1. Bruce Draper Department of Computer Science Colorado State University
Early Vision
Bruce Draper
Department of Computer Science
Colorado State University

2. Overview “The Biomimetic Vision Trilogy” Selective Attention
Understanding the problem
Last week
Early Vision
Understanding the literature
Today
Ventral vision
Understanding object recognition
March 9 (next week)

3. General Theme Vision evolved to serve the needs of animals
Vision is action oriented (it guides behavior)
Actions may be immediate (e.g. grasp, navigate)
Actions may be delayed (“perception”)
Vision is not one system
As animals became more complex, more and more visual capabilities evolved in separate systems
Note: this is not a new idea. See The Visual Brain in Action by Milner & Goodale 1996; The Metaphorical Brain by Arbib 1972; or even Cybernetics by Weiner 1948.

4. Input: The Eye(s) Start at the beginning: Lens focuses light
Iris serves as aperture
Retina contains receptors
Optic nerve transmits to brain
Lens, iris are controlled by muscles under the control of the brain
S. Palmer. Vision Science. P. 27

5. Retina as Processor Five cell types: receptor (rod/cones)
S. Palmer. Vision Science. P. 30
Five cell types:
receptor (rod/cones)
Species dependent
horizontal
bipolar cells
amacrine cells
ganglion cells
Its inside out!
Blind spot where optic nerve passes through retina

6. Retina (cont.) Ganglion Cells
The first cells to produce spike discharges
Other retinal cells use graded potentials
Spikes are needed for long distance communication
On-center off-surround
Off-center on-surround

7. Two Types of Ganglion Cells
P ganglion cells in primates (like Y cells in cats):
Large receptive fields (low frequency?)
Transient response
Fast transmission
Receive inputs from all colors and from rods
P ganglion cells (like X cells in cats):
Small receptive fields (high frequency?)
Sustained response
Medium transmission
Color opponent channels

8. Fields of View & Stereo
Right hemisphere receives the left visual field from both eyes
And vice-versa
Splitting the field of view supports disparity computations
High resolution in fovea, lower elsewhere
Fovea is ±2° (thumbnail at arms length)

9. Visual Projections The eye + optic nerve is a shared device
There are eleven projections (“endpoints”) of the optic nerve:
Retinogeniculate Projection
Onto LGNd (Lateral Geniculate Nucleus, dorsal) and then to V1 (a.k.a. primary visual cortex, striate cortex)…
This path is dominant in people; barely evident in non-mammals
Retinotectal Projection
Onto Superior Colliculus, then the Pulvinar Nucleus, then LGN, V1, MT, higher level centers…
This path is dominant in non-mammals; evolutionarily older
Involved in eye movements, motion, tracking

10. S. Palmer. Vision Science. P. 25.
Projections (LGN & S.C.)
S. Palmer. Vision Science. P. 25.

11. Projections (II) At least 8 more (minor) projections!
Retina Suprachiasmatic Nucleus
Circadian rhythms
SN is part of the hypothalamus (like LGNd)
SN receives multi-modal projections
Retina Nucleus of the Optic Tract (NOT)
Optokinetic nystagmus
Retina  Accessory Optic Nuclei
Visual control of posture, locomotion
Retina  Pretectum
Pupillary Light Reflex

12. Two LGNd Channels
P cells in the retina project to the two magnocellular (“large cell”) layers in the LGN.
Livingstone & Hubel: color-blind, fast, high contrast sensitivity, low spatial resolution
P cells in the retina project to the four parvocellular (“small cell”) layers in the LGN.
L&H: color selective, slow, low contrast sensitivity, high spatial resolution
LGNd also has interlaminar layers with unknown role/properties
Receives projections from optic nerve, S.C.
Right at the levels of cells; wrong at the level of populations

13. Primary Visual Cortex (V1)
First cortical visual area
Columnar (like all cortex)
Retinotopically mapped
Ocular dominance columns
Edges (Gabor filters), color, disparity & motion maps
Connects to other retinotopic areas (V2, V3, MT)

14. Proof of Retinotopic Mapping
Tootell, et al
Proof of Retinotopic Mapping
Pattern flashed (like a strobe) in front of monkey injected with sugar dye
Left primary visual cortex of the same monkey

15. Single Cell Recordings in V1

16. Two Channels in V1 P  Magnocellular LGN Layers  layer 4C of V1.
Projects further to layer 4B
Motion direction selective
Orientation selectivity & binocular
No color
P  Parvocellular LGN  4C of V1
Projects to layers 2 & 3.
Layers 2 & 3 subdivide into “blobs” and “interblobs”:
Blobs are color selective, simple receptive fields
No orientation/movement direction selectivity, binocularity.
Prefer low frequencies, have small Magnocellular input
Interblobs have reduced (non-zero) color selectivity
Binocular, high-frequency, orientation selective

17. Jones & Palmer 1987
Simple Cells
The first orientation selective cells found in V1 were labeled “simple cells”
Well approximated by Gabor functions with fixed orientations, scales and phases

18. Complex Cells
The second set of orientation selective cells were called complex cells
Well modeled as combining 90° out-of-phase Gabor responses (quadrature pairs)
Captures energy at a particular orientation & scale
even
filter  + 
odd
filter 

19. Organization of cells in V1
Hubel & Weisel proposed the following organization for cells in V1

20. Well, a little more complex…
Ocular dominance
columns
Color-coded orientation
Sensitivity columns

21. More on V1 Only about 27% of V1 cells are orientation selective
About 70% of orientation selective cells are complex cells
Orientation selective cells also include end-stopped cells (a.k.a. hypercomplex cells), and grating cells.
Non-orientation selective cells include cells that respond to:
Color (Hue/Sat maps?)
Disparity
Motion

22. From Van Essen 1992. Image can be found at
V1 Connections
V1 is the starting point of cortical visual processing.
Dorsal projections lead to somatosensory and motor control areas
Ventral projections lead toward associative memories
From Van Essen Image can be found at

23. Anatomical Maps of Visual Cortex
1983 Version
1990 Version

24. Two Visual Subsystems
In 1982, Ungeleider & Mishkin propose that there are two primary visual pathways in humans and primates:
The dorsal (or “what”) pathway
Ends in the posterior parietal cortex
The ventral (or “where”) pathway
Ends in the inferotemporal cortex

25. Visualizing Two Subsystems
D. Milner & M. Goodale, The Visual Brain in Action, p. 22