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The Effect of a Prism Manipulation on a Walking Distance Estimation Task

The Effect of a Prism Manipulation on a Walking Distance Estimation Task. Jonathan Giles Beverley Ho Jessica Blackwood-Beckford Aurora Albertina Dashrath Gautam. Background Information. Optic flow: The visual motion that is perceived during movement

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The Effect of a Prism Manipulation on a Walking Distance Estimation Task

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  1. The Effect of a Prism Manipulation on a Walking Distance Estimation Task Jonathan Giles Beverley Ho Jessica Blackwood-Beckford Aurora Albertina Dashrath Gautam

  2. Background Information Optic flow: • The visual motion that is perceived during movement Redlick, Jenkin, and Harris (2001): • Subjects presented with visual target and provided with optic flow. • Subjects able to walk to a virtual target position using optic flow alone

  3. Redlick et al. (2001)

  4. Background Information The Blind Walking Task: -Project 1. Thomson (1983): • Subjects could walk to the distance of a previously viewed target without vision with the same accuracy as with vision. • Emphasizes the importance of non-visual cues in distance estimation

  5. Does one dominate when the other is impaired?

  6. Background Information II Ooi, Wu, and He (2001) • Use base up prism = underestimation • Angular declination: the angle between ones line of sight from eye level, and the line of sight to a certain object • Angular declination hypothesis: The visual system can compute distance using eye height and angular declination below the horizon • Dependent on eye level

  7. Base Up Prism:

  8. Base Up Goggles

  9. Base Down Prism

  10. Base Down Goggles

  11. Objectives Objective 1: • Verify the effect of a prism manipulation on static distance estimation Objective 2: • See how visual/non-visual cues are weighted in brain using a prism manipulation while walking

  12. Given… The importance of optic flow in walking The importance of non-visual cues in a blind walking task The prism manipulation How do we test our research question?

  13. Test Trial • Subject viewed a static target at one of four distances with one set of goggles • Then walked the estimated distance in the opposite direction with another set of goggles • Three goggle manipulations used • Base up goggles • Base down goggles • Normal goggles • Location : Hallway of MDCL • 7 conditions tested 3 times in order

  14. 7 Conditions:

  15. MDCL Test Location

  16. Hypothesis: • Base up prisms causes underestimation and base down prisms causes overestimation as per Ooi et al. (2001) • Using same prism goggles to view target and walk distance causes double the effect • Due to optic flow: distance estimates would be affected by walking with the prism goggles

  17. Results of Test Trial

  18. What Went Wrong??? • Importance of randomization of conditions • Distance estimation tasks: low environmental cues • Subjects took over an hour to test, show fatigue after first 30 trials out of 78

  19. A New Design… In order to improve on the initial experimental design, the study was divided into two experiments…

  20. Experiment 1 Purpose: Confirm the effect of prisms on distance estimation to a static target Hypothesis: • Viewing through Base up will cause underestimation in walked response* • Viewing through Base down will cause overestimation in walked response* * With respect to baseline (viewing normally)

  21. Experiment 2 Purpose: Investigate the effects of prisms on the visuomotor system Hypothesis: • Walking with Base up will cause an underestimation in distance walked* • Walking with Base down will cause an overestimation in distance walked* * Relative to the normal (baseline) condition

  22. Subjects • n = 6 • 18 - 21 years (M = 20) • Normal vision or corrected eyesight • Naïve to the walking distance estimation task • Received compensation for their participation Note: Experiments are completely independent (total # of participants = 12)

  23. Apparatus • Corridor at McMaster Children’s Hospital (3rd floor) • 28 m linear scale was laid out • 5 start positions • 4 distances: 6, 8, 10, 12m • A large bright orange pillon was used as a target • Exposure to the target was timed for 3s

  24. Experiment Locale

  25. Experimental Conditions

  26. Experiment Set Up

  27. Results Graphs, ANOVAs, and t-tests

  28. Results 3 x 4 ANOVA • Interaction and Main effects Post-Hoc, paired t-test • Experiment 1: Normal-Normal vs Base Up-Normal Normal-Normal vs Base Down-Normal

  29. Experiment 1: Main Effect of Distance F3,15 = 7.619 p = 0.014

  30. Experiment 1: Main Effect of Condition F2,10= 6.116 p = 0.041

  31. Experiment 1: Interaction Effect F6, 30 =2.969 p =0.083

  32. Experiment 1: Post-Hoc • Normal-Normal vs Base Up-Normal • t5, 0.05 = 2.340, p = 0.066 • Normal-Normal vs Base Down-Normal • t5, 0.05 = -1.718, p = 0.146

  33. Experiment 2: Main Effect of Condition F2,10 = 2.551 p = 0.130

  34. Experiment 2: Main Effect of Distance F3,15= 1.955 p = 0.219

  35. Experiment 2: Interaction Effect F6, 30 = 2.115 p = 0.154

  36. Experiment 1 Experiment 2

  37. Discussion What we found and why it matters…

  38. Discussion Experiment 1: • Significant effect of condition • Comparing normal-normal to base up – normal and normal-normal to base down-normal was not significant • May need 8.2 degree prisms to find a significant effect • Overall trend seen in experiment 1 and 2 of prisms having an effect in the shorter distances

  39. Experiment 1 Reasons we failed to reproduce a significant results similar to that of Ooi et al. (2001): -Use stronger prisms (5.73 vs 4.1) -Shorter distances 1.5m, 3.0m, 4.5m, 6.0m, and 7.5 m -Use more subjects (13 vs 6) Cognitive effects: -Using environmental cues -Prism manipulation being noticeable

  40. Discussion • Prism manipulation had a larger impact on Experiment 1 compared to 2 • With distorted vision while walking a remembered distance, non-visual cues may have played a role in distance estimation.

  41. Experiment 2 • Vision manipulated constantly during experiment • Start relying on constant non-visual cues • 1) Proprioception/Efference copy: sense that is felt when the body is in motion • 2) Kinaesthesia /Vestibular cues: detects change of directional or linear speed. Sense of balance

  42. Experiment 2 -Adaptation to goggles -Confidence level -Fatigue effects

  43. Further Studies: • Examine conditions including both viewing and walking with the same prism manipulation • What types of non-visual cues are used? • Tests subjects with corrected vision • Investigate further into prism manipulation in distance estimation, especially its impact for longer distances • Test point of adaptation over distance

  44. Other Prism Uses: • 1) Map the adaptation of the visual system to varying degrees • 2) Aid in Orthoptics for diagnosis and treatment for impairments in eye coordination and binocular vision • 3) Robotics, this knowledge could be used in the design of distance estimation module for an onboard navigation system

  45. Take Home Message • Found evidence of both visual cues and non-visual cues in walking with a prism manipulation • Past studies have not used prisms in a distance past 7.5m • Starting point in investigating the effect of prisms in longer distances

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