Biomedical subjects

Geert J P Savelsbergh

Publications and source records attributed to Geert J P Savelsbergh.

At least 19 recordsLinked to original sources

PubMed2006

Postural adjustments and bearing angle use in interceptive actions.

The experiment investigates the effect of ball velocity and walking direction on the adherence to the bearing angle (BA) strategy in adults. Adult participants (N=12) approached a moving ball in order to manually intercept it at a predefined target area. Results revealed that during locomotion the BA strategy was implemented, but on reaching the point of interception, this strategy broke down and the BA strategy of the wrist compensated for the movement requirements relative to the ball velocity and approach angle. Larger deviations from the BA occurred when the angle of approach was decreased and when the ball velocity increased. When the BA strategy was adhered to, postural adjustments were reduced. Increased movements occurred in a proximal-distal direction with an increasing approach angle and a faster ball velocity.

Adaptation, Physiological↗

PubMed2006

Differences in gait between children with and without developmental coordination disorder.

In the present study the walking pattern of 10 children with developmental coordination disorder (DCD) was investigated and compared to that of 10 typically developing, matched control children. All children walked at a similar velocity that was scaled to the length of the leg on a motor-driven treadmill. Three-dimensional kinematics were recorded with a motion capture digital camera system. The spatiotemporal parameters of the gait pattern revealed that children with DCD walked with shorter steps and at a higher frequency than the typically developing children. In addition, the children with DCD exhibited a body configuration that demonstrated increased trunk inclination during the entire gait cycle and enhanced during the entire gait cycle. At toe-off a less pronounced plantar flexion of the ankle was observed in children with DCD. In conclusion, it appeared that children with DCD make adaptations to their gait pattern on a treadmill to compensate for problems with neuromuscular and/or balance control. These adaptations seem to result in a safer walking strategy where the compromise between equilibrium and propulsion is different compared to typically developing children.

Biomechanical Phenomena↗

PubMed2006

Reorganization of catching coordination under varying temporal constraints.

In the present study, the limits of human catching behavior were challenged to investigate quantitative and qualitative adaptations of the catching movement when performing under varying ball speeds, implying minor as well as severe temporal constraints. Nine male participants caught balls approaching at speeds ranging from 8.5 to 19.7 m/s with their preferred hand. Although a decrease in catching performance was undeniable, several quantitative adaptations provided the catcher with extra time and allowed to compensate the decrease in spatial accuracy with increasing speed. More importantly, changes in the coordination between hand, elbow, and shoulder emerged with increasing movement velocity. More demanding temporal constraints lead to a shift from relatively independent activity of each joint towards a mode in which several joints act as one unit. This reorganization of the coordination pattern of the catch is discussed in the context of Bernstein's degrees of freedom problem.

Adolescent↗

PubMed2005

Three- to eight-month-old infants' catching under monocular and binocular vision.

We report a cross-sectional and a longitudinal experiment that examined developmental changes in the relative contribution of monocular and binocular variables in the guidance of interceptive arm movements. Three- to eight-month-old infants were observed while presented with differently sized balls that approached frontally with a constant velocity under both monocular and binocular viewing conditions. Movement onset indicated that with age infants increasingly came to rely on binocular variables in controlling the timing of the interceptive arm movements. That is, from 7 to 8 months of age movement onset was independent from object size under binocular but not under monocular viewing. In contrast, binocular viewing enhanced the spatial accuracy of the interceptive arm movements at all ages. We concluded that attunement to binocular information is a key process in infants' gaining adaptive control of goal-directed arm movements. However, interceptive arm movements entail the formation of multiple on-line couplings between optic and movement variables, each of which appears to develop at its own pace.

Humans↗

PubMed2005

The impact of task-constraints on the planning and control of interceptive hitting movements.

On the basis of research in self-paced aiming movements, Glover [S. Glover, Separate visual representations in the planning and control of action, Behav. Brain Sci., 27 (2004) 3-24] proposed a dichotomy between visual systems that accommodate planning and on-line control of action. Specifically, the planning-versus-control model posits that the on-line control system solely adjusts the spatial parameters of a movement. We examined whether this proposition is also adequate for interceptive hitting movements that require being at a specific location at the right time. Participants had to hit an approaching ball by first moving the bat away from the interception point (preparatory phase) and subsequently make the hitting movement (strike phase). The ball had to be projected to a landing location that could be near or far. To examine the ability of actors to use online visual information to adapt to unexpected changes in impact requirements, we perturbed the distance of the landing location from near to far during the unfolding of the movement. No adjustments were observed when the perturbation occurred at the onset of the strike phase. When the perturbation occurred at the onset of the preparatory phase the impact velocity increased and, therefore, the ball traveled a larger distance. This was realized by decreasing the duration of the strike phase and increasing the movement amplitude. So, both spatial and temporal characteristics of the hitting movement were adjusted to comply with an online perturbation of target distance. This observation is incongruent with Glover's recent proposition that the online visual system only accommodates spatial parameters.

Adult↗

PubMed2005

Does intra-uterine environment influence fetal head-position preference? A comparison between breech and cephalic presentation.

BACKGROUND: Cephalic fetuses have increasing lateralised head-position near term. AIM: Is this development affected by breech presentation? SUBJECTS AND METHODS: Fetal head-position was studied longitudinally in 13 healthy fetuses in breech presentation and 10 healthy fetuses in cephalic presentation by means of real-time ultrasound. Recordings were obtained weekly from 33 weeks gestational age until birth. RESULTS: As in previous research, a significant (p = 0.045) decrease in midline head-position was found for the cephalic fetuses with advancing gestational age. The development of a lateralised head-position preference was clearly less outspoken in the breech fetuses when compared to the cephalic ones, especially after 36 weeks gestational age. Furthermore, as cephalic fetuses showed a preference for a right-sided head-position, breech fetuses that did show a lateralised head-position did not have a clear preference for left or right. Our data show an association between the orientation of the fetal vertebral column and head-position predominance in the group of cephalic fetuses, which complies with Previc's left-otolithic dominance theory. No association could be detected between fetal head shape and head-position preference. CONCLUSIONS: This study shows evidence that development in head laterality is influenced by the breech presentation. The discussion addresses possible explanations for the differences we found between the breech and cephalic fetuses.

Breech Presentation↗

PubMed2005

Influence of breech presentation on the development of fetal arm posture.

BACKGROUND: In previous research, an age-related developmental trend towards increasing arm flexion has been found for cephalic fetuses. AIM: To determine if the development of arm posture in breech fetuses is comparable to that of cephalic ones. SUBJECTS AND METHODS: Fetal arm posture was studied longitudinally by means of real-time ultrasound in 13 healthy breech and 10 healthy cephalic fetuses. Observations started from 33 weeks gestational age until birth and were performed weekly in the breech group and every 2 weeks in the cephalic group. RESULTS: No difference could be found in arm posture between the left and the right arm in either group. Both breech and cephalic fetuses showed a clear preference for flexion in elbow and finger joints at all studied ages. After 36 weeks gestational age, the breech group showed significantly less wrist flexion when compared to the cephalic group (p = 0.037). A clear preference for location of the fetal hands near the fetal head could be observed for both groups. CONCLUSIONS: As there is no evidence for an abnormal neuromotor development in healthy breech fetuses, the observed difference in wrist flexion is probably due to differences in intrauterine environment. Because of the preference for location of the hands in the vicinity of the fetal head, breech fetuses probably experience a less restricted environment (in the upper part of the uterus) than cephalic fetuses (in the lower part of the uterus).

Arm↗

PubMed2005

Visual timing and adaptive behavior in a road-crossing simulation study.

In this road-crossing simulation study, we assessed both participant's ability to visually judge whether or not they could cross a road, and their adaptive walking behavior. To this end, participants were presented with a road inside the laboratory on which a bike approached with different velocities from different distances. Eight children aged 5-7, ten children aged 10-12, and ten adults were asked both to verbally judge whether they could cross the road, and to actually walk across the road if possible. The results indicated that the verbal judgments were not similar to judgments to actually cross the road. With respect to safety and accuracy of judgments, groups did not differ from each other, although the youngest group tended to be more cautious. All groups appeared to use a strategy to cross the road based both on the distance and the velocity of the approaching bike. Young children waited longer on the curb before crossing the road than older children and adults. All groups adjusted their crossing time to the time-to-arrival of the bike. These findings are discussed in relation to the ecological psychological approach and the putative dissociation between vision for perception (i.e. verbal judgment) and vision for action (i.e. actual crossing).

Accidents, Traffic↗

PubMed2005

Perceptual-motor organization of children's catching behaviour under different postural constraints.

The experiment investigates the perceptual-motor organization underlying children's catching performance when the demands on the postural system are varied. For this purpose, one-handed catching performance was observed under different postural constraints in children aged 9-10 years. Two groups of eleven participants, classified as either good or poor catchers, performed one-handed catches under three different postural conditions: standing, sitting, and standing while pressing a button positioned to a postural support aid (PSA). Results revealed, first, that when seated, poor catchers approached the level of the good catchers' performance. Second, poor catchers improved their performance by using the PSA, but not to the same performance as when sitting. Third, there was no effect of postural condition on the performance of the good catchers. The performance increase in the poor catchers is attributable to a combined change in functional postural sway and better timed movement of the catching hand, made possible by exploiting the extra surface support area afforded by sitting.

Biomechanical Phenomena↗

PubMed2005

Catching and matching bars with different orientations.

The hypothesis that perception enslaves action is examined by assessing whether systematic distortions in perceptual judgments are reflected by inaccuracies in catching. In the first experiment, participants had to align manually the orientation of a reference bar placed at different distances in the frontoparallel plane. In the second experiment participants had to catch differently orientated moving bars, which became invisible at different distances from the interception point. In the matching experiment, systematic errors in the alignment of orientation were found in particular for oblique orientations, the magnitude of which increased with increasing distance of the reference bar. The inaccuracies in the final hand orientation during the catching task, however, did not mirror this pattern of deviations. The findings are interpreted to be more consistent with recent views that vision for perception (i.e., matching) and vision for action (i.e., catching) are dissociated than with the view that perception enslaves action.

Adult↗

PubMed2005

Bi-phasic hitting with constraints on impact velocity and temporal precision.

The aim of the experiment was to investigate how bi-phasic hitting movements are organized to comply with both impact and temporal precision constraints. 'Bi-phasic' refers to a sequential movement with a preparatory movement away from the interception location followed by a strike phase. The interception location was fixed, as the motion of the hitting device was constrained to follow a straight path orthogonal to that of the approaching balls. We manipulated the required temporal precision by projecting balls with different constant approach speeds (1, 1.5, and 2m/s). Different impact constraints were imposed by instructing participants first to simply hit the ball and subsequently to hit the ball to a designated target area located either 55 or 105 cm away from the interception location. We determined several kinematic variables and used Principal Component Factor Analysis to classify these variables. The analysis revealed two independent factors: a 'velocity' factor (formed by impact velocity, peak velocity of the preparatory phase, peak velocity of the strike phase, and amplitude of the strike) and a 'timing' factor (formed by onset of the preparatory phase, moment of peak velocity of the preparatory phase, and onset of the strike phase). The 'velocity' factor scaled significantly with the required impact constraint and the 'timing' factor scaled significantly with ball speed.

Acceleration↗

PubMed2005

Coordination of reaching in children with spastic hemiparetic cerebral palsy under different task demands.

Coordination of reaching with the impaired and non-impaired arm in 10 children with spastic hemiparetic cerebral palsy (SHCP) was examined in a stationary ball and moving ball context. Kinematic data on trunk, arm, and wrist movements, and coordination patterns between joint angles of elbow, shoulder, and trunk, were analyzed to determine how reaching was influenced by impairment and object motion. Results showed longer deceleration time and movement time and greater trunk contribution following decreased elbow and shoulder excursion when reaching with the impaired arm compared to the non-impaired arm. The coordination of joint angle pairs showed little linearity for the impaired arm, indicating more segmented movements of shoulder and elbow. It was also found that coordination patterns between elbow, shoulder, and trunk displayed less similarity when reaching with the impaired arm compared to the non-impaired arm in both stationary and moving ball conditions. Regardless of the timing constraints, children with SHCP could make successful interceptions using the impaired arm, indicating that they coordinated and controlled the degrees of freedom within their own functional possibilities.

Arm↗

PubMed2005

Planning and control in a manual collision avoidance task by children with hemiparesis.

We examined whether deficits in planning and control during a manual collision avoidance task in children with hemiparesis are associated with damage to the left or right hemisphere (LHD and RHD). Children pushed a doll across a scale-size road between two approaching toy cars. Movement onset and velocity served as indicators of planning and control. In Experiment 1, children with hemiparesis collided more frequently, and controlled velocity less appropriately compared to typically-developing children. Children with LHD initiated their movement later than children with RHD. Experiment 2 compared the preferred and non-preferred hand of children with LHD and RHD. Children with RHD crossed less with their non-preferred hand, while children with LHD initiated later than children with RHD. Moreover, the groups showed differences in velocity control. It is argued that planning deficits may be related to LHD. The hypothesized association between control deficits and RHD, however, was not confirmed.

Adolescent↗

PubMed2004

The contribution of stereo vision to one-handed catching.

Participants with normal (StereoN) and weak (StereoW) stereopsis caught tennis balls under monocular and binocular viewing at three different speed conditions. Monocular or binocular viewing did not affect catching performance in catchers with weak stereopsis, while the StereoN group caught more balls under binocular vision as compared with the monocular condition. These effects were more pronounced with increasing ball speed. Kinematic analysis of the catch partially corroborated these findings. These results indicate that StereoW catchers have not developed a compensatory strategy for information pick-up, and that negative effects of a lack of stereopsis grow larger as temporal constraints become more severe. These findings also support the notion that several monocular and/or binocular information sources can be used in the control of interceptive action.

Adaptation, Physiological↗

PubMed2004

Coordinating degrees of freedom during interceptive actions in children.

The aim of the experiment was to examine how children coordinate the degrees of freedom of the arm and trunk when performing interceptive actions that correspond to daily life activities. For that purpose, children were required to reach and grasp a stationary ball while standing (condition C1), a stationary ball while walking (C2), and a moving ball while standing (C3). The resulting movements were measured in world-centered and body-centered coordinates, and then subjected to three-dimensional kinematic analysis. The different coordinate frames of reference were used to determine the interaction between arm and trunk movements. Children adapted their coordination in the two moving conditions (C2 and C3) by decelerating longer towards the ball and exhibiting more interaction between the arm and trunk movements than in the stationary condition (C1). These results indicate that, like adult participants, children adapt to the constraints imposed by complex, interceptive actions by recruiting additional degrees of freedom of the trunk, which are coordinated with the hand to produce a movement that preserves an appropriate level of impact at hand/object collision.

Adaptation, Physiological↗

PubMed2004

Timing of goal-directed hitting: impact requirements change the information-movement coupling.

In hitting, performers are found to adapt to the approach speed of the ball, i.e. they tend to initiate their movement at a shorter time before contact for faster approaching balls. A change in movement time is always accompanied by a change in movement velocity when the movement trajectory is kept constant. Hence, a fast-approaching ball might induce high impact velocity that is in conflict with low impact constraints, such as propelling the ball towards a near goal. In this study we investigated the capacities of participants to perform one-dimensional hitting movements in the frontal plane to balls approaching on a head-on collision course. The temporal precision (i.e. ball approach speed: 1, 1.5, and 2 m/s) and impact requirements (i.e. No-Goal, Near-Goal, and Far-Goal) were manipulated to examine the influence of task constraints on the temporal regulation of a stroke. The results showed that timing and speed were significantly affected by ball approach speed when the hit was not directed to a goal. In contrast, no speed-coupling and a constant time-to-impact strategy were found when impact velocity was constrained (i.e. aiming for a near goal). We were particularly interested in the nature and relation of information sources and timing patterns of movement initiation. Therefore, the relation between the time evolution of three optical sources related to the approach of the ball and the observed patterns of swing onset were evaluated quantitatively. The analyses revealed that a viable explanation for the two observed qualitatively different onset patterns of the swing is a regulation based on the absolute rate of expansion or a co-varying variable. The flexible adaptation of timing to impact constraints may be realized by an adjustment of the critical region of this optical variable.

Adult↗

PubMed2004

Object rotation effects on the timing of a hitting action.

We investigated how perturbing optical information affects the guidance of an unfolding hitting action. Using monocular and binocular vision, six participants were required to hit a rectangular foam object, released from two different heights, under four different approach conditions, two with object rotation (to perturb the viewed surface area) and two without. Participants made more misses under monocular conditions, and the presence of rotation had a significant effect on the duration between the arm's peak velocity and its contact with the object. We conclude that binocular information contributes to the timing of interceptive tasks. In addition, the guidance of interceptive actions does not appear to be based solely on object expansion information picked up from the viewed surface area.

Adult↗

PubMed2003

Children's search for targets located within and beyond the field of view: effects of deafness and age.

The localisation time of visual targets within and beyond the field of view and the relative timing of the onsets of eye and head movements were examined in deaf and hearing children of two age groups: 5-7 years and 10-12 years. Compared to their hearing peers, the deaf children showed more often a mode of eye-head coordination in which the head leads the eye. The discrepancy between the onsets of eye and head movements were greater for the younger than for the older groups. Furthermore, the deaf children took more time than the hearing children to localise the targets; especially the young deaf differed from their hearing contemporaries. These findings support the view that during development the differences in visual search between deaf and hearing children decrease. The results are discussed in the context of a distinction between representational and sensorimotor control of eye-head responses.

Age Factors↗