1. Color perception in the intermediate periphery of the visual field Thorsten Hansen, Lars Pracejus & Karl R. Gegenfurtner Abteilung Allgemeine Psychologie

2. Introduction Perception in the periphery Contrast sensitivity Fine details (high spatial frequencies) are harder to detect in the periphery. This can be compensated by magnifying the image.

3. Introduction Cone density in the human retina Curcio et al. (1990) Steep decline towards periphery. Nasal retina has a higher density than temporal retina. Nasal Fovea Temporal  1000 /mm²

4. Introduction Color opponency in the fovea Derrington (2001). The RF center of a parvo ganglion cell in the fovea is driven by a single cone.

5. Introduction Color opponency at larger eccentricities …is expected to be weaker and will eventually be zero when the center and surround is driven by an equal ratio of L:M cells Fovea Periphery

6. Introduction Psychophysics vs. physiology Psychophysics (Human) Cell recording (Macaque) Macaque ganglion cells remain color sensitive, while human performance drops. Martin et al. (2001). Nature.

7. Introduction Psychophysics Mullen, Sakurai & Chu (2005). Perception. »Thus we conclude that there is little or no L/M cone opponent response measurable psychophysically beyond 20–30 deg of eccentricity in the nasal visual field.« Lum S−(L+M) L−M

8. Methods Setup: Elumens Vision station

9. Methods Cone-opponent axes

10. Methods DKL color space An achromatic axis: Lum Two chromatic axes: L−M and S − (L+M)) L−ML−M S−(L+M) Lum L−ML−M S−(L+M) Derrington Krauskopf Lennie

11. Short presentation stimuli (500 ms) forced choice (4AFC) threshold measured by standard stair-case procedure Exp 1 & 2: Detection & Identification Exp. 3: Discrimination Methods Procedure

12. Results Chromatic detection (5 deg stimulus) N = 7 in % 10° 20° 30° 40° 50°

13. Results Identification (5 deg stimulus) in % 10° 50° N = 7

14. Results Chromatic detection (8 deg stimulus) N = 3 L−M S−(L+M) Eccentricity (deg) Lum

15. Comparison color varied along 8 chromatic directions Methods Chromatic discrimination Ellipse was fit to the data to characterize discrimination performance

16. Results Control: Foveal discrimination …as expected: Best at the adaptation point Elongated along the saturation axes Krauskopf & Gegenfurtner (1992). Vision Res.; Hansen, Giesel & Gegenfurtner (in press), J. Vision.

17. Results Discrimination at 50° Larger size of ellipses: Discrimination is worse, but not absent! Greatest increase along L−M axis Leads to rounder shapes of ellipses off the L−M axis

18. Summary Chromatic processing in the periphery Detection Identification Discrimination As long as the stimuli are large enough, peripheral color vision is just like foveal vision.

19. Supplementary material

20. Discussion Size matters (Mullen et al. 2005) “sinring” stimuli: Radial size was only 1.5 deg.

21. Introduction Cortical representation Cortical magnification factor The central part of the visual field (10 deg) is represented by about half of all neurons in primary visual cortex V1

22. Introduction Color in the periphery: Previous work Noorlander, Koenderink, den Ouden, & Edens, 1983 Mullen & Kingdom, 2002 Mullen, Sakurai & Chu, 2005 Sakurai & Mullen, 2006

23. Cone density in the retina (1D)

24. Introduction Physiology Size of the receptive fields Cortical representation Center – surround ratio Random wiring Results physiology – psychophysics

25. Introduction Open questions Ψ ? ? Derrington (2001). Nature. Do humans have similar cone-opponency at the early stages, which somehow got lost at higher processing? Is the macaque a bad model color processing in humans?

26. Discussion Biased sample? (Martin et al. 2001) 34/53 overt red-green response 28/35 cone-opponent 11 not significantly different from foveal cells

27. Results Cone-opponent thresholds Further evidence for chromatic discrimination

28. Introduction Color opponency at larger eccentricities Several factors can contribute to preserve color opponency selective wiring (vs. random wiring) elongated RFs unequal/random distribution of cone types at each retinal location

29. Introduction Physiology „Random Wiring“ vs. „Selective Wiring“ Jusuf et al., 2006

30. Introduction Selectivity by elongated RFs Martin et al., 2001 Midget RF centers are elongated and may rotate to sample one cone type more than the other to increase cone-purity

31. Introduction Elongated RFs can increase the L/(L+M) ratio Martin et al., 2001

32. Methods Calibration