The Effects of Sensory Adaptation on the Blind Walking Task by XWNj40k

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                   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
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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 deteriation 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
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number of practice trials given (Elliott, 1986). Elliott (1986) 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 that 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 and 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
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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.

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 an Ethics

board requirement. The purpose of the experiment was disclosed to the subjects.

Method

               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 blindfolded. Subjects were given a blindfold to wear in order to
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eliminate vision. The target distances were measured in advance using with 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.

       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.




COMMENTS
Intro:
There was a general intro to material however no citations were provided
Could have been more defining done with some of key terms ie. I don’t think
sensory adaptation was ever clearly defined
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I think author had difficulty picking out relevant studies ie talked about Thompson
much more than I think was really necessary
Did describe other studies in detail; although I would question if there was a true
understanding of Proffitt’s work
Independent variables were defined wrong; although dependent variable was
correct
A detailed hypothesis was given
Significance of this study was given briefly could definitely have been expanded
on
Found to be lots of spelling, grammar mistakes and awkward sentences, a more
thorough proof read is needed next time.
Overall 6.5/10

Methods
Completely missing a third of the section (apparatus)
6/10

								
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