Launching awareness and chasing consciousness: Unconscious processing of causality and animacy.

The mystery of conscious visual experience has intrigued many philosophers, psychologists, and neuroscientists for decades, if not centuries. One of the insights research on this topic has yielded is that there is no one-to-one correspondence between physical visual input and our corresponding perceptual experience. Indeed, in some specific situations visual input can be presented to the observer, while remaining invisible. The ultimate goal of this dissertation was to achieve a better understanding of the representational nature of a perceptually suppressed visual stimulus. More specifically, the overarching research question was: “To what extent does perceptual organization take place in the visual system for stimuli rendered invisible through continuous flash suppression?”.

Indeed, throughout this PhD we have relied on a paradigm called “continuous flash suppression (CFS)” to manipulate the contents of visual awareness. The research presented in this dissertation is divided into two main parts, the first part being oriented to more theoretical aspects regarding the mechanisms of suppression through CFS while the second part focuses on the representation of the suppressed stimulus.

The first two chapters present two studies on the determinants of effective suppression through CFS and the temporal characteristics of the time series of suppression durations. In Chapter 2, we show that feature overlap between the mask and suppressed stimulus is more important to enable effective suppression than the dynamic nature of the CFS mask. In Chapter 3, we report that suppression durations are not independent, yet show small, but significant sequential correlations, implying that CFS elicits a hallmark characteristic of other multistable phenomena, perceptual memory. Based on the results of these two studies, we conclude that CFS relies on mechanisms similar to binocular rivalry, and that it might constitute a stronger form of binocular rivalry.

In the following seven chapters, which comprise the second part of the dissertation, we present seven studies that tap into the representation of the perceptually suppression stimulus. In Chapter 4, we consider whether the surface induced by the classic Kanizsa stimulus is represented during suppression. In Chapter 5, we ask whether a supraliminal auditory stimulus can influence suppression strength of a perceptually suppressed looming stimulus. In Chapters 6 to 8, we show that launching events (an exemplary stimulus of causality perception) enter awareness faster than pass or pseudo-launch events, biological motion stimuli do not yield an inversion effect, and that faces presented in familiar configurations break suppression faster, respectively. Finally, Chapters 9 and 10 consider complex, high-level processing under CFS. In Chapter 9, we fail to replicate a previously observed result in which incongruent scenes broke suppression faster compared to congruent ones. In Chapter 10, we ask whether words are processed during suppression, but observe neither a word frequency nor a word type (word vs. pseudo-word) effect.

In sum, the results presented in the second part of this dissertation show very limited visual processing during CFS, the implications of which are discussed in Chapter 11.