Lec 6: Central Visual Pathways

What is the result of phototransduction after the retina is exposed to light?

A. Depolarization of photoreceptors.

B. Decreased action potential frequency in photoreceptors.

C. Depolarization of rods, but not cones.

D. Hyperpolarization of photoreceptors

E. Reduced action potential firing of all retinal ganglion cells.

Hyperpolarization of photoreceptors

6 steps of phototransduction

1. channels open

2. photon absorption

3. activation of transducin + PDE

4. cGMP breakdown

5. channel closure

6. hyperpolarization

In the dark, rods are _____

depolarized

True or False, each eye has its own visual field

true

In the retina visual field, the image is flipped…

over both axes

The right visual field information projects to the ____ optic tract and vice versa

left

How many layers are in the visual cortex

six layered

What layer does the LGN project into

layer 4

What do simple cells in V1 “see”?

Process information about edges and convert it into orientation

3 things that are overlaid in V1

• location (retinotropic map)

• orientation of edges

• eye specificity (ocular dominance)

Things about depth that are gathered from monocular cues

• motion parallax

• shading

• texture

Define retinal disparity

Slight differences between images captured by left and right eye due to their different positions on the face

What is the fact about ocular dominance columns (ODCs)?

A. ODCs develop postnatally via axon pruning

B. ODCs are located in the cortical layer 2/3

C. ODC development is dependent on GABA signaling

D. All the above

D. All the above

_____ ____ _____: Columnar strips of neurons in V1 that preferentially respond to input derived from a single eye

Ocular dominance columns

Layer 4 neurons are _____; while layer 2/3, 5, and 6 neurons are _____

monocular; binocular

Where is the first step of binocular input

V1 cortical neurons

Near cells: respond to disparities in planes ____ to the plane of fixation

Far cells: respond to disparities in planes _____ from the plane of fixation

closer; further

What is the accomodation-convergence reflex

Used to focus on near objects

What does MRI imaging rely on

Manipulation of H+ spins to detect relaxation of protons across different mediums

What are the two visual processing streams

• Ventral pathway: “what” (object recognition and form)

• Dorsal pathway: “where” (motion and position of objects)