(Warning: neuroscience weeds)
Stanislas Dehaene recently called attention to a paper in Nature studying the brain dynamics of something becoming conscious. The study supports the global neuronal workspace theory that consciousness involves “bifurcation” dynamics, an “ignition”, a phase transition between preconscious and conscious processing. Prior to the transition, the processing is feedforward and fleeting. After the transition, it becomes more recurrent and sustained. (Across the span of hundreds of milliseconds.)
One issue that has become an ongoing controversy is to what extent the sustained activity represents report or behavioral decision making instead of just conscious access of the information. In order to control for that, various no-report paradigms have been developed. This study uses one. The percept being studied was a French vowel sound communicated at various signal to noise ratios. In half the trials, the subjects were asked to report when they heard the vowel. In the other half, they weren’t asked to report and were given unrelated tasks to perform. The order was varied up in order to control for report behavior from the active report trials spilling over into the passive ones.
In both the active and passive trials, the bifurcation dynamics were observed. (Although the “observation” involved a lot of analysis, which is described in the paper.) However, what I find interesting is the variances in activation between the active and passive trials, a difference that seems compatible with the results of other recent studies showing that the P300 event isn’t a clear indicator of conscious access.
The activations from the passive trials seem much more localized and briefer. To some extent, this should be expected since the participants’ attention was focused on an unrelated task. If the sound made it into their consciousness, we wouldn’t expect it to be there for long or make much of an impact. On the other hand, it seems to indicate that the idea of an all or nothing global dynamic as to what makes it into consciousness is too simple.
To be clear, while it’s more localized than the active version, it’s still much broader than just the local auditory cortex, so this doesn’t seem like a validation of local recurrent processing theory. There seems to be widespread activation of the temporal lobe (likely including the hippocampus) and even some of the frontal lobe, although the authors admit that the frontal lobe activity could be an artefact of their analysis.
The authors, noting this difference in scope, suggest that prior to the global workspace, there may be a smaller scoped range of activity, which they suggest calling the global playground.
The present results indicate that covert conscious access might be subtended not by a global workspace, but rather by a subset of it, which we may term a “global playground”. This “global playground” would be a broad network of areas among which sensory representations are shared and maintained for several hundreds of milliseconds, thus offering wider cognitive possibilities than automatic unconscious processing, but with no specific agenda. When a task is required, this global playground is augmented by decision-making processes and turns into a global workspace.
This is an interesting idea, but I’m left wondering just how global the playground is, and whether there couldn’t be multiple playgrounds happening at the same time. The bifurcation dynamics seem to pull us away from Dennett’s multiple drafts model, where there is no clear consciousness finish line, and whether something makes it into consciousness is an assessment we can only make after it’s become reportable. On the other hand, the limited scope seems to indicate his version might yet have more life in it.
In any case, it seems to indicate that things are more complex than straightforward global workspace theory implies. Unless of course I’m missing something?