Blackshot: An Unexpected Dimension of Human Sensitivity to Contrast

Michael S. LandyNew York University

Charles ChubbUniversity 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

Nth-Order, Orthogonal Histogram Modulators

Contrast

Res

pons

e1

765

432

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

1 or 2 Amplitude

f CE

L A

mpl

itud

e

-1 0 1

1

0or or

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)