Temporal Processing VT and Impact of Lenses and Filters on Learning

1. Temporal Processing VT and Impact of Lenses and Filters on Learning Linda Marks, O.D., F.A.A.O .

2. Reading Eye Movements • Reading eye movements are saccadic • Involves series of fixation-saccade-fixation sequences • Each word fixated slightly to left of center • Larger words have multiple fixations • Average duration of fixation • Mature vs. beginning readers

3. Disabled Readers • More frequent saccades • Longer fixation duration • More frequent regressions • Great difficulty with return sweeps

4. Symptoms of Eye movement disorders in reading • Loss of place VERY common • Leads to: • Re-reading words or lines • Word/line omissions, transpositions • Natural compensation: • Use finger or marker to keep place

5. Eye mvmt. symptoms cont. • Return Sweep Confusion • Specific loss of place finding next line • Illusory Text Mvmt. • Words or letters appear to be moving • Ineffective saccadic suppression

6. Illusory text movement

7. Symptoms cont. • Leads to: • Reduced reading rate • Reduced comprehension • Asthenopia • Generalized fatigue • Loss of Place

8. Visual Attention • The brain can’t process all visual stimuli simultaneously • Attention helps you to: • Focus on the important stimulus • Filter out unimportant information

9. Visual Attention

10. Visual Attention • Attention is an active process of extracting information from ongoing events in a selective, active, and efficient manner • Visual attention has been defined as a neural process that enhances the processing of visual information from an attended location and suppresses information outside of it. (Steinman et al., 1998) • Involves multiple cortical areas

11. Components of Visual Attention • Activation (engagement) to stimulus of interest • Orienting (directing) to new locus in visual field • Locking on attended locus • Suppressing irrelevant information from other loci in visual field • Division of attention between two or more loci

12. Components of Attention • Maintaining attention: • Waiting to completely process all of a present target’s visual information • Waiting for an expected new stimulus • Disengagement (in preparation to process new information, possibly at another location)

13. Benefits of Attentional Focus • Focusing on the particular location in the visual field attention is directed to • Proper attention accelerates visual response times • Enhances detectability and discriminability of visual stimuli

14. Spot-light • Attention like a spotlight • Small portion of visual field illuminated at one time • Visual processing is accelerated for stimuli which fall within the attentional spotlight

15. Zoom lens model • Modification of spotlight model • “Zoom lens” of attention allows narrowing and widening of attentional focus • During reading, spotlight is moved to new word, then narrowed while the word is processed • Smaller focus restricts region of visual space processed but allows finer spatial resolution

16. Description of attention • Spotlight • Zoom-lens model

17. Neurological classification of visual attention • Transient attention • involuntary attentional response to a sudden change in the visual field • fully activated by 50 ms and dissipates by 250 ms • involves bottom up processing +

18. M and P Pathways in reading • Parallel pathways • Magnocellular pathway (transient system) • Designed to process information quickly • Motion sensitive • Parvocellular pathway (sustained system) • Fixation • Processes info at a slower pace than transient system

19. M-pathway • Receives input from rods and cones across the entire extent of the retina • P-pathway • Input from cones, primarily from central retina

20. The M- pathway or “where” channel • Sensitive to low spatial, high temporal frequency information • Responds to moving stimuli and stimulus off and on sets • Highest sensitivity to SF < 1 cpd • For high contrast targets sensitivity to flicker up to 50 to 60 Hz

21. P- pathway or “ what” channel • Sustained response , provides information about what an object is • Carries information about high spatial frequencies and color • Highest sensitivity to SF > 1cpd • Does not respond to flicker > 30 Hz

22. Normal reader’s attention • Transient attention • A reflexive response to a new stimulus in the visual field • Overrides voluntary attention • Rapid activation (50 ms); Dissipation by 200-300 ms • Sustained attention • “Paying attention” • Holding attention at a desired location

23. Attentional Focus and Eye Movements • Attentional Focus can move independently of eye movements • While we can attend to a non-fixated locus…. • We MUST move attention before an eye movement signal can be programmed to saccade to that location

24. Mechanism of Visual Processing in Reading • P-Pathway is activated during a fixation and extracts the details of the text • Rapid saccade pattern activates M-pathway channels which are sensitive to stimulus movements across the retina • The stimulation of M-pathway then inhibits (suppresses) the visible persistence of the sustained (P) system from the previous fixation

25. Attention and Saccades in Reading • Attention precedes the saccade • Examples of attentional shifts in reading: • This is how attention works when we read. It shifts from word to word. • This is how attention works when we read. It shifts from word to word. • This is how attention works when we read. It shifts from word to word. • This is how attention works when we read. It shifts from word to word.

26. Do you enjoy reading? Do you enjoy reading? Visual Attention and Reading Our neural system employs a serial search task using an attentional spotlight during reading During fixation, the attentional spotlight selects a couple of letters within a word for processing. It sweeps across 6 to 7 letters in the same manner before a saccade is executed Do Do you enjoy reading? Do you enjoy reading? joy Do you enjoy reading? rea

27. Attention and RD • Strength of transient attention is less in reading disabled subjects • Duration over which transient attention is activated is shorter • Attentional focus narrower • Deeper inhibition • Poorly sustained attention

28. Implications of attention deficit in RD • Decreased ability to process textual information to the right of fixation • Decreased ability to program reading saccadic eye movements • Decreased time to derive meaning from attended words.

29. Timing of M and P pathways • With perfect timing, the effect of the transient (M) channel on the sustained (P) system is to erase the pattern info, and prevent “trailing persistence” of the preceding sustained pattern from interfering with the information analyzed in the subsequent fixation

30. Poor Timing • When poor timing between the 2 pathways occurs, the transient (M) system is the principal offender • If timing is not synchronized to form a complete visual perception, visual activity from a previous fixation can persist and interfere with sustained (P) activity of the following activity • Leads to superimposition of successive inputs

31. Causes Disruption in the Visual System • Deficits in the transient (M) system may be found in 75% of disabled readers • M pathway is selectively compromised in dyslexics • If the transient system is slowed, the perfect timing required for efficient visual processing during reading is disturbed • Strength of transient attention is less in reading disabled subjects

32. Implications of visual processing disorders in RD • Decreased ability to process textual information during fixation • Decreased ability to program reading saccadic eye movements • Decreased time to derive meaning from attended words.

33. Case Reports Test for Visual attention and magnocellular integrity (coherent motion) in good versus poor readers. Attention tests identified 95.7% of poor readers Coherent Motion identified 78.3% of poor readers Combined identified 91.3% of poor readers.

34. Types of Tests • M-cell sensitivity using random dot kinematogram • Visual attention using selective stimuli, green spelling in blue and say blue

35. Attention Therapy Perceptual Accuracy (Tachistoscope) Visual Efficiency Visual Search Visual Scan Visual Span

36. PTS - II

37. Perceptual Accuracy (Tachistoscope)

38. Visual Efficiency (Visual Sequential Processing)

39. Visual Search

40. Visual Scan

41. Visual Span

43. Outcome • Visual Attention is maleable • Following 12 one hour weekly sessions • Visual attention increased from 41st percentile to 77th • Mean Reading Comprehension increased from 23rd percentile to 35th percentile

44. Dioptric Lenses • Plus • Minus • Prismatic Lenses • Base In, Base Out • Yoked Prism • Colored Lenses • Filters • Overlays

45. Alleviating prism • Light bends toward the base of a prism • Image viewed is displaced toward apex • Base-Out prism (base toward ear) may relieve convergence excess by shifting images inward

46. Prism adapters • Check for prism Adaptation!!!! -Do not prescribe when Pt. adapts to prism

47. Yoked Prism • Prism Base placed in same direction • Base Left • Base Right • Base Up • Base Down

48. Ambient vision • Aspect of vision involved in spatial organization • Body posture • Locomotion • Perception of self-motion • Deficits in sensory function are one of the hallmark findings in a patient with autism. • “Postural Orientation Modification” • Toe Walking

49. Yoked Prism in Autism • Try five prism diopters of yoked prism in several different directions to elicit an improvement in walking, sitting down and even playing catch. • If one direction works best, introduce a lower amount into the spectacle prescription.

50. Colored Filters • Colors can change the rate at which information can be processed by the brain • May improve visual processing • Reasons remain obscure • May include placebo effects ***Filters do not cure dyslexia***