Lecture 6 - Visual stimulus recognition Flashcards
what are the 3 main brain areas involved in visual stimulus recognition?
lateral geniculate nucleus
ventral/dorsal pathways
cortex
describe the structure of the LGN
relay station
ganglion cell axons have 1:1 connection with LGN projection neurons
2 magnocellular layers on ventral side
4 parvocellular layers on dorsal side
mixture of ipsilateral and contralateral neurons
Describe the main structural features of the ventral pathway
the ‘what’ pathway
parvocellular ganglions
temporal
describe the main structural features of the dorsal pathway
the ‘where’ pathway
magnocellular ganglion
parietal
describe the layering in the cortex
6 layers
oldest neurons at the bottom
What are the 3 kinds of columnar organisation in the cortex
Ocular dominance
orientation columns (direction)
blobs (colour)
what are the 2 experimental ways of showing ocular dominance columns
inject radioactive proline into one eye
inject radioactive glucose into the cortex and stimulate one eye with light
What are ocular dominance columns important for
depth perception
What do the experiments with ocular dominance columns show
that different layers receive inputs from different eyes
What do blobs do
process colour info
Where do blobs receive input from
parvocellular cells of LGN
What can you stain blobs with
cytochrome oxidase
what do orientation columns do
respond to different orientations of stimulus
Describe the Hubel Wiesel experiment
Used anesthetized cats with electrodes inserted into V1
.
Presented different visual stimuli on a screen.
Recorded neural activity in response to these stimuli.
Key Findings
Simple Cells in V1 respond best to bars or edges with a specific orientation.
Complex Cells respond to oriented edges regardless of position within their receptive field.
Hierarchy of Processing: Simple cells combine inputs from the retina and LGN, while complex cells integrate inputs from multiple simple cells.
Where are simple cells located
layers 4 and 6 of cortex
Describe receptive field of simple cells
bigger and elongated than retinal cells
has specifc stim / inhib zones
this allows them to respond to bars of certain FIXED orientation
Where are complex cells located
layers 2,3 and 5 of cortex
describe the receptive field of complex cells
no distinct stim / inhib zones
respond to MOVING stimulus anywhere in receptive field
when all of stimulus is in receptive field- response
some of stimulus out= no response
some stimulus out but in diff orientation = response(lower)
describe the hierarchical model of stimulus recognition
1) edges - retina and LGN
2)contours- primary visual cortex
3)object parts - primary visual cortex
4) objects from one point of view- inferotemporal cortex
5) invarient object detection
What happens to the complexity and receptive field of the neurons are we go further down hierarchical model
complexity increases
increase in receptive field
What does the Jenifer Aniston neuron show
the neuron responds to presentation of a specific object
What is an issue of the Jenifer Aniston model
doesnt take into account feedbacks from higher cortical areas
