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Attention Schema Theory
Attention schema theory is a theory that explains how humans can be conscious of the world and their own mental processes, proposed by Michael Graziano and Sabine Kastler in 2011. According to the theory, our consciousness is computed by the machinery that is also responsible for social perception and social cognition, mainly involving the temporoparietal junction (TPJ), the superior temporal sulcus (STS) and the medial prefrontal cortex (MPFC). We build our own mind models in the way as we build other people’s minds. Like other perceptual models, Graziano and Kastner suggested that consciousness can be seen as representations of our attentional processes. Not only the things we are conscious of but also the consciousness itself emerge as and are processed as information in our brains. The theory aims to solve the hard problem of consciousness, which is how humans can be conscious of the world, our own thoughts, and emotions. In light of this theory, our understanding of consciousness changes from something ethereal to brain signals which can be empirically examined by the neuropsychological evidence.

In the following paragraphs, the hypotheses of the theory will be firstly introduced, followed by three lines of neuropsychological evidence that is consistent with their predictions. Finally, some challenges of this theory will be illustrated.

Hypothesis
Researchers have given evidence that consciousness (or awareness, which is used interchangeably in this theory) and attention are two distinct processes. An example when attention and consciousness diverge is the cases of blindsight patients. In a studying using Posner cueing task, the blindsight patient’s reaction time of detecting valid-cued targets in his blind visual field was much shorter than responding to invalid-cued objects, which demonstrated that human can still attend to visual stimuli even without consciously seeing them. In the attention schema theory, Graziano and Kastner further suggested that consciousness is actually a descriptive model of our attentional processes; that is, a schema of attention. The hypotheses in their theory include:

1.	Everything we are conscious of, including consciousness itself, are processed as information in our brains.

2.	Through the ability of social perception, we can infer other people’s minds and such ability is mainly involved in TPJ, STS, and MPFC.

3.	We use a same machinery to compute our own minds and other people’s minds.

4.	The process of building mental mind models involves binding spatial information to each model, which allows us to differentiate our own attentional state from others.

5.	We always have a more detailed and more accurate mind model of our own attentional state, since we have access to everything happens in our attentional processes.

Supporting evidence
In terms of the supporting evidence of the attention schema theory, there are mainly three lines of studies that are consistent with their predictions. The first line of evidence comes from neglect patients. People with hemispatial neglect have the syndrome of losing consciousness of one side of space regardless of different stimulus modalities, but can still unconsciously process objects in the neglected field. Researchers have reported that impairment at the TPJ and STS was commonly found in severe cases of hemispatial neglect, which are also regarded as the centre of our social perception. Such cases could be seen as the evidence supporting the attention schema theory, since deficit in the brain regions responsible for social perception leads to inability to become consciousness of everything in the neglected field. Furthermore, the evidence demonstrates the relationship between social perception and consciousness. These two functions might work under similar mechanism and are both controlled by TPJ and STS.

Secondly, this theory claims that our consciousness is actually a schema of the attentional state; therefore, it is reasonable to conjecture that brain regions responsible for consciousness, which is social circuitry (mainly TPJ, STS, and MPFC) in this theory, would be activated by attentional tasks. In a study conducted by Corbetta, Kincade, Ollinger, McAvoy and Shulman (2000), right TPJ was found to associate with the invalid targets in Posner cueing tasks, which implied that right TPJ may be specifically involved in reorienting our attention to unexpected objects. Such result was replicated by Astafiev, Shulman and Corbetta (2006) and they further verified that the role of right TPJ seems to be independent of different response modalities. In light of these studies, at least some subregions in right TPJ serves the function of shifting our attention to an unattended location and it match the prediction in the attention schema theory that consciousness is the representation of attention process in our brains. However, further experiment is warranted to clarify the relationship between attention, consciousness, and social perception.

The most direct evidence is probably from studies examining whether manipulating one’s sense of consciousness would cause activation in the TPJ. Blanke et al. (2005) demonstrated that tasks of rotating one’s own body in the mind elicited the brain activity in TPJ, but such activation was not found in letter transformation tasks. This result revealed the peculiarity of the conscious experience of one’s own body, which is different from the consciousness of other external objects, and implied that TPJ may play a role in altering spatial perspective of one’s body. In addition, when applying transcranial magnetic stimulation (TMS) at TPJ, the ability of own body transformation would be impaired. Other study also showed that performing electrical stimulation at TPJ induced out-of-body experiences (OBEs), which is a condition of experiencing the consciousness of one’s body originating from an external location outside the physical body. OBEs can be seen as an error of computing a mind model with a wrong spatial source and this condition also sheds light on mechanism for consciousness, consisting binding spatial information to each mind model.

In summary, aforementioned evidence first denotes the correlation between consciousness and social centre in human brains. Second, previous studies have shown that our social mechanism may be involve in shifting attention tasks. Finally, the consciousness of one’s own body seems to be controlled by TPJ and the process of computing a normal sense of consciousness requiring attributing a correct source to our own mind model. All these studies give some evidence to the hypotheses of attention schema theory, but it is still questionable whether such studies are sufficient to advocate the whole theory. In the next section, challenges of this theory will be discussed.

Challenges of the attention schema theory
Studies of consciousness have long faced profound difficulties. Some might be rooted in the nature of consciousness that humans are almost always conscious of themselves and the world, which makes it extremely difficult to extract consciousness from other mental processes. Other challenges existing in the present theory include the absence of direct and comprehensive evidence that justifies the whole theory. Different predictions of the theory were supported by independent studies and research examining the relationship between consciousness, attention, and brain regions for social perception is still needed. Lastly, human brain regions work in a highly cooperative way. This makes explaining neuroimaging data even harder, since different ways of interpreting data may exist. For example, brain activation in TPJ when doing attentional tasks or own body rotation tasks might be due to similar properties of these functions, or could be illustrated as versatile subregions in TPJ that are able to perform different functions, rather than under a single mechanism.

Attention schema theory is a relatively new theory and offers psychologists a novel way to think about consciousness that can be tested by empirical experiments. Although it has received some feedback from other researchers, still not enough evidence have been provided and hence it merits further research to examine the validity of its hypotheses.