lecture 7: vision

Question 1

The Visual System is composed of:

Answer 1

• The problem of perception
• Sensation: eye and photoreceptors
• Pathways to the brain
• Early visual coding: striate cortex – V1, simple cells
• Later visual coding: extrastriate cortex
• V2, V3, V4, V5 (MT)
• What and Where pathways
• Specialized Faces, Places, Body Parts, Objects

Question 2

Optical illusions show:

Answer 2

perception of the world is dependent on the mind’s ability to transform incoming
information

Question 3

Sensation

Answer 3

Translation of external information (light, sound,
touch, odor, taste) into neural codes
Perception:
The organization and interpretation of sensations
into a coherent percept of the world

Question 4

Perception

Answer 4

The organization and interpretation of sensations
into a coherent percept of the world

Question 5

how are sensation and perception related

Answer 5

Sensation constrains perception

Question 6

where does vision begin

Answer 6

Vision begins at the eye with sensation

Question 7

what is light

Answer 7

Light is electromagnetic energy
that travels in waveforms that
have intensity (brightness) and
wavelength (color)

Question 8

Two Types of Receptors

Answer 8

rods and cones

Question 9

RODS

Answer 9

high-sensitivity, but low-resolution vision (poor acuity),
no color (black & white), good for low-light conditions

Question 10

CONES

Answer 10

good for high-resolution vision, and for color vision

Question 11

visual angle

Answer 11

how far i am from the fovea at any given time

Question 12

fovea

Answer 12

a small depression in the retina of the eye where visual acuity is highest. The center of the field of vision is focused in this region, where retinal cones are particularly concentrated.

Question 13

retina

Answer 13

The retina is a layer of photoreceptors cells and glial cells within the eye that captures incoming photons and transmits them along neuronal pathways as both electrical and chemical signals for the brain to perceive a visual picture

Question 14

blind spot

Answer 14

where the nerves leave your eye to form the optic nerve that goes to the brain

The blind spot function is the ability of the eye to see objects in its blind spot. This is because the eye has a blind spot in the back of the eye where the optic nerve enters the eye. This blind spot is about the size of a pea and is not visible to the eye. When an object is in the blind spot, the eye cannot see it

Question 15

lens

Answer 15

light passes through the lens (a clear inner part of the eye). The lens works together with the cornea to focus light correctly on the retina

Question 16

iris

Answer 16

The iris (the colored part of the eye) controls how much light the pupil lets in.

Question 17

pupil

Answer 17

The pupil is the opening at the center of the iris through which light passes

Question 18

cornea

Answer 18

The cornea is the clear window on the front of your eye. It’s made of tough, transparent tissue. Together with the sclera (white of your eye), the cornea helps protect your eye. It keeps out dirt, germs and other particles

Question 19

optic nerve

Answer 19

The optic nerve is critical to your vision. It’s an extension of your central nervous system, which includes your brain and spine. The optic nerve transmits electrical impulses from your eyes to your brain. Your brain processes this sensory information so that you can see

Question 20

Adaptation

Answer 20

there is a gradual decline in the reaction
to any stimulus if the stimulus persists unchanged.
Sensory systems respond more to change in
stimulation.

• Occurs in all sensory systems, both in the sensory receptors
  and the brain
• In color vision, sensitivity of cones to specific spectrums
  become saturated. Aftereffect of staring at one color is a
  temporary increased sensitivity to opponent (or
  complementary) color

Question 21

retinal ganglion cells

Question 22

bipolar cells

Question 23

amacrine cells

Question 24

cone receptor cells

Question 25

rod receptor cells

Question 26

horizontal cells

Question 27

Visual Computations in the Eye (what order are cells in the eye?)

Answer 27

Question 28

on-center RGC

Answer 28

bright in the center and dark in the immediate surround elicits strongest increase in activity

Question 29

off-center RGC

Answer 29

dark in the center and bright in the immediate surround elicits strongest increase in activity

Question 30

Retinogeniculate Visual Pathway

Answer 30

The retinogeniculate visual pathway (RGVP) conveys visual information from the retina to the lateral geniculate nucleus

Question 31

Left visual field images are communicated to

Answer 31

right visual cortex

Question 32

Right visual field images are communicated to

Answer 32

left visual cortex

Question 33

how does the visual system work

Answer 33

Your visual system is “cross wired" When light hits the retina (a light-sensitive layer of tissue at the back of the eye), special cells called photoreceptors turn the light into electrical signals. These electrical signals travel from the retina through the optic nerve to the brain. Then the brain turns the signals into the images you see

Question 34

Optic chiasm

Answer 34

Think of this like an intersection. It's where the nerves cross over, allowing your primary cortex to get information from both eyes. the optic nerve fibers from the nasal halves of the retinas cross to the opposite sides, where they join the fibers from the opposite temporal retinas to form the optic tracts

Question 35

V1 simple cells respond to

Answer 35

respond to orientation or lines (edges) Simple Cells are V1 neurons that respond to stimuli with particular orientations to objects within their receptive field. Like cells in the lateral geniculate nucleus (LGN), they have clear excitatory and inhibitory regions

Question 36

lateral geniculate nucleus

Answer 36

In neuroanatomy, the lateral geniculate nucleus (LGN; also called the lateral geniculate body or lateral geniculate complex) is a structure in the thalamus and a key component of the mammalian visual pathway. It is a small, ovoid, ventral projection of the thalamus where the thalamus connects with the optic nerve. In mammals, the visual thalamus, the lateral geniculate nucleus (LGN), relays visual information from the retina to the primary visual cortex (V1) and also receives feedback from V1. Both retinal and cortical inputs are critical to processing visual information within the LGN.

Question 37

hubel and wiesel

Answer 37

Hubel and Wiesel concluded that such plasticity is limited to early life, and called this a 'critical period' of visual cortex development. The discovery of critical periods demonstrated how experience shapes the developing brain's circuitry, thus perception of the external world

Question 38

retinotopic map

Answer 38

V1 has retinotopic map that codes for simple visual features

Question 39

Blindsight

Answer 39

some ‘vision’ via a subcortical visual pathway Blindsight is a phenomenon in which patients with damage in the primary visual cortex of the brain can tell where an object is although they claim they cannot see it. Scientists now provide compelling evidence that blindsight occurs because visual information is conveyed bypassing the primary visual cortex.

Question 40

Perception

Answer 40

Perception combines visual stimuli (bottom-up) and expectations (top-down)

Question 41

how do visual stimuli (bottom-up) and expectations (top-down) work together for the visual system

Answer 41

One “rule” the visual system seems to use to arbitrate between possible interpretations is to prefer the “non- accidental view” (the one that’s simplest, most probable, as opposed to least probable). How does the visual system solve this problem?

Question 42

When in visual processing do ‘top down’ processes influence perception?

Answer 42

Attention to regions of space can alter or enhance responding in V1 (and even LGN), but the response properties are the same

Question 43

how does v2 work

Answer 43

V2 shows responses to ‘illusory’ lines: V2, like V1, responds to lines and edges and has a retinotopic map, but it also responds to ‘illusory’ lines, suggesting it combines input from V1 and higher order cortical areas coding for expectations based on experience V2 (and V3) have dorsal and ventral components, after which the visual pathways split

Question 44

what pathway

Answer 44

(temporal lobe) The occipital-temporal visual area refers to the ventral or “what” pathway, where your brain recognizes objects and shapes. The temporal areas provide your long-term visual memories, helping them to recall what they’ve seen before and attach meaning to it. (For example, once you’ve seen a baseball, you know what it is next time you come across one!) Ventral damage can cause: Impairments in contrast sensitivity, form and color vision, and depth perception Impairments in object and face perception and route-finding

Question 45

where pathway

Answer 45

(parietal lobe) The occipital-parietal visual area refers to the beginning of the dorsal or “where” pathway. Here, your child's brain assesses where things are in space, like a ball zooming across a field or a puppy running toward a lap. Dorsal damage can cause: Trouble with spatial perception and perception of complex movement.

Question 46

Akinetopsia

Answer 46

Impaired motion perception due to cortical damage.

Question 47

Achromatopsia

Answer 47

Impaired color perception due to cortical damage. Different from peripheral color blindness due to absence of certain photoreceptors

Question 48

How does activation vary as a function of stimulus properties?

Answer 48

Color vs. Motion

Question 49

hemiachromatopsia

Answer 49

Hemiachromatopsia is defined as a disorder of impaired color perception with relative preservation of form vision in one-half of the visual field.

Question 50

what does color vision depend on

Answer 50

Depends on wavelength (cones) and luminance (or presumed luminance)

Question 51

Color Constancy & Luminance: the “non-accidental view”

Answer 51

Color constancy refers to our ability to perceive colors as relatively constant over varying illuminations (i.e. light sources). For example, a red apple will still look red on a sunny day or cloudy day – or in a grocery store or a home

Question 52

v5

Answer 52

codes for direction of motion

Question 53

Fusiform Face Area (FFA)

Answer 53

The fusiform face area (FFA) is a region of the cortex in the inferior temporal lobe of the brain that has been shown to respond most strongly to faces compared with other types of input (e.g., objects) for typically developing individuals.

Question 54

parahippocampal place area or PPA

Answer 54

The parahippocampal place area (PPA) is a functional region of the brain that responds more strongly to images of scenes and places compared to other classes of visual stimuli and is critical for scene and place recognition, as well as navigation

Question 55

Prosopagnosia

Answer 55

(“face agnosia”) Prosopagnosia (also known as face blindness or facial agnosia) is a neurological disorder characterized by the inability to recognize faces -Sometimes following damage to fusiform area -sometimes congenital (from birth; runs in families)

Question 56

ffa vs ppa

Answer 56