The Impact of Viewing Distance and Proprioceptive Manipulations on a Virtual Reality Based Balance Test.

Our ability to maintain our balance plays a pivotal role in day-to-day activities. This ability is believed to be the result of interactions between several sensory modalities including vision and proprioception. Past research has revealed that different aspects of vision including relative visual motion (i.e., sensed motion of the visual field due to head motion), which can be manipulated by changing the viewing distance between the individual and the predominant visual cues, have an impact on balance. However, only a small number of studies have examined this in the context of virtual reality, and none examined the impact of proprioceptive manipulations for viewing distances greater than 3.5 m. To address this, we conducted an experiment in which 25 healthy adults viewed a dartboard in a virtual gymnasium while standing in narrow stance on firm and compliant surfaces. The dartboard distance varied with three different conditions of 1.5 m, 6 m, and 24 m, including a blacked-out condition. Our results indicate that decreases in relative visual motion, due to an increased viewing distance, yield decreased postural stability - but only with simultaneous proprioceptive disruptions.

Joint Contributions of Auditory, Proprioceptive and Visual Cues on Human Balance.

One's ability to maintain their center of mass within their base of support (i.e., balance) is believed to be the result of multisensory integration. Much of the research in this literature has focused on integration of visual, vestibular, and proprioceptive cues. However, several recent studies have found evidence that auditory cues can impact balance control metrics. In the present study, we sought to better characterize the impact of auditory cues on narrow stance balance task performance with different combinations of visual stimuli (virtual and real world) and support surfaces (firm and compliant). In line with past results, we found that reducing the reliability of proprioceptive cues and visual cues yielded consistent increases in center-of-pressure (CoP) sway metrics, indicating more imbalance. Masking ambient auditory cues with broadband noise led to less consistent findings; however, when effects were observed they were substantially smaller for auditory cues than for proprioceptive and visual cues - and in the opposite direction (i.e., masking ambient auditory cues with broadband noise reduced sway in some situations). Additionally, trials that used virtual and real-world visual stimuli did not differ unless participants were standing on a surface that disrupted proprioceptive cues; disruption of proprioception led to increased CoP sway metrics in the virtual visual condition. This is the first manuscript to report the effect size of different perturbations in this context, and the first to study the impact of acoustically complex environments on balance in comparison to visual and proprioceptive contributions. Future research is needed to better characterize the impact of different acoustic environments on balance.

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.

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.

The contribution of interoceptive signals to spatial orientation: A mini-review.

Humans' sensory systems work synergistically to allow us to determine where our head and body are relative to the environment. To date, most research on this topic has focused on the visual and vestibular systems. There has been much less research on the contributions of interoceptive signals to spatial orientation, so the overall picture of how spatial orientation works is incomplete. This gap in the literature is especially problematic for aviation and spaceflight, where spatial disorientation is more likely to occur due to less common gravity conditions (i.e. microgravity and hypergravity) and can lead to fatal errors. In the present manuscript we review and summarize the current literature on this topic. Based upon the available evidence it would seem that interoceptive signals, particularly patterns of fluid/organ displacement, may play a role in sensing where our body is relative to the environment. More research utilizing experimentally induced perturbations to interoceptive receptors is needed before quantitative conclusions regarding the role of these interoceptive receptors can be drawn.

Comparing the impact of the method of adjustment and forced-choice methodologies on subjective visual vertical bias and variability.

BACKGROUND: Previous research suggested that the method of adjustment and forced choice variants of the subjective visual vertical (SVV) produce comparable estimates of both bias and variability. However, variants of the SVV that utilize a method of adjustment procedure are known to be heavily influenced by task parameters, including the stimulus rotation speed, which was not accounted for in previous SVV research comparing the method of adjustment to forced-choice. OBJECTIVE: The aim of the present study was to determine if (1) the SVV with a forced-choice procedure produces both bias and variability estimates that are comparable to those obtained using a method of adjustment procedure, (2) to see if rotation speed impacts the comparability of estimates and (3) quantify correlations between the estimates produced by different procedures. METHODS: Participants completed a variant of the SVV which utilized a forced-choice procedure as well as two variants of the SVV using a method of adjustment procedure with two different rotation speeds (6°/s and 12°/s). RESULTS: We found that the bias estimates were similar across all three conditions tested and that the variability estimates were greater in the SVV variants that utilized a method of adjustment procedure. This difference was more pronounced when the rotation speed was slower (6°/s). CONCLUSIONS: The results of this study suggest that forced-choice and method of adjustment methodologies yield similar bias estimates and different variability estimates. Given these results, we recommend utilizing forced-choice procedures unless (a) forced-choice is not feasible or (b) response variability is unimportant. We also recommend that clinicians consider the SVV methods when interpreting a patient's test results, especially for variability metrics.

Preliminary Evaluation of the Moving Rubber Foot Illusion in a Sample of Female University Students.

The Rubber Foot Illusion (RFI) is an illusion in which one is made to feel that a model foot is their own through synchronous visuo-tactile stimulation. Previous research suggests that the conditions the RFI can be elicited under are similar to those of the Rubber Hand Illusion (RHI). However, it was unknown if the RFI could be elicited by synchronous movement of a participant's foot and a model foot. To examine this, we developed the Moving Rubber Foot Illusion (mRFI) and compared participants' experience of it to the RFI. The results of this study suggests that the RFI can be elicited through synchronous movement, and results in more proprioceptive drift than a static variant of the RFI. More work is needed to better understand the mechanisms underlying the mRFI.

The Impact of Experimentally Induced Limb Ischemia on the Rubber Hand Illusion.

The rubber hand illusion (RHI) is a perceptual illusion in which one experiences an object as part of their body when synchronous visuo-tactile stimulation is applied to one's hand and the object. There are a variety of factors that can impact the occurrence of the RHI. In the present study, we demonstrate that experimentally induced peripheral ischemia can impact the RHI, namely it can result in larger alterations to the perceived position of one's hand. This study suggests that alterations to the cardiovascular system may be a source of individual differences in the RHI literature. Future studies with samples of individuals with cardiovascular pathology are recommended.

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.

Geriatric Complex Figure Test: A test for the assessment of planning, visual spatial ability, and memory in older adults.

The present study describes the development of a simplified complex figure for older adults. This new figure is based on theoretical organizational strategy models developed for the Rey Complex Figure Test and combines several new technologies for the enhancement of the data capture. The study shows that the accuracy and memory scores for the new measure correlate significantly with Trail Making Test, Five Point Test, and RBANS Complex Figure scores. The new figure's strategy scores correlate with predominantly nonverbal and to a lesser extent with verbal executive functions, supporting the construct validity of these scores and illustrating that computer-based data recording methodologies can reliably discern the multiple cognitive operations that impact performance on this and similar graphomotor measures.

Base-rate data and norms for the Rey Auditory Verbal Learning Embedded Performance Validity Indicator.

The present study examines the Rey Auditory Verbal Learning Test (RAVLT) Embedded Performance Validity Indicator (EPVI) for detecting performance validity. This retrospective study analyzes the performance of four groups of 879 participants comprised of 464 clinically referred patients with suspected dementia, 91 forensic patients identified as not exhibiting adequate effort on other measures of response bias, 25 patients with well documented TBI, and a random sample of 198 adults collected in the Gulf State of Oman. The EPVI was also put to the test using normative data collected from the literature. Using sensitivity and specificity analyses, the results indicate moderate to high sensitivity yet low specificity. In conclusion, the study shows that the EPVI is a reasonably good indicator for inadequate effort on the RAVLT but those who fail this measure might not necessarily be exhibiting adequate effort. The limitations and benefits of utilizing the EPVI in clinical practice are discussed.