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Nervous System

Explore David Marr's concept of a computational theory for understanding how the brain processes information. Discover how sensory inputs such as light, sound, and skin pressure are transduced and perceived, and how motor responses such as limb movement and speech are generated. Dive into the visual pathway, the geometry of projection, and intriguing visual illusions like Ponzo's and Muller-Lyer. Uncover the hierarchical and parallel processing in the brain and the limitations of studying individual components without a comprehensive computational theory.

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Nervous System

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  1. Nervous System Perception Memory Planning …… Sensory inputs: light, sound, skin pressure, odor … Motor responses: limb movement, facial expression, speech …

  2. Sensory Systems

  3. Light Projection on Retina

  4. Transduction

  5. Transduction

  6. Transduction

  7. Cone Response

  8. Fechner’s Law Membrane Response V Subjective Intensity I Log S Log S Log S’o Log So Fechner’s law: I = A log (S/So) for S > So I = 0 for S < So S:Physical stimulus intensity So:Threshold stimulus intensity A:Constant V = A’ log (S/S’o) for the linear range S:Physical stimulus intensity S’o:Threshold stimulus intensity A’:Constant

  9. Weber’s Law I I dI dI Log S S Log So dS dS Fechner’s law: I = A log (S/So) Differentiate: dI = A dS/S dS needed to get a fixed dI: dS = (dI/A) S Weber’s Law: dS = K S where K = dI/A

  10. Visual pathway

  11. Decussation

  12. Hierarchical and Parallel Processing

  13. Receptive Field

  14. Geometry of Projection

  15. Geometry of Projection Retinal image size is inversely proportional to distance

  16. Left eye Right eye

  17. Ponzo’s Illusion

  18. Muller-Lyer Illusion

  19. “Circular World” of the Zulus (South Africa)

  20. David Marr’s Concept of a Computational Theory for Understanding an Information Processing Task in the Brain We cannot understand how a bird flies by only studying its wings, but need, in addition, an aerodynamic theory of lift generation by the flow patterns around the wings. We cannot understand how a computer works by only studying the transistors on the circuit boards and their connections, but need, in addition, concepts of operating system, data structure, and application programs.

  21. David Marr’s Concept of a Computational Theory for Understanding an Information Processing Task in the Brain Therefore, even if some day we had complete knowledge of every molecule in the brain, and could record the electrical activities of every cell at any time, we would still not understand how the brain processes information. We need, in addition, a computational theory which specifies how the electrical signals carried by a large number of neurons could act in concert to solve a certain perceptual problem.

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