University of Colorado, Boulder CU Scholar Undergraduate Honors Theses Honors Program Spring 017 The Effects of Vision and Internal and External Focus of Attention on Balance in a Yoga Pose Eun Kim Eun.B.Kim@Colorado.EDU Follow this and additional works at: https://scholar.colorado.edu/honr_theses Part of the Other Medicine and Health Sciences Commons Recommended Citation Kim, Eun, "The Effects of Vision and Internal and External Focus of Attention on Balance in a Yoga Pose" (017). Undergraduate Honors Theses. 1376. https://scholar.colorado.edu/honr_theses/1376 This Thesis is brought to you for free and open access by Honors Program at CU Scholar. It has been accepted for inclusion in Undergraduate Honors Theses by an authorized administrator of CU Scholar. For more information, please contact cuscholaradmin@colorado.edu.
1 The Effects of Vision and Internal and External Focus of Attention on Balance in a Yoga Pose By Eun Bi Kim Integrative Physiology, University of Colorado Boulder April 5, 017 Thesis Advisor David Sherwood, Integrative Physiology Defense Committee: David Sherwood, Integrative Physiology, Alaa Ahmed, Integrative Physiology, James Walker, Undergraduate Enrichment Programs
Abstract This research study attempted to find the effects of internal and external focus of attention (FOA), with vision and without vision, on a subject s balance. The experiment consisted of six testing conditions with each condition consisting of three ten-second trials each, a total of eighteen trials per subject. The subject participated in each condition: control with vision and without vision (n=0), internal FOA with vision and without vision (n=0), and external FOA with vision and without vision (n=0). Subjects assumed an intermediate level yoga pose, tree pose, on a Wii Balance Board throughout the experiment, while force in kilograms from each of the board s four sensors was collected. The level of performance was measured by the standard deviation of COPx and COPy calculated by the data recorded from the board s four sensors, as well as the standard deviation of COP distance from the center in the x-direction and y-direction in centimeters. The subject being off centered resulted in a larger variation in the four measurements whereas a smaller variation in the four measurements was measured in subjects who had superior balance. The findings showed that there was a significant effect of vision on balance providing evidence that visual input is an important factor in postural stability. However, there was no significant effect of FOA on balance, providing no evidence for the constrained action hypothesis. Though there was no significant effect of FOA on balance, this is a relatively new area of research and additional studies are required before a conclusion may be made.
3 Introduction Effects of Vision Postural stability is maintained when the postural control systems, musculoskeletal, sensory, and central nervous system, work together. Feedback from active sensory systems is continuously monitored by the nervous system. To avoid falls, the central nervous system uses sensory information to generate musculoskeletal responses that correct and regulate postural control in an individual. The visual system, somatosensory, and vestibular system are the three sources which comprise sensory input. With vision loss, sensory input from the visual system is lost. This loss of visual input contributes to postural instability and there is a greater risk for falling in persons with visual impairments. In a study conducted by Tomomitsu, Alonso, Morimot, Bobbio, and Greve (013) the effects of reduced visual information and its importance to postural control were studied by comparing low-vision adults and normal-vision adults. Those who had a visual acuity of less than 6/18 but equal to or better than 3/60, or had a corresponding visual field loss of less than twenty degrees in the better eye with the best possible correction were considered low-vision subjects. Normal-vision subjects were chosen after a Snellen's optometric scale assessment. Both low-vision and normal-vision subjects were evaluated for balance in both static and dynamic conditions. The study had four protocols. The Modified Clinical Test of Sensory Interaction on Balance on firm and foam surfaces with eyes opened and closed, and the Unilateral Stance with eyes opened and closed protocols measured static balance whereas the Tandem Walk and Step Up/Over protocols measured dynamic balance. Sway velocity in degrees per second ( /s)
4 was collected in the static balance protocols. The dynamic balance protocol focused more on the characteristics of gait. Their results presented that the low-vision group had greater postural sway compared to the normal-vision group while balancing on a foam surface (p 0.001), the Unilateral Stance test for both limbs (p 0.001), and the Tandem Walk test. Their study displayed that visual input and visual feedback are critical for postural control. The relationship between changes in visual input and balance, especially in cases regarding single-leg stances, is fairly novel. Research in this field can lead to different strategies for preventing falls in populations with low-vision. Effects of Internal and External Focus of Attention (FOA) Attentional focus, either an internal FOA, details of one s actions, or an external FOA, details on the effects of one s movement, can influence motor behavior. When an athlete is learning a new skill, coaches often want to facilitate and optimize the athlete s performance. Performance in movement, such as balance, differs when attentional focus shifts from an internal to external FOA and vice versa. When a subject is asked to focus externally, movement outcome for example, movement performance is enhanced compared to subjects given an internal FOA, such as movement kinematics or muscle activity (Wulf, 01). The difference in performance by having either an internal or external FOA can be explained by the constrained action hypothesis (Wulf, McNevin, & Shea, 001). The hypothesis proposes that an internal FOA could constrain or interfere with automatic control processes, which normally regulate movement. This leads to poor performance as compared to receiving an external FOA, which allows the motor system to more naturally self-organize. In the study conducted by Sherwood, Lohse, and Healy (014) the effects of FOA
5 and vision on dart throwing were assessed. Participants began with six baseline throws with vision. Afterwards, participants were blindfolded and participated in three different conditions. On a rating scale between one and six, participants in the external FOA condition were asked to estimate the spatial accuracy of each dart throw depending on the horizontal or vertical approximations of the dart position. Internal FOA conditions asked participants to estimate either their shoulder or elbow angle at the time of dart release. It was found that the external FOA conditions, estimating the landing point of the dart, resulted in better accuracy as compared to estimating shoulder and elbow joint angles. It was also found that an external FOA resulted in better performance compared to an internal FOA in non-vision conditions. Although this finding implied that vision could be disassociated from FOA in dart throwing, it has not yet been explored in other types of movements and skills such as balance tasks. This study explores the effects of vision and FOA on balance, and by testing vision as a variable within this study, results can indicate whether or not vision can be disassociated from FOA in balance related tasks. Wulf, Ho ß, and Prinz (1998, Experiment 1), conducted an experiment in which subjects stood on a ski-simulator and were given either an internal or external FOA. In the external FOA condition, participants were asked to focus on the pressure they exerted on the wheels of the platform on which they were standing, and for internal FOA conditions, participants were asked to focus on their feet that were exerting the force. The external FOA condition had larger movement amplitudes compared with the control condition, no FOA requirements, and the internal FOA condition on a retention test. This study was then replicated with the subjects also having to balance on a stabilometer (Wulf, Ho ß, & Prinz, 1998, Experiment ). As shown in the first experiment, subjects
6 who were given an external FOA, keeping markers on the balance platform horizontal, had greater and more effective balance learning as compared to being given an internal FOA, keeping their feet horizontal on the balance platform. This study randomly assigned thirty-three participants to one of three groups: control, and internal and external FOA. There are limitations to a between subject design. Limitations include: practicality, individual variability, and generalization. Another limitation of this study design is the need to test a large number of participants to generate useful data for analysis. The present study uses a within-subject design, which has two fundamental strengths, power and the reduction in error variance associated with individual differences. Wulf, Shea, and Park (001), also conducted a study which examined the individual differences in the preference for and effectiveness of a type of FOA for motor learning. A balance task was again performed on a stabilometer and participants were asked to determine whether focusing on their feet, an internal FOA, was more effective than focusing on two markers in front of their feet, an external FOA. In Experiment 1, subjects switched FOA from trial to trial on Day 1 and chose their preferred FOA on Day. The purpose of this first experiment was to determine if, given the choice between an internal or external FOA, would participants chose one over the other, and if there would be differences in performance if participants chose a method they believed was best suited for them. After Day 1 of practice, an equal number of participants chose internal and external FOA as most effective for them, and there were no differences between the groups. No differences between the groups were also found on Day. Only on Day 3 did differences occur, suggesting that the difference in effects between internal and external FOA arises after a certain amount of practice. For Experiment, subjects were free to
7 switch FOA any time during the two days. On Day 3, retention tests were performed. It was found that most participants chose to use an external FOA after two days of practice and they were more effective in retention as compared to the participants who preferred using an internal FOA. With more time given to participants to assess the effectiveness of the two attentional foci, more participants chose an external FOA. In a different study conducted by Abdollahipour, Wulf, Psotta, and Nieto (015), it was found that an external FOA was again more beneficial when learning or performing a motor skill than an internal FOA. Gymnasts were assessed on movement quality when performing a maximum vertical jump with a 180-degree turn while airborne, with their hands crossing in front of their chest. In this study, the external FOA condition, focusing on the direction the tape marker attached to their chest was pointing after the turn, resulted in both greater jump height and superior movement, compared to the control and internal FOA conditions, focusing on the direction of their hands after the turn. This research found that form-based skills, depending on external FOA instructions, could enhance the performance of these skills. This study however only tested gymnasts with an average length of gymnastics training of 5.3 years. Since the participants were experienced gymnasts, their expertise could have allowed them to better adapt to performing the task with a FOA instruction, as compared to novices. For experienced gymnasts, the task to perform a vertical maximum jump does not require as much thought. For novices, performing this jump and concentrating on FOA instructions could have resulted in a difference of findings. Unit of Measure Center of pressure (COP) is an index used for postural stability. Center of
8 pressure is the point at which the pressure of the body over the soles of the feet would be if it were concentrated in one spot (Ruhe, Fejer, & Walker, 011). Deviations in the location of COP on the surface of a force platform can assess postural sway. Perturbations in postural stability are translated by an increase in COP magnitude, therefore indicating that a decrease in COP measurements correlates with greater postural stability. Although COP is an index for postural stability, this index is not often used in studies of FOA. For the Wulf studies on FOA and balance, the proficiency of performing a task on the stabilometer was measured using root-mean-square error (RMSE) with the 0-degree position as the criterion (Wulf et al., 1998; Wulf et al., 001; Wulf et al., 001; Wulf, 01). In the study conducted by Tomomitsu et al., the measure used to determine postural stability was sway velocity ( /s). By using COP as a measure to determine balance, this study will fill a gap in the literature. Studies between FOA and balance are still a relatively new area of research. By providing precise measures of balance and stability, this study provides evidence of whether or not the constrained action hypothesis is present when performing balance related tasks. Since visual impairment contributes to postural instability, the magnitude of deviation in COP data collected from the non-vision condition should be greater compared to those in the vision condition. With the internal or external FOA conditions, the external FOA condition should have a lower magnitude deviation of COP compared to the data collected in the internal FOA condition. Overall, the testing condition with both vision and an external FOA should have a lower magnitude deviation in COP compared to the non-vision and internal FOA conditions. Method
9 Subjects. Data was collected from 0 subjects (11 female, 9 male). Subjects must have had less than 30 days of yoga experience, self-reported through a questionnaire given prior to the experiment, to participate in this study. Subjects were recruited from the Introduction to Statistics class in the Department of Integrative Physiology at the University Of Colorado, Boulder. The expected age, gender, and ethnicity reflected the undergraduate student population at the University Of Colorado, Boulder in the college of Arts and Sciences. Subjects needed to be at least 18 years old with no upper age limit to participate. Apparatus and Measurements. BrainBlox is a software developed by the Neuromechanics Laboratory in the Department of Integrative Physiology at the University of Colorado Boulder. The software provides an interface to capture, record, and visualize data provided by the Wii Balance Board. The interface is compatible starting with Windows XP and new versions, and requires a Bluetooth transceiver to connect the software to the Wii Balance Board. Any Bluetooth with Blue Solie software is suitable, including the Windows built-in Bluetooth software-hardware combination. The data obtained from the Wii Balance Board: time in milliseconds elapsed since the program was opened, force from sensor 1 (top left) in kilograms, force from sensor (top right) in kilograms, force from sensor 3 (bottom left) in kilograms, force from sensor 4 (bottom right) in kilograms, COP distance from the center in the x-direction in centimeters, COP distance from the center in the y-direction in centimeters, and total force (the sum of forces from sensors 1-4 in kilograms) was saved as an Excel file. The center of pressure in the x-direction and y-direction were calculated using the equations, COPx =!"(!"!!"!!"!!" )!"!!"!!"!!" (1)
10 COPy =!"!"!!"!!"!!"!"!!"!!"!!" () Procedure. Upon arrival to the Motor Behavior Laboratory, verbal consent was obtained from the subjects. Afterwards, subjects filled out a short questionnaire asking for their height, weight, and previous yoga experience. The subjects participated in a total of six testing conditions with each condition consisting of three trials each (a total of eighteen trials). The subject began the study with the control condition with vision or without vision in a randomized order for each subject. The testing order for the internal FOA condition with vision and without vision, and the external FOA condition with vision and without vision was determined by randomly assigning each subject to one of four testing orders. In the vision control condition, subjects assumed an intermediate level yoga pose, (i.e., the tree pose), with their non-dominant foot on the center of the Wii Balance Board. The non-dominant foot was used throughout the entire study. The subject was directed to stare at a point on the wall at their eye level, and once the position was set, data was recorded for ten seconds. In the non-vision control condition, subjects followed the same procedures as the vision control condition but a blindfold was placed over their eyes. For the internal and external FOA conditions, the subjects performed the same actions as in the control condition but were given either an internal FOA instruction to focus on exerting consistent muscle force on their non-dominant leg, or an external FOA instruction to focus on providing consistent pressure on the Wii Balance Board. The internal and external FOA conditions were further broken down into the internal FOA condition with vision and without vision, and the external FOA condition with vision and without vision. At the end of each ten-second trial in each of the internal and external FOA conditions, the subject was asked to give a rating between one and five on how well
11 they were able to focus either internally or externally while balancing. Subjects were given one minute of rest between each condition. Experimental Design. The study used a within-subject design. Each subject was tested on tree pose in the six conditions: control with vision and without vision, internal FOA with vision and without vision, and external FOA with vision and without vision. A Wii Balance Board was used to collect the data. The four sensors in the Wii Balance Board collected force in kilograms, and COPx and COPy were calculated with the data from the four sensors. The variation in COP indicated how centered or balanced the subject was throughout the data collection period. If subjects were off centered during the data collection period, a larger variation in COP was measured. The standard deviation of the COP distance from the center in the x-direction and y-direction in centimeters was also calculated. The standard deviation of COPx, COPy, and the COP distance from the center in the x-direction and y-direction in centimeters determined for each of the six testing conditions were the main variables used in the data analysis. A two-way ANOVA, 3 (FOA) x (Vision) and (FOA) x (Vision), was used to determine the effects of vision and FOA on balance, and a three-way ANOVA, (FOA) x (Vision) x 5 (Time), was used to determine the effects of vision, FOA, and time on balance. Data Analysis. For the eighteen trials, COPx, COPy, and the COP distance from the center in the x-direction and y-direction in centimeters for the first five of the ten seconds were used for calculations. Subjects were unable to stay on the Wii Balance Board for the entirety of the ten seconds, but all subjects were able to stay on for five seconds. COPx and COPy was calculated using equations 1 and respectively, and the standard deviation for COPx and COPy was then calculated. The standard deviations for
1 the COP distance from the center in the x-direction and y-direction in centimeters was also found. Since each of the six testing conditions had three trials each, the three separate measurements for COPx, COPy, and COP distance from the center in the x- direction and y-direction in centimeters were averaged across the three trials. To determine the effect of time, the first five seconds of data used were further separated into five one-second increments. COPx and COPy was calculated for each one-second increment and then standard deviation of COPx and COPy were calculated. The three separate measurements calculated for COPx and COPy in the three trials, in the six testing conditions were again averaged. Results Effects of Vision and FOA Including the Control Condition. Figures 1 through 4 illustrate the interaction of vision and FOA for the four measurements: COPx, COPy, and COP distance from the center in the x-direction and y-direction in centimeters. The average standard deviation for the listed four measures in the three conditions, control and internal and external FOA, along with the vision and non-vision conditions are shown. There was a significant effect of vision for COPx, COPy, and the COP distance from the center in the x-direction and y-direction in centimeters. COPx, F(1,18) = 130.63, p < 0.0001, η p = 0.879, COPy, F(1,18) = 77.989, p < 0.0001, η p = 0.81, COP distance in the x-direction in centimeters, F(1,18) = 138.643, p < 0.0001, η p = 0.885, and COP distance in the y-direction in centimeters, F(1,18) = 138.897, p < 0.0001, η p = 0.885. There was a significant effect of FOA for COPx and the COP distance from the center in the x-direction in centimeters, COPx, F(,36) = 6.995, p = 0.003, η p = 0.80,
13 COP distance in the x-direction in centimeters, F(,36) = 6.868, p = 0.003, η p = 0.76. There was no significant effect however of FOA conditions for COPy and the COP distance from the center in the y-direction in centimeters, COPy, F(,36) = 1.178, p = 0.30, η p = 0.061, COP distance in the y-direction in centimeters, F(,36) =.697, p = 0.081, η p = 0.130. In addition to the significant effect of FOA for COPx and the COP distance from the center in the x-direction in centimeters, there was a significant interaction between vision and FOA for COPx and the COP distance from the center in the x-direction in centimeters, COPx, F(,36) = 4.874, p = 0.014, η p = 0.1, COP distance in the x- direction in centimeters, F(,36) = 4.807, p = 0.014, η p = 0.11. There was again no significant effect between vision and FOA however for COPy and the COP distance from the center in the y-direction in centimeters. COPy, F(,36) = 0.840, p = 0.440, η p = 0.045, and COP distance in the y-direction in centimeters, F(,36) = 0.734, p = 0.487, η p = 0.039. Although there was a significant effect of FOA and a significant interaction between vision and FOA, these effects could have been due to a practice effect since the control condition always preceded the internal and external FOA conditions. The second section presents the results of vision and FOA when only the internal and external FOA conditions were considered.
14 Average Standard Deviation COPx FOA and Vision: Standard Deviation of COPx.5 1.5 1 0.5 0 Control External FOA Condition Internal FOA With Vision Without Vision Figure 1: Average standard deviation for COPx for with vision and without vision and control, external and internal FOA conditions (n=0). Average Standard Deviation COPy FOA and Vision: Standard Deviation of COPy 1.6 1.4 1. 1 0.8 0.6 0.4 0. 0 Control External FOA Condition Internal FOA With Vision Without Vision Figure : Average standard deviation for COPy for with vision and without vision and control, external and internal FOA conditions (n=0).
15 Average Standard Deviation X- Direction FOA and Vision: Standard Deviation of COP Distance From the Center in the X- Direction in Centimeters 3.5 1.5 1 0.5 0 Control External FOA Condition Internal FOA With Vision Without Vision Figure 3: Average standard deviation for COP distance from the center in the x-direction in centimeters for with vision and without vision and control, external and internal FOA conditions (n=0). Average Standard Deviation Y- Direction FOA and Vision: Standard Deviation of COP Distance From the Center in the Y- Direction in Centimeters 1.5 1 0.5 0 Control External FOA Condition Internal FOA With Vision Without Vision Figure 4: Average standard deviation for COP distance from the center in the y-direction in centimeters for with vision and without vision and control, external and internal FOA conditions (n=0). Effects of Vision and FOA Without the Control Condition. Figures 5 through 8 illustrate the interaction of vision and FOA conditions for the four measurements: COPx, COPy, and COP distance from the center in the x-direction and y-direction in centimeters without the control condition. The average standard deviation for the listed four measures in the two conditions, internal and external FOA, along with the vision and non-vision conditions are shown. The statistically significant effect of vision indicates that the manipulation of vision plays a key role in the variation of COPx, COPy and the
16 COP distance from the center in the x-direction and y-direction in centimeters. COPx, F(1,19) = 91.404, p < 0.0001, η p = 0.88, COPy F(1,19) = 49.713, p < 0.0001, η p = 0.73, COP distance in the x-direction in centimeters, F(1,19) = 101.966, p < 0.0001, η p = 0.843, and COP distance in the y-direction in centimeters, F(1,19) = 116.38, p < 0.0001, η p = 0.860. As such, we reject our null hypothesis of no effect, suggesting that visual feedback is an important sensory system needed for postural stability. The lack of a significant effect of FOA however, indicates that the manipulation of FOA had no significant role on the variation of COPx, COPy, and COP distance from the center in the x-direction and y-direction in centimeters. COPx, F(1,19) = 0.015, p = 0.903, η p = 0.001, COPy, F(1,19) = 0.49, p = 0.49, η p = 0.05, COP distance in the x- direction in centimeters, F(1,19) = 0.005, p = 0.947, η p = 0.000, and COP distance in the y-direction in centimeters, F(1,19) = 0.036, p = 0.85, η p = 0.00. As such, we fail to reject our null hypothesis of no effect, suggesting that the constrained action hypothesis was not supported by these data. Average Standard Deviation COPx FOA and Vision: Standard Deviation of COPx 1.5 1 0.5 0 External FOA Condition Internal FOA With Vision Without Vision Figure 5: Average standard deviation for COPx for with vision and without vision and external and internal FOA conditions (n=0).
17 Average Standard Deviation COPy FOA and Vision: Standard Deviation of COPy 1.4 1. 1 0.8 0.6 0.4 0. 0 External FOA Condition Internal FOA With Vision Without Vision Figure 6: Average standard deviation for COPy for with vision and without vision and external and internal FOA conditions (n=0). Average Standard Deviation X- Direction FOA and Vision: Standard Deviation of COP Distance From the Center in the X- Direction in Centimeters.5 1.5 1 0.5 0 External FOA Condition Internal FOA With Vision Without Vision Figure 7: Average standard deviation for COP distance from the center in the x-direction in centimeters for with vision and without vision and external and internal FOA conditions (n=0).
18 Average Standard Deviation Y- Direction FOA and Vision: Standard Deviation of COP Distance From the Center in the Y- Direction in Centimeters 1.5 1 0.5 0 External FOA Condition Internal FOA With Vision Without Vision Figure 8: Average standard deviation for COP distance from the center in the y-direction in centimeters for with vision and without vision and external and internal FOA conditions (n=0). Effects of Vision, FOA, and Time Without the Control Condition. Figures 9 and 10 illustrate the interaction between vision and time. The average standard deviations of COPx and COPy, with and without vision across time are shown in the figures. The control condition was not considered in this data analysis. The significant effect between vision and time indicates that the manipulation of both vision and time had a significant effect on the variation of COPx, COPx, F(4,76) = 8.944, p < 0.0001, η p = 0.30. There however was not a significant effect on the variation of COPy, COPy, F(4,76) =.454, p < 0.053, η p = 0.114. In figure 9, it is shown that for COPx, scores tended to increase as time passed in the non-vision conditions whereas scores tended to decrease in the vision conditions. In figure 10, it is shown that COPy did not follow the same trends as the nonvision condition for COPx. As time continued to pass, scores decreased for three seconds but increased afterwards in the non-vision conditions. The scores for COPy in the vision conditions however tended to decrease. This was the same trend shown in figure 9 for COPx. The change in variation between the vision and non-vision conditions for COPx and COPy were also not equal. There was a larger change in variation between the vision
19 and non-vision conditions for COPx than there was in COPy. Although there was a significant effect between vision and time for COPx and almost a significant effect between vision and time for COPy, we fail to reject our null hypothesis of no effect. There was however a significant effect of time for both COPx and COPy. This finding indicates that across the five one-second intervals, there was a significant variation of COPx and COPy, F(4,76) = 3.606, p = 0.010, η p = 0.160 and COPy, F(4,76) = 4.33, p = 0.003, η p = 0.186. As such, we reject our null hypothesis of no effect, suggesting that time is an important factor for postural stability. The lack of significant effect of FOA and time however, indicates that the manipulation of FOA had no significant effect on the variation of COPx and COPy. COPx, F(4,76) = 0.88, p = 0.044, η p = 0.154 and COPy, F(4,76) = 0.44, p = 0.91, η p = 0.013. As such, we fail to reject our null hypothesis of no effect, suggesting that the constrained action hypothesis was not supported by this experiment. Vision and Time: Standard Deviation of COPx Average Standard Deviation COPx 1.6 1.4 1. 1 0.8 0.6 0.4 0. 0 1 Second Seconds3 Seconds4 Seconds 5 Seconds Time (s) With Vision Without Vision Figure 9: Average standard deviation for COPx for with vision and without vision conditions separated into five one-second intervals (n=0).
0 Vision and Time: Standard Deviation of COPy Average Standard Deviation COPy 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0. 0.1 0 1 Second Seconds 3 Seconds 4 Seconds 5 Seconds Time (s) With Vision Without Vision Ratings on FOA Instructions. For non-vision conditions, subjects provided lower ratings of attentional focus across the three trials for both the internal and external FOA conditions. The average ratings for the internal and external FOA conditions without vision were.75 and.667 respectively. Higher ratings were noted for the vision conditions across the three trials for both the internal and external FOA conditions. The average ratings for the internal and external FOA conditions with vision were 3.963 and 3.967 respectively. There was a significant effect of vision F(1,19) = 51.831, p < 0.001, η p = 0.73 but there was no significant effect of FOA F(1,19) = 0.053, p = 0.81, η p = 0.003. Discussion Figure 10: Average standard deviation for COPy for with vision and without vision conditions separated into five one-second intervals (n=0). The experiment conducted provided evidence on the importance of vision and its effects on balance. There was a significant effect of vision in the analysis ran with and without the control condition. The variation in all four measures: COPx, COPy, and the
1 COP distance from the center in the x-direction and y-direction in centimeters, was lower in the vision conditions compared to the non-vision conditions. The variation in COPx was also lower in vision conditions compared to the non-vision conditions across time. In the Tomomitsu et al. (015) experiment, they found that the low-vision group compared to the normal-vision group had greater postural sway while balancing on a foam surface. The results of this study were similar to their findings. The visual system is one of three systems which comprise sensory input. Loss of visual feedback clearly contributes to postural instability. This experiment however did not provide enough evidence for the constrained action hypothesis, which states that having an internal FOA could constrain or interfere with autonomic control processes, which normally regulate movement, leading to poor performance. In the Sherwood et al. (014) study, it was found that an external FOA led to better accuracy in dart throwing. It was also shown that there was potentially an interaction between visual information and attentional focus. Participants should have the attentional capacity available when performing a task when instructed with either an internal or external FOA due to automatic control of the movement. As shown in the Sherwood et al., (014) study as well as the studies conducted by Wulf et al. (1998; 001; 01), an internal FOA disrupts normal control processes. For participants in the nonvision conditions then, attentional capacity must be available for the internal or external FOA. This is due to participants being unable to use the attention demanding perceptual vision system for movement planning. Similarly in the Wulf (01) study, there was a significant effect of FOA in external FOA conditions compared to internal FOA conditions. In Experiment 1,
participants stood on a ski-simulator and the participants of the external FOA condition had larger movement amplitudes on a retention test. In Experiment, the effects of FOA on balance were tested. Participants directed to keep markers on the balance platform horizontal, an external FOA, had more effective balance learning as compared to participants asked to keep their feet horizontal on the balance platform, an internal FOA. Unlike the Sherwood et al. (014) and Wulf et al. (1998; 001; 01) studies where there was a significant effect of FOA, this study did not provide enough evidence for the constrained action hypothesis. When assessing the effects of FOA on balance with the control condition, there was only a significant effect in FOA for COPx and the COP distance from the center in the x-direction in centimeters as well as a significant interaction effect between vision and FOA for COPx and the COP distance from the center in the in the x-direction in centimeters. In assessing the effects of FOA on balance as well as the interaction effect of vision and FOA, without the control condition, it was shown that there was no significant effect in all four measures. Future studies can test the effects of vision and balance across a longer time period to better assess whether or not postural stability improves over time. The discrepancy of the significant effect of FOA between the analysis run with the control condition and without the control condition could be due to the disadvantages of a within-subject design. Carryover effects occur when the participation in one condition affects the performance in other conditions due to practice or fatigue. Carryover effects create a confounding extraneous variable, which varies with the independent variable. In this repeated measures study, subjects always started the experiment in the control condition before participating in either the internal or external
3 FOA conditions. Within each of the six testing conditions, subjects were given three trials each, amounting to a total of eighteen trials per subject. Since the participants of this study had multiple trials within each testing condition, they may have become more adept to completing the tasks assigned. Participants could have also adjusted to the challenges in their balance throughout the study. Although there was a significant effect between internal and external FOA when the control condition was present, the lack of significance in FOA without the control condition present does not provide enough evidence to support the constrained action hypothesis. The failure of this present study to replicate the same results as the literature studies could have also been due to a combination of the task performed and the participants. The constrained action hypothesis is dependent upon the internal and external FOA cues the subject is given. Due to needing less attentional capacity when receiving an external FOA, participants in the Sherwood et al. (014) and Wulf et al. (1998; 001; 01) studies were found to have better performance in motor behavior tasks when given an external FOA. Subjects in this particular study were asked to focus on exerting consistent muscle force in their non-dominant leg for internal FOA conditions, whereas for external FOA conditions, subjects were asked to focus on exerting consistent pressure on the Wii Balance Board. The subjects were then asked to give a rating between one and five on how well they were able to focus on the given FOA cue for each trial. When subjects were being tested in the vision condition in both the internal and external FOA conditions, higher ratings on attentional focus were noted. In the non-vision condition in both the internal and external FOA conditions, lower ratings of attentional focus were noted. This trend was expected however because participants
4 would direct more of their attentional capacity to compensate for the loss of their visual feedback compared to directing their attentional capacity to the FOA cues provided. To better assess the effects of FOA on balance, the experiment could manipulate balance using a beginners level yoga pose instead of an intermediate level pose, to allow for more attentional capacity to be directed to the FOA cues. Participants struggled to keep their balance for ten seconds especially during the non-vision conditions. The vision variable could also be removed from future experiments so subjects may direct more attentional capacity to the FOA cues instead. The discrepancy of the significant effect of FOA could also have been due to practice time. As shown in Experiment 1 of the Wulf et al. (001) study, there was no difference in effect between internal and external FOA during the first two days of practice. A significant difference in effect only occurred on Day 3 during the retention test. It was suggested that effects between internal and external FOA arise only after a certain amount of practice. In Experiment, when participants were given two days of practice before choosing a method best suited for them, there was a clear difference between the FOA conditions, with better performance occurring when participants focused externally. Although the subjects in this present study participated in eighteen ten-second trials, a total of 180 seconds, this may have not provided enough practice time for differences in attentional focus to occur. For future studies, participants could start by providing baseline levels, practice over a period of two days, and then perform a retention test on day 3. With more practice, a difference in effect of FOA could be potentially noticeable and the changes in progress could also be tracked as the days pass.
5 Testing the predictions of the constrained action hypothesis and the effects of internal and external FOA on balance is a new area of research. Although this study failed to provide enough statistically significant evidence for the constrained action hypothesis, further studies in this area are required before conclusions may be made.
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7 Wulf, G., Shea, C., & Park, J. (001). Attention and Motor Performance: Preferences for and Advantages of an External Focus. Research Quarterly for Exercise and Sport, 7(4), 335-344. doi:10.1080/0701367.001.10608970 Wulf, G. (01, September 4). Attentional focus and motor learning: a review of 15 years. International Review of Sport and Exercise Psychology. Retrieved December 09, 016, from http://www.tandfonline.com/doi/figure/10.1080/1750984x.01.7378?scroll=t op&needaccess=true