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PubMed2006

Individual skill differences and large-scale environmental learning.

Spatial skills are known to vary widely among normal individuals. This project was designed to address whether these individual differences are differentially related to large-scale environmental learning from route (ground-level) and survey (aerial) perspectives. Participants learned two virtual environments (route and survey) with limited exposure and tested on judgments about relative locations of objects. They also performed a series of spatial and nonspatial component skill tests. With limited learning, performance after route encoding was worse than performance after survey encoding. Furthermore, performance after route and survey encoding appeared to be preferentially linked to perspective and object-based transformations, respectively. Together, the results provide clues to how different skills might be engaged by different individuals for the same goal of learning a large-scale environment.

Altitude↗

PubMed2001

Optic flow is used to control human walking.

How is human locomotion visually controlled? Fifty years ago, it was proposed that we steer to a goal using optic flow, the pattern of motion at the eye that specifies the direction of locomotion. However, we might also simply walk in the perceived direction of a goal. These two hypotheses normally predict the same behavior, but we tested them in an immersive virtual environment by displacing the optic flow from the direction of walking, violating the laws of optics. We found that people walked in the visual direction of a lone target, but increasingly relied on optic flow as it was added to the display. The visual control law for steering toward a goal is a linear combination of these two variables weighted by the magnitude of flow, thereby allowing humans to have robust locomotor control under varying environmental conditions.

Models, Biological↗

PubMed2006

Accuracy of facial plaster casts.

OBJECTIVE: The aim of this study was to evaluate the accuracy of facial plaster casts and their suitability for 3-D mapping. MATERIALS AND METHODS: All measurements were carried out on 15 adult probands (seven female and eight male; age range 19-31 years, mean 24.7 years). A plaster cast of the facial surface was prepared for all probands using alginate impressions. The plaster casts and the probands faces were digitized using a three-dimensional laser-scanner operating with structured light. The resulting point clouds were matched in a virtual environment to analyze the deviations between the cast and the facial surfaces, both qualitatively and quantitatively. RESULTS: The average deviations depended on the facial area and lay between 0.95 and 3.55 mm. Marked differences between the plaster cast and the facial surface were found, particularly in the area of the lips, at the roof of the nose, at the cheeks, and in the entire lower facial area. CONCLUSIONS: The regionally exacerbated soft tissue deformations that occur during impression of the facial surface lead to inaccuracies in the resulting plaster cast that forbids any use for morphometric analysis. Documentation of pathological findings in cleft lip and palate using facial plaster casts does appear to be justifiable.

Adult↗

PubMed2003

[New perspectives of locomotor rehabilitation after stroke].

The task-oriented approach incorporating treadmill walking for retraining gait early after stroke has contributed to promote locomotor recovery. To augment practice, training strategies such as mental practice and training in virtual environments are proposed. While the former offers more practice with less physical exertion, the latter allows safe practice in a variety of challenging environments. Work is under way to assess whether these new strategies can further enhance locomotor recovery.

Gait↗

PubMed2000

Route navigating without place recognition: what is recognised in recognition-triggered responses?

The use of landmark information in a route-navigation task has been investigated in a virtual environment. After learning a route, subjects were released at intermediate points along the route and asked to indicate the next movement direction required to continue the route. At each decision point, three landmarks were present, one of which was viewed centrally and two which appeared in the periphery of the visual field when approaching the decision point. In the test phase, landmarks could be replaced either within or across places. If all landmarks combined into a new place had been associated with the same movement direction during training, subjects performed as in the control condition. This indicates that they did not need to recognise places as configurations of landmarks. If, however, landmarks that had been associated with conflicting movement directions during training were combined, subjects' performance was reduced. We conclude that local views and objects are recognised individually and that the associated directions are combined in a voting scheme. No evidence was found for a recognition of places as panoramic views or configurations of objects.

Humans↗

PubMed2002

Path integration from optic flow and body senses in a homing task.

We examined the roles of information from optic flow and body senses (eg vestibular and proprioceptive information) for path integration, using a triangle completion task in a virtual environment. In two experiments, the contribution of optic flow was isolated by using a joystick control. Five circular arenas were used for testing: (B) both floor and wall texture; (F) floor texture only, reducing information for rotation; (W) wall texture only, reducing information for translation; (N) a no texture control condition, and (P) an array of posts. The results indicate that humans can use optic flow for path integration and are differentially influenced by rotational and translational flow. In a third experiment, participants actively walked in arenas B, F, and N, so body senses were also available. Performance shifted from a pattern of underturning to overturning and exhibited decreased variability, similar responses with and without optic flow, and no attrition. The results indicate that path integration can be performed by integrating optic flow, but when information from body senses is available it appears to dominate.

Adult↗

PubMed2003

Efficient extrapolation of the view with a dynamic and predictive stimulus.

In the real-world, the retinal projection of an object changes as we move, or as a moving object passes in front of us. We have to recognise objects, despite such retinal-projection changes. Many studies have shown that the time required to identify objects after a change in the retinal projection is longer than when there is no retinal-projection change. This recognition cost is referred to as the view-dependent effect. Previous researchers have studied the view-dependent effect while disregarding the predictability of retinal-projection changes. Here, we demonstrate that there is no view-dependent effect when the predictability is introduced, in the case where participants track moving objects by head-turning or eye-movement in a virtual environment. Violation of the predictability, such as an unpredictable retinal-projection change or a movement of the first stimulus that was inconsistent with a subsequent retinal-projection change, caused a view-dependent effect. Moreover, we found that extraretinal information such as head-turning or eye-movement was unnecessary for view-independent recognition. These results indicate that humans can extrapolate to the tested view from the studied view in a view-independent way when retinal-projection change is predictable from the visual stimulus.

Adult↗

PubMed2004

Visual guidance of intercepting a moving target on foot.

How do people walk to a moving target, and what visual information do they use to do so? Under a pursuit strategy, one would head toward the target's current position, whereas under an interception strategy, one would lead the target, ideally by maintaining a constant target-heading angle (or constant bearing angle). Either strategy may be guided by the egocentric direction of the target, local optic flow from the target, or global optic flow from the background. In four experiments, participants walked through a virtual environment to reach a target moving at a constant velocity. Regardless of the initial conditions, they walked ahead of the target for most of a trial at a fairly constant speed, consistent with an interception strategy (experiment 1). This behavior can be explained by trying to maintain a constant target-heading angle while trying to walk a straight path, with transient steering dynamics. In contrast to previous results for stationary targets, manipulation of the local optic flow from the target (experiment 2) and the global optic flow of the background (experiments 3 and 4) failed to influence interception behavior. Relative motion between the target and the background did affect the path slightly, presumably owing to its effect on perceived target motion. We conclude that humans use an interception strategy based on the egocentric direction of a moving target.

Adult↗

PubMed2006

Sleep after spatial learning promotes covert reorganization of brain activity.

Sleep promotes the integration of recently acquired spatial memories into cerebral networks for the long term. In this study, we examined how sleep deprivation hinders this consolidation process. Using functional MRI, we mapped regional cerebral activity during place-finding navigation in a virtual town, immediately after learning and 3 days later, in subjects either allowed regular sleep (RS) or totally sleep-deprived (TSD) on the first posttraining night. At immediate and delayed retrieval, place-finding navigation elicited increased brain activity in an extended hippocampo-neocortical network in both RS and TSD subjects. Behavioral performance was equivalent between groups. However, striatal navigation-related activity increased more at delayed retrieval in RS than in TSD subjects. Furthermore, correlations between striatal response and behavioral performance, as well as functional connectivity between the striatum and the hippocampus, were modulated by posttraining sleep. These data suggest that brain activity is restructured during sleep in such a way that navigation in the virtual environment, initially related to a hippocampus-dependent spatial strategy, becomes progressively contingent in part on a response-based strategy mediated by the striatum. Both neural strategies eventually relate to equivalent performance levels, indicating that covert reorganization of brain patterns underlying navigation after sleep is not necessarily accompanied by overt changes in behavior.

Adult↗

PubMed2000

Evaluation of acoustic beacon characteristics for navigation tasks.

The goal of the present study was to investigate the human factors issues related to acoustic beacons used for auditory navigation. Specific issues addressed were: (1) the effect of various beacon characteristics on human accuracy in turning toward the direction of the acoustic beacon; (2) the difference between real and virtual environments on human accuracy in turning toward the acoustic beacon; and (3) the perceived sound quality of various acoustic beacons. Three experiments were conducted in which acoustic beacons were presented in a background of 80 dBA pink noise. Results of the localization tasks revealed that (a) presentation mode (continuous versus pulsed beacon sound) did not affect the overall localization accuracy or number of front-back confusion errors; and (b) the type of acoustic beacon affected the size of localization error. Results of the sound quality assessment indicated that listeners had definite preferences regarding the type of sound being used as a beacon, with (a) non-speech beacons preferred over speech beacons, (b) a beacon repetition rate of 1.1 rps preferred over either the 0.7 or 2.5 rps rates, and (c) a continuous operation of a beacon preferred over a pulsed operation. Finally, sound quality ratings and localization errors were highly negatively correlated. This finding demonstrates the usefulness and practical values of sound quality judgements for audio display design and evaluation.

Acoustics↗

PubMed2004

Assessing stroke patients' prospective memory using virtual reality.

There is a dearth of empirical evidence about prospective memory (remembering to perform actions in the future) in stroke patients. A probable reason for this is that it is difficult to perform a realistic and controlled assessment of prospective memory ability in a rehabilitation setting. Virtual reality may provide a solution to this difficulty by allowing prospective memory to be tested in a simulation of a real-life situation whilst retaining a laboratory level of scientific control. This exploratory study assessed the performance of stroke patients and age-matched control participants on event-, time- and activity-based prospective memory retrieval tasks in a personal computer-based virtual environment. Stroke patients were severely impaired at the event- and activity-based tasks compared with age-matched controls, but only marginally impaired at the time-based task. The additional knowledge gained from this form of assessment could direct rehabilitation more effectively towards specific impairments of individual patients.

Aged↗

PubMed2006

Memory for object location and route direction in virtual large-scale space.

In everyday life people have to deal with tasks such as finding a novel path to a certain goal location, finding one's way back, finding a short cut, or making a detour. In all of these tasks people acquire route knowledge. For finding the same way back they have to remember locations of objects like buildings and additionally direction changes. In three experiments using recognition tasks as well as conscious and unconscious spatial priming paradigms memory processes underlying wayfinding behaviour were investigated. Participants learned a route through a virtual environment with objects either placed at intersections (i.e., decision points) where another route could be chosen or placed along the route (non-decision points). Analyses indicate first that objects placed at decision points are recognized faster than other objects. Second, they indicate that the direction in which a route is travelled is represented only at locations that are relevant for wayfinding (e.g., decision points). The results point out the efficient way in which memory for object location and memory for route direction interact.

Adult↗

PubMed2003

Improving spatial functioning in children with cerebral palsy using computerized and traditional game tasks.

PURPOSE: To examine the effectiveness of combining virtual environment (VE) instruction with additional desk-top tasks, based on the Luria-Vygotsky methodology, for spatial remediation in children having complex motor disabilities restricting movement. METHODS: In Experiment 1, from among children attending for residential rehabilitation, an experimental subgroup had additional spatial training using a VE and corresponding desk-top models. All children were tested at the start and end of training, using four spatial tests. In Experiment 2, larger groups of children (pair-matched for initial performance) were given the same training as in Experiment 1, but experimentals received both VE-based training and supporting tasks designed to improve executive functions and verbal regulation of spatial functioning. Assessment involved a wider range of tests than in Experiment 1. RESULTS: In Experiment 1, both groups showed improvement at retest, but experimentals showed greater improvement. Children beginning with the lowest level of cognitive performance failed to benefit from the additional training. In Experiment 2 the experimental group made significantly greater improvement than controls, irrespective of initial performance level. CONCLUSIONS: VE-based spatial training is effective for children with complex disabilities, particularly when combined with training that remediates cognitive weaknesses.

Adolescent↗

PubMed2003

Developing a virtual interdisciplinary research community in higher education.

As multidisciplinary collaboration in both clinical and research settings is becoming a key aspect of contemporary health care, strategies to enhance interprofessional interaction in postgraduate research programmes can offer important experiences to facilitate ongoing interprofessional relationships. This paper provides a retrospective appraisal of a strategy which used computer-mediated communication to develop a virtual community network, known as'health_voice' accessed through a web page. The rationale for developing the network is presented, and the process of designing and establishing the web-site through an action research approach is described The outcome of the strategy is reviewed with regard to the relationships between the real' and 'virtual' community. Reflections on the developmental process contextualise the initiative within a concept of a community-of-practice. It is acknowledged that the use of a virtual arena for communication within a research community involves a cultural change in the dynamics of higher degree teaching and learning. Future plans to further embed the virtual environment within a postgraduate research culture are given.

Cooperative Behavior↗

PubMed2006

Comparing distances in mental images constructed from visual experience or verbal descriptions: the impact of survey versus route perspective.

Mental images constructed after visual examination of a spatial configuration or after processing a verbal description of that configuration have been shown to share similar properties, in particular the capacity to preserve metric information contained in the configuration represented. In the present study, we investigated the properties of mental images constructed under learning conditions resulting from the combination of a visual or a verbal mode of acquisition and a survey or route perspective. Participants memorized a virtual environment (a garden containing six objects) under one of four learning conditions: (a) viewing a map of the garden (visual-survey); (b) viewing a video presentation of a journey along the path around the garden (visual-route); (c) listening to a verbal description of the map of the garden (verbal-survey); and (d) listening to a verbal description of the journey around the garden (verbal-route). The participants were then invited to compare the distances separating objects in the garden mentally. Experiment 1, where the pairs of distances to be compared had a common starting point, revealed that the frequency of correct responses was higher, and response times were shorter when participants had learned about the environment visually rather than by a verbal description. The conditions involving a survey perspective resulted in a higher frequency of correct responses and shorter response times than those involving a route perspective. Lastly, a symbolic distance effect was obtained in the first three conditions, in that the greater the difference between the two distances being compared, the higher the frequency of correct responses, and the shorter the response times. Experiment 2, where the pairs of distances had different starting points, replicated these results, although longer response times revealed that the comparison process was more costly. Taken together, these findings support the view that mental spatial representations derived from different sources and adopting different perspectives contain genuine metric properties, except when the verbal modality and the route perspective are combined during learning.

Adolescent↗

PubMed2001

The actor-observer effect in virtual reality presentations.

The use of virtual reality (VR) presentations are becoming a more and more frequent means of communicating information and displaying data to large groups of viewers. VR presentations put heavy demands on reproduction of visual, aural, and tactile information. A common situation in VR presentations is that one actor acts in the virtual environment (VE), while a group of people observes the actors actions in the VE, often from the perspective of the actor. The current paper aims to study actors' (participants actively interacting with the VE) and observers' (participants passively observing the actors' interaction with the VE) evaluations of the VR presentation. In an experiment, 16 actors and 16 observers either acted in or observed a VE and performed ratings of the quality of the presentation. The results showed that actors experienced higher presence and realism, and enjoyed the VR experience more than observers did. Observers, on the other hand, experienced that external events distracted their attention more than actors did. Finally, actors experienced more symptoms of simulation sickness. However, no differences between actors and observers were found for ratings of audio quality.

Adult↗

PubMed2003

The illusion of presence in immersive virtual reality during an fMRI brain scan.

The essence of immersive virtual reality (VR) is the illusion it gives users that they are inside the computer-generated virtual environment. This unusually strong illusion is theorized to contribute to the successful pain reduction observed in burn patients who go into VR during woundcare (www.vrpain.com) and to successful VR exposure therapy for phobias and post-traumatic stress disorder (PTSD). The present study demonstrated for the first time that subjects could experience a strong illusion of presence during an fMRI despite the constraints of the fMRI magnet bore (i.e., immobilized head and loud ambient noise).

Adult↗

PubMed2003

Definition of a VR-based protocol to treat social phobia.

Social phobia is an anxiety disorder that is accessible to two forms of treatment yielding scientifically validated results: drugs and cognitive-behavioral therapies. Graded exposure to feared social situations is fundamental to obtain an improvement of the anxious symptoms. Traditionally, exposure therapies are done either in vivo or by imagining the situations. In vivo exposure is sometimes difficult to control and many patients have some difficulties in using imagination. Virtual reality (VR) seems to bring significant advantages. It allows exposures to numerous and varied situations. This paper reports the definition of a clinical protocol whose purpose is to assess the efficiency of a VR therapy compared to a CBT and to the absence of treatment for social phobic patients. It explains the illness' diagnosis and its usual treatments. It exposes all the architecture of the study, the assessment tools, the content and unfold of the therapy sessions. It finally reports first results of a clinical trial in a between-group design in 10 patients suffering from social phobia. The virtual environments used in the treatment reproduce four situations that social phobics feel the most threatening: performance, intimacy, scrutiny and assertiveness. With the help of the therapist, the patient learns adapted cognitions and behaviors with the aim of reducing her or his anxiety in the corresponding real situations. The novelty of our work is to address a group of situations that the phobic patient is most likely to experience and to treat patients according to a precise protocol.

Adult↗