Lecture 11: Vision 2 Flashcards
What are the ganglion cells?
output neurons of the retina
What are the characteristics of M (parasol) ganglion cells?
magnocellular = large
large receptive fields
motion detection, flicker and analysis of gross features
What are the characteristics of P (midget) ganglion cells?
parvocellular = small
more numerous
visual acuity and colour vision
What are the output targets of ganglion cells?
many brain regions
majority target the lateral geniculate nucleus (thalamus)
What is the sequence of the visual pathway?
retina -> optic nerve -> lateral geniculate nucleus -> optic radiations -> visual cortex (V1)
What is the optic chiasm formed by?
combination of the fibres from right and left optic nerves
the optic chiasm is where these fibres cross
Where does the optic chiasm lie?
at the base of the brain, anterior to the pituitary
What is the right visual hemifield “viewed” by?
the left hemisphere of the brain
What is the left visual hemifield “viewed” by?
the right hemisphere of the brain
What is a visual hemifield?
one half of the visual field, usually divided vertically through the fovea into the left or the right visual field
What is the lateral geniculate nucleus and what is its role?
LGN is part of the thalamus and its role is to receive functional streams of information
Which cells are contained within the LGN? What is their role?
magnocellular cells in layers 1,2 and parvocellular cells in layers 3-6
magnocellular cells receive input from M (parasol) ganglion cells and parvocellular cells receive input from P (midget) ganglion cells
How many layers are in the lateral geniculate nucleus?
six layers (numbered 1-6)
Where is the primary visual cortex?
in the occipital lobe at the back of the brain
What is the role of the back of the calcerine fissure?
represents the location of interpretation of central vision
Where is input from the LGN received?
layer 4C
How are cells arranged in cortex V1?
cells are arranged vertically in columns and comprise a functional unit
What are ocular dominance columns?
refers to the function of neurons in layer 4C
two LGNs-receive input from each eye (but segregated into different layers)
What do neurons respond best to in orientation columns?
neurons respond best to a bar of light at a specific orientation
What do layer 4C neurons respond to?
bars of light of different orientation and from a specific eye
How is information coming from both eyes segregated?
segregation of information from different types of LGN cells
M type GC/LGN input to layer 4Cɑ
P type GC/LGN input to layer 4Cβ
How is information coming from both eyes integrated?
mixing of information from each eye occurs in layers IVB and layer III
What are the two large cortical streams of visual processing?
dorsal and ventral
What is the role of the middle temporal lobe?
an area of the brain specialised for processing object motion
What is the role of area V4?
receives input from the blob and interblob regions of the primary visual cortex via V2
What are the receptive fields of neurons in V4 selective for?
orientation and colour
therefore, these neurons are important for perception of shape and colour
What is the role of the inferior temporal area?
a major output of area V4
important for visual memory, perception and perception of faces
