Studies of scalp-recorded brain event-related potentials in humans currently depend on the electronic averaging of many responses to the stimulus. In non-averaged single responses, it is sometimes possible to see late components such as the so-called P300, but not the shorter latency components that are much smaller and masked in background noise. We tried to identify short-latency cognitive potentials evoked by finger stimulation by comparing single trial responses that are concomitantly recorded at the contralateral and ipsilateral parietal scalp respectively. We developed a single trial topographic mapping method that proved important for assessing whether any left-right difference at short latency indeed reflected genuine cognitive electrogeneses. These results make it possible to analyze on a trial-by-trial basis the short latency cognitive processing in somatic perception.