Intercepting moving targets: does memory from practice in a specific condition of target displacement affect movement timing?

This investigation aimed at assessing the extent to which memory from practice in a specific condition of target displacement modulates temporal errors and movement timing of interceptive movements. We compared two groups practicing with certainty of future target velocity either in unchanged target velocity or in target velocity decrease. Following practice, both experimental groups were probed in the situations of unchanged target velocity and target velocity decrease either under the context of certainty or uncertainty about target velocity. Results from practice showed similar improvement of temporal accuracy between groups, revealing that target velocity decrease did not disturb temporal movement organization when fully predictable. Analysis of temporal errors in the probing trials indicated that both groups had higher timing accuracy in velocity decrease in comparison with unchanged velocity. Effect of practice was detected by increased temporal accuracy of the velocity decrease group in situations of decreased velocity; a trend consistent with the expected effect of practice was observed for temporal errors in the unchanged velocity group and in movement initiation at a descriptive level. An additional point of theoretical interest was the fast adaptation in both groups to a target velocity pattern different from that practiced. These points are discussed under the perspective of integration of vision and motor control by means of an internal forward model of external motion.

Use of peripheral vision in the interception of moving targets

Use of peripheral vision to organize and reorganize an interceptive action was investigated in young adults. Temporal errors and kinematic variables were evaluated in the interception of a virtual moving target, in situations in which its initial velocity was kept unchanged or was unexpectedly decreased. Observation of target approach was made through continuous visual pursuit (focal vision) or keeping visual focus at the origin of the trajectory or at the contact spot (peripheral vision). Results showed that visual focus at the contact spot led to temporal errors similar to focal vision, although showing a distinct kinematic profile, while focus at the origin led to an impoverished performance

Study of the effects of moving targets in SAR images for their detection.

Synthetic Aperture Radar’s (SAR) are systems designed in the early 50’s that are capable of obtaining images of the ground using electromagnetic signals. Thus, its activity is not interrupted by adverse meteorological conditions or during the night, as it occurs in optical systems. The name of the system comes from the creation of a synthetic aperture, larger than the real one, by moving the platform that carries the radar (typically a plane or a satellite). It provides the same resolution as a static radar equipped with a larger antenna. As it moves, the radar keeps emitting pulses every 1/PRF seconds —the PRF is the pulse repetition frequency—, whose echoes are stored and processed to obtain the image of the ground. To carry out this process, the algorithm needs to make the assumption that the targets in the illuminated scene are not moving. If that is the case, the algorithm is able to extract a focused image from the signal. However, if the targets are moving, they get unfocused and/or shifted from their position in the final image. There are applications in which it is especially useful to have information about moving targets (military, rescue tasks,studyoftheflowsofwater,surveillanceofmaritimeroutes...).Thisfeatureiscalled Ground Moving Target Indicator (GMTI). That is why the study and the development of techniques capable of detecting these targets and placing them correctly in the scene is convenient. In this document, some of the principal GMTI algorithms used in SAR systems are detailed. A simulator has been created to test the features of each implemented algorithm on a general situation with moving targets. Finally Monte Carlo tests have been performed, allowing us to extract conclusions and statistics of each algorithm.

The moving targets algorithm for difficult temporal credit assignment problems

The 'moving targets' algorithm for training recurrent networks is reviewed and applied to a task which demonstrates the ability of this algorithm to use distant contextual information. Some practical difficulties are discussed, especially with regard to the minimization process. Results on performance and computational requirements of several different 2nd-order minimization algorithms are presented for moving target problems.

The 'moving targets' training algorithm

A simple method for training the dynamical behavior of a neural network is derived. It is applicable to any training problem in discrete-time networks with arbitrary feedback. The algorithm resembles back-propagation in that an error function is minimized using a gradient-based method, but the optimization is carried out in the hidden part of state space either instead of, or in addition to weight space. Computational results are presented for some simple dynamical training problems, one of which requires response to a signal 100 time steps in the past.

The 'moving targets' training algorithm

A simple method for training the dynamical behavior of a neural network is derived. It is applicable to any training problem in discrete-time networks with arbitrary feedback. The method resembles back-propagation in that it is a least-squares, gradient-based optimization method, but the optimization is carried out in the hidden part of state space instead of weight space. A straightforward adaptation of this method to feedforward networks offers an alternative to training by conventional back-propagation. Computational results are presented for simple dynamical training problems, with varied success. The failures appear to arise when the method converges to a chaotic attractor. A patch-up for this problem is proposed. The patch-up involves a technique for implementing inequality constraints which may be of interest in its own right.

Control of interceptive actions is based on expectancy of time to target arrival

In this study the hypothesis that interceptive movements are controlled on the basis of expectancy of time to target arrival was tested. The study was conducted through assessment of temporal errors and kinematics of interceptive movements to a moving virtual target. Initial target velocity was kept unchanged in part of the trials, and in the others it was decreased 300 ms before the due time of target arrival at the interception position, increasing in 100 ms time to target arrival. Different probabilities of velocity decrease ranging from 25 to 100% were compared. The results revealed that while there were increasing errors between probabilities of 25 and 75% for unchanged target velocity, the opposite relationship was observed for target velocity decrease. Kinematic analysis indicated that movement timing adjustments to target velocity decrease were made online. These results support the conception that visuomotor integration in the interception of moving targets is mediated by an internal forward model whose weights can be flexibly adjusted according to expectancy of time to target arrival.

Tiedon hajautus johtamisjärjestelmässä ja DDS-teknologia

Verkostokeskeisessä sodankäynnissä tietojärjestelmien suurimpana haasteena on oikean tiedon hajauttaminen oikeaan paikkaan ja aikaan. Tietojärjestelmissä esitettävän ilmatilannekuvan tulee vastata reaalimaailman tilannetta parhaalla mahdollisella tavalla. Ilmatorjunnassa reaaliaikaisuus nousee erityisen suureen rooliin nopeasti liikkuvien kohteiden takia. Tämä diplomityö on tehty Insta DefSec Oy:ssä liittyen johtamisjärjestelmän uudistamishankkeeseen. Työn vaatimuksina olivat standardeihin perustuvat ratkaisut, joista keskeisimmäksi nousi Data Distribution Service -standardi (DDS) ja sen hyödyntäminen osana johtamisjärjestelmän tiedon hajautusta. Työssä esitellään johtamisjärjestelmien tiedon hajautukseen liittyviä haasteita sekä paikallisessa että maantieteellisesti hajautetussa toimintaympäristössä. Työssä toteutettiin liityntäohjelmisto nykyisen ja uuden johtamisjärjestelmän välille. Liityntäohjelmiston tehtävänä on tuottaa reaaliaikaista ilmatilannekuvaa nykyisestä johtamisjärjestelmästä uuteen johtamisjärjestelmään. DDS-standardin toteuttavana välikerrosarkkitehtuurina käytettiin OpenSplice DDS -tuotetta. Valittu teknologia tarjoaa edistykselliset julkaisija–tilaaja-mallin mukaiset menetelmät tiedon reaaliaikaiseen hajauttamiseen. DDS:n arkkitehtuuri ja palvelun laadun mekanismit mahdollistavat tiedon hajautuksen sodanajan johtamisjärjestelmille.

A Psychophysical Assessment of Multisensory Processing and Multiple Object Tracking in Autism Spectrum Disorders

Les troubles du spectre autistique (TSA) sont actuellement caractérisés par une triade d'altérations, incluant un dysfonctionnement social, des déficits de communication et des comportements répétitifs. L'intégration simultanée de multiples sens est cruciale dans la vie quotidienne puisqu'elle permet la création d'un percept unifié. De façon similaire, l'allocation d'attention à de multiples stimuli simultanés est critique pour le traitement de l'information environnementale dynamique. Dans l'interaction quotidienne avec l'environnement, le traitement sensoriel et les fonctions attentionnelles sont des composantes de base dans le développement typique (DT). Bien qu'ils ne fassent pas partie des critères diagnostiques actuels, les difficultés dans les fonctions attentionnelles et le traitement sensoriel sont très courants parmi les personnes autistes. Pour cela, la présente thèse évalue ces fonctions dans deux études séparées. La première étude est fondée sur la prémisse que des altérations dans le traitement sensoriel de base pourraient être à l'origine des comportements sensoriels atypiques chez les TSA, tel que proposé par des théories actuelles des TSA. Nous avons conçu une tâche de discrimination de taille intermodale, afin d'investiguer l'intégrité et la trajectoire développementale de l'information visuo-tactile chez les enfants avec un TSA (N = 21, âgés de 6 à18 ans), en comparaison à des enfants à DT, appariés sur l’âge et le QI de performance. Dans une tâche à choix forcé à deux alternatives simultanées, les participants devaient émettre un jugement sur la taille de deux stimuli, basé sur des inputs unisensoriels (visuels ou tactiles) ou multisensoriels (visuo-tactiles). Des seuils différentiels ont évalué la plus petite différence à laquelle les participants ont été capables de faire la discrimination de taille. Les enfants avec un TSA ont montré une performance diminuée et pas d'effet de maturation aussi bien dans les conditions unisensorielles que multisensorielles, comparativement aux participants à DT. Notre première étude étend donc des résultats précédents d'altérations dans le traitement multisensoriel chez les TSA au domaine visuo-tactile. Dans notre deuxième étude, nous avions évalué les capacités de poursuite multiple d’objets dans l’espace (3D-Multiple Object Tracking (3D-MOT)) chez des adultes autistes (N = 15, âgés de 18 à 33 ans), comparés à des participants contrôles appariés sur l'âge et le QI, qui devaient suivre une ou trois cibles en mouvement parmi des distracteurs dans un environnement de réalité virtuelle. Les performances ont été mesurées par des seuils de vitesse, qui évaluent la plus grande vitesse à laquelle des observateurs sont capables de suivre des objets en mouvement. Les individus autistes ont montré des seuils de vitesse réduits dans l'ensemble, peu importe le nombre d'objets à suivre. Ces résultats étendent des résultats antérieurs d'altérations au niveau des mécanismes d'attention en autisme quant à l'allocation simultanée de l'attention envers des endroits multiples. Pris ensemble, les résultats de nos deux études révèlent donc des altérations chez les TSA quant au traitement simultané d'événements multiples, que ce soit dans une modalité ou à travers des modalités, ce qui peut avoir des implications importantes au niveau de la présentation clinique de cette condition.

Investigating novel point-select techniques for older people

As the number and proportion of older people worldwide continues to grow, robotic devices can play a role in helping older people continue to live independent and active lives. Graphical user interfaces (GUIs) and interactions that involve pointing to items and selecting them are becoming more common in assistive robots. The authors are currently working on a project investigating techniques to improve point-select interactions for older people. In particular, the project studies how older people respond to expanding and moving targets. The research is ongoing, and this paper describes the methods that will be used in upcoming experiments.

Automatic camera control in virtual environments augmented using multiple sparse videos

Automated virtual camera control has been widely used in animation and interactive virtual environments. We have developed a multiple sparse camera based free view video system prototype that allows users to control the position and orientation of a virtual camera, enabling the observation of a real scene in three dimensions (3D) from any desired viewpoint. Automatic camera control can be activated to follow selected objects by the user. Our method combines a simple geometric model of the scene composed of planes (virtual environment), augmented with visual information from the cameras and pre-computed tracking information of moving targets to generate novel perspective corrected 3D views of the virtual camera and moving objects. To achieve real-time rendering performance, view-dependent textured mapped billboards are used to render the moving objects at their correct locations and foreground masks are used to remove the moving objects from the projected video streams. The current prototype runs on a PC with a common graphics card and can generate virtual 2D views from three cameras of resolution 768 x 576 with several moving objects at about 11 fps. (C)2011 Elsevier Ltd. All rights reserved.

Video target tracking by using competitive neural networks

A target tracking algorithm able to identify the position and to pursuit moving targets in video digital sequences is proposed in this paper. The proposed approach aims to track moving targets inside the vision field of a digital camera. The position and trajectory of the target are identified by using a neural network presenting competitive learning technique. The winning neuron is trained to approximate to the target and, then, pursuit it. A digital camera provides a sequence of images and the algorithm process those frames in real time tracking the moving target. The algorithm is performed both with black and white and multi-colored images to simulate real world situations. Results show the effectiveness of the proposed algorithm, since the neurons tracked the moving targets even if there is no pre-processing image analysis. Single and multiple moving targets are followed in real time.

Post processing of multiple GPS receivers to enhance baseline accuracy

Inexpensive, commercial available off-the-shelf (COTS) Global Positioning Receivers (GPS) have typical accuracy of ±3 meters when augmented by the Wide Areas Augmentation System (WAAS). There exist applications that require position measurements between two moving targets. The focus of this work is to explore the viability of using clusters of COTS GPS receivers for relative position measurements to improve their accuracy. An experimental study was performed using two clusters, each with five GPS receivers, with a fixed distance of 4.5 m between the clusters. Although the relative position was fixed, the entire system of ten GPS receivers was on a mobile platform. Data was recorded while moving the system over a rectangular track with a perimeter distance of 7564 m. The data was post processed and yielded approximately 1 meter accuracy for the relative position vector between the two clusters.

Scanned Ion Beam Therapy for Thoracic Tumors

Although frequently cured of Hodgkin lymphoma, adolescents and young adults can develop radiation induced second cancers. These patients could potentially benefit from scanned ion radiotherapy yet likely would require motion mitigation strategies. In theory, four-dimensional (4D) optimization of ion beam fields for individual motion states of respiration can enable superior sparing of healthy tissue near moving targets, compared to other motion mitigation strategies. Furthermore, carbon-ion therapy can sometimes provide greater relative biological effectiveness (RBE) for cell sterilization in a target but nearly equivalent RBE in tissue upstream of the target, compared to proton therapy. Thus, we expected that for some patients with Hodgkin lymphoma, carbon-ion therapy would reduce the predicted risk of second cancer incidence in the breast compared with proton therapy. The purpose of this work was to determine whether 4D-optimized carbon-ion therapy would significantly reduce the predicted risk of radiation induced second cancers in the breast for female Hodgkin lymphoma patients while preserving tumor control compared with proton therapy. To achieve our goals, we first investigated whether 4D-optimized carbon beam tracking could reduce dose to volumes outside a moving target compared with 3D-optimized carbon beam tracking while preserving target dose coverage. To understand the reliability of scanned carbon beam tracking, we studied the robustness of dose distributions in thoracic targets to uncertainties in patient motion. Finally, we investigated whether using carbon-ion therapy instead of proton therapy would significantly reduce the predicted risk of second cancer in the breast for a sample of Hodgkin lymphoma patients. We found that 4D-optimized ion beam tracking therapy can reduce the maximum dose to critical structures near a moving target by as much as 53%, compared to 3D-optimized ion beam tracking therapy. We validated these findings experimentally using a scanned carbon ion synchrotron and a motion phantom. We found scanned carbon beam tracking to be sensitive to a number of motion uncertainties, most notably phase delays in tracking, systematic spatial errors, and interfractional motion changes. Our findings indicate that a lower risk of second cancer in the breast might be expected for some Hodgkin lymphoma patients using carbon-ion therapy instead of proton therapy. For our reference scenario, we found the ratio of risk to be 0.77 ± 0.35 for radiogenic breast cancer after carbon-ion therapy versus proton therapy. Our findings were dependent on the RBE values for tumor induction and the radiosensitivity of breast tissue, as well as the physical dose distribution.

Analytical evaluation of uncertainty on active antenna arrays

An analytical method for evaluating the uncertainty of the performance of active antenna arrays in the whole spatial spectrum is presented. Since array processing algorithms based on spatial reference are widely used to track moving targets, it is essential to be aware of the impact of the uncertainty sources on the antenna response. Furthermore, the estimation of the direction of arrival (DOA) depends on the array uncertainty. The aim of the uncertainties analysis is to provide an exhaustive characterization of the behavior of the active antenna array associated with its main uncertainty sources. The result of this analysis helps to select the proper calibration technique to be implemented. An illustrative example for a triangular antenna array used for satellite tracking is presented showing the suitability of the proposed method to carry out an efficient characterization of an active antenna array.