When I was writing about Consciousness and the Brain by Stanislas Dehaene, I was struck by the question
is it possible that impairments that we think of as impairments of consciousness, are actually impairments in some of these necessary preconditions which occur via preconscious/subliminal processes
This is of special concern to me as I’m working on a system to assist those with cognitive disabilities perform their daily “maintenance tasks” by reminding them via subtle, “ambient cues.”
I’m going to proceed on the incompletely ungrounded assumption that all of our cognitive processes have a similar “hierarchical stack” organization, pushing a bit on the implications and the empirical questions that arise.
First, what do we know?
The Visual Cortex
The visual cortex is one of the most thoroughly studied systems in the mammalian brain. In performing object identification/recognition, it exhibits a mix of bottom up and top down processing. The bottom up processes calculate low level features based upon retinal data (stabilized for saccades and lighting variations) which become more complex (edges -> corners -> areas of constant color/texture) as they are combined by processes in higher levels of the brain (the parts that are more removed from the retina).
Top down processes perform the complementary roles of disambiguation and directing attention
The deployment of attention to a particular location in space (spatial attention) or to a particular feature or object (feature-based or object-based attention) can occur either by virtue of a stimulus physical salience (exogenous, involuntary or bottom-up attention) or according to internal, behavioral goals (endogenous, voluntary or top-down attention).
Attending to particular areas in the visual field, specific types of objects and filtering out transients and mistaken identification.
Visual Reflex Reactions
Even reflex responses to visual stimuli, which are much, much, quicker than top down processes have affordances for top down modulation, allowing reflexes to be modulated by expectations. The basis for this appears to be the amygdala which has connectivity affording more conscious control 1
A recent review of grid cells 2 Outlined similar structures in multiple sensory modalities.
“Box 1: Hierarchy of cortical representation” explicitly draws comparison to the processing hierarchy of the visual and auditory systems:
- The first level is very much a direct map of the sensory input.
- A second level combines these simple features into compound features.
- The third level represents more complex maps, e.g., time differences between the two ears; stereo maps of the visual field.
- The fourth layer becomes more “thought oriented” and is the layer at which grid cells operate (grid cells are neurons that fire when an animal traverses a specific locations — note grid cells form the basis of another representational hierarchy, which, for mice at least, goes on to incorporate such features as head direction)
What we’re presented with are multiple moderately independent systems, operating primarily in a bottom up mode, with top down affordances for direction and disambiguation.
Top Down Processes
Conscious processing, however, inherently consists of some top down communication from the “conscious” layer to perceptual and motor layers.
Edelman (& later Edelman and Tononi) 3 is one of the best known in this space with his delineation of the role of reentrant connections for reinforcement and synchronization across modalities and scales. In Edelman’s model, the top-down processes involve not only conscious direction, but also cross modal communication and synchronization.
Dehaene’s work, exemplified in his recent Neuron paper 4 builds upon the work of Edelman, and others, to develop one of the most comprehensive models of consciousness to date. Such detailed models have become possible since researchers have recently identified a strong marker for conscious processing. This marker is very distinct: a significant strengthening of global communication between multiple parts of the brain.
If you look at the figures in the referenced papers, it’s as if all the relevant parts of the brain suddenly light up upon becoming conscious of an item.
Such an unambiguous marker allows researchers to clearly delineate conscious from non-conscious activity with an number of surprising results, e.g., some semantic disambiguation and some processing of transitive properties do not involve conscious activity
Transitive inferences can also be deployed non-consciously: after non-conscious exposure to arbitrary word pairs such as ‘winter-red’ and ‘red- computer’, word association effects generalize to non- adjacent pairs (‘winter-computer’), a transitive link mediated by the hippocampus . 5
The thing is, if consciousness is a phenomenon identified by its global behavior, and this global behavior relies upon functioning components, some cognitive disabilities may indicate component failure, rather than the failure of the (global) conscious processes. Since many of the processes involved in activity cueing are potentially dependent upon particular components to function, e.g., procedural memory, it’s still an open as to whether pre/sub conscious activity cueing is possible in these individuals. The question then becomes, how much cueing is possible for those with cognitive disabilities, and even if it is possible, how effective can it be? At the moment I don’t have the data to answer this question with any confidence. Certainly the existence of significant, separate preconscious activity indicates that it is possible that cueing can trigger adaptive/proactive responses in those with cognitive disabilities, but it a literature review, coupled with empirical study will likely be required.
The encouraging part so far is that so much processing occurs without conscious activity, that it doesn’t seem a priori impossible that such cues could be effective.
I’m going to do a more thorough search of what is known of the brain areas affected by specific disabilities and their impact upon available cues/cued activities, and will summaries in a later post.
- The Amygdaloid Complex: Anatomy and Physiology P. SAH, 20030 ↩
- Moser, E. I., Roudi, Y., Witter, M. P., Kentros, C., Bonhoeffer, T., & Moser, M.-B. (2014). Grid cells and cortical representation. Nature Publishing Group, 15(7), 466–481. http://doi.org/10.1038/nrn3766 ↩
- Edelman, G., & Tononi, G. (1998). Consciousness and complexity. Science. ↩
- Dehaene, S., & Changeux, J.-P. (2011). Experimental and theoretical approaches to conscious processing. Neuron, 70(2), 200–227. http://doi.org/10.1016/j.neuron.2011.03.018 ↩
- Dehaene, S., Charles, L., King, J.-R., & Marti, S. (2014). Toward a computational theory of conscious processing. Current Opinion in Neurobiology, 25, 76–84. http://doi.org/10.1016/j.conb.2013.12.005 ↩