Arcadio Reyes-Lecuona

Characterisation of Web traffic

In this work the authors show how the behaviour of Web users strongly affects the dynamics of TCP connections in Internet. Analysing actual and systematically generated HTTP traces, it is proved that the time between the download of two pages is critical to determine the re-utilisation of TCP connections. On the other hand, the study also shows that the utilisation of version 1.1 of the HTTP standard does not significantly affect the traffic generated by HTTP 1.0. In this sense, the heavy-tailed nature of the size of HTTP connections can be considered as an invariant property.

Improvement of perceived stiffness using auditory stimuli in haptic virtual reality

This paper describes a psychophysical experimental study to determinate whether time duration auditory information may improve the haptic perception of surface stiffness in a virtual environment (VE). In the experiment, the subjects were given the task of deciding which of two virtual surfaces is the stiffer one, via PHANToM, a haptic force feedback device, and displayed on a computer screen. They must tap both surfaces only one time and every time a surface is tapped, an auditory stimulus, synchronized with the tap, is played. Results indicate that auditory stimuli interfere on stiffness haptic perception. It showed that stiffness-duration factors interaction significantly influences on stiffness perception. We found that the subjects perceive coherence between auditory and haptic stimuli when shorter auditory stimuli are associated with stiffer haptic stimuli and vice versa. In case of non-coherence (stiffer surfaces associated to longer auditory stimuli and vice versa), the auditory stimulus misleads the subject providing a negative effect in the task of discerning the stiffer surface. Designers of VEs could use these results for improving stiffness haptic perception of virtual objects

The role of mismatches in the sensory feedback provided to indicate selection within a virtual environment

It is generally understood that virtual reality simulations have a high computational cost. Hence, they rarely can reduce completely all the incoherence within the cross-modal sensory outputs provided. The main research approaches to date have consisted in technically reducing possible mismatches, however minimal research has been conducted so as to analyse their influence on human capabilities. Thus, the objective of this study is to provide further insights to the designers of virtual reality about the negative influence of simulation lags and interesting design implications. To clearly show this, we have investigated the importance of coherent sensory feedback by incorporating time delays and spatial misalignments in the feedback provided by the simulation as a response to participant´s actions to mimic computationally expensive environments. We have also evaluated these misalignments considering two typical interaction setups. In particular, the sensory mismatches influence has been assessed in human factors, such as the sense of presence, task performance and delay perception. Our experimental results indicate that the closer the interaction conditions are to real configurations the higher the sensory requirements are regarding accuracy. The implications of this study offer the designer guidelines to prioritise the reduction of those mismatches in the sensory cues provided depending on the simulations goals.

Influence of Binocular Disparity in Depth Perception Mechanisms in Virtual Environments

In this chapter, an experimental study is presented for evaluating the importance of binocular disparity in depth perception within a Virtual Environment (VE), which is assumed to be critical in many manipulation tasks. In this research work, two assumptions are made: Size cues strongly contaminate depth perception mechanisms and binocular disparity optimizes depth perception for manipulation tasks in VE. The results outline size cues as possible cause of depth perception degradation and binocular disparity as an important factor in depth perception, whose influence is altered by the position within a VE.

A High-Level Haptic Interface for Enhanced Interaction within VirtoolsTM

Haptics is the outstanding technology to provide tri-dimensional interaction within Virtual Environments (VE). Nevertheless, many software solutions are not fully prepared to support Haptics. This paper presents a user-friendly implementation of Sensable Phantom haptic interfaces onto the interactive VE authoring platform, Virtools 4.0. Haptics implementation was realized using the Haptic Library (HLAPI) from OpenHaptics toolkit 2.0 which provides highly satisfactory custom forces effects. The integration of Phantom interaction at end-user development fulfils logical VE interactive authoring under Virtools. Haptics implementation was qualitatively assessed in a manual maintenance case, a welding task, as a part of the national Finnish project, VIRVO. Manipulation enhancements provided by the integration of Phantom interaction in Virtools suggest many further improvements for more complicated industrial pilot experiments as a part of the European Commission funded project ManuVAR.

The influence of different sensory cues as selection feedback and co-location in presence and task performance

For some applications based on virtual reality technology, presence and task performance are important factors to validate the experience. Different approaches have been adopted to analyse the extent to which certain aspects of a computer-generated environment may enhance these factors, but mainly in 2D graphical user interfaces. This study explores the influence of different sensory modalities on performance and the sense of presence experienced within a 3D environment. In particular, we have evaluated visual, auditory and active haptic feedback for indicating selection of virtual objects. The effect of spatial alignment between proprioceptive and visual workspaces (co-location) has also been analysed. An experiment has been made to evaluate the influence of these factors in a controlled 3D environment based on a virtual version of the Simon game. The main conclusions obtained indicate that co-location must be considered in order to determine the sensory needs during interaction within a virtual environment. This study also provides further evidence that the haptic sensory modality influences presence to a higher extent, and that auditory cues can reduce selection times. Conclusions obtained provide initial guidelines that will help designers to set out better selection techniques for more complex environments, such as training simulators based on VR technology, by highlighting different optimal configurations of sensory feedback.

New interaction paradigms in virtual environments

The way of interacting between user and environment is one of the main characteristics that increases the sense of presence inside a virtual world. However, interaction could be the weak point of virtual environments based applications. In this paper we present a very brief taxonomy of 3D interaction for virtual environments and discuss why interaction is, in our opinion, a key element in the new developments of virtual reality technology

Interference of Auditory Information with Haptic Perception of Stiffness in Virtual Reality

This paper describes an experimental study about how auditory stimuli interfere with haptic perception. Specifically, the interference of auditory stimulus duration with haptic perception of surface stiffness within a virtual environment is analysed. An experiment was performed in which subjects were asked to tap two virtual surfaces and to report which was stiffer. Our results show that there is an association between short auditory and stiff haptic stimuli, and between long auditory and soft haptic stimuli. Moreover, the influence of auditory information was stronger in the case of discriminating similar haptic stimuli when either facilitating or hindering this haptic discrimination.

The Delay Mirror: a Technological Innovation Specific to the Dance Studio

This paper1. evaluates the use of the Delay Mirror (DM) in the dance studio. The DM is a device that records a video stream which is rendered immediately on a large screen, but with a delay of a few seconds. A dancer can observe her own movements in the same way she would do so when looking at a normal mirror. However, the delay allows her to observe dynamic movements which cannot usually be observed other than in video. We evaluate whether this device can be useful in the context of a dance class, and whether it complements the normal mirror, while being less intrusive than a normal video recording which is recorded and then re-played, possibly interrupting workflow. Qualitative evaluation was performed in the context of an advanced-level adult ballet course.

Natural locomotion based on a reduced set of inertial sensors: decoupling body and head directions indoors

Inertial sensors offer the potential for integration into wireless virtual reality systems that allow the users to walk freely through virtual environments. However, owing to drift errors, inertial sensors cannot accurately estimate head and body orientations in the long run, and when walking indoors, this error cannot be corrected by magnetometers, due to the magnetic field distortion created by ferromagnetic materials present in buildings. This paper proposes a technique, called EHBD (Equalization of Head and Body Directions), to address this problem using two head- and shoulder-located magnetometers. Due to their proximity, their distortions are assumed to be similar and the magnetometer measurements are used to detect when the user is looking straight forward. Then, the system corrects the discrepancies between the estimated directions of the head and the shoulder, which are provided by gyroscopes and consequently are affected by drift errors. An experiment is conducted to evaluate the performance of this technique in two tasks (navigation and navigation plus exploration) and using two different locomotion techniques: (1) gaze-directed mode (GD) in which the walking direction is forced to be the same as the head direction, and (2) decoupled direction mode (DD) in which the walking direction can be different from the viewing direction. The obtained results show that both locomotion modes show similar matching of the target path during the navigation task, while DD’s path matches the target path more closely than GD in the navigation plus exploration task. These results validate the EHBD technique especially when allowing different walking and viewing directions in the navigation plus exploration tasks, as expected. While the proposed method does not reach the accuracy of optical tracking (ideal case), it is an acceptable and satisfactory solution for users and is much more compact, portable and economical.