The Effect of a Prism Manipulation on a Walking Distance

Estimation Task

Jonathan Giles Beverley Ho

Jessica Blackwood-BeckfordAurora 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: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

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 = 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)

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

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

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

F3,15 = 7.619

p = 0.014

Experiment 1: Main Effect of Condition

F2,10 = 6.116

p = 0.041

Experiment 1: Interaction Effect

F6, 30 =2.969

p =0.083

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

Experiment 2: Main Effect of Condition

F2,10 = 2.551

p = 0.130

Experiment 2: Main Effect of Distance

F3,15 = 1.955

p = 0.219

Experiment 2: Interaction Effect

F6, 30 = 2.115

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