Surface potentials for Geodesic Sensor Net (128-channel) recordings of right-handed, healthy adults (N=17), showing topographies for tonal and phonetic target stimuli when subjects responded with a left or right button press, or silently counted the targets. Note the lateralization of N2 (200-220 ms) and P3 (300-440 ms) to the right hemisphere for tonal targets, but to the left hemisphere for phonetic targets. These task-dependant asymmetries are superimposed by response-related asymmetries (i.e., a relative frontocentral negativity contralateral to the button press).