Graziano Lab

  Department of Psychology, Princeton University, Princeton, NJ 08544

Michael Graziano, Phone : (609) 258-7555, Fax : (609)258-1113, Email :


Consciousness Research

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One Possible Scientific Account of Consciousness...

Since 2010 my lab has begun to study the brain basis of consciousness. This research has focused on the relationship between awareness, attention, and social perception in the human brain.

We have proposed an overarching theory, the "Attention Schema" theory, to account for at least some of the many properties of consciousness. (See Consciousness and the Social Brain, 2013, Oxford University Press). Here the most basic aspects of the theory are summarized.

(For previous research topics in my lab, see:


The Attention Schema Theory

The theory at a glance: from selective signal enhancement to consciousness.

About half a billion years ago, nervous systems evolved an ability to enhance the most pressing of incoming signals. Gradually, this ability to focus on selected signals came under top-down control and became what is now called attention.

In control theory, if a brain is to control something, it should have an internal model of the thing to be controlled. According to the "attention schema theory", to effectively deploy its own attentional focus, the brain needed a constantly updated simulation or model of attention. Otherwise the brain would not possess explicit knowledge about its changing state of attention. This model of attention was schematic and lacking in detail. Instead of attributing to the self a complex enhancement of neuronal signals, the model attributed to the self an experience of X -- the property of being conscious of something. In this theory, a brain attributes to itself "I am currently aware of X," because that attribution helps keep track of the ever-changing state of attention. Just as the brain can direct attention to external signals or to internal signals, that model of attention can attribute to the self a consciousness of external events or of internal events.

As the model of attention increased in sophistication, we hypothesize that it came to be used for a variety of other cognitive purposes. It may have enhanced the integration of information in the brain. For example, if you are attending to an apple, a model of that internal state requires a model of yourself, of the apple, and of attention. These disparate pieces of information must be linked together. An internal model of attention therefore fundamentally links information across many domains, especially between information about the self and information about the outside world.

Another use of an internal model of attention is to model the attentional state of other individuals to gain better prediction of their behavior. The very construct of a mind that experiences something is, effectively, a schematic model of a brain focusing its processing on something. We suggest that in the human brain, similar and partly overlapping mechanisms attribute awareness to oneself and attribute awareness to others.

It is not clear when in evolution the social attribution of awareness began to emerge. The accompanying diagram places it at the start of primate evolution, 65 million years ago (MYA), but it could have begun much earlier. Perhaps birds have some ability to attribute awareness to each other. Our common ancestor with birds was about 350 MYA. Another possibility is that the social use of awareness expanded much later with hominins, beginning about 6 MYA. Now, in humans, consciousness plays a major role in social and cultural capability. We paint the world with perceived consciousness. Family, friends, pets, spirits, gods, these are all suffused with attributions of consciousness.

In this theory, awareness, the ability of brains to attribute to themselves a subjective experience of something, emerged first with a specific function related to the control of attention. It continues to evolve, however, expanding its cognitive role, becoming the intricate lattice of properties we call consciousness.

Timeline: Hydras evolved approximately 550 MYA with no selective signal enhancement. Animals that do show selective signal enhancement diverged from each other approximately 530 MYA. Animals that show sophisticated top-down control of attention diverged from each other approximately 350 MYA. Primates first appeared approximately 65 MYA. Hominins appeared approximately 6 MYA. Homo sapiens appeared approximately 0.2 MYA.