Relative Position Of Target Research Articles

Competitive interactions in sensorimotor cortex: oscillations express separation between alternative movement targets.

Choice behavior is influenced by factors such as reward and number of alternatives but also by physical context, for instance, the relative position of alternative movement targets. At small separation, speeded eye or hand movements are more likely to land between targets (spatial averaging) than at larger separation. Neurocomputational models explain such behavior in terms of cortical activity being preshaped by the movement environment. Here, we manipulate target separation, as a determinant of motor cortical activity in choice behavior, to address neural mechanisms of response selection. Specifically, we investigate whether context-induced changes in the balance of cooperative and competitive interactions between competing groups of neurons are expressed in the power spectrum of sensorimotor rhythms. We recorded magnetoencephalography while participants were precued to two possible movement target locations at different angles of separation (30, 60, or 90°). After a delay, one of the locations was cued as the target for a joystick pointing movement. We found that late delay-period movement-preparatory activity increased more strongly for alternative targets at 30 than at 60 or 90° of separation. This nonlinear pattern was evident in slow event-related fields as well as in beta- and low-gamma-band suppression. A comparable pattern was found within an earlier window for theta-band synchronization. We interpret the late delay effects in terms of increased movement-preparatory activity when there is greater overlap and hence less competition between groups of neurons encoding two response alternatives. Early delay-period theta-band synchronization may reflect covert response activation relevant to behavioral spatial averaging effects.

Representation of Spatial- and Object-Specific Behavioral Goals in the Dorsal Globus Pallidus of Monkeys during Reaching Movement

The dorsal aspect of the globus pallidus (GP) communicates with the prefrontal cortex and higher-order motor areas, indicating that it plays a role in goal-directed behavior. We examined the involvement of dorsal GP neurons in behavioral goal monitoring and maintenance, essential components of executive function. We trained two macaque monkeys to choose a reach target based on relative target position in a spatial goal task or a target shape in an object-goal task. The monkeys were trained to continue to choose a certain behavioral goal when reward volume was constant and to switch the goals when the volume began to decrease. Because the judgment for the next goal was made in the absence of visual signals, the monkeys were required to monitor and maintain the chosen goals during the reaching movement. We obtained three major findings. (1) GP neurons reflected more of the relative spatial position than the shape of the reaching target during the spatial goal task. During the object-goal task, the shape of the reaching object was represented more than the relative position. (2) The selectivity of individual neurons for the relative position was enhanced during the spatial goal task, whereas the object-shape selectivity was enhanced during the object-goal task. (3) When the monkeys switched the goals, the selectivity for either the position or shape also switched. Together, these findings suggest that the dorsal GP is involved in behavioral goal monitoring and maintenance during execution of goal-oriented actions, presumably in collaboration with the prefrontal cortex.

Research of Intelligent Localization of Target for Manipulator Based on the Monocular Vision

A kind of calculation model of 3D space transformation is introduced, which is applicable to the monocular vision of robot manipulator, and the three-dimensional space plane mapping problem of image plane to the actual horizontal plane of monocular vision has been solved. It transforms the imaging coordinate system of target in monocular vision into the world coordinate system of the manipulator, so as to calculate the relative position of targets and the manipulator. The algorithm has better accuracy and reliability, which is proved by contrasting and testing the calculation result of object coordinate system transformed to the actual position coordinates to the sampling points in embedded platform.

ADAPTIVE RADIOTHERAPY TO ACCOUNT FOR GEOMETRIC DISCREPANCIES

Image-guidance for radiation therapy (IGRT) has emerged as a vital means of controlling the accuracy and precision of target localization in treatment delivery. In the case of imaging modalities that assess soft-tissues, the ability to direct radiation therapy by frequent imaging also opens the door to assess anatomical changes over the course of treatment. Anatomical changes can include, for example, tumour response to radiation and chemotherapy, variations in organ filling, deformation of the skeleton, weight loss/gain, all of which can alter the relative position and shape of targets and normal tissues and affect the delivery of the dose distribution with the accumulation of each treatment fraction.An treatment would respond, to at least some of this information, by guiding alterations to the treatment plan. The term Adaptive Radiation Therapy (ART) has been used to embody strategies that respond to patient setup uncertainties and organ movement, gross anatomical changes, and even physiological changes observed by MRI/MRS and PET. Changes to the treatment plan can mitigate uncertainties that compromise the dose to the target and critical structures or, should it arise, exploit an opportunity to improve normal tissue sparing. It is important to weight the benefit of these opportunities against the risks of introducing errors, reducing treatment efficiency, and increasing workload. The costs and benefits and approach to adaptation can be expected to be highly dependent on the disease site and the overall duration of treatment. The developing concepts of adaptive intervention have broad implications for radiotherapy treatment and the assessment of response. This presentation will review ART concepts, considerations for workflow, and its implications for error management, quality control and quality assurance. The role of imaging and image registration in the assessment of geometric variations and uncertainties will be reviewed, and some of the methods of quantifying uncertainties will be presented. The status of tools for supporting clinical workflow and appropriate quality assurance will be discussed.

Uncertainty of target volume and organ at risk during fractional radiotherapy

Anatomic structures and their relative position of the target and organs at risk surrounded will change more or less during fractional radiotherapy.These uncertainties will affect the practice of treatment planning correctly.The degree of these uncertainties can be investigated by imaging verification system during clinical practice.The possible reasons of these uncertainties may be tumor volume variations,organ motions orshape changes,patients weight or form changes and set-up errors.The development and practice of imageguided radiotherapy,dose guided radiotherapy and adaptive radiotherapy can offer rational approaches to over-come the uncertainties of the target and organ at risk surrounded during radiotherapy. Key words: Radiotherapy,conformal; Dose fractionation; Organ at risk

Assessing human reorientation ability inside virtual reality environments: the effects of retention interval and landmark characteristics

The purpose of the present study was to assess the navigational behaviour of adult humans following a disorientation procedure that perturbed their egocentric frame of reference. The assessment was carried out in a virtual reality (VR) environment by manipulating the disorientation procedure, the retention interval, the relative positions of target and landmark. The results of experiment I demonstrated that adding a physical rotation to a virtual disorientation procedure did not yield an additional decrease in searching performance. The results of experiment II showed that shortening the delay between study and test phase decreased the errors more markedly for geometric than landmark ones. An orientation specificity effect due to the manipulation of the relative position between target and landmark was discussed across the experiments. In conclusion, VR seemed to be a valuable method for studying human reorientation. Moreover, the virtual experimental setting involved here promoted knowledge of the relationship between working memory and spatial reorientation paradigm.

Transabdominal Ultrasonography, Computed Tomography and Electronic Portal Imaging for 3-Dimensional Conformal Radiotherapy for Prostate Cancer

To evaluate the feasibility and accuracy of daily B-mode acquisition and targeting ultrasound-based prostate localization (BAT) and to compare it with computed tomography (CT) and electronic portal imaging (EPI) in 3-dimensional conformal radiotherapy (3-D CRT) for prostate cancer. Ten patients were treated with 3-D CRT (72 Gy/30 fractions, 2.4 Gy/fraction, equivalent to 80 Gy/40 fractions, for alpha/beta ratio of 1.5 Gy) and daily BAT-based prostate localization. For the first 5 fractions, CT and EPI were also performed in order to compare organ-motion and set-up error, respectively. 287 BAT-, 50 CT- and 46 EPI-alignments were performed. The average BAT-determined misalignments in latero-lateral, antero-posterior and cranio-caudal directions were -0.9 mm+/-3.3 mm, 1.0 mm+/-4.0 mm and -0.9 mm+/-3.8 mm, respectively. The differences between BAT- and CT-determined organ-motion in latero-lateral, antero-posterior and cranio-caudal directions were 2.7 mm+/-1.9 mm, 3.9+/-2.8 mm and 3.4 +/- 3.0 mm, respectively. Weak correlation was found between BAT- and CT-determined misalignments in antero-posterior direction, while no correlation was observed in latero-lateral and cranio-caudal directions. The correlation was more significant when only data of good image-quality patients were analyzed (8 patients). BAT ensures the relative positions of target are the same during treatment and in treatment plan, however, the reliability of alignment is patient-dependent. The average BAT-determined misalignments were small, confirming the prevalence of random errors in 3-D CRT. Further study is warranted in order to establish the clinical value of BAT.

Kalman filtering for dynamic pose and relative motion estimation in orbit

<Abstract>The task of a space vision system for rendezvous, capture, and servicing of satellites on-orbit is the real-time determination of the relative pose of a target satellite as observed from a chaser spacecraft. The basic stand-alone task of a vision system is to return a snapshot and measurement of the position and orientation of the target at a moment in time. Augmenting this basic architecture with a Kalman filter, incorporating a dynamic model and the ability to propagate motion, synthesizes a system that is potentially more efficient and robust. Such a filter was designed and tested in a simulated orbital rendezvous scenario. This paper demonstrates a dynamics estimation filter based on extended Kalman filtering that can provide the vision system routines with improved initialization, leading to faster convergence and less computation, reliable pose estimation at slower sampling rates, and the ability to estimate target relative position, velocity, orientation, angular velocity, and mass-centre location.

Visual layout modulates Fitts’s law: The importance of first and last positions

When a target in the last position of a structured visual array is aimed for, movement times (MTs) are shorter than predicted by Fitts's law (Adam, Mol, Pratt, & Fischer, 2006). That study, however, confounded relative target position with absolute target location. To determine whether target position does, indeed, produce changes in the speed-accuracy trade-off function, the present experiment manipulated relative target position (e.g., first or last) independently of absolute target location (e.g., nearest or farthest). This was accomplished by presenting connected placeholders at three adjacent locations from a set of five possible locations (i.e., the middle location could be the first, middle, or last placeholder position in an array). The results of a speeded manual-pointing task showed that relative position is important for Fitts's law; when absolute location was held constant, shorter MTs were found for last-position than for middle-position targets. In addition, a similar effect was found for first-position targets. These results suggest that Fitts's law holds within, but not between, relative target positions in visible structured arrays.

The interaction of shape- and location-based priming in object categorisation: Evidence for a hybrid “what + where” representation stage

The relationship between part shape and location is not well elucidated in current theories of object recognition. Here we investigated the role of shape and location of object parts on recognition, using a classification priming paradigm with novel 3D objects. In Experiment 1, the relative displacement of two parts comprising the prime gradually reduced the priming effect. In Experiment 2, presenting single-part primes in locations progressively different from those in the composite target had no effect on priming. In Experiment 3, manipulating the relative position of composite prime and target strongly affected priming. Finally, in Experiment 4 the relative displacement of single-part primes and composite targets did influence response time. Together, these findings are best interpreted in terms of a hybrid theory, according to which conjunctions of shape and location are explicitly represented at some stage of visual object processing.

The education of attention in aiming at a far target: Training visual control in basketball jump shooting

We examined the effects of perceptual training on basketball jump shooting using a combination of single‐subject and group design. Six participants received eight weeks of visual control training in which they only had vision during the final ∼350 ms before ball release (the final period). Taking an ecological approach to perceptual learning, we expected that this would force participants to pick up relevant information until ball release, allowing for the use of the latest possible update of the relative target position. The training consisted of shooting from behind a screen and shooting while wearing liquid‐crystal goggles. Participants increased their final period duration. In addition, they increased their field goal and three‐point percentages in games, in contrast to four control participants from the same team. It is concluded that visual control training can change the temporal pattern of shooting and improve performance by enhancing the timing of information detection.

Fission and Fusion at the End of the Periodic System

We calculate in a macroscopic-microscopic model fission potential-energy surfaces for neutron-rich actinides and fission-fusion potential-energy surfaces relevant to the analysis of heavy-ion reactions employed to form heavy-element evaporation residues. We study the latter multidimensional potential-energy surfaces both inside and outside the touching point. Inside the point of contact we define the potential on a multi-million-point grid in 5D deformation space where elongation, merging projectile and target spheroidal shapes, neck radius and projectile/target mass asymmetry are independent shape variables. The same deformation space and the corresponding potential-energy also describe the shape evolution from the nuclear ground-state to separating fragments in fission, and the fast-fission trajectories in incomplete fusion. For separated nuclei we study the macroscopic-microscopic potential energy, that is the collision surface between a spheroidally deformed target and a spheroidally deformed projectile as a function of three coordinates which are: the relative location of the projectile center-of-mass with respect to the target center-of-mass and the spheroidal deformations of the target and the projectile. We limit our study to the most favorable relative positions of target and projectile, namely that the symmetry axes of the target and projectile are collinear. We also calculate fission barriers for a long sequence of uranium isotopes. The aim is to understand another attempted production mechanism for superheavy elements, namely neutron-capture in thermonuclear explosions.

Influences of response-activating stimuli and passage of time on the Simon effect

Two possible explanations for an interaction between the Simon effect and the flanker-congruence effect (Hommel, 1997) were tested: (1) Direct contributions by the locations of the response-activating flankers to the Simon effect, and (2) the passage of time since the target's onset. In three experiments, little evidence for both explanations was observed. The data confirmed an assumed origin of the Simon effect at the stage of response selection. Further, the results are in line with the assumption that context stimuli contribute indirectly to the Simon effect of the target (i.e., by changing the target's relative position), and extend previous findings to show that the assumption holds for clearly response-activating context stimuli, too. Finally, the results suggest that Simon effects follow different time courses depending on whether they are induced by observer-relative or context-relative target positions.

ファジー推論ニューラルネットワークによる位置関係を考慮した風景画像の認識

In this paper, we propose a new system for recognition of scenery images, by learning. The proposed system consists of 2 parts. One is the part which infers based on absolute position of target. The other is the part which infers based on relative position of target. Each part consists of Fuzzy Inference Neural Network (FINN) which can extract fuzzy if-then rules automatically. So the system can extract knowledge about absolute position and relative position. Through computer experiments, it can be seen that the proposed system can recognize the image much correctly.

Terminal Area Navigation Using Relative GPS Bias States with a Terrain Scene

ABSTRACT: By using GPS target relative position bias states in the Kalman filter of a guided weapon, the effects of GPS pseudorange bias errors and absolute target location errors can be removed almost entirely if the bias states are invoked following a high-quality terrain scene position update. The performance of a guided weapon with these bias states is analyzed by means of a covariance simulation along with, for the sake of comparison, the performance of a relative GPS scheme employing a correction vector established at the terrain scene, outside of the system Kalman filter. The scenario investigated is an air-launched cruise missile flying a trajectory with a terrain scene preceding the target by 75 nmi in an environment with no GPS jammers, with three high-powered GPS jammers, and with an array of low-powered GPS jammers.

Range accuracy: One more peculiarity of the dolphin’s sonar

In order to measure range accuracy in the dolphin, a range difference discrimination experiment should be performed. However, when two targets are presented at different distances simultaneously, even at an angle as big as 40–60=B0, one dolphin’s click can cause echoes from both targets. As a result, the targets can be distinguished by the difference in the echo arrival time without measuring the target distance. The best way to prevent the dolphin from simultaneous targets insonifying by each click turned out to be successive submerging of the targets in water at different distances from the dolphin. Nevertheless, it proved to be impossible to force the dolphin to measure the distance from itself to the targets. Two dolphins solved the task by measuring the time interval between the target echo and echo from a reference object; that could be the pool walls or even a nylon net. There was no consistent change in the threshold range difference with the targets’ range, whereas it regularly decreased when the targets were moved closer to the reference object. The dolphins preferred to measure the relative target position even if the reference object was at a much greater distance than the targets.

Sensor-based fuzzy reactive navigation of a mobile robot through local target switching

Fuzzy reactive control, incorporating a local target switching scheme, is applied to the automatic navigation of an intelligent mobile robot in an unknown and changing environment. Sensed-ranging signals and relative target position signals are input to the fuzzy controller. The steering angle and the velocity change are inferred to drive the mobile robot. A reactive rule base governing the robot behavior is synthesized from the human heuristics with respect to various situations of environment. A local target switching scheme is proposed to serve as a front-end processor of the fuzzy active controller and to deal with the local trapping and wandering cycle problem in the navigation of a behavior based mobile robot. The algorithm is described, together with some particular considerations about implementation. Efficiency and effectiveness of the proposed approach are verified through simulation and experiments conducted on a Nomad 200 mobile robot.

Fuzzy reactive control of a mobile robot incorporating a real/virtual target switching strategy

Real-time fuzzy reactive control is investigated for automatic navigation of an intelligent mobile robot in an unknown and changing environment. The reactive rulebase governing the robot behavior is synthesized corresponding to the various situations defined by the instant robot motion, environment and target information. Navigation control of the robot is realized through fuzzy coordination of all the rules. Sensed ranging and relative target position signals are input to the fuzzy controller while the steering angle and the velocity change are inferred to drive the mobile robot. For the robot to efficiently tackle unwanted local trapping and oscillation problems, a real/virtual target switching strategy is presented to serve as a preprocessor for the proposed fuzzy reactive controller. Simulation and experimental results are presented to validate the approach.

Real-time self-reaction of a mobile robot in unstructured environments using fuzzy reasoning

The automatic reaction of a mobile robot, computed in real time during its movement towards a target, in an open field with obstacles present, is dealt with in this paper. Two types of reaction strategies are worked out, based on human experience, and reaction rules governing the system behavior are synthesized corresponding to the different situations defined by the obstacle position, the target orientation and the robot's direction of movement. Navigation control of the robot is then realized through fuzzy reasoning of the above heuristic rules. Sensed ranging and relative target position signals are input to the controller, while a steering output is inferred to drive the mobile robot. The processes of fuzzy reaction are described in terms of information flow, including fuzzification, inference, aggregation and defuzzification. Simulation results of a mobile robot avoiding unknown obstacles are given to demonstrate the effectiveness of the approach presented.

A pop-out induced extinction-like phenomenon in neurologically intact subjects

A series of tachistoscopic search experiments was performed to investigate variations of distractor effects dependent on the relative position and salience of target and distractor. It was found that highly salient (pop out) items distracted search for less salient (conjunction) targets and vice versa. However, only the effect of pop-out distractors was lateralized when paired with a contralateral target, RVF-distractors leading to a stronger latency increase. With unimanual response, this effect was stronger in the right hand. When the distractors were presented in the same visual halffield (VF) as the targets, effects were of comparable size in both VF.