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At least 505 records · Page 28Linked to original sources

PubMed2006

Field of view and base of support width influence postural responses to visual stimuli during quiet stance.

We explored the destabilizing effect of visual field motion as the base of support (BOS) and the field of view (FOV) were narrowed. Visual field motion was achieved using an immersive virtual environment (scene) that moved realistically with head motion (natural motion) and translated sinusoidally at 0.1Hz in the fore-aft direction (augmented motion). Natural motion was presented in stereo while augmented motion was presented in both stereo and non-stereo. Subjects viewed scene motion under wide (90 degrees and 55 degrees in the horizontal and vertical directions) and narrow (25 degrees in both directions) FOV conditions while standing flatfooted (100% BOS) and on two blocks (45% and 35% BOS). Head and whole body center of mass (COM) and ankle angle root mean square (RMS) were determined as were head, whole body, and shank COM FFTs. During natural motion, the primary effect emerged in the head RMS which was significantly smaller with a 35% BOS and the wide FOV compared to the narrow FOV. However, the primary effect of augmented motion emerged in the power analysis of head and whole body COM which significantly increased with the wide FOV for a 35% BOS compared to 100% BOS. Statistical analysis indicated an effect of BOS on depth perception for head and whole body RMS; however, post hoc comparisons revealed no significant differences between stereo and non-stereo augmented motion. We conclude that reducing the BOS increased reliance on peripheral visual information to stabilize the head in space even when the augmented visual motion promoted postural instability.

Adult↗

PubMed2006

Prospective strategies underlie the control of interceptive actions.

The purpose of this study was to test whether a constant bearing angle strategy could account for the displacement regulations produced by a moving observer when attempting to intercept a ball following a curvilinear path. The participants were asked to walk through a virtual environment and to change, if (deemed) necessary, their walking speed so as to intercept a moving ball that followed either a rectilinear or a curvilinear path. The results showed that ball path curvature did indeed influence the participants' displacement kinematics in a way that was predicted by adherence to a constant bearing angle strategy mode of control. Velocity modifications were found to be proportional to the magnitude of target curvature with opposing curvatures giving rise to mirror displacement velocity changes. The role of prospective strategies in the control of interceptive action is discussed.

Adult↗

PubMed2005

Real-time synthesis of bleeding for virtual hysteroscopy.

In this paper we present a method for simulating bleeding in a virtual reality hysteroscopic simulator for surgical training. The simulated bleeding is required to be visually appealing while at the same time instantaneously responsive to any feedback that the surgeon may be conducing to the virtual environment. In order to meet these real-time requirements, we have based the simulation on graphical fluid solvers. These solvers primarily work best over a 2D domain. For correct visualization in the hysteroscopic simulator, it is, however, necessary to perform the simulation fully in 3D. Therefore in this paper we also present the design modifications for 3D graphical fluid solving and show how to use parallelization to maintain real-time behavior. We also discuss how the incorporation of massless particles into the simulation can improve the visual quality of the results by limiting numerical dissipation effects.

Blood Flow Velocity↗

PubMed2005

Age differences in the neural systems supporting human allocentric spatial navigation.

Age-related declines in spatial navigation are well-known in human and non-human species. Studies in non-human species suggest that alteration in hippocampal and other neural circuitry may underlie behavioral deficits associated with aging but little is known about the neural mechanisms of human age-related decline in spatial navigation. The purpose of the present study was to examine age differences in functional brain activation during virtual environment navigation. Voxel-based analysis of activation patterns in young subjects identified activation in the hippocampus and parahippocampal gyrus, retrosplenial cortex, right and left lateral parietal cortex, medial parietal lobe and cerebellum. In comparison to younger subjects, elderly participants showed reduced activation in the hippocampus and parahippocampal gyrus, medial parietal lobe and retrosplenial cortex. Relative to younger participants elderly subjects showed increased activation in anterior cingulate gyrus and medial frontal lobe. These results provide evidence of age specific neural networks supporting spatial navigation and identify a putative neural substrate for age-related differences in spatial memory and navigational skill.

Adult↗

PubMed2005

"To me, it's my life": medical communication, trust, and activism in cyberspace.

This paper studies the conversations and activities of an online support group for breast cancer sufferers and survivors and their supporters. Using communications medium theory and social capital theory, it examines the mundane and profound exchanges, the poignant self-disclosures, the creative expressions of solidarity, and the minor but not-insignificant political actions of people--initially strangers--who come together as a 'virtuous circle,' not only to assist with medical issues but also to meet emotional and even material needs. Sponsored by the Canadian nonprofit organization Breast Cancer Action Nova Scotia (BCANS), this virtual community has logged over a half million messages since 1996. Not every BCANS participant is an activist--many are just trying to grapple with their disease--but some find ways to shatter the professional "information monopoly," and to press for healthcare improvements. The study illustrates the scope, passion, and complexity of peer-to-peer medical communication in a virtual environment that promotes "thick trust". BCANS participants discuss with candor, warmth and even humor such painful topics as death and dying and the crises in intimate relationships brought about by a terminal illness. The sharing of confidences and fears enables participants to pool their 'collective intelligence' about many things, from how to cope with swelling, to how to think about end-of-life issues, to how to improve social policy.

Adolescent↗

PubMed2005

Optic-flow and egocentric-direction strategies in walking: central vs peripheral visual field.

The impact of a central or peripheral visual field loss on the vision strategy used to guide walking was determined by measuring walking paths of visually impaired participants. An immersive virtual environment was used to dissociate the expected paths of the optic-flow and egocentric-direction strategies by offsetting the walker's point of view from the actual direction of walking. Environments consisted of a goal within a forest, the goal alone, or the forest alone following a brief presentation of the goal. The first two environments allowed an evaluation of the visual information used in a goal-directed task whereas the third environment investigated the information used in a memory-guided task. Participants had either a central (CFL) or peripheral visual field loss (PFL) or were fully sighted (FS). Results showed that, for the goal-directed task, the CFL group was less influenced by optic flow than was an age-matched FS group. Optic flow decreased heading error by only 1.3 degrees (16%) in the CFL group compared to 3.6 degrees (42%) in the FS group. The PFL group showed an optic-flow influence (2.4 degrees or 26%) comparable to an older, age-matched FS group (2.9 degrees or 31%). For the memory-guided task, all but the PFL group had heading errors comparable to those obtained in the goal-alone scene, demonstrating the ability to use an egocentric-direction strategy with a stored representation of either the goal's position or an offset relative to a landmark instead of a visible goal. The paths of the PFL group veered significantly from the predicted paths of both the optic-flow and egocentric-direction strategies. The findings of this study suggest that central vision is important for using optic flow to guide walking, whereas peripheral vision is important for establishing and/or updating an accurate representation of spatial structure for navigation.

Adult↗

PubMed2001

Cybersickness in the presence of scene rotational movements along different axes.

Compelling scene movements in a virtual reality (VR) system can cause symptoms of motion sickness (i.e., cybersickness). A within-subject experiment has been conducted to investigate the effects of scene oscillations along different axes on the level of cybersickness. Sixteen male participants were exposed to four 20-min VR simulation sessions. The four sessions used the same virtual environment but with scene oscillations along different axes, i.e., pitch, yaw, roll, or no oscillation (speed: 30 degrees/s, range: +/- 60 degrees). Verbal ratings of the level of nausea were taken at 5-min intervals during the sessions and sickness symptoms were also measured before and after the sessions using the Simulator Sickness Questionnaire (SSQ). In the presence of scene oscillation, both nausea ratings and SSQ scores increased at significantly higher rates than with no oscillation. While individual participants exhibited different susceptibilities to nausea associated with VR simulation containing scene oscillations along different rotational axes, the overall effects of axis among our group of 16 randomly selected participants were not significant. The main effects of, and interactions among, scene oscillation, duration, and participants are discussed in the paper.

Adult↗

PubMed1999

Improving cognitive function after brain injury: the use of exercise and virtual reality.

OBJECTIVE: To assess the impact of exercise and virtual reality (VR) on the cognitive rehabilitation of persons with traumatic brain injury (TBI). DESIGN: Before-after trial assessed cognitive function after a 4-week intervention program. A random allocation crossover assessed changes in reaction and movement times after a single bout of VR exercise and a no-exercise control condition. SETTING: Brain injury rehabilitation unit in Edinburgh, Scotland. PATIENTS: (1) Four-week intervention: a consecutive sample of 13 suitable TBI adults were compared to control populations (n > 25) of previous TBI patients of similar age, severity, and time postinjury. (2) Single-bout intervention: a consecutive sample of 13 suitable adults with moderate TBI, 6.29 to 202.86 weeks postinjury. INTERVENTION: Nonimmersive VR exercise. MAIN OUTCOME MEASURES: (1) Tests of attention, information processing, learning, and memory. (2) Reaction and movement times. RESULTS: After the 4-week intervention patients performed significantly better than controls on the digit symbol (p < .01). verbal (p < .01), and visual learning tasks (p < .05). Significant improvements in reaction times (p < .01) and movement times (p < .05) were gained following a single bout of VR exercise. CONCLUSION: Exercising in a virtual environment offers the potential for significant gains in cognitive function.

Adolescent↗

PubMed2002

Visual short-term memory and motor planning.

Despite extensive experimental work showing that memory for visual information in prior fixations is limited, the nature and content of the information maintained across fixations, when vision functions in its natural context, is not well determined. To gain insight into what memory representations might be needed to support vision in the natural world, we examined eye and hand movements while subjects made a sandwich and while they copied a toy model in a virtual environment. Patterns of eye-hand coordination and fixation sequences suggest the need for planning and coordinating movements over a period of a few seconds. Since the movement plan is initiated when the eye is in a different position from that when the movement itself is made, the planning must be in a coordinate frame that is independent of eye position. Movement planning thus requires a representation of the spatial structure in a scene that is built up over different fixations.

Fixation, Ocular↗

PubMedDate not supplied

A 6 D.O.F. opto-inertial tracker for virtual reality experiments in microgravity.

Gravity plays a role in many different levels of human motor behavior. It dictates the laws of motion of our body and limbs, as well as of the objects in the external world with which we wish to interact. The dynamic interaction of our body with the world is molded within gravity's constraints. The role played by gravity in the perception of visual stimuli and the elaboration of human movement is an active research theme in the field of Neurophysiology. Conditions of microgravity, coupled with techniques from the world of virtual reality, provide a unique opportunity to address these questions concerning the function of the human sensorimotor system. The ability to measure movements of the head and to update in real time the visual scene presented to the subject based on these measurements is a key element in producing a realistic virtual environment. A variety of head-tracking hardware exists on the market today, but none seem particularly well suited to the constraints of working with a space station environment. Nor can any of the existing commercial systems meet the more stringent requirements for physiological experimentation (high accuracy, high resolution, low jitter, low lag) in a wireless configuration. To this end, we have developed and tested a hybrid opto-inertial 6 degree-of-freedom tracker based on existing inertial technology. To confirm that the inertial components and algorithms will function properly, this system was tested in the microgravity conditions of parabolic flight. Here we present the design goals of this tracker, the system configuration and the results of 0g and 1g testing.

Acceleration↗

PubMed1998

Synaptic changes in rat maculae in space and medical imaging: the link.

Two different space life sciences missions (SLS-1 and SLS-2) have demonstrated that the synapses of the hair cells of rat vestibular maculae increase significantly in microgravity. The results also indicate that macular synapses are sensitive to stress. These findings argue that vestibular maculae exhibit neuroplasticity to macroenvironmental and microenvironmental changes. This capability should be clinically relevant to rehabilitative training and/or pharmacological treatments for vestibular disease. The results of this ultrastructural research also demonstrated that type I and type II hair cells are integrated into the same neuronal circuitry. The findings were the basis for development of three-dimensional reconstruction software to learn details of macular wiring. This software, produced for scientific research, has now been adapted to reconstruct the face and skull directly from computerized tomography scans. In collaboration with craniofacial reconstructive surgeons at Stanford University Medical Center, an effort is under way to produce a virtual environment workbench for complex craniofacial surgery. When completed, the workbench will help surgeons train for and simulate surgery. The methods are patient specific. This research illustrates the value of basic research in leading to unanticipated medical applications.

Acoustic Maculae↗

PubMedDate not supplied

eLoom and Flatland: specification, simulation and visualization engines for the study of arbitrary hierarchical neural architectures.

eLoom is an open source graph simulation software tool, developed at the University of New Mexico (UNM), that enables users to specify and simulate neural network models. Its specification language and libraries enables users to construct and simulate arbitrary, potentially hierarchical network structures on serial and parallel processing systems. In addition, eLoom is integrated with UNM's Flatland, an open source virtual environments development tool to provide real-time visualizations of the network structure and activity. Visualization is a useful method for understanding both learning and computation in artificial neural networks. Through 3D animated pictorially representations of the state and flow of information in the network, a better understanding of network functionality is achieved. ART-1, LAPART-II, MLP, and SOM neural networks are presented to illustrate eLoom and Flatland's capabilities.

Computer Simulation↗

PubMed1998

Virtual reality: a tutorial.

Virtual reality (VR) technology is complex and relies on multidisciplinary knowledge. VR applications are attracting an increasing interest among neuroscientists, in particular in the study of the human brain. Here we present a brief tutorial in which we address aspects of VR methodology that are most relevant to neurophysiology applications. After a brief survey of possible applications to neurophysiology, we discuss the following issues in VR: display technology, visual stimulus presentation techniques, visual spatial resolution and accuracy, devices for real-time interaction with the virtual environment and force-feedback.

Humans↗

PubMed2004

Strategies for stroke rehabilitation.

Rehabilitation after hemiplegic stroke has typically relied on the training of patients in compensatory strategies. The translation of neuroscientific research into care has led to new approaches and renewed promise for better outcomes. Improved motor control can progress with task-specific training incorporating increased use of proximal and distal movements during intensive practice of real-world activities. Functional gains are incorrectly said to plateau by 3-6 months. Many patients retain latent sensorimotor function that can be realised any time after stroke with a pulse of goal-directed therapy. The amount of practice probably best determines gains for a given level of residual movement ability. Clinicians should encourage patients to build greater strength, speed, endurance, and precision of multijoint movements on tasks that increase independence and enrich daily activity. Imaging tools may help clinicians determine the capacity of residual networks to respond to a therapeutic approach and help establish optimal dose-response curves for training. Promising adjunct approaches include practice with robotic devices or in a virtual environment, electrical stimulation to increase cortical excitability during training, and drugs to optimise molecular mechanisms for learning. Biological strategies for neural repair may augment rehabilitation in the next decade.

Arm↗

PubMed2000

Eye height scaling of absolute size in immersive and nonimmersive displays.

Eye-height (EH) scaling of absolute height was investigated in three experiments. In Experiment 1, standing observers viewed cubes in an immersive virtual environment. Observers' center of projection was placed at actual EH and at 0.7 times actual EH. Observers' size judgments revealed that the EH manipulation was 76.8% effective. In Experiment 2, seated observers viewed the same cubes on an interactive desktop display; however, no effect of EH was found in response to the simulated EH manipulation. Experiment 3 tested standing observers in the immersive environment with the field of view reduced to match that of the desktop. Comparable to Experiment 1, the effect of EH was 77%. These results suggest that EH scaling is not generally used when people view an interactive desktop display because the altitude of the center of projection is indeterminate. EH scaling is spontaneously evoked, however, in immersive environments.

Adult↗

PubMed2003

Behavioral dynamics of steering, obstacle avoidance, and route selection.

The authors investigated the dynamics of steering and obstacle avoidance, with the aim of predicting routes through complex scenes. Participants walked in a virtual environment toward a goal (Experiment 1) and around an obstacle (Experiment 2) whose initial angle and distance varied. Goals and obstacles behave as attractors and repellers of heading, respectively, whose strengths depend on distance. The observed behavior was modeled as a dynamical system in which angular acceleration is a function of goal and obstacle angle and distance. By linearly combining terms for goals and obstacles, one could predict whether participants adopt a route to the left or right of an obstacle to reach a go (Experiment 3). Route selection may emerge from on-line steering dynamics, making explicit path planning unnecessary.

Adolescent↗

PubMed2005

Task demands control acquisition and storage of visual information.

Attention and working memory limitations set strict limits on visual representations, yet researchers have little appreciation of how these limits constrain the acquisition of information in ongoing visually guided behavior. Subjects performed a brick sorting task in a virtual environment. A change was made to 1 of the features of the brick being held on about 10% of trials. Rates of change detection for feature changes were generally low and depended on the pick-up and put-down relevance of the feature to the sorting task. Subjects' sorting decision suggests that changes may be missed because of a failure to update the changed feature. The authors also explore how hand and eye behavior are coordinated for strategic acquisition and storage of visual information throughout the task.

Adolescent↗

PubMed2004

Orientation and perspective dependence in route and survey learning.

Three experiments investigated the role of egocentric orientation in subsequent memory for layouts learned via route (ground-level) and survey (aerial or overview) perspectives. Participants learned virtual environments from text descriptions (Experiment 1) or visual presentation (Experiments 1-3). In all experiments, scene recognition for route and survey images revealed a cost for switching perspective from study to test. In addition, recognition performance was facilitated when the test view matched the observer's learned orientation but only for the same-perspective recognition test. Experiment 3 demonstrated orientation dependence in judgments of relative direction, with a strong emphasis on initial heading. Together, these results suggest that establishing a reference system for representing spatial information is dependent on specific characteristics of the learning situation.

Cues↗