A couple of years ago, when writing about panpsychism, I introduced a five layer conception of consciousness. The idea back then was to show a couple of things.
One was that very simple conceptions of consciousness, such as interactions with the environment, were missing a lot of capabilities that we intuitively think of as belonging to a conscious entity.
But the other was to show how gradually the emergence of all these capabilities were. There isn’t a sharp objective line between conscious and non-conscious systems, just degrees of capabilities. For this reason, it’s somewhat meaningless to ask if species X is conscious, as though consciousness is something they either possess or don’t. That’s inherently dualistic thinking, essentially asking whether or not the system in question has a soul, a ghost in the machine.
I’ve always stipulated that this hierarchy isn’t itself any new theory of consciousness. It’s actually meant to be theory agnostic, at least to a degree. (It is inherently monistic.) It allows me to keep things straight, and can serve as a kind of pedagogical tool for getting ideas across. And I’ve always noted that it might change as my own understanding improved.
Well, although disagreeing with him on a number of important points, after reading Joseph LeDoux’s account of the evolution of the mind, as well as going through a lot of papers in the last year, along with many of the conversations we’ve had, it’s become clear that my hierarchy has changed.
Here’s the new version:
- Reflexes and fixed action patterns. Automatic reactions to sensory stimuli and automatic actions from innate impulses. In biology, these are survival circuits which can be subject to local classical conditioning.
- Perception. Predictive models built from distance senses such as vision, hearing, and smell. This expands the scope of what the reflexes are reacting to. It also includes bottom-up attention, meta-reflexive prioritization of what the reflexes react to.
- Instrumental behavior / sentience. The ability to remember past cause and effect interactions and make goal driven decisions based on them. It is here where reflexes start to become affects, dispositions to act rather than automatic action. Top down attention begins here.
- Deliberation. Imagination. The ability to engage in hypothetical sensory-action scenario simulations to solve novel situations.
- Introspection. Sophisticated hierarchical and recursive metacognition, enabling mental-self awareness, symbolic thought, enhancing 3 and 4 dramatically.
Note that attention has been demoted from a layer in and of itself to aspects of other layers. It rises through them, increasing in sophisticating as it does, from early bottom up meta-reflexes, to deliberative and introspective top down control of focus.
Note also that I’ve stopped calling the fifth layer “metacognition”. The reason is a growing sense that primal metacognition may not be as rare as I thought when I formulated the original hierarchy, although the particularly sophisticated variety used for introspection likely remains unique to humans.
Some of you who were bothered by sentience being so high in the hierarchy might be happy to see it move down a notch. LeDoux convinced me that what I was lumping together under “Imagination” probably needed to be broken up into at least a couple of layers, and I think sentience, affective feelings, start with the lower one, although they increase in sophistication in the higher layers.
I noted that mental-self awareness is in layer 5. I don’t specify where body-self awareness begins in this hierarchy, because I’m not sure where to put it. I think with layer 2, the system has to have a body-self representation in relation to the environment, so it’s tempting to put it there, but putting the word “awareness” at that layer feels misleading. (I’m open to suggestions.)
It seems clear that all life, including plants and unicellular organisms, have 1, reflexes.
All vertebrates, arthropods, and cephalopods have 2, perception. It’s possible some of these have a simple version of 3, instrumental behavior. (Cephalopods in particular might have 4.)
All mammals and birds have 3.
Who has 4, deliberation, is an interesting question; LeDoux asserts only primates, but I wouldn’t be surprised if elephants, dolphins, crows, and some other species traditionally thought to be high in intelligence show signs of it. And again, possibly cephalopods.
And only humans seem to have 5.
In terms of neural correlates, 1 seems to be in the midbrain and subcortical forebrain regions. 2 is in those regions as well as cortical ones. LeDoux identifies 3 as being subcortical forebrain, although I suspect he’s downplaying the cortex here. 4 seems mostly a prefrontal phenomenon, and 5 seems to exist at the very anterior (front) of the prefrontal cortex.
Where in the hierarchy does consciousness begin? For primary consciousness, my intuition is layer 3. But the subjective experience we all have as humans requires all five layers. In the end, there’s no fact of the matter. It’s a matter of philosophy. Consciousness lies in the eye of the beholder.
Unless of course, I’m missing something? What do you think? Is this hierarchy useful? Or is it just muddying the picture? Would a different breakdown work better?