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1.
We manipulated the visual information available for grasping to examine what is visually guided when subjects get a precision
grip on a common class of object (upright cylinders). In Experiment 1, objects (2 sizes) were placed at different eccentricities
to vary the relative proximity to the participant’s (n = 6) body of their thumb and finger contact positions in the final grip orientations, with vision available throughout or
only for movement programming. Thumb trajectories were straighter and less variable than finger paths, and the thumb normally
made initial contact with the objects at a relatively invariant landing site, but consistent thumb first-contacts were disrupted
without visual guidance. Finger deviations were more affected by the object’s properties and increased when vision was unavailable
after movement onset. In Experiment 2, participants (n = 12) grasped ‘glow-in-the-dark’ objects wearing different luminous gloves in which the whole hand was visible or the thumb
or the index finger was selectively occluded. Grip closure times were prolonged and thumb first-contacts disrupted when subjects
could not see their thumb, whereas occluding the finger resulted in wider grips at contact because this digit remained distant
from the object. Results were together consistent with visual feedback guiding the thumb in the period just prior to contacting
the object, with the finger more involved in opening the grip and avoiding collision with the opposite contact surface. As
people can overtly fixate only one object contact point at a time, we suggest that selecting one digit for online guidance
represents an optimal strategy for initial grip placement. Other grasping tasks, in which the finger appears to be used for
this purpose, are discussed. 相似文献
2.
Sosnoff JJ Jordan K Newell KM 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2005,167(1):76-85
The experiment examined the force fluctuations during two and three digit grip configurations to investigate the relationship
between task performance and inter-digit individuation as a function of force level and visual information intermittency rate
over ∼100-fold range (0.21–20 Hz). Subjects grasped an object with either the index finger (two digit grip) or the index and
middle finger (three digit grip) opposing the thumb and produced isometric force to match a low and high total force level
target. Force accuracy was lower at the large visual intermittency conditions and the higher force level. The force variability
was lower in the three digit grip. Inter-digit individuation increased as a function of visual intermittency rate and was
greater at the low force level. There was no improvement in performance or inter-digit individuation when visual feedback
intermittency was greater than ∼6 Hz (∼150 ms). Linear regression between the measures of task performance and inter-digit
individuation yielded a significant negative relationship that was only present in the two digit grip when visual feedback
rate was 1.67 Hz or lower and in the three digit grip when the feedback rate was 10 Hz or lower. The greater biomechanical
degrees of freedom in the three digit grip configuration enable the subject to use, more effectively, visual information feedback
at faster timescales in maximizing task performance by increasing digit independence. The shift from visual to nonvisual dominated
motor control processes is dependent on the interaction of informational and biomechanical degrees of freedom. 相似文献
3.
Cole KJ Potash M Peterson C 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2008,184(2):157-163
When repetitively lifting an object with mechanical properties that vary from lift-to-lift, the fingertip forces for gripping
and lifting are influenced strongly by the previous lift, revealing a ‘sensorimotor’ memory. Two recent reports indicate that
the sensorimotor memory for grip force is easily disrupted by an unrelated task like a strong pinch or vibration, even when
the lift was performed with the hand contralateral to the vibration or preceding pinch. These findings indicate that this
memory may reflect sensory input or muscle contraction levels, rather than object properties or the specific task of gripping
and lifting. Here we report that the predictive scaling of lift force was not disrupted by conditioning tasks that featured exerting a vertical isometric force with the upper extremity. When subjects
lifted a 2 N object repetitively the peak lift force rate was 26.4 N/s. The lift force rate increased to 36.1 N/s when the
2 N object was lifted (regardless of hand) after lifting the 8 N object with the right hand, which reveals the expected ‘sensorimotor’
memory. The lift force rate did not increase (24.8 vs. 26.4 N/s for the control condition) when a bout of isometric exertion
(9.8 N) in the vertical direction with the distal right forearm preceded lifts of the 2 N object. This finding was confirmed
with another isometric task designed to more closely mimic lifting an object with a precision grip. This difference in the
sensitivity of grip versus lift force to a preceding isometric contraction indicates that separate sensorimotor memories contribute
to the predictive scaling of the commands for gripping and lifting an object. 相似文献
4.
Y. Hu R. Eagleson M. A. Goodale 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1999,126(1):109-116
We examined the effect on manual prehension of introducing a 5-s delay between viewing a target object and initiating a grasping
movement. Subjects were tested in four conditions: three involved grasping the object and a fourth involved estimating its
size. In the main experimental condition (Open Loop Delay), subjects viewed a target object for 300 ms, but did not initiate
a grasping movement until an auditory signal was presented 5 s later. In this condition, subjects had to rely on stored visual
information for guiding their grasp after the delay. In another condition (Open Loop), subjects initiated their grasping movement
as soon as the target appeared. In both of these open-loop conditions, subjects reached out and grasped the object without
seeing their hand. In the third grasping condition (Closed Loop), the target object and the hand were visible throughout the
reach. In the three grasping conditions, subjects were instructed to pick up the object across its width using their index
finger and thumb. In a final condition (Perceptual Estimation), subjects gave a manual estimate of the object’s width with
their index finger and thumb after viewing the object for 300 ms. In all four conditions, subjects were presented with a target
object in which the height, length and width were independently varied from trial to trial. The results of the experiment
indicated that reaching and grasping movements made in the Open-Loop and Closed-Loop conditions did not differ in any kinematic
measures. In contrast, when subjects performed in the Open-Loop Delay condition, their reaches took significantly longer and
achieved peak velocity proportionately earlier. As well, their maximum grip aperture was significantly larger. In addition,
reaching movements in all three grasping conditions were affected by both the object’s width (the ’relevant’ dimension) and
height. The manual estimates in the Perceptual-Estimation condition, however, reflected only the object’s width. These results,
together with evidence from other studies, suggest that motor actions performed after a delay use different transformations
than those used for ’real-time’ grasping. We argue that the stored visual information used to drive delayed actions arises
from a perceptual rather than a visuomotor analysis of the target object.
Received: 10 July 1998 / Accepted: 4 December 1998 相似文献
5.
Children's coordination of force output in a pinch grip task 总被引:1,自引:0,他引:1
This study examined the role of sensorimotor system noise in the organization of the force output of the thumb and index finger and the coordination between the two digits in an isometric pinch grip force task as a function of age (6, 8, 10, 18-22 years), feedback condition (with and without visual feedback information), and force level (5, 15, 25, and 35% of maximal voluntary force. With increases in age under the visual feedback conditions, the signal-to-noise ratio increased, the sequential structure of the force output signals became more irregular, the degree of coherence between the digits at higher force levels was enhanced, and the digits exhibited a greater degree of coherence across the higher frequencies of the power spectrum at all force levels. However, these age differences were either minimized or eliminated under conditions without feedback. These findings show that the age-related performance differences in grip force variability are primarily due to more effective use of visual information rather than age differences in intrinsic sensorimotor noise. 相似文献
6.
Schlicht EJ Schrater PR 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2007,182(1):47-57
To successfully lift an object, a person’s fingers must be moved to locations where forces can be applied that are sufficient
for maintaining contact and that allow for easy object manipulation. Obtaining such finger positions becomes more difficult
when there is perceptual uncertainty about the location of the hand and object. However, knowledge about the amount of uncertainty
could be incorporated into grasp plans to mitigate its effect. For example, during peripheral viewing the fingers could open
wider to avoid colliding with or missing the object. The goal of this study is to determine the degree to which people incorporate
their understanding of visual uncertainty when making a precision grasp. To investigate, subjects reached to a spatially fixed
object whose retinal location was varied by fixating points 0–80° to the left of the object. This manipulation controlled
the visual uncertainty of the hand and target without affecting the kinematic demands of the task. We found that people systematically
changed their grasping behavior as a function of the amount of visual uncertainty in the task. Specifically, subjects’ maximum
grip aperture increased linearly with target eccentricity. Moreover, the effect of visual uncertainty on finger trajectories
could be captured by a single dimension of change along an axis. Together, these findings suggest that the sensorimotor system
estimates visual uncertainty and behaviorally adjusts for it during grasping movements. 相似文献
7.
McIsaac TL Fuglevand AJ 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2006,174(4):769-774
The mechanisms by which the nervous system coordinates multiple muscles for the control of finger movements are not well understood. One possibility is that groups of muscles may be enlisted into synergies by last-order inputs that project across multiple motor nuclei. In this study we investigated the role that tactile input might play in coupling together the activities of motor units in two muscles involved in generating the precision grip. Cross-correlation analysis was used to assess the degree of synchrony in the discharge times of pairs of motor units recorded from index-finger and thumb flexor muscles while human subjects performed an isometric task that mimicked a precision grip. The magnitude of synchrony is thought to reflect the extent to which divergent last order inputs provide common synaptic input across motor neurons. Synchrony was evaluated under two simulated-gripping conditions: gripping with normal tactile input and gripping when tactile input from the digit pads was eliminated by applying flexion forces to fittings glued to the finger nails. Synchrony between motor units of index finger flexor and thumb flexor muscles, while substantial, was not significantly different across the two tactile-input conditions. These findings suggest that tactile input is not required to activate the divergent last-order inputs that couple together the activities of the index finger and thumb flexor muscles during the precision grip. 相似文献
8.
Sabah?Master Fran?ois?Tremblay 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2009,194(2):163-172
Task-dependant changes in corticomotor excitability have been described mainly in the context of grasp-oriented actions, neglecting
the sensory aspects of hand function. Here, we contrasted task-dependant facilitation in small hand muscles [i.e., first dorsal
interosseous (FDI) and abductor digiti minimi (ADM)] in the context of finger movements involving either discrimination or
non discrimination (ND) of tactile features. Healthy young individuals (n = 16) were trained to produce rhythmic to and fro movements at the sound of metronome ticks (0.8 Hz frequency, 5 s total
duration) with either the index or the little finger of the right hand. In the tactile discrimination (TD) condition, participants
were asked to attend to the location of two different 2-D tactile shapes disposed on the explored surface, whereas in the
ND condition, the finger was moved over a blank surface. In both conditions, a transcranial magnetic stimulation (TMS) pulse
was delivered at a specific time point in the course of the finger movement. Corticomotor excitability was assessed by monitoring
changes in the amplitude and latency of motor evoked potentials (MEPs) in the FDI and ADM. Changes in the duration of the
silent period were also assessed. The analysis revealed a significant large effect of task conditions (P < 0.001) on MEP amplitude, owing to the increase in MEP size observed during the TD, as compared to the ND condition. No
interaction between “Task” and “Muscle” was detected, however, indicating that MEPs in the two muscles were equally affected
by the task conditions. No significant changes were detected for variations in MEP latency or in the SP duration. An additional
control experiment performed in a subset of the participants (n = 9) showed that MEP facilitation was substantially reduced when attention to sensations arising from finger contact with
the shapes was diverted away by completion of a concurrent cognitive task (counting backward by three). These findings provide
further insights into the factors influencing task-dependant changes in corticomotor excitability during hand actions. Our
results highlight the importance of behavioral context and attention, in particular, in leading to further enhancement in
corticomotor excitability when the finger is actively engaged in TD. 相似文献
9.
Nowak DA Hermsdörfer J 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2006,173(4):650-660
We comparatively investigated predictive and reactive grip force behaviour in 12 subjects with basal ganglia dysfunction (six subjects with Parkinson’s disease, six subjects with writer’s cramp), two subjects chronically lacking all tactile and proprioceptive sensory feedback and 16 sex- and age-matched control subjects. Subjects held an instrumented receptacle between the index finger and thumb. A weight was dropped into the receptacle either unexpectedly from the experimenter’s hand with the subject being blindfolded or expectedly from the subject’s opposite hand. This paradigm allowed us to study predictive and reactive modes of grip force control. All patients generated an overshoot in grip force, irrespective of whether the weight was dropped expectedly or unexpectedly. When the weight was dropped from the experimenter’s hand, a reactive grip force response lagged behind the load perturbation at impact in patients with basal ganglia dysfunction and healthy controls. When the weight was dropped expectedly from the subject’s opposite hand, patients with basal ganglia dysfunction and healthy subjects started to increase grip force prior to the release of the weight, indicating a predictive mode of control. We interpret these data to support the notion that the motor dysfunction in basal ganglia disorders is associated with deficits of sensorimotor integration. Both deafferented subjects did not show a reactive mode of force control when the weight was dropped unexpectedly, underlining the importance of sensory feedback to initiate reactive force responses. Also in the predictive mode, grip force processing was severely impaired in deafferented subjects. Thus, at least intermittent sensory information is necessary to establish and update predictive modes of grasping force control. 相似文献
10.
Ansuini C Santello M Tubaldi F Massaccesi S Castiello U 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2007,180(1):85-96
This study assessed how hand shaping responds to a perturbation of object shape. In blocked trials (80% of total), subjects were instructed to reach, to grasp and lift a concave or a convex object. In perturbed trials (20% of total), a rotating device allowed for the rapid change from the concave to the convex object or vice versa.
In this situation subjects grasped the last presented object. Flexion/extension at the metacarpal-phalangeal and proximal
interphalangeal joints of all digits was measured by resistive sensors embedded in a glove. In the blocked condition we found
that most joints of the fingers were modulated by the type of the to-be-grasped object during the reach. When object shape
was perturbed, reach duration was longer and angular excursion of all fingers differed with respect to blocked trials. For
the ‘convex → concave’ perturbation, a greater degree of finger extension was found than during the blocked ‘concave’ trials.
In contrast, for the ‘concave → convex’ perturbation, fingers were more flexed than for the blocked ‘convex’ trials. The thumb
reacted to the perturbation showing a similar pattern (i.e., over-flexion with respect to the blocked trials) regardless the
‘direction’ of the perturbation. The present results suggest that applying an object shape perturbation during a reach-to-grasp
action determines a reorganization of all digits. This pattern is suggestive of a control strategy, which assigns to opposing
digits different roles. 相似文献
11.
Vaughan G. Macefield Ronald S. Johansson 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1996,108(1):172-184
Pulling or pushing forces applied to an object gripped between finger and thumb excite tactile afferents in the digits in a manner awarding these afferents probable roles in triggering the reactive increases in grip force and in scaling the changes in grip force to the changes in applied load-force. In the present study we assessed the possible contributions from slowly adapting afferents supplying muscles involved in the generation of grip forces and from digital joint afferents. Impulses were recorded from single afferents via tungsten microelectrodes inserted percutaneously into the median or ulnar nerves of awake human subjects. The subject held a manipulandum with a precision grip between the receptor-related digit (index finger, middle finger, ring finger or thumb) and an opposing digit (thumb or index finger). Ramp-and-hold load forces of various amplitudes (0.5–2.0 N) and ramp rates (2–32 N/s) were delivered tangential to the parallel grip surfaces in both the distal (pulling) and the proximal (pushing) directions. Afferents from the long flexors of the digits (n=19), regardless of their muscle-spindle or tendon-organ origin, did not respond to the load forces before the onset of the automatic grip response, even with the fastest ramp rates. Their peak discharge closely followed the peak rate of increase in grip force. During the hold phase of the load stimulus, the afferents sustained a tonic discharge. The discharge rates were significantly lower with proximally directed loads despite the mean grip-force being similar in the two directions. This disparity could be explained by the differing contributions of these muscles to the finger-tip forces necessary to restrain the manipulandum in the two directions. Most afferents from the short flexors of the digits (n=17), including the lumbricals, dorsal interossei, opponens pollicis, and flexor pollicis brevis, did not respond at all, even with the fastest ramps. Furthermore, the ensemble pattern from the joint afferents (n=6) revealed no significant encoding of changes in finger-tip forces before the onset of the increase in grip force. We conclude that mechanoreceptors in the flexors of the digits and in the interphalangeal joints cannot be awarded a significant role in triggering the automatic changes in grip force. Rather, their responses appeared to reflect the reactive forces generated by the muscles to restrain the object. Hence, it appears that tactile afferents of the skin in contact with the object are the only species of receptor in the hand capable of triggering and initially scaling an appropriate change in grip force in response to an imposed change in load force, but that muscle and joint afferents may provide information related to the reactive forces produced by the subject. 相似文献
12.
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
13.
Does the location of the touch from the contralateral finger application affect grip force control while lifting an object? 总被引:1,自引:0,他引:1
It was recently shown that the magnitude of grip force used to lift and transport a hand-held object decreased if a light finger touch from the contralateral arm was provided to the wrist of the target arm [A.S. Aruin, Support-specific modulation of grip force in individuals with hemiparesis, Arch. Phys. Med. Rehabil. 86 (2005) 768-775]. In this study, we investigated whether the location of the finger touch along the target arm affects the way grip force is reduced. Subjects performed the same task of lifting and transporting an instrumented object with no involvement of the contralateral arm and when an index finger touch of the contralateral arm was provided to the wrist, thumb, mid-forearm, and the hand-held object. Grip force was reduced by approximately the same amount in all conditions with the finger touch compared to the no touch condition suggesting that its reduction was not associated with a particular point of contact of the finger with the target arm. The results of the study provide additional evidence to support of the use of a second arm in the performance of activities of daily living and stress the importance of future studies investigating contralateral arm sensory input on grip force control. 相似文献
14.
Zong-Ming Li Mark L. Latash Karl M. Newell Vladimir M. Zatsiorsky 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1998,122(1):71-78
The goal of the study was to investigate force-sharing patterns in multi-finger tasks. Maximal normal force (MNF) as well
as the force-time curves produced by individual fingers were measured in 10 young male subjects in three tasks: (1) holding
an instrumented handle in a pad opposition with the thumb at seven different locations, from opposing the index finger (L0) to opposing the little finger (L6); (2) holding the handle in a pad opposition with the thumb at an individually selected comfortable location; and (3) pressing
with the four fingers against the same handle fixed to the external support. We found that: (1) The moment due to the normal
finger forces changed systematically when the thumb position varied from L0 to L5 /L6, and it was equal to zero at a certain middle position of the thumb, the neutral position. At this position, the shear force produced by the fingers was zero. (2) The total MNF changed in an ascending-descending
manner when the thumb position varied from L0 to L5 /L6. The highest value of the maximal total normal force was produced at a position of the thumb that was preferred as the most
comfortable position in the grip task. (3) In the press task, the neutral line – the line with respect to which the moment
generated by the four fingers equals zero – was at the same location as the preferred thumb position in the grip tasks. (4)
Larger total normal force corresponded to smaller total shear forces. (5) In grip tasks, with the thumb in a comfortable position,
the force-force relationships among fingers were approximately linear. Hence, in these thumb positions, the force-sharing
pattern was established at the beginning of the trial. At the extreme positions of the thumb, irregular patterns of the force-force
relationships were observed. (6) In trials with different thumb locations, a significant correlation was found between the
maximal force produced by the index and small fingers. (7) Peak force exerted by individual fingers in the multi-finger tasks
was much smaller than the maximal force displayed by the same fingers in the single-finger tasks. The peak force depended
on the thumb position and varied from 11.3% to 65.2% of the maximal force exerted by the same finger in the single-finger
task. With the thumb in the comfortable position, the relative peak force for all fingers was approximately at the same level,
50–55%. The data are in agreement with the hypothesis that the total force is shared among individual fingers, minimizing
the moment with respect to the functional hand axis.
Received: 18 August 1997 / Accepted: 19 March 1998 相似文献
15.
Bock O Jüngling S 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1999,125(1):61-66
The present study investigated the control of manual prehension movements in humans. Subjects grasped luminous virtual discs
with the thumb and index finger, and we recorded the instantaneous grip aperture, defined as the 3-D distance between the
thumb and index finger. Target size could remain constant (single-step trials) or unexpectedly change shortly after target
appearance (double-step trials). In single-step responses, grip aperture varied throughout the movement in a consistent fashion.
Double-step responses exhibited distinct corrective modifications, which followed the target change with a latency similar
to the normal reaction time. This suggests that visual size information has a fast and continuous access to the processes
involved in grip formation. The grip-aperture profiles of single-step responses had a different shape when the target called
for an increase than when it called for a decrease in the initial finger distance. The same asymmetry was observed for aperture
corrections in double-step trials. These findings indicate that increases and decreases of grip aperture are controlled through
separate processes, engaged equally by the appearance and by the size change of a target. Corrections of grip aperture in
double-step trials had a higher peak velocity and reached their maximum as well as their final value earlier than the aperture
profiles of single-step trials. Nevertheless, the total duration of double-step trials was prolonged. These response characteristics
did not fit with either of the three corrective strategies previously proposed for double-step pointing movements, which could
indicate that grasping and pointing movements are controlled by different mechanisms. However, more data are needed to substantiate
this view.
Received: 20 April 1998 / Accepted: 28 October 1998 相似文献
16.
H. Forssberg H. Kinoshita A. C. Eliasson R. S. Johansson G. Westling A. M. Gordon 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1992,90(2):393-398
Summary The development of anticipatory control during lifts with the precision grip was examined in 100 children aged 1 to 15 years and in 15 adults. The children were instructed to lift an instrumented test object by using the precision grip between the thumb and index finger. The employed grip force, load force (vertical lifting force), vertical position and their corresponding time derivatives (i.e., grip and load force rates and acceleration) were recorded. The weight of the object was varied between trials to access the influence of the object's weight in the previous trial on the isometric force output. Already by the second year, children began to use information pertaining to the object's weight in the previous lift, i.e., they began to use an anticipatory control strategy. This occurred concomitant to the development of mainly bell shaped force rate profiles (Forssberg et al. 1991). The succeeding development of a more mature anticipatory control was gradual and adult-like capacity was not reached until 8–11 years of age.
Correspondence to: Department of Pediatrics 相似文献
17.
Prediction of object contact during grasping 总被引:1,自引:0,他引:1
Säfström D Edin BB 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2008,190(3):265-277
The maximum grip aperture (MGA) during prehension is linearly related to the size of objects to be grasped and is adapted
to the haptically sensed object size when there is a discrepancy between visual and haptic information. We have investigated
what information is used to drive this adaptation process and how the onset of fingertip forces on the object is triggered.
Subjects performed a reach-to-grasp task, where the object seen and the object grasped physically never were the same. We
measured the movements of the index finger and the thumb and the contact forces between each fingertip and the object. The
subjects’ adaptation of the MGA was unrelated both to different fingertip velocities at the moment of object contact, or the
fingertip forces. Instead, the ‘timing’ of contact between the fingers and the object was most consistently influenced by
introducing a size discrepancy. Specifically, if the object was larger than expected, the moment of contact occurred earlier,
and if the object was decreased in size, then the contact occurred later. During adaptation, these timing differences were
markedly reduced. Also, the motor command for applying forces on the object seemed to be released in anticipation of the predicted
moment of contact. We therefore conclude that the CNS dynamically predicts when contact between the fingertips and objects
occur and that aperture adaptation is primarily driven by timing prediction errors. 相似文献
18.
Barbara F. M. Marino Natale Stucchi Elena Nava Patrick Haggard Angelo Maravita 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2010,202(2):499-505
Vision of the body is known to affect somatosensory perception (e.g. proprioception or tactile discrimination). However, it
is unknown whether visual information about one’s own body size can influence bodily action. We tested this by measuring the maximum grip aperture (MGA) parameter of grasping while eight subjects viewed a real size,
enlarged or shrunken image of their hand reaching to grasp a cylinder. In the enlarged view condition, the MGA decreased relative
to real size view, as if the grasping movement was actually executed with a physically larger hand, thus requiring a smaller
grip aperture to grasp the cylinder. Interestingly, MGA remained smaller even after visual feedback was removed. In contrast,
no effect was found for the reduced view condition. This asymmetry may reflect the fact that enlargement of body parts is
experienced more frequently than shrinkage, notably during normal growth. In conclusion, vision of the body can significantly
and persistently affect the internal model of the body used for motor programming. 相似文献
19.
Y. N. Turrell F.-X. Li A. M. Wing 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1999,128(1-2):86-91
This experiment investigated the prediction of load force (LF) in impulsive collisions inferred from anticipatory adjustments
of grip force (GF) used to stabilise a hand-held object. Subjects used a precision grip to hold the object between thumb and
index finger of their right hand and used the arm either: (1) to move the object to produce a collision by hitting the lower end of a pendulum, causing it to swing to one of three target angles, or (2) to hold the
object still while receiving a collision produced by the experimenter releasing the pendulum from one of three angles. Visual feedback of the pendulum’s
trajectory was available in the production task only. In all conditions, subjects increased GF in advance of the collision.
In receiving the collision without advance information, subjects set GF levels to the mid-range of the experienced forces.
When subjects possessed knowledge about the maximum angle of pendulum swing – either because they were going to produce it
or because they were verbally informed – magnitude of the anticipatory-GF magnitude response was scaled to the predicted LF
magnitude. Furthermore, GF was scaled to LF with a higher gain when producing compared to receiving the collision. This suggests
that updating forward models through a semantic route is not as powerful as when the updating is achieved through the more
direct route of dynamic exploration.
Received: 31 July 1998 / Accepted: 16 March 1999 相似文献
20.
Task goal and grip force dynamics 总被引:2,自引:0,他引:2
Jordan K Newell KM 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2004,156(4):451-457
This study examined the effect of task goal on the structure of isometric force variability during precision grasping. In general, variability of isometric force production decreases when participants are asked to maintain a particular force output and are provided with visual feedback, although the irregularity of force output tends to increase under these conditions. In the current study we compared the tasks of holding an object using a precision grip and holding an object using a precision grip while matching a force target. Adults held an object between the index finger and thumb and force output was measured using load cells. The mass (92, 276, 460 g) and the grip aperture (5.5 and 8.5 cm) of the object were varied producing six different object conditions. The goal of the task was to either: (a) hold the object comfortably in a stable position (holding task) or (b) hold the object comfortably in a stable position while maintaining a constant target force level that matched the grip force of the holding condition (target task). The results showed that the amount of force variability in the target condition was lower than during the holding condition, while the force output was more regular in the holding condition. Increments in object mass increased force regularity in the holding condition whereas increments of force level decreased regularity in the target condition. The level of coherence between the two digits was very high (approximately 0.98) and maximum coherence occurred at a higher frequency during the target (0.94 Hz) as opposed to the holding (0.70 Hz) condition. The findings reveal that the goal of the task can qualitatively change the dynamical organization of the force output in prehension, even when the average force level produced is the same. This effect on the control strategy was mediated by visual information processes that interact with level of force output in determining the structure of variability. Theorizing about the organization of isometric force output should include the effects of task goals as well as the level of force per se. 相似文献