Vision

• What is the wavelength range of light that humans can see?


  400 to 700 nanometres
• What is the purpose of the cornea in the human eye?


  It starts the process of bending light
• What is the purpose of the pupil in the human eye?


  It is an opening in the muscles of the iris
• What happens to the image in the human eye?

  The image is reversed in the lens
• Where is the fovea located in the human eye?


  At the centre of the macula
• What is the function of the fovea in the human eye?

  It is specialized for visual acuity
• Where do the axons and blood vessels leave the eye?

  Through the optic nerve
• What is the location of the optic disk in the human eye?

  It is located where the optic nerve exits
• What is the function of rods in the human eye?

  They are responsible for scotopic vision
• What is the function of cones in the human eye?

  They are responsible for photopic vision
• How many rods and cones are there in the human eye?

  120 million rods, 6 million cones
• What are the three types of cones in the human eye?

  Blue, green, and red cones
• Why did color vision evolve to be trichromatic in humans?

  According to Christine Ladd-Franklin's theory
• What is the main difference between mild and severe color blindness?

  In mild, one type of cones is lacking, in severe all cones are lacking
• What is the function of horizontal cells in the retinal organization?

  They receive inputs from photoreceptors and provide output to bipolar cells
• What is the function of bipolar cells in the retinal organization?

  They provide a direct pathway for information from photoreceptors to the brain
• What is the function of ganglion cells in the retinal organization?

  They convey the output of the retina
• What is the receptive field of ganglion cells?

  The area where a stimulus elicits a response
• How does visual information become lateralized in the visual system?

  It becomes lateralized at the optic chiasm
• What is the difference between a monocular and a half visual field defect?

  Monocular is before the optic chiasm, half visual field is after the optic chiasm
• Where do 10% of the optic nerve axons project to?

  The superior colliculus
• Where do 90% of the optic nerve axons project to?

  The lateral geniculate nucleus in the thalamus
• What is the function of the superior colliculus?

  It coordinates head and eye movements towards stimuli
• How is the lateral geniculate nucleus (LGN) organized?

  It is organized into 6 layers
• What is the difference between the M and P pathways in the LGN?

  M pathway is for light and low contrast, P pathway is for color and high spatial resolution
• What is the primary visual cortex (V1) also called?

  The striate cortex
• How is the input from the LGN mapped onto V1?

  It is mapped retinotopically, with the fovea represented by a larger area
• Who was the first to realize that the visual field is mapped onto the visual cortex?

  Tatsuji Inouye
• How do V1 cells differ from retinal cells?

  V1 cells do not respond to simple dots of light
• What three classes of cells did Hubel and Wiesel identify in V1?

  Simple, complex, and hypercomplex cells
• What is the columnar organization of the visual cortex?

  All cells in the same column from layer 1 to 6 have similar properties
• What are the three types of columns found in V1?

  Orientation columns, ocular dominance columns, and color blobs
• What are the main characteristics of cerebral visual impairment (CVI)?

  Loss of vision due to lesion of the striate cortex, problems with depth perception and face identification, preference to look at things from the side
• What is the function of area V2 in the visual cortex?

  V2 neurons respond to illusory contours
• What is the function of area V4 in the visual cortex?

  V4 neurons respond to complex shapes and may provide the substrate for face recognition
• What is the function of area MT in the visual cortex?

  MT neurons respond to movement and lesions to MT impair motion perception
• What are the main methods used to investigate the visual system?

  Lesion studies, electrophysiology, neuroimaging, and psychophysics
• What is the purpose of psychophysics?

  To study the quantitative relations between sensations and the stimuli that produce them
• What is the absolute threshold in psychophysics?

  The smallest level of stimulus that can be detected at least half the time
• What is Weber's law in psychophysics?

  The ratio of the increment threshold to the background intensity is a constant