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The Role of Adaptation in the Blind Walking Task
Spatial perception is a critical aspect of everyday life, such as judging distances to
maneuver around objects. An important part of spatial navigation is distance. Measuring
perception of distances has been a challenge for many psychologists. An initial method of
measuring people’s perception of distances was asking subjects to judge how far a target was and
verbally describe the distance (Loomis, Fujita, Da Silva and Fukusima, 1992). The issue with
this method was everyone has a different representation of a measure. This makes it difficult to
compare and contrast results between subjects. In 1983, Thomson came up with the blind
walking task which involved subjects viewing a target and walking to where they believe that
distance is while blindfolded (Thomson, 1983). This task eliminated the verbal description of
distance judgments and proved to be more accurate (Loomis, Fujita, Da Silva and Fukusima,
1992).
Thomson gave feedback during practice trials to allow subjects to feel comfortable with
the task during experimental trials (Thomson, 1983). Digby Elliott attempted to replicate
Thomson’s study but he did not give feedback during practice (Elliott, 1987). Elliott was unable
to replicate Thomson’s results. The lack of feedback was pointed out as a flaw in the
experimental design, so Elliott redid the study. The second study had a group that practiced and
were not given feedback and a group that practiced and were given feedback. Significant results
were not found for these two groups. In Elliott’s first effort to replicate the blind walking task,
the subjects had fifteen practice trials (Elliott, 1986) and in the second study the subjects had
twenty (Elliott, 1987). The subjects with more practice were less likely to undershoot the target
distance, meaning subjects walked further (Elliott, 1987). A relationship between the number of
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trials and the distance the subject walked was found. However, Elliott’s study did not look at
whether this relationship was due to adaptation to walking without vision.
In another study which looked at perceiving distance, subjects walked on a treadmill with
or without optic flow and were asked before and after the treadmill walking to verbally estimate
distances to a target (Proffitt, Stefanucci, Banton and Epstein, 2003). The purpose of this
experiment was to see if adaptation to a lack of optic flow changed the subject’s perceived
distance to a target. It was found that participants with no optic flow estimated larger distances
after walking on the treadmill, than before walking on the treadmill. Subjects adapted to walking
with no optic flow and related that more effort was necessary to walk to a target (Proffitt,
Stefanucci, Banton and Epstein, 2003). The increase in perceived effort increased the subject’s
perceived distance.
Verbal estimates of distance are less accurate than matching the distance seen to a motor
output, such as the blind walking task (Loomis, Fujita, Da Silva, Fukusima, 1992). Verbal
descriptions of distance were used in the study by Proffitt, Stefanucci, Banton and Epstein
(2003). This study examined if the same adaptation to lack of optic flow while walking affected
the results of the blind walking task. After repeating the blind walking task a number of times, is
there an adaptation to walking such that subjects walk further to compensate for the decrease in
sensitivity?
The subjects participated as part of a non-visual group, in which they experienced freely
blind walking before starting trials or as part of a visual as compared to walking with vision
before starting the trials. Also, the trials were divided into three blocks, first, middle and last, and
were compared to examine changes within the experiment.
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Elliott’s study found that increased practice of the blind walking task reduced the
tendency to undershoot the target, meaning that subjects walked further (Elliott, 1987). Proffitt’s
study found that after adapting to lack of optic flow, subjects verbally estimated distances to be
further than before walking. This study tested whether adaptation played a role in the tendency to
reduce undershooting the target after many trials. This was done by eliminating practice trials
altogether and instead observing trends within blocks of trials. As such, we expect that the last
block of blind walking trials will show that subjects have adapted to the lack of visual flow and
will walk further than the first block of trials. Also, subjects who walked freely with a blindfold
before the trials began should walk further than subjects who walked freely with vision before.
The blind walking task would be deemed irrelevant, as adaptation to practice changes
results as the experiment is conducted. It could be possible to adapt to a new environment
without vision, since a recalibration of distance judgment occurs.
Method
Subjects
The Subjects were 4 male and 4 female undergraduates from McMaster University who
participated in this experiment for a lab course. The participants were all in their early twenties.
Each participant was part of the visual walking group on one day and non-visual walking group
on the other day.
Apparatus
Trials were conducted on a grassy flat field at McMaster University. A measuring tape
was used to measure distances from 1-25 meters and golf tees were placed at every meter along
it. The tees were used as markers for where to place the construction cone which was used as the
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target to estimate the distance to. They were hidden in the grass so subjects were unable to see
them. Subjects wore a black, cloth blindfold during the trials.
Procedure
On the first day of the study, the subjects were randomly assigned to the visual or non-visual
walking group. On the second day of the study the subjects were switched to the other group.
Subjects in the visual walking group freely walked in the open field for ten minutes. At the
end of the free walk they were brought to the starting position, which changed by one or two
meters each trial. The construction cone was placed 6, 9, 12 or 15 meters from the subject. The
subject removed their blindfold to see the target for 3 seconds, replaced the blindfold and walked
the distance they believe the target was at. The distance that the subject walked was measured
and recorded without giving any feedback. The subject remained blindfolded and was led to the
next starting position. The order of distances for the target placement was random and the
process was repeated so that each subject completed twelve trials.
Subjects in the non-visual walking group freely walked in the open field with a blindfold on
for ten minutes. The subject was then led to the starting position and the same procedure was
followed as for the visual walking subjects.
The design involved a 2 group (visual, non-visual) x 3 blocks of four trials (block 1, 2 and 3)
x 4 distance (6, 9, 12 and 15 m) factorial arrangement.
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References
Elliott, D. (1986). Continuous Visual Information May Be Important After All: A Failure To
Replicate Thomson (1983). Journal of Esperimental Psychology: Perception and Performance,
12(3), 388-391
Elliott, D. (1987). The Influence of Walking Speed and Prior Practice on Locomotor Distance
Estimation. Journal of Motor Behavior, 19(4), 476-485.
Loomis, J.M., Fujita, N., Da Silva, J.A. and Fukusima, S.S. (1992). Visual Perception and
Visually Directed Action. Journal of Experimental Psychology: Human Perception and
Performance, 18(4), 906-921.
Proffitt, D.R., Stefanucci, J., Banton, T. and Epstein, W. (2003). The Role of Effort in Perceiving
Distance. Psychological Science, 14(2), 106-112.
Thomson, J.A. (1983). Is Continuous Visual Monitoring Necessary in Visually Guided
Locomotion? Journal of Experimental Psychology: Human Perception and Performance, 9(3),
427-443.