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The Effect of a Prism Manipulation on a Walking Distance
Estimation Task
Jonathan Giles Beverley Ho
Jessica Blackwood-BeckfordAurora Albertina Dashrath Gautam
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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
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Redlick et al. (2001)
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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
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Does one dominate when the other is impaired?
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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
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Base Up Prism:
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Base Up Goggles
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Base Down Prism
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Base Down Goggles
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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
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How do we test our research
question?
Given…
The importance of optic flow in walking
The importance of non-visual cues in a blind walking task
The prism manipulation
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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
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7 Conditions:Condition View Walk
1 Normal Normal
2 Base Up Normal
3 Base Down Normal
4 Normal Base Up
5 Normal Base Down
6 Base Up Base Up
7 Base Down Base Down
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MDCL Test Location
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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
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Results of Test Trial
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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
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A New Design…
In order to improve on the initial experimental design, the
study was divided into two experiments…
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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)
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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
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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)
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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
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Experiment Locale
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Experimental Conditions
Condition View Walk
Experiment 1
1 Normal Normal
2 Base up Normal
3 Base down Normal
Experiment 2
1 Normal Normal
2 Normal Base up
3 Normal Base down
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Experiment Set Up
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Results
Graphs, ANOVAs, and t-tests
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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
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Experiment 1: Main Effect of Distance
F3,15 = 7.619
p = 0.014
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Experiment 1: Main Effect of Condition
F2,10 = 6.116
p = 0.041
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Experiment 1: Interaction Effect
F6, 30 =2.969
p =0.083
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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
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Experiment 2: Main Effect of Condition
F2,10 = 2.551
p = 0.130
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Experiment 2: Main Effect of Distance
F3,15 = 1.955
p = 0.219
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Experiment 2: Interaction Effect
F6, 30 = 2.115
p = 0.154
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Experiment 1
Experiment 2
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Discussion
What we found and why it matters…
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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
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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
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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.
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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
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Experiment 2
-Adaptation to goggles
-Confidence level -Fatigue effects
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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
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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
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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