Blackshot: An Unexpected
Dimension of Human
Sensitivity to Contrast
Michael S. Landy
New York University
Charles Chubb
University of California, Irvine
John Econopouly
Outline
•
•
•
•
Back pocket model of texture segregation
Investigating a nonlinearity: IID textures
Filling in the missing information
Result: Blackshot
Texture Segregation
Luminance Edge
Texture Edge
The Back Pocket Model
Application of the Back Pocket Model
Input
Vertically
filtered
Squared
2nd-Order
filtered
The Back Pocket Model
How to Measure the Nonlinearity
• Simple case: Independent, Identically
Distributed (IID) textures
• Appearance indicates at least two channels or
nonlinearities: perceived brightness and
contrast
• Technique: Histogram Contrast Analysis
(Chubb, Econopouly & Landy, 1994)
• Result: a third perceptual dimension
IID Textures: The Uniform Histogram
IID Textures: 1st-Order Modulator =
Brightness
IID Textures: 2nd-Order Modulator =
Contrast
Histogram Modulators
Response
Nth-Order, Orthogonal Histogram
Modulators
1
2
3
5
6
7
Contrast
4
Histogram Contrast Thresholds
The Result (Chubb et al., 1994): fCEL
fCEL: 3rd- through 7th-order components
The New Technique: Tradeoff of 1 or
2 with fCEL
fCEL Amplitude
1
0
or
or
-1
0
1 or 2 Amplitude
1
Experimental Details
• 3 Subjects
• Carefully linearized lookup table
• 200 ms display
Task: 4-AFC Shape Discrimination
Results: Three Thresholds


Results: Reconstructed Nonlinearity
Conclusions
• Full measurement of a novel nonlinearity
• Blackshot: Exquisite sensitivity to the darkest texels
• Thus, 3 dimensions of IID texture appearance:
brightness, contrast and blackshot
• A striking precedent: Whittle (1986)