PSY368 Section 2

Question 1

What percentage of information from the world comes through the visual system?

Answer 1

80%

Question 2

70% of the sensory receptors in the whole body are located in

Answer 2

the retinas

Question 3

The stimulus for vision is

Answer 3

electromagnetic radiation, specifically, the visible spectrum

Question 4

The function of the eye

Answer 4

focus electromagnetic energy, transduce it into a neural signal, then begin signal processing

Question 5

Why do humans have binocular vision?

Answer 5

Binocular vision occurs in primates to help us use tools

Question 6

Cornea (definition)

Answer 6

transparent front part of the eye

Question 7

Sclera (definition)

Answer 7

white part of the eye; gives structure

Question 8

Vascular Tunic (definition)

Answer 8

contains blood vessels that feed the eye

Question 9

Iris (definition)

Answer 9

colored diaphragm muscle that determines pupil size

Question 10

Pupil (definition)

Answer 10

the aperture through which light enters the globe

Question 11

Cells composing the Retina

Answer 11

Photoreceptors
Bipolar Cells
Ganglion cells
Horizontal Cells
Amacrine Cells

Question 12

Photoreceptors (definition)

Answer 12

pigmented cells that produce electrical signals when struck by light

Question 13

Bipolar cells (definition)

Answer 13

synaptically connects cones and rods with ganglion cells

Question 14

Ganglion cells (definition)

Answer 14

axons composing the optic nerve and leave the eye via the optic disc

Question 15

Horizontal cells (definition)

Answer 15

modulate activity between the photoreceptors and the bipolar cells

Question 16

Amacrine cells (definition)

Answer 16

modulate activity between the bipolar and the ganglion cells

Question 17

The Blind Spot (definition)

Answer 17

a hole in the retina through which the ganglion cells axons leave the eye and travel to the brain

Question 18

Why do we not see a black hole due to the blind spot?

Answer 18

Our visual system fills in the hole with the color and texture of the surrounding region – known as perceptual filling-in

Question 19

The two ocular mechanisms for bending light

Answer 19

Cornea - accounts for about 80%
Lens - accounts for about 20%

Question 20

What is the difference between the ocular mechanisms of the cornea and the lens

Answer 20

The cornea bends light needed to focus on the retina
The lens bends light already partially bent by the cornea and focuses it precisely on the retina

Question 21

How does the lens change to focus objects?

Answer 21

Light focused behind/in front of the retina causes blurry vision. When needed, the lens thickens to bend more light and bring objects into focus - a process called accommodation

Question 22

Near point (definition)

Answer 22

the nearest distance that an object can be focused

Question 23

Presbyopia (definition)

Answer 23

the hardening of the lens over time, resulting in a lengthening of the near point

Question 24

Cataract (definition)

Answer 24

loss of lens transparency

Question 25

Hypermetropia (definition)

Answer 25

the eye is too short; near things are blurry - the lens cannot bend enough light even at its thickest

Question 26

Myopia (definition)

Answer 26

the eye is too elongated; far things are blurry - even when relaxed the lens is bending too much light

Question 27

Treatment for hypermetropia

Answer 27

Adding a convex corrective lens which helps the eye's lens by bending light before it reaches the eye

Question 28

Treatment for myopia

Answer 28

Adding a concave corrective lens solves this problem by causing parallel lights rays from far objects to diverge

Question 29

The Fovea (definition)

Answer 29

the part of the retina with the best visual acuity

Question 30

Visual acuity (definition)

Answer 30

the ability to resolve fine details

Question 31

To have the clearest possible view of an object, we want the image to focus

Answer 31

on our fovea

Question 32

Visual angle (definition)

Answer 32

the angle that a stimulus subtends on the retina

Question 33

Visual acuity ____ with increasing distance from the fovea

Answer 33

decreases

Question 34

The more photoreceptors converging on a ganglion cell,

Answer 34

the greater loss of spatial information

Question 35

Rods operate under ___ lighting conditions, cones operate under ____ lighting conditions

Answer 35

dim; brighter

Question 36

Photopic vision (definition)

Answer 36

day vision, mediated by cones

Question 37

Scotopic vision (definition)

Answer 37

night vision, mediated by rods

Question 38

Differences between Rods and Cones

Answer 38

Rods: Peripheral vision, poor spatial resolution, more light sensitive, function in dim light Cones: central vision, good spatial resolution, less light sensitive, function in daylight, color vision

Question 39

Rhodopsin (definition)

Answer 39

pigment coating rod outer segments; composed of Retinal and Scotopsin molecules

Question 40

Isomerization (definition)

Answer 40

a photo of light hits rhodopsin, the retinal and scotopsin binding changes which causes the rhodopsin to change its shape

Question 41

Visual Sensory Transduction in the eye

Answer 41

After isomerization, receptor sites open resulting in cell hyperpolarization. This is the moment visual sensory transduction occurs as light energy changes into neural energy

Question 42

Brightness is the perceptual correlate of ____

Answer 42

luminance

Question 43

Dark adaptation (definition)

Answer 43

change in brightness sensitivity to accommodate the current level of illumination

Question 44

Absolute thresholds for light intensity ____ with time spent in the dark

Answer 44

decrease

Question 45

Dark adaptation is mediated by

Answer 45

both rods and cones; Cones provide us with a fast boost in sensitivity but quickly max out. Rods are slower to kick in but enable us to see in extremely dim lights

Question 46

Neuronal computation (definition)

Answer 46

describes how neuron systems interact to produce behavior (spatial and temporal interactions)

Question 47

Receptive field (definition)

Answer 47

the region of your visual field that a given cell "sees"

Question 48

To measure the receptive field

Answer 48

an electrode is inserted into a brain cell and the experimenter observes where a stimulus must be presented for the cell to fire; create a map representing the receptive field of that cell

Question 49

In general, the greater the convergence, _______

Answer 49

the larger the size of the receptive field

Question 50

Receptive fields are roughly ____ in shape

Answer 50

circular

Question 51

Receptive field diameter generally ____ with convergence

Answer 51

increases (explains why cells coding central vision have small RFs and peripheral vision have larger RFs)

Question 52

Center-Surround Antagonist Organization

Answer 52

The receptive field has an excitatory center and an inhibitory surround - The firing rate of a cell increases with stimulation of the center and decreases with stimulation of the surround

Question 53

Lateral inhibition (definition)

Answer 53

inhibition that spreads laterally in a neuronal circuit

Question 54

In the retina, the horizontal and amacrine cells laterally inhibit the ______, resulting in the ______

Answer 54

ganglion cells; center-surround RF organization

Question 55

Lateral inhibition explains

Answer 55

Center-surround antagonistic organization The Hermann Grid Mach Bands

Question 56

The dots in the Hermann grid are caused by

Answer 56

strong lateral inhibition at the grid intersections (relative to the rest of the grid) and center-surround RFs

Question 57

Mach bands are caused by

Answer 57

differential lateral inhibition from cells on either side of the band

Question 58

Mach bands may benefit us as

Answer 58

they serve to enhance perceptual edges (edge enhancement)

Question 59

Edge Enhancement (definition)

Answer 59

a term referring to the low-level accentuation of an edge so as to make that edge more easily used by a perceptual system

Question 60

More lateral inhibition means ____; Less Lateral inhibition means _____

Answer 60

less firing; more firing