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1.
Zhang W Gordon AM McIsaac TL Santello M 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2011,211(1):17-26
Tactile signals from the fingertips play a crucial role in the planning and control of object manipulations. Specifically,
subjects adapt their digit forces to the object physical properties, including the friction at the object surface, to perform
object manipulation while preventing slipping or dropping. This study addressed the adaptation of multi-digit forces to friction
that occurs within a trial (from contact to onset of object manipulation) and across trials. Ten healthy participants were
instructed to grasp, lift, hold, and release a grip device with five digits under four texture conditions: (1) all digits
on rayon (R–R), (2) all digits on sandpaper (S–S), (3) thumb on sandpaper and fingers on rayon (S–R), and (4) thumb on rayon
and fingers on sandpaper (R–S). Changing the texture conditions elicited significant changes from object contact to lift onset
on digit normal force and center of pressure, as well as on the safety margins and force sharing patterns, e.g., normal forces
exerted by each finger expressed as percentage of thumb normal forces. Furthermore, these friction effects were found on the
very first trial and were observed throughout the remainder of the trials, thus indicating that force adaptation occurred
within the first manipulation. Finally, a highly linear relation between the safety margin at object lift onset and object
hold confirmed that digit force adaptation to friction occurred before object lift onset. These findings are discussed in
relation to the role of tactile input in force modulation during the early phase of multi-digit grasping. 相似文献
2.
Optimal feedback control postulates that feedback responses depend on the task relevance of any perturbations. We test this prediction in a bimanual task, conceptually similar to balancing a laden tray, in which each hand could be perturbed up or down. Single-limb mechanical perturbations produced long-latency reflex responses ("rapid motor responses") in the contralateral limb of appropriate direction and magnitude to maintain the tray horizontal. During bimanual perturbations, rapid motor responses modulated appropriately depending on the extent to which perturbations affected tray orientation. Specifically, despite receiving the same mechanical perturbation causing muscle stretch, the strongest responses were produced when the contralateral arm was perturbed in the opposite direction (large tray tilt) rather than in the same direction or not perturbed at all. Rapid responses from shortening extensors depended on a nonlinear summation of the sensory information from the arms, with the response to a bimanual same-direction perturbation (orientation maintained) being less than the sum of the component unimanual perturbations (task relevant). We conclude that task-dependent tuning of reflexes can be modulated online within a single trial based on a complex interaction across the arms. 相似文献
3.
Tara L. McIsaac Marco Santello Jamie A. Johnston Wei Zhang Andrew M. Gordon 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2009,194(1):79-90
During multi-digit grasping both local and non-local digit force responses occur in response to changes in texture at selected
digits depending on the grasp configuration. However, the extent to which the specific patterns of force distribution depend
on the requirement to hold the object against gravity remains to be determined. In the present study, we examined whether
grasp force sharing patterns are invariant when the constraint of maintaining the object orientation vertical against gravity
is removed. We used changes in object texture to elicit force changes at single digits during two grasping tasks with different
behavioral contexts. One task entailed holding an object against gravity (object hold [OH]). A second (force production [FP])
task consisted of generating lifting forces on an object clamped to the tabletop that were matched to those used during OH.
Unlike OH, the FP task lacks the behavioral consequences associated with erroneous sharing of normal and tangential digit
forces, e.g., object tilt. Ten subjects lifted and simulated lifting an instrumented object measuring grasping normal and
vertical tangential forces at all five digits when the textures were uniformly high-friction sandpaper or low-friction rayon
and when one digit contacted a different frictional texture than the other four digits. We found that in both tasks texture
changes at individual digits elicited force changes at that digit as well as other digits. However, the specific pattern of
force distribution changes differed during OH compared to FP. While subjects modulate the normal and tangential digit forces
to different degrees depending on object texture and the grasping task, they ignore the requirement of moment equilibrium
when this has no consequences on object orientation (FP task). These findings indicate that multi-digit force responses to
texture revealed by previous studies are not obligatory and suggest that the behavioral context of a task should be considered
when inferring general principles of multi-digit force coordination. 相似文献
4.
In the human upper limb a proportion of the descending corticospinal command may be relayed through cervical propriospinal premotoneurons. This may serve to coordinate movements involving multiple joints of the arm, such as reaching. The present study was conducted to determine whether a shoulder stabilizing muscle, infraspinatus (INF), is functionally integrated into the putative cervical propriospinal network, and whether there is task-dependent modulation of the network. Fourteen healthy adults participated in this study. Responses in the right INF were evoked by transcranial magnetic stimulation over the motor cortex and compared with responses conditioned by ulnar nerve stimulation. Interstimulus intervals were chosen to summate inputs at the level of the premotoneurons. Participants performed a forearm and shoulder muscle cocontraction task or a grip-lift task that also coactivated forearm and shoulder muscles. During the cocontraction task, INF motor-evoked potentials were significantly facilitated by ulnar nerve stimulation at low intensities and suppressed at higher intensities. Only facilitation reached significance during the grip-lift task. We have shown for the first time that propriospinal pathways may connect the hand to the rotator cuff of the shoulder. The modulation of facilitation/suppression during the grip-lift task suggests that inhibition of propriospinal premotoneurons is down-regulated in a task-dependent manner to increase the gain in the feedback reflex loop from forearm and hand muscles as required. 相似文献
5.
Budgeon MK Latash ML Zatsiorsky VM 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2008,189(3):345-359
We explored adjustments in multi-digit coordinated action on a hand-held object with finger addition and removal. The subjects
(n = 7) kept a vertically oriented handle at rest using a prismatic grasp as if holding a glass of liquid and then either added
one finger to the grasp, the index (I) or little (L) finger, or removed one finger. Three external torques were applied on
the apparatus: clockwise, counterclockwise, and no torque. The individual digit forces and moments were recorded with six-component
sensors. The change in grasping force, normal force of the thumb and virtual finger (VF, an imagined finger that generates
the same mechanical effect as all fingers together), depended on the function of the manipulated finger, i.e. on whether the
finger resisted external torque (torque agonist) or assisted it (torque antagonist). There was a significant increase of the
grasping force when an antagonist was added or when an agonist was removed. These force increases were not necessary for slipping
prevention: the normal forces prior to the manipulation were large enough to prevent slipping. All other finger manipulations
exhibited no significant change in the grip force, except for the antagonist removal during the supination efforts (after
removing the I finger the grasping force decreased). In contrast, the changes in the tangential force of the thumb depended
on the manipulated finger, not on the finger function with respect to external torque. There was a significant thumb tangential
force increase when the I finger was added or when the L finger was removed; opposite changes were seen when the L finger
was added or the I finger was removed. The changes of the virtual finger (VF) tangential force were equal and opposite to
the thumb tangential force alterations; these opposite changes caused changes in the moments, these forces generated. The
changes in the moments of the tangential forces were counterbalanced by the opposite changes in the moments of normal forces
such that the total moment remained constant and the handle orientation was maintained. At the level of individual finger
(IF) forces two strategies of error compensation were found: (a) local error compensation—the opposite action of the neighboring finger, i.e. force decrease in response to a force increase (finger addition), and
vice versa and (b) distant error compensation—similar action by a finger that is a torque antagonist to the manipulated finger. During the transient periods, the changes
in the thumb and VF forces were simultaneous and equal in magnitude. The normal forces increased or decreased concurrently
while the changes in the tangential forces were opposite in direction. The data support the existence of chain effects in
the digit force adjustments to finger addition or removal. We conclude that the digit force adjustments during the object
manipulation are controlled mainly in a feed-forward manner. The obtained data agree with the principle of superposition reported
previously. The findings agree with earlier reports on the limited ability of CNS to organize synergies at two levels of a
control hierarchy simultaneously. 相似文献
6.
A. Hess E. Kunesch J. Classen J. Hoeppner K. Stefan R. Benecke 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1999,124(3):321-330
In 11 healthy subjects motor-evoked potentials (MEPs) and silent periods (SPs) were measured in the right first dorsal interosseus
(FDI) and abductor pollicis brevis muscles (APB): (1) when transcranial magnetic cortex stimulation (TMS) was applied at tonic
isometric contraction of 20% of maximum force, (2) when TMS was applied during tactile exploration of a small object in the
hand, (3) when TMS was applied during visually guided goal-directed isometric ramp and hold finger flexion movements, and
(4) when at tonic isometric contraction peripheral electrical stimulation (PES) of the median nerve was delivered at various
intervals between PES and TMS. Of the natural motor tasks, duration of SPs of small hand muscles was longest during tactile
exploration (APB 205±42 ms; FDI 213±47 ms). SP duration at tonic isometric contraction amounted to 172±35 ms in APB and 178±31
ms in FDI, respectively. SP duration in FDI was shortest when elicited during visually guided isometric finger movements (159±15
ms). At tonic isometric contraction, SP was shortened when PES was applied at latencies –30 to +70 ms in conjunction with
TMS. The latter effect was most pronounced when PES was applied 20 ms before TMS. PES-induced effects increased with increasing
stimulation strength up to a saturation level which appeared at the transition to painful stimulation strengths. Both isolated
stimulation of muscle afferents and of low-threshold cutaneous afferents shortened SP duration. However, PES of the contralateral
median nerve had no effect on SPs. Amplitudes of MEPs did not change significantly in any condition. Inhibitory control of
motor output circuitries seems to be distinctly modulated by peripheral somatosensory and visual afferent information. We
conclude that somatosensory information has privileged access to inhibitory interneuronal circuits within the primary motor
cortex.
Received: 24 November 1997 / Accepted: 11 August 1998 相似文献
7.
Ferrera VP 《Journal of neurophysiology》2000,84(6):2725-2738
To investigate the transformation of retinal image velocity into smooth pursuit eye velocity, eye movements were measured in the presence of two moving targets. In the first experiment, the targets were identical in all respects except for direction of motion, and the monkey was not cued to attend to either target. In this experiment, smooth pursuit eye velocity elicited by two targets was the vector average of the response evoked by each target alone. In subsequent experiments, we examined the effects of stimulus and task parameters on the selectivity of pursuit. When the targets were made different colors and monkeys were cued for the color of the rewarded target, their pursuit eye movements were biased in the direction of the rewarded target, but still showed a substantial influence of the nonrewarded target (distractor). It did not matter whether the same target color was used for an entire session or whether the color was randomized from trial to trial. Reducing uncertainty about the axis of motion of the rewarded target also had little effect. However, the pattern of image motion appeared to have a substantial effect; radial image motion favored averaging, and winner-take-all pursuit was found only with nonradial image motion. We conclude that the sensorimotor interface for pursuit uses a flexible decision rule that can vary continuously from vector averaging to winner-take-all. We present a simple recurrent network model that reflects this range of behavior. The model has allowed us to identify three computational elements (selection bias, competitive inhibition, and response normalization) that should be taken into consideration in future models of smooth pursuit. 相似文献
8.
Prehension of half-full and half-empty glasses: time and history effects on multi-digit coordination
Sun Y Zatsiorsky VM Latash ML 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2011,209(4):571-585
We explored how digit forces and indices of digit coordination depend on the history of getting to a particular set of task
parameters during static prehension tasks. The participants held in the right hand an instrumented handle with a light-weight
container attached on top of the handle. At the beginning of each trial, the container could be empty, filled to the half
with water (0.4 l), or filled to the top (0.8 l). The water was pumped in/out of the container at a constant, slow rate over
10 s. At the end of each trial, the participants always held a half-filled container that has just been filled (Empty-Half),
emptied (Full-Half) or stayed half-filled throughout the trial (Half-Only). Indices of covariation (synergy indices) of elemental
variables (forces and moments of force produced by individual digits) stabilizing such performance variables as total normal
force, total tangential force, and total moment of force were computed at two levels of an assumed control hierarchy. At the
upper level, the task is shared between the thumb and virtual finger (an imagined digit with the mechanical action equal to
that of the four fingers), while at the lower level the action of the virtual finger is shared among the actual four fingers.
Filling or emptying the container led to a drop in the safety margin (proportion of grip force over the slipping threshold)
below the values observed in the Half-Only condition. Synergy indices at both levels of the hierarchy showed changes over
the Full-Half and Empty-Half condition. These changes could be monotonic (typical of moment of force and normal force) or
non-monotonic (typical of tangential force). For both normal and tangential forces, higher synergy indices at the higher level
of the hierarchy corresponded to lower indices at the lower level. Significant differences in synergy indices across conditions
were seen at the final steady state showing that digit coordination during steady holding an object is history dependent.
The observations support an earlier hypothesis on a trade-off between synergies at the two levels of a hierarchy. They also
suggest that, when a change in task parameters is expected, the neural strategy may involve producing less stable (easier
to change) actions. The results suggest that synergy indices may be highly sensitive to changes in a task variable and that
effects of such changes persist after the changes are over. 相似文献
9.
Valero-Cuevas FJ 《Journal of neurophysiology》2000,83(3):1469-1479
Human fingers have sufficiently more muscles than joints such that every fingertip force of submaximal magnitude can be produced by an infinite number of muscle coordination patterns. Nevertheless, the nervous system seems to effortlessly select muscle coordination patterns when sequentially producing fingertip forces of low, moderate, and maximal magnitude. The hypothesis of this study is that the selection of coordination patterns to produce submaximal forces is simplified by the appropriate modulation of the magnitude of a muscle coordination pattern capable of producing the largest expected fingertip force. In each of three directions, eight subjects were asked to sequentially produce fingertip forces of low, moderate, and maximal magnitude with their dominant forefinger. Muscle activity was described by fine-wire electromyograms (EMGs) simultaneously collected from all muscles of the forefinger. A muscle coordination pattern was defined as the vector list of the EMG activity of each muscle. For all force directions, statistically significant muscle coordination patterns similar to those previously reported for 100% of maximal fingertip forces were found for 50% of maximal voluntary force. Furthermore the coordination pattern and fingertip force vector magnitudes were highly correlated (r > 0.88). Average coordination pattern vectors at 50 and 100% of maximal force were highly correlated with each other, as well as with individual coordination pattern vectors in the ramp transitions preceding them. In contrast to this consistency of EMG coordination patterns, predictions using a musculoskeletal computer model of the forefinger show that force magnitudes =50% of maximal fingertip force can be produced by coordination patterns drastically different from those needed for maximal force. Thus when modulating fingertip force magnitude across the voluntary range, the number of contributing muscles and the relative activity among them was not changed. Rather, the production of low and moderate forces seems to be simplified by appropriately scaling the magnitude of a coordination pattern capable of producing the highest force expected. 相似文献
10.
Tinazzi M Farina S Tamburin S Facchini S Fiaschi A Restivo D Berardelli A 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2003,150(2):222-229
We evaluated motor evoked potentials (MEPs) and duration of the cortical silent period (CSP) from the right first dorsal interosseous
(FDI) muscle to transcranial magnetic stimulation (TMS) of the left motor cortex in ten healthy subjects performing different
manual tasks. They abducted the index finger alone, pressed a strain gauge with the thumb and index finger in a pincer grip,
and squeezed a 4-cm brass cylinder with all digits in a power grip. The level of FDI EMG activity across tasks was kept constant
by providing subjects with acoustic-visual feedback of their muscle activity. The TMS elicited larger amplitude FDI MEPs during
pincer and power grip than during the index finger abduction task, and larger amplitude MEPs during pincer gripping than during
power gripping. The CSP was shorter during pincer and power grip than during the index finger abduction task and shorter during
power gripping than during pincer gripping. These results suggest excitatory and inhibitory task-dependent changes in the
motor cortex. Complex manual tasks (pincer and power gripping) elicit greater motor cortical excitation than a simple task
(index finger abduction) presumably because they activate multiple synergistic muscles thus facilitating corticomotoneurons.
The finger abduction task probably yielded greater motor cortical inhibition than the pincer and power tasks because muscles
uninvolved in the task activated the cortical inhibitory circuit. Increased cortical excitatory and inhibitory functions during
precision tasks (pincer gripping) probably explain why MEPs have larger amplitudes and CSPs have longer durations during pincer
gripping than during power gripping.
Electronic Publication 相似文献
11.
D.J. Serrien Mario Wiesendanger 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1999,128(1-2):76-80
The study examined the anticipatory grip force modulations to load force changes during a drawer-opening task. An impact
force was induced by a mechanical stop which abruptly arrested movement of the pulling hand. In performing this task, normal
subjects generated a typical grip force profile characterized by an initial force impulse related to drawer movement onset,
followed by a ramp-like grip force increase prior to the impending load perturbation. Finally, a reactive response was triggered
by the impact. In patients with bilateral cerebellar dysfunction, the drawer-opening task was performed with an alternative
control strategy. During pulling, grip force was increased to a high (overestimated) default level. The latter suggests that
cerebellar patients were unable to adjust and to scale precisely the grip force according to the load force. In addition,
the latency between impact and reactive activity was prolonged in the patients, suggesting an impaired cerebellar transmission
of the long-latency responses. In conclusion, these data demonstrate the involvement of cerebellar circuits in both proactive
and reactive mechanisms in view of predictable load perturbations during manipulative behavior.
Received: 27 July 1998 / Accepted: 19 December 1998 相似文献
12.
13.
Using functional MRI we examined the task-dependency of brain activation patterns evoked by vibrotactile stimulation. For this purpose, we measured activations after identical stimulation of the fingers of the right hand in three different task conditions: passive attention, localization of the vibrations, and discrimination of temporal noise within the vibrations. Further, we investigated whether, regardless of task demands, the characteristics of the vibrations – periodic versus noisy – had an effect on brain topography. Vibrotactile processing was associated with activation in a variety of cortical areas including contralateral primary somatosensory cortex (SI), bilateral posterior parietal cortex, parietal operculum (second somatosensory cortex, SII), insula, and superior temporal gyrus, as well as ipsilateral middle temporal gyrus, precentral, and middle frontal gyrus. However, identical stimuli evoked different brain activity patterns in different task conditions: significantly stronger activity in the hand representation of SI was found for stimulus localization than for noise detection. In contrast, significantly higher activation for noise detection than for finger localization was found in the thalamus. Activation tended to be lower for noisy stimuli in both hemispheres. Significant stimulus-related differences, however, could be found only in the contralateral postcentral and parietal cortex, particularly during noise discrimination. In summary, in response to vibrotactile stimulation, the level of activation in processing circuits ranging across thalamus and many cortical regions is dictated by the perceptual operation carried out on the vibration. We speculate that different nodes in the network carry signals that can be optimally decoded for either spatial or temporal information and that the degree of activation reflects those nodes’ relative contributions to the decoding process. 相似文献
14.
Voelcker-Rehage C Alberts JL 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2005,166(1):61-70
The aim of this study was to determine the effect of age on the modulation of forces produced by the digits and to determine the effects of practice on the control of these forces in young and older adults. Young (n = 14, 19-28 years) and old (n = 12, 67-75 years) adults used a precision grip to perform a variable force-tracking task (sine wave, 5-25% of maximum voluntary force) with their dominant hand. Participants performed 100 practice trials over 2 consecutive days. Results indicated that both groups improved accuracy of force tracking as a result of practice. Younger adults performed the task at a higher level in pre- and post-test conditions compared with older adults. Younger adults showed improvements in force control in force generation and release phases. Older adults reached performance levels comparable with younger adults' pre-test performance, but only after extended practice. In contrast to young adults, older adults' performance during the force release phases remained quite variable. These data suggest that older adults are impaired in the accurate release of grip force. Varied force release patterns that disrupt the precision of force modulation may contribute to older adults' diminished dexterous abilities. 相似文献
15.
16.
J. Liepert J. Classen L. G. Cohen M. Hallett 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1998,118(3):421-426
The motor-evoked potential (MEP) to transcranial magnetic stimulation (TMS) is inhibited when preceded by a subthreshold
TMS stimulus at short intervals (1–6 ms; intracortical inhibition, ICI) and is facilitated when preceded by a subthreshold
TMS at longer intervals (10–15 ms; intracortical facilitation, ICF). We studied changes in ICI and ICF associated with two
motor tasks requiring a different selectivity in fine motor control of small hand muscles (abductor pollicis brevis muscle,
APB, and fourth dorsal interosseous muscle, 4DIO). In experiment 1 (exp. 1), nine healthy subjects completed four sets (5
min duration each) of repetitive (1 Hz) thumb movements. In experiment 2 (exp. 2), the subjects produced the same number of
thumb movements, but complete relaxation of 4DIO was demanded. Following free thumb movements (exp. 1), amplitudes of MEPs
in response to both single and paired TMS showed a trend to increase with the number of exercise sets in both APB and 4DIO.
By contrast, more focal, selective thumb movementsinvolving APB with relaxation of 4DIO (exp. 2) caused an increase in MEP
amplitudes after single and paired pulses only in APB, while a marked decrease in MEPs after paired pulses, but not after
single TMS, in the actively relaxed 4DIO. This effect was more prominent for the interstimulus interval (ISI) of 1–3 ms than
for longer ISIs (8 ms, 10 ms, and 15 ms). F-wave amplitudes reflecting excitability of the alpha motoneuron pool were unaltered
in APB and 4DIO, suggesting a supraspinal origin for the observed changes. We conclude that plastic changes of ICI and ICF
within the hand representation vary according to the selective requirements of the motor program. Performance of more focal
tasks may be associated with a decrease in ICI in muscles engaged in the training task, while at the same time ICI may be
increased in an actively relaxed muscle, also required for a focal performance. Additionally, our data further supports the
idea that ICI and ICF may be controlled independently.
Received: 20 September 1996 / Accepted: 1 October 1997 相似文献
17.
This study examined what changes occur in upper-limb bilateral coordination during clapping as the movement frequency requirements were increased to the maximum. Subjects were required to begin the clapping action at approximately 1 Hz and gradually increase the movement speed until their maximal frequency was achieved. Hand and finger displacement and surface electromyograms (EMG) from finger flexor/extensor muscles were recorded. The results showed that the maximal attainable movement frequency was between 7 and 8 Hz. As the action approached the ceiling frequency (>5 Hz), there was a significant reduction in movement amplitude of the non-preferred limb accompanied by increased co-activation of the muscles within this limb. The movement amplitude of preferred limb was maintained. Subsequently, there was a decrease in coupling between the two limbs with the bilateral coordination pattern transitioning from an in-phase pattern to an asymmetric mode, where only the preferred limb was moving. These findings reveal that there is a frequency induced transition to single-limb motion that reflects a stability boundary at the upper frequency limits of bimanual coordination. 相似文献
18.
N. V. Dounskaia S. P. Swinnen C. B. Walter A. J. Spaepen S. M. P. Verschueren 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1998,121(3):239-254
The present paper focused on the role of mechanical factors arising from the multijoint structure of the musculoskeletal system
and their use in the control of different patterns of cyclical elbow-wrist movements. Across five levels of cycling frequency
(from 0.45 Hz up to 3.05 Hz), three movement patterns were analyzed: (1) unidirectional, including rotations at the elbow
and wrist in the same direction; (2) bidirectional, with rotation at the joints in opposite directions, and (3) free-wrist
pattern, which is characterized by alternating flexions and extensions at the elbow with the wrist relaxed. Angular position
of both joints and electromyographic activity of biceps, triceps, the wrist flexor, and the wrist extensor were recorded.
It was demonstrated that control at the elbow was principally different from control at the wrist. Elbow control in all three
patterns was similar to that typically observed during single-joint movements: elbow accelerations-decelerations resulted
from alternating activity of the elbow flexor and extensor and were largely independent of wrist motion at all frequency plateaus.
The elbow muscles were responsible not only for the elbow movement, but also for the generation of interactive torques that
played an important role in wrist control. There were two types of interactive torques exerted at the wrist: inertial torque
arising from elbow motion and restraining torque arising from physical limits imposed on wrist rotation. These interactive
torques were the primary source of wrist motion, whereas the main function of wrist-muscle activity was to intervene with
the interactive effects and to adjust the wrist movement to comply with the required coordination pattern. The unidirectional
pattern was more in agreement with interactive effects than the bidirectional pattern, thus causing their differential difficulty
at moderate cycle frequencies. When cycling frequency was further increased, both the unidirectional and bidirectional movements
lost their individual features and acquired features of the free-wrist pattern. The deterioration of the controlled patterns
at high cycling frequencies suggests a crucial role for proprioceptive information in wrist control. These results are suppportive
of a hierachical organization of control with respect to elbow-wrist coordination, during which the functions of control at
the elbow and wrist are principally different: the elbow muscles generate movement of the whole linkage and the wrist muscles
produce corrections of the movement necessary to fulfill the task.
Received: 5 August 1997 / Accepted: 29 January 1998 相似文献
19.
This study investigated the interactive influence of organismic, environmental, and task constraints on the organization of redundant force coordination patterns and the hypothesis that each of the three categories of constraints is weighted based on their relative influence on coordination patterns and the realization of the task goal. In the bimanual isometric force experiment, the task constraint was manipulated via different coefficients imposed on the finger forces such that the weighted sum of the finger forces matched the target force. We examined three models of task constraints based on the criteria of task variance (minimum variance model) and efficiency of muscle force output (coefficient-independent and coefficient-dependent efficiency models). The environmental constraint was quantified by the perceived performance error, and the organismic constraint was quantified by the bilateral coupling effect (i.e., symmetric force production) between hands. The satisficing approach was used in the models to quantify the constraint weightings that reflect the interactive influence of different categories of constraints on force coordination. The findings showed that the coefficient-dependent efficiency model best predicted the redundant force coordination patterns across trials. However, the within-trial variability structure revealed that there was not a consistent coordination strategy in the online control of the individual trial. The experimental findings and model tests show that the force coordination patterns are adapted based on the principle of minimizing muscle force output that is coefficient dependent rather than on the principle of minimizing signal-dependent variance. Overall, the results support the proposition that redundant force coordination patterns are organized by the interactive influence of different categories of constraints. 相似文献
20.
Moerchen VA Lazarus JC Gruben KG 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2007,180(2):367-376
The organization of thumb and index finger forces in a pinch formation was investigated under conditions where kinetic constraints
on interdigit force coupling were removed. Two visually guided isometric force tasks at submaximal levels were used to characterize
the spatial and temporal aspects of interdigit force coupling. Task 1 provided an initial characterization of interdigit force
coordination when the force relationship between the digits was not specified. Task 2 probed the extent to which a preferred
coordination of the thumb and index finger could be decoupled, both temporally and with respect to force magnitude, by specifying
the coordination between the digit forces. Digit forces were measured using a pinch apparatus that was instrumented to record
the magnitude and direction of the thumb (F
t) and index finger (F
i) forces, independently. Two apparatus conditions allowed further examination of interdigit force coordination when the relationship
between digit forces was mechanically constrained (pivot condition), and when the relationship between digit forces was not
constrained, allowing the neuromotor system to select a preferred pattern of interdigit coordination (fixed condition). Sixteen
right-handed adults exerted a pinch force against the apparatus to match a single-cycle sine wave that varied between 15 and
35% of each participant’s maximal voluntary pinch force. The target was presented with positive or negative target sense,
to vary the order of force level and direction of force change across the trials. When the mechanical constraints allowed
selection of a preferred coordination pattern, F
t = F
i was a robust result. In contrast, when the coordination between the digit forces was specified by the requirement to simultaneously
produce and control independent thumb and index finger forces while acting on a stable object, subjects were able to produce
forces that markedly deviated from the F
t = F
i coordination. The organization of pinch is characterized by a preferred, tight coupling of digit forces, which can be modified
based on task demands. 相似文献