Target Width Research Articles

Age-related changes of movement patterns in discrete Fitts’ task

BackgroundInspired by the framework of dynamical system theory, we aimed at exploring how the behavioural repertoire of the sensorimotor system can be reshaped with aging. Our reasoning was founded on the assumption that, with age, some of the existing patterns can be destabilized or even lost. In the present paper, this issue was investigated through the study of age-related changes in the movement patterns that are used to perform a discrete Fitts’ task. We analysed the performance of two groups of participants (young and older adults) across nine task difficulty levels, obtained via manipulation of target width.ResultsTwo movement patterns were revealed by the fact that increase in the index of the difficulty (ID) was accommodated through either the lengthening of both acceleration (AT) and deceleration (DT) times (co-variation pattern), or only DT (dissociation pattern). Analysis of the discontinuity in ID-AT relation showed that young participants switched from the co-variation to the dissociation pattern as ID increased. Pattern switching was accompanied by concomitant changes in the variability of AT/DT ratio. Older adults, on the other hand, used the dissociation pattern regardless of the ID. Consequently, they showed neither an abrupt discontinuity in ID-AT relation nor significant changes in the variability of AT/DT ratio across difficulty levels. Though the dissociation pattern was adaptive in young adults for high accuracy constraints, in older adults, it compromised task performance for lower difficulty levels.ConclusionThese findings support the view that aging may result in a compression of the neuro-behavioural repertoire. In sensorimotor tasks, it can lead to a loss of multi-stability in terms of available movement patterns, thereby compromising the ability of the neuro-musculo-skeletal system to adapt and face task constraints.

Sharpening Sidescan Sonar Images for Shallow-Water Target and Habitat Classification With a Vertically Stacked Array

Sidescan imagery is commonly used to provide a 2-D real-time “look” at the seafloor in high resolution. In shallow-water environments, however, interference from surface scattering and from multipath signals may deteriorate the quality of the sidescan images to the point where target detection and classification are no longer achievable. This paper investigates the extent to which this interference may be suppressed by a small array which employs across-track beamforming. A sidescan array utilizing a vertical stack of six receive elements was constructed, and is shown to be effective at providing a clear view of the seafloor when surface and multipath interference is present. A theoretical analysis examines the relative path strengths of the received signals for different across-track beam patterns, and examines how these signals are affected when beamforming is applied on transmit and/or receive. Shadow contrast reduction caused by the along-track beamwidth is also considered for different along-track beam patterns and different target widths. A simulator was created to illustrate the impact of interference contributing to the received signal, and to show how the received signal is affected when beamforming is applied. The across-track beam patterns of the experimental array were measured, and these data are used to enhance the theoretical and simulated predictions of received signal strength. Experimental data are also presented in which a sidescan image, heavily contaminated by interference, is significantly improved using across-track beamforming. It is concluded that a vertically stacked multielement sidescan sonar which employs across-track beamforming on receive is a valuable tool for suppressing the multipath and surface interference which arise in shallow-water surveys.

Trial-to-Trial Reoptimization of Motor Behavior Due to Changes in Task Demands Is Limited

Each task requires a specific motor behavior that is tuned to task demands. For instance, writing requires a lot of accuracy while clapping does not. It is known that the brain adjusts the motor behavior to different task demands as predicted by optimal control theory. In this study, the mechanism of this reoptimization process is investigated by varying the accuracy demands of a reaching task. In this task, the width of the reaching target (0.5 or 8 cm) was varied either on a trial-to-trial basis (random schedule) or in blocks (blocked schedule). On some trials, the hand of the subjects was clamped to a rectilinear trajectory that ended 2 cm on the left or right of the target center. The rejection of this perturbation largely varied with target width in the blocked schedule but not in the random schedule. That is, subjects exhibited different motor behavior in the different schedules despite identical accuracy demands. Therefore, while reoptimization has been considered immediate and automatic, the differences in motor behavior observed across schedules suggest that the reoptimization of the motor behavior is neither happening on a trial-by-trial basis nor obligatory. The absence of trial-to-trial mechanisms, the inability of the brain to adapt to two conflicting task demands and the existence of a switching cost are discussed as possible sources of the non-optimality of motor behavior during the random schedule.

Micro-movements of varying difficulties: wrist and arm movements

An experiment was designed to determine the degree to which reducing movement amplitude (16°, 8°, to 4°) while keeping the relative accuracy requirements (IDs 1.5, 3, 4.5, and 6) and visual feedback display constant by increasing the display gain proportional to the decrease in amplitude (1×, 2×, 4×) influences reciprocal aiming movements of the wrist and arm. Research on smaller amplitude movements is limited and inconclusive, but these types of movement conditions are becoming increasingly more important as microsurgery and micro-mechanical applications increase. Participants were asked to flex/extend their limb/lever in the horizontal plane at the wrist (arm stabilized) or elbow joint (wrist stabilized) in an attempt to move back and forth between two targets as quickly and accurately as possible. The targets and current position of the limb were projected on the screen in front of the participant. Target width was manipulated with amplitude constant (16°, 8° or 4°). Results indicated that the linear relationship between MT and ID, typically observed for Fitts' tasks, was observed. There were moderate decreases in MT as amplitude was decreased but only for high ID movements. ID 6 movements at 4° amplitude, for example, were produced more quickly than at amplitude 16° without sacrificing end-point accuracy. The decrease in movement time was, however, related to increased dwell time and very low peak velocities.

Aging of sensorimotor processes: a systematic study in Fitts’ task

Though age-related decrease in information-processing capacities is hypothesized to be a prominent cause of behavioral slowing, it has been scarcely systematically studied in goal-directed motor tasks. The present study investigated how the decrease in information processing affects the sensorimotor processes underlying the control of a discrete Fitts' task. The index of difficulty (ID) of the task was manipulated using changes in either target distance (D) or target width (W). In each manipulation, movement (MTs), acceleration (ATs) and deceleration times (DTs) of young and older participants were compared across eight ID levels. They were analyzed with efficiency functions, state traces and Brinley plots. Our results showed that older participants were always slower. However, in both age groups, MTs were longer in D manipulation, which resulted from a slowing of both ATs and DTs, while W manipulation affected mainly DTs. In D manipulation, equivalent age-related slowing ratios were observed for AT and DT (1.3). In W manipulation, ATs of older participants were additively slower than those of young participants. Conversely, DTs presented a multiplicative slowing ratio of 1.3. These findings showed that ID manipulations differentially loaded information processing in the nervous system and that age-related slowing of multisensory control processes was independent of the manipulated dimension. Nevertheless, ID manipulations revealed different age-related adaptations to task constraints, suggesting that D and W manipulations are complementary means to assess age-related slowing of the processes involved in target-directed rapid-aiming tasks, with D scaling being more specific to capture the slowing of force-impulse control.

Double Relativistic Electron Accelerating Mirror

In the present paper, the possibility of generation of thin dense relativistic electron layers is shown using the analytical and numerical modeling of laser pulse interaction with ultra-thin layers. It was shown that the maximum electron energy can be gained by optimal tuning between the target width, intensity and laser pulse duration. The optimal parameters were obtained from a self-consistent system of Maxwell equations and the equation of motion of electron layer. For thin relativistic electron layers, the gaining of maximum electron energies requires a second additional overdense plasma layer, thus cutting the laser radiation off the plasma screen at the instant of gaining the maximum energy (DREAM-schema).

Feasibility of transrectal ultrasonography for assessment of cervical cancer

To retrospectively compare the maximum target width and target thickness in patients with locally advanced cervical cancer between magnetic resonance imaging (MRI) and transrectal ultrasonography (TRUS) in the course of primary radiochemotherapy. T2-weighted MRI and TRUS were performed on patients with locally advanced cervical cancer at the same timepoint-either at the time of diagnosis, or at the time of brachytherapy before or after insertion of the applicator. Patients treated from 2009 to 2011 were selected for this study based on the availability of MRI and TRUS at the defined time points. The target was defined as the complete macroscopic tumor mass and the remaining cervix and was measured on transversal planes. Descriptive statistics and a linear regression analysis were performed for the groups. Images from 17 patients were available for analysis. Mean maximum target width was 4.2 ± 0.83 cm and 4.2 ± 0.79 cm for MRI and TRUS, respectively. Mean maximum target thickness was 3.3 ± 1.03 cm and 3.1 ± 1.15 cm for MRI and TRUS, respectively. Linear regression analysis for target width and thickness between TRUS and MRI demonstrated a correlation with R(2) = 0.842 and R(2) = 0.943, respectively. The feasibility of TRUS for the assessment of local target extension could be demonstrated. Comparison of the target width and thickness showed a high correlation between TRUS and MRI, indicating the potential of TRUS for target definition in image-guided adaptive brachytherapy.

Two-Part Models Capture the Impact of Gain on Pointing Performance

We establish that two-part models of pointing performance (Welford’s model) describe pointing on a computer display significantly better than traditional one-part models (Fitts’s Law). We explore the space of pointing models and describe how independent contributions of movement amplitude and target width to pointing time can be captured in a parameter k . Through a reanalysis of data from related work we demonstrate that one-part formulations are fragile in describing pointing performance, and that this fragility is present for various devices and techniques. We show that this same data can be significantly better described using two-part models. Finally, we demonstrate through further analysis of previous work and new experimental data that k increases linearly with gain. Our primary contribution is the demonstration that Fitts’s Law is more limited in applicability than previously appreciated, and that more robust models, such as Welford’s formulation, should be adopted in many cases of practical interest.

Agonistic and antagonistic interaction in speed/accuracy tradeoff: A delta-lognormal perspective

This paper reports the results of a model-based analysis of movements gathered in a 4×4 experimental design of speed/accuracy tradeoffs with variable target distances and width. Our study was performed on a large (120 participants) and varied sample (both genders, wide age range, various health conditions). The delta-lognormal equation was used for data modeling to investigate the interaction between the output of the agonist and the antagonist neuromuscular systems. Empirical observations show that the subjects must correlate more tightly the impulse commands sent to both neuromuscular systems in order to achieve good performances as the difficulty of the task increases whereas the correlation in the timing of the neuromuscular action co-varies with the size of the geometrical properties of the task. These new phenomena are discussed under the paradigm provided by the Kinematic Theory and new research hypotheses are proposed for further investigation of the speed/accuracy tradeoffs.

Optimum 2-D Nonuniform Spatial Sampling for Microwave SAR-Based NDE Imaging Systems

Microwave and millimeter-wave synthetic aperture radar (SAR)-based imaging techniques, which are used for nondestructive evaluation (NDE), have shown tremendous usefulness for the inspection of a wide variety of complex composite materials and structures. An important practical issue associated with these imaging techniques is the required criteria associated with the physical gathering of the imaging data. In previous work on uniform sampling optimization, it was shown that the (uniform) spatial sampling density should be higher than the Nyquist density if preservation of spatial resolution, as defined by the half-power width of an ideal point target, is of interest. Conversely, nonuniform sampling has shown to provide effective signal reconstruction even for average spatial sampling densities below the Nyquist density-a distinct advantage over uniform sampling. This paper presents a comprehensive study into the optimization of nonuniform sampling for microwave SAR-based NDE imaging using three typical reconstruction techniques for nonuniformly sampled data, including natural interpolation, area-weighted Fourier integration, and conjugate gradient residual error minimization methods. To study the efficacy of these reconstruction methods, simulations of a point target were performed for a range of target distances and a range of average spatial sample separations. Resulting SAR images from the reconstruction techniques are then analyzed and compared according to two metrics: error between an image and an ideal image and resolution as determined by the half-power width of a point target. This is followed by experimental results corroborating the simulation results. Finally, nonuniform sampling requirements, given a minimum metric performance, are generalized for a given imager aperture size.

Additional load decreases movement time in the wrist but not in arm movements at ID 6

An experiment using reciprocal arm and wrist aiming movements with an amplitude of 16(o) and target width of .5° (ID=6) was conducted to determine the impact of adding external loads. We predicted that wrist and arm performance may be differentially impacted by the added mass. Participants were asked to flex/extend their limb/lever in a horizontal plane at the wrist (arm stabilized) or elbow joint (wrist stabilized) in an attempt to move back and forth between the two targets as quickly and accurately as possible. External loads of 0, .568, or 1.136kg were fixed at the distal end of the limb/lever. The targets and the current position of the limb were projected on the screen in front of the participant. The results indicated significant Group×Load interactions for movement time and percent time to peak velocity. Movement time decreased as load increased for the wrist but remained stable across loads for arm movements. Percent movement time utilized to accelerate the limb increased as load increased for wrist movements but only increased from 0 to .568kg load for the arm movements. For both groups increased load had no significant effect on endpoint variability. The present findings suggest that the additional load allowed the control advantages of the wrist muscles to be exploited.

Timekeeping strategies operate independently from spatial and accuracy demands in beat-interception movements

The prevailing paradigm for researching sensorimotor synchronisation in humans involves finger tapping and temporal accuracy measures. However, many successful sensorimotor synchronisation actions require not only to be 'in time', but also to be in a predefined spatial position. Reaching this spatial position in many everyday actions often exceeds the average amplitude of a finger movement. The aim of this study is to address how people coordinate their movement to be in the right place at the right time when the scale of the movement varies. Does the scale of the movement and accuracy demands of the movement change the ability to accurately synchronise? To address these questions, a sensorimotor synchronisation task with three different inter-beat intervals, two different movement amplitudes and two different target widths was used. Our experiment demonstrated that people use different timing strategies--employing either a movement strategy (varying movement time) or a waiting strategy (keeping movement time constant) for large-scale movements. Those two strategies were found to be equally successful in terms of temporal accuracy and variability (spread of errors). With longer interval durations (2.5 and 3.5 s), variability of sensorimotor synchronisation performance increased (measured as the spread of errors). Analysing the data using the Vorberg and Wing (Handbook of perception and action. Academic Press, New York, pp 181-262, 1996) model shows a need to develop further existing timing models of sensorimotor synchronisation so that they could apply to large-scale movements, where different movement strategies naturally emerge.

Is Fitts' law continuous in discrete aiming?

The lawful continuous linear relation between movement time and task difficulty (i.e., index of difficulty; ID) in a goal-directed rapid aiming task (Fitts’ law) has been recently challenged in reciprocal performance. Specifically, a discontinuity was observed at critical ID and was attributed to a transition between two distinct dynamic regimes that occurs with increasing difficulty. In the present paper, we show that such a discontinuity is also present in discrete aiming when ID is manipulated via target width (experiment 1) but not via target distance (experiment 2). Fitts’ law’s discontinuity appears, therefore, to be a suitable indicator of the underlying functional adaptations of the neuro-muscular-skeletal system to task properties/requirements, independently of reciprocal or discrete nature of the task. These findings open new perspectives to the study of dynamic regimes involved in discrete aiming and sensori-motor mechanisms underlying the speed-accuracy trade-off.

Finishing mill thread speed set-up and control by interval type 1 non-singleton type 2 fuzzy logic systems

The set-up of the finishing mill (FM) thread speed to achieve the desired strip temperature as measured by the finish mill delivery temperature sensor is made by an intelligent controller based on interval type 2 fuzzy logic system. The controller calculates the FM thread speed required to achieve the strip FM exit target temperature, and the interstand strip surface temperature profiles. The interval type 2 fuzzy set-up controller uses as inputs the predicted transfer bar FM entry temperature, the transfer bar thickness, the target strip FM exit temperature, the target strip FM exit gauge, last stand draft reduction, last stand work roll diameter, last stand rolling force, %C of strip, and target width. Taking into account that the measurements are modelled as type 1 non-singleton fuzzy numbers, the authors present the so called interval type 1 non-singleton type 2 fuzzy logic system controllers. As reported in the literature, interval type 2 fuzzy logic systems have greater approximation capacity than that of its type 1 counterpart and it has the advantage to develop more robust and reliable solutions than the latter. The experiments of these applications were carried out for three different types of coils, from a real hot strip mill. The results proved the feasibility of the developed system for FM thread speed set-up and control, and for interstand strip temperature profile prediction. Comparisons with the online mathematical based models show that the proposed interval type 2 fuzzy logic system equalises the performance in FM strip thread speed, and temperature set-up and control under the tested conditions characterised by high uncertainty levels.

Modeling Object Pursuit for Desktop Virtual Reality

Models of interaction tasks are quantitative descriptions of relationships between human temporal performance and the spatial characteristics of the interactive tasks. Examples include Fitts' law for modeling the pointing task and Accot and Zhai's steering law for the path steering task. Interaction models can be used as guidelines to design efficient user interfaces and quantitatively evaluate interaction techniques and input devices. In this paper, we introduce and experimentally verify an interaction model for a 3D object-pursuit interaction task. Object pursuit requires that a user continuously tracks an object that moves with constant velocities in a desktop virtual environment. For modeling purposes, we divide the total object-pursuit movement into a tracking phase and a correction phase. Following a two-step modeling methodology that is originally proposed in this paper, the time for the correction phase is modeled as a function of path length, path curvature, target width, and target velocity. The object-pursuit model can be used to quantitatively evaluate the efficiency of user interfaces that involve 3D interaction with moving objects.

Extended practice of reciprocal wrist and arm movements of varying difficulties

An experiment was designed to determine the degree to which reciprocal aiming movements of the wrist and arm with various accuracy requirements (Fitts' tasks) are enhanced by extended practice. The vast majority of research on motor learning shows performance improvement over practice. However, literature examining the effect of practice on Fitts' task performance is limited and inconclusive. Participants were asked to flex/extend their limb/lever in the horizontal plane at the wrist (arm stabilized) or elbow joint (wrist stabilized) in an attempt to move back and forth between two targets as quickly and accurately as possible. The targets and current position of the limb were projected on the screen in front of the participant. Target width was manipulated with amplitude constant (16°) in order to create indexes of difficulty (ID) of 1.5, 3, 4.5, and 6. Contrary to the earlier reports, after 20days of practice, we found minimal changes in movement time or the movement time–ID relationships for the arm and wrist over practice. However, the variability in the movement endpoints decreased over practice and wrist movements at ID=6 were characterized by shorter movement times and longer dwell times relative to arm movements with dwell time for the wrist increasing over practice. These data are consistent with the notion that Fitts' tasks provide a stable measure of perceptual-motor capabilities.

EEG correlates of Fitts’s law during preparation for action

Humans’ inability to move fast and accurately at the same time is expressed in Fitts’s law. It states that the movement time between targets depends on the index of difficulty, which is a function of the target width and the inter-target distance. The present study investigated the electrophysiological correlates of Fitts’s law during action planning using high-density electroencephalography. Movement times were scaled according to Fitts’s law, indicating that participants could not overcome the speed–accuracy trade-off during a 1-s preparation period. Importantly, the index of difficulty of the planned movement correlated linearly with the amplitudes of the cognitive N2 and P3b components, which developed during the planning period over parieto-occipital areas. These results suggest that the difficulty of a movement during action planning is represented at a level where perceptual information about the difficulty of the ensuing action is linked to motor programming of the required movement.

Motor imagery of tool use: relationship to actual use and adherence to Fitts’ law across tasks

A Fitts’ task was used to investigate how tools are incorporated into the internal representations that underlie pointing movements, and whether such knowledge can be generalized across tasks. We measured the speed-accuracy trade-offs that occurred as target width was varied for both real and imagined movements. The dynamics of the pointing tool used in the task were manipulated--regular pen, top-heavy tool, and bottom-heavy tool--to test the fidelity of internal representations of movements involving the use of novel tools. To test if such representations can be generalized, the orientation of the pointing task was also manipulated (horizontal vs. vertical). In all conditions, both real and imagined performances conformed to the speed-accuracy relationship described by Fitts’ law. We found significant differences in imagined MTs for the two weighted tools compared to the regular pen, but not between the weighted tools. By contrast, real movement durations differed between all tools. These results indicate that even relatively brief experience using novel tools is sufficient to influence the internal representation of the dynamics of the tool-limb system. However, in the absence of feedback, these representations do not make explicit differences in performances resulting from the unique dynamics of these weighted tools.

Development of Experimental Pulsed SprayDevice for Spot Application

An experimental pulsed spray device was developed and studies were conducted on targeted spraying and spray application rate. The discharge of carrier fluid and chemical were measured at different set of pressures by using two types of hollow cone nozzles viz BAN nozzle and NMD hollow cone nozzle. Carrier fluid pressure was maintained from 0.05 to 0.2 MPa and the chemical tank pressure was varied from 0.05 to 0.3 MPa. The important characteristics of pulsed spray system were evaluated at different pressures and it was found that, at pressure 1 MPa the VMD was medium spray and at pressure 0.15 to 0.4 MPa VMD was fine spray. It is noticed that the applied volume per unit area is uniform when the pressure is within 0.15 to 0.4 MPa. The results showed that the quantity of chemical applied per pulse varied between 0.4 to 1.2 ml per pulse for different operating pressures and target widths. From the prediction equation, the quantity of chemical applied over the plant was calculated as 2.6 ml when the area of the plant is 78 cm2 . Hence the application rate of chemical was estimated as 0.33 ml/cm 2.

Bivariate pointing movements on large touch screens: Investigating the validity of a refined Fitts’ Law

On the basis of three empirical studies Fitts' Law was refined for bivariate pointing tasks on large touch screens. In the first study different target width parameters were investigated. The second study considered the effect of the motion angle. Based on the results of the two studies a refined model for movement time in human-computer interaction was formulated. A third study, which is described here in detail, concerns the validation of the refined model. For the validation study 20 subjects had to execute a bivariate pointing task on a large touch screen. In the experimental task 250 rectangular target objects were displayed at a randomly chosen position on the screen covering a broad range of ID values (ID= [1.01; 4.88]). Compared to existing refinements of Fitts' Law, the new model shows highest predictive validity. A promising field of application of the model is the ergonomic design and evaluation of project management software. By using the refined model, software designers can calculate a priori the appropriate angular position and the size of buttons, menus or icons.