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Problem 2: Connections (How do cells function in the visual cortex to…
Problem 2: Connections
Which areas of the brain are responsible for perception (functions)?
Sourced from Blake
Optic chasm: the convergence of optic nerves
ipsilateral (temporal): crossed
contralateral (nasal): uncrossed
80% to LGN / 20% to SC: respond to all orientations
LGN: Distributes retinal input; feedback loop w/ cortex and reticular activating system (controls level of arousal). 2 magno (borders), 4 parvo (colors).
SC: controls eye movements, have multi sensory cells (audio and vision), primal roots w/ receptive fields
V1: primary visual cortex (LGN and SC)
V2: feedback function
V3 (from powerpoint): formilocal moment, from interblobs
V3 > V4 (from powerpoint) = object identification
V5 (from powerpoint): global motion
V6 (from powerpoint): color; info from blobs
Bino/monocular. Ocular dominance: cells excited thru both eyes
Duality of visual processing (Goldstein): feedback system, intersect, up & out direction
Ventral/Temporal: “what” pathway
identifying objects
Dorsal/Parietal: “where” pathway
locating objects; action
retinotophic map from testing by electrode in LGN layers(Goldstein)
What happens to ganglion cells? (Blake, Chapter 4)
Ganglion cells: Process neural info and generates action potentials to visual stages
Bipolar cells connect to horizontal cells.
(response to decrease or increase in glutamate level: decrease = more light)
Photoreceptors are interconnected by horizontal cells
(amplifies photoreceptor signals)
amacrine cells receives input from bipolar cells and modify reponses of bipolar cells .
Amacrine cells are feedback cells that switches whether ganglion cells receive bipolar cell signal from either rods or cones
How do cells function in the visual cortex to different orientation?
Orientation selectivity: Cortical cells respond to lines and gradient (Blake)
hypercomplex cells (response to contour length + orientation)
complex cells (no well-defined zones but orientation preference)
simple cells (well-defined zones)
Cortical cells as feature detectors
ambiguity problem: no specific response of specific cells
adaptation: less responsive aft amt of time
e.g. tilt aftereffect: temp change w/ changed orientation of lines
blobs: neutrons that respond to lower division cells, has color opponency
Hypercoloums : aggregation of adjacent columns
Specialize and describe diff aspectsof visual perception (orientation, size, etc.)
Receptive feilds overlap same retinal territory. Patches of active cells throughout inactive cells bc of uneven spacing
V1 Neurons = contours (Blake & Goldstein)
Duck & rabbit challenge
What do different disorders tell us about the brain?
Specialisation in the Brain?
Achromatopsia: loss of color vision
interor part of occipital lobe on junction w/ temporal lobe
Propagnosia: can’t recognize familiar faces
portion of temporal lobe
FFA
EBA
PPA
Akinetopsia: affects motion perception
MT area
Meridional amblyopia : astigmatism (Blake)
All orientations are equally sharp = cannot experience oblique effect
Genetic factors: studies w/ babies
Carpented env: we 've seen more vertical/horizontal contours
Scotomas: patches of blindness in the field (Blake)
Head movement and fixating important
Foveal receptive fields small. Scotia damages larger cells
Occipital lobe in visual processing
