Chapter 6: Vision

Question 1

Pupil

Answer 1

opening through centre of eye where light enters

Question 2

Lens

Answer 2

focuses light (adjustable)

Question 3

Cornea

Answer 3

Focuses light (not adjustable)

Question 4

Retina

Answer 4

• where light is projected onto
• rear surface of eye
• lined with visual receptors

Question 5

Visual path to brain

Answer 5

-image is coded by different types of neuronal activity

back of eye -> bipolar cells -> ganglion cells-> ganglion axons that join together and travel back to brain

Question 6

Amackine cells

Answer 6

refine and input to ganglion cells and enable them to respond to shapes, movement, and other visual features

Question 7

Fovea

Answer 7

• acute detailed vision

- each receptor connects to single ganglion cell that has axon to the brain

Question 8

Midget Ganglion Cells

Answer 8

• small
• responds to a single cone
• each cone in fovea is connected to the brain with direct route that registers exact location of input
• 70% of input provided by midget ganglion cells therefore vision is dominated by what we see in the fovea

Question 9

process by which three types of cones, and the neurons they connect with, can produce a rich spectrum of perceived color

Answer 9

3 types of cones

1) short wavelength
2) medium wavelength
3) long wavelength

Question 10

Trichromatic or Young Helmholtz Theory

Answer 10

• perceive colour through relative rates of response by the 3 kinds of cones
• compare the response to cone with response of other cones
• discriminate wavelengths by ratio of activity across 3 types of cones
  ex) light @550nm excites medium and long receptors equally but not short receptors at all. This ratio determines perception of yellow-green
• mice only have 1 type of cone and are colourblind

Question 11

Opponent Process Theory

Answer 11

• perceive colour in terms of opposites
• brain has a mechanism that perceives colour on a continum
• cerebral cortex must be responsible for after images not individual receptors

Question 12

trade-off between acuity for detail and sensitivity to dim light.

Answer 12

cones=colour vision, abundant in fovea, useful in bright light, essential for colour vision
rods=good in dim light, abundant in periphery, respond to faint light, not useful in day light because bright light bleaches them
-20:1 more rods than cones
-each cone has own line to brain due to midget ganglion cells
-periphery rod receptors share a line with 10,00-100,00 other rods which is why acuity is not good

Question 13

Receptive Field

Answer 13

• area in visual space that excites or inhibits it
• point in space from which light strikes the cell
• receptive field grows as info becomes more processed (receptive fields converge)
• cone/rod -> bipolar cell -> ganglion cell

Question 14

Parvocellular Neuron

Answer 14

• small cell body
• small receptive field
• mostly near fovea

Question 15

Magnocellular neuron

Answer 15

• large cell body
• large receptive field
• evenly throughout retina

Question 16

Koniocellular neuron

Answer 16

• small cell body
• throughout retina
• axons from ganglion cells form optic nerve that goes to optic chiasm, where 1/2 axons cross to opposite hemisphere
• most go into lateral geniculate nucleus of thalamus
• when info reaches cortex it becomes more complex
• info from lateral geniculate nucleus of thalamus goes to primary visual cortex in occipital lobe aka Area V1
• primary visual cortex processes conscious visual perception

Question 17

Simple Cells

Answer 17

• receptive field with fixed excitatory and inhibitory zones
• more light that shines on excitatory=more cells respond
• more light that shine in inhibitory zone=less cells respond

Question 18

Complex Cells

Answer 18

• do not respond to exact location of stimulus
• respond to pattern of light in a particular orientation anywhere in its receptive field
• responds strongly to moving stimulus

Question 19

End stopped or hypercomplex cells

Answer 19

-similar to complex but has strong inhibitory area at 1 end of bar shaped receptive field

Question 20

Area V1 neurons respond strongly to…

Answer 20

-bar or edge shaped patterns meaning activity of this cell is perception of bar, line, or edge and spatial frequency

Question 21

Feature Detector

Answer 21

• neuron whose responses indicate presence of particular feature
• 80 brain areas (at least process info)

Question 22

Ventral Stream

Answer 22

-what pathway
-specializes in identifying and recognizing objects
ventral and dorsal stream communicate and help each other

Question 23

Dorsal Stream

Answer 23

-where pathway
-help motor system locate objects
ventral and dorsal stream communicate and help each other

Question 24

Area V1

Answer 24

Primary visual cortex

• sends info to Area V2 (secondary visual cortex)
• simple and complex cells
• connections are reciprocal
• V1 sends info to V2, V2 returns info to V1

Question 25

Area V2

Answer 25

- processes info and transmits it to additional areas - connections are reciprocal - V1 sends info to V2, V2 returns info to V1

Question 26

Inferior Temporal Cortex

Answer 26

- responds to identifiable objects - cells respond to what the viewer perceives not what the stimulus actually is - physically can recognize different views of the same object

Question 27

Area V4

Answer 27

- colour perception | - colour of an object in V4 corresponds to apparent or perceived colour depending on context

Question 28

Motion Perception

Answer 28

- Area MT (middle temporal cortex) aka area V5 and Area MST (middle superior temporal cortex) - receive most info from magnocellular path - MT=colour insensitive

Question 29

Area MT

Answer 29

- middle temporal cortex - responds selectively - detects acceleration and absolute speed - responds to motion in all dimensions - responds to photos of movement

Question 30

Area MST

Answer 30

- middle superior temporal cortex - responds best to expansion, contraction, or rotation of large visual scene (dorsal part) - message converges to temporal part of MST where cells respond object that moves in relation to its background - MST neurons enable you to distinguish between results of eye movement and result of object movements

Question 31

Early visual deprivation: one eye

Answer 31

- deprived experience in one eye: synapses in cortex become unresponsive to input from deprived eye - need to fix eye problems in sensitive period or eyes will not adapt or heal as quickly after this period is over

Question 32

Early visual deprivation: two eys

Answer 32

-deprived experience in both eyes: when both eyes have no input there is no competition for at least 3 weeks cortex remains responsive to visual input -over 3 weeks response starts to become sluggish and lose well defined receptive fields -eventually visual cortex starts responding to auditory or touch stimuli -cortical plasticity is greatest in early life but never ends -need to fix eye problems in sensitive period or eyes will not adapt or heal as quickly after this period is over

Question 33

Strabismus

Answer 33

- eyes do not point in same direction - children attend to 1 eye but not the other - impacts developing depth perception - need to fix eye problems in sensitive period or eyes will not adapt or heal as quickly after this period is over

Question 34

Astigmatism

Answer 34

- blurring of vision for lines in 1 direction caused by asymmetric curvature of eyes - need to fix eye problems in sensitive period or eyes will not adapt or heal as quickly after this period is over