1. Global visual perception Velitchko Manahilov Uma Shahani Gael Gordon William Simpson

2. Outline   Reverse correlation analysis   Classification image approach   Perceptive fields for global motion in individuals with: - normal vision - amblyopia - dyslexia - persistent migraine aura   Conclusions

3. Reverse correlation technique Visual neurons are stimulated by noise images and the spike output is cross-correlated with the input.

4. Reverse correlation technique Multifocal ERG & VEP

5. What is a classification image? The classification image shows how the observer weights the information in the image to reach a decision.

6. Signal Detection Theory

7. Noise+Signal 0246810 Internal response Probability MISSHIT Criterion response + +

8. Noise 0246810 Internal response Probability Corr rej False alarm Criterion response + +

9. Classification image + + + + CI = - + - =

10. Manahilov & Simpson, VR, 2005.

11. Beard & Ahumada, JOSA, 1999. H-M F-C

12. Gold, J.M., Murray, R.F., Bennett, P.J., & Sekuler, A.B. Current Biology 2000.

13. Gosselin F. & Schyns P. Psychological Science, 14, 504-509, 2003. Internal representation? Observers were presented with 20,000 noise samples. They were told that the letter “S” was present on 50% of the trials. No more detail was given regarding the shape of the letter. No signal was ever presented. The classification image resembles the letter “S”.

14. Black discs disc diameter - 20’ speed - 5 deg/s 4 frames of 50 ms display size - 10x10 deg Global motion direction

15. SignalResponseRightLeft Right RR (N RR ) LR (N LR ) Left RL (N RL ) LL (N LL )

16. Perceptive field of ideal observer if  MD i > 0 => Right if  MD i Left

17. Global motion direction normal observers Subj. DD

18. Global motion direction normal observers Subj. JPK

19. Global motion direction normal observers Subj. IMK

20. Global motion direction normal observers Subj. LS

21. Global motion direction normal observers Average

22. Amblyopia Amblyopia (lazy eye) is the loss or lack of development of central vision in one eye. It is unrelated to any eye health problem and is not correctable with lenses. It can result from a failure to use both eyes together. Lazy eye is often associated with crossed-eyes or a large difference in the refractive errors between the two eyes. It usually develops before the age of 6, and it does not affect side vision.

23. Global motion direction Subj. CH Amblyopic eye Fellow eye

24. Global motion direction Subj. KH Amblyopic eye Fellow eye

25. Global motion direction Subj. LW Amblyopic eye Fellow eye

26. Global motion direction Average Amblyopic eye Fellow eye

27. Global motion direction Subj. DD Subj. JPK VA 6/18

28. Global motion direction

32. Dyslexia Developmental dyslexia is manifested as a difficulty with reading given normal individual intelligence that cannot be explained by other factors such as sensory acuity, learning opportunities or brain injuries.

33. Global motion direction Dyslexia

35. Average

36. Persistent Migraine Aura Persistent migraine aura is a rare but well documented complication of migraine. Patients experience continuous aura lasting weeks or months. These patients offer a unique opportunity to examine the migraineous brain during the aura phase of the attack.

37. Global motion direction Persistent Migraine Aura

39. Average

40. SUMMARY 1. Classification image technique provides a new powerful tool for estimating the observers’ behavioural template for detecting objects. 4. The wider perceptive fields of these individuals may be related to reduced suppression of global (attentional) mechanisms which allows integrating motion information over a much larger field. 2. Normal observers use localised perceptive fields when integrate global motion information. They extract motion information from central moving discs and suppress peripheral items. 3. The perceptive fields of individuals with amblyopia, dyslexia and persistent migraine aura are wider than the perceptive fields of normal observers. 5. In the presence of environmental noise, these individuals may have deficits in exclusion of unwanted distractors.

41. Thank you.

42. Perceptual noise-exclusion deficits in dyslexia Sperling et al., (2005). Nature Neuroscience, 8, 862-863.

43. Perceptual noise-exclusion deficits in dyslexia

44. Global motion direction Persistent Migraine Aura