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Perceptual Strategy: a tale of letters and shapes

Perceptual Strategy: a tale of letters and shapes

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Perceptual Strategy: a tale of letters and shapes

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  1. Perceptual Strategy: a tale of letters and shapes Cees van Leeuwen Laboratory for Perceptual Dynamics, KU Leuven In collaboration with Thomas Lachmann Kaiserslautern University of Technology

  2. Overview • Introduction: two ways in which knowledge influences perception • Reading deficits as a consequence of learning the wrong strategy • Differentiation in strategies between nonletters and letters • Conclusions

  3. Two ways in which knowledge influences perception

  4. 1. What we know influences what we perceive The figure is determined based on familiarity. Peterson & Gibson (1993).

  5. 2. Knowledge influences how we perceive

  6. Perceiving items as shapes vs perceiving items as letters Habitual, as a result of learning to read!

  7. Are Letters Special?

  8. They are perfectly natural!

  9. If letters are normal, why do some children have difficulty in learning to read and write? Developmental Dyslexia

  10. Reading Errors • Slowness of reading; problems in understanding written materials • Losing their Line • Omissions, Repetitions, Substitution, Insertions • Distortions of Words, Parts of Words • Reversal Errors: was ∞ saw b ∞ d • ORTON (1925) Cardinal symptom

  11. The Causes are unknown After morethan 100 yearsof experimental studies ------------------------------------------------------------------------------------------------------------- AcousticinformationprocessingVERSUSphonologicaldeficit versus versus Visual informationprocessingorthographicaldeficit But perhapsitisboth, or a moregeneraldeficit.

  12. Thomas Lachmann’s Functional Coordination Deficit model Not a deficit of automatization, but automatization of the wrong strategy

  13. Our participants 57 third/fourth graders School psychologists‘ diagnosis in Grade 2 Own diagnosis prior to experiment: Discrepancy Definition (2 SD Reading time SLRT vs. Raven)

  14. The Cardinal Symptom b vs. d vs. p vs. q Problem with visuospatial processing of symbols?

  15. Mental Rotation with Letters Mental Rotation P ress mirrored Cooper & Shepard (1973) Rusiak, Lachmann, Jaskowski, van Leeuwen (Perception, 2007) N = 16 Dyslexics N = 12 Controls R, F, G, e, k (0-180° in 45°) “normal” oder “mirror images”?

  16. Mental Rotation with Letters • Typical Mental Rotation Effect • Group effect (> 100 ms) • No Interaction (no visuospatial processing deficit)

  17. The Cardinal Symptom b vs. d vs. p vs. q If the problem is not with visuospatial processing, perhaps it has something to do with the structure of the configuration SYMMETRY

  18. Symmetry Makes your world simpler Simple patterns have few alternatives

  19. Rotation and Reflection Symmetry Groups Equivalence Sets (ES) Equivalence Sets Size (ESS)

  20. Garner Patterns

  21. Task Serial presentation of pairs of stimuli ISI = 500 ms Same or different Irrespective of pattern orientation

  22. General preference for Symmetry

  23. Detailed model predictions possible from Degree of Pattern Symmetry (ESS) and Degree of “Sameness” (IM, CM, or NM) Lachmann & van Leeuwen (2004) Scientific Psychology Series

  24. Model Fit Lachmann & van Leeuwen, 2005, Quarterly Journal of Experimental Psychology

  25. Letters vs Shapes Normals vsDyslexics Lachmann & van Leeuwen, 2007, Developm. Neuropsychology

  26. Results Material**; Symmetry**; Group*; Material x Symmetry x Group ** Normal reading children Dyslexics No effects on error rate No effects on error rate

  27. Model fit*

  28. *Note on Model fit Model fit was based on different assumptions for Normals and Dyslexics Degree of symmetry for patterns was counted for both Normals and Dyslexics Degree of symmetry for letters was counted for Dyslexics but ignored for Normals Dyslexics are faster because they give equal importance to Symmetry in Letters and Shapes ------------

  29. Dyslexics: Outperform normal readers on this task The task involves letters Why don’t dyslexics read better than normals?

  30. Symmetry? Symmetry helps in perceiving shapes, but hinders in perceiving letters Strategy, based on reading practice When learning to read is difficult  anomalous strategies  letter symmetry may be suppressed actively

  31. Configurations

  32. Emergent Properties (J.R. Pomerantz) ( ( (( () Configurations

  33. Difficulty of recognizing the letter “E” when embedded in a Good figure Configurations

  34. Some Congruence Effects GREEN RED Push the button on the Right 

  35. Letters versus Shapes Letters vs Shapes Congruent versus Incongruent

  36. Van Leeuwen & Lachmann, Perception & Psychophysics, 2004 Binary Classification

  37. Van Leeuwen & Lachmann, Perception & Psychophysics, 2004 Binary Classification

  38. Binary Classification Rotated letters Pseudo-letters, and Geometrical Shapes show Congruence Effects. Letters show Negative Congruence Effects. Is the effect related to the response alternatives?

  39. Contrasting Response Categories Similarity Press Left Button: C or Circle or L or Rectangle Press Right Button: H or Square or A or Triangle No Similarity Press Left Button: C or Square or L or Triangle Press Right Button: H or Circle or A or Rectangle

  40. Similarity Contrasting Response Categories No Similarity

  41. What about less experienced readers? What about developmental dyslexics? Binary Classification In normal adult readers: Dissociation in Early Visual Integration Processes of Letters and Shapes

  42. Normal ReadingChildren DyslexicChildren RT (ms) RT (ms) • Weaker dissociation in normal children than in adults • Dyslexics have increased response times and variance AND an adult dissociation pattern •  PUZZLE

  43. Puzzle Normal reading children have a weaker dissociation than adults  strategy differentiation not yet well established? Dyslexics probably do not have more reading experience  dissociation should be same or even weaker Quod Non!

  44. Puzzle Our Dyslexics sample has: -slow response rates -strong dissociation Does this mean that all individuals in the sample have both these characteristics?

  45. Puzzle Perhaps: -slow response rates  Subpopulation I -strong dissociation  Subpopulation II Subtypes of Dyslexia? Analogy with Lachmann (2003, 2005)

  46. Puzzle Diagnostic subgroups Reading test: SLRT (Landerl, Wimmer, & Moser, 1997) word and non-word reading subtests Non-Word Reading Impaired (NWRI): at least reading time in non-word reading > 2 SD Frequent Word Reading Impaired (FWRI): reading time in frequent word reading > 2 SD, but normal non-word reading time (within 1 SD)

  47. Puzzle FWRI NWRI Delayed auditory/visual syllable discrimination Delayed letter identification Attenuated mismatch negativity syllables Pronounced fast-same effect in visual conditions Fuchs & Lachmann (2003) Lachmann (2007) Lachmann et al. (2005) Large modality effects Normal mismatch negativity increased response times but normal between conditions effects specific effects enhanced mostly involving visuo-auditory coordination

  48. Same-Different Task Sequential presentation of two items First always isolated, second isolated or in congruent or incongruent surroundings Letters, Pseudo-letters, Shapes; No mixed-category pairs Adults, normal reading children, FWRI vs NWRI dyslexics

  49. Material x congruence x group .

  50. Summary No differences in visuospatial manipulation Dyslexics sometimes even better than Normals Letter/Non-letter Dissociation Anomalous in Dyslexics Subgroups can be identified: -- “General Slowing down” in FWRI -- Enhanced Dissociation in NWRI