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Week 3 in Perception

Week 3 in Perception. Recitation: Week of 2/17/13. Chapter 3 (pg 55-62). Visual pathway past the retina Blindsight Magno & Parvo cells Acuity Sine wave gratings/Spatial frequency Fourier analysis, Modular Transfer Function, Contrast Sensitivity Function

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Week 3 in Perception

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  1. Week 3 in Perception Recitation: Week of 2/17/13

  2. Chapter 3 (pg 55-62) • Visual pathway past the retina • Blindsight • Magno & Parvo cells • Acuity • Sine wave gratings/Spatial frequency • Fourier analysis, Modular Transfer Function, Contrast Sensitivity Function • Properties of sine wave gratings (phase)

  3. Visual Pathway Post-Eye

  4. Principle of Lateralization The right half of the brain receives information about the left half of the visual field (not just from the left eye). Note that the fibers cross over at the optic chiasm.

  5. Visual field deficits

  6. M and P Cells – DO NOT MEMORIZE

  7. M and P Cells – What You Need To Know • (Parasol cells/M ganglion cells): project to the magnocellular layers of LGN/the magnocellular parallel pathway, they have big dendritic fields, involved in fast & transient visual processing (motion) • (Midget ganglion cells/P cells): project to the parvocellular layers of LGN/the parvocellular parallel pathway, they have small dendritic fields, involved in slow and prolonged visual processing (color) • Both cover the entire retina • Their outputs are recombined starting in V1, but they are parallel pathways before this point

  8. Acuity • Acuity: The smallest spatial detail that can be resolved

  9. CSF – Contrast Sensitivity Function (Not Cerebrospinal Fluid this time) Describes how sensitive an observer is to sine wave gratings as a function of their spatial frequency.

  10. CSF • Everyone has their own unique CSF, although they may be similar to people of the same age and distance from the stimulus

  11. Spatial Frequency In audition, the basic stimulus used in linear systems theory is the sine wave. The analogous stimulus for vision is the sine wave grating. Such gratings can vary in spatial frequency (measured in cycles/degree, for a retinal image), orientation, phase and contrast.

  12. Contrast Gratings • (top) 1 • (middle) .5 • (bottom) 0

  13. Properties of Sine Wave Gratings • Contrast – We’ll get to this more after Exam 1 • This is represented by a number that ranges from 0 to 1, where • 0 the bright and dark bars have the same intensity as the mid-gray, in other words the grating is invisible • 1 the bright bars are twice the intensity of the mean and the dark bars are black • Spatial frequency • How often sinusoidal components of the structure repeat per unit of distance (for a retinal image we measure it in cycles/degree). • Orientation (“line swag”) – We’ll get to this after Exam 1 • Phase – You are accountable for this. See page 62, Figure 3.10.

  14. Good Luck, Guys!  • Be confident. • Be clear. • Be calm – It won’t matter what you get on this exam in 10 years. It’s never worth stressing about.  • YOU GOT THIS!

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