neural circuits for vision

Question 1

receptive field

Answer 1

area on the receptor surface that when stimulated, affects the firing of that neuron

in ganglion cells
sensory neurons in retina
receive impulses from photoreceptors and transmit information to brain

Question 2

Hartline

Answer 2

first to discover receptive fields in visual fields

isolated activity of single nerve cell in optic nerve
light shone onto different areas of retina
single cell only responds when light shone onto small, specific area (receptive field)

Question 3

transduction

Answer 3

converting environmental energy into electrical signals or nerve impulses

Question 4

transmission

Answer 4

when signals are sent from receptors to sensory neurons and from sensory neurons to brain

Question 5

spatial summation of rod cells

Answer 5

may rods cels converge onto one ganglion cell

means light shining onto area of retina, even two points in same region, can cause single ganglion cell to fire

receptive fields of many geach receptive field made of converging activity of many photoreceptors
ganglion cells overlap so many ganglion cells respond

Question 6

Kuffler

Answer 6

cells respond differently to light present in centre of field than light on outsider - centre surround receptive fields

some ganglion cells increased firing rate when light shone on centre and reduce when shone on outside
however some had opposite
on/off centre cells

Question 7

on-centre cells

Answer 7

increasing firing rate when light shone in centre
reduced when shone on outside

excitatory centre
inhibitory surround

Question 8

off-centre cells

Answer 8

decreased firing rate when light shone in centre
increased when shone on outside

inhibitory centre
excitatory surround

Question 9

Hubel and Weisel

Answer 9

instead of light shining onto retina
stimuli presented onto screen
cats sedated so eyes didn’t move

recording single neuron electrical activity using electrodes near neuron
measured firing rate/production of action potentials

clicking showed when neurons firing
more firing when light shone on centre for on centre cells

Question 10

Hubel and Weisel results

Answer 10

on centre cell
firing rate strongest when stimulus presented in centre compared to the surround

off centre cells
firing rate strongest when surround stimulated compared to centre

Question 11

centre surround antagonism

Answer 11

unresponsive when stimulus covered all receptive field

sum of inhibitory and excitatory input determines response of neurons
cancel each other out

Question 12

centre surround antagonism of on centre cells

Answer 12

maximally responsive when entire centre is stimulated without any stimulation of surround

when larger stimulus covers surround
inhibitory input cancels out excitatory input
firing rate decreases

Question 13

off centre cells

Answer 13

maximally stimulated when entire surround stimulated without any stimulation of centre

when larger dot covers centre as well
inhibitory input decreases neuron firing rate
cancels out excitatory input so rat decreases

Question 14

lateral inhibition

Answer 14

photoreceptors in centre of receptive field transmit excitatory signals to the ganglion cell
photoreceptors in surrounding receptive field transmit excitatory signals to intermediate neurons
intermediate neurons recieven input from surrounding receptive field send inhibitory signals to the ganglion cells

Question 15

importance of receptive fields of retinal ganglion cells

Answer 15

all visual information sent to brain encoded in responses of cells
ganglion cells form optic nerve

receptive fields extract, capture and enhance features in our vision
each captures from different areas of the receptive field

fundamental for understanding our perception of colour, luminance contrasts and edges

Question 16

cells in an on centre cell

Answer 16

photoreceptors in centre send excitatory inputs to bipolar cells then ganglion cells

inhibitory input from surround sent by horizontal and amacrine cells

receive excitation from photoreceptors in surrounding areas of retina
send inhibitory input to ganglion cell instead of excitatory

Question 17

stimulation of the receptive field

Answer 17

initial response, no response - stimulus outside receptive field entirely
passes into surround - firing of cell decreases, inhibitory
moves into centre - firing increases, excitatory
decreases as more inhibitory surround stimulated
decreases more when entire receptive field stimulated due to antagonism

Question 18

colour opponent of ganglion cells

Answer 18

can process differences in wavelengths

some have red-green colour oppenancy
- excited by red wavelengths in centre (long)
- inhibited by green in surround (medium)
or vice versa

some have blue-yellow opponent
- excited by blue in centre (short)
- inhibited by yellow in surround (long or medium)
or vice versa

Question 19

what can a centre surround receive field encode?

Answer 19

differences in luminance
position of edges
differences in colour

cant encode orientation
- stimulus presented with result in same response no matter orientation
information on orientation comes from further up in visual system

Question 20

thalamus

Answer 20

receives all sensory input from organs before filtering
sends to correct area of cerebral cortex

subcortical structure, sits below cerebral cortex
acts s sensory related system for brain

Question 21

pathway in visual system

Answer 21

from ganglion cells, visual information sent along optic nerve
sent to area of thalamus
Lateral Geniculate Nucleus
information then transmitted to primary visual cortex

Question 22

retinotopic map

Answer 22

LGN and primary visual cortex contain a retinotopic map

each part responds to a specific part of the retina
electrical signalling from specific areas sent by specific ganglion cells to specific area of LGN

LGN organised according to areas of retina it processes information from

Question 23

LGN cells

Answer 23

also have centre surround organisation of receptive fields

when entirety of excitatory centre stimulated, neural firing rate increases
only surround stimulated, inhibits firing rate
some of surround and centre, cancel out, little change in firing rate relative to no light at all

Question 24

lateral geniculate nucleus

Answer 24

relay system for visual information sent from eye to primary visual cortex

first area where information segregated between left and right visual field

receives input from retina and primary visual cortex
separates visual information from both left and right visual field

Question 25

left and right areas of visual field

Answer 25

light on right side of visual field reflected to left side of retina on each eye - nasal region left side of field reflected onto right side of retina - temporal retina light reflected onto opposing sides of retina in each eye optic Neve from nasal retina decussates at optic chiasm

Answer 26

light reflected on nasal retina crosses over to other side of brain fibres crossing decussate at optic chiasm information from temporal retina does not cross at chiasm creates fibre track carrying information from nasal portion of one eye and temporal of another carries information from one side of visual field

Question 27

what does each side process from?

Answer 27

left side temporal of left retina and nasal from right carries information from right visual field right side temporal of left retina and nasal from left carries information from left visual field information then sent to LGN

Question 28

Hubel and Weisel in neurons in primary visual cortex (orientation)

Answer 28

cat with microelectronics recording action potential of single neuron from primary visual cortex cat sedated and gave fixed onto point straight bar presented onto screen and moved around until receptive field of neuron identified neuron doesn't respond to stimuli presented outside of receptive field once field identified stimulus altered to record respond of neon - orientation changed

Question 29

neurons in primary visual cortex

Answer 29

don't display simple centre surround receptive field like ganglion cells cells respond best to those presented at a specific angle sensitive to orientation of stimulus when bar horizontal or vertical = little response strongest response when bar presented at 50 degree angle still have excitatory and inhibitory areas - can be cancelled out with bar = excitatory outside = inhibitory reduced firing rate when more of area outside bar is stimulated

Question 30

orientation tuning curve of a neuron

Answer 30

change in firing rate in response to different orientation of lines

Question 31

simple cells

Answer 31

cells in primary visual cortex receptive fields elongated selected for specific line orientations

Question 32

complex cells

Answer 32

also respond to bars of light of a particular orientation but also respond to movement of bars of light in specific directions

Question 33

end stopped cells

Answer 33

respond to moving lines of specific length moving corners or angle moving in a particular direction don't respond to stimuli the are too long or large

Question 34

feature detectors in visual system

Answer 34

simple cells complex cells end stopped cells

Question 35

disparity selective cells

Answer 35

stereoscopic depth perception (3D) relies on binocular disparity (difference between 2 images reflected onto retina of each eye) selectively respond to the amount of disparity between images presented to each retina perform better when light reflected onto non-corresponding point of each eye

Question 36

zero disparity cells

Answer 36

perform better (fire stronger) when light reflected onto non-corresponding points of each eye different areas of the retina

Question 37

DeAngelis et al

Answer 37

monkey trained to indicate depth from disparate images disparity selective neurons activated by this process experimenter used micro stimulation (electrode) to activate different disparity selective neurons in visual cortex monkey shifted judgment to the artificially stimulated disparity rather than actual

Question 38

horopter

Answer 38

curved line or surface / area of visual field that represents the points in space that stimulate corresponding points on the retina of each eye

Question 39

pathway from retina to cortex

Answer 39

single sfrom retina travel through the optic nerve to the LGN then to portion of optic nerve carrying information from nasal retina decussates at optic chiasm to contralateral hemisphere towards LGN primary visual cortex in occipital love then processed in secondary visual accusation cortex then through 2 pathways to the temporal lobe and parietal lobe

Question 40

dorsal and ventral streams

Answer 40

dorsal carries information superiorly to parietal lobe ventral stream carries information inferiorly to inferior parietal lobe dorsal = where involved in processing object location, depth and purpose venture = what involved in object identification and recognition

Question 41

Ungerleider and Mishkin

Answer 41

distinguished between ventral and dorsal pathways projecting from the primary visual cortex to the inferior temporal cortex and the posterior parietal cortex these pathways are involved in object identification and location