Three dimensional vector analysis of the spatial components and voltage magnitudes of the P300 response during different attentional states and stimulus modalities

The spatial orientation and vector magnitude of the P300 event related potential (ERP) were investigated under both passive and active attentional states using stimuli presented to two sensory modalities. Three orthogonal electrode pairs were used to establish a tri-axial reference frame. By combining the separate single channel data recordings into a Cartisian coordinate system, both the spatial orientation and the vector magnitude of the P300 response could be derived and described as a hypothetical dipole. Results suggested that changes in amplitudes, recorded with individual electrode pairs, can be attributed largely to changes in the spatial orientation of a rotating P300 response dipole, and not simply to the altered magnitude of the response. The combined-axes P300 response occurs in two separate spatial domains, depending on stimulus modality and attentional state.