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At least 343 records · Page 19Linked to original sources

PubMed2002

Adaptation of reflexive feedback during arm posture to different environments.

In this study we have examined the ability of the central nervous system (CNS) to use spinal reflexes to minimize displacements during postural control while continuous force perturbations were applied at the hand. The subjects were instructed to minimize the displacements of the hand from a reference position that resulted from the force perturbations. The perturbations were imposed in one direction by means of a hydraulic manipulator of which the virtual mass and damping were varied. Resistance to the perturbations came from intrinsic and reflexive stiffness, and from the virtual environment. It is hypothesized that reflexive feedback during posture maintenance is optimally adjusted such that position deviations are minimal for a given virtual environment. Frequency response functions were estimated, capturing all mechanical properties of the arm at the end point (hand) level. Intrinsic and reflexive parameters were quantified by fitting a linear neuromuscular model to the frequency responses. The reflexive length feedback gain increased strongly with damping and little with the eigenfrequency of the total combined system (i.e. arm plus environment). The reflexive velocity feedback gain decreased slightly with relative damping at the largest eigenfrequency and more markedly at smaller eigenfrequencies. In the case of highest reflex gains, the total system remained stable and sufficiently damped while the responses of only the arm were severely underdamped and sometimes even unstable. To further analyse these results, a model optimization was performed. Intrinsic and reflexive parameters were optimized such that two criterion functions were minimized. The first concerns performance and penalized hand displacements from a reference point. The second one weights afferent control effort to avoid inefficient feedback. The simulations showed good similarities with the estimated values. Length feedback was adequately predicted by the model for all conditions. The predicted velocity feedback gains were larger in all cases, probably indicating a mutual gain limiting relation between length and velocity afferent signals. The results suggest that both reflex gains seem to be adjusted by the CNS, where in particular the length feedback gain was optimal so as to maximize performance at minimum control effort.

Adult↗

PubMed2003

Spatial navigation in virtual reality environments: an EEG analysis.

Past research has linked theta oscillations (electroencephalographic activity in the 4-8-Hz range) to spatial navigation in rodents and humans, and to the encoding and retrieval of spatial information in rodents. In the present study, electroencephalographic activity was measured while humans navigated through virtual mazes. Results confirmed previous findings that the frequency of theta episodes is directly related to the difficulty of maze navigation. We were also able to show that theta episodes occur most likely at points in a maze where new hallways come into view, or after navigational mistakes have been realized and are being corrected. This indicates that, just as in rodents, theta episodes in humans are related to the encoding and retrieval of spatial information.

Adult↗

PubMedDate not supplied

[Comparative assessment of the risk of handling of objects with an analysis protocol and the use of digital human models].

In this work the Authors propose a methodology based on the use of an ergonomic software in alternative to the traditional methods to evaluate muscular-skeletal diseases caused by incongruous postures or conditions of mechanical overload. This methodology allows to simulate, in a virtual environment, both a workplace and a digital human model whose behaviours are similar, from a kinematical and a dynamical point of view, to that ones of a real person. Through the simulation in a virtual environment of an operation of Manual Material Handling (MMH) in a pharmaceutics industry, the Authors have evaluated, in real time, the strengths and the reaction-moments in the axial, sagittal and lateral plane on the L4 and L5 lumbar vertebras and on the shoulder of the workers. In the work the single movements carried out by the operator are analysed using manikins of different percentiles. The results are compared with the ones coming from the use of the traditional methods to evaluate muscular skeletal disease.

Humans↗

PubMed1997

Hyper Hospital on the satellite multi-media network.

We have been developing the Hyper Hospital, a network based VR mediated medical care system. The Hyper Hospital is composed of two seamlessly integrated environments, that is, the virtual and the real worlds. Of them, its virtual environment expands the conventional medical care system using the virtual reality technology as a principal human interface and a collaboration tool, in the present study, an attempt to extend the Hyper Hospital system to various modalities of communication network is reported. A satellite communication based multi-media network using Internet protocols with the WWW interface is used. Data transmission rate and other performances were measured under various conditions and the satellite network was shown to be suitable to the Hyper Hospital network.

Computer Communication Networks↗

PubMed2004

An integrated approach to the ergonomic analysis of VR in psychotherapy: panic disorders, agoraphobia and eating disorders.

To face the aspects connected with VR environments usability for psychotherapeutic applications means to dare a double challenge from a methodological point of view: from one side, the need to adapt and to integrate on a heuristic basis classic usability evaluation methods to specific artefacts such as 3D Virtual Environments for clinical applications; from the other hand, the problems arisen by integration of expert evaluation of VR environments user-based tests carried out in real context of use. The theoretical background of our analytical stance is based upon an ethnomethodological approach, a perspective that gives evidence of how people, in specific social situations, are able to solve complex tasks producing shared meanings and achieving their goals during interaction. According to this perspective, the methodological objective consisted also in the identification of the usability requirements of the specific community of practice. The virtual environments considered were two of the four VR modules in the framework of the VEPSY project: Panic Disorders--Agoraphobia and Eating Disorders.

Agoraphobia↗

PubMed2006

The United States military's thigh trauma simulator.

Computer-generated virtual environments bring the potential to practice complex mental and physical tasks in safe and controlled conditions. When applied to medical procedures, they could allow students to gain experience with a wide variety of cases, in optimal order, and with no patient risk. The United States military is funding the development of a virtual environment to present a variety of health care providers, including orthopaedic surgeons, with case scenarios based on thigh trauma resulting in femur fractures. Data from the Visible Human project are being used to create the underlying virtual anatomy. This paper discusses an effort to imbue models created from the Visible Human male with thigh trauma related to femur fractures and to display the results in clinically relevant ways including virtual fluoroscopy and radiography, ultrasound, palpation, and nonclinical but educationally useful methods including transparency.

Computer Simulation↗

PubMed2002

'Putting it on the table': direct-manipulative interaction and multi-user display technologies for semi-immersive environments and augmented reality applications.

Collaborative virtual environments for diagnosis and treatment planning are increasingly gaining importance in our global society. Virtual and Augmented Reality approaches promised to provide valuable means for the involved interactive data analysis, but the underlying technologies still create a cumbersome work environment that is inadequate for clinical employment. This paper addresses two of the shortcomings of such technology: Intuitive interaction with multi-dimensional data in immersive and semi-immersive environments as well as stereoscopic multi-user displays combining the advantages of Virtual and Augmented Reality technology.

Computer Graphics↗

PubMed2006

Visual motion combined with base of support width reveals variable field dependency in healthy young adults.

We previously reported responses to induced postural instability in young healthy individuals viewing visual motion with a narrow (25 degrees in both directions) and wide (90 degrees and 55 degrees in the horizontal and vertical directions) field of view (FOV) as they stood on different sized blocks. Visual motion was achieved using an immersive virtual environment that moved realistically with head motion (natural motion) and translated sinusoidally at 0.1 Hz in the fore-aft direction (augmented motion). We observed that a subset of the subjects (steppers) could not maintain continuous stance on the smallest block when the virtual environment was in motion. We completed a posteriori analyses on the postural responses of the steppers and non-steppers that may inform us about the mechanisms underlying these differences in stability. We found that when viewing augmented motion with a wide FOV, there was a greater effect on the head and whole body center of mass and ankle angle root mean square (RMS) values of the steppers than of the non-steppers. FFT analyses revealed greater power at the frequency of the visual stimulus in the steppers compared to the non-steppers. Whole body COM time lags relative to the augmented visual scene revealed that the time-delay between the scene and the COM was significantly increased in the steppers. The increased responsiveness to visual information suggests a greater visual field-dependency of the steppers and suggests that the thresholds for shifting from a reliance on visual information to somatosensory information can differ even within a healthy population.

Adult↗

PubMed1997

Virtual reality for the treatment of body image disturbances.

This chapter describes the characteristics and preliminary evaluation of The Virtual Environment for Body Image Modification (VEBIM), a set of tasks aimed at treating body image disturbances and body dissatisfaction associated with eating disorders. Two methods are commonly used to treat body image: (1) a cognitive/behavioural therapy to influence patients' feelings of dissatisfaction; (2) a visual/motorial therapy with the aim of influencing the level of bodily awareness. VEBIM tries to integrate these two therapeutic approaches within an immersive virtual environment. This choice would not only make it possible to intervene simultaneously on all of the forms of bodily representations, but also to use the psycho-physiological effects provoked on the body by the virtual experience for therapeutic purposes. The chapter, together with the description of the VEBIM theoretical approach, it also presents a study on two preliminary samples (71 normal subjects, uncontrolled study, 48 normal subjects, controlled study) to test its efficacy.

Adult↗

PubMed2003

Internet-based telehealth system for the treatment of agoraphobia.

In this work that is being validated within the VEPSY project, we present a system that allows the patient to continue a psychological virtual reality treatment from his or her home PC as complementary therapy. In the consulting room, we have been using virtual therapy for panic disorder and agoraphobia treatment to expose the patient to several situations. For the complementary therapy, a structured treatment via the Internet has been prepared, which consists of several parts: an assessment protocol; a structured treatment protocol organized in several blocks (such as psychoeducation and exposure); and an outcome protocol. The same situations as in the consulting room have been selected for the exposure, but each of them has been divided into several virtual environments with specific characteristics that limit its difficulty level. The stimuli that are used at each level are controlled automatically by the system. The information of the patient is stored in a database, which is placed in a remote server using XML format and used to control which stages of the treatment he or she can access. The psychologist can limit the evolution of the patient. The virtual environments are installed in the patient's PC, and they are implemented with a mechanism that ensures that they can only be run when the patient connects to the web. The user should not have any special virtual reality hardware at home, so head rotations have been simulated with the navigation system.

Agoraphobia↗

PubMed2000

Humans with traumatic brain injuries show place-learning deficits in computer-generated virtual space.

Spatial learning and memory has been linked to the hippocampus and temporal lobes and though these areas are often damaged in traumatic brain injury (TBI), spatial learning deficits after TBI have not received much attention. In the present study, a virtual environment was used to challenge people with TBI to solve a task comparable to the Morris water maze, which in turn has been shown to be highly sensitive to hippocampal and frontal lobe dysfunction in laboratory animals. A regular computer monitor was used to present 12 participants with TBI and 12 age- and sex-matched comparison participants with a computer-generated, three-dimensional "virtual arena maze," consisting of a large round arena within a very large square room. Participants were required to learn the place of an invisible target on the floor of the room based solely on distal cues on the walls of the room. Eight of the 12 participants with moderate to severe TBI showed substantial place-learning deficits in comparison to the uninjured participants. Performance in the virtual environment correlated with self-reported frequency of wayfinding problems in everyday life and with scores on a test of episodic memory, the Rivermead Behavioural Memory Task. These data confirm that deficits in spatial learning and memory follow TBI, and suggest that the virtual arena maze may provide a new method for objectively assessing them.

Adult↗

PubMed2005

Immersive visualization training of radiotherapy treatment.

External radiation beam treatment of cancer tumours involves delivery of invisible radiation beams through the body where internal structures can not be seen. Beam targeting of patient anatomy has to very accurate to achieve the desired therapeutic result. Good understanding of radiotherapy treatment (RT) concepts is essential to training. This paper presents a virtual environment simulator developed by the authors for training and education of intensity modulated radiotherapy (IMRT) treatment of cancer. This simulator employs immersive visualization to provide a high fidelity spatial awareness of the complex relationships between tumour, organs at risk, treatment beam and radiation dose. All these visualization are provided by a 3D virtual environment based on the patient in a RT treatment room. Immersive visualization using this simulator is being used to train radiation oncologist and radiation physicists about radiotherapy treatment.

Computer Simulation↗

PubMed2002

Can virtual reality be used to measure and train surgical skills?

The quantitative literature on the use of virtual environments to measure and train a variety of surgical skills is critically reviewed. We selected works from the years 1995-2000. Theoretical perspectives, such as those of Saltzman (1979), Bernstein (1967) and Schmidt (1975) and techniques, such as hierarchical task analysis, are presented and contrasted with the largely atheoretical approach of the practitioners of virtual surgery. It is concluded that the quantitative work discussed provides few findings of value to practising surgeons. This may be due in part to the lack of consideration paid to fundamental issues in the learning of motor skills, such as whether motor skills learning is most effective with varying training conditions and the distinction between purely motoric aspects and knowledge of procedures. Possible ways forward for surgical training are outlined. It is suggested that the theoretical perspectives and techniques available in the area of motor behaviour should be incorporated into future experimental studies of surgery in virtual environments.

Computer Simulation↗

PubMed2006

Visuomotor learning in immersive 3D virtual reality in Parkinson's disease and in aging.

Successful adaptation to novel sensorimotor contexts critically depends on efficient sensory processing and integration mechanisms, particularly those required to combine visual and proprioceptive inputs. If the basal ganglia are a critical part of specialized circuits that adapt motor behavior to new sensorimotor contexts, then patients who are suffering from basal ganglia dysfunction, as in Parkinson's disease should show sensorimotor learning impairments. However, this issue has been under-explored. We tested the ability of 8 patients with Parkinson's disease (PD), off medication, ten healthy elderly subjects and ten healthy young adults to reach to a remembered 3D location presented in an immersive virtual environment. A multi-phase learning paradigm was used having four conditions: baseline, initial learning, reversal learning and aftereffect. In initial learning, the computer altered the position of a simulated arm endpoint used for movement feedback by shifting its apparent location diagonally, requiring thereby both horizontal and vertical compensations. This visual distortion forced subjects to learn new coordinations between what they saw in the virtual environment and the actual position of their limbs, which they had to derive from proprioceptive information (or efference copy). In reversal learning, the sign of the distortion was reversed. Both elderly subjects and PD patients showed learning phase-dependent difficulties. First, elderly controls were slower than young subjects when learning both dimensions of the initial biaxial discordance. However, their performance improved during reversal learning and as a result elderly and young controls showed similar adaptation rates during reversal learning. Second, in striking contrast to healthy elderly subjects, PD patients were more profoundly impaired during the reversal phase of learning. PD patients were able to learn the initial biaxial discordance but were on average slower than age-matched controls in adapting to the horizontal component of the biaxial discordance. More importantly, when the biaxial discordance was reversed, PD patients were unable to make appropriate movement corrections. Therefore, they showed significantly degraded learning indices relative to age-matched controls for both dimensions of the biaxial discordance. Together, these results suggest that the ability to adapt to a sudden biaxial visuomotor discordance applied in three-dimensional space declines in normal aging and Parkinson disease. Furthermore, the presence of learning rate differences in the PD patients relative to age-matched controls supports an important contribution of basal ganglia-related circuits in learning novel visuomotor coordinations, particularly those in which subjects must learn to adapt to sensorimotor contingencies that were reversed from those just learned.

Adaptation, Physiological↗

PubMed1999

Virtual endoscopic environments in modern neurosurgical practice.

Modern radiographic techniques have allowed the creation of high-definition planar images that can provide important anatomical as well as physiological data. Planar imaging sets can be reformatted into three-dimensional (3-D) data sets that can then be manipulated to demonstrate important anatomical or gross pathological features. Three-dimensional data sets have been used with success in modern image-guided or frameless stereotactic surgery. Another potential application is so-called "virtual endoscopy" or "scopeless endoscopy," in which a 3-D anatomical data set is reformatted into a volume-rendered image that can then be viewed. By reformatting images in this way, a "surgeon's-eye" view can be obtained, which can aid in presurgical planning and diagnosis. The use of virtual endoscopy has the potential to increase our understanding of the appropriate anatomy and the anatomical relationships most apparent during neurosurgical approaches. In so doing, virtual endoscopy may serve as an important means of planning for therapeutic interventions. On the other hand, one must always be cognizant of the technical limitations of these studies regardless of the quality of the reconstructed images. Prospective, correlative, clinical studies in which the anatomical advantages of virtual-based endoscopy are evaluated in large cadaver or patient series must be performed. Until then, the only potential ways to compensate for errors that exist in the algorithms and reconstructions of 3-D endoscopic images are based on the surgeon's understanding of the clinical state of the patient and prior experience with the anatomy in the region of question.

Journal Article↗

PubMed2004

The representation of self reported affect in body posture and body posture simulation.

It is taken for granted that the non-verbal information we acquire from a person's body posture and position affects our perception of others. However, to date human postures have never been described on an empirical level. This study is the first approach to tackle the unexplored topic of human postures. We combined two approaches: traditional behavior observation and modern anthropometric analysis. Photographs of 100 participants were taken, their body postures were transferred to a three dimensional virtual environment and the occurring body angles were measured. The participants were asked to fill in a questionnaire about their current affective state. A principal component analysis with the items of the affect questionnaire (Positive Negative Affect Scales, PANAS) revealed five main factors: aversion, openness, irritation, happiness, and self-confidence. The body angles were then regressed on these factors and the respective postures were reconstructed within a virtual environment. 50 different subjects rated the reconstructed postures from the positive and negative end of the regression. We found the ratings to be valid and accurate in respect to the five factors.

Adult↗

PubMed2006

Reality check: the role of realism in stress reduction using media technology.

There is a growing interest in the use of virtual and other mediated environments for therapeutic purposes. However, in the domain of restorative environments, virtual reality (VR) technology has hardly been used. Here the tendency has been to use mediated real environments, striving for maximum visual realism. This use of photographic material is mainly based on research in aesthetics judgments that has demonstrated the validity of this type of simulations as representations of real environments. Thus, restoration therapy is developing under the untested assumption that photorealistic images have the optimal level of realism, while in therapeutic applications 'experiential realism' seems to be the key rather than visual realism. The present paper discusses this contrast and briefly describes data of three studies aimed at exploring the importance and meaning of realism in the context of restorative environments.

Communications Media↗

PubMed2006

A virtual reprise of the Stanley Milgram obedience experiments.

BACKGROUND: Stanley Milgram's 1960s experimental findings that people would administer apparently lethal electric shocks to a stranger at the behest of an authority figure remain critical for understanding obedience. Yet, due to the ethical controversy that his experiments ignited, it is nowadays impossible to carry out direct experimental studies in this area. In the study reported in this paper, we have used a similar paradigm to the one used by Milgram within an immersive virtual environment. Our objective has not been the study of obedience in itself, but of the extent to which participants would respond to such an extreme social situation as if it were real in spite of their knowledge that no real events were taking place. METHODOLOGY: Following the style of the original experiments, the participants were invited to administer a series of word association memory tests to the (female) virtual human representing the stranger. When she gave an incorrect answer, the participants were instructed to administer an 'electric shock' to her, increasing the voltage each time. She responded with increasing discomfort and protests, eventually demanding termination of the experiment. Of the 34 participants, 23 saw and heard the virtual human, and 11 communicated with her only through a text interface. CONCLUSIONS: Our results show that in spite of the fact that all participants knew for sure that neither the stranger nor the shocks were real, the participants who saw and heard her tended to respond to the situation at the subjective, behavioural and physiological levels as if it were real. This result reopens the door to direct empirical studies of obedience and related extreme social situations, an area of research that is otherwise not open to experimental study for ethical reasons, through the employment of virtual environments.

Adult↗