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Visual process


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Visual process

  1. 1. M.Mohamed Rizwan
  2. 2. <ul><li>Transduction </li></ul><ul><ul><ul><li>the process by which our sensory systems convert stimulus energy into neural messages </li></ul></ul></ul><ul><li>Wavelength </li></ul><ul><ul><ul><li>The distance from one wave peak to the next </li></ul></ul></ul><ul><li>Hue </li></ul><ul><ul><ul><li>The color we experience (determined by wavelength) </li></ul></ul></ul><ul><li>Amplitude </li></ul><ul><ul><ul><li>Height of the wave peak </li></ul></ul></ul><ul><li>Intensity </li></ul><ul><ul><ul><li>Amount of energy in light waves, influences brightness (determined by amplitude) </li></ul></ul></ul>
  3. 3. *Note: the retina has many receptor cells which convert the inverted image (light energy) into neural impulses. When sent to the brain, these neural impulses are reassembled to create a perceived, upright-seeming image. Lens – focuses the incoming rays by changing its curvature (called accommodation) Iris – a colored muscle that surrounds and dilates or constricts the pupil (regulates amount of light entering) Pupil - small opening which allows light to enter. Retina – the light-sensitive surface on which the rays focus – the multilayered tissue that lines the inside of the back of the eyeball
  4. 5. <ul><li>Light travels through outer </li></ul><ul><li>cells to buried receptor cells </li></ul><ul><li>called rods and cones . </li></ul><ul><li>The rods and cones generate </li></ul><ul><li>neural signals to alert the next </li></ul><ul><li>layer of cells called the bipolar cells . </li></ul><ul><li>The bipolar cells activate the ganglion cells , whose axons converge like strands of rope to form an optic nerve that carries information to the brain. </li></ul><ul><li>Where the optic nerve leaves the eye there are no receptor cells, creating a blind spot . </li></ul><ul><li>The fovea is where the cones are clustered, the retina’s area of central focus (no rods). </li></ul>
  5. 6. <ul><li>Rods </li></ul><ul><li>Do not have their own bipolar cells, they share with other rods. </li></ul><ul><li>No color. </li></ul><ul><li>Remain sensitive in dim light, takes about 20 minutes to adjust </li></ul><ul><li>120 million </li></ul><ul><li>Periphery of retina </li></ul><ul><li>High sensitivity in dim light – help see in the dark. </li></ul><ul><li>Cones </li></ul><ul><li>Many have their own bipolar cells – aids in precise info and detection of fine detail. </li></ul><ul><li>Color vision </li></ul><ul><li>Do not respond in dim light (can’t see colors in dim light) </li></ul><ul><li>6 million </li></ul><ul><li>Center of retina </li></ul><ul><li>Low sensitivity in dim light </li></ul>
  6. 7. Visual Information Processing <ul><li>Feature Detectors </li></ul><ul><ul><ul><li>Certain cortical neurons which receive visual info and respond to only certain features of a scene </li></ul></ul></ul><ul><li>Parallel Processing </li></ul><ul><ul><ul><li>The brain’s capability to process visual components simultaneously (i.e. a face as opposed to an eye, a nose, etc.) – it breaks vision down into sub-dimensions such as color, depth, movement, and form </li></ul></ul></ul>
  7. 8. <ul><ul><li>We can discriminate 7 million different shades! </li></ul></ul><ul><ul><li>1 in 50 people are “color-deficient” </li></ul></ul><ul><ul><li>(esp. males – genetic) </li></ul></ul><ul><li>Young-Hemholz Trichromatic Theory </li></ul><ul><ul><li>The retina has 3 types of color receptors – each sensitive to red , green , or blue . When we combine these, we get all the other colors </li></ul></ul><ul><li>Herring: afterimages – Opponent Process Theory </li></ul><ul><ul><li>After leaving the receptor cells, visual information is analyzed in terms of opponent colors </li></ul></ul><ul><ul><ul><li>Red/Green; Blue/Yellow; Black/White </li></ul></ul></ul><ul><ul><ul><ul><li>White contains all colors in spectrum </li></ul></ul></ul></ul>
  8. 9. <ul><li>Summary </li></ul><ul><ul><li>The retina’s red, green, and blue cones respond in varying degrees to different stimuli; their signals are then processed by the nervous system’s opponent-process cells en route from the thalamus to the visual cortex </li></ul></ul><ul><li>Color Constancy </li></ul><ul><ul><li>Perceiving familiar objects as having consistent color, even if changing illumination alters the wavelengths reflected by the objects </li></ul></ul><ul><ul><ul><li>Perception of color is influenced by the context </li></ul></ul></ul>