Neural Construction of Conscious Perception

Abstract

Out of a myriad of sensory stimulations, our brain constructs a unified, self-consistent reality that we consciously experience. Little is known about how or where in the brain’s processing stream of physical input a conscious percept emerges into awareness. A remarkable property of conscious perception is that even though external input is often ambiguous, the perceptual interpretation of the world that our brain generates is consistent across multiple layers of representation, e.g., figure-ground segmentation and object identity. We thus set out to study how the interaction between different nodes in the brain generates and propagates new conscious percepts. Since the code of object identity is already well-understood, in particular for faces as reviewed in this thesis, we decided to get a handle on segmentation signals first. It turned out that consistent segmentation signals are hard to find, however, we found functionally defined modules in the brain that contained consistent cells from which figure-ground signals can be decoded. We next investigated whether face cells in object recognition areas actually encode the conscious percept of a face or are just passive filters of visual input. To distill conscious perception from other cognitive processes, such as decision making, introspection, and reporting of the percept, which often accompany new conscious percepts, we developed a no-report binocular rivalry paradigm that relies on an active fixation task rather than report, and therefore eliminates these confounding factors. We found that face patches in inferotemporal cortex indeed encode the conscious percept of a face. Using novel high-yield electrodes, we were able to decode what the animal was consciously perceiving at a given time. Preliminary and future experiments of population recordings from multiple nodes of the cortical hierarchy simultaneously promise to go beyond correlates of consciousness and reveal the mechanisms of how and where conscious percepts are constructed.