Age and Not the Preferred Limb Influences the Kinematic Structure of Pointing Movements.

In goal-directed movements, effective open-loop control reduces the need for feedback-based corrective submovements. The purpose of this study was to determine the influence of hand preference and aging on submovements during single- and two-joint pointing movements. A total of 12 young and 12 older right-handed participants performed pointing movements that involved either elbow extension or a combination of elbow extension and horizontal shoulder flexion with their right and left arms to a target.

Coordination deficits during trunk-assisted reach-to-grasp movements in Parkinson's disease.

The present study investigated how Parkinson's disease (PD) affects temporal coordination among the trunk, arm, and fingers during trunk-assisted reach-to-grasp movements. Seated participants with PD and healthy controls made prehensile movements. During the reach to the object, the involvement of the trunk was altered based on the instruction; the trunk was not involved, moved forward (flexion), or moved backward (extension) in the sagittal plane.

Effect of aging on coordinated eye and hand movements with two-segment sequence.

This study examined how aging compromises coordinative eye-hand movements with multiple segments. Older adults and young controls performed two-segment movements with the eyes only or with the eyes and hand together. The results showed minimal age-related changes on the initiation and execution of primary saccade during the first segment.

Control of aperture closure initiation during trunk-assisted reach-to-grasp movements.

The present study investigated how the involvement and direction of trunk movement during reach-to-grasp movements affect the coordination between the transport and grasping components. Seated young adults made prehensile movements in which the involvement of the trunk was varied; the trunk was not involved, moved forward (flexion), or moved backward (extension) in the sagittal plane during the reach to the object. Each of the trunk movements was combined with an extension or flexion motion of the arm during the reach.

Adaptation of gaze anchoring through practice in young and older adults.

During visually guided manual movements, gaze is usually fixated to a target until a pointing movement is completed to that target, showing gaze anchoring. We previously examined gaze anchoring during a two-segment eye-hand task under a low accuracy constraint. Eye movements were made to predetermined first and second targets, while hand movements were varied across two conditions: (1) stop at the first target and discontinue (HS1) and (2) stop at both the first and the second targets (HS1S2).

Auditory instructional cues benefit unimanual and bimanual drawing in Parkinson's disease patients.

The present study investigated performance of unimanual and bimanual anti-phase and in-phase upper limb line drawing using three different types of cues. Fifteen Parkinson's disease (PD) patients, 15 elderly, and 15 young adults drew lines away from and towards their body on a tabletop every 1000 ms for 30 s under three different cueing conditions: (1) verbal ('up', 'down'); (2) auditory (high tone, low tone); (3) visual (target line switched from top to bottom). PD patients had larger and more variable amplitudes which may be related to the finding that they also produced more curvilinear movements than young and elderly adults.

Effects of hand termination and accuracy requirements on eye-hand coordination in older adults.

This study investigated how aging compromises the control of saccades and eye-hand coordination when accuracy constraints and termination requirements of hand movement are altered. Seventeen older adults and seventeen young controls performed two-segment aiming movements. The first segment had two target sizes to alter accuracy constraints.

Effects of hand termination and accuracy constraint on eye-hand coordination during sequential two-segment movements.

The purpose of this study was to examine the effects of accuracy constraints and termination requirements of hand movement on eye-hand coordination. Healthy adults performed two-segment eye and hand aiming movements to predetermined stationary targets. While two-segment eye movements were made to the first and second targets for all conditions, hand movements were varied across conditions.

Phase dependence of transport-aperture coordination variability reveals control strategy of reach-to-grasp movements.

Based on an assumption of movement control optimality in reach-to-grasp movements, we have recently developed a mathematical model of transport-aperture coordination (TAC), according to which the hand-target distance is a function of hand velocity and acceleration, aperture magnitude, and aperture velocity and acceleration (Rand et al. in Exp Brain Res 188:263-274, 2008). Reach-to-grasp movements were performed by young adults under four different reaching speeds and two different transport distances.

Linguistic and perceptual-motor contributions to the kinematic properties of the braille reading finger.

Recordings of the dominant finger during the reading of braille sentences by experienced readers reveal that the velocity of the finger changes frequently during the traverse of a line of text. These changes, not previously reported, involve a multitude of accelerations and decelerations, as well as reversals of direction. We investigated the origin of these velocity intermittencies (as well as movement reversals) by asking readers to twice read out-loud or silently sentences comprising high- or low-frequency words which combined to make grammatical sentences that were either meaningful or nonmeaningful.

Control of aperture closure initiation during reach-to-grasp movements under manipulations of visual feedback and trunk involvement in Parkinson's disease.

The present project was aimed at investigating how two distinct and important difficulties (coordination difficulty and pronounced dependency on visual feedback) in Parkinson's disease (PD) affect each other for the coordination between hand transport toward an object and the initiation of finger closure during reach-to-grasp movement. Subjects with PD and age-matched healthy subjects made reach-to-grasp movements to a dowel under conditions in which the target object and/or the hand were either visible or not visible. The involvement of the trunk in task performance was manipulated by positioning the target object within or beyond the participant's outstretched arm to evaluate the effects of increasing the complexity of intersegmental coordination under different conditions related to the availability of visual feedback in subjects with PD.

Hypometria and bradykinesia during drawing movements in individuals with Parkinson's disease.

To address the hypothesis that Parkinson's disease (PD) patients have deficits in controlling acceleration, a drawing task was used in which target size, frequency, and weight of pen were manipulated. In accordance with previous results, it was found that, relative to controls, PD patients produced movements at the required frequency, but moved significantly slower, produced less acceleration, and drew smaller-than-required stroke sizes. This resulted in smaller-than-required movement amplitudes, suggesting that hypometria and bradykinesia in drawing and/or handwriting are related.

Biased wrist and finger coordination in Parkinsonian patients during performance of graphical tasks.

Handwriting impairments in Parkinson's disease (PD) have been associated with micrographia, i.e. diminished letter size.

Integration deficiencies associated with continuous limb movement sequences in Parkinson's disease.

The present study examined the extent to which Parkinson's disease (PD) influences integration of continuous limb movement sequences. Eight patients with idiopathic PD and 8 age-matched normal subjects were instructed to perform repetitive sequential aiming movements to specified targets under three-accuracy constraints: 1) low accuracy (W = 7 cm) - minimal accuracy constraint, 2) high accuracy (W = 0.64 cm) - maximum accuracy constraint, and 3) mixed accuracy constraint - one target of high accuracy and another target of low accuracy.

Movement structure in young and elderly adults during goal-directed movements of the left and right arm.

Elderly adults often exhibit performance deficits during goal-directed movements of the dominant arm compared with young adults. Recent studies involving hemispheric lateralization have provided evidence that the dominant and non-dominant hemisphere-arm systems are specialized for controlling different movement parameters and that hemispheric specialization may be reduced during normal aging. The purpose was to examine age-related differences in the movement structure for the dominant (right) and non-dominant (left) during goal-directed movements.

Quantitative model of transport-aperture coordination during reach-to-grasp movements.

It has been found in our previous studies that the initiation of aperture closure during reach-to-grasp movements occurs when the hand distance to target crosses a threshold that is a function of peak aperture amplitude, hand velocity, and hand acceleration. Thus, a stable relationship between those four movement parameters is observed at the moment of aperture closure initiation. Based on the concept of optimal control of movements (Naslin 1969) and its application for reach-to-grasp movement regulation (Hoff and Arbib 1993), it was hypothesized that the mathematical equation expressing that relationship can be generalized to describe coordination between hand transport and finger aperture during the entire reach-to-grasp movement by adding aperture velocity and acceleration to the above four movement parameters.

Role of vision in aperture closure control during reach-to-grasp movements.

We have previously shown that the distance from the hand to the target at which finger closure is initiated during the reach (aperture closure distance) depends on the amplitude of peak aperture, as well as hand velocity and acceleration. This dependence suggests the existence of a control law according to which a decision to initiate finger closure during the reach is made when the hand distance to target crosses a threshold that is a function of the above movement-related parameters. The present study examined whether the control law is affected by manipulating the visibility of the hand and the target.

Force development during target-directed isometric force production in Parkinson's disease.

Performing various daily activities requires precise application and control of forces, which has been well addressed in neurologically healthy individuals. Recent experiments have demonstrated that in young, normal subjects generating rapid force pulses over various force amplitudes was accomplished by linearly increasing the rate of force development while keeping time to peak force approximately constant (i.e.

Effect of speed manipulation on the control of aperture closure during reach-to-grasp movements.

This study investigates coordination between hand transport and grasp movement components by examining a hypothesis that the hand location, relative to the object, in which aperture closure is initiated remains relatively constant under a wide range of transport speed. Subjects made reach-to-grasp movements to a dowel under four speed conditions: slow, comfortable, fast but comfortable, and maximum (i.e.

Altered coordination patterns in parkinsonian patients during trunk-assisted prehension.

We examined whether coordination between movement components during trunk-assisted prehension was compromised in PD patients in response to varying constraints (experiment 1: reach speed, object size, movement amplitude; experiment 2: movement sequence). In general, both PD patients and controls responded similarly to the changes in these three variables. PD patients, however, demonstrated less synchronized movements in terms of timing between onsets and offsets of aperture formation, endpoint motion and trunk motion.

The role of vision in the control of continuous multijoint movements.

The authors investigated whether visual fixations during a continuous graphical task were related to arm endpoint kinematics, joint motions, or joint control. The pattern of visual fixations across various shapes and the relationship between temporal and spatial events of the moving limb and visual fixations were assessed. Participants (N=16) performed movements of varying shapes by rotating the shoulder and elbow joints in the transverse plane at a comfortable pace.

Effect of combined variation of force amplitude and rate of force development on the modulation characteristics of muscle activation during rapid isometric aiming force production.

Studies of rapid target-directed limb movements have suggested that various control schemes can be defined by the modulation pattern of the muscle activity. The present study was aimed to address the question regarding the extent to which a simultaneous control of force amplitude, and rate of force development influences the modulation characteristics of muscle activation associated with producing rapid isometric aiming forces at the elbow joint. The subjects were instructed to produce rapid isometric force pulses to three different force amplitudes (15, 35, and 55% of their maximal voluntary contractions) under systematically varied force-rate conditions ranging from a fast and accurate force-rate to the fastest force-rate possible.

Disruptions in joint control during drawing arm movements in Parkinson's disease.

Impairments in control of multi-joint arm movements in Parkinson's Disease (PD) were investigated. The PD patients and age-matched elderly participants performed cyclical arm movements, tracking templates of a large circle and four differentially oriented ovals on a horizontal table. The wrist was immobilized and the movements were performed with shoulder and elbow rotations.

Multiple frames of reference for pointing to a remembered target.

Pointing with an unseen hand to a visual target that disappears prior to movement requires maintaining a memory representation about the target location. The target location can be transformed either into a hand-centered frame of reference during target presentation and remembered under that form, or remembered in terms of retinal and extra-retinal cues and transformed into a body-centered frame of reference before movement initiation. The main goal of the present study was to investigate whether the target is stored in memory in an eye-centered frame, a hand-centered frame or in both frames of reference concomitantly.

Effect of orienting the finger opposition space in the control of reach-to-grasp movements.

Participants (N = 13) made reach-to-grasp movements to an elongated object with or without a forearm pronation movement. Grasp and transport components of movements performed without forearm pronation differed from those performed when participants preplanned forearm pronation. The transport distance traveled after peak aperture (aperture closure distance) was unchanged, however, suggesting that participants initiated aperture closure on the basis of the distance of the hand from the target.