Global workspace theory (GWT) is the proposition that consciousness is composed of contents broadcast throughout the brain. Various specialty processes compete for the limited capacity of the broadcasting mechanisms, to have their content broadcast to the all the other specialty processes.
Global neuronal workspace (GNW) is a variant of that theory, popularly promoted by Stanislas Dehaene, which I’ve covered before. GNW is more specific than generic GWT on the physical mechanisms involved. It relies on empirical work done over the years demonstrating that conscious reportability involves wide scale activation of the cortex.
One of the observed stages is a massive surge about 300 milliseconds after a stimulus, called the P3b wave. Previous work seemed to establish that the P3b wave is a neural correlate of consciousness. Dehaene theorized that it represents the stage where one of the signals achieves a threshold and wins domination, with all the other signals being inhibited. Indeed, the distinguishing mark of the P3b is that it is massively negative in amplitude, indicating that most of it comes from inhibitory action.
The P3b has been replicated extensively and been seen as a pretty established phenomenon associated with attention and consciousness. But this is science, and any result is always provisional. Michael Cohen and colleagues have put out a preprint of a study that may demonstrate that the P3b wave is not associated with conscious perception, but with post perceptual processing.
The study tests the perception of subjects, showing various images while measuring their brain waves via EEG. Using a no-report protocol, in half of the tests, the subjects were asked to report on whether they saw something, but in the other half they were not asked to report. Crucially, the P3b wave only manifested in the reported cases, never in the non-report ones, even when the non-report image were exactly the same as the ones that did generate affirmative reports.
To control for the possibility that the subjects weren’t actually conscious of the image in the non-report cases, the subjects were given a memory test after a batch of non-report events, checking to see what they remember perceiving. Their memories of the perception correlated with the results in the report versions.
So, the P3b wave, a major piller of GNW, may be knocked down. The study authors are careful to make clear that this does not invalidate GWT or other cognitive theories of consciousness. They didn’t test for all the other ways the information may have propagated throughout the cortex. Strictly speaking, it doesn’t even invalidate GNW itself, but it does seem to knock out a major piece of evidence for it.
However, this is a more interesting discussion if we ask, what would it mean if all cortical communication beyond the sensory regions were ruled out, that the ability to acquire a memory of a sight only required the local sensory cortices? It might seem like a validation of views like Victor Lamme’s local recurrent processing theory, which holds that local processing in the sensory cortices is sufficient for conscious perception.
But would it be? Dehaene, when discussing his theory, is clear that it’s a theory of conscious access. For him, something isn’t conscious until it becomes accessible by the rest of the brain. Content in sensory cortices may form, but it isn’t conscious until it’s accessible. Dehaene refers to this content as preconscious. It isn’t yet conscious, but it has the potential to become so.
In that view, the content of what the subjects perceived in the non-report tests may have been preconscious, unless and until their memories were probed, at which point it became conscious.
This may be another case where the concept of consciousness is causing people to argue about nothing. If we describe the situation without reference to it, the facts seem clear.
Sensory representations form in the local sensory cortex. A temporary memory of that representation may persist in that region, so if probed soon enough afterward, a report about the representation can be extracted from it. But until there is a need for a report or other usage, it is not available to the rest of the system, and none of the activity, including the P3b, normally associated with that kind of access is evident.
This reminds me of Daniel Dennett’s multiple drafts theory (MDT) of consciousness. MDT is a variant of GWT, but minus the idea that there is any one event where content becomes conscious. It’s only when the system is probed in certain ways that one of the streams, one of the drafts, become selected, generally one of the ones that has managed to leave its effects throughout the brain, that has achieved “fame in the brain.”
In other words, Dennett denies that there is any one finish line where content that was previously unconscious becomes conscious. In his view, the search for that line is meaningless. In that sense, the P3b wave may be a measure of availability, but calling it a measure of consciousness is probably not accurate. And it’s not accurate to say that the Lamme’s local recurrent processing is conscious, although it’s also not accurate to relegate it completely to the unconscious. What we can say is that it’s at a particular point in the stream where it may become relevant for behavior, including report.
Maybe this view is too ecumenical and I’m papering over important differences. But it seems like giving up the idea of one finish line for consciousness turns a lot of theories that look incompatible into models of different aspects of the same overall system.
None of this is to say that GWT or any of its variants might not be invalidated at some point. These are scientific theories and are always subject to falsification on new data. But if or when that happens, we should be clear about exactly what is being invalidated.
Unless of course I’m missing something?