Distinguishing the Neural Correlates of Perceptual Awareness and Postperceptual Processing

Abstract

To identify the neural correlates of perceptual awareness, researchers often compare the differences in neural activation between conditions in which an observer is or is not aware of a stimulus. While intuitive, this approach often contains a critical limitation: to link brain activity with perceptual awareness, observers traditionally report the contents of their perceptual experience. However, relying on observers' reports is problematic because it is difficult to know whether the neural responses being measured are associated with conscious perception or with postperceptual processes involved in the reporting task (e.g., working memory, decision-making). To address this issue, we combined a standard visual masking paradigm with a recently developed "no-report" paradigm in male/female human participants. In the visual masking paradigm, observers saw images of animals and objects that were visible or invisible, depending on their proximity to masks. Meanwhile, on half of the trials, observers reported the contents of their perceptual experience (i.e., report condition), while on the other half of trials they refrained from reporting about their experiences (i.e., no-report condition). We used electroencephalography to examine how visibility interacts with reporting by measuring the P3b event-related potential, one of the proposed canonical "signatures" of conscious processing. Overall, we found a robust P3b in the report condition, but no P3b whatsoever in the no-report condition. This finding suggests that the P3b itself is not a neural signature of conscious processing and highlights the importance of carefully distinguishing the neural correlates of perceptual awareness from postperceptual processing.

Late cortical potentials are not a reliable marker of somatosensory awareness

“…The P300 has repeatedly been demonstrated to depend on report requirements in visual tasks (Cohen et al, 2020;M. Pitts, Padwal, Fennelly, Martinez, & Hillyard, 2014;Schlossmacher et al, 2020) and we show that the same is true in the somatosensory domain.…”

“…Most notably, in a series of studies, Pitts and colleagues have demonstrated that the visual P300 only indexes conscious perception when stimuli are reported, i.e. when 3 they are behaviourally relevant to the task (Cohen, Ortego, Kyroudis, & Pitts, 2020;M. A. Pitts, Metzler, & Hillyard, 2014;Schlossmacher, Dellert, Pitts, Bruchmann, & Straube, 2020).…”

Growing evidence for separate neural mechanisms for attention and consciousness

“…No report paradigms have raised interesting questions regarding the relationship between attention and consciousness (M. A. Cohen, Ortego, Kyroudis, & Pitts, 2020;Frassle et al, 2014;Montemayor & Haladjian, 2019;Wilke et al, 2009). For example, eliminating report also challenges whether the (low frequency) gamma activity that has been associated with consciousness might be related to post-perceptual decision making and/or motor planning instead (Pitts, Padwal, Fennelly, Martinez, & Hillyard, 2014).…”

Representational Dynamics Preceding Conscious Access

“…Thus, AB-related differences in late-stage T1 processing are not consistently observed across studies. Notably, a novel line of evidence suggests that the P3b component does not track perception and encoding, but rather post-perceptual processes (e.g., decision making) (Cohen et al, 2020;Pitts, Martínez, & Hillyard, 2012;Pitts, Padwal, Fennelly, Martínez, & Hillyard, 2014).…”

“…Awareness of stimuli such that they can be reported is typically associated with a late (300-500ms) broadly distributed positive P3 ERP component (Cohen, Ortego, Kyroudis, & Pitts, 2020;Dehaene & Changeux, 2011;Derda et al, 2019;Sigman & Dehaene, 2008). For example, it has been shown that only seen T2s elicit a P3 (Vogel, Luck, & Shapiro, 1998).…”