Browsing by Author "Li, Ruixuan"

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    APAL "Sensitivity to changes in dynamic affordances for walking on land and at sea" Data Sets
    (2019-09-17) Walter, Hannah; Li, Ruixuan; Peterson, Nicolette; Stoffregen, Thomas; Wagman, Jeffrey; walte666@umn.edu; Walter, Hannah; University of Minnesota Affordance Perception-Action Lab
    We investigated the perception of affordances for walking along a narrow path. We asked whether participants could perceive changes in affordances brought about by manipulation of properties of the body, or of the environment, without direct practice of the to-be-perceived affordance, and without external feedback about the accuracy of perception. In Experiment 1, participants made a series of 8 judgments of how far they could walk along a narrow path either, 1) without added weight, 2) while wearing a weighted vest, or 3) while wearing weights on their ankles. Before walking, mean judgments were lower when wearing weights than in the no-weight condition. In addition, in both weight conditions judgments changed across the series of 8 judgments, in the direction of greater accuracy. Control of the body in walking also can be influenced by motion of the ground surface, as commonly happens in vehicles. In Experiment 2, on a ship at sea, we evaluated the effects of walking with or without weight added to the body at the ankles. We again asked participants (experienced maritime crewmembers) to judge how far they could walk along a narrow path, with versus without ankle weights. As in Experiment 1, judgments made before walking mirrored the observed differences in walking performance. In addition, we again found evidence that judgment improved (without walking practice, or feedback) over the series of judgments. We conclude that participants were sensitive to (and spontaneously learned about) how affordances for walking were influenced by changes in the dynamics of body and the environment.
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    APAL 2019: Postural Data, Game Performance, and Subjective Responses of Cybersickness in Virtual Reality Head-Mounted Displays
    (2019-12-16) Curry, Christopher; Li, Ruixuan; Peterson, Nicolette; Stoffregen, Thomas; curry134@umn.edu; Curry, Christopher; University of Minnesota Affordance Perception-Action Laboratory
    Cybersickness is a subset of motion sickness and is experienced by users after they are immersed in a computer-generated virtual environment. Prior motion sickness research has shown that individuals that become motion sick display distinct kinematic patterns that differ from those that do not become sick. For this reason, kinematic data were collected before virtual reality (VR) exposure, and during exposure. Following exposure, some participants reported motion sickness. Subjects that reported motion sickness were classified into the sickness group, while those that did not report any symptoms were classified into the well group. This data set includes the collected kinematic data, subjective responses on the simulator sickness questionnaire, and game performance data. Kinematic data was collected before exposure via a force plate, and during exposure using a Polhemus Electromagnetic Tracker. The data are shared to follow guidelines as required by the journals we are submitting to.
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    APAL Coupling Study 2019
    (2019-03-04) Walter, Hannah; Li, Ruixuan; Munafo, Justin; Curry, Christopher; Peterson, Nicolette; Stoffregen, Thomas; walte666@umn.edu; Walter, Hannah; University of Minnesota Affordance Perception-Action Lab
    Motion sickness is preceded by differences in the quantitative kinematics of body sway between individuals who (later) become sick and those who do not. In existing research, this effect has been demonstrated only in measures of body sway, relative to the earth. However, body sway can become coupled with imposed oscillatory motion of the illuminated environment, and the nature of this coupling may differ between individuals who become sick and those who do not. We asked whether body sway would become coupled to complex oscillations of the illuminated environment, and whether individual differences in such coupling might be precursors of motion sickness. Standing participants were exposed to complex oscillation of the illuminated environment. We examined the strength of coupling as a function of time during exposure. Following exposure, some participants reported motion sickness. The nature and temporal evolution of coupling differed between participants who later reported motion sickness and those who did not. Our results show that people can couple the complex dynamics of body sway with complex imposed motion, and that differences in the nature of this coupling are related to the risk of motion sickness.
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    Postural Time-To-Contact, Real-Time Visual Feedback Of Postural Activity, And Motion Sickness
    (2018-12) Li, Ruixuan
    The postural instability theory of motion sickness predicts that the subjective symptoms of motion sickness will be preceded by unstable control of posture. In previous research, it has been confirmed with measures of the spatial magnitude and temporal dynamic of postural activity. In the first chapter, I introduced a new measure (postural time-to-contact (VTC)) which is related to the risk of falling. Standing participants were exposed to visual oscillation stimuli. I measured the kinematics of the body’s center of pressure. The results show that postural time-to-contact differed between the Well and Sick groups before and during the exposure to the visual motion stimuli. The multifractality of sway differed between the Well and Sick groups during the room exposure. In Chapter 2, I examined the real-time feedback of body’s center of pressure with the same protocol as Chapter 1. The chi-square test between the sickness and the display format (blank screen and real-time feedback) suggests that the real-time feedback increases the risk of motion sickness. Body sway also differed before any participants experienced subjective symptoms of motion sickness. In Chapter 3, I measured the correlation between postural measures and motion sickness symptoms severity (TSS). The change of TSS has a higher Pearson correlation to the VTC in the blank screen condition than the motion sickness susceptibility total score (MSSQt). Principal component analysis (PCA) and linear discriminant analysis (LDA) were implemented to construct motion sickness susceptibility score of postural activity (MSSPA). The LDA score in the blank screen condition outperformed the PCA score in both conditions, the LDA score in the feedback condition and the MSSQt regarding its relation to motion sickness symptom severity score. Since this experiment was completed in a moving room setting (open-loop), further examination of MSSPA in the tablet computer, simulator and virtual reality (closed-loop).
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    RV Atlantis 2019 Ship Data
    (2019-01-25) Walter, Hannah; Li, Ruixuan; Stoffregen, Thomas; Wagman, Jeffrey; walte666@umn.edu; Walter, Hannah, J.
    Ocean waves cause oscillatory motion of ships. Oscillatory ship motion typically is greater in roll (i.e., the ship rolling from side to side) than in pitch (i.e., tipping from front to back). Affordances for walking on a ship at sea should be differentially influenced by ship motion in roll and pitch. When roll exceeds pitch, the maximum walkable distance within a defined path should be greater when walking along the ship’s short, or athwart axis than when walking along its long, or fore-aft axis. When pitch exceeds roll, this relation should be reversed. We asked whether such changes in ship motion would be reflected in judgments of direction-specific affordances for walking. Participants (experienced maritime crewmembers) judged how far they could walk along a narrow path on the ship deck. On different days, sailing conditions were such that the relative magnitude of pitch and roll was reversed. Judgments of direction-specific affordances for walking mirrored these changes in ship motion. The accuracy of judgments was consistent across directions, and across changes in ship motion. We conclude that experienced maritime crewmembers were sensitive to dynamic variations in affordances for walking that were, themselves, a function of dynamic properties of the animal-environment system.