1. Blackshot: An Unexpected Dimension of Human Sensitivity to Contrast Michael S. Landy New York University Charles Chubb University of California, Irvine John Econopouly

2. Outline Back pocket model of texture segregation Investigating a nonlinearity: IID textures Filling in the missing information Result: Blackshot

3. Texture Segregation Luminance EdgeTexture Edge

4. The Back Pocket Model

5. Application of the Back Pocket Model InputVertically filtered Squared2 nd -Order filtered

6. The Back Pocket Model

7. 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

8. IID Textures: The Uniform Histogram

9. IID Textures: 1 st -Order Modulator = Brightness

10. IID Textures: 2 nd -Order Modulator = Contrast

11. Histogram Modulators

12. N th -Order, Orthogonal Histogram Modulators Contrast Response 1 7 6 5 4 3 2

13. Histogram Contrast Thresholds

14. The Result (Chubb et al., 1994): f CEL f CEL : 3 rd - through 7 th -order components

15. The New Technique: Tradeoff of 1 or 2 with f CEL 1 or 2 Amplitude f CEL Amplitude 01 1 0 or

16. Experimental Details 3 Subjects Carefully linearized lookup table 200 ms display

17. Task: 4-AFC Shape Discrimination

18. Results: Three Thresholds

19. Results: Reconstructed Nonlinearity

20. 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)