PubMed Health⌕ Search

Biomedical subjects

G J Savelsbergh

Publications and source records attributed to G J Savelsbergh.

At least 19 recordsLinked to original sources
PubMed2001

Fetal handedness and head position preference: a developmental study.

Hand-head contacts were observed by means of serial ultrasound recordings in 10 healthy fetuses from 12 to 38 weeks of gestational age. Contacts were distinguished as being unimanual or bimanual, and if unimanual, whether they were made with the right or left hand. Both types of contact and ones made unimanually with the right or left hand were identified at each age as to whether they were associated with a preferential head position. A strong unimanual bias was evident at each age except for Week 36. At this age, there was a bimanual bias. Unimanual contacts did not develop a lateralized preference, and neither type of contact established a stable relationship with head position. Furthermore, there was no evidence to support the suggestion that hand contact and head position codevelop to form a preferred ipsilateral synergy. Findings are discussed relative to contradictory evidence from other fetal and neonatal studies.

Choice Behavior↗
PubMed2000

Discriminating the role of binocular information in the timing of a one-handed catch. The effects of telestereoscopic viewing and ball size.

Previous work using prediction-motion tasks has indicated that time-to-contact estimates are based exclusively on binocular information when the approaching object is small. The aim of this study was to examine the influence of object size on the use of binocular information sources in specifying time-to-contact in one-handed catching. Subjects (n = 10) were required to time their grasp to catch different-sized balls (60, 80, and 100 mm in diameter) approaching with a constant spatial trajectory and constant velocity of 2.0 m/s. Binocular information was manipulated with a telestereoscope that increased the individuals' effective interocular separation. Subjects performed six trials with each of the different-sized balls in normal and telestereoscopic viewing conditions. It was found that subjects closed the hand earlier when catching the small and medium balls under telestereoscopic viewing compared with normal viewing; furthermore, that subjects closed their hand earlier for the small and medium balls compared with the large ball under telestereoscopic viewing. With regard to hand aperture, there was an effect of ball size, with the hand being opened to a wider aperture for each increase in ball size. Subjects also opened the hand to a wider aperture when catching the small and medium balls under telestereoscopic viewing. These findings are consistent with the notion of an increased reliance on the use of binocular information when the approaching object is small. Furthermore, they indicate that binocular and monocular sources of information are not used in isolation, but rather in combination to support the timing of one-handed catching.

Adult↗
PubMed1999

Object size effects on initial lifting forces under microgravity conditions.

Individuals usually report for two objects of equal mass but different volume that the larger object feels lighter. This so-called size-weight illusion has been investigated for more than a century. The illusion is accompanied by increased forces, used to lift the larger object, resulting in a higher initial lifting speed and acceleration. The illusion holds when subjects know that the mass of the two objects is equal and it is likely that this also counts for the enlarged initial effort in lifting a larger box. Why should this happen? Under microgravity, subjects might be able to eliminate largely the weight-related component of the lifting force. Then, if persistent upward scaling of the weight-related force component had been the main cause of the elevated initial lifting force under normal gravity, this elevated force might disappear under microgravity. On the other hand, the elevated initial lifting effort in the large box would be preserved if it had been caused mainly by a persistent upward scaling of the force component, necessary to accelerate the object. To test whether the elevated initial lifting effort either persists or disappears under microgravity, a lifting experiment was carried out during brief periods of microgravity in parabolic flights. Subjects performed whole-body lifting movements with their feet strapped to the floor of the aircraft, using two 8-kg boxes of different volume. The subjects were aware of the equality of the box masses. The peak lifting forces declined almost instantaneously with approx. a factor 9 in the first lifting movements under microgravity compared with normal gravity, suggesting a rapid adaptation to the loss of weight. Though the overall speed of the lifting movement decreased under microgravity, the mean initial acceleration of the box over the first 200 ms of the lifting movement remained higher (P=0.030) in the large box (1.87+/-0.127 m/s2) compared with the small box (1.47+/-0.122 m/s2). Under normal gravity these accelerations were 3.30+/-0.159 m/s2 and 2.67+/-0.159 m/s2, respectively (P=0.008). A comparable trend was found in the initial lifting forces, being significant in the pooled gravity conditions (P=0.036) but not in separate tests on the normal gravity (P=0.109) and microgravity (P=0.169) condition. It is concluded that the elevated initial lifting effort with larger objects holds during short-term exposure to microgravity. This suggests that upward scaling of the force component, required to accelerate the larger box, is an important factor in the elevated initial lifting effort (and the associated size-weight illusion) under normal gravity.

Adult↗
PubMed1999

Adaptation of center of mass control under microgravity in a whole-body lifting task.

Human balance in stance is usually defined as the preservation of the vertical projection of the center of mass (COM) on the support area formed by the feet. Under microgravity conditions, the control of equilibrium seems to be no longer required. However, several reports indicate preservation of COM control in tasks such as arm or leg raising, tiptoe standing, or trunk bending. It is still unclear whether COM control is also maintained in complex multijoint movements during short term exposure to microgravity. In the current study, the dynamics of equilibrium control were studied in four subjects performing two series of seven whole-body lifting movements under microgravity during parabolic flights. The aims of the study were to examine whether the trajectory of horizontal COM motion during lifting movements changes in short-term exposure to microgravity and whether there is any sign of recovery after several lifting movements. It was found that, compared with control movements under normal gravity, the horizontal position of the COM was shifted backward during the entire lifting movement in all subjects. In the second series of lifting movements under microgravity, a partial recovery of the COM trajectory toward the normal gravity situation was found. Under microgravity, angles of the ankle, knee, hip, and lumbar joints differed significantly from the angles found under normal gravity. Recovery of joint angular trajectories in the second series of lifting movements mainly occurred for those angles that could contribute to a reduction of the backward COM shift. It is to be pointed out that COM control under microgravity is not redundant but functional. Persisting COM control under microgravity may be required for pure mechanical reasons, since rotational movements of the body are dependent on adequate control of the COM position with respect to external forces. It is shown that, from a mechanical perspective, subjects can benefit from a backward displacement of the COM in the downward as well as the upward phase of the lifting movement under microgravity.

Adaptation, Physiological↗
PubMed1999

Timing a one-handed catch. I. Effects of telestereoscopic viewing.

The aim of this study was to examine the role of binocular and monocular information sources in specifying time-to-contact. More specifically, it was investigated whether the timing of the one-handed catch is consistent with a binocular tau-function strategy. Subjects (n=8) were required to time their grasp to catch a ball approaching with a constant spatial trajectory. The ball approached at three different constant velocities (1.5, 2.0 and 2.5 m/s). Vergence and disparity were manipulated through subjects wearing a telestereoscope to increase the effective interocular separation, under both binocular and monocular viewing. Subjects performed 24 trials in each of the four conditions. Subjects' started the opening of the hand earlier in the binocular telestereoscope condition when a ball approached with velocity of 1. 5 m/s. They then closed the hand earlier in the binocular telestereoscope condition at all ball approach velocities. There were no effects of telestereoscope on the timing of hand opening and closing under monocular viewing. This finding suggests the use of the binocular information in timing the grasp. However, there were effects of approach velocity under all conditions of monocular and binocular viewing. Subjects' closed the hand earlier as a function of increasing approach velocity. Together, the effects of the telestereoscope and approach velocity indicate that timing of the one-handed catch is not consistent with the use of a binocular "tau-function" variable. Rather, it is concluded that multiple sources of monocular and binocular information contribute to the regulation of timing.

Female↗
PubMed1999

Timing a one-handed catch. II. Adaptation to telestereoscopic viewing.

A pre-exposure, exposure, post-exposure design was used to assess the adaptation of the timing of a one-handed catch during telestereoscopic viewing. More specifically, it was examined whether the adaptation involved: (1) ignoring binocular sources of information and selecting other information, or (2) a recalibration of the coupling between the effected binocular information and the catching movement, and (3), if it is recalibration, whether it is restricted to the manipulated binocular information. To test these hypotheses, subjects (n=16) were assigned to one of two groups, each group performing three blocks of 15 trials in the dark with only the ball visible. In the exposure condition, both groups were required to catch balls under binocular telestereoscopic viewing. In the pre-exposure and post-exposure conditions, subjects performed under binocular and monocular viewing, respectively. Kinematics of the grasping movement were recorded. It was predicted that, in the case of a selection process, no after effects would occur in the post-exposure condition, whereas, in the case of recalibration, aftereffects would occur. Moreover, if the recalibration is restricted to the manipulated information, only the group that was provided with binocular vision during the pre- exposure and post-exposure conditions would show aftereffects. Significant condition (pre-exposure, exposure, post-exposure) by block (first three trials, last three trials) effects were found for the moments of grasp onset, peak opening velocity and hand closure, indicating that the hand was opened and closed earlier in the first three trials of telestereoscopic viewing. This coincided with an increase in catching failures. In addition, for the moments of hand closure and peak closing velocity, negative aftereffects were found in the post-exposure condition. The hand was closed later in the first three trials after removal of telestereoscope. With respect to the presence of the aftereffects, no differences were found between the groups. It was concluded that adaptation to telestereoscopic viewing in the timing of a one-handed catch is due to the recalibration of the coupling between information and movement, rather than a selection of another source of information. Moreover, it is likely that the recalibration was not restricted to the single, manipulated information. Rather, the recalibration involves multiple binocular and monocular optical and oculomotor sources of information.

Adult↗
PubMed1999

Newborns spontaneous arm movements are influenced by the environment.

The spontaneous arm movements of 28 healthy full-term newborn infants were observed for 1 min in four different environmental conditions: each infant was placed in a vertical position in a bathtub filled with water with the water level up to her or his neck in a vertical position in water with the water level up to her or his waist in a supine position out of the water in a vertical position out of the water. It was hypothesised that these different environmental constraints would influence the infants spontaneous activity. From video recordings spontaneous arm movements were categorised according to the classifications of Hannan (Hannan TE. Young infant's hand and finger expressions: An analysis of category reliability. In: Field T, Fogel A, editors. Emotion and Early Interaction. New Jersey: Elbaum 1982;253-265). The statistical analyses showed, firstly, that the frequency of occurrence of various arm movements is greater out of the water than in the water. Secondly, for those out of the water the frequency of occurrence of various arm movements is greater in the vertical position in comparison to the supine position. Thirdly, the infants showed more active arm movements (more upward movements) in the vertical position out of the water in comparison to the two water and supine conditions. These findings lead to the conclusion that different environmental constraints influenced the spontaneous arm movements.

Arm↗
PubMed1999

Intercepting moving objects during self-motion: effects of environmental changes.

The purpose of this study was to examine the role of background texture on an interception task during self-motion. Twenty-six participants modulated tricycle speed along one arm of a V-shaped track so as to intercept a ball approaching horizontally on the other arm of the V. Either a plain or a textured background (consisting of contrasting vertical stripes) was used. Velocity modulations occurred so as to keep the angle beta between the direction of heading and the line head-ball constant (constant bearing angle, or CBA strategy), indicating that this observer-environment relation might regulate the approach phase. In the textured condition, participants initially drove faster than predicted by the CBA model and compensated by slowing down in the second half. This is in line with the texture-induced overestimation of the ball velocity and implies that absolute velocity information is also used.

Analysis of Variance↗
PubMed1999

Is it pointing to grasping or grasping pointing?

The Smeets and Brenner view on grasping is simple: grasping is in fact pointing. In our comments we examine the model beyond the reach-to-grasp task, namely, by grasping (without reaching) of moving objects and eating. The model fits the data of both tasks. Although generalization of a model to different tasks usually strengthens its acceptance, in the present case it reveals its shortcomings, namely, both tasks include a clear grasping component that is hard to accept as pointing.

Biomechanical Phenomena↗
PubMed1998

A developmental transition in prehension modeled as a cusp catastrophe.

The purpose of the study was to show that the change from reaching without grasping to reaching with grasping during the first 6 months of life carried the characteristics of a discontinuous phase transition (catastrophe). A cross-sectional study was carried out with 58 infants between 60 and 408 days old. The infants were seated in a specially designed seat, and presented with nine detachable balls on a black curved board within reaching distance at shoulder height. The number of reaches without and with grasping were scored from video. A cusp catastrophe model was fitted to the data. A Likelihood-Ratio test indicated that the likelihood of the cusp model was significantly higher, p < .001, than a linear regression model. The cusp model was also compared with a logistic model. Akaike's Information criterion for the cusp catastrophe exceeded the logistic model, thus indicating a general better fit. Based on prior research, the following potential control parameters were chosen: crown-heel length, total body weight, arm length, arm circumference, ponderal index, arm volume, arm weight, and body position relative to the horizontal. The cusp model predicted that arm weight and arm circumference significantly contributed to the control parameters. It was found that these two variables had their largest contribution to the asymmetry control parameters.

Anthropometry↗
PubMed1998

Evidence for a phase transition in the early development of prehension.

A longitudinal study was conducted to examine the hypothesis that the development of prehension during the first 5 months of life is characterized by the presence of a discontinuous phase transition. Ten infants were observed weekly from 8 to 24 weeks of age. Video recordings were made of movements toward an attractive object which were classified according to two behavioral categories: reaching without grasping and reaching with grasping. The time evolution of the relative incidence of these behavioral categories was analyzed statistically. Evidence was found for a sudden jump from a (developmental) state in which reaching without grasping is predominant to a state in which reaching with grasping is predominant. Evidence was also found for bimodality, inaccessibility, and anomalous variance. In combination, these findings support the hypothesis that the investigated behavioral change constitutes a discontinuous phase transition. The behavioral change in question occurred at the moment in developmental time at which the attractor strength of reaching for objects as such relative to that of other behavioral activities appeared to be increased.

Age Factors↗
PubMed1998

Body-scaled ratio as a control parameter for prehension in 5- to 9-year-old children.

The purpose of the experiment was threefold: (a) To find evidence that grasping is body-scaled and thus remains invariant during development; (b) to seek evidence that the body-scaled ratio of cube and hand size serves as a control parameter for the phase transition from one-handed to two-handed grasping by identifying the presence of sudden jump, enhanced variance, multistability, and hysteresis; and (c) to examine whether the stability properties of the observed grasping patterns increase with age. Thirty-three children aged 5, 7, and 9 years old were required to grasp and lift 14 cardboard cubes of different sizes (2.2, 3.2, 4.2, etc. to 16.2 cm diameter). Three conditions were used: (a) an increasing condition with sizes ordered from the smallest size to the largest; (b) a decreasing condition, with the sizes ordered from the largest to the smallest; and (c) twice in a different random order. Video recordings were analyzed and scored for the percentage of one-handed grasps. The results showed that the shift from one-handed to two-handed grasping occurred at the same body-scale ratio between cube size and finger span for all three age groups. Evidence was found for the presence of a sudden jump, enhanced variance, multistability, and hysteresis, indicating that the body-scaled ratio of cube and hand size serves as a control parameter. No change with age for the stability properties of the grasping patterns were observed.

Anthropometry↗
PubMed1996

The spatiotemporal structure of control variables during catching.

The discrepancy between traditional (force scaling models) and the more recently conceived dynamic explanations of load compensation (lambda model) was the departure point for the present study. By using the complex "open" motor skill of catching a ball--rather than the traditional "closed" skills--under "normal" (baseline) conditions and under conditions where a spring load was applied to the catching hand (thereby changing the dynamics of the skeletomuscular system) it was hoped to provide further clarification of this issue. Traditional force scaling models, in this respect, would predict that maximal closing velocity of the grasp action, and movement time would not be significantly different between a control and a spring-load condition. In contrast, a dynamic system perspective would maintain that spring loading would be compensated for by a change in the rate of shift of the reciprocal command (R-command). The obtained results showed a significant difference for conditions with regard to the maximal closing velocity of the grasp action, the baseline condition being higher than the two spring-load conditions. Furthermore, a significant difference was found for the aperture at moment of catch, the aperture at moment of catch being smaller in the baseline condition than that under the two spring-load conditions. With regard to the temporal variables, no significant differences were obtained. A comprehensive overall explanation of the obtained data in terms of the force scaling models was not realisable. It may be that findings supporting such theories are task specific and that for constrained tasks--such as catching a ball--different underlying organisational principles apply. The lambda model, however, could explain adequately the obtained results. It was concluded that, except for the preparatory phase associated with load compensation before the onset of the movement of the ball, the spatiotemporal structure of the control pattern underlying catching remains the same (invariant) in both baseline and load conditions. Thereby, the spatiotemporal structure of the resulting movement changes under the influence of the load and thus is not the same for load and baseline condition.

Adult↗
PubMed1994

The effect of body orientation to gravity on early infant reaching.

The purpose of the study was to examine the effect of body orientation with respect to gravity on infant's reaching quantity and quality. Two groups, 12- to 19-week-old and 20- to 27-week-old infants, were seated in three positions: vertical (90 degrees from horizontal), recline (60 degrees), and supine (0 degrees). Nine balls on a black board were presented. Video recordings were used to measure quantity of reaching (number and duration of reaches) and quality of reaching (open or closed hand, starting position of the arm, and position of touched and grasped balls). On the quantity measure there was a significant age x body position interaction that indicated that the 12- to 19-week-olds showed reaching behavior in the vertical position equal to that of 20- to 27-week-old infants in all positions. A similar tendency, although not significant, was found for the quality measurements. These findings indicate that the development of reaching does not just reflect maturation of the central nervous system, but a changing interaction between organismic and environmental constraints.

Age Factors↗
PubMed1994

The control and coordination of one-handed catching: the effect of temporal constraints.

The aim of the experiment was to identify the control mechanisms involved in a goal-directed task by manipulating the temporal constraints. Subjects were required to catch, with one hand, table tennis balls projected by a ball-projection machine under five temporal conditions (ball speed ranged from 5.7 to 9 m/s, giving rise to flight times of 550-350 ms). By means of three-dimensional kinematics analysis the following results were obtained, which are some spatio-temporal adaptations of the catching movement to the increase of temporal constraints: (1) a decrease in movement time, (2) an increase in the straightness of the trajectory of the wrist, and (3) a shift backwards of the place of ball-hand contact while (4) the grasping time was kept constant. Moreover, as a result of increasing temporal constraints, the acceleration phase of the transportation component was kept constant while the deceleration phase was progressively decreased and nearly suppressed. Further, an increased correlation of the initial direction of the transportation component with the initial direction of the ball path was found. These findings show some spatio-temporal adaptations of the catching movement when the time available is manipulated. They also support the contention of a shift in the control mechanisms involved in one-handed catching facing different temporal constraints.

Goals↗
PubMed1993

The visual guidance of catching.

In order to explore the nature and amount of information in the optic array used by subjects required to carry out one-handed catching actions, the optical expansion pattern (using a deflating ball) and the duration of viewing time (using liquid crystal spectacles) of the ball were varied. Subjects were required to catch luminous balls (two of constant physical size and one of changing physical size during approach) attached to a pendulum in a totally dark room, while the liquid spectacles were closed at 0, 100, 200 or 300 ms before hand-ball contact. The results confirmed previous findings that the timing of the catching action is based on retinal expansion information and that conclusion was strengthened when an additional dependent variable (time of the maximal opening velocity of the grasp) was used. Further, for the viewing time duration manipulations, the time of the maximal closing velocity of the hand was later, while no effect was found on the time of the maximal opening velocity, when the last 300 ms of the trajectory of the ball was occluded. Adjustments to the catching action in response to the different ball sizes under the 0 ms condition differed significantly from the adjustments under the 300 ms condition. Both findings point to the importance of relative optical expansion information, available between 300 and 200 ms before ball-hand contact, in maintaining a (relatively) continuous perception-action coupling in the act of catching.

Adult↗
PubMed1992

The role of predictive visual temporal information in the coordination of muscle activity in catching.

This study addresses the question as to the nature of the information on which the preactivation of the appropriate muscles in the grasping of the ball in a one-handed catching task is initiated and coordinated. High speed film and electromyograms were recorded while experiences subjects (N = 4) caught balls--projected towards them by a ball-machine at different speeds (11.9, 13.9 and 16.2 m/s--resulting in significantly different flight times of 508, 443 and 355 ms, respectively). Tau-margins (times to contact) values were calculated at the time of the initiation of the grasp movement for each subject at each speed. No significant differences were found between tau-margins at different speeds. Further, the onset of the muscle activity for the initiation of the grasp movement was shown to be independent of ball speed. These findings lend support to the contention that the initiation of the grasp movement in catching is controlled and coordinated by the optical variable tau which specifies (directly) this time-to-contact. Given that the muscle group selected includes both flexors and extensors, co-activation on the basis of tau information is evidenced.

Adult↗