Visual process
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The document summarizes key aspects of vision and color perception. It explains that light is detected by the retina's rods and cones and transmitted as neural signals. The young-Hemholtz theory proposes that the three color-sensitive cone types process red, green and blue wavelengths and combine to perceive other colors. Further processing in the visual system analyzes color opponent channels before color perception in the visual cortex.
Visual process
- 2. Transduction the process by which our sensory systems convert stimulus energy into neural messages Wavelength The distance from one wave peak to the next Hue The color we experience (determined by wavelength) Amplitude Height of the wave peak Intensity Amount of energy in light waves, influences brightness (determined by amplitude)
- 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
- 5. Light travels through outer cells to buried receptor cells called rods and cones . The rods and cones generate neural signals to alert the next layer of cells called the bipolar cells . 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. Where the optic nerve leaves the eye there are no receptor cells, creating a blind spot . The fovea is where the cones are clustered, the retina’s area of central focus (no rods).
- 6. Rods Do not have their own bipolar cells, they share with other rods. No color. Remain sensitive in dim light, takes about 20 minutes to adjust 120 million Periphery of retina High sensitivity in dim light – help see in the dark. Cones Many have their own bipolar cells – aids in precise info and detection of fine detail. Color vision Do not respond in dim light (can’t see colors in dim light) 6 million Center of retina Low sensitivity in dim light
- 7. Visual Information Processing Feature Detectors Certain cortical neurons which receive visual info and respond to only certain features of a scene Parallel Processing 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
- 8. We can discriminate 7 million different shades! 1 in 50 people are “color-deficient” (esp. males – genetic) Young-Hemholz Trichromatic Theory 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 Herring: afterimages – Opponent Process Theory After leaving the receptor cells, visual information is analyzed in terms of opponent colors Red/Green; Blue/Yellow; Black/White White contains all colors in spectrum
- 9. Summary 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 Color Constancy Perceiving familiar objects as having consistent color, even if changing illumination alters the wavelengths reflected by the objects Perception of color is influenced by the context