Exam 2 - Vision

Question 1

Sensation

Answer 1

Process in which specialized cells of the nervous system
detect environmental stimuli & transform their energy into
action potentials. All senses possess sensory receptors aka neurons

Question 2

Perception

Answer 2

Conscious experience & interpretation of info from the sense & involves neurons in the CNS

Question 3

Sensation to Perception Pathway

Answer 3

Energy –> action potentials –> nervous system –> perception

Question 4

Light as a stimulus

Answer 4

Range of wavelengths we call “light” is the part of the
electromagnetic spectrum we can see
Wavelength between 380nm & 760nm

Question 5

3 stimulus properties of light/visual stimuli

Answer 5

hue, saturation, and brightness

Question 6

Hue

Answer 6

Determined by wavelength. Slower oscillations lead to longer wavelengths & vice versa

Question 7

saturation

Answer 7

Relative purity of the light being perceived. (more pure aka higher saturation or muted aka lower saturation).
high saturation - single dominant wavelength
low saturation - mix of multiple wavelengths

Question 8

brightness

Answer 8

determined by the intensity of the light. Higher amplitude of the light wavelength means brighter. This can be light or dark

Question 9

sclera

Answer 9

tough white, outer layer. Opaque, doesn’t allow entry of light into eye

Question 10

Conjunctiva

Answer 10

Mucous membrane lining the eyelid & attaching to the eye

Question 11

cornea

Answer 11

transparent part where light first enters. Provides 2/3 of the focusing power – bends light rays & helps form image on the retina

Question 12

iris

Answer 12

colored part of the eye, ring of muscles behind the cornea, provides an opening to form the pupil

Question 13

pupil

Answer 13

allows light to enter the eye

Question 14

Crystalline lens

Answer 14

located immediately behind iris, Contributes to 1/3 of the focusing power, attached to the ciliary muscle. cataracts (cloudy lens) can be treated with lens replacement

Question 15

ciliary muscle

Answer 15

attached to the lens, controls the shape of the lens and involved in accommodation. Accommodation - changes in the thickness of the lens, focuses near or distant objects on the retina to form a sharp image

Question 16

Fovea

Answer 16

central region of the retina, responsible for high-acuity vision. Ex. reading, depth perception

Question 17

Retina

Answer 17

the inner lining of the eye, has photoreceptors here. Fovea is located here

Question 18

optic disk

Answer 18

“blind spot.” Exit point in the retina for the optic nerve to leave

Question 19

3 layers of nerve cells in the retina (in order of signal transmission) and what are their functions?

Answer 19

photoreceptors, bipolar cell layer, ganglion cells. The photoreceptors and bipolar cells release NT (Glutamate) and form synapses with each other. Ganglion cell axons carry info to the brain

Question 20

Photoreceptor layer

Answer 20

the rods and cones are the photoreceptors on the retina. Rods detect low light and black and white vision. There # of rods outnumbers the cones. They are more concentrated in the peripheral retina. Cones provide us with most of the visual info about our environment. They are less effective in low light, are responsible for daytime vision, color vision, small features (acuity). Cones are more concentrated around the fovea.

Question 21

Rods and Cones segments description

Answer 21

Rods and cones have an inner segment and outer segment. The outer segment contains lamellae, which contains photopigments, which are chemicals that release energy when they are struck by light (light detection). The photopigments have 2 parts: opsin and retinal

Question 22

opsin and retinal

Answer 22

Opsin - protein that binds to retinal, many diff types
Retinal - lipid that binds to opsin

Question 23

Bipolar cell layer

Answer 23

in inner nuclear layer of retina. There are 3 types of cells in this layer: bipolar cells, horizontal cells, and amacrine cells. Bipolar cells are retinal cells that receive input from the photoreceptors and transfer them to ganglion cells.
Horizontal cells –> photoreceptor-bipolar cell connections
Amacrine cells –> bipolar-ganglion cell connections

Question 24

ganglion cells

Answer 24

axons that make up the optic nerve, carries visual info to the rest of the brain

Question 25

Transduction

Answer 25

Process by which energy from environment (stimulus) is converted to a change in membrane potential in a
neuron. The brain codes info based on which neurons are active and how active they are in any moment

Question 26

Signal transduction - Vision

Answer 26

1. Rod - Light breaks rhodopsin into its 2 parts: opsin & retinal. Rod’s membrane becomes hyperpolarized. This reduces the rod’s glutamate release.
2. Bipolar cell - Reduction in glutamate causes the cell to depolarize. No action potential occurs. This increases bipolar cell’s glutamate release.
3. Ganglion cell - Glutamate causes ganglion cells to depolarize. Triggers action potential. AP is carried to brain via optic nerve

Question 27

Central and Peripheral vision –> Receptive field

Answer 27

Part of the visual field that an individual neuron “sees,” which depends on the location of photoreceptors that provide it w/ visual info
- If a neuron receives info from photo receptors in the fovea, its receptive field will be at the fixation point (point where the eye is looking)
- If a neuron receives info from photoreceptors located in the periphery of a retina, its receptive field will be located off to one side

Question 28

Central and Peripheral vision –> 3 types of eye movement controlled by extraocular muscles

Answer 28

vergence, saccade, pursuit

Question 29

Vergence (eye movement)

Answer 29

the cooperative movements between the two eyes to focus on the same target. Eyes can also move in opposition.

Question 30

saccade (eye movement)

Answer 30

describes the very small, jerky movements when scanning a scene

Question 31

pursuit (eye movement)

Answer 31

the smooth movement of the eyes to track a moving target

Question 32

Overview of Visual Pathway

Answer 32

1. Optic nerves - formed by bundled axons of the retinal ganglion cells
2. Optic nerve from each eye join together at the base of the brain to form the Optic Chiasm
3. exits the eye and conveys info from the retinas to the lateral geniculate nucleus (LGN) in the thalamus
4. Neurons in the LGN send their axons to the primary visual cortex in the occipital lobes. (each hemisphere receives info from the contralateral side of visual scene)

Question 33

brain structures for Visual pathway

Answer 33

1. retina
2. optic nerve
3. LGN
4. Striate cortex
5. Extrastriate cortex

Question 34

Lateral Geniculate Nucleus (LGN)

Answer 34

step after optic nerves. located in the thalamus. made of 6 layers of neurons (including magnocellular layers and parvocellular layers). Receives info from the retinal ganglion cells.

Question 35

Magnocellular and Parvocellular layers

Answer 35

Magnocellular layers - 1, 2. MORE cell bodies, transmit info regarding perception of form, movement, and small difference in brightness. Parvocellular layers - 3, 4, 5, 6. Some layers have LESS cell bodies, transmit info regarding color perception and fine details.
Extra: Layers 1, 4, 6 receive info from 1 eye. Layers 2, 3, 5 receive info from other eyes

Question 36

Primary Visual/Striate Cortex/V1

Answer 36

receives info from LGN. First cortical region involved in combining visual info from several sources (Combines info from ganglion cells and does Basic processing). Contains map of the contralateral half of the visual field. has 6 layers

Question 37

V1/Striate cortex info cont.

Answer 37

Cytochrome oxidose (CO) blobs (get CO from layers 2 and 3 of LGN, color info is sent via these blobs from the parvocellular layers.
Modular organization - (Approx. 2,500 modules. Approx. 150,000 neurons)
Each module focused on a specific part of the visual field (Like a piece of a mosaic or puzzle piece).
Modules send info to other modules and V2/Extrastriate cortex

Question 38

Visual Association/Extrastriate Cortex/ V2+

Answer 38

Hierarchically arranged, combines info from individual modules (ex. perception of objects and visual scenes). Each region is specialized –> neurons respond to certain kinds of visual info Ex. Orientation, movement, spatial frequency, retinal disparity, color. Get full pic bc of fine details

Question 39

V2+/Extrastriate Cortex info cont.

Answer 39

There are two pathways: ventral stream and dorsal stream.
Ventral - “what info,” Size, shape, color, texture of objects, including people
Dorsal - “where info,” Where an object is, if it’s moving & speed/direction, guides navigation & skilled movements directed towards objects

Question 40

Role of retinal Ganglion cells in light/dark perception

Answer 40

ganglion cells in our retina each have a receptive field (everything in our range of vision. the portion of the visual field where the presentation of visual stimuli will produce a change in the firing rate of the ganglion cell APs). Aka the receptive field is the area of the visual field that excites or inhibits ganglion cells

Question 41

Two parts/types of receptive fields in ganglion cells

Answer 41

center/inner and surround/outer

Question 42

3 types of ganglion cells that can have increased or decreased firing rate

Answer 42

on, off, on/off

Question 43

On ganglion cell (inner)

Answer 43

EXCITATORY burst of APs when light falls on center
DECREASE in firing rate by light falling in surround

Question 44

Off ganglion cell (outer)

Answer 44

DECREASE in firing when light falls on center
INCREASE in firing rate when surround is illuminated

Question 45

On/off ganglion cells

Answer 45

Fire briefly when illumination changes (when light is suddenly turned on or off)

Question 46

Trichromatic theory

Answer 46

3 color theory. Level of the CONES, Different opsins absorb particular wavelengths more readily than others. Diff cones are sensitive to either blue, green, or red. Depends on the particular opsin a photoreceptor contains.

Question 47

Opponent processing

Answer 47

levels of GANGLION cells, 3-color code gets converted into an opponent-color system. focusing on prominence of a color. Perceiving color in terms of opposites. Retinal ganglion cells are sensitive to color Ex. red-green or yellow-blue. Other ganglion cells that receive input from cones encode relative brightness; serve as black and white detectors

Question 48

Effect of Opponent processing theory

Answer 48

rebound effect - If ganglion cells are excited for prolonged period of time, they will overcompensate briefly & fire faster or slower than baseline. results in negative after-image - image seen after a portion of the retina is exposed to an intense visual stimulus

Question 49

Unilateral neglect

Answer 49

inability to attend to one half of the visual field. usually after having a stroke, damage in right part of brain affects left side of visual field

Question 50

Agnosia

Answer 50

“without knowledge.” partial or complete inability to recognize sensory stimuli; NOT explained by a primary sensory deficit, dementia or delirium, or inability to speak/comprehend language (aphasia). 3 Types of Visual Agnosia: apperceptive, associative, prosopagnosia

Question 51

Apperceptive agnosia

Answer 51

Inability to develop a percept of the structure of an object.
Can’t perceive correct form of the object. Patient unable to recognize, copy, or match simply shapes. Cannot draw the bunny or group it w/ similar objects. Usually from gross bilateral damage to lateral parts of occipital lobes.

Question 52

Associative Agnosia

Answer 52

Preserved visuospatial skills, yet can’t recognize objects, can’t provide name or semantic knowledge about the object. Patient could copy bunny but not identify it. affects “Higher” cognitive processing and Memory.
More likely from damage to regions in the ventral stream

Question 53

Prosopagnosia

Answer 53

“face blindness.” inability to recognize faces. caused by damage to fusiform face area or bilateral damage.