obtained during perceptual learning experiments.