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PSYC 330: Perception

PSYC 330: Perception. Simple Neural Processes and Vision. The Neuron. The Resting Potential. The Action Potential. The Synapse. The Doctrine of Specific Nerve Energies. Johannes Muller – the sensation experienced depends upon the neurons stimulated…. NOT on HOW they are stimulated

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PSYC 330: Perception

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  1. PSYC 330: Perception Simple Neural Processes and Vision

  2. The Neuron

  3. The Resting Potential

  4. The Action Potential

  5. The Synapse

  6. The Doctrine of Specific Nerve Energies • Johannes Muller – the sensation experienced depends upon the neurons stimulated…. NOT on HOW they are stimulated • We “see” firing in the visual system; not light

  7. Brain or Bust!

  8. VISION BASICS – Let there be light!

  9. Properties of Light • Particle wave duality • Speed • Absorption - gather • Scatter - spread • Reflection - bounce • Refraction - bend • Transmission - send

  10. Capturing Light • The Eye is like a camera • Shutter • Lens • Film • Pupil • Lens • Retina

  11. Focusing In… Fixed Refraction: cornea humors Accommodation: ciliary muscles  zonules of Zinn  lens when relaxing lens is flat (good distance) to focus on close objects muscles must contract to make lens fatter presbyopia – ARRRRRGGHHHHH!!!!!!! myopia – nearsighted; eyeball too long hyperopia – farsighted; eyeball too short

  12. Transduction – the retina Rods and cones http://www.youtube.com/watch?v=KosDT4z6NBc Graded potentials sent to bipolar cells – more photons, less glutamate in synapse

  13. Retinal Information Processing

  14. Rods low intensity threshold; sensitive to low levels of illumination detect movement detect direction of movement achromatic; one channel responding only to intensity and not variation in wavelength (black, white, shades of gray response) Cones higher intensity threshold than rods; more intense light necessary for a response; less sensitive Three types of cones with best responsiveness to short, medium and long wavelengths of electromagnetic radiation in the range of approximately 400 to 700 nM. The output signals from the three cone types feed into four chromatic color channels

  15. One night, after you have been outside for a while, look up at the stars. Look directly at a star that seems fairly bright. Without shifting your gaze from the bright star, notice other dimmer appearing stars around the bright star. Then shift your gaze to look at some of the dimmer appearing stars that were in your peripheral vision. Some of the dimmer stars will disappear when you look directly at them. What accounts for the disappearance?

  16. Neural Processing in the Eye • Rods and cones • Lateral pathway (lateral inhibition) • Horizontal and amacrine cells • Vertical pathway • Receptors  bipolar  ganglion • Periphery • Diffuse bipolar cells (50/1 receptor-bipolar)and convergence (increases in sensitivity) • Foveal • Midget bipolar cells (1/1 receptor-ganglion)(increases in acuity) • ON and OFF bipolar cells (one cone, 2 bipolar to detect on and offset) • Ganglion cells • P ganglion cells  midget bipolar cells (parvocellular path) • M ganglion cells  diffuse bipolar cells (magnocellular path)

  17. Receptive Fields • Definition: “an area in which stimulation leads to response of a particular sensory neuron” (Levine & Shefner, 1991) • Necessary features of experimental determination • Stimulus (e.g. light projected onto a screen) • Subject (often an anesthetized animal) • Single cell recording electrode • Spike recorder (measurement of the action potential)

  18. A visual example: Kuffler, 1953

  19. Brain or Bust!

  20. The Crossroads Left brain, right brain Left world, right world Optic Chiasm Ipsilateral Contralateral

  21. Visual Fields in the LGN • Thalamus • Lateral Geniculate Nucleus • Topographical Mapping • Magnocellularlayers (1,2) • Parvocellularlayers (3-6)

  22. Striate Cortex

  23. REFLECTION “PAPER” #1 Groups of 6 students http://sites.sinauer.com/wolfe3e/chap3/startF.htm Activities: 3.1 Visual Angle 3.2 Foveal Acuity 3.3 Gabor Patches 3.4 Striate Receptive Fields 3.5 Hypercolumns Explore all links, perform experiments, play with simulations, etc. Develop a 10-15 lesson for the rest of the class on your assigned topic. Be sure to read corresponding portions of text to place information in context. Group presentations on TUESDAY!!

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