This post examines the paper: “Are There Levels of Consciousness?” written by
Tim Bayne, Jakob Hohwy, and Adrian M. Owen, that appeared in Trends in Cognitive Sciences, June 2016, Vol. 20, No. 6. The paper is described as opinion and for me bridges ideas of predictive processing with some of the ideas of Stanislas Dehaene. Jakob Hohwy is an important describer of predictive processing. The paper argues that the levels-based or continuum based framework for conceptualizing global states of consciousness is untenable and develops in its place a multidimensional account of global states.
Consciousness is typically taken to have two aspects: local states and global states. Local states of consciousness include perceptual experiences of various kinds, imagery experiences, bodily sensations, affective experiences, and occurrent thoughts. In the science of consciousness local states are usually referred to as ‘conscious contents. By contrast, global states of consciousness are not typically distinguished from each other on the basis of the objects or features that are represented in experience. Instead, they are typically distinguished from each other on cognitive, behavioral, and physiological grounds. For example, the global state associated with alert wakefulness is distinguished from the global states that are associated with post-comatose conditions.
The authors suggest that to describe global states as levels of consciousness is to imply that consciousness comes in degrees, and that changes in a creature’s global state of consciousness can be represented as changes along a single dimension of analysis. Bayne, Hohwy, and Owen see two problems with this. One person can be conscious of more objects and properties than another person, but to be conscious of more is not to be more conscious. A sighted person might be conscious of more than someone who is blind, but they are not more conscious than the blind person is. The second problem that they see with the level-based analysis of global states is that there is good reason to doubt whether all global states can be assigned a determinate ordering relative to each other. The authors provide the example of the relationship between the global conscious state associated with rapid eye movement (REM) sleep and that which is associated with light levels of sedation. They do not believe that one of these states must be absolutely ‘higher’ than the other. Perhaps states can be compared with each other only relative to certain dimensions of analysis: the global state associated with REM sleep might be higher than that associated with sedation on some dimensions of analysis, whereas the opposite might be the case on other dimensions of analysis (Figure 1A).
The authors recognize two clear dimensions, but suggest there are likely several more. The first is gating. In some global states the contents of consciousness appear to be gated in various ways, with the result that individuals are able to experience only a restricted range of contents. MCS patients, patients undergoing absence seizures, and mildly sedated individuals can consciously represent the low-level features of objects, but they are typically unable to represent the categories to which perceptual objects belong. Thus, the gating of conscious contents is likely to provide one dimension along which certain global states can be hierarchically organized. The second dimension of consciousness is often captured by saying that the contents of consciousness are globally available for the control of thought and action. However, there is good reason to think that it is compromised in a number of pathologies of consciousness. For example, patients undergoing absence seizures can engage in perceptual-driven motor responses even though their capacities for reasoning, executive processing, and memory consolidation are typically limited. With respect to this dimension, the global state of consciousness associated with the EMCS is ‘higher’ than that which is associated with the MCS, for EMCS patients have access to a wider range of cognitive and behavioral consuming systems than MCS patients do.
Beyond the dimensions of gating of contents and the availability associated with consciousness, the authors suggest there might there be a role for attention in structuring global states. There is also the question of the possibility of interaction between some of the dimensions that structure consciousness. Although some dimensions may be completely independent of each other, others are likely to modulate each other. For example, there might be interactions between the gating of contents and functionality such that consciousness cannot be high on the gating dimension but low on certain dimensions of functionality (Figure 1C).
This idea that global states of consciousness are best understood as regions in a multidimensional space seems to me a natural progression as we learn more about consciousness and its underpinnings. An example is the time when you are completely immersed in some task and you don’t notice time passing or who walked by. Your attention is completely focused and gated so that you are missing other things. It is not a higher level of consciousness, but a different level of consciousness. The spotlight is focused on a smaller area. The light itself is not any brighter. At the same time, the argument that Bayne, Hohwy and Owen are making seems to be focused at very limited consciousness. Most of us just see a sleeping person as unconscious without an active global neuronal workspace. We do not see a person as conscious until some threshold or phase change occurs so that the light is brighter so that the availability is greater. There must be some level of error coming back from our predictions. Several previous posts including Consciousness. Confessions of a Romantic Reductionist, The Global Neuronal Workspace, and Dehaene: Consciousness and Decision Making, have looked at consciousness. This paper did not address the consciousness of other animals. It also did not address Intuition which is often considered unconscious in some ways since it is typically effortless as we perceive it. Global availability seems important to the idea. Of course, as you develop expertise, global availability is not so necessary for certain subjects. Auto-pilot can handle normal situations once you have expertise so maybe we all have different conscious realms since we have different expertise.
Frankly, I doubt that many would argue that consciousness has only a single dimension. Dehaene may ignore multiple dimensions, but I would suggest that he does this to make the idea more understandable to laymen.