Consciousness The final frontier!

Transcription

1 Consciousness The final frontier!

2 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

3 How to Study it? Philosophical Psychological Computational Neuroscience Ethically and Theologically Idea of responsibility for actions. accountability

4 A science of consciousness

5 Three Approaches Neuroscience and psychological Computational Neuroscience Philosophy

6 Neuroscience and psychological Logothetis using neural responses psychological measures of behavior looking for the neural correlates of consciousness test case - visual perception

7 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.

8 Philosophy Chalmers The true theory of everything consciousness an elementary feature Irreducible Information physical experiential

9 VISION A window on consciousness A scientific study of consciousness What is the difference between neural processes that correlate with a conscious experience and those that do not?? Definition borrowed from Crick and Koch

10 A conscious percept ambiguous visual stimuli.

11 Bistable stimuli Two interpretations valid Only one at a time can be perceived conscious experience of the phenomenon alternates between interpretations

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14 Local and Global Discord

15 Visual Perception Methods preferred stimulus receptive field of neurons measured by neural activity perceived stimulus what an animal perceives measured by behavior

16 Opposition opposition between : preferred - receptive field perceived - response preferred orientations motion - direction and speed and orientation wavelength stereoscopic disparity

17 Visual Hierarchy receptive fields Retinae LGN - parvo- and magno- V1 V2 - form/color V3 - form V4 - color V5/MT

18 Motion Perception V1 - cells sensitive to direction of motion orthogonal to an orientation i.e., they like an oriented line moving in a direction perpendicular to the preferred orientation.

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23 Cell fires.. BUT..

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27 Aperture Problem A neuron in the visual system sees the world through an aperture For motion selective neurons Direction of motion And speed are confounded

28 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

29 Methods drifting sine wave grating variables spatial frequency speed direction

30 Stimulus- Part 1 one grating drifts rightward orientation 80 degrees spatial frequency - whatever speed whatever You see.

31 Stimulus - Part 2 one grating drifts rightward orientation 50 degrees spatial frequency - whatever speed whatever You see.

32 Combined Stimulus Superimpose 1 and 2 You see.???

33 Percept Well it depends. Sometimes you see 2 gratings drifting over each other Sometimes they cohere You see a plaid moving in one direction

34 Moving Plaid Demo Demo of a moving plaid grating: + = Demo: (Search on "plaid")

35 Percept Which you see depends on relative orientation relative spatial frequency relative speed whatever Play around until you get it to cohere.

36 The Neural Stimulus 2 components Receptive field properties can be found to match both components.. C1 C2

37 Neural Part Find a neuron that likes C1 Find a neuron that likes C2 Find a neuron that likes the motion direction that results if the motions cohere to a plaid...

38 Neural Part V1 neurons MT/V5

39 Behavioral Part macaques trained to respond to motion direction. using simple sine wave grating after training. plaids where the coherent motion is in one of the trained directions..

40 Behavioral-Neural Parts record neural response during responding awake and behaving macaques

41 Results V1 cells respond to only the C1 and C2 motion directions MT/V5 responds to the perceived motion direction!

42 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 cell in MT during the task changed the monkey s response!

43 Conclusions Lower level visual processing cell preference over percept Higher level visual processing percept over all...

44 Consciousness visual perception What you experience As opposed to what you see

45 Computational Neuroscience Crick and Koch Problem of consciousness is ill-posed Ill-posed problems Under-constrained mathematically 3D to 2D and back

46 Computational Neuroscience vision as inference construct the visual world from hints

47 Blindsight Patients damage to visual cortex people report being blind Yet.. point to objects reliably eyes can track moving objects

48 Visual Awareness If visual awareness at any given moment corresponds to a set of neurons firing Where are these neurons? The bridge locus.d. Teller Linking propositions

49 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...

50 The Binding Problem specialized visual areas unified visual percept

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56 Cortical Oscillations synchronized firing in cat visual cortex about 40 Hertz Theory they bind object properties together? They segment the visual world?

57 Philosophy - Brain and Mind Chalmers Consciousness The easy problem The hard problem

58 The Easy Problem Relating neural events to experience Examples integrating sensory information discriminate sensory stimuli disambiguate perceptual stimuli Answers in neuroscience and cognition

59 The Hard Problem How physical phenomena in the brain give rise to subjective experience Why is the existence accompanied by a conscious access to the experience?

60 Explanatory Gap Chalmers - something else needed Conscious experience should be considered a fundamental feature, irreducible to anything more basic Example of electromagnetic charge

61 True Theory of Everything Laws Physical laws Psychophysical laws Bridging Information Physical Experiential

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63 Binocular Rivalry