Sight and Visual Pathways Flashcards
how can vision be experienced differently?
through
- motion
- 3D vision
- HD
- technicolour
where does sensory processing start?
in the eye, as the retina is part of the brain
what must the retina cope with?
transmitting the right amount of data in order to see the world clearly, but not enough to require a greater processing power
how do retinal images begin?
the wrong way around and flipped side to side - variable resolution
what must the brain do to retinal images?
change to the correct image outside of our conscious awareness
- shows how conscious perceptions of reality are different to mental interpretations of excited visual neurones
how does the eye grab information?
through receptive fields
receptive fields
region in the sensory periphery within which stimuli influence the electrical activity of sensory cells
when do photoreceptors only respond?
when light falls on their receptive field
output of photoreceptors
take the form of action potentials in retinal ganglion cells, whose axons take up the optic nerve
what happens to receptive fields as they get deeper into the brain?
get more structured and specific
how are receptive fields organised?
to detect changes in vision, by having different regions which turn cells on and off
where are retinal ganglion cells?
on the inner surface of the retina
what are retinal ganglion cells?
the output of the eye, which can have different receptive fields
this changes understanding of how the brain detects contrast and change
receptive fields of RGC
on-centre and off-surround cells become active and fire AP when receiving information that is greater when compared to the surround
other types of RPG receptive fields
off-centre and on-surround
the consequence of centre-surround antagonism
“simultaneous contrast illusion”
“simultaneous contrast illusion”
- on-centre receptive fields (on the darker background) are not inhibited, as there is less light to activate the off-surround, so the bar appears lighter
- on-centre cell (on the lighter background) is inhibited because there is more light to activate the off-surround, so the bar appears darker
how is retinal output used to signal changes?
by detecting edges over space, which breaks pictures apart due to centre-surround features and high sensitivity
what does edge detection provide the brain with?
lots of information about a scene to distinguish objects from their background
what do RGC respond to?
sudden changes in light over time
however, if this light stays on for a prolonged period of time then cells become inhibited
craik o’brien cornsweet illusion is a consequence of…
seeing only edges, as images containing only edges pass through the retina unchanged, whereas normal images are converted into edges
- interpreted in the same way by the brain
what are troxler fading and after-images?
an optical illusion where the fixation point disappears after focusing on this for a short period of time
how are after-images produced?
sudden removal of a prolonged image causes an after-image, as inhibition has a time lag
what does output from the retina reach?
the lateral geniculate nucleus
what is the LGN?
where information from the left and right VF combines in the brain, and RGC become specialised for motion or colour
what cells appear in the LGN?
parvocellular and magnocellular
parvocellular cells
respond to red-green colour, slow response, sensitive to detail, fine-detail resolution information
what do parvocellular cells respond to?
magnocellular cells
- used for motion, faster response, peripheral dominant, course detail
the LGN is the main…
relay point from the optic nerve on the way to the cortex
what is the LGN important for?
filtering what information reaches the cortex, by serving as the spotlight of attention to highlight information from certain parts of the VF
LGN and cortex
LGN provides top-down input to cortex
LGN layers
six layers - 3 are from ganglion cells, and 3 from eye axons
information is represented in both LGNS for each eye, kept segregated
different layers contain different information about motion and colour
layers 1 and 2
receive information about motion
layers 3, 4, 5, 6
receive information about colour
which LGN sees which VF?
left LGN sees the right VF
right LGN sees the left VF
information arrives in separate halves of the brain before entering the visual cortex
division of visual pathways
dorsal stream
ventral stream
dorsal stream
where objects are processed in space, motion, and depth
V3, V5/MT, V6, V7
ventral stream
recognising faces, places, and objects
V1, V2, V4, V8, LOC, OFA, FFA, PPA
