Detecting alpha rhythm phase reset by phase sorting: caveats to consider.

One method being proposed for disentangling whether the ERP is generated by an evoked potential that is independent of and adds linearly to the ongoing rhythm or by (partial) phase resetting of the ongoing rhythm is sorting trials according to the pre-stimulus phase of the ongoing rhythm. The subsequent subtraction of phase-sorted resting-state trials is supposed to correct for phase-sorting effects otherwise maintained in the post stimulus time. Consequently, a true phase dependency of the ERP, considered to be indicative for a phase-reset (Risner, M.L., Aura, C.J., Black, J.E., Gawne, T.J., 2009. The visual evoked potential is independent of surface alpha rhythm phase. NeuroImage), would then become apparent. Here we disclose possible pitfalls of this approach causing invalid inferences. We also highlight that inferences based on this approach first depend on the assumed concept of a phase reset, and second can provide a hint at but are not sufficient for disentangling different mechanisms of ERP generation. We will discuss other criteria necessary for further confirmation of the phase reset theory.