REDUCTION OF OCULAR ARTIFACTS IN-SOURCE CURRENT-DENSITY BRAIN MAPPINGS BY ARX2 FILTERING

Sweep by sweep analysis of event-related potentials (ERP) of the human scalp represents a reliable tool for both the diagnosis of neurologic diseases and the study of the central nervous system during cognitive tasks. The off-line procedure based on stochastic parametric identifi cation and filtering herewith described allows an accurate analysis of single-sweep ERP and a drastic reduction of ocular artefacts variousl y propagating through the skull. Moreover, the spatial distribution of the recorded ERP in bidimensional form was enhanced by using the Lapl acian operator in order to get an estimate of the source current densi ty (SCD) flow from the skull into the scalp. Complete single-trial sig nals were filtered according to an autoregressive model of signal gene ration with 2 exogenous inputs (ARX2). The ARX2 procedure models the r ecorded signal as the sum of three signals: (a) the background EEG act ivity, modelled as an autoregressive process driven by a while noise; (b) a filtered version of a reference signal carrying the average info rmation contained in each sweep; (c) a signal due to the ocular artefa ct propagation. The evaluation of the effect of artefact suppression o n those channels close to the eyes was compared with standard ordinary bart squares method (OLS) based on a linear model of the influence of EOG on ERP. Finally, the better results obtainable through ARX filter ing on sweep-by-sweep brain mappings are also presented.