There has been an enormous wealth of theories about consciousness,
but I think that very few are valid or even useful. – Stanislas Dehaene
In 2009, neuroscientist Stanislas Dehaene spoke at an EDGE meeting in Paris. His topic in his presentation, “Signatures of Consciousness,” was the question of the point at which consciousness occurs.
His report was a summary of the insights his team had gathered in a decade of empirical research.
As Dehaene noted, there is a truckload of theories about consciousness, but many of them are intuitive or speculative, with little experimental evidence behind them. Dehaene’s group is trying to change that.
The central outcome of Dehaene’s research is that “in experiment after experiment, we have seen the same signatures of consciousness: physiological markers that all, simultaneously, show a massive change when a person reports becoming aware of a piece of information.” And when information is presented subliminally, below a critical level of perception, none of the “signatures of consciousness” are present.
It seems that Dehaene’s team has established the fact that consciousness has a specific cognitive threshold. At least, the simplest kind of consciousness — awareness — does.
Some people, when they talk about consciousness, think that we can only move forward if we gain an understanding of “the self” — the sense of being I or Me. But I am not going to talk about that. There is also a notion of consciousness as a “higher order” or “reflexive” state of mind — when I know that I know. Again, this meaning of the term remains very difficult to address experimentally. We have a few ideas on this, but it’s not what I want to talk about this evening.
Considering this on/off state of conscious awareness, Dehaene reports that “when the information processed exceeds a threshold for large-scale communication across many brain areas, the network ignites into a large-scale synchronous state, and all our signatures suddenly appear.”
Dehaene’s experiments are designed to make the “basic distinction between all the stimuli that enter the nervous system, and the much smaller set of stimuli that actually make it into our conscious awareness.”
By limiting his focus this way, Dehaene avoids the controversy over “self” vs. “mind” and the argument about the role of “higher order” consciousness. He asks, simply, at what point does consciousness — awareness — occur? His experiments are designed to identify the specific moment when information passes from subliminal to conscious. He leaves for others the philosophical implications of the physical findings.
In doing this, he leaves himself open to the criticism that he’s producing a relief map when we need a political map, but he seems content to sidestep all of the messy bits that follow from his data.
Based on his experimental results, Dehaene proposed that while the brain does have areas that seem to be “responsible” for processing different kinds of information, consciousness is not an agglomeration of separate, discrete areas with independent, specific functions. Instead, he argues that consciousness is the product of the brain operating as a “global neuronic workspace,” a cognitive state that arises when an information signal becomes strong enough to “go global.”
What we mean by being conscious of a certain piece of information is that it has reached a level of processing in the brain where it can be shared.
Consciousness is “a state that involves long distance synchrony between many regions.” This synchrony is dynamic, and it operates in both “directions”: a strong information signal excites “higher” activity, one aspect of which is to feed back and strengthen the original signal.
In any dynamic system that is self-connected and amplifies its own inputs, there is a nonlinear threshold. As a result, there will be either a dying out of the activation (and I claim that this state of activity correspond to subliminal processing), or there will be selfamplification and a nonlinear transition to this highup state where the incoming information becomes stable for a much longer period of time.
Dehaene emphasized that consciousness have an “all-or-none property. You either make it into the conscious workspace, or you don’t. This is a system that discretizes the inputs. It creates a digital representation out of what is initially just a probability distribution.”
And, he suggested, once consciousness is excited in one area, that response can become the stimulus for another process, making more complex cognition possible.
Once information is available in this global workspace, it can be piped to any other process. What was the output of one process can become the input of another, thus allowing for the execution of long and purely mental algorithms — a human Turing machine.
Dehaene speculates that the global workspace evolved as an advantageous solution to the isolation of different brain functions in different areas of brain anatomy. In other words, the more complex kinds of thinking we practice were not always present but were selected because they provided powerful new cognitive tools.
In the course of evolution, sharing information across the brain was probably a major problem, because each area had a specialized goal. I think that a device such as this global workspace was needed in order to circulate information in this flexible manner. It is extremely characteristic of the human mind that whatever result we come up with, in whatever domain, we can use it in other domains. It has a lot to do, of course, with the symbolic ability of the human mind. We can apply our symbols to virtually any domain.
This is highly speculative, but it’s also attractive, since it is one way of explaining the “sudden” emergence of a brain so much more complex and powerful than the brains of other primates.
In upcoming articles, I want to look at two related topics. One, Michael Gazzaniga’s complementary belief that human brains are not “just like” other mammal brains. And two, V. S. Ramachandran’s cautionary assertion that mapping the brain can not bridge the gap between one person and another’s experiences of selfhood.