Unit 2A: Visual processing

Question 1

Visual field

Answer 1

the entire area or field of view that can be seen when an eye is fixed straight at a point on space.
Descriptions of the visual field include:
1. vertical meridian- line dividing the field of view into left/right halves;
2. horizontal meridian- line dividing field of view into top and bottom halves

Question 2

hemifield

Answer 2

‘half the visual field’, typically refers to left and right halves only (not top/bottom halves)

Question 3

quarter field

Answer 3

‘one quarter or quadrant of the visual field’, defined by the quadrant created by the vertical and horizontal meridian lines

Question 4

Cornea

Answer 4

the transparent dome-shaped anterior portion of the outer covering of the eye

Question 5

Lens

Answer 5

situated behind the iris of the eye, it focuses light entering the eye onto the retina

Question 6

Sclera

Answer 6

the white part of the eye that, with the cornea, forms the protective outer covering of the eye

Question 7

Iris

Answer 7

the colored portion of the eye, a muscular diaphragm that controls the size of the pupil, which in turn controls the amount of light that enters the eye

Question 8

Pupil

Answer 8

the hole located in the center of the iris of the eye that allows light to strike the retina. It appears black because light rays entering the pupil are either absorbed by the tissues inside the eye

Question 9

Retina

Answer 9

the back of the eyeball, considered a part of the brain, where light hits the photoreceptive cells and visual information begins being processed

Question 10

Fovea

Answer 10

the part of the retina, where vision is most acute and color vision is best. Cone photoreceptors are most prevalent here.

Question 11

Blind spot

Answer 11

the place in the visual field that corresponds to the lack of light detecting photoreceptor cells on the optic disc of the retina where the axons of the retinal ganglion cells exit the retina and form the optic nerve.

Question 12

photoreceptor cells

Answer 12

cells that line the back of the retina and have parts that change shape when they are hit with a photon, allowing them to detect light in a certain part of the visual field. The overall function of the photoreceptor cell is to convert light energy of the photon into a form of energy communicable to the nervous system and readily usable to the organism.

Question 13

Rods

Answer 13

photoreceptor cells that are located outside the fovea. They are highly sensitive to light and thus responsible for low light vision, like under starlight. Rods also contribute to visual motion detection, but have poor visual acuity. They also do not differentiate between colors.

Question 14

Cones

Answer 14

Photoreceptor cells that are concentrated in the fovea, but also more sparsely extend into the periphery. They are responsible for high acuity vision, but take more photons of light to activate (good for daytime vision- photopic). There are three types, each most responsive to different wavelengths of light (long, middle, and short). The combination of inputs from different cone types through opponent processing produces for color vision.

Question 15

photoreceptor proteins

Answer 15

light sensitive protein molecules involved in the sensing and response to light in a variety of organisms by undergoing a structural change when they absorb light. This structural change opens ion channels, which causes a change in the graded potential of the photoreceptor

Question 16

opsins

Answer 16

a type of photosensitive pigment proteins found in photoreceptors.
-rhodopsin in rods
-photopsin in cones
-melanopsin in melanopsin containing retinal ganglion cells

Question 17

Retinal ganglion cells

Answer 17

cells in the retina that receive input from modulatory neurons and transmit the information down the optic nerve to the brain. Primary types of retinal ganglion cells are the midget cells, parasol cells, and small bi-stratified cells.

Question 18

Opponent processing color vision theory

Answer 18

color vision theory that color is processed in 3 different opponency channels created by specific wiring together of cone photoreceptors and retinal ganglion cells
-red (L cone) vs. green (M cone)
-blue (s cone) vs. yellow (L+M cone)
-dark vs bright (red/L+green/M+blue/S)

Question 19

Optic nerve

Answer 19

composed of the axons of the retinal ganglion cells that leave the retina and head back towards the optic chiasm in the brain, taking with them visual information. This nerve is the reason humans have a blind spot, because no photoreceptive cells exist where the optic nerve exits the eye.

Question 20

Parvocellular pathway

Answer 20

a visual processing stream that pools over fewer receptors. The cells (MIDGET RETINAL GANGLION CELLS) have a sustained response and are involved in the processing color, fine details, textures, and depth.

Question 21

Magnocellular pathway

Answer 21

A visual processing stream that pools over many receptors, whose retinal ganglion cells (PARASOL RETINAL GANGLION CELLS) fire in bursts and are useful for detecting motion.

Question 22

Koniocellular pathway

Answer 22

a visual processing stream that gets S-cone input only (from SMALL BI-STRATIFIED CELLS), processing low acuity visual information, and inervating V1 and extrastriate cortex.

Question 23

Melanopsin-containing retinal ganglion cells

Answer 23

are a recently discovered type of retinal ganglion cell that can directly absorb light. They contain the photopigment melanopsin (related to melanin), which allows them to function like the photoreceptors that transduce light for the rod and cone retinal ganglion cells. These ganglion cells have a very large dendritic tree, which contributes to the role of these cells in signaling gross changes in light intensity. This information is sent to subcortical structures and is thought to be used in circadian rhythms and pupil constriction.

Question 24

Optic chiasm

Answer 24

when the optic nerves cross in the brain, allowing information from the left visual field (from both eyes) and right visual field (from both eyes) to be separated and directed to the appropriate contralateral hemisphere

Question 25

Thalamus

Answer 25

a part of the brain involved in relaying sensory information from sensory organs to processing areas of the cerebral cortex

Question 26

Lateral geniculate nucleus (LGN)

Answer 26

a part of the thalamus where the visual processing streams pass through on their way to the optic radiations and primary visual cortex

Question 27

optic radiations

Answer 27

nerve pathway along the visual processing stream from the LGN to primary visual cortex

Question 28

Primary sensory cortex

Answer 28

refers to the first location in cortex that receives input from the peripheral sensory receptors

Question 29

Primary visual cortex (V1)

Answer 29

the first area in the brain where visual information is processed at a low level. Visual information flows into here from the retina and flows to higher levels of visual processing (V2, V3, etc.) that do increasingly complex visual processing. V1 is also called striate cortex due to the visible stripe of inputs from retina to layer 4 of V1.