When perceptual or motor sets are changed: Effects of updating demands on structure and energy of P300

It was attempted to disentangle the effect of two updating processes on P300. Three conditions were created by a priming paradigm: (1) No updating, (2) updating perceptual but no motor information, and (3) updating both perceptual and motor information. As expected, both updating conditions led to a P300-complex with more energy, but the additional demand of motor updating did not affect P300. Effects were similar for both delayed (experiment 1) and immediate responding (experiment 2).

Both experiments confirmed earlier observations that P300 consists of at least three subcomponents, namely P3a, P3b, and a positive Slow Wave (pSW). Perceptual updating affected in particular the energy of P3b and pSW. Further, pSW was related to the complexity of the updating operations. When stimuli consisted of abstract symbols there was more energy in pSW than when stimuli were concrete symbols with direct spatial relations to the response.

The structure and energy changes of P300 suggest that P3b and pSW do not provide an unambiguous picture of the underlying source structure. In some conditions only one peak (P3b) was observed in the surface structure; this still seemed to be the result of two underlying waves. In other conditions these waves were separated in time showing a clear double peak in the surface structure.