Overlap between P300 and movement-related-potentials: a response to Verleger.

In reply to Verleger's commentary, I first clarify what the term "MRP overlap" implies; by means of a simple additive simulation it is shown that overlap between a stable P300 and a MRP that moves in time with reaction-time, may cause two types of artefacts--amplitude reduction and double peaking of P300. Following Verleger's suggestion, it is then argued that the effects of stimulus-degradation on P300 amplitude in our experiments was, at least in part, due to overlap with negative components of the MRP (in the go-intact condition), and with positive CNV return (in the nogo-intact condition). It is concluded that MRP overlap is not only an artefact but also a useful index of motor-preparation in reaction tasks, and that more refined methods should be developed in future research for accurate estimation of MRP overlap in stimulus-locked ERP waveforms.