Lecture 9

How do the visual pathways work in many animals?
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How do the visual pathways work in many animals?
The right visual view gets projected to the left side of the brain and vice versa. In humans, both eyes see to both sides to some degree, giving us much more accurate depth perception.
What is an important thing to note about the visual pathways of a forward looking eye?
Left side of the visual field, left side of each eye (from fixated point) goes to the right brain and vice versa. Inside information (closest to the nose) side of each eye is crossed in the brain, but not the outside field.
What does a left optic nerve injury do to the eye?
Most likely the individual doesn't realize. Causes impaired depth perception.
What does a tumor at the optic chiasm cause?
Most likely the individual doesn't realize. Impaired depth perception. Headaches.
What does an aneurysm of left Internal Carotid cause?
Once again, the individual does not realize they are essentially .25% blind. Maybe some headaches.
What happens at the LGN?
Retinal ganglion cells terminate at the LGN and superior colliculus.
What is a key thing to remember about the superior colliculus?
Everything that happens here is unconscious, such as pupil dialiation, blinking when a hand is waved in front of you, etc. Only 10% of fibers go here since humans are such conscious creatures.
What is blindsight?
The superior colliculus may allow blind people to perceive moving stimuli. Such as throwing a ball at them, they will duck or catch even though they are blind.
How many layers does the LGN have?
6 layers.
What is the purpose of the LGN having different layers?
Each individual layer only receives information from one eye or the other. This is NOT the place where the brain is putting these signals from both eyes together.
What kind of receptive fields does the LGN have?The LGN has circular receptive fields.What is spatial organization (retinotopic map)?There is an image of the world on the retina, now there is an image of the world on each layer of the LGN but for only one eye and of half the world in each layer. This is the mapping of the world on the LGN layers.What are layers 1-2 of the LGN and some characteristics of them?- Layers 1-2 = Dorsal (Where) Pathway. Information from these layers end up at the top of the brain. Such as reaching to grab something. Larger cells, mostly from rods. - This causes more neural convergence. - Sensitivity and motion.What are layers 3-6 of the LGN and some characteristics of them?- Layers 3-6 = Ventral (What) Pathway. Information from here ends up at the bottom and sides of the brain. Responsible for object recognition. - Smaller cells, most from cones, this causes a smaller receptive field here. - Resolution and color.The LGN has an ___ channel for black and white vision.Achromatic.The LGN has __ ___ channels for color vision.2 Chromatic channels.What are the 2 chromatic channels for color vision?Red and green. Yellow and blue.What is color contrast?The same wavelength of light can appear to be a different color depending on what color it is next to. This is why layer certain colors over others can make a color look different.What is a better name for complementary colors?Opponent colors, as they are essentially fighting to be perceiving by your brain.What happens in the red and green channel?The receptive fields are either red center activation, green surrounding inhibition OR green center activation, red surrounding inhibition. Like looking for an apple in a tree, or red dot in an olive. This channel does not care about blue or yellow and uses M + L cones.What happens in the blue and yellow channel?Receptive fields are either blue center activation, yellow surrounding inhibitory OR yellow center activation, blue surrounding inhibitory. Uses S cones to perceive blue. Uses M + L cones to perceive yellow. This channel does not care about green or red.What is color opponency?Staring at colors and switching to a white screen shows an after image of the opposite colors. The excitation of one cone inhibits the other. This causes adaption and afterimages. Examples include, Green, yellow, and black flag having an after image of red, white, and blue flag. This can happen with other sense and motion. Think of a scale, you cannot see something as more blue without seeing it as less yellow.