neural circuits for vision Flashcards
receptive field
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
Hartline
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)
transduction
converting environmental energy into electrical signals or nerve impulses
transmission
when signals are sent from receptors to sensory neurons and from sensory neurons to brain
spatial summation of rod cells
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
Kuffler
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
on-centre cells
increasing firing rate when light shone in centre
reduced when shone on outside
excitatory centre
inhibitory surround
off-centre cells
decreased firing rate when light shone in centre
increased when shone on outside
inhibitory centre
excitatory surround
Hubel and Weisel
instead of light shining onto retina
stimuli presented onto screen
cats sedated so eyes didnβt 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
Hubel and Weisel results
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
centre surround antagonism
unresponsive when stimulus covered all receptive field
sum of inhibitory and excitatory input determines response of neurons
cancel each other out
centre surround antagonism of on centre cells
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
off centre cells
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
lateral inhibition
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
importance of receptive fields of retinal ganglion cells
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
cells in an on centre cell
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
stimulation of the receptive field
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
colour opponent of ganglion cells
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
what can a centre surround receive field encode?
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
thalamus
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
pathway in visual system
from ganglion cells, visual information sent along optic nerve
sent to area of thalamus
Lateral Geniculate Nucleus
information then transmitted to primary visual cortex
retinotopic map
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
LGN cells
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
lateral geniculate nucleus
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
left and right areas of visual field
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
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
what does each side process from?
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
Hubel and Weisel in neurons in primary visual cortex
(orientation)
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 doesnβt respond to stimuli presented outside of receptive field
once field identified stimulus altered to record respond of neon
- orientation changed
neurons in primary visual cortex
donβt 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
orientation tuning curve of a neuron
change in firing rate in response to different orientation of lines
simple cells
cells in primary visual cortex
receptive fields elongated
selected for specific line orientations
complex cells
also respond to bars of light of a particular orientation
but also respond to movement of bars of light in specific directions
end stopped cells
respond to moving lines of specific length
moving corners or angle
moving in a particular direction
donβt respond to stimuli the are too long or large
feature detectors in visual system
simple cells
complex cells
end stopped cells
disparity selective cells
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
zero disparity cells
perform better (fire stronger) when light reflected onto non-corresponding points of each eye
different areas of the retina
DeAngelis et al
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
horopter
curved line or surface / area of visual field that represents the points in space that stimulate corresponding points on the retina of each eye
pathway from retina to cortex
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
dorsal and ventral streams
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
Ungerleider and Mishkin
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