Visual awareness and the levels of processing hypothesis: A critical review.

The transition from unaware to aware visual experience may follow different patterns depending on the type of stimulus being processed. For low-level features such as stimulus energy, awareness appears to emerge gradually (graded), whereas for high-level features such as letters, words, or meaning, awareness seems to switch on abruptly (dichotomous). This review critically examines behavioral and brain-based evidence for the level of processing hypothesis, noting challenges including differences in conceptualizations, awareness scale issues, attentional confounds, and divergences in experimental factors or statistical analyses. The hypothesis is promising but requires further methodological and experimental work, especially neuroimaging studies, to clarify the neural correlates of consciousness.

Study at a glance

Abstract

Does a visual percept emerge to consciousness in a graded manner (i.e. evolving through increasing degrees of clarity), or according to a dichotomous, "all-or-none" pattern (i.e. abruptly transitioning from unawareness to awareness)? The level of processing hypothesis (LoP; B. Windey and A. Cleeremans, 2015) recently proposed a theoretical framework where the transition from unaware to aware visual experience is graded for low-level stimulus representations (i.e. stimulus "energy" or "feature" levels) whereas it is dichotomous for high-level (i.e. the perception of "letters", "words" or "meaning") stimulus perception. Here, we will critically review current behavioral and brain-based evidence on the LoP hypothesis and discuss potential challenges (such as differences in LoP conceptualizations, awareness scale related issues, attentional confounds and divergences on experimental factors or statistical analyses) which might be of use for future research within the field. Overall, the LoP hypothesis is a recent and promising proposal that attempts to integrate divergent evidence on the graded vs. dichotomous emergence of awareness debate. Whereas current evidence validates some of the assumptions proposed by the LoP account, there is still much work to do on both methodological and experimental levels. Future neuroimaging studies might help to disentangle the current complex pattern of results found in LoP studies and, importantly, shed some light on the ongoing debate about the search for the Neural Correlates of Consciousness (NCC).