thepoliblog

Consciousness and Attention

Meditating in Madison Square Park, Manhattan, New York City, photographed 22 June 2010 by Beyond My Ken .

The previous post suggested a framework for thinking about the phenomenon of consciousness.  The same framework can suggest measurements to test hypotheses about the mechanisms of consciousness, and tell us the values of the parameters in those mechanisms.

The suggested framework asserts that consciousness is closely related to attention.  Specifically, consciousness occurs when a multitude of processors in the brain are all paying attention to the same set of inputs to the brain.  Typically, some of those inputs are the result of the processing of signals from sensory nerves by smaller numbers of pre-processors; the pre-processing is therefore unconscious.  (For example, in vision, one of the pre-processors identifies edges.)  Other inputs are signals from the brain itself about other signals from the brain itself.  These meta-signals are called ‘thoughts’.  Depending upon the identities and number of processors that are paying attention to a thought, it will or will not be a conscious thought.  The special feature of consciousness is that the relevant multitude of processors are all paying attention to all of the momentary subjects of consciousness at the same time.

We do not yet know the identities and number of the processors whose simultaneous attention is needed for making a signal a subject of conscious attention.  We don’t even know whether the relevant processors are always the same, or vary with the subjects of consciousness.  Techniques that image the location of increased activity in the brain could test the suggested framework, and if it proves useful, they could identify the relevant processors.

Some of the needed data may already be available, and just need to be re-analyzed to answer these new questions.

Caption on http://en.wikipedia.org/wiki/FMRI : These fMRI images are from a study showing parts of the brain lighting up on seeing houses and other parts on seeing faces. The ‘r’ values are correlations, with higher positive or negative values indicating a better match. Image from the US National Institute for Mental Health.

Functional magnetic resonance imaging (fMRI) shows which regions of the brain receive increased blood flow when a person receives a particular stimulus.  (Many interesting fMRI scans can be viewed here , but most of the pictures of fMRI reached via that URL are copyrighted, and so cannot be re-used. )

Daniel G. Amen has developed a large collection of single-photon emission computed tomography (SPECT) scans of brains of people performing mental tasks.  Regardless of what you think of the utility of these images for diagnosing ADD and related conditions, this collection could be a treasure trove for scientific research on the locations of increased brain activity during various mental tasks.  Each measurement takes roughly 10 minutes, so the technique may not be able to capture what happens while the brain shifts its attention from one subject to another.  Also the spatial resolution of SPECT is not as good as that of fMRI.  But the large size of the database makes the SPECT data a potentially valuable supplement to other kinds of data.
Rebecca Saxe, at MIT, has developed techniques for non-invasively localizing the changing distribution of activity in the human brain when a person is shown stimuli and then responds to questions.  The techniques were developed and then applied to provide data on the scientifically, socially and legally important topic of how we infer what other people are thinking.  Her techniques would also be useful for providing data on attention.  A non-technical video presentation of her work can be viewed by visiting http://scicolloq.gsfc.nasa.gov/GSFCWeb_Fall2012.html , then clicking on the line  ”Nov. 2   Rebecca Saxe   Massachusetts Institute of Technology  How We Think about Other People’s Thoughts   V”, and then clicking on the ‘V’ (for ‘video’) at the far right.

A new technique, multi-photon microscopy, is being developed to nondestructively image in 3D the top millimeter or so of the living brain, with much better spatial resolution than the other techniques, but without being able to image as deep as the other techniques.  (See. for example, Ke Wang, Nicholas G. Gorton, Chris Xu, “Going Deep: Brain Imaging with Multi-Photon Microscopy”, Optics and Photonics News, volume 24, number 11, pp.32-39, November 2013.)

Typical questions about consciousness that might be answered by techniques that image the changing pattern of activity in the brain are:

– When conscious attention is trained on more than one subject, are the signals about the ever-changing status of those diverse subjects multiplexed onto a single serial communications channel?  Or do they travel via parallel communication channels?  Which processor receives the information?  If the information arrives multiplexed onto a serial communication channel, how is it de-multiplexed and distributed amongst the processors that can do something with the information on a particular subject?

– Since conscious attention can be trained on more than one subject, there must be special processors in the brain that decide (1) when a new subject should be admitted to conscious attention (“That car has suddenly come very close to us!”), (2) whether a current subject of conscious attention must be relegated to unconscious attention to make room for the new subject, or simply because it no longer merits conscious attention, and (3) when a subject of conscious attention suddenly merits undivided attention.  Where are those special processors?  What auxiliary signals do they use in arriving at their decisions?  What neural pathways are activated to carry the current information about a particular subject into conscious attention, or to transfer that information to a processor that receives only unconscious attention?
– Meditation (more accurately, of mindfulness) seems to have many benefits.  Why?  Is it restorative for the brain to not have to divide its attention amongst multiple subjects for a while?  Is the relief due to the temporary suspension of the metabolic and processing burdens needed for managing and monitoring more than one subject of conscious attention?

– You are talking with someone, but become momentarily distracted by your own thoughts, and don’t consciously hear something that was said.  You soon  realize that you missed something important, but you are reluctant to admit that you hadn’t paid attention.  If you recognize the problem soon enough, sometimes you can recall what you hadn’t consciously heard.  How does your brain identify the relevant unconscious processor, and bring its contents into conscious attention?

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