Vision Flashcards
Fovea
Cones only At the retina’s periphery, only rods
Parts of the eye (front to back)
Cornea, pupil/iris, lens, retina (fovea, blind spot)
Connection between sensorireceptors and retinal ganglion cells
Rods and cones connect with bipolar neurons Bipolar neurons connect to ganglion cells Ganglion cells group together to form optic nerve
Convergence in the retina
Cones converge less, more likely to have one-to-one connection through bipolar to ganglion cell: greater acuity Rods have higher convergence: better sensitivity to to light but lessened visual acuity
Visual field as it corresponds to retina
Right side of each eye’s visual field forms left half of each eye’s retina; left side of visual field forms on right half of each eye’s retina
Pathway from Visual Field to Cortex
Visual field –> retina –> optic nerve (crossover occurs) –> nasal fibers from left eye go to right hemisphere and nasal fibers from right eye go to left hemisphere, however temporal side fibers do not cross over (all left visual field info ends up in right hemisphere and all right visual field info ends up in left hemisphere) –> LGN (lateral geniculate nucleus of thalamus) –> visual cortex, association areas, & superior colliculus
Hubel and Wiesel found neural basis for…
Feature detection theory: certain cells are maximally sensitive to certain features of stimuli Simple, complex, and hypercomplex
“Simple cells” in visual cortex
give information about orientation and boundaries of a visual object
“Complex cells” in visual cortex
respond to more advanced information about orientation, such as movement
“Hypercomplex cells” in visual cortex
Give information about more abstract concepts, like object shape
Hubel and Wiesel (methodology)
single-cell recording; recording from single nerve fibers Place microeletrode in cortex so sensitive it records activity of single cell
Illumination vs. Brightness
Illumination: physical measurement of amount of light Brightness: subjective experience of light intensity
Adaptation
Adapt to darker environment: dark adaptation Adapt to brighter environment: light adaptation
Rhodopsin
Photochemical/photopigment used by rods; Made of retinal (vitamin A derivative) and opsin (a protein)
Rhodopsin function
When rhodopsin absorbs photon of light, pigment decomposes into retinal and opsin: “bleaching” Dark adaptation is the time is takes for rhodopsin to regenerate after bleaching Vitamin A deficiency –> difficulty seeing in the dark
Simultaneous brightness contrast
A target area of a particular luminance appears brighter when surrounded by a darker stimulus than when surrounded by a lighter stimulus
Lateral inhibition
Adjacent retinal cells inhibit one another causing simultaneous brightness contrast. If a cell is excited, neighboring cells are inhibited. Creates contrast; sharpen and highlights the borders between dark and light areas
Wavelength of light
Color perception. Humans: 400 to 800 nm
Subtractive color mixture
Occurs when we mix pigments. (Ex. Blue + yellow = green)
Additive color mixing
Has to do with lights. Primary colors with additive mixing are red, blue, and green.
Young-Hemholtz theory
Trichromatic theory. Suggests that the retina contains three different types of cones which are differentially sensitive to different colors: red, green, blue. Combine stimulation of these receptors produces all color. Young demonstrated that by mixing the three primary lights, all other colors of the spectrum can be produced
Ewald Hering & Opponent-Process Theory of Color
Criticized the trichromatic theory of color vision; held that yellow must be one of the primary colors, and yellow was a basic color along with red, blue, and green. Organized in opposing hair cells: red would excite a red-green cell and green would inhibit the red-green cell. (Hence, you can’t see reddish-green). Also included an opposing parent to code brightness (something like black-white).
Modern research in color processing
Supports Helmholtz’s theory. Are indeed three types of cones, each one maximally sensitive to a different primary color. However, cells in LGN of thalamus may apply a system similar to the opponent-process theory
Afterimages
This concept led Hering to his theory. The visual perception that appears after prolonged or intense exposure to a stimulus.