Comparison of late event-related potentials (ERPs) to somatosensory, auditory and visual stimulation

ERPs were recorded on somatosensory, auditory and Visual stimuli in two stimulus conditions to make a comparative study of the endogenous components in the ERPs. Air-puff stimulation at the tip of the index finger of the right hand was used to evoke somatosensory ERPs. A lone pip presented via a pair of headphones, and a flash located 2 m from the subject were used to evoke auditory and visual ERPs. In one condition, a single stimulus was delivered with a random interval sequence. In another condition double stimuli composed of a single stimulus and a paired stimulus with a 300 ms interval were randomly presented, with the probabilities of the paired stimulus being 5, 7 and 9%. Subjects were instructed to count only the single stimulus and averaging was made for the single stimulus ERPs in bath conditions. A positive shift after 400 ms for the double stimulus sequence showed a larger amplitude and longer duration than that for the single stimulus sequence. The late positive potentials are related to a continued late processing far the discrimination of the paired stimulus from the double stimulus sequence and this late processing is not dependent on the modalities of stimulation.