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Global visual perception

Global visual perception. Velitchko Manahilov Uma Shahani Gael Gordon William Simpson. Outline. Reverse correlation analysis Classification image approach Perceptive fields for global motion in individuals with: - normal vision - amblyopia - dyslexia - persistent migraine aura

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Global visual perception

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  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. + + + + <M> + + + + <H> Criterion Noise+Signal response Probability MISS HIT 0 2 4 6 8 10 Internal response

  8. + + + + <CR> + + + + <FA> Criterion Noise response Probability Corr rej False alarm 0 2 4 6 8 10 Internal response

  9. + + + + <M> + + + + <H> + + + + <CR> + + + + <FA> CI = <H> - <M> + <FA> - <CR> = Classification image

  10. Manahilov & Simpson, VR, 2005.

  11. H-MF-C Beard & Ahumada, JOSA, 1999.

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

  13. 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”. Gosselin F. & Schyns P. Psychological Science, 14, 504-509, 2003.

  14. Global motion direction Black discsdisc diameter - 20’speed - 5 deg/s4 frames of 50 msdisplay size - 10x10 deg

  15. Perceptive field of ideal observerif SMDi> 0 => Right if SMDi< 0 => Left

  16. Global motion directionnormal observersSubj. DD

  17. Global motion directionnormal observersSubj. JPK

  18. Global motion directionnormal observersSubj. IMK

  19. Global motion directionnormal observersSubj. LS

  20. Global motion directionnormal observersAverage

  21. 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.

  22. Global motion directionSubj. CHAmblyopiceye Fellow eye

  23. Global motion directionSubj. KHAmblyopiceye Fellow eye

  24. Global motion directionSubj. LWAmblyopiceye Fellow eye

  25. Global motion directionAverageAmblyopiceye Fellow eye

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

  27. Global motion direction

  28. Global motion direction

  29. Global motion direction

  30. Global motion direction

  31. 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.

  32. Global motion direction Dyslexia

  33. Global motion direction Dyslexia

  34. Average Global motion direction Dyslexia

  35. 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.

  36. Global motion directionPersistent Migraine Aura

  37. Global motion directionPersistent Migraine Aura

  38. Average Global motion directionPersistent Migraine Aura

  39. SUMMARY1. Classification image technique provides a new powerful tool for estimating the observers’ behavioural template for detecting objects. 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. 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. 5. In the presence of environmental noise, these individuals may have deficits in exclusion of unwanted distractors.

  40. Thank you.

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

  42. Perceptual noise-exclusion deficits in dyslexia

  43. Global motion direction Persistent Migraine Aura

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