Running Head: 3MM3 Traversed Distance Estimation / 1
Abstract
The blind walking task was initially used by Thomson in 1983, but for our purposes we used the task to test whether sensory adaptation played a crucial role during the task. Initially it was expected that subjects would overestimate their distance from a target during the blind walking task based on previous research conducted by Thomson, Elliott and Proffitt. Eight McMaster University students were randomly selected as participants. They were required to attend two testing trials 24 hours apart, one day they received 10 minutes of prior exposure to the blindfold and the next day they had 10 minutes of exposure to regular visual cues. With the aid of golf tees, experimenters were able to set up markers for the 4 target distances (6m,9m,10m,12m) and the 5 starting positions (-2,-1,0,1,2). The subjects were then blindfolded and shown a target for 3 seconds and asked to walk to it for a total of 12 trials a day. A retractable tape measure was used to measure the distance the target had walked. Results indicated that sensory adaptation did not play a role in the blind walking task and subjects did not overestimate their distances from the target. Further research will be conducted in order to understand the following results.
The Effects of Sensory Adaption on the Blind Walking Task
Introduction
Spatial perception is essential for movement throughout any environment. Whether it be walking to a door or picking up a cup of coffee we need to be able to perceive extent and distance around us. Spatial perception is the ability to perceive space relative to yourself. The physical characteristics of spatial perception deal with object location, more specifically distance and direction. Distance and direction are perceived egocentrically when encountered in an environment.
Due to the fact that spatial perception is critical for daily survival James Thomson created the blind walking task to further understand this phenomenon. The blind walking task is a fundamental aspect of spatial perception that was first used by Thomson in his experiment back in 1983, which was testing the extent of visuomotor control related to continuous sensory monitoring (Thomson, 1983). The blind walking task involves testing subjects’ ability to perceive a distance and walk to the given distance using two conditions; normal visual control or the exclusion of visual control. With the aid of the blind walking task it is possible now to test if sensory adaptation affects the blind walking task.
Thomson (1983) suggested that without the aid of vision our accuracy is somewhat affected, yet it does not interfere with performance especially during the earlier parts of the act. Thomson introduced a two stage model for visuomotor control and conducted a series of experiments to test his hypothesis. Thomson believed that the ability to preplan activity may possibly be a general feature of control and the six experiments tested this possibility (Thomson, 1983). The first experiment showed that locomotion could substantially help guide one over a distance of 12 meters without vision accurately, this lead Thomson to his next finding that time was a fundamental variable in determining accuracy and information was internalized. He found that times elapsing 8 seconds lead to a decrease in overall accuracy (Thomson, 1983). Thomson’s third experiment found that errors that occurred were due to fading of information and showed accuracy deterioration after 7 to 8 seconds. The following experiment also confirmed that time delays showed a decrease in accuracy after 6 meters. The following two experiments showed that locomotion over greater distances is controlled by internalized spatial representations and accuracy was due to nonmotoric spatial information retention (Thomson, 1983). Thomson (1983) suggested that his overall findings concluded that locomotion can be controlled with the exclusion of vision. Thomson did show this phenomenon but he gave his subjects feedback which could technically allow the subject to overshoot or undershoot their distance depending on the feedback given. Thomson also did not account for fatigue nor could he prove why Elliott could not replicate his results.
Digby Elliott also used the blind walking task in order to replicate Thomson’s findings that visual information was useful during movement up to an interval of 8 seconds, but was unsuccessful in doing so. Elliott did find some similarities such as the fact that vision did not interfere with performance especially over the earlier parts of the act and that accuracy increased when asked to walk to the target immediately (Elliott, 1986). Yet Elliot (1986) stated that continuous visual input was necessary for accurate movement control and that no form of visual representation could be used as a substitute. Soon after Thomson indicated that there were two flaws in Elliott’s work, which is why he was unsuccessful in replicating the same results (Elliott, 1986). Elliott then conducted another experiment in order to reconcile discrepancies within their work. He tested walking speed and practice and found that there was an increase in overshooting distances as the distances increased, and that the tendency to undershoot decreased with the number of practice trials given (Elliott, 1987). Elliott (1987) concluded that there was no significance of distance or speed just the number of trials, still unsuccessful in replicating Thomson’s results. Although Elliott did not give his subjects feedback he did have other limitations subjects were able to give verbal responses which tend to provide smaller estimates.
In addition to the studies mentioned above Dennis Proffitt also built on the work of Thomson in the three experiments he conducted. Proffitt (2003) has noted that space is perceived in terms of effort. He described gross motor action in terms of slant and extent, with respect to distance he said that it is a function of distal extent and the effort required to walk a distance (Proffitt, 2003). Proffitt conducted his experiments on a treadmill using virtual reality, and found that those subjects exposed to a stationary scene versus a moving scene had a tendency to move forward as an after effect as well as the fact that optic flow disrupted their visual cues. In addition, he found that in the third experiment when subjects experienced no optic flow during adaptation they tended to overestimate distances caused by the after effect (Proffitt, 2003). Proffitt’s work also had limitations such as; using a treadmill which could possibly create a difference in results because the subject in confounded to one position whereas walking in an open space is more natural. Movement may differ accordingly.
The purpose of our experiment is to test if sensory adaptation affects the blind walking task and creates an overestimation of perceived distance. We strictly wanted to measure if sensory adaptation occurred during the blind walking task so we built on the ideas and research of the experimenters mentioned above. Overestimating perceived distance could be possibly due in part to sensory adaptation; walking confidence or even less confidence in distance estimation and the experiment will help clarify this. Having no visual control one should overestimate and with visual control one should underestimate. The experiment is intended to measure the independent variable distance walked using two conditions which include; prior exposure to blind walking versus no exposure and a comparison of the number of trials. The dependent variable is error. We eliminated the idea of forgetting because we did not incorporate time delays or the effects of practice because subjects were not given the opportunity to practice. Speed was also not a factor we needed to account for because we were not measuring the 8 seconds programming that Thomson suggested. The design also eliminates the idea of perceived effort and optic flow introduced by Proffitt. In addition, all our subjects were also blindfolded using an actual blindfold to avoid subjects from accidently opening their eyes and we accounted for fatigue by giving them the opportunity to adapt to their environment for 10 minutes prior to their task. The blind walking task gives us essential information when dealing with the blind walking task, if in fact we are dealing with sensory adaptation the blind walking task is in fact not useful with respect to locomotion and the blind.
Methods
Subjects
For the experiment there was a random selection of eight university students, of whom four were female and the other four were male all between the ages of 19 to 25. The two groups of subjects were then divided into two groups ensuring subjects have normal-to-corrected to normal vision. All subjects were asked to complete an informed consent form which is a Ethics board requirement. The purpose of the experiment was disclosed to the subjects.
Apparatus
In order to conduct the experiment a flat large area was desired therefore the oval field beside the David Braley Athletic Centre was chosen as the conduction site. The site consisted of minimal visual and auditory cues. The subjects were also required to walk around for a time span of ten minutes and were timed using a timer. Subjects were given a blindfold to wear in order to eliminate vision. The target distances were measured in advance using golf tees and a retractable measuring tape at various distances including; 6,9,12 and 15 meters. Experimenters also marked five starting points with golf tees at; -2, -1, 0, 1- 2 meters before starting.
Procedure
The subjects randomly selected were required to complete the experiment under two conditions, blindfolded and not blindfolded over the course of a two day span. The conditions were assigned in an alternating manner. The four distances and starting positions were measure by the experimenters before the subjects had arrived. All distances were marked using golf tees in order to distinguish these marks. All participants were required to walk for 10 minutes with or without visual cues in order to ensure that there was no optic flow. Once the subjects were blindfolded an experimenter was helping the subject for their own safety. Once the 10 minute period was up the experimenter lead the subject to the testing ground where they would then be tested. The other subjects where then required to walk around the field with visual cues in order to fatigue them of the same manner. Subjects were exposed to normal optic flow unlike the previous subjects. These subjects were then lead to the site of the experiment once the ten minutes has elapsed. No feedback was given to either subject during their trials to ensure accuracy of results. All subjects were then released and ask to come back in 24 hours to conducts the other half of the experiment. The second consisted of the same procedure but the original subject that had prior exposure to the blindfold now did not have prior exposure and the subject who did not receive the prior exposure was now exposed.
Results
The experiment tested for sensory adaptation during the blind walking task using two variables. The first was prior exposure to vision vs. no prior exposure to vision, and the second was blocks. It was predicted that participants would be subject to sensory adaptation and therefore they would become less sensitive to the target distances and overestimate based on this hypothesis. After the conduction of the blind walking task results indicated that the means and standard deviation for each condition in each of the three blocks differed. The mean of vision block 1 (M = .1888, SD = 2.24095) was higher than the mean for both visual block two and three respectively (M = -.3581, SD = 1.70436, M = -.2272, SD = 1.67542). The mean for non vision block 3 (M = -.0069, SD = 2.22458) was higher than non vision block 1 and 2 respectively
(M = .1028, SD = 2.01993, M = -.7194, SD = 1.64276). The mean for vision block 1 (M = .1888,
SD = 2.24095) is higher than non vision block 3 (M = -.0069, SD =2.22458). The overall means for block 1 for both conditions are higher than block 2 and 3. Refer to figure 1. The error for the blocks for both conditions is shown in figure 2 and the error for the distances for both conditions is shown in figure 3. The two graphs depict no effect between the conditions and the varying factors which are blocks and distances, respectively.
In order to further analyse the data a general linear model and 2x3 repeated measures ANOVA was performed. The general linear model is helpful because it allows for analysis of large amounts of data or information and summarizes a wide range of outcomes. The repeated measures ANOVA is helpful because we are testing within group and between group and all are being tested under various conditions as a repeated factor. With the comparison of the prior exposure to vision and no prior exposure to vision results were as follows (F(1,31) = 0.198,
p = 0.660) indicating that there was no significance. A comparison of the three blocks also showed no significant results (F (2,62) = 2.074, p = 0.134). In addition, the interaction between the two conditions and the three blocks showed no significance as well (F (2,62) = 0.953,
p = 0.391). Given the previous analysis the values for p˃.05 suggested that there were no significant results throughout the experiment.
Figure 1 – The graph depicts the means for visual and non visual conditions as per each of the three blocks. The bars on each of the points indicate standard error.
Figure 2 – The graph displays the error for the visual and non visual conditions within each block.
Figure 3 – The graphs illustrates the error for the visual and non visual conditions for each distance measured.
Figure 1
Figure 2
Figure 3
Discussion
The blind walking task is used in order to help understand traversed distance estimation. For the current study the blind walking task was used to uncover the effects of sensory adaptation on distance estimation from an egocentric perspective. It was hypothesized that sensory adaptation would cause subjects to overestimate the target distances because they would be subject to a decrease in sensitivity. The results of all analysis completed indicated that there was no significant effect which did not support our hypothesis of the blind walking task. This means that during the experiment subjects were not affected by sensory adaptation and therefore did not have a tendency to overestimate target distances. The results were rather surprising because previous research conducted has shown that subjects do tend to overestimate distances, which was clearly not in accordance with our findings.
The blind walking task which was first introduced by Thomson was used by various other researchers such as Digby Elliott and Dennis Proffitt to reveal certain aspects of spatial perception. Thomson (1983) suggested that without the use of vision accuracy is only affected to a degree, but performance is not affected. Implicating that we do not need continuous visual input in order to navigate or control our movement throughout space. Our results on the other hand indicated that we do require continuous visual input because our data yielded no significant effect between conditions or blocks.
Digby Elliott found similar results to Thomson only when it came to performance not being affected by vision but he also found that there was an increase in overshooting distances as the distances began to increase (Elliott, 1986). This suggested that when subjects were asked to walk to a specific distance they would overestimate target distances. Unfortunately our results implied no such effect. Having prior exposure to vision or no prior exposure to vision had no effect on the distances walked by subjects nor did the blocks.
Another famous study conducted by Dennis Proffitt provided data that implied that walking a distance is related to effort and having no optic flow would cause subjects to overestimate distances after exposure to the blind walking task using virtual reality and a treadmill (Proffitt, 2003). Although we did not use a treadmill or virtual reality our results were also inconsistent with Proffitt.
Due to the fact that our results were inconsistent with previous research conducted, many issues must be addressed regarding the analysis of the 2x3 repeated measures ANOVA that yielded insignificant effects. The experiments procedure was extremely straightforward but could have had loopholes such as; the adaptation period being too long or too short. Our subjects were given a 10 minute adaptation period vs. Proffitt (2003) who used a 2 minute adaptation period. In addition our subjects were not naive to the experiment; they were aware of the conditions and predicted outcomes. This unfortunately may have influenced the subjects’ ability to estimate a distance because they may have used strategies to count the trials, order and steps to the target distance. Other effectors could have been that the population of subjects was extremely small (8) which may have caused outliers drastically changing the data analysis. Also, due to the fact that there were approximately 12 experimenters the experiment could be subject to variability. Experimenters may have instructed subjects or conducted certain aspects of the experiment using slight variations which could possibly affect the subjects distance estimation. Many subjects were tested on different day and the weather conditions could have also played into the results. One of the major issues encountered during the experiment was that one of subjects was switched during the condition switch over the 2 day span. The fact that one of the groups used data for 2 different subjects could quite possibly have affected the significance of the results.
In order to address these issues further research must be conducted and the experiment can be elaborated on in order to reconcile differences in data from previous research. With the aid of more funding we may be able to test more subjects who are naive to the experiment and increasing our data. In addition, adding variations of adaptation time can aid in determining if adaptation period plays a role. Limiting the number of experimenters could also decrease the variability in the conduction of the experiment. Also, testing all subjects for one condition on one specific day and the subjects for another condition on another could have yielded results that may have been in accordance with the hypothesis. The last major issue can be addressed simply by ensuring that all data for each condition is consistent with each subject and if a subject must be switched all data provided by the previous subject is discarded and the new subject is tested for all conditions again.