Chp 5.3: Vision

Question 1

Cornea

Answer 1

a transparent protective structure at the front of the eye

Question 2

Pupil

Answer 2

an adjustable opening that can dilate or constrict to control the amount of light that enters the eye.

Question 3

Iris

Answer 3

Controls the size of the pupil by muscles (colour part of eye)

Question 4

lens

Answer 4

• the transparent structure behind the pupil that changes its shape to focus images on the retina (thinner for far, thicker for near)

Question 5

retina

Answer 5

the light-sensitive back surface of the eye that contains the visual receptors

Question 6

Myopia (nearsightedness) (3)

Answer 6

• Difficulty seeing far away objects
• Eyeball is longer - back to front
• Lens focuses light in front of retina

Question 7

Hyperopia (farsightedness) (3)

Answer 7

• Difficulty seeing close-up objects
• Eyeball is too short
• Lens focuses light behind retina

Question 8

Rods (3)

Answer 8

•Function best in low illumination
•500 times more sensitive to light than cones
•Found mostly in periphery of retina –
though everywhere in retina except fovea

Question 9

Cones (4)

Answer 9

• For colour and detail
• Function best in high illumination
• Concentrated in centre of retina
• Fovea (in centre of retina) contains only cones

Question 10

fovea

Answer 10

a small area in the centre of the retina that contains only cones and in which visual acuity (clearness) is greatest

Question 11

bipolar cells

Answer 11

the second layer of retinal cells with which the rods and cones synapse

Question 12

ganglion cells

Answer 12

the third layer of retinal cells with which the bipolar cells synapse and whose axons form the optic nerve

Question 13

optic nerve

Answer 13

a bundle of ganglion cell axons in the retina that transmits visual information to the brain

Question 14

visual acuity

Answer 14

the ability to see fine detail

Question 15

Visual transduction (3)

Answer 15

• Action of photopigments inside rods and cones
• Absorption of light changes rate of neurotransmitter release
• Greater rate of release = the stronger the signal passed on

Question 16

photopigments

Answer 16

protein molecules within the rods and cones whose chemical reactions when absorbing light result in nerve impulses being generated

Question 17

dark adaptation

Answer 17

the progressive increase in brightness sensitivity that occurs over time as photopigments regenerate themselves during exposure to low levels of illumination

Question 18

Rods are insensitive to _____ light wavelengths

Answer 18

red

Question 19

trichromatic theory (5)

Answer 19

(Young-Helmholtz)
•Three types of colour receptors in retina
•Cones most sensitive to blue, green, red wavelengths
•Visual system combines activity from these cells
•Colours are perceived by additive mixture of impulses
•If all are equally activated - white colour is produced

Question 20

opponent-process theory

Answer 20

the theory proposed by Hering that the retina contains three sets of colour receptors that respond differentially to red-green, blue-yellow, and black-white; the opponent processes that result can produce a perception of any hue

Question 21

dual-process theory (3)

Answer 21

• Combines trichromatic and opponent process theories
• 3 cone types sensitive to short (blue), medium (blue), and long (red) wavelengths stimulate opponent-process reactions
• Opponent processes occur in ganglion cells, neurons in relay stations, and visual cortex

Question 22

Trichromats (2)

Answer 22

• Normal colour vision

* They are sensitive to all three systems: red-green, yellow-blue, and black-white

Question 23

Dichromat (2)

Answer 23

-A person who is colour-blind in only one of the systems (red-green or yellow-blue).
•Deficiency is caused by an absence of hue-sensitive photopigment in certain cone types.

Question 24

Monochromat

Answer 24

•Sensitive only to the black-white system and is totally colour-blind

Question 25

Thalamus

Answer 25

the brain’s sensory switchboard

Question 26

primary visual cortex

Answer 26

the area of the occipital lobe which receives impulses generated from the retina via the thalamus and analyzes visual input by using its feature detectors

Question 27

feature detectors

Answer 27

sensory neurons that respond to particular features of a stimulus, such as its shape, angle, or colour

Question 28

parallel processing

Answer 28

our ability to use our senses to take in a variety of information about an object and construct a unified image of its properties

Question 29

visual association cortex (3)

Answer 29

• Attaching meaning to what we see
• Information goes to visual association cortex
• Interpreted in terms of our memories and knowledge

Question 30

How does low/high levels of illumination change the pupil

Answer 30

• Low levels of illumination cause the pupil to dilate, letting more light into the eye to improve optical clarity
• Bright light triggers constriction of the pupil