Using Nonlinear Kinematic Parameters as a Means of Predicting Motion Sickness in Real-Time in Virtual Environments.

OBJECTIVE: This article presents two studies (one simulation and one pilot) that assess a custom computer algorithm designed to predict motion sickness in real-time. BACKGROUND: Virtual reality has a wide range of applications; however, many users experience visually induced motion sickness. Previous research has demonstrated that changes in kinematic (behavioral) parameters are predictive of motion sickness. However, there has not been research demonstrating that these measures can be utilized in real-time applications. METHOD: Two studies were performed to assess an algorithm designed to predict motion sickness in real-time. Study 1 was a simulation study that used data from Smart et al. (2014). Study 2 employed the algorithm on 28 new participants' motion while exposed to virtual motion. RESULTS: Study 1 revealed that the algorithm was able to classify motion sick participants with 100% accuracy. Study 2 revealed that the algorithm could predict if a participant would become motion sick with 57% accuracy. CONCLUSION: The results of the present study suggest that the motion sickness prediction algorithm can predict if an individual will experience motion sickness but needs further refinement to improve performance. APPLICATION: The algorithm could be used for a wide array of VR devices to predict likelihood of motion sickness with enough time to intervene.

Muscle activity prior to experiencing the rubber hand illusion is associated with alterations in perceived hand location.

The rubber hand illusion (RHI) is a perceptual illusion in which one is made to feel that a hand-shaped object is part of their body. This illusion is believed to be the result of the integration of afferent information. However, there has been an increasing amount of evidence that suggests efferent information plays a role in this illusion as well. Previous research has found that individuals who are afflicted by pathological lack of movement experience the RHI more vividly than control participants. Whereas individuals who move their hands more than the general population (i.e. professional pianists) experience the RHI less vividly than control participants. Based upon the available evidence it would seem that muscle activity prior to experiencing the RHI should be associated with how vividly one experiences different indices of the illusion. In the present study we tested this possibility by having participants perform a maximum voluntary muscle contraction task prior to experiencing three variants of the RHI (moving active, moving passive and classic). It was found that electromyographic features known to be indicative of muscle fatigue exhibited a positive association with proprioceptive drift when stimulation was synchronous or visual movement only (with the exception of the passive moving RHI synchronous condition). More work is needed to better characterize the muscular processes associated with experiencing the RHI.

The anger superiority effect revisited: a visual crowding task.

Visual search studies have shown that threatening facial expressions are more efficiently detected among a crowd of distractor faces than nonthreatening expressions, known as the anger superiority effect (ASE). However, the opposite finding has also been documented. The present study investigated the ASE in the visual periphery with a visual crowding task. In the study, the target face either appeared alone (uncrowded condition) or was crowded by four neutral or emotional faces (crowded condition). Participants were instructed to determine whether the target face was happy or angry. Experiment 1 showed an ASE when crowded by neutral faces. Intriguingly, this superiority vanished when the target face was crowded by emotional faces that had a different expression from the target as well as when the target face was presented alone. Experiment 2 replicated this result in an independent sample of East Asians (vs. Caucasians in Experiment 1) and thus demonstrated the robustness and cross-cultural consistency of our findings. Together, these results suggest that the ASE in the visual periphery is contingent on task demands induced by visual crowding.

Perceptual Validation of Nonlinear Postural Predictors of Visually Induced Motion Sickness.

Virtual reality (VR) technology has become increasingly prevalent in our society and has been used for a myriad of applications ranging from psychotherapy to training members of the military. However, one issue that arises from the use of VR is motion sickness, thus making predictors and indicators of motion sickness desirable. To date, a number of indicators of motion sickness have been derived based on nonlinear characteristics of human motion recorded using motion capture systems. While it is known that nonlinear measures can be used to predict motion sickness, it is not known whether people are perceptually sensitive to these particular nonlinear parameters. The aims of this study included establishing whether individuals consistently sort phase plots of sick and well individuals' postural motion without being explicitly told to do so; determining what nonlinear movement parameters could be used to represent these judgments; and assessing the stability of nonlinear measures found to be successful at predicting motion sickness by Smart et al. (2014). Through two methods of analysis (perceptual and quantitative), this research demonstrated that participants can indeed sort the graphic depictions of sick and well participants' postural motion and seem to be perceptually sensitive to nonlinear parameters (normalized path length, path length, elliptical area) that are known to be predictive of motion sickness.

Responding to Other People's Posture: Visually Induced Motion Sickness From Naturally Generated Optic Flow.

Understanding the relationship between our actions and the perceptual information that is used to support them is becoming increasingly necessary as we utilize more digital and virtual technologies in our lives. Smart et al. (2014) found that altering the relationship between perception and action can have adverse effects, particularly if the perceptual information cannot be used to guide behavior. They also found that motion characteristics varied between people who remained well and those that became motion sick. The purpose of this study was to determine the influence of naturally produced virtual motion on postural regulation and examine how people respond to different types of optical flow (produced by other people). Participants were either exposed to optic flow produced by the postural motion of a person who did not become motion sick, or a person who did exhibit motion sickness from Smart et al. (2014). It was discovered that participants exhibited both stronger coupling and more incidents of motion sickness in response to optic flow generated by a non-sick participant. This suggests that participants recognized the potentially usable nature of the well-produced optic flow- but the open loop nature of the stimuli made this perception disruptive rather than facilitative.

The extraction of natural scene gist in visual crowding.

The gist of natural scenes can be extracted very rapidly and even without focal attention. However, it is unclear whether and to what extent the gist of natural scenes can break through the bottleneck of crowding, a phenomenon in which object recognition will be immensely impaired. In the first two experiments, a target scene, either presented alone or surrounded by four flankers, was categorized at basic (Experiment 1) or global levels (Experiment 2). It was showed that the elimination of high-level semantic information of flankers greatly alleviated the crowding effect, demonstrating that high-level information played an important role in crowding of scene gist. More importantly, participants were able to categorize the scenes in crowding at rather high accuracies, suggesting that the extraction of scene gist might be a prioritized process. To test this hypothesis, in Experiment 3 we compared the crowding effect of three types of stimuli, namely, scenes, facial expressions and letter "E"s. The results showed that scenes could be better categorized than the other two types of stimuli in the crowding condition. This scene gist advantage thus supported our hypothesis. Together, the present studies suggest that scene gist is highly recognizable in crowding, probably due to its prioritization in visual processing.

Effect of the Alexander Technique on Muscle Activation, Movement Kinematics, and Performance Quality in Collegiate Violinists and Violists: A Pilot Feasibility Study.

Musicians are trained to attend to aural and visual senses, to the detriment of kinesthetic awareness, which often results in unnecessary muscle tension and narrowed attentional focus. The Alexander technique (AT) addresses these concerns by approaching action using a process of whole-body consciousness. Incorporation of AT concepts into skill practice may reduce static tension in playing and result in both prevention of injury and improved quality of performance, but objective evidence of these effects is lacking. This pilot feasibility study was designed to determine if muscle activation, movement kinematics, musical performance, and qualitative self-assessment over the course of a 10- week AT intervention are viable means to assess the efficacy of AT in violinists/ violists. Two groups of collegiate violinists and violists participated: Group A (n=4) participated in weekly 1-hour group AT lessons and kept a personal journal of their progress. Group B (n=3) received no AT lessons. Pre- and post tests included muscle activation recorded using electromyography (EMG) and movement kinematics recorded via motion tracking as musicians played a scale and a Kreutzer étude. Performance was also video-recorded and evaluated by an expert for quality and kinesthetic awareness. The results suggest that the measures and intervention employed could, with some adaptation, be a viable means of determining the potential benefits of AT training.

Structural changes in postural sway lend insight into effects of balance training, vision, and support surface on postural control in a healthy population.

Postural sway was assessed [via center of pressure (COP) 95% elliptical area (EA), path length (PL), normalized path length (PL(n)) and sample entropy (SEn)] in four conditions of bipedal upright stance [compliant (Foam) vs. non-compliant (Hard) with eyes-open (EO) vs. eyes-closed (EC)] prior to, and immediately following, a six-week balance training intervention in a group of healthy adults (N = 26). The intervention was comprised of nine exercises progressed in difficulty based on the subjective assessments of individual competency. Results showed that EA and PL were increased, while PL(n) and SEn were decreased, in EC and Foam stance conditions (collapsed across effects of balance training). Interpretations were that restricted vision and a compliant surface represented constraints to postural control that caused increases in the amount (PL) and area (EA) of sway, but decreases in its coordinative twisting/turning (PL(n)) and temporal complexity (SEn). It was argued that these changes might represent compensatory adaptations in effort to maintain postural control given the demands of the imposed constraints. Balance training caused no change to EA, but did result in decreased PL, PL(n), and SEn for stance conditions performed on the Foam (either EO or EC). These changes were interpreted to reflect improved postural control, potentially through the learned adoption of a more deterministic postural control strategy that is uniquely defined by the constraints imposed on upright stance by the compliant surface.

Not just standing there: the use of postural coordination to aid visual tasks.

Postural control is an integral part of all physical behavior. Recent research has indicated that postural control functions in a manner that facilitates other higher order (suprapostural) tasks. These studies, while showing that postural sway is modulated in a task specific manner, have not examined the form of postural coordination that allows for the achievement of these higher behavioral goals. The current study examined the relation between visual task constraints (viewing distance), environmental constraints (changes in the surface of support), and the postural coordination employed to complete the task. Thirty-one participants were asked to perform a reading task while standing on various surfaces. Postural motion was recorded from the head, cervico-thoracic spine, sacrum (hip), and ankle. It was found that body segment coordination changed as a function of surface characteristics and task constraints. Additionally, the overall pattern of postural sway (head motion) replicated that which was found by Stoffregen et al. [J. Exp. Psychol. Human Percep. Perform. 25 (6) (1999) 1641]. These findings suggest that postural adaptation involves more than basic reduction or increase of motion; it involves the functional coordination of body segments to achieve a particular goal. The data further suggest that there is a need to examine postural control in the absence of external perturbations.

Visually induced motion sickness predicted by postural instability.

We investigated whether postural instability can predict motion sickness and studied relations among instability, motion sickness, and vection. Nine men and 4 women (mean age = 19.85 years) were exposed, while standing, to an optical simulation of body sway. Head motion was recorded using a magnetic tracking system. Postural instabilities were observed prior to the onset of motion sickness. Vection was reported by most participants, including all who became ill. A discriminant analysis revealed that parameters of postural motion accurately predicted motion sickness. The results confirm that postural instability precedes motion sickness and suggest that measures of postural motion may serve as reliable predictors of motion sickness. Potential applications of this research include the development of on-line diagnostic tools that will allow for the prevention of motion sickness in operational and training settings.