Page 1 of 9 3MM3_P1ReportPart2_09

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.

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.

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 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.

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.
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

Table 1:

Tests of Within-Subjects Effects
Measure:MEASURE_1
Source / Type III Sum of Squares / df / Mean Square / F / Sig.
condition / 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
Error(condition) / 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
block / 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
Error(block) / 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
condition * block / 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
Error(condition*block) / 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

Figure 1:

Figure 2: