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Bayesian Cognition Winter School Chamonix, January 6-11, 2008

Bayesian Cognition Winter School Chamonix, January 6-11, 2008. Probabilistic interpretation of physiological and psychophysical data. Jacques Droulez Laboratoire de Physiologie de la Perception et de l’Action CNRS – Collège de France jacques.droulez@college-de-france.fr.

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Bayesian Cognition Winter School Chamonix, January 6-11, 2008

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  1. Bayesian Cognition Winter School Chamonix, January 6-11, 2008 Probabilistic interpretation of physiological and psychophysical data Jacques Droulez Laboratoire de Physiologie de la Perception et de l’Action CNRS – Collège de France jacques.droulez@college-de-france.fr

  2. Black box view of an agent The agent … Sensory inputs: ot Motor outputs: at

  3. Black box view of a situated agent The agent … ot at The world …

  4. Black box view of a situated agent (with an internal model of the world…) St ot at The agent … ot at The world … Question: P(St | a0→t-1 o0→t) and P(At | a0→t-1 o0→t)

  5. a o Action Observation

  6.    ?

  7.  ?

  8. An evolutionary perspective Eukaryotes Opisthokonts Algae Plants Others... Lebert, M. & Häder, D-P (2000) Photoperception and phototaxis in flagellated algae. Res. Adv. Photochem. Photobiol. 1: 201-226. Streb et al (2002) Sensory transduction of gravitaxis in Euglena gracilis. J. Plant. Physiol., 159: 855-862.

  9. An evolutionary perspective Eukaryotes Opistokonts Algae Plants Others...

  10. Adapted behaviors already exist in unicellular organisms, with: - specialized organelles for sensory signals (mechano / chemo / photoreceptors) - macromolecular assemblies and messengers for signal processing (ionic channels) - various effectors for locomotion / defense / predation Bucci et al (2005) A role for GABAA receptors in the modulation of Paramecium swimming behaviour. Neuroscience Letters, 386:179-183

  11. Evolutionary perspective Eukaryotes Opistokonts Algae Plants Others... Metazoan Fungi Cell specialization Sponges Nervous system Medusas Segmented brain Bilateria worms ... human

  12. The space-time problem for multicellular organism ... Diffusion law: ∂[C]/∂t = D ∂2[C]/∂x2 D ≈ 1 µm2/ms Time Length2 ⇒ Coordinated movements (in Sponges) are slow ... Nickel, M. (2004) Kinetic and rhythm of body contractions in the sponge Tethya wilhelma, J. of Experimental Biology, 207:4515-4524

  13. Evolutionary perspective Eukaryotes Opistokonts Algae Plants Others... Metazoan Fungi Cell specialization Sponges Nervous system Medusas Segmented brain Bilateria worms ... human

  14. Schematic view of a cnidarian eye Ciliary type photoreceptor in red Melanin pigment cells in yellow Biconvex lens in blue Nervous system of the cubomedusae jellyfish RN: ring nerve Rh: rhopalia (eye + graviceptors) Garm et al (2006) Cell Tissue Res. 325: 333-343

  15. Fast, single cell reaction (nematocysts) Coordinated behaviour (nerve ring) Intracellular recording of action potentials in motoneurons Interpulse histogram for: 1 (A) 2 (B) 3 (C ) 4(D) rhopalia (Bin width: 250 msec) Satterlie & Nolen (2001) J. of Exp. Biol. 204: 1413-1419

  16. Evolutionary perspective Eukaryotes Opistokonts Algae Plants Others... Metazoan Fungi Cell specialization Sponges Nervous system Medusas Segmented brain Bilateria worms ... human

  17. Evolution of the nervous system in bilaterian C E B D 1: neurones 2: cerebral ganglion 3: medullae 4: architecture en « échelle de corde » A A: flatworms B et C: molluscs D: annelids E: arthropods (from G. Roth & M.F. Wulliman, Brain evolution and cognition, 2001)

  18. Supra-spinal nervous system in some vertebrates frog reptile bird rodent horse OB: olfactory bulb OT: optic tectum T: forebrain Cb: cerebellum D: diencephalon

  19. Three hierarchically organized levels Ligand binding site Stretching sensitivity Voltage sensor Chemical sensors Photosensors (eyespot), … Sensors Neurotransmitter release Mechanical effectors, … Channel open/closed Catalytical action, … effectors Macromolecule Organism Cell

  20. The brain as a (segmented) agent Observations Actions Olfaction Vision Oculomotor (Eye/ Pupil) Trochlear (Eye movement) Trigeminal Abducens (Eye movement) Facial Vestibulo-cochlear …etc …

  21. Example of cellular agent: the photoreceptor cell Action: chemical release Observation: Light intensity Depolarization cGMP Ca2+/Na+ Glu In darkness: high cGMP (2µM)  Ca2+ & Na+ Inflow  [Ca2+]i = 550 nM V = – 40 mV  Voltage gated Ca2+ channels are open Continuous release of glutamate Hyperpolarization Photons In the light: hydrolysis of cGMP  channels are closed  [Cal+]i = 50 nM V = – 80 mV  Voltage gated Ca2+ channels are closed Reduction of glutamate release

  22. Example of molecular agent: a voltage gated Ca2+ channel Observation: electric field across the membrane (~ 15 106 V/m !!) Action: Ca2+ Inflow

  23. 10-12 s 10-9 s 10-6 s 103 s 1 s 10-3 s Plastic adaptation Elementary relaxation (macromolecule) Tertiary structure transitions Channels Open/ closed Membrane time constant / spike propagation Basic behaviours

  24.  ?

  25. This page is intentionally black

  26. The perception viewed as an (ill-posed) inverse problem... P(S) P(O | S) Physical State S (self motion / object properties) Observed sensory data O (inertial and visual sensors) P(S | O)  P(S).P(O | S)

  27. P ≠ P(S) ● Blood pressure ● Attentional blindness ● neural activity under anesthesia

  28. Primary & secondary light sources Object characteristics : position, orientation, shape, texture, movement, .. Optic properties of the eye & Eye movements Media properties (absorption, diffusion, ...) The complete model is too complex for a Brain with limited resources...

  29. Incidence of small ocular movements on visual perception Akiyoshi Kitaoka, Out of focus (2001)

  30. 1. Luminance perception

  31. Vincent Van Gogh, Nuit étoilée sur le Rhône (1888) Oliviers avec ciel jaune et soleil (1889) ~ 109 photon/µm2/s ~ 1 photon/µm2/s Dawson (1990)

  32. « Discrepancies between the real world and the world depicted by artists reveal as much about the brain within us as the artist reveals about the world around us. » P. Cavanagh, The Artist as Neuroscientist, Nature, 2005. Girl reading a Letter at an Open Window (Jan Vermeer, 1657)

  33. Deviation from Weber-Fechner’s laws: Perceived brightness versus luminance (Cd/m2) B A Data from Nundy & Purves (2002) PNAS 99:14482-14487

  34. The probabilistic explanation by Purves et al (2004) Psychol. Rev. 111:142-158 Luminance ~ Illumination x Reflectance: I constant  R  L R constant  I  L I  R  R  I  L1/2 L > Background L L < Background

  35. Basic functional schema of the retina h PhR H H H Glutamate GABA Hemi gap junction Bip Gap junction GABA, Gly, Ser, ACh A A A G Except for ganglion and some amacrine cells, information propagates without spikes.

  36. 2. Visual motion perception (dx,dy,dt) I(x+dx, y+dy,t+dt) I(x,y,t) Hypothesis of conservation of loal luminous intensity: I(x+dx, y+dy, z+dt) ≈ I(x, y,z) or dI/dt = < Gt , V > = 0 Hypothesis not always nor eveywhere valid ! Ex.: apparition/disparition, occlusion, variation of luminous sources …

  37. The aspect is globally conserved, but the local luminous intensity is not exactly the same in succesive images  P(It+dt | It V) or P(Gt | V)

  38. Motion integration: numerous sources of uncertainty: Nonhomogeneous distribution of contrasts Low Contrast, Aperture problem, False correspondences ? ? ? G = 0 single oriented G multiple G

  39. P(G V) = P(V). P(G | V) P(V | G)  P(V).P(G | V) P(V): prior favorable aux faibles vitesses Weiss, Simoncelli & Adelson: Motion Illusions as Optimal Percepts. Nature (2002)

  40. More recent works on the « low velocity prior » idea: Carandini, M. (2006) Measuring the brain’s assumptions. Nat. Neuroscience, 4:469. Stocker, A. A. & Simoncelli, P. (2006) Noise characteristics and prior expectations in Human visual speed perception. Nat. Neuroscience, 4: 578. Thomson et al (2006) Speed can go up as well as down at low contrast: implications for models of motion perception. Vision Research, 46: 782-786. 2AFC speed discrimination From Stocker & Simoncelli (2006)

  41. Scale ambiguity: The depth & velocity scales cannot be estimated from the optic flow alone V R D v R d

  42. Knowledge of self motion can be used (in principle) to solve the scale ambiguity problem. V d D

  43. Comparison SM (subject motion) versus OM (object motion) Subject’s Task: report whether or not the object is closer than 1 meter Same relative velocity All trials Panerai, Cornilleau-Pérès & Droulez, Perception & Psychophysics, 64: 717-731(2002)

  44. The convex/concave ambiguity: ● absent in large field stimulation ● important in small field but strongly reduced in self-motion condition Dijskra, Cornilleau-Pérès, Gielen & Droulez, Vision Research, 1995

  45. Several examples of optic flow ambiguities Perceptive inversion(Fronto-parallel plane symmetry for both object & motion) ≃ Passive Active ≃ Wexler, Lamouret & Droulez, Vision Research, 41, 3023-3037 (2001)

  46. Similar optic flows result from different combinations of rotation and translation Results show a preference for thestationary object, even if it does not correspond to the mostrigid solution Wexler, Lamouret & Droulez, Vision Research, 41, 3023-3037 (2001)

  47. Variability of perceptive responses (« shear effect ») Van Boxtel, Wexler & Droulez, Journal of Vision 3(5) : 318-332. (2003)

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