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 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

Redlick et al. (2001)

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

Does one dominate when the other is impaired?

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

Base Up Prism:

Base Up Goggles

Base Down Prism

Base Down Goggles

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

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

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

7 Conditions: ConditionViewWalk 1Normal 2Base UpNormal 3Base DownNormal 4 Base Up 5NormalBase Down 6Base Up 7Base Down

MDCL Test Location

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

Results of Test Trial

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

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

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)

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

Subjects n = 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)

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

Experiment Locale

Experimental Conditions ConditionViewWalk Experiment 1 1Normal 2Base upNormal 3Base downNormal Experiment 2 1Normal 2 Base up 3NormalBase down

Experiment Set Up

Results Graphs, ANOVAs, and t-tests

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

Experiment 1: Main Effect of Distance F 3,15 = p = 0.014

Experiment 1: Main Effect of Condition F 2,10 = p = 0.041

Experiment 1: Interaction Effect F 6, 30 =2.969 p =0.083

Experiment 1: Post-Hoc Normal-Normal vs Base Up-Normal t 5, 0.05 = 2.340, p = Normal-Normal vs Base Down-Normal t 5, 0.05 = , p = 0.146

Experiment 2: Main Effect of Condition F 2,10 = p = 0.130

Experiment 2: Main Effect of Distance F 3,15 = p = 0.219

Experiment 2: Interaction Effect F 6, 30 = p = 0.154

Experiment 1 Experiment 2

Discussion What we found and why it matters…

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

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

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.

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

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

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

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

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