Target Cursor Research Articles

Use of Target Information for Preparing Initial Motor Command of Target Force Production Task.

The present study examined how humans use the target information provided immediately before the onset of motor output to prepare the initial motor command in the target force production task. Twenty healthy individuals participated in this study. A target cursor indicating the target force, and a force cursor indicating the force produced with index finger flexion were presented, and participants produced force in response to the appearance of the force cursor so that it moved toward the target cursor as fast as possible. The rate of force development in a time window of 0-100ms after the onset of force development, representing the intensity of the initial motor command without online feedback adjustment, was measured. The present findings support the hypotheses that humans use the target information provided immediately before the onset of motor output to prepare the initial motor command, and they simultaneously prepare the initial motor command for the intermediate of multiple potential targets using the information of targets provided in previous trials. Another hypothesis, that humans use the information of the target or motor process of the trial immediately before the current trial to prepare the initial motor command, was not supported.

Dimensionality effect of myoelectric-controlled interface on the coordination of agonist and antagonist muscles during voluntary isometric elbow flexion and extension

Abstract This study aimed to investigate the dimensionality effect of myoelectric-controlled interface (MCI) on the coordination of agonist and antagonist muscles during voluntary isometric elbow flexion and extension. Eighteen healthy subjects were recruited to control a controllable cursor to track a target cursor by real-time modulating the biceps and triceps activities within one-dimensional and two-dimensional MCIs. Electromyographic (EMG) signals were collected to calculate the normalized muscle activation, while the slope of the best-fitting linear relationship between the normalized agonist and antagonist activations was used to quantify the muscle co-activation. The tracking error and the normalized net torque of the elbow joint were also calculated. Results showed that no significant difference was found in the tracking error between one-dimensional and two-dimensional MCIs. The normalized antagonist activation, the muscle co-activation and the normalized net torque were significantly lower within two-dimensional MCI than within one-dimensional MCI. In addition, significant decrease in the normalized agonist activation was also found during elbow extension. These results implied that within two-dimensional MCI, subjects were able to modulate the coordination of agonist and antagonist precisely by inhibiting unnecessary muscle activities. Therefore, two-dimensional MCI might be applied as a rehabilitation tool aiming at fine control of abnormal muscle coordination.

Real-time, simultaneous myoelectric control using visual target-based training paradigm

A training strategy for simultaneous and proportional myoelectric control of multiple degrees of freedom (DOFs) is proposed. Ten subjects participated in this work in which wrist flexion–extension, abduction–adduction, and pronation–supination were investigated. Subjects were prompted to elicit contractions corresponding and proportional to the excursion of a moving cursor on a computer screen. Artificial neural networks (ANNs) were used to map the electromyogram (EMG) signals obtained from forearm muscles, to the target cursor displacement. Subsequently, a real-time target acquisition test was conducted during which the users controlled a cursor using muscular contractions to reach targets. The results show that the proposed method provided controllability comparable (p>0.1) with the previously reported mirrored bilateral training approach, as measured by completion rate, completion time, target overshoot and path efficiency. Unlike the previous approach, however, the proposed strategy requires no force or position sensing equipment and is readily applicable to both unilateral and bilateral amputees.

Are deficiencies in manual tracking associated with upper extremity cumulative trauma disorders?

To examine the reliability of manual tracking performance and its association with impairment and disability in individuals symptomatic of an upper extremity cumulative trauma disorder (CTD). Volunteer and physician referred subjects (100 control, 140 CTD) tracked a target cursor moving quasi-randomly using a hand-held stylus interfaced with a digitizing tablet. Impairment was physician-rated and the Disability of the Arm, Shoulder and Hand questionnaire measured disability. Subsamples of 25 subjects per group were tested on three occasions. Reliability of tracking performance was excellent (ICC > or = 0.88) and sensitivity was 81%. Performance was superior in controls (p < 0.001) and deteriorated as a function of impairment level (p < 0.001). Tracking and impairment rating explained 65% of the disability score. Tracking performance may be an important outcome for monitoring change over time and the impact of a CTD on function in everyday activities.

Guiding contact by coupling the taus of gaps.

Animals control contact with surfaces when locomoting, catching prey, etc. This requires sensorily guiding the rate of closure of gaps between effectors such as the hands, feet or jaws and destinations such as a ball, the ground and a prey. Control is generally rapid, reliable and robust, even with small nervous systems: the sensorimotor processes are therefore probably rather simple. We tested a hypothesis, based on general tau theory, that closing two gaps simultaneously, as required in many actions, might be achieved simply by keeping the taus of the gaps coupled in constant ratio. tau of a changing gap is defined as the time-to-closure of the gap at the current closure-rate. General tau theory shows that tau of a gap could, in principle, be directly sensed without needing to sense either the gap size or its rate of closure. In our experiment, subjects moved an effector (computer cursor) to a destination zone indicated on the computer monitor, to stop in the zone just as a moving target cursor reached it. The results indicated the subjects achieved the task by keeping tau of the gap between effector and target coupled to tau of the gap between the effector and the destination zone. Evidence of tau-coupling has also been found, for example, in bats guiding landing using echolocation. Thus, it appears that a sensorimotor process used by different species for coordinating the closure of two or more gaps between effectors and destinations entails constantly sensing the taus of the gaps and moving so as to keep the taus coupled in constant ratio.

Control Strategies When Intercepting Slowly Moving Targets

In 3 experiments, the authors investigated and described how individuals control manual interceptive movements to slowly moving targets. Participants (N = 8 in each experiment) used a computer mouse and a graphics tablet assembly to manually intercept targets moving across a computer screen toward a marked target zone. They moved the cursor so that it would arrive in the target zone simultaneously with the target. In Experiment 1, there was a range of target velocities, including some very slow targets. In Experiment 2, there were 2 movement distance conditions. Participants moved the cursor either the same distance as the target or twice as far. For both experiments, hand speed was found to be related to target speed, even for the very slowly moving targets and when the target-to-cursor distance ratios were altered, suggesting that participants may have used a strategy similar to tracking. To test that notion, in Experiment 3, the authors added a tracking task in which the participants tracked the target cursor into the target zone. Longer time was spent planning the interception movements; however, there was a longer time in deceleration for the tracking movements, suggesting that more visually guided trajectory updates were made in that condition. Thus, although participants scaled their interception movements to the cursor speed, they were using a different strategy than they used in tracking. It is proposed that during target interception, anticipatory mechanisms are used rather than the visual feedback mechanism used when tracking and when pointing to stationary targets.

Target velocity effects on manual interception kinematics

Participants generated manual interception movements toward a target cursor that moved across a computer screen. The target reached its peak velocity either during the first third, at the midpoint, or during the last third of the movement. In Experiment 1 the view of the target was available for either the first 316, 633, 950, or 1267 ms, after which it disappeared. Results showed that for all viewing conditions, the timing of the interception velocity was related to the temporal properties of the target’s trajectory. In Experiment 2, when the portion of the target trajectory that was viewed was reversed (such that participants did not see the first 316, 633, 950, or 1267 ms of the trajectory, but instead saw only the later portions of the trajectory), there was no clear relationship between the target trajectory and the timing of the aiming trajectory. These results suggest that participants use visual information early in the target’s trajectory to form a representation of the target motion that is used to facilitate manual interception.

Increased use of target cues during visuo‐motor tracking in Parkinson's disease

The effect of temporarily suppressing the visual display of either the target or actual movement trajectory upon the accuracy of visuo-motor tracking was studied in patients with Parkinson's disease (PD) and healthy subjects. Subjects made wrist movements to superimpose a movement cursor upon a target cursor on a VDU screen. The tracking of slow ramp and sinewave target waveforms was investigated. Trials involving the three conditions of visual suppression, namely, target suppressed (TS), movement suppressed (MS) and non-suppressed (NS) were ordered randomly. In TS and MS trials, respectively, the target or movement cursor disappeared from the subject's view for a 4 s period whilst in NS trials both the target and movement cursors were continuously present. Prior to experimental trials, subjects initially practised a series of NS movements. Tracking errors were analysed by ANOVA for group, suppression condition and waveform effects. The tracking performance of the PD patients, during each form of suppression condition, was worse than that of healthy subjects. Both TS and MS elicited significant reductions in accuracy across groups and waveforms. TS induced a more pronounced impairment of tracking accuracy in the PD group than in the control group suggesting that parkinsonians exhibit an abnormally increased reliance upon visual information of the required trajectory during the present visuo-motor tracking tasks. By contrast, there was no between-group effect of MS in these tasks, suggesting that PD patients show a comparable dependence upon visual feedback of their own movements to that shown by controls.

Increased dependence upon visual information of movement performance during visuo-motor tracking in cerebellar disorders

The effect of temporarily suppressing the visual display of either the target (desired) trajectory or the actually movement trajectory upon the accuracy of visuo-motor tracking was studied in 6 patients with cerebellar syndromes and 6 healthy subjects. Subjects made extension and flexion movements of the wrist to superimpose a cursor displaying their movement (movement cursor) upon one indicating target (target cursor) on a VDU screen. The target trajectory consisted of a sawtooth pattern of slow (4 deg/sec) ramp extension and instantaneous flexion return phases. Following practice, the tracking of cerebellar patients was significantly less accurate than that of healthy subjects for each phase ( P = 0.02). Temporary suppression of the movement cursor during both the mid-section of the ramp phase ( P = 0.05) and around the reversal phase ( P = 0.04) caused a significant increase in tracking errors in the patients whereas suppression of the target cursor did not alter their performance. Suppression of neither cursor altered the tracking accuracy of healthy subjects during the ramp extensions whilst suppression of either caused reduced ( P = 0.02) performance for the reversal phase. We interpret the increased dependence of patients upon visual information of their movements during slow trajectories as indicating an impairment of proprioceptive guidance.

A method for studying the control of three-dimensional isometric forces using dynamic stereogram

A system has been developed for measuring the three-dimensional (3D) isometric forces produced by the arm in response to a visual stimulus. The output of 3 load cells is combined to determine the components of the 3D response force. The maximum force range of the load cells is 2000 g which can be read with a resolution of 4 g and with a measured accuracy of + / - 10 g. An overload stop protects the device to a load of 23 kg. The visual instruction to the subject concerning the direction and magnitude of the 3D force vector to be produced is presented using a vivid spherical stereogram. This stereogram is produced using the anaglyphic technique where the left and right images are separated by color filters. A dense aggregation of points defines the target cursor, which can be positioned anywhere inside or on the surface of the sphere. This cursor can represent a stationary or a moving target. A force feedback cursor can be provided to indicate to the subject his/her response. The color display on the cathode ray tube is produced by a display generator driven by a computer.

Eye Movement—Retina Delayed Feedback

Time delays between ocular movement and retinal input have been studied by yoking a visual target to eye movement by experimental programming methods and a laboratory real-time computer system. The subject's task was to manipulate this eye movement-yoked target cursor to perform either compensatory or pursuit eye tracking. The computer thereafter was programmed to store input eye-movement signals and read them out after a delay interval to control the yoked visual target cursor controlled by the eye movements. Delay time constants of 0.1 second significantly affected tracking. Eye movement-retinal feedback delays appeared to have an even more marked effect on positive pursuit eye tracking.