Materialist Models of Consciousnesses
Materialism seek to explain subjective perspectives from a strictly physiological, neuronal point of view and thereby lend no creedence to the idea that consciousness is either separate from the functionalities of the body, or a fundamental property of matter. Most materialist models of consciousness therefore seek to find correlations between when consciousness is supposedly taking place and which unique parts and processes of the brain are active at that time. This ‘Correlates of Consciousness’ approach tries to pinpoint where exactly in the brain consciousness is localized and treats it like any other neurological process.
The Subjectivity Problem
While subjectivity can’t be inherently measured outside oneself, the materialist view is that since consciousness can be observed in oneself, so to the assumption is that it works similarly in others and shares similar markers. For example, even though there is no way to prove that another human being is actually subjectively thinking rather than having their brain algorithmically calculating sensory data, per materialism it is still fair to assume that since oneself thinks in a subjective manner, so to others do the same, considering their otherwise similar objective makeup. Therefore, when another person displays signs of thought that are relatable to how oneself thinks, it is useful to assume that they are actually ‘thinking’. In this way, observing ‘Correlates of Consciousness’ in other individuals seeks to pinpoint the process of consciousness.
The Global Workspace Theory
Historically, one of the most popular models of consciousness has been the “Global Workspace Theory”. This model insists that consciousness occurs anytime when neural activity is non-localized, rather than when it is strictly confined to just one brain region. Per this theory, a stimulus that is processed by the brain completely locally in merely one region would be perceived as unconscious where a stimuli that is processed and distributed to multiple areas of the brain would be perceived as conscious. Therefore, if a neural process is globally accessible and integrated, elements of conscious experience would result.
This model is enforced by studies from France’s National Institute for Health that showed that when stimuli is presented to volunteers and perceived unconsciously, there are 270 milliseconds of EEG activity followed by tempering off. However, when the stimuli is perceived as conscious, intense brain activity follows these 270 millseconds of activity. This additional EEG Signal is commonly referred to as “PB3” and is thought to be a ‘correlate of consciousness’ in the sense that when it is present, so is conscious interpretation of stimuli.
The Global Neuronal Workspace Model
A strictly neuronal variation of this theory was proposed in 2003 by researchers Dehaene and Changeux that puts forth a specific physiological process to explain the neural workings of consciousness. This model proposes that upon sensory stimuli, excitatory neurons send long distance signals through cortical to cortical spanning axons producing a pattern of activity throughout certain neurons globally in the brain. This global pattern of neural activity constitutes consciousness and is therefore directly influenced by sensory stimuli.
A Criticism of Correlates of Consciousness
One issue with the ‘Correlates of Consciousness’ approach to subjectivity is that trying to correlate the experience of consciousness and brain functionaliy is extremely difficult considering it isn’t entirely clear when consciousness is present. For example, when a person is sleeping, they are technically unconscious, though upon waking up they will have memories of having dreamt. This indicates that while sleeping, the person was in fact consciousness albeit in an altered state. Furthermore, consciousness can only be said to be happening when the neural function of memory is also taking place. For example, if while sleeping one is in fact fully conscious but in a state where they are not able to record memories, then surely upon awakening, they will report that they were not conscious while sleeping, since they wouldn’t have memories of them being conscious. Therefore, trying to pinpoint neural activities isolated to consciousness is extremely difficult considering memory retrieval would always also have to be present. This presents a fundamental problem with trying to correlate consciousness to an isolated neuronal process.