Theta-burst transcranial magnetic stimulation to the prefrontal or parietal cortex does not impair metacognitive visual awareness

Abstract

Neuroimaging studies commonly associate dorsolateral prefrontal cortex (DLPFC) and posterior parietal cortex with conscious perception. However, such studies only investigate correlation, rather than causation. In addition, many studies conflate objective performance with subjective awareness. In an influential recent paper, Rounis and colleagues addressed these issues by showing that continuous theta burst transcranial magnetic stimulation (cTBS) applied to the DLPFC impaired metacognitive (subjective) awareness for a perceptual task, while objective performance was kept constant. We attempted to replicate this finding, with minor modifications, including an active cTBS control site. Using a between-subjects design for both DLPFC and posterior parietal cortices, we found no evidence of a cTBS-induced metacognitive impairment. In a second experiment, we devised a highly rigorous within-subjects cTBS design for DLPFC, but again failed to find any evidence of metacognitive impairment. One crucial difference between our results and the Rounis study is our strict exclusion of data deemed unsuitable for a signal detection theory analysis. Indeed, when we included this unstable data, a significant, though invalid, metacognitive impairment was found. These results cast doubt on previous findings relating metacognitive awareness to DLPFC, and inform the current debate concerning whether or not prefrontal regions are preferentially implicated in conscious perception.

On a ‘failed’ attempt to manipulate visual metacognition with transcranial magnetic stimulation to prefrontal cortex

“…Bor et al (2017) recently attempted to replicate this result. However, they adopted an experimental design that reduced their chance of obtaining positive findings.…”

Response to Ruby et al: On a ‘failed’ attempt to manipulate conscious perception with transcranial magnetic stimulation to prefrontal cortex

“…1), where type II FARs approaching 0 or HRs approaching 1 cause meta d' values to significantly deviate from their previously linear path. Note that the unreliability of the measure seems to be a particular issue for the SSE method, which was the main version of meta d' used both in the Rounis et al (2010) and our Bor et al (2017) studies (in order to keep close to the Rounis et al methods).…”

“…Subject exclusion, FP rates, and the value of 'clean' data Ruby et al motivate their simulations by saying that our main reason for subject exclusion was to avoid a high FP rate. Ruby et al claim that excluding the subjects as we did in Bor et al (2017) was 'unnecessary', on the basis of their computer simulations showing that FP rates are unaffected by such exclusions. Although we still maintain that including unreliable meta d' results ("unreliable" meaning no longer measuring what it purports to, no longer a smooth, linear function, so that now a small change in underlying psychological components, such as hit rate, can lead to a large jump in the measure) may well increase FP rates (see below for reasons), this is a secondary issue, and is a misrepresentation of our reasoning, which is the critical point of disagreement between us.…”

“…In Barrett et al (2013), we showed that it is principled to apply these criteria because, otherwise, as we stated in the Bor et al (2017) As this is such a critical point, let us rephrase it here: When hit rates or false alarm rates (HR/FARs) are not near 0 or 1, there is a roughly linear relationship between changes in HRs or FARs and meta d'. Such smooth, approximately linear relationships are good indicators of a reliable measure (i.e.…”

“…The other design changes in Bor et al (2017) were also made in a principled way, and captured in full the spirit of the original Rounis et al experiment. These changes are fully described in Bor et al (see,for example,p.…”