VISUAL INFORMATION-PROCESSING - TOPOGRAPHY OF BRAIN ELECTRICAL-ACTIVITY

Multichannel recordings allow the non-invasive assessment of the elect rical fields of the brain. Topographical analysis of EEG and EPs shoul d not be restricted to the qualitative graphical display of maps at ma ny time points instead of time series at many recording points. It is mandatory that quantitative methods are applied to EEG and evoked pote ntial data in order to extract relevant information from such series o f maps. For spontaneous EEG data the spatial analysis of frequency ban ds is of major interest while evoked potential fields are analyzed in terms of latencies and amplitudes of individual components. The comput ation of global field power, global dissimilarity as well as the locat ion of potential maxima, minima or centroids enable a meaningful data reduction and the statistical evaluation of the effects of different e xperimental conditions and the comparison of various clinical populati ons. In a similar way multivariate statistical techniques may be emplo yed in order to detect characteristic potential field configurations. Topographical methods to analyze brain electrical activity are illustr ated with multichannel data evoked by localized visual stimuli and by stereoscopic stimulation as well as with evoked potential data obtaine d during perceptual learning experiments.