The retina, LGN + visual pathways Flashcards
What is actually presented on the back of the eye on the surface of the retina?
Upside down
Its flipped left or right
Poor resolution
How does the eye grab information from the world?
Receptive fields
Describe a receptive field
No retinal cell sees all the image
Each one only gets light from a small part of space
This part of space is called the cells “receptive field”
When do photoreceptors respond?
- when light falls on their receptive field
- whose output takes form of action potentials in retinal ganglion cells
How does the brain form an image of the world?
The brain has to pull together all of the output from many retinal ganglion cells to construct an image of the world
What are retinal ganglion cells?
Receive output from photoreceptors and its the axons of these cells that are sensitive to edge information
What are centre surround cells?
fired/ activated when light hits the centre of their receptive field whereas light stimulating the surrounding area causes inhibition
sensitive to contrast (light vs dark)
What is the the consequence of centre- surround antagonism
“simultaneous contrast illusion”
The surrounding background is influencing our perception of the target colour - this is because of receptive fields
What is the consequence of seeing edges?
“Craik-O’brein-cornsweet illusion”
a very small area effects the perception of entire large areas,
How does signalling change over time?
Inhibition over time causes neurons to reduce their activity (save energy)
How does signalling change over space?
Lack of crisp edges mean that spatial location is not signalled well
What is the LGN?
Gateway the cortex
Information from the eyes crosses over at the optic chiasm and ends up at the LGN
Information starts to get separated in terms of colour and emotion
It is structured of different layers, in between those layers are cells
What is the function of K cells
process information about blue and yellow
What is the function of P cells
respond slowly to colour (specifically red and green), fovea dominant, fine detail
What is the function of M cells
respond fast to colour, motion and depth sensitive, peripheral dominant, coarse detail
What does each layer in the LGN contain?
a complete retinotopic map of half of the visual field
How does the LGN receive input?
No cell in each half of the LGN receives input from both eyes
But each LGN receives input from eyes
What is the “where” pathway?
Dorsal stream/ pathway
V3, V5, V6, V7
Motion, 3D shape,events, sequences, emotions
What is the “what” pathway?
Ventral stream/ pathway
V1,V2,V4,V8
LOC, OFA, FFA, PPA
Outlines, colour, form, objects, facial identity
Where do illusions occur?
Illusions are in the eye not the mind
