Module 18 Review in Module 18 Vision: Sensory and Perceptual Processing

The hue we perceive in light depends on its wavelength, and its brightness depends on its intensity.
After entering the eye through the cornea, passing through the pupil and iris, and being focused by the lens, light energy particles (from a thin slice of the broad spectrum of electromagnetic energy) strike the eye’s inner surface, the retina.

The retina’s light-sensitive rods and color-sensitive cones convert light energy into neural impulses.
Cones are found in and around the fovea. Many cones have a direct hotline to the brain, transmitting their message to a single bipolar cell that relays it to the visual cortex. Rods are found in the retina’s outer regions. Several rods together transmit their energy to a single bipolar cell.
Cones and rods each provide a special sensitivity—cones to detail and color, rods to faint light and peripheral motion.
After processing by bipolar and ganglion cells in the eyes’ retina, neural impulses travel through the optic nerve, to the thalamus, and on to the visual cortex.

The Young-Helmholtz trichromatic (three-color) theory proposed that the retina contains three types of color receptors. Contemporary research has found three types of cones, each most sensitive to the wavelengths of one of the three primary colors of light (red, green, or blue).
Hering’s opponent-process theory proposed three additional color processes (red-versus-green, blue-versus-yellow, white-versus-black). Contemporary research has confirmed that, en route to the brain, neurons in the retina and the thalamus code the color-related information from the cones into pairs of opponent colors.
These two theories, and the research supporting them, show that color processing occurs in two stages.

Feature detectors, specialized neurons in the occipital lobe’s visual cortex, respond to specific aspects of the visual stimulus.
They receive information from individual ganglion cells in the retina and pass it to other cortical areas, where supercell clusters respond to more complex patterns.

Through parallel processing, the brain handles many aspects of vision (color, movement, form, and depth) simultaneously. Other neural teams integrate the results, comparing them with stored information and enabling perceptions.

Yasser is colorblind and is unable to see colors the same way as his wife. Describe which theory of color vision best explains this deficiency and explain which theory of color vision best explains why he might see an afterimage.

(2 points)