Vision Flashcards
Path to the cortex:
1) Outside world
2) Retina
3) Optical chiasm/nerve
4) LGN e SC (thalamus)
5) Optical radiation
6) Primary visual cortex
The visual field of human eye are overlapping. The consequence is that:
-> information from the left visual field: right brain
-> information from the right visual field: left brain
The retina have 2 cells:
1) Rods -> scotopic system (night vision)
2) Cones -> photopic system (day vision)
The rods cells are
hyperpolarized (less chance of action potential).
lateral inhibition
neighbour cells send a signal to the neighbour for inhibit them. This function serve to detect edges and contours.
Blindsight
cortical blindness. Damage to V1 can lead to blindness for stimulus that are in the receptive field of those cortical regions.
Evolution of the eye
slow process, the only requirement appears to be the existence of light-sensitive cells
Thalamus
main gateway between external organs and the cortex.
LGN
lateral geniculate nucleus, composed by multiple layers (6), input from cones and rods. LGN receptive field have very similar organisation compared to ganglion cells (centre on, lateral off).
Hubel and Wiesel discover
ice cube model of visual cortex, different cells that respond to stimuli with different orientations -> orientation columns and ocular dominance column.
Simple cortical cells
get information from NGN -> understand the bar of light. They are composed by 3 ganglion cells that project into it -> a bar of light is projected into the screen.
Complex cells
receive information from simple cortical cells -> complex perceive the motion of the bar of light.
2 theories for colour vision
- Von Helmholtz: trichromatic hypothesis -> 3 kinds of receptors (blue, green and red) that composed the entire spectrum
- Herringer: opponent-process hypothesis -> blue vs yellow, red vs green and black vs white.
2 visual pathways:
1) Dorsal (where) -> where the stimuli occur in the environment (more magnocellular). It is fast, motion sensitive and it guides action
2)Ventral (what) -> more parvocellular. It identify colours, precise shape and it interact with memory (slower).
When you see an object in your left visual field, the information from LGN arrive at
the contralateral occipital cortex (not confuse right eye with right visual field)
When light falls onto the retina, it
hyperpolarises receptor cells (less neurotransmitter being release -> 2 possible effects, depending on the type of cells)
In the retina the fovea contains mostly
cones, because they are particularly good for processing colour vision and day light (while outside mostly rods)
When light falls on the retina outside the fovea, the first cells it reaches are
ganglion cells (they cover the entire area, they are being activated all the time). In other species that live in deep sea (don’t need light see) the receptor are at the front of the retina -> natura arrangement of the retina
Patients with blindsight have suffered damage to
the primary visual cortex (paradox, something to do with superior colliculus .. )
The mechanism of colour vision in ganglion and LGN cells is
spectral opponency (important to consider the theory
Jennifer Aniston cells were found in
Hippocampus