On a ‘failed’ attempt to manipulate conscious perception with transcranial magnetic stimulation to prefrontal cortex

It has been reported that continuous theta burst transcranial magnetic stimulation (TMS) to the dorsolateral prefrontal cortex (DLPFC) impairs metacognitive awareness in visual perception (Rounis et al., 2010). Bor et al. (2017) recently attempted to replicate this result. However, the authors modified the experimental design of the original study considerably, meaning that this was not strictly a replication. In some cases, the changes are a priori expected to lower the chance of obtaining positive findings. Despite these changes, the researchers in fact still found an effect similar to Rounis et al.’s, but they claimed that it was necessary to adopt certain criteria to discard ∽30% of their subjects, after which a null result was reported. Using computer simulations, we evaluated whether the subject exclusion criteria Bor et al. adopted was appropriate or beneficial. We found that, contrary to their intended purpose, excluding subjects by their criteria does not actually reduce false positive rates. Taking into account both their positive result (without subject exclusion) and negative result (after exclusion) in a Bayesian framework, we further found that their results suggest a 75% or greater likelihood that TMS to DLPFC does in fact impair metacognition, directly contradicting their claim of replication failure. That lesion and chemical inactivation studies are known to demonstrate positive effects in similar paradigms further suggests that Bor et al.’s alleged negative finding cannot be taken as evidence against the role of the prefrontal cortex in conscious perception in general.