Antonio Capobianco

Starfish: a selection technique for dense virtual environments

We present Starfish - a new target selection technique for virtual reality (VR) environments. This technique provides a solution to accurately select targets in high-density 3D scenes. The user controls a 3D pointer surrounded by a starfish-shaped closed surface. The extremity of each branch ends exactly on preselected near targets. The shape is an implicit surface built on the segments going from the pointer to each of these targets. As the pointer moves across the scene, the starfish shape is dynamically rebuilt. When it is locked the pointer is allowed to move inside the volume, slide down the desired branch, reach and select the corresponding target. Since the pointer stays within the shape, targets are easy to reach and select.

Statistical study of parameters for deep brain stimulation automatic preoperative planning of electrodes trajectories.

PurposeAutomatic methods for preoperative trajectory planning of electrodes in deep brain stimulation are usually based on the search for a path that resolves a set of surgical constraints to propose an optimal trajectory. The relative importance of each surgical constraint is usually defined as weighting parameters that are empirically set beforehand. The objective of this paper is to analyze the use of these parameters thanks to a retrospective study of trajectories manually planned by neurosurgeons. For that purpose, we firstly retrieved weighting factors allowing to match neurosurgeons manually planned choice of trajectory on each retrospective case; secondly, we compared the results from two different hospitals to evaluate their similarity; and thirdly, we compared the trends to the weighting factors empirically set in most current approaches.MethodsTo retrieve the weighting factors best matching the neurosurgeons manual plannings, we proposed two approaches: one based on a stochastic sampling of the parameters and the other on an exhaustive search. In each case, we obtained a sample of combinations of weighting parameters with a measure of their quality, i.e., the similarity between the automatic trajectory they lead to and the one manually planned by the surgeon as a reference. Visual and statistical analyses were performed on the number of occurrences and on the rank means.ResultsWe performed our study on 56 retrospective cases from two different hospitals. We could observe a trend of the occurrence of each weight on the number of occurrences. We also proved that each weight had a significant influence on the ranking. Additionally, we observed no influence of the medical center parameters, suggesting that the trends were comparable in both hospitals. Finally, the obtained trends were confronted to the usual weights chosen by the community, showing some common points but also some discrepancies.ConclusionThe results tend to show a predominance of the choice of a trajectory close to a standard direction. Secondly, the avoidance of the vessels or sulci seems to be sought in the surroundings of the standard position. The avoidance of the ventricles seems to be less predominant, but this could be due to the already reasonable distance between the standard direction and the ventricles. The similarity of results between two medical centers tends to show that it is not an exceptional practice. These results suggest that manual planning software may introduce a bias in the planning by proposing a standard position.

An experimental analysis of the impact of Touch Screen Interaction techniques for 3-D positioning tasks

The use of Touch Screen Interaction (TSI) for 3-D interaction entails both the addition of new haptic cues and the separation of the manipulation of the Degrees of Freedom (DoF) of the task: a 3 DoF task must be transformed into a 2-D+1-D task to be completed using a touch screen. In this paper, we investigate the impact of these two factors in the context of a 3-D positioning task. Our goal is to identify their respective influence on subjective preferences and performance measurements. To that purpose, we conducted an experimental comparison of five positioning techniques, isolating the influence of each of these two factors. The results we obtained suggest that the addition of haptic cues does not influence the user precision. However, the decomposition of the task has a strong influence on accuracy. More precisely, separating the manipulation of the depth dimension leads to an increased precision while isolating other dimensions does not influence the results. To explain this result, we realised a behavioural analysis of the data. This study suggests that the differences in the performance may be linked to the perceptual structure of the techniques. A technique isolating the manipulation of the depth seems to have a more adapted perceptual structure than a technique separating the height, even if those two dimensions are equally involved in the realisation of the task.

HardBorders: a new haptic approach for selection tasks in 3D menus

In this paper, we introduce a 3D menu with a new technique of haptic guidance, for virtual environments. The 3D menu consists in a thin polyhedral shape, with the items at the corners. The HardBorders technique haptically simulates the collisions of the pointer with the borders of the polyhedron, making it glide towards the items of the menu. A comparison with 2 reference modalities has been performed, showing a clear advantage of our HardBorders technique.

A hybrid projection to widen the vertical field of view with large screens to improve the perception of personal space in architectural project review

In this paper, we suggest using a hybrid projection to increase the vertical geometric field of view without incurring large deformations to preserve distance perception and to allow the seeing of the surrounding ground. We have conducted an experiment in furnished and unfurnished houses to evaluate the perception of distances and the spatial comprehension. Results show that the hybrid projection improves the perception of surrounding ground which leads to an improvement in the spatial comprehension. Moreover, it preserves the perception of distances and sizes by providing a performance similar to the perspective one in the task of distance estimation.

SPEED: prédiction de cibles

We present the SPEED method to predict endpoints, based on analysis of the kinetic characteristics of the pointing gesture. Our model splits the gesture into an acceleration phase and a deceleration phase to precisely detect target. The first phase allows us to identify a velocity peak that marks the beginning of the second phase. This phase is approached with a quadratic model to predict gesture endpoint. A pilot study shows that SPEED predicts a target more precisely than other existing methods, for 1D tasks without distractors.

Dynamic decomposition and integration of degrees of freedom for 3-D positioning

In this paper we present a new interaction technique based on degrees of freedom (DoF) decomposition for accurate positioning in virtual reality environments. This technique (called DIOD for Decomposition and Integration Of Degrees of freedom) is based on an adaptation of the Two-Component Model. It provides two different control levels regarding DoF coordination, one integrating and one separating the manipulation of the DoF. Our hypothesis is that each control level is appropriated to a different phase of the positioning task. During the ballistic phase, users manipulate all the dimensions of the task at the same time. However, during the control phase, users try to manipulate specific dimensions individually. The results of a preliminary study we conducted seem to indicate that the DIOD technique is more efficient than existing techniques.

Evaluation of factors affecting distance perception in architectural project review in immersive virtual environments

Distances are perceived as being more compressed in immersive virtual environments (IVEs) than in real environments. The goal of this study is to identify the most important factors that influence decision making and accuracy of distance perception in the context of architectural project reviews. Technical factors such as field of view, display devices and motion parallax were widely studied. In this paper, we have investigated other individual and contextual factors. We conducted a between-subject experiment using an immersive large screen display to examine the influence of the three factors: 1) the cognitive profile of the user (visual, auditory and kinesthetic - VAK), 2) the furnishing of the house, and 3) the locomotion speed, on distance perception. Results reveal that participants with visual profile were more accurate in distance estimation. Further, furnished houses were more suitable for virtual visits. The locomotion speed also seems to influence virtual visits which were better with a slow locomotion speed. Based on the results of our study, we finally present guidelines for setting up architectural project review tools which employ similar setup.

Feeling of control of an action after supra and subliminal haptic distortions.

Here we question the mechanisms underlying the emergence of the feeling of control that can be modulated even when the feeling of being the author of ones own action is intact. With a haptic robot, participants made series of vertical pointing actions on a virtual surface, which was sometimes postponed by a small temporal delay (15 or 65 ms). Subjects then evaluated their subjective feeling of control. Results showed that after temporal distortions, the hand-trajectories were adapted effectively but that the feeling of control decreased significantly. This was observed even in the case of subliminal distortions for which subjects did not consciously detect the presence of a distortion. Our findings suggest that both supraliminal and subliminal temporal distortions that occur within a healthy perceptual-motor system impact the conscious experience of the feeling of control of self-initiated motor actions.

A Preliminary Study of Two-Handed Manipulation for Spatial Input Tasks in a 3D Modeling Application

We developed a free form deformation application for an immersive environment in which users can interact freely using data gloves. To ensure better comfort and performances, we added the possibility of bimanual interaction in our environment. To investigate the actual gain obtained by this interaction technique, we designed an experimental protocol based on spatial input tasks. In our experiment, we asked our subjects to use only the dominant hand to achieve the different tasks or, on the contrary, to use both hands. Comparison of users’ performances – time and precision – shows that, without proper training, executing a task using two hands can be more time consuming than using one hand. In fact, the degree of symmetry of the tasks performed with each hand seems to have a significant impact on whether users take advantage of bimanual possibilities. Our results also show that bimanual interaction can introduce proprioceptive cues that can be of help to achieve more precision in the placement or selection only when proper visual information are missing.