The Effect of Sensory Adaptation on the Blind Walking Task



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The Effect of Sensory Adaptation on the

Blind Walking Task


Introduction
The ability of an individual to navigate through space is essential for their survival. Here, space can be defined as “the physical expanse which surrounds something” (Oxford). Spatial perception is critical to survival; however there is no adequate way to directly measure what an individual perceives at any given moment (Hershenson, 1999). Therefore, the experimenter must rely on verbal and motor cues to infer what an individual perceives at any given moment in time (Hershenson, 1999). Unfortunately, it was discovered that verbal reports had low reliability, so scientists needed to discover a way to observe an individual’s motor cues. This was the blind walking task first used by Thomson in 1983. The blind walking task, first used, consisted of showing the subject a target that ranged from 6-21m away from a starting point. Subjects were then blindfolded and asked to walk until they were at the target (Thomson, 1983). This was believed to be a more reliable test to study one’s spatial perception, due to the fact that humans complete the blind walking test with reasonably high accuracy (Sun, 2004). This finding led to the idea that in order for people to be using visual information they do not have to be continuously receiving novel visual input (Thomson, 1983). Previous research by Elliot measured if there was a relationship between walking speed, prior practice and walking delay on the blind walking task. Here, it was found that these variables had no relationship to performance on the blind walking task (Elliott, 1987).

Proffitt designed an experiment to test whether removing optic flow had an effect on spatial perception. He got subjects to walk on a treadmill and wear a device that removed all optic flow. After, he got the subjects off the treadmill and blindfolded them; subjects were then directed to walk on the spot (Proffitt, 2003). It was found that subjects who had optic flow removed walked forwards when intending to walk on the spot (Proffitt, 2003). This result is seen because of the fact that the subject did not receive any optic flow while walking forwards, so to the subject it seemed as though they were walking on the spot. This phenomenon is referred to as sensory adaptation which occurs when sensitivity to stimulation is decreased due to repeated exposure to the stimulation (Sun, 2008).

This experiment incorporates both Thomson and Proffitt’s studies to determine whether sensory adaptation affects the distance a person walks during the blind walking task. The two independent variables being measured are prior exposure to blind walking and the trial block. Each subject will perform the blind walking test twice, once with prior exposure to blind walking and once without prior exposure. Prior exposure to blind walking is created by having the subject walk around an open field blindfolded at a moderate pace. In order to control for fatigue effects, even when subjects were not in the exposure to blind walking group they were required to walk for the same amount of time. There were three trial blocks, with each block being made up of four trials at four separate distances.

It is predicted that sensory adaptation will affect the distance walked during the blind walking task. The expected trend is that the subjects in the prior exposure (non visual) experimental group will, on average, walk further than the no prior exposure (visual) control group. Additionally, it is also expected that over the blocks the visual group will adapt to blind walking and subjects in this group will, on average walk, further in later blocks when compared to the earlier blocks.

This study will help in understanding how sensory adaptation can influence spatial representations. Information about how sensory adaptation works is valuable because it could help people who have become blind during the course of their life. For these individuals it can be thought that there would be a period of sensory adaptation that they would go through. Further research with sensory adaptation and the blind walking test need to be done in order to develop techniques to help this group of people develop through the adaptation period.

Furthermore, assuming it is found that sensory adaptation does influence the blind walking task, the results of the experiments above may be found to be invalid. This is due to the fact that during those experiments sensory adaptation was not controlled for.

Methods

Subjects: Eight undergraduate students taking the cognitive neuroscience class were used as subjects. They consisted of four females and four males whose age ranged from 18-22. Subjects completed the experiment for each condition on two separate days; the condition they performed first was randomly assigned with half the subjects taking part in the non visual condition on day one and the other half completing the visual condition on day one.

Apparatus: The experiment was performed on a quiet open field. A measuring tape was used to measure one meter intervals, in total 18 intervals were measured and marked using 18 golf tees. An orange stake was placed into the ground and used as the target.

Procedure: There were two conditions, the visual and non-visual condition, the difference was that in the non visual condition, participants were blindfolded, and in the visual condition they were not. Subjects were then instructed to walk around the open field for ten minutes at a moderate pace. After the ten minutes participants completed 12 blind walking task trials at distances of 6,9,12 and 15 meters. The distances were each completed three times in random order and the starting point was varied randomly from -2,-1, 0, 1 and 2 meters. The participants were placed at the starting point, their blindfolds were removed. Next, the subjects looked at the target for a minimal amount of time and their blindfolds were replaced. The subject was then instructed to walk to the target; once they were there, the experimenter measured from their toe to the start to find the total distance walked. The subject was given no feedback and then was walked back to the start by the experimenter to start the next trial. The subjects then returned at least 24 hours later to perform the experiment in the opposite condition.

In order to analyze the data a 2x3 within-subjects analysis of variance was used. The variables were visual and non visual with the other factor being block number (1, 2, 3). The F value, as well as significance value, will be calculated for the condition, block number as well as if there is an interaction effect.


References

Elliott, D. (1987). The Influence of Walking Speed and Prior Practice on Locomotor Distance Estimation. Journal of Motor Behaviour, 19(4), 476-485.


Hershenson, M. (1999). Visual Space Perception. Cambridge, Massachusetts: MIT Press, 238pp.
Proffitt, D.(2003). The Role of Effort in Perceiving Distance. Psychological Science, 14(2), 106-112.
“space.” Oxford English Dictionary Online. 2007.

http://dictionary.oed.com.libaccess.lib.mcmaster.ca/cgi/findword?query_type=word&queryword=space (26 Sept 2008).
Sun, H., et al. (2004). The Contributions of Static Visual Cues, Nonvisual Cues, and optic flow in distance estimation. Perception, 33, 49-65.
Sun, H. Introduction. [PSYCH 3MM3]. PC/204. McMaster University. September 22, 2008.
Thomson, J.(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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