Perception Of Visual Speed While Moving

During self-motion, the world normally appears stationary. In part, this may be due to reductions in visual motion signals during self-motion. In 8 experiments, the authors used magnitude estimation to characterize changes in visual speed perception as a result of biomechanical self-motion alone (treadmill walking), physical translation alone (passive transport), and both biomechanical self-motion and physical translation together (walking). Their results show that each factor alone produces subtractive reductions in visual speed but that subtraction is greatest with both factors together, approximating the sum of the 2 separately. The similarity of results for biomechanical and passive self-motion support H. B. Barlow\u27s (1990) inhibition theory of sensory correlation as a mechanism for implementing H. Wallach\u27s (1987) compensation for self-motion. (PsycINFO Database Record (c) 2013 APA, all rights reserved)(journal abstract

Influence of Auditory Cues on the visually-induced Self-Motion Illusion (Circular Vection) in Virtual Reality

This study investigated whether the visually induced selfmotion illusion (“circular vection”) can be enhanced by adding a matching auditory cue (the sound of a fountain that is also visible in the visual stimulus). Twenty observers viewed rotating photorealistic pictures of a market place projected onto a curved projection screen (FOV: 54°x45°). Three conditions were randomized in a repeated measures within-subject design: No sound, mono sound, and spatialized sound using a generic head-related transfer function (HRTF). Adding mono sound increased convincingness ratings marginally, but did not affect any of the other measures of vection or presence. Spatializing the fountain sound, however, improved vection (convincingness and vection buildup time) and presence ratings significantly. Note that facilitation was found even though the visual stimulus was of high quality and realism, and known to be a powerful vection-inducing stimulus. Thus, HRTF-based auralization using headphones can be employed to improve visual VR simulations both in terms of self-motion perception and overall presence

Sensory Augmentation for Balance Rehabilitation Using Skin Stretch Feedback

This dissertation focuses on the development and evaluation of portable sensory augmentation systems that render skin-stretch feedback of posture for standing balance training and for postural control improvement. Falling is one of the main causes of fatal injuries among all members of the population. The high incidence of fall-related injuries also leads to high medical expenses, which cost approximately $34 billion annually in the United States. People with neurological diseases, e.g., stroke, multiple sclerosis, spinal cord injuries, and the elderly are more prone to falling when compared to healthy individuals. Falls among these populations can also lead to hip fracture, or even death. Thus, several balance and gait rehabilitation approaches have been developed to reduce the risk of falling. Traditionally, a balance-retraining program includes a series of exercises for trainees to strengthen their sensorimotor and musculoskeletal systems. Recent advances in technology have incorporated biofeedback such as visual, auditory, or haptic feedback to provide the users with extra cues about their postural sway. Studies have also demonstrated the positive effects of biofeedback on balance control. However, current applications of biofeedback for interventions in people with impaired balance are still lacking some important characteristics such as portability (in-home care), small-size, and long-term viability. Inspired by the concept of light touch, a light, small, and wearable sensory augmentation system that detects body sway and supplements skin stretch on one’s fingertip pad was first developed. The addition of a shear tactile display could significantly enhance the sensation to body movement. Preliminary results have shown that the application of passive skin stretch feedback at the fingertip enhanced standing balance of healthy young adults. Based on these findings, two research directions were initiated to investigate i) which dynamical information of postural sway could be more effectively conveyed by skin stretch feedback, and ii) how can such feedback device be easily used in the clinical setting or on a daily basis. The major sections of this research are focused on understanding how the skin stretch feedback affects the standing balance and on quantifying the ability of humans to interpret the cutaneous feedback as the cues of their physiological states. Experimental results from both static and dynamic balancing tasks revealed that healthy subjects were able to respond to the cues and subsequently correct their posture. However, it was observed that the postural sway did not generally improve in healthy subjects due to skin stretch feedback. A possible reason was that healthy subjects already had good enough quality sensory information such that the additional artificial biofeedback may have interfered with other sensory cues. Experiments incorporating simulated sensory deficits were further conducted and it was found that subjects with perturbed sensory systems (e.g., unstable surface) showed improved balance due to skin stretch feedback when compared to the neutral standing conditions. Positive impacts on balance performance have also been demonstrated among multiple sclerosis patients when they receive skin stretch feedback from a sensory augmentation walker. The findings in this research indicated that the skin stretch feedback rendered by the developed devices affected the human balance and can potentially compensate underlying neurological or musculoskeletal disorders, therefore enhancing quiet standing postural control

Virtual equivalence : matching visual scene and treadmill walking speeds in virtual reality

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2004.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections."September 2004."Includes bibliographical references (p. 73-75).(cont.) The last experiment showed that individual subjects PER values changed over time intervals as short as ten minutes, and revealed the importance of the subject's prior experience in PER experiments. This suggests that limitations of working memory may effect the repeatability of the PER measure. The definition and measure of PER for each subject may also provide a means for quantifying the magnitude of a clinical condition known as oscillopsia, where we perceive the world as non-stationary, such as moving independently of our head motions. These findings are important for a perceptually sensitive environment, such as virtual reality. Designers of virtual environments that utilize self-motion perception should consider calibrating PERs within a session for each individual user and be aware that that the subject's calibration may change over time.If we walk on a treadmill and are looking in the direction of motion of a moving virtual environment, the perceptions from our various senses are harmonious only if the visual scene is moving in a narrow range of speeds that are, typically, greater than our walking speed. This observation has been reported when we project a virtual environment through a display with a restricted field-of-view, such as a head-mounted display (HMD). When the subject feels that the scene-motion is natural for their walking speed, the ratio of the speed of his visual surround to that of the treadmill walking speed is defined as his perceptual equivalence ratio (PER) in that setting. Four experiments explored a set of conditions under which the PER measured on a treadmill is constant. The experiments, motivated by several hypotheses, investigated the relationship between PER and display type (HMD vs. either desktop monitor or on-screen projection), sense of presence in the virtual environment, and the magnitude of illusory self-motion (vection). We also investigated differences among subjects, and the stability of PER over time due to the limitations of working memory. Most experiments considered more than one hypothesis. The first two experiments found that PER was affected by the type of display used, but found no correlation of PER with the sense of presence reported by the subject. A third experiment showed that PER was nearly the same whether we manipulated visual or treadmill speed (and asked the subject to match the other.) While PER values were often constant versus treadmill speed for any individual subject, they were very different from subject to subject. PER appears to be relatively stable over a short test session, but may be highly variable over extended periods of time.by Kevin R. Duda.S.M