a neural mechanism for robust junction representation in the visual cortex university of ulm dept....
Post on 22-Dec-2015
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TRANSCRIPT
A neural mechanism for robust junction representation
in the visual cortex
University of UlmDept. of Neural Information Processing
Thorsten Hansen and Heiko Neumann
Overview of the talk
1. Motivation: Why junctions are important
2. Detection: The basic idea and its failure for natural images
3. Approach and Model
4. Simulations and ROC analysis
Role of junctions for object recognition(Biederman 1987)
Role of junctions for brightness perception (e.g., Adelson 2000):
Definition of corners and junctions
(from Adelson 2000)
Corners and junctions are points where two or more lines join or intersect
Junction detection in natural images
Junctions often cannot be detected locally(McDermott 2001):
13 pixel closeup 13 25 49 97 pixels
Neural representation of corners and junctions
2. Read-out of distributed information
measure of circular variance
distributed activity for multiple orientations within a cortical hypercolumn
1. Robust generation of coherent contours
model of recurrent long-range interactionsin V1
Approach:
Key mechanisms of the proposed V1 model
1. Excitatory long-range interactions between cells with colinear aligned RF (Bosking et al. 1997)
2. Inhibitory short-range interactions
3. Modulating feedback Initial bottom-up activity is necessary
(Hirsch & Gilbert 1991)
Model architecture
Recurrent interaction
modulating feedback
inhibition in both spatial andorientational domain
divisive inhibition
excitatory long-rangeinteraction
Properties of the proposed model
input stimulus complex cells long-range
background: noise suppression
edge: enhancement of coherent structures
corner: preservation of circular variance
high significance
Read-out of distributed information
low significance
orientation significance
circular variance
Batschelet 1981: Circular Statistics
Length of the resulting orientation vector
Corner and junction detection
Corner candidates: high circular variance and high overall activity:
Corner points: sufficiently large local maxima of corner candidates
Simulation I: distance from true location
V1 long-range model
feedforward complex cells
Simulation II: feedforward vs. feedback
complex cells long-range
Real world camera image
Simulation III: feedforward vs. feedback
complex cells
long-range
Attneave‘s cat
Simulation IV: ROC analysis
Comparison of the new scheme to standard methods based on Gaussian curvature and the structure tensor (black)
input image
Conclusions
• corners and junctions can be robustly represented by distributed activity within a cortical hypercolum
• recurrent colinear long-range interactions serve as a multi-purpose mechanism for
• contour enhancement• noise suppression• junction detection
• model performance superior to local junction detection schemes used in Computer Vision