Disentangling neural correlates of consciousness and task relevance using EEG and fMRI
How does our brain generate consciousness, that is, the subjective experience of what it is like to see face or hear a sound? Do we become aware of a stimulus during early sensory processing or only later when information is shared in a wide-spread fronto-parietal network? Neural correlates of consciousness are typically identified by comparing brain activity when a constant stimulus (e.g., a face) is perceived versus not perceived. However, in most previous experiments, conscious perception was systematically confounded with post-perceptual processes such as decision-making and report. In this talk, I will present recent EEG and fMRI studies dissociating neural correlates of consciousness and task-related processing in visual and auditory perception. Our results suggest that consciousness emerges during early sensory processing, while late, fronto-parietal activity is associated with post-perceptual processes rather than awareness. These findings challenge predominant theories of consciousness and highlight the importance of considering task relevance as a confound across different neuroscientific methods, experimental paradigms and sensory modalities.
Rule learning representation in the fronto-parietal network
We must constantly adapt the rules we use to guide our attention. To understand how the brain learns these rules, we designed a novel task that required monkeys to learn which color is the most rewarded at a given time (the current rule). However, just as in real life, the monkey was never explicitly told the rule. Instead, they had to learn it through trial and error by choosing a color, receiving feedback (amount of reward), and then updating their internal rule. After the monkeys reached a behavioral criterion, the rule changed. This change was not cued but could be inferred based on reward feedback. Behavioral modeling found monkeys used rewards to learn the rules. After the rule changed, animals adopted one of two strategies. If the change was small, reflected in a small reward prediction error, the animals continuously updated their rule. However, for large changes, monkeys ‘reset’ their belief about the rule and re-learned the rule from scratch. To understand the neural correlates of learning new rules, we recorded neurons simultaneously from the prefrontal and parietal cortex. We found that the strength of the rule representation increased with the certainty about the current rule, and that the certainty about the rule was represented both implicitly and explicitly in the population.
Networks for multi-sensory attention and working memory
Converging evidence from fMRI and EEG shows that audtiory spatial attention engages the same fronto-parietal network associated with visuo-spatial attention. This network is distinct from an auditory-biased processing network that includes other frontal regions; this second network is can be recruited when observers extract rhythmic information from visual inputs. We recently used a dual-task paradigm to examine whether this "division of labor" between a visuo-spatial network and an auditory-rhythmic network can be observed in a working memory paradigm. We varied the sensory modality (visual vs. auditory) and information domain (spatial or rhythmic) that observers had to store in working memory, while also performing an intervening task. Behavior, pupilometry, and EEG results show a complex interaction across the working memory and intervening tasks, consistent with two cognitive control networks managing auditory and visual inputs based on the kind of information being processed.