In the modern neuroscientific study of consciousness, most of the key experiments can be boiled down to a simple question: What is the difference in the brain between unconscious and conscious processing? While many theories of consciousness disagree about the specifics, they all agree that some types of neural activity reflect unconscious processing, while other types result in conscious experience. This transition from unconscious to conscious processing is sometimes called a “bifurcation”. New research from a team led by Michael Pitts at Reed College and Michael Cohen at Amherst College is aimed at measuring the neural dynamics underlying this bifurcation.

The team’s experiments focus on visual perception in healthy human subjects. The main predictions are as follows: When the intensity of a stimulus (such as a flash of light) is manipulated in a linear fashion, unconscious sensory processing should show corresponding linear changes, whereas the conscious processing looks more like an on/off switch. But scientists don’t yet know exactly when or where these different kinds of processing take place.

Researchers know that subjects’ reports about what they consciously see show nonlinear patterns (that look like “S-shaped” curves in neuroimaging data), but conscious vision occurs whether or not we reflect on it or report our experiences to others. At the same time, when a subject reacts to the stimulus to tell us what they saw, various parts of the brain become active, so it’s very difficult to know what brain processes reflect their conscious experience and which ones accompany their act of reporting what they have seen. Thus, it is crucial to measure conscious perception independently from subjects’ reports.

With a set of experiments, this new project will measure brain activity with non-invasive EEG using two new tests that include both report and no-report conditions. In the report conditions, the results should closely replicate previous studies. In the new no-report conditions, researchers will assess whether (and if so, when and where) bifurcated neural patterns (that look more like on/off signals) are generated. The results will inform leading theories of consciousness that posit a bifurcation between unconscious and conscious processing at different time-points and in different brain regions.