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Psychology Notes Perception (2nd year) Notes

2 Visual Pathways Notes

Updated 2 Visual Pathways Notes

Perception (2nd year) Notes

Perception (2nd year)

Approximately 27 pages

Topics include: general revision summary, important concepts, visual pathways, cortical structure & function, and object perception (including theories/models and evaluation). Relevant evidence for each topic is outlined, including methodology and findings.

These notes are informative, to the point, and easy to follow. They are drawn from a wide range of sources utilising additional course reading and independent reading....

The following is a more accessible 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:

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… Cells have… Cells show…
1-4 Parvocellular P-cells Small RFs

Sustained responses to stimuli

Ie respond as long as the stimulus is visible

5-6 Magnocellular M-cells Large RFs Fleeting responses

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 cells Orientation selective

Respond best to bars/edges in a given orientation

Optimised for edge and orientation detection

Do not respond at all to bars in the orthogonal orientation

Responds to light onset in a given orientation in the centre and offset in the surround

Doesn’t matter about length of bar just needs to cover the excitatory region of RF

Simple cell RFs have separate inhibitory and excitatory regions (like ganglion cells)

BUT instead of a concentric organisation they are side-by-side and are rectangular

Complex cells Direction selective

Prefer bars or edges in a particular orientation

Respond...

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