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Results
To test whether adaptation to walking occurs after numerous trials of the blind walking
task are performed, different blocks of trials were compared. It is hypothesized that with
increased practice subjects will reduce undershooting the target, suggesting that subjects will
walk further in later blocks than in earlier blocks. Also, the non-visual (NV) group is
hypothesized to reduce undershooting the target compared to the visual (V) group.
It was found that subjects tended to overshoot the distance in block 1 for both V and NV
conditions (M=0.0038, SD= 0.207). In block 2 subjects tended to undershot the target (M=0.0528, SD= 0.140). Subjects tended to undershoot and were overall most accurate in block 3,
with the smallest percent error of all blocks (M=-0.0242, SD=0.176). The vision group made
fewer errors and underestimated less overall compared to the non-vision group (V: M=-0.015,
SD=0.1833; NV: M=-0.0338, SD=0.1719).
As shown in Figure 1, the percent errors for all blocks of the non-visual condition were
all negative, meaning that subjects tended to undershoot the target throughout the experiment.
For the visual condition, subjects overshot the target in the first block but then undershot in the
second and third blocks. Figure 2 shows that as distance increased, the accuracy of subjects
distance estimation had a slight increase.
There were no main effects for the condition variable or block variable. Also, no
interaction was found between condition and block. A 2 x 3 (condition x block) repeated analysis
of variance (ANOVA) showed there is no main effect of blocks (F(2,62) = 2.074, p > 0.05). The
same ANOVA revealed no main effect of condition (F(1,31) = 0.198, p > 0.05). The interaction
between condition and block was also found to be insignificant (F(2,62) =.953, p > 0.05). This
shows that prior exposure to the task and vision conditions did not have significant results.
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Discussion
This experiment was to study whether sensory adaptation occurred within the blind
walking task as a result of prior practice. Elliott (1987) found that with prior practice, subjects of
the blind walking task were less likely to undershoot the target. This could be explained by
adaptation occurring after many walking many trials blindfolded. In the study by Proffitt,
Stefanucci, Banton and Epstein (2003) it was found that when subjects walked blindfolded on a
treadmill before verbally estimating distances to a target, they were less likely to undershoot the
distance. This study looked at whether freely walking while blindfolded before distance
estimation affected the results of the blind walking task and also reduced tendency to undershoot
the target.
The results showed that there were no significant results for the blocks, visual conditions
or the interaction between the two. The subjects did not have any significant changes in distance
estimation over blocks of trials. The vision and non-vision conditions were not significantly
different. As shown in Figure 1, the visual condition tended to walk further than the non-visual
group which contradicts the hypothesis. Therefore, the data does not support the hypothesis that
adaptation occurs in the bind walking task.
The purpose of this study was to determine whether the blind walking task is an accurate
way of testing one’s perception of depth. Had the hypothesis been supported, the blind walking
task would not be an accurate measure of depth perception since adaptation may occur within the
task. If more practice with the task affected the results, the task would not be an accurate
measure of perception. Since the data does not support this hypothesis, no flaw in the blind
walking task has been found, however more research is necessary.
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In the studies by Elliott (1987), practicing the blind walking task was shown to reduce
undershooting the target, however it was not specified how this may have occurred. This study
looked at the different blocks of trials individually to see whether there is a reduction in
undershooting within the trials. Unlike Elliott’s experiment, this experiment was unable to find
that with more practice the target distance was undershot less. It was found that a lack of optic
flow while walking on a treadmill caused subjects to verbally estimate longer distances than
before (Proffitt, Stefanucci, Banton and Epstein, 2003). Walking on a treadmill is not as natural
of a movement as walking on ground, so this study had subjects walk with and without optic
flow freely in a field instead. The data did not support that after walking without optic flow
distances are underestimated less than after walking with optic flow. Also, since verbal
estimations of a distance are not as accurate as motor estimations (Loomis, Fujita, Da Silva and
Fukusima, 1992) the experiment involved blind walking instead.
The data collected in this study did not support the hypothesis; however this could have
been caused by many factors. One source of error could be that there were not enough subjects
participating in the study. Increasing the sample size would decrease the variance of the study so
there would be greater chance of finding a significant result. Also, the subjects were not naïve to
some aspects of the experiment since the subjects were participating in the study as part of a
course. The subjects wore a blindfold which may not have completely blinded them. Both of
these factors could have changed the responses of participants and allowed them to rely on
something other than egocentric distance estimation.
Another possible problem with the methodology of the study is that it is uncertain
whether ten minutes was enough time for participants to adapt to a lack of optic flow. If As this
was part of a class assignment, four groups of researchers conducted the study for two
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participants per group. Having so many researchers carry out the study at different times means
that there may have been differences in procedure and data collection. Even slight differences in
procedure could have affected the results and caused inconsistent data. Although the study was
carried out in the same location, each group did the study at a different time of day and with a
different number of days between the visual and non-visual condition for subjects.
For this study to be replicated it would be necessary to improve upon the experimental
design such that there are fewer researchers and more subjects. This could decrease the
variability and have a greater chance of significant results. The overall design of the experiment,
such as the adaptation time for visual and non-visual conditions and comparing blocks of the
blind walking task, could yield significant results if details of the study were improved upon.
Previous research has indicated that prior exposure to the blind walking task may affect a
subject’s response and that optic flow plays a role in distance estimation. Both of these factors
should be studied and manipulated further to gain a better understanding.
In order to improve on methods of measuring one’s depth perception it must be further
studied if adaptation plays a role in the blind walking task. The blind walking task has been used
for decades as a generally accepted way of measuring perception through motor output.
However, studies need to be conducted to find if adaptation to the task itself is occurring.
Manipulations to the method of blind walking tasks would need to be found in order to have a
study which accurately measures depth perception.
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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.
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Table 1: This table shows the many statistical tests performed on the condition and block
variables, as well as the interaction between the two. None of the tests show significant
results between the variables.
Figure 1: This graph shows the mean percent error of the interactions between the condition and
block variables. Both of the conditions indicate that subjects undershot the target more in block 2
than block 1 and 3. Error bars=0.05
Figure 2: This graph illustrates the mean percent error relationship between target distance and
condition. The trend for both conditions is that as distance increased mean percent error became
closer to zero. Error bars=0.05
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Table 1:
Tests of Within-Subjects Effects
Measure:MEASURE_1
Type III Sum of
Source
condition
Error(condition)
block
Error(block)
condition * block
Error(condition*block)
Squares
df
Mean Square
F
Sig.
Sphericity Assumed
.998
1
.998
.198
.660
Greenhouse-Geisser
.998
1.000
.998
.198
.660
Huynh-Feldt
.998
1.000
.998
.198
.660
Lower-bound
.998
1.000
.998
.198
.660
Sphericity Assumed
156.580
31
5.051
Greenhouse-Geisser
156.580
31.000
5.051
Huynh-Feldt
156.580
31.000
5.051
Lower-bound
156.580
31.000
5.051
Sphericity Assumed
11.559
2
5.780
2.074
.134
Greenhouse-Geisser
11.559
1.817
6.361
2.074
.139
Huynh-Feldt
11.559
1.924
6.008
2.074
.136
Lower-bound
11.559
1.000
11.559
2.074
.160
Sphericity Assumed
172.808
62
2.787
Greenhouse-Geisser
172.808
56.334
3.068
Huynh-Feldt
172.808
59.648
2.897
Lower-bound
172.808
31.000
5.574
Sphericity Assumed
3.227
2
1.614
.953
.391
Greenhouse-Geisser
3.227
1.935
1.668
.953
.389
Huynh-Feldt
3.227
2.000
1.614
.953
.391
Lower-bound
3.227
1.000
3.227
.953
.337
Sphericity Assumed
104.985
62
1.693
Greenhouse-Geisser
104.985
59.973
1.751
Huynh-Feldt
104.985
62.000
1.693
Lower-bound
104.985
31.000
3.387
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Figure 1:
Effect of Block and Condition
on Accuracy of BWT
0.1
Error(%)
0.05
0
1
2
-0.05
-0.1
-0.15
Block
3
NV
V
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Figure 2:
Effect of Distance and Condition on Accuracy of
BWT
0.1
Error (%)
0.05
0
NV
6
9
12
-0.05
-0.1
-0.15
Distance (m)
15
V