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Consciousness

The final frontier!

How to Define it???

awareness perception - automatic and controlled memory - implicit and explicit ability to tell us about experiencing it attention…. And the bottleneck of the human mind

How to Study it?

Philosophical Psychological Computational Neuroscience Ethically and Theologically Idea of responsibility for actions…. accountability

A science of consciousness

Three Approaches

Neuroscience and psychological Computational Neuroscience Philosophy

Neuroscience and psychological

Logothetis using neural responses psychological measures of behavior looking for the neural correlates of

consciousness test case - visual perception

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Computational Neuroscience

Crick and Koch The binding problem Neural correlates of the global perception Unfragmenting the fragmented brain Putting together the pieces The homonculus Cortical oscillations….

Philosophy

Chalmers The true theory of everything consciousness an elementary feature Irreducible

Information physical experiential

VISION A window on consciousness

A scientific study of consciousness

What is the difference between neuralprocesses that correlate with a consciousexperience and those that do not??

Definition borrowed from Crick and Koch

A conscious percept

ambiguous visual stimuli….

Bistable stimuli

Two interpretations valid

Only one at a time can be perceived

conscious experience of the phenomenonalternates between interpretations

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Local and Global Discord

Visual Perception Methods

preferred stimulus receptive field of neurons measured by neural activity

perceived stimulus what an animal perceives measured by behavior

Opposition

opposition between : preferred - receptive field perceived - response

preferred orientations motion - direction and speed and orientation wavelength stereoscopic disparity

Visual Hierarchy receptive fields

Retinae LGN - parvo- and magno- V1 V2 - form/color V3 - form V4 - color V5/MT

Motion Perception

V1 - cells sensitive to direction of motion orthogonal to an orientation

i.e., they like an oriented line moving in adirection perpendicular to the preferredorientation….

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Cell fires …..

BUT …..

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Aperture Problem

A neuron in the visual system sees theworld through an aperture

For motion selective neurons Direction of motion And speed are confounded

BUT

animal sees the correct direction of motion

solution in MT? disambiguation via pooling the responses of

many neurons with different selectivities

Movshon and colleagues…late 80’s

Methods

drifting sine wave grating

variables spatial frequency speed direction

Stimulus- Part 1

one grating drifts rightward orientation 80 degrees spatial frequency - whatever speed whatever

You see….

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Stimulus - Part 2

one grating drifts rightward orientation 50 degrees spatial frequency - whatever speed whatever

You see….

Combined Stimulus

Superimpose 1 and 2

You see….???

Percept

Well it depends….

Sometimes you see 2 gratings driftingover each other

Sometimes they “cohere” You see a plaid moving in one direction

Moving Plaid Demo

Demo of a moving plaid grating:

+ =

Demo:

(Search on "plaid")

Percept

Which you see depends on…

relative orientation relative spatial frequency relative speed whatever

Play around until you get it to cohere….

The Neural Stimulus

2 components

Receptive field properties can be found tomatch both components….. C1 C2

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Neural Part

Find a neuron that likes C1

Find a neuron that likes C2

Find a neuron that likes the motiondirection that results if the motions cohereto a plaid...

Neural Part

V1 neurons

MT/V5

Behavioral Part

macaques trained to respond to motiondirection…. using simple sine wave grating

after training…. plaids where the coherent motion is in one of

the trained directions…..

Behavioral-Neural Parts

record neural response

during responding… awake and behaving macaques…

Results

V1 cells respond to only the C1 and C2motion directions

MT/V5 responds to the perceived motion direction!

Further data

Newsome and colleagues correlated dot patterns…. N percent move in one direction Smallest percent to see global motion

stimulation of the competing motion cellin MT during the task

changed the monkey’s response!

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Conclusions

Lower level visual processing cell preference over percept

Higher level visual processing percept over all...

Consciousness

visual perception What you experience As opposed to what you “see”

Computational Neuroscience

Crick and Koch Problem of consciousness is ill-posed

Ill-posed problems Under-constrained mathematically 3D to 2D and back

Computational Neuroscience

vision as inference construct the visual world from hints

Blindsight Patients

damage to visual cortex

people report being blind

Yet.. point to objects reliably eyes can track moving objects

Visual Awareness

If visual awareness at any given momentcorresponds to a set of neurons firing…

Where are these neurons?

The bridge locus….D. Teller Linking propositions

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The Cartesian Theater

Dennett The homunculus …. No single place in the cortex where the

output comes together….

global representations ... in a fragmented brain…? Modularity….backlash...

The Binding Problem

specialized visual areas unified visual percept

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Cortical Oscillations

synchronized firing in cat visual cortex about 40 Hertz

Theory they bind object properties together…? They segment the visual world?

Philosophy - Brain and Mind

Chalmers Consciousness

The easy problem

The hard problem

The Easy Problem

Relating neural events to experience Examples integrating sensory information discriminate sensory stimuli disambiguate perceptual stimuli

Answers in neuroscience and cognition

The Hard Problem

How physical phenomena in the braingive rise to subjective experience

Why is the existence accompanied by aconscious access to the experience?

Explanatory Gap

Chalmers - something else needed

Conscious experience should beconsidered a fundamental feature,irreducible to anything more basic

Example of electromagnetic charge

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True Theory of Everything

Laws Physical laws Psychophysical laws

Bridging Information Physical Experiential

Binocular Rivalry