Written by Brett Weiss
February 2019
A common definition of consciousness is awareness of self and the world /environment. Differing explanations of what ‘awareness’ and ‘self’ mean abound in literature on this topic. Not only that, but many scholars call the scientific attempt to explain consciousness impossible.
The most notable philosophical obstacle presented to scientists attempting to explain consciousness comes from the hard problem of consciousness. David Chalmers, a world-famous philosopher and cognitive scientist, first formulated the problem in his 1995 paper “Facing Up to the Problem of Consciousness.” The hard problem arises from science’s purported inability to explain subjectivity with the material (physical) measurements that science uses. Subjectivity refers to qualia (qualitative experience or the ‘what it’s like’ aspect of experience). Chalmers identifies as a naturalistic dualist. In essence, Chalmers believes that physical systems (brains) cause mental states. At the same time, he believes that mental states are ontologically distinct from physical systems and lack reducibility.
One can break down the hard problem with three seemingly plausible theses that lay in tension with one another: 1) All objects of physics and other natural sciences have a reducible structure that science can analyze, 2) Consciousness has something above structure and relations, and 3) The nature of consciousness can be explained with natural sciences (Loorits, 2014). Dualists, such as Chalmers, believe that the second thesis is true; and thus, thesis three must be false. Many who use science to explain consciousness, though, reject the second thesis. Hence, they believe that consciousness has a reducible structure. The following paragraphs will give a description of the work that a prominent neuroscientist has done to develop a comprehensive, neuroscientific theory of consciousness. While the debate as to whether scientific inquiry can analyze a reducible structure of consciousness or not remains, many scientists believe they have made headway in explaining this phenomenon. The purpose of the article does not entail extrapolating on the philosophical debate of materialism vs dualism but will focus on a materialistic theory that a prominent neuroscientist from Princeton University, Michael S.A. Graziano, developed with application of neuroscience principles.
Michael Graziano developed attention schema theory, which posits that awareness (a term used interchangeably with ‘consciousness’) is a simplified model of attention. Furthermore, the theory states that without the model of attention (awareness) poor control of attention and subsequent behavioral reaction occurs. In other words, awareness provides some control of attention. In order to further discuss these theses, one must define the terms ‘attention’ and ‘awareness.’
Attention has many different definitions throughout scientific literature. Graziano uses an influential theory that Desimone and Duncan (1995) put forward, ‘biased competition.’ In ‘biased competition,’ attention arises as a signal competition within the brain. Signals compete for deeper processing in the brain, which can influence behavior. The signal competition occurs at early processing stages in the central nervous system and continues through every stage. Different factors can influence or ‘bias’ the outcome of the attentional processing competition. For instance, an intense stimulus can ‘grab’ attention when it enters the retina for subsequent visual processing in a bottom-up manner. As the signals progress through the nervous system, top-down neural mechanisms increasingly influence the competition for attention. Top-down processes relate to task demands, goals, and are task relevant. Both bottom-up processing and top-down, task-related mechanisms are involved in the ‘biased competition’ for attention.
Awareness refers to the subjective state whereby someone can report that he/she perceives a stimulus. For attention schema theory, Graziano regards awareness as graded in that different degrees of confidence can be associated with the perceived stimulus. Just as attention can be graded, with more or less attention focused on a stimulus, so too can awareness, an internal model of attention.
According to the theory, the subjective report ‘I am aware of X’ involves multiple steps of neural processing. The stimulus (visual, auditory, sensory, olfactory, or taste) competes with many other stimuli for the brain’s processing resources. If stimulus X wins the competition, it gets encoded in the brain through deep processing. In order to report the subjective experience of the attended stimulus X, the brain has to compute a model of the process of attention. The model of the complex process of attention facilitates a mysterious, physically impossible property– awareness (Webb and Graziano, 2015). An example of the inaccuracy of the model in depicting attention comes from people’s perception of white light. White light reflects the full spectrum of colors in a ‘dirty’ mixture; however, the brain perceives white light as a ‘solid’ beam of whiteness, a physical impossibility. Although the models of attention (that awareness depicts) contain physical inaccuracies, their computations in the brain have been ‘good enough’ for survival throughout evolution.
In the same way that awareness depicts an inaccurate representation of external stimuli, internal stimuli give rise to the body schema, which can also contain inaccuracies. For example, after a limb (arm, forearm, leg, etc.) has been given anesthesia, individuals in experiments cannot tell that a limb has been moved. In other words, the brain does not update the body schema if the individual does not feel the limb being moved.
The brain constructs simplified models of complex processes of attention in the attention schema theory. The resulting construct, awareness, can contain any type of information that the brain pays attention to, including thoughts, emotions, and ideas. Awareness, the representation of attention, can apply to all types of information that the brain attends to.
Studies have sought to localize attention, even awareness, to certain areas of the brain. In patients with hemineglect, where damage occurs in the temporoparietal junction (on the side of the brain) on the right side, patients do not report seeing anything in their left visual field. At the same time, these patients correctly respond above chance to stimuli in the left visual field. For instance, a study was done on these patients where they had to choose between two different houses to live in, one presented in the left visual field or one presented in the right visual field. The house depicted in the left visual field was on fire. The patients performed above chance saying that they would rather live in the house on the right, even though they had no awareness of why they made that choice (they had no vision in the left visual field). This, among other sources of evidence, lead Graziano to believe that awareness arises in a converging zone of attention and sensory neural networks in the temporoparietal junction, especially on the right side of the brain. In fact, Graziano and his team have employed fMRI, measuring blood flow to areas of the brain, to perform studies whereby they have provided evidence that awareness does in fact localize to activity in the temporoparietal junction, a neural correlate of consciousness (Webb et al., 2016).
Although the debate continues as to whether consciousness or awareness actually has a reducible structure that science can explain, some neuroscientists, like Graziano, continue their research to explain this profound and fundamental phenomenon in human experience. Graziano may have already found a neural correlate of consciousness in the temporoparietal junction. He has also made a testable hypothesis about how awareness controls attention– if awareness and attention can be dissociated in research, then attention should persist in a less controlled manner on the stimulus under attention. Whether his explanations stand the test of scientific inquiry and experimentation or not, Graziano has paved the way for future scientists to use their methodologies to explain the puzzling phenomenon of consciousness.
References
1. Loorits K (2014). “Structural qualia: a solution to the hard problem of consciousness.” Front Psychol. 5(237): 1-9.
2. Webb TW and Graziano MS (2015). “The attention schema theory: a mechanistic account of subjective awareness.” Front Pyschol. 6(500): 1-11.
3. Webb TW, Ingelstrom KM, Schurger A, Graziano MS (2016). “Cortical networks involved in visual awareness independent of visual attention.” Proc Natl Acad Sci USA. 113(48): 13923-13928.
