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Results
The purpose of this experiment was to examine the effects of sensory adaptation on spatial perception using the blind-walking test. Before running this experiment, we hypothesized that subjects in the non-visual experimental condition will experience sensory adaptation with repeated trials. Consequently, we predicted subjects would over-estimate distances more in the non-visual condition than in the visual condition. This hypothesis is based on the assumption that adapted subjects will become increasingly less sensitive to the distance walked during each trial. We also hypothesized that subjects will walk longer distances in the last block of trials than in the first block.
After analyzing the data collected from our experiment, the results were found non-significant. A 2 x 3 (condition x block) repeated analysis of variance (ANOVA) revealed no main effect of block (F(2,62) = 2.074, p > 0.05). In addition, there was no main effect for the condition variable (F(1,31) = .198, p >0.05). Lastly, there was no interaction between condition and block, as results proved non-significant (F(2,62) =.953, p > 0.05). Overall, our experiment did not provide any significant results.
Discussion
The ability to perceive and respond to characteristics such as size and depth of objects in the environment is called spatial perception. Numerous studies have used the blind-walking test to explore the phenomenon of spatial perception. However, the possibility of acquiring sensory adaptation while doing this test is commonly overlooked. This experiment examines the possibility of sensory adaptation and it’s effect on spatial perception demonstrated through distance estimation. We hypothesized subjects would over-estimate distances more while in the experimental condition than in the control condition. We also predicted more overshooting in the last block of trials than in the first block, showing gradual adaptation.
After collecting and analyzing the data, it was found that none of our results were significant. There were no main effects for the condition and block variable, as well as no interaction effects. Contrary to our prediction, subjects in the experimental condition continuously under-estimated distances throughout all 3 blocks of trials (refer to figure 1). Although we had predicted that subjects would overshoot distance estimations more while in the experimental group than in the control group, our results show that subjects did the exact opposite. Individuals over-estimated more in the control condition (refer to figure 1). It was also hypothesized that subjects would walk longer with progressive trials, resulting in the greatest distances accumulated in the last block. However, in the control condition, subjects over-estimated more in the first block of trials than the last(refer to figure 1). Furthermore, the changing distances over trials did not have a significant effect on accuracy of distance estimation. The percent error of distance estimations made by non-visual and visual groups were similar (refer to figure 2).
Although we were unable to derive any significant results, research in this field is impeccably important. Strengthening our understanding of spatial perception and adaptation has tremendous practical importance. For example, research findings can be applied to improving the rehabilitation of non-visual people. Professionals can aid those who have lost their sight with becoming adapted and more familiar with their environment.
When conducting a study, it is important to be well informed of previous research completed in the field of interest. For example, Digby Elliot manipulated walking speed, prior practice and walking delay to determine if they had an impact on distance estimation (Elliot, 1987). Although he was unable to replicate Thomson’s results, he still managed to make some important conclusions. For instance, he found that at the 12 m target, subjects performed better with a brief delay before walking to a target (Elliot, 1987). Further, Elliot’s studies with pointing demonstrate the existence of a brief mental representation that could be useful for quick manual movements (Elliot, 1987).
There are similarities and differences between this study and Elliot’s in terms of both methodology and findings. For example, participants in both experiments were instructed to walk in a non-visual condition towards targets positioned at varying distances. Also, subjects in Elliot’s study were given time to practice. Similarly in this experiment, subjects walked around for 10 minutes prior to the blind-walking trials to either control for fatigue or allow for sensory adaptation. On the other hand, major differences between our study and Elliot’s include his manipulation of changing walking delay times and walking speed. While running our experiment, subjects had a consistent walking delay of 3 seconds, during which they removed the blindfold to briefly view the location of the target. Our participants were also not given a time limit to complete each trial. Further, Elliot’s research on target pointing has revealed a brief representation that could lead to important applications. Unlike Elliot’s study, our experiment did not lead to any significant results. Finally, our experiment looked at the potential effects of sensory adaptation, while Elliot did not take this fact into consideration.
In a more recent study, Proffitt and his colleagues conducted three experiments, which show that spatial perception is influenced by locomotor effect (Proffitt, Stefanucci, Banton, Epstein, 2003). The first experiment showed that perceived distance is increased when an observer is wearing a heavy backpack. The second experiment revealed that people acquire a visual-motor aftereffect when walking on a treadmill without optic flow, but not with optic flow. And with the final experiment, it was found that participants without optic flow over-estimated extents more after treadmill-walking adaptation than before adaptation was acquired (Proffitt et al., 2003).
With knowledge and comprehension of Proffitt’s experiment, the similarities and differences between his study and our own become evident. The two studies are similar in the fact that they both focus on spatial perception and how it is influenced by locomotor effect. Also, in both experiments, subjects were not given feedback after making distance estimations. Although there are some obvious commonalities, the ways in which Proffitt’s study differs are also important to note. In Proffitt’s study, subjects had a 3-minute adaptation period, which is significantly shorter than the 10 minutes we allowed non-visual subjects to adapt to the surroundings before testing. Also, Proffitt’s participants made verbal distance judgments, while our subjects estimated distances with blind-walking. Lastly, Proffitt made important discoveries, including the influence of optic flow on distance judgments and visual-motor aftereffects. Unfortunately, we did not attain any significant results with our experiment and are thus unable to provide any new conclusions to the field.
There are a variety of possible reasons as to why our results do not support our hypothesis or any of the predictions made prior to testing. Sample size is a very important factor in running an experiment, as a larger sample size provides larger power. We only used eight subjects in our experiment, which may have contributed to our non-significant results. A smaller sample size is also more strongly affected by outliers in the data. For example, if one of the participants tended to greatly undershoot distance judgments with each trial, his or her data would strongly affect the mean estimates of all subjects. In addition, a subject in one of the four experimental groups was unexpectedly unable to complete their second day of testing, and thus only participated in one of the two conditions. Since this experiment looks at within-subject effects, changing participants could have had a grave influence on our results.
Our experiment allowed for an adaptation time of 10 minutes prior to testing in the non-visual condition. It is possible that the acquisition of sensory adaptation requires walking around blindfolded for a longer duration. This leads us to wonder if having an adaptation time of 20 minutes would have provided significant results. As well, we conducted 12 trials per condition, which may not have been sufficient to attain significant results. Overall, if this research were to be replicated, we would improve this experiment by using a larger sample size and by making sure all subjects are used for both conditions. We would also consider increasing trials and adaptation time.
Research on spatial perception has very important implications, particularly in improving the rehabilitation of non-visual individuals. In a related study from 2006, Orly Lahav looked at sensorial channels other than the visual channel as a device for mental mapping unknown spaces, thus improving spatial perception for blind individuals (Lahav, 2006). The study focused on using virtual reality, which is built on haptic and auditory feedback, to help those who are blind explore and learn about their environments (Lahav, 2006). Numerous other studies have been conducted that aim to understand the dynamics of spatial perception, the effects of sensory adaptation, and ultimately, the human mind.
Figure 1: Percent error of performance by subjects in both conditions for 3 blocks of trials is represented with this figure. Contrary to our predictions, subjects in neither group over-estimated more in the last block than the first.
Figure 2: Percent error of varying distance estimations by subjects in non-visual and visual condition. This graph illustrates the similarities in performance between the two groups and over various trials.
Appendix
Figure 1
Figure 2
References
Proffitt, Dennis R., Stefanucci, Jeanine., Banton, Ton., Epstein, Willian. (2003).The Role of Effort in Perceiving Distance. Psychological Sicence, 14 (2, 106-122).
Elliot, Digby. (1987). The Influence of Walking Speed and Prior Practice on Locomotor Distance Estimation. Journal of Motor Behavior, 19 (4, 476-485).
Lahav, Orly. (2006). Using Virtual Environment to Improve Spatial Perception by People Who Are Blind. CyberPsychology & Behavior, 9 (2, 174-177).