1. RESOLVING PERCEPTUAL AMBIGUITY Tim Andrews University of Durham

2. The visual system uses context to resolve ambiguity

4. Binocular rivalry

6. What triggers binocular rivalry (or fusion)?

7. Alternations in perception can occur between physically identical stimuli. Dominance Duration (sec) 0246810121416 0.0 0.1 0.2 0.3

8. Binocular integration of chromatic signals is dependent on context no context context n=8 * TT

9. Can context encourage fusion of physically dissimilar objects? no context context n=8 * Andrews and Lotto (2004) Curr. Biol. 14: 48-23

10. + What rivals during rivalry? = Pattern motion

11. Independent binocular integration of form and motion during binocular rivalry.... Pattern motion + Right eye Left eye = Right eye dominant Left eye dominant.... Patch Size: 4 deg Spatial Freq: 1 cycle/deg. Velocity: 1 cycle/s Contrast: 30% Gratings: Sinusoidal Presentation: 60 sec

12. The proportion of binocular pattern motion decreases as the two gratings are made more different in spatial frequency, velocity, colour, contrast and orientation Andrews and Blakemore (2002) Vision Res. 42: 301-9

13. + = + = + = + = direction of pattern motion Patch Size: 0.8 deg Spatial Freq: 1 cycle/deg. Velocity: 1 cycle/s Contrast: 30% Gratings: Sinusoidal Presentation: 1.5 sec Can completely suppressed contours contribute to pattern motion during binocular rivalry?

14. % component motion S2S1S2S1 RivalrousNon-rivalrous 50 25 0 50 75 100 % pattern motion Form and motion have independent access to perception Andrews and Blakemore (1999) Nature Neurosci. 2: 405-406

15. + Can other attributes of vision interact independently during binocular rivalry?

16. + rivalry + adapt % reported right (45) % reported left (-45) Adapting orientation (deg) 80 60 40 20 100 0 0 1530-15 -30-4545 80 60 40 20 100 0 (-45) (0) (45) Adaptation paradigm

17. % reported blue % reported red %reported fused Colour 80 60 40 20 RedBlueGrey 0 0 0 100 + adapt + rivalry

18. + Independent binocular integration for form and colour adapt + rivalry percept or Holmes, Hancock and Andrews (in preparation)

19. Conclusions Fusion and rivalry are dependent on the perceptual meaning of visual stimuli. Different attributes of stimulus can interact independently during binocular rivalry.

20. New project: using TMS to determine where in the visual system binocular rivalry is resolved?

21. control 1 context control 2

22. Panum’s fusional area and rivalryEF Left E Right F