I just finished reading Stanislas Dehaene’s Consciousness and the Brain. Dehaene is a French psychologist and cognitive neuroscientist who is bullish on the idea of consciousness being something that can be scientifically investigated. It’s an interesting book, one that I recommend for anyone interested in the science of consciousness.
Dehaene accomplishes his scientific investigation by focusing on what he calls “conscious access”, which is roughly equivalent to Ned Block’s access consciousness and David Chalmers’ easy problems, that is, the ability of our minds to hold content available for reasoning, decision making, and verbal report. He holds this distinct from the sense of self and metacognition, which he sees being built on top of it.
And as I mentioned in the last post, he is not concerned with phenomenal awareness, typically characterized as raw experience. He actually barely mentions it in the book, being largely dismissive of it. He characterizes the hard problem as ill defined, and the idea of qualia, pure mental experiences detached from any information processing role, as an idea that in time will go the way of vitalism. (Those of you who know me may wonder if I’m projecting my own views here, but no, my views in this area just happen to match his pretty closely, right down to using similar language.)
After discussing the empirical tests able to identify what kinds of stimulus lead to conscious perception, as opposed to unconscious ones, he identifies four signatures of conscious access:
- The amplification of an early sensory signal leading it to an “ignition” of circuits in the parietal and prefrontal circuits
- The appearance of a slow P3 wave in an electroencephalogram, a slow massive wave throughout the parietal and prefrontal regions about 300 milliseconds after the stimulus
- A late and sudden burst of high frequency oscillations, gamma band power
- A synchronization of information exchanges across distant brain regions with oscillations in sync
All of this is referred to as “the conscious avalanche”, the widespread activation of neural activity in a network including the prefrontal and parietal regions whenever a perception makes it into consciousness.
Which leads to Dehaene’s theory of consciousness, the global neuronal workspace, a variation of Barnard Baars’ global workspace theory. The main idea is summed up by Dehaene as:
When we say that we are aware of a certain piece of information, what we mean is just this: the information has entered into a specific storage area that makes it available to the rest of the brain. Among the millions of mental representations that constantly crisscross our brains in an unconscious manner, one is selected because of its relevance to our present goals. Consciousness makes it globally available to all our high-level decision systems. We possess a mental router, an evolved architecture for extracting relevant information and dispatching it.
…According to this theory, consciousness is just brain-wide information sharing. Whatever we become conscious of, we can hold it in our mind long after the corresponding stimulation has disappeared from the outside world. That’s because our brain has brought it into the workspace, which maintains it independently of the time and place at which we first perceived it. As a result, we may use it in whatever way we please. In particular, we can dispatch it to our language processors and name it; this is why the capacity to report is a key feature of a conscious state. But we can also store it in long-term memory or use it for our future plans, whatever they are. The flexible dissemination of information, I argue, is a characteristic property of the conscious state.
Dehaene, Stanislas. Consciousness and the Brain (p. 163-164). Penguin Publishing Group. Kindle Edition.
The workspace is held to be in a network of regions including the prefrontal cortex, the anterior cingulate cortex, and parietal regions. I’ve discussed before that the middle parietal regions are the central integration of sensory association processing in the cortex, and the prefrontal cortex is the central integration of motor planning, so it makes sense that these regions would be highly interconnected and interactive, with ongoing recurrent loops of communication between the sensorium and the motorium.
I’ve also written about the central importance of the prefrontal cortex in imagination, the simulation and evaluation of action scenarios. This fits with Dehaene’s view of the central importance of this region for the workplace. Indeed, Dehaene implies that conscious access is centered on the prefrontal cortex, which fits with its role as the executive center of the brain.
So this theory appears to have a lot going for it. And viewed from a purely instrumental perspective, it seems predictive of a lot of observations. Unlike Tononi’s Integration Information Theory, it doesn’t aspire to recognize consciousness in systems outside of the brain, just in the brain itself, particularly in human or primate brains. (Although Dehaene does think it could provide insights into possible architectures for consciousness in AI systems.)
And yet, like most grounded scientific theories of consciousness, I tend to think it captures aspects of the reality, but not the whole reality itself. Even if we restrict ourselves to conscious access, the descriptions of the workplace feel a bit too simple to me. It’s described like its one big thing, like a type of giant data bus.
This isn’t to say I think conscious access doesn’t involve wholesale activation of the regions that Dehaene discusses, but I’m not sure I buy the implicit description of it as one unified whole. Based on all the reading I’ve done, it strikes me more as a complex web of disparate subsystems communicating with each other, with cross talk between the streams creating an emergent thing that may resemble the global workspace, but more messy, noisy, and less coherent than the theory implies.
But maybe I’m just quibbling here. Dehaene might argue that it’s the final result that matters, and he’d be right. And the global neuronal workspace seems general enough to be compatible with a lot of observations, as well as other theories such as HOT (Higher Order Theory). I suspect before it’s over we’ll need a collection of theories to account for all observations. But only time and more research will tell.