Three-channel Lissajous′ trajectories of auditory event-related potentials to target stimuli

Three orthogonal recordings ('X', 'Y' and 'Z') of event-related potentials (ERPs) evoked by auditory target stimuli were represented in 3-dimensional voltage-space, to produce 3-channel Lissajous′ trajectories (3-CLTs). Stimuli were verbal or non-verbal and were differentiated by their pitch, phonemic or phonetic attributes. Visual inspection and quantitative evaluations unexpectedly revealed that the 3-CLT of these ERPs strongly resembles a 'hair-pin' trajectory. This trajectory tilted in space at characteristic angles with each of the analysis axes: 133° with the 'X' axis, 87° with the 'Y' axis, and 54° with the 'Z' axis. The relatively small inter-subject variability observed in the geometrical measures, particularly in orientation, may be attributed to the slight variation in the underlying generators. 3-CLT analysis could be useful in future clinical as well as source studies of ERP generators.