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2 Visual Pathways Notes

Psychology Notes > Perception (2nd year) Notes

This is an extract of our 2 Visual Pathways document, which we sell as part of our Perception (2nd year) Notes collection written by the top tier of Durham University students.

The following is a more accessble plain text extract of the PDF sample above, taken from our Perception (2nd year) Notes. Due to the challenges of extracting text from PDFs, it will have odd formatting:

Visual pathways
The visual pathways from retina to primary visual cortex:
 Info leaves through the optic nerve
 Goes through the optic chiasm to the LGN
 Striate cortex (V1)
 Retinotopic map
 Simple, complex and hypercomplex cells
Geniculostriate pathways = involved in conscious perceptual experience
G pathway = via the ganglion cells  LGN V1
Visual info is passed to LGN and cortex via 2 independent and parallel channels: the M and P channels
 P-channel transmits info about colour and form
 M-channel transmits info about motion
LGN = first stop for visual info after retina for conscious vision  where retinal output is organised into layers
LGN has 6 layers with different RF properties:
Layers Type of layers Layer gets input from…
1-4
Parvocellular
P-cells

5-6

Magnocellular

M-cells

Cells have…

Cells show…

Small RFs

Sustained responses to stimuli
Ie respond as long as the stimulus is visible
Fleeting responses

Large RFs

LGN has a retinotopic map = location of neurons in LGN corresponds to locations in the world
Because of their RF properties:
P-cells = form and colour perception
M-cells = motion perception
= shown in lesion studies:
 Where either the P or M layers of the LGN have been damaged
 By recording from these cells directly and characterising their response properties
LGN cells have similar RF properties to retinal ganglion cells
LGN keeps the inputs from the 2 eyes in separate layers
Each LGN represents the contralateral visual field  right LGN represents L VF
Info from the LGN  layer 4 of V1
Neurons in V1 also form a retinotopic form
Neuron properties in the input layer are similar to LGN neurons
BUT when the visual signal is further processed in others layers of V1, RF properties become more complex
Hubel & Wiesel: research into V1 RF properties
V1 neurons have oriented RF  prefer elongated stimuli in specific orientations
Simple

Orientatio

Respond best to bars/edges in a given orientation

Buy the full version of these notes or essay plans and more in our Perception (2nd year) Notes.