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Computational Vision
CSCI 363, Fall 2012
Lecture 8
Striate Cortex
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Response of Retinal Ganglion
Cells
Retinal Ganglion cells and bipolar cells have receptive fields that
exhibit a center-surround structure.
Question: What is
the center-surround
structure good for?
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From Retina to V1
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Types of Cells in V1
Hubel and Wiesel identified 3 types of cells in V1:
1. Simple Cells
2. Complex Cells
3. End-stopped Cells
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Simple Cells
Simple cells have discrete regions that have on or off responses to
a bar or an edge.
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Simple Cell Responses
Simple cells are selective for orientation and position.
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Orientation response
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A possible circuit for simple
cells
Hubel and Wiesel suggested this circuit to construct a simple
cell from a group of LGN cells.
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Complex Cells
•Complex cell responses are not divided into discrete on and off regions.
•Complex cells are orientation selective.
•Many complex cells respond best to moving stimuli.
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•Some complex cells are direction selective.
Complex Cell Circuit
Hubel and Wiesel proposed this circuit to construct a complex cell
from simple cells.
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End-stopped
Cells
Complex cells show
increased response with
the length of a line up
to some maximum
length. The response
then levels off.
End-stopped cells show
inhibition when a line
stimulus is too long.
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Direction Selectivity
Direction selective cells respond to motion in one direction, but
not to motion in the opposite direction.
The color of the bar (dark or light) does not matter for the
direction selectivity.
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Direction selective circuit
Barlow and Levick proposed this
circuit for direction selectivity.
Neurons are connected by delayed
inhibition along the null (nonresponding) direction of motion.
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Ocular Dominance Columns
Input from the LGN to layer 4C is segregated by eye. Inputs
alternate between the left and right eyes.
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Ocular Dominance columns on
the cortical surface
Labeling the cortex with a radioactive tracer from one eye
reveals that the ocular dominance columns form stripes on the
cortical surface.
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Ocular Preference
1 => responds only
to the contralateral
eye.
7 => responds only
to the ipsilateral
eye.
4 => responds
equally to both
eyes.
In V1, many cells respond to both eyes, but most prefer one eye over
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the other.
Orientation Columns
Preferred orientation varies smoothly across the cortex.
Cells in columns perpendicular to the surface have the same
orientation preference.
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Blobs and interblobs
When the cortex is stained with cytochrome oxidase, patches on
the surface stain more darkly than the rest of the cortex.
The patches are called "blobs".
Cells within the blobs have non-oriented receptive fields. They
respond well to particular wavelengths of light (color).
Blobs overlap the orientation and ocular dominance columns.
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A Hypercolumn
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Cortical Magnification
About 25% of striate cortex processes
the central 2.50 of the visual field.
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