Chapter 6

Question 1

Law of specific nerve energies

Answer 1

Muller - Whatever excites a particular nerve establishes a special kind of energy unique to that nerve (action potentials from auditory nerve as sounds, olfactory as odours etc)

Question 2

Pupil

Answer 2

Opening in the centre of the iris that lets light into eye

Question 3

retina

Answer 3

Rear surface of the eye, lined with visual receptors; light from above strikes bottom of retina, light from below strikes top

Question 4

bipolar cells

Answer 4

messages from receptors at the back of the eye to bipolar cells located closer to the centre of the eye

Question 5

Ganglion cells

Answer 5

Messages from bipolar cells go to ganglion cells even closer to centre of the eye; ganglion cell axons join together and travel to the brain

Question 6

Amacrine cells

Answer 6

gather information from bipolar cells and send it to other bipolar, amacrine and gangion cells; various types refine input to ganglion cells and enable them to respond specifically to shapes, mvts and other features

Question 7

optic nerve

Answer 7

ganglion cell axons form optic nerve which travels out the back of the eye to the brain, 1 million axons in optic nerve

Question 8

blind spot

Answer 8

point at which the optic nerve exits the back of the eye, has no receptors because it is occupied by exiting axons and blood vessels; brain fills in gap in vision, and anything in blind spot of one eye is in vision of the other

Question 9

fovea

Answer 9

tiny area specialized for acute, detail vision; nearly unimpeded vision due to lack of axons and vessels near fovea, only cone receptors which each connect to their own bipolar cell which in turn connects to their own ganglion cell

Question 10

midget ganglion cell

Answer 10

ganglion cells in the fovea; small and respond to a single cone; provide 70% of visual input to brain

Question 11

rods

Answer 11

visual receptor abundant in periphery of the human retina that responds to faint light but bleached by bright light, outnumber cones 20:1 (120 million)

Question 12

cones

Answer 12

abundant in and near the fovea, less active in dim light, essential for colour vision, provide 90% of brain’s visual input (6 million)

Question 13

photopigments

Answer 13

chemicals that release energy when struck by light; 11-cis-retinal bound to opsins which modify sensitivity to various wavelengths of light; light converts 11-cis-retinal to all-trans-retinal and releases energy

Question 14

Trichromatic theory

Answer 14

Young-Helmholtz; we perceive colour through the relative rates of response by three kinds of cones, each maximally sensitive to a different set of wavelengths; short - blue, medium - green, long - red/yellow, all - white or grey (incomplete as a theory)

Question 15

visual field

Answer 15

the part of the world that you can see

Question 16

negative colour after image

Answer 16

the colour you see after looking at something under a bright light and then looking at a white surface - should be the “opposite” colour

Question 17

opponent-process theory

Answer 17

we perceive colour in terms of opposites

Question 18

colour constancy

Answer 18

ability to recognize colours despite changes in lighting

Question 19

retinex theory

Answer 19

Land; accounts for colour and brightness constancy; cortex compares information from carious parts of the retina to determine the brightness and colour for each area

Question 20

red-green colour vision deficiency

Answer 20

most common - long and medium wavelength cones have same photopigments; gene causing this is on X chromosome; 8% men, 1% women affected

Question 21

horizontal cells

Answer 21

inhibitory contact onto bipolar cells, horizontal and cells connect neurons across retina

Question 22

lateral geniculate nucleus

Answer 22

part of the thalamus, sends axons to other parts of the thalamus and occipital cortex

Question 23

lateral inhibition

Answer 23

reduction of activity in one neuron due to activity in neighbouring neurons; heightens contrast

Question 24

receptive field

Answer 24

area in visual space which excited or inhibits a cell

Question 25

parvocellular neurons

Answer 25

small cell bodies, small receptive field, mostly in or near the fovea, colour sensitive, respond to detailed analysis of stationary objects

Question 26

magnocellular neurons

Answer 26

larger cell bodies, larger receptive fields, throughout the retina, not colour sensitive, respond to movement and broad outlines of shape

Question 27

koniocellular neurons

Answer 27

small cell bodies, mostly small receptive fields though variable, throughout the retina, some are colour sensitive, respond to varied stimuli

Question 28

primary visual cortex (V1)

Answer 28

main visual cortex, accepts most visual input from LGN and thalamus, necessary for conscious visual perception

Question 29

blindsight

Answer 29

ability to respond in a limited way to visual information without perceiving it consciously (i.e. pointing toward an object or moving eyes toward an object)

Question 30

simple cell

Answer 30

located in V1, smallest receptive field, responds to bar or edge shaped stimuli with fixed excitatory and inhibitory zones

Question 31

complex cell

Answer 31

located in V1 and V2, medium sized receptive field, responds to bar or edge shaped stimuli without fixed excitatory or inhibitory zones

Question 32

End-stopped cell

Answer 32

aka hypercomplex cell; located in V1 and V2, largest receptive field, responds to bar or edge shaped stimuli with a strong inhibitory zone at one end

Question 33

feature detector

Answer 33

neurons whose response indicates the presence of a particular feature

Question 34

sensitive period

Answer 34

time period where experience has a particularly long and enduring influence

Question 35

retinal disparity

Answer 35

stereoscopic depth perception relies on this ability of the brain to detect the discrepancy between what the left and right eye sees

Question 36

strabismus

Answer 36

strabismic amblyopia; lazy eye - eyes do not point in the same direction

Question 37

astigmatism

Answer 37

blurring of vision for lines in one directon cause by an asymmetric curvature of the eyes (70% of infants, 10% of 4 year olds)

Question 38

secondary visual cortex V2

Answer 38

info from V1 comes here for further processing and transmission to further areas including back to V1

Question 39

Ventral stream

Answer 39

“what” pathway; through temporal cortex, specialized for identifying and recognizing objects

Question 40

Dorsal stream

Answer 40

“where” pathway; through parietal cortex, helps motor system locate objects

Question 41

inferior temporal cortex

Answer 41

cells respond to identifiable objects - what the viewer perceives, not what the stimulus is physically

Question 42

visual agnosia

Answer 42

usually result of damage in temporal cortex, an inability to recognize objects despite otherwise satisfactory vision

Question 43

fusiform gyrus

Answer 43

important for facial recognition; of the inferior temporal cortex, especially in the right hemisphere

Question 44

prosopagnosia

Answer 44

inability to recognize faces

Question 45

area MT

Answer 45

middle temporal cortex; area activated by motion, aka area V5, with MST

Question 46

area MST

Answer 46

medial superior temporal cortex

Question 47

motion blindness

Answer 47

ability to see objects but impairment at seeing if they are moving, or, if so, in what direction and how fast

Question 48

saccades

Answer 48

voluntary eye movements; several visual areas of the brain decrease activity during saccades