Early processing in primary visual cortex is necessary for conscious and unconscious vision while late processing is necessary only for conscious vision in neurologically healthy humans

Overlapping and unique neural circuits are activated during perceptual decision making and confidence

“…Nevertheless, it must be appreciated that even though we observed similar activation patterns for decision and confidence, the computations that underlie these two processes may still be very different. Such differences are implied by accuracy-confidence dissociations (Lau and Passingham, 2006;Rahnev et al, 2011bRahnev et al, , 2015Vlassova et al, 2014;Song et al, 2015;Spence et al, 2015;Zylberberg et al, 2016;Samaha et al, 2016;Boldt et al, 2017;Ferrigno et al, 2017;Desender et al, 2018), neurological phenomena such as in blindsight (Weiskrantz, 1986), and studies that delivered transcranial magnetic stimulation (TMS) to the early visual cortex and found separable effects on accuracy and confidence (Rahnev et al, 2012b(Rahnev et al, , 2013Hurme et al, 2017). Moreover, a recent study provided direct evidence that sensory neural signals are indeed used in different ways in making perceptual decisions and confidence judgments (Peters et al, 2017).…”

TMS of V1 eliminates unconscious processing of chromatic stimuli

“…Furthermore, monkeys with V1 lesions manifest blindsight-like behavior in response to small and briefly presented stimuli (Mohler & Wurtz, 1977), and human patients with blindsight can unconsciously process small and brief stimuli (e.g., Savina & Guitton [2018] used a 0.5° stimulus with an 86-ms duration). We also previously showed that the RTE could be observed when similar small and brief achromatic contrast stimuli were suppressed by the TMS of the V1 at a 90-ms SOA (Hurme et al, 2017). Based on these findings, we suggest that stimulus intensity is likely not the reason why we have not found unconscious chromatic processing, although this question should be directly addressed in future studies.…”

“…The TMS intensity was set at 85% of the maximum stimulator output. In our previous studies, performed with the Nexstim stimulator, we used a 65–75% stimulation intensity (Hurme et al, 2017, 2019). Pilot experiments suggested that with the MagPro X100 stimulator, approximately 85% intensity is required to reach equally strong visual suppression as with the Nexstim Eximia stimulator.…”

“…During the two-stimulus condition, the additional target is called the redundant target because it is not necessary for the task performance. The RTE has been found even when the redundant target is reported as unconscious in patients with V1 lesions (Marzi, Tassinari, Aglioti, & Lutzemberger, 1986; Tamietto et al, 2010; Tomaiuolo, Ptito, Marzi, Paus, & Ptito, 1997) and in neurologically healthy participants (Hurme et al 2017, 2019; Savazzi & Marzi, 2002). A promising candidate that can explain the unconscious RTE is a neural pathway that connects the superior colliculus (SC) to the extrastriate cortex and bypasses the V1 (Savazzi & Marzi, 2004).…”

“…Since then, studies have tried to demonstrate that after suppressing the conscious perception of a stimulus with TMS pulses to the V1, it is possible to reveal “TMS-induced blindsight” in neurologically healthy observers. Some of the studies have found evidence of this phenomenon with varying stimulus types (Koenig & Ro, 2018; Boyer, Harrison, & Ro, 2005; Railo & Koivisto, 2012; Ro, Shelton, Lee, & Chang, 2004; Christiansen, Kristiansen, Rowe, & Nielsen, 2008), but a larger number of the studies have concluded that both conscious and unconscious visual processing rely on the V1 in neurologically healthy individuals (de Graaf, Koivisto, Jacobs, & Sack, 2014; Hurme, Koivisto, Revonsuo, & Railo, 2017, 2019; Koivisto, Henriksson, Revonsuo, & Railo, 2012; Koivisto, Mäntylä, & Silvanto, 2010; Persuh & Ro, 2013, Railo, Andersson, Kaasinen, Laine, Koivisto, 2014; Sack, van der Mark, Schuhmann, Swarzbach, & Goebel, 2009)…”