The levels of perceptual processing and the neural correlates of increasing subjective visibility.

Transitions from unconscious to conscious perception may be more gradual for low-level visual features and more dichotomous for high-level features. In an fMRI study using backward masking, participants reported a target digit's magnitude (high-level) or its color (low-level) and rated visibility. Intermediate visibility was reported more often in the low-level task, supporting the levels-of-processing hypothesis. Visible targets activated insulo-fronto-parietal regions in both tasks, while visual areas showed higher activity in the low-level task across all visibility levels. The findings suggest that attentional modulation of feature-representing brain regions mediates how processing level shapes conscious perception.

Study at a glance

Abstract

According to the levels-of-processing hypothesis, transitions from unconscious to conscious perception may depend on stimulus processing level, with more gradual changes for low-level stimuli and more dichotomous changes for high-level stimuli. In an event-related fMRI study we explored this hypothesis using a visual backward masking procedure. Task requirements manipulated level of processing. Participants reported the magnitude of the target digit in the high-level task, its color in the low-level task, and rated subjective visibility of stimuli using the Perceptual Awareness Scale. Intermediate stimulus visibility was reported more frequently in the low-level task, confirming prior behavioral results. Visible targets recruited insulo-fronto-parietal regions in both tasks. Task effects were observed in visual areas, with higher activity in the low-level task across all visibility levels. Thus, the influence of level of processing on conscious perception may be mediated by attentional modulation of activity in regions representing features of consciously experienced stimuli.