Prehensile Movements Research Articles

Effects of deep brain stimulation on prehensile movements in PD patients are less pronounced when external timing cues are provided

It has been repeatedly demonstrated that the movements of patients with Parkinson’s disease (PD) are less impaired when external timing cues are provided. This suggests that the basal ganglia, which are impaired in PD, are less involved in the control of externally timed movements. In the present study, we tested this hypothesis by contrasting the effect of deep brain stimulation (DBS) in the basal ganglia (more precisely, the internal globus pallidum) on internally versus externally timed movements. Our first movement task was a standard prehensile task involving a reach-to-grasp movement. In the externally-timed condition, the target object was moving rapidly away from the subject; in the internally-timed condition, the target object was stationary. We found, that for most aspects of the prehensile movement the effect of DBS was less pronounced in the externally than in the internally timed condition. A similar reduction of the DBS effects in the externally-timed condition was also found for a second movement task, which required an isolated grasping movement. We conclude that the basal ganglia are significantly less involved in the control of externally timed movements.

The effects of intermittent vision on prehension under binocular and monocular viewing.

The aim of the present study was to examine the effects of intermittent binocular and monocular vision on the preparation and execution of the transport and grasp phases of prehension, and hence the temporal limit of binocular and monocular integration. Participants in two groups (speed or accuracy) performed prehensile movements of two amplitudes (20 and 40 cm) to either a large or small object (6 x 6 x 2 and 6 x 4x 2 cm) under conditions of binocular and monocular viewing. The interval between visual samples was manipulated with liquid crystal goggles (continuous vision, 20on/60off, and 20on/120off ms). A kinematic analysis indicated that participants modified variables associated with the preparation and execution of prehension in the intermittent vision conditions when instructed to emphasize accuracy. Participants instructed to emphasize speed, modified variables associated with the preparation phase only. The impact of intermittent vision was similar under binocular and monocular viewing. Thus, for prehension, it appears that consecutive binocular or monocular samples need to occur less than 60 ms apart in order to be fully integrated for limb control.

Neural architectures for robot intelligence.

We argue that direct experimental approaches to elucidate the architecture of higher brains may benefit from insights gained from exploring the possibilities and limits of artificial control architectures for robot systems. We present some of our recent work that has been motivated by that view and that is centered around the study of various aspects of hand actions since these are intimately linked with many higher cognitive abilities. As examples, we report on the development of a modular system for the recognition of continuous hand postures based on neural nets, the use of vision and tactile sensing for guiding prehensile movements of a multifingered hand, and the recognition and use of hand gestures for robot teaching. Regarding the issue of learning, we propose to view real-world learning from the perspective of data-mining and to focus more strongly on the imitation of observed actions instead of purely reinforcement-based exploration. As a concrete example of such an effort we report on the status of an ongoing project in our laboratory in which a robot equipped with an attention system with a neurally inspired architecture is taught actions by using hand gestures in conjunction with speech commands. We point out some of the lessons learnt from this system, and discuss how systems of this kind can contribute to the study of issues at the junction between natural and artificial cognitive systems.

The role of binocular information in the 'on-line' control of prehension.

Binocular visual information may be involved in the selection of appropriate motor programs before a reach is executed or it may be involved during the movement-execution phase in order to monitor and guide the hand to the target object. Here we introduced binocular information after 0%, 25%, 50% or 75% of the movement-execution phase and determined its effects on the kinematic indices of prehensile movements made to objects of different sizes placed at different distances. Kinematic indices linked to the transport component, such as peak velocity and time-to-peak velocity, were unaffected by the presence of binocular cues whereas later occurring indices, such as peak grip aperture and time in the slow phase, were significantly affected. Although the magnitude of the peak grip was affected by the presence of binocular cues, the time at which it occurred did not change. This pattern of results suggest that the visuo-motor control of prehensile movements utilises both feedforward and feedback strategies and that binocular cues are particularly important for the fine manual adjustments typical of the latter.

Reaching for virtual objects: binocular disparity and the control of prehension

Although, in principle, binocular cues provide veridical information about the three-dimensional shape of objects, our perception on the basis of these cues is distorted systematically. The consequences of these distortions may be less serious than they first appear, however, since in everyday life we rarely are required to judge the absolute shape, size or distance of objects. An important exception to this is in the control of prehension, where veridical information about an object to be grasped is required to plan the transport of the hand and to select the most appropriate grip. Here we investigate whether binocular cues provide accurate depth information for the control of prehension using disparity-defined, virtual objects and report that whilst binocular disparity can support prehensile movements, the kinematic indices, which reflect distance-reached and perceived size, show clear biases. These results suggest that accurate metric depth information for the control of prehension is not available from binocular cues in isolation.

Binocular vision and prehension in middle childhood

Binocular cues have been shown previously to make an important contribution to the control of natural prehensile movements in adults [Visual Cognition 4 (1997) 113, Vision Research 32 (1992) 1513, Neuropsychologia 38 (2000) 1473]. The present study examined the role of binocular vision in the control of prehension in middle childhood. Fourteen children aged 5–6 years, and 16 children aged 10–11 years reached out and grasped different sized objects at different distances, in either binocular or monocular viewing conditions. In contrast to adult data, many of the principal kinematic indices of the children’s reaches were unaffected by the removal of binocular information. The older children, like adults, spent an increased amount of time in the final approach to the object when only monocular information was available. However, both peak wrist velocities and peak grip apertures were unaffected by the removal of binocular information and continued to scale with object properties in the normal way. These results suggest that the use of binocular cues to control prehensile movements is not yet mature at the age of 10–11 years.

Binocular information in the control of prehensile movements in multiple-object scenes.

Recent evidence suggests that the visual control of prehension may be less dependent on binocular information than has previously been thought. Studies investigating this question, however, have generally only examined reaches to single objects presented in isolation, even though natural prehensile movements are typically directed at objects in cluttered scenes which contain many objects. The present study was designed, therefore, to assess the contribution of binocular information to the control of prehensile movements in multiple-object scenes. Subjects reached for and grasped objects presented either in isolation or in the presence of one, two or four additional 'flanking' objects, under binocular and monocular viewing conditions. So that the role of binocular information could be clearly determined, subjects made reaches both in the absence of a visible scene around the target objects (self-illuminated objects presented in the dark) and under normal ambient lighting conditions. Analysis of kinematic parameters indicated that the removal of binocular information did not significantly affect many of the major indices of the transport component, including peak wrist velocity. However, peak grip apertures increased and subjects spent more time in the final slow phase of movement, prior to grasping the object, during monocularly guided reaches. The dissociation between effects of binocular versus monocular viewing on transport and grasp parameters was observed irrespective of the presence of flanking objects. These results therefore further question the view that binocular vision is pre-eminent in the control of natural prehensile movements.

A dissociation of perception and action in normal human observers: the effect of temporal-delay

Neuropsychological results support the proposal that the human visual system is organised into distinct processing pathways, one for conscious perception and one for the control of action. Here, we compare perceptual and action responses following a pre-response-delay. Experiment 1 required participants to reproduce remembered locations and found that although perceptual matches were unaffected by delays of up to 4 s, pointing responses were significantly biased after only 2 s. Experiment 2 examined whether both the transport and grasp components of a natural prehensile movement were similarly affected by delay. Both peak wrist velocities and peak grip-apertures were affected equivalently by delay, suggesting that the two components of a prehensile movement have similar temporal constraints. The results from both experiments are consistent with the general perception–action dichotomy as originally proposed by Milner and Goodale [The visual brain in action, Oxford: Oxford University Press, 1995].

The effect of a pictorial illusion on closed-loop and open-loop prehension.

It has been proposed that movements to visible and remembered targets are sensitive to qualitatively different types of visual information. When the target is continuously visible, prehensile movements are thought to reflect veridical object size, whereas memory-dependent prehension is sensitive to the perceived size of the object. This hypothesis was explored by assessing the influence of illusory target width on prehension kinematics in three visual conditions: closed-loop (CL; full vision during the response), open-loop brief-delay (OL; visual occlusion coincident with the movement initiation cue) and open-loop 3-s delay (OL3; visual occlusion 3 s prior to movement initiation). To modulate illusory target width, objects were placed on backgrounds consisting of three forms of the Müller-Lyer (ML) figure. Peak grip aperture was sensitive to the ML figure in the OL and OL3, but not CL conditions, suggesting that perceptual information is used to modulate this grasping parameter when the movement is programmed and executed on the basis of visual memory. Peak-aperture velocity was affected by the ML illusion in all three visual conditions, suggesting that perceived object size might be important for modulating this aspect of prehension, independent of memory requirements. The different sensitivity of grip aperture and aperture velocity to illusory target width in the CL condition suggests that grasp preshaping might reflect multiple visuomotor processes. The results of this study are consistent with the tenets of the two-stream model of visual processing.

A test between two hypotheses and a possible third way for the control of prehension.

We used an obstacle avoidance task to test two opposing accounts of how the nervous system controls prehension. The visuomotor account supposes that the system independently controls the grip formation and transport phase of prehensile movements. In contrast, the digit channel hypothesis suggests that the system controls the thumb and finger more or less independently. Our data strongly favoured the traditional visuomotor channel hypothesis and demonstrated that the time taken to grasp an object in the presence of obstacles was well predicted by a Fitts' law relationship. We suggest a "thirdway" hypothesis in order to retain the advantages of the digit channel hypothesis within the visuomotor framework. The third-way hypothesis suggests that the nervous system selects a single digit to transport to the object. We speculate that the actual digit selected might depend upon attention and the nature of the prehension task. This hypothesis is able to account for most of the empirical findings unearthed by researchers investigating the control of prehension.

Imagining the impossible: intact motor representations in hemiplegics.

Motor imagery is known to involve brain regions vital to the performance of motor skills including primary motor cortex. The present results show that, following cerebral vascular accidents (CVAs) affecting a variety of these regions, many adults with left or right upper-limb paralysis (i.e. hemiparesis/hemiplegia) retain the ability to accurately represent prehensile movements involving the impaired limb. This suggests that during the acute phase of recovery many CVA patients can use motor imagery to activate partially damaged motor networks; a process that may facilitate functional reorganization. This ability was, however, compromised in cases with right posterior parietal or left frontal lesions. This pattern is consistent with the hypothesis that imagined prehension, like actual reaching and grasping, involves a network of highly interconnected areas distributed throughout parietal and frontal cortices.

The use of vergence information in the programming of prehension.

Human prehension requires accurate information on the properties of an object and on the position of the object relative to the body. In principle, prehension might be more accurate with binocular rather than monocular vision. Previous studies have shown that the kinematics of prehension are altered when one eye is covered. Unfortunately, the source of the useful binocular information cannot be established using this approach. In the current study, we used a perturbation technique to explore whether the human nervous system uses a signal from vergence in prehension. Perturbing vergence caused predictable changes in the kinematics of prehension. Our results thus provide clear evidence that the nervous system uses vergence information in the programming of prehensile movement.

Effects of unilateral brain damage on grip selection, coordination, and kinematics of ipsilesional prehension.

To determine whether the left and right hemispheres play specific roles in goal-directed movements, prehension with the ipsilesional hand was tested in patients with unilateral brain damage. The task required that subjects rotate the hand while reaching for a bar that was presented in different orientations in the frontal plane, thus making high demands on visuospatial processing. The grasped bar had to be put into a hole: under one task condition the placement of the bar was specified, while under another it was not. The constrained task required that the subject anticipate the placing action when planning the initial prehensile movement. Grip selection, reaction times, kinematics of the transport movement, and coordination of hand rotation during transport were assessed in ipsilesional movements of 22 patients with either left or right brain damage (LBD and RBD) and in control subjects. Patients in both groups exhibited performance deficits; however, impairment characteristics differed profoundly between the groups. RBD patients showed prolonged reaction time and degraded kinematics in the unconstrained task, whereas LBD patients performed relatively well when only the orientation of the bar varied, but slowly and frequently incoordinated when the subsequent action was specified. Our findings emphasize the dominant role of the right hemisphere in processing visuospatial aspects of goal-directed movements, whereas the left hemisphere subserves non-spatial aspects of preplanning under increased task demands. Correlations of the patient's performance with results from clinical tests showed that neither deficits in visuospatial perception of RBD patients nor apraxia of LBD patients could account for the observed abnormalities in the use of the ipsilesional hand.

Trigeminal deafferentation and conditioned pecking in pigeons

To clarify the contribution of peripheral trigeminal input to the control of pecking behavior we examined head and jaw movement kinematics and peck localization in pigeons with surgical section of trigeminal nerves providing somatosensory input to the beak. Conditioning procedures were used to bring the pecking/grasping components of pecking under the control of a visual target. Conditioned head and jaw movements were monitored `on-line' using movement transducers and terminal peck location was recorded using `touch-screen' technology. The periodic delivery of a food reinforcer provided repeated opportunities to monitor the kinematics of ingestive pecks. Deafferentation produced deficits in mandibulation during ingestive pecking and in the coordination of head and jaw movements during conditioned pecking. These results are attributed to disruptions in trigeminal feedback and feedforward mechanisms, respectively. In contrast with previous studies, deafferentation did not impair the precision of peck localization. Possible reasons for the absence of localization deficits are presented. The results are discussed in relation to the role of peripheral inputs in the control of prehensile movements.

Analysis of voluntary finger movements during hand tasks by a motion analyzer

Finger movements have primarily been classified by the final position of the hand and finger during deliberate hand activities, rather than as a description of the movement process. In addition, as of yet there have been no reports based upon objective data from the analysis of the motion of three finger joints during movement, and no reports exist that describe the relationship of the three joints' motion during these movements. This paper describes the relationship of the three finger joints during simple finger movements and hand tasks using measurements and analysis from a two-dimensional motion analyzer. Two prehensile movements were examined in 15 healthy volunteers: pure finger extension from finger flex position in different wrist positions (dorsi-flexion position, neutral position and palmar-flexion position of the wrist joint) and the grasping of discs of different diameter (10, 11, 12 and 13 cm). In the sequence of pure finger extension, where the grasping task was not requested, results showed that the movement was started from the proximal joint and extended to the distal joint of the finger, and full finger extension accomplished from distal to proximal, one after another, in any wrist position in most subjects. With the grasping of a disc, however, joint movement was initiated from distal to proximal and the final motion for grasping was carried to completion from the proximal to distal joints of the finger in most subjects. In addition, it was recognized that the proportion of the angular change in each of the three joints was different, as were the time duration of the joint motion and the pattern of the angular change. From these results, it is suggested that deliberate activities of the finger and sophisticated joint movements provided delicate adjustments to fit the fingers to the size of the object, as compared to the simple finger extension movement.

The timing of prehensile movements in subjects with cerebral palsy

In this study, a paradigm is presented for the assessment of manual dexterity in subjects with cerebral palsy (CP) that divides the prehensile action into a 'time-to-contact' phase and a 'time-in-contact' phase. Two experiments were performed that determined the effect of object weight on the timing of both phases for the impaired hand and non-impaired hand of subjects with spastic hemiparesis (N = 14). In the first experiment, subjects had to reach for and lift a tube at their own preferred speed. The results showed that the prehensile deficit of the impaired limb is to a large degree manifested by a longer time spent in contact with the object before it was lifted. The time-in-contact phase was decreased after repeated lifts, suggesting that subjects with CP can control and modify force output in advance based on weight information from preceding lifts. In the second experiment speed of movement execution was stressed to examine whether the observed timing pattern of the first experiment is characteristic of prehensile movements of the paretic arm or represents a movement strategy adapted to the disorder. The results of the second experiment showed that subjects could comply with the instruction by reducing the absolute duration of both phases of the prehensile movement. Furthermore, the anticipation effects were eliminated to a large degree. In both experiments the time-in-contact phase was longer for the impaired limb. These results indicate a pathological constant in the time-in-contact phase for the impaired limb. This assumption is discussed in relation to the application of grip and lift forces during this phase. It is concluded that the paradigm is well suited for use in a practical setting as a simple and broad clinical test to assess the prehensile decrements of subjects with CP.

Oral contraceptive use affects manual praxis but not simple visually guided movements

A detailed analysis of both motor sequencing and visually guided movements was carried out in a group of neurologically normal women who were receiving exogenous estrogen in the form of oral contraceptives. Women were tested under both low and high estrogen conditions, in order to examine any hormone‐related facilitation in the speed or accuracy of movement. Kinematic parameters examined on the visually guided motor tasks included movement onset time, duration of the reach, peak velocity, deceleration time, and endpoint accuracy (resultant error). The results showed that variations in motor performance were associated with fluctuations in estrogen level, but that this hormone sensitivity was task selective. Improved performance on a test of speeded motor sequencing, the Manual Sequence Box, was found under higher estrogen conditions, but this effect did not occur consistently in tests of rapid prehensile movements. Results are interpreted in terms of differential reliance of these tasks on left‐hemisphere praxic systems.

On the Hand Transport Component of Prehensile Movements

Jeannerod (1981) proposed that prehensile movements involve two independent visuomotor channels that are responsible for hand transport and hand aperture. In many studies, the movement of a marker placed on the wrist has been used as an index of hand transport because wrist movement is unaffected by the movements of the digits responsible for hand aperture. In the present study, the spatial paths of the wrist, index finger, and thumb of 5 adults, each performing 50 reaching movements, were measured with a WATSMART movement tracking system, and their variability was analyzed. The measures of movement variability suggest that the motor system is more concerned with thumb position than with wrist position during hand transport. Although the wrist is a technically convenient index of hand transport, the thumb may be a more appropriate index from the point of view of motor control.

What can and what cannot be adjusted in the movement patterns of cerebellar patients?

This commentary reviews the case of a patient who could alter the coordination of her prehensile movements when removal of visual feedback reduced her kinetic tremor, but could not coordinate her hand aperture with her hand transport within a single movement. This suggests a dissociation between different subtypes of cerebellar context-response linkage, rather than a single, general association function, [THACH]

Skilled forelimb movements in prey catching and in reaching by rats ( Rattus norvegicus) and opossums ( Monodelphis domestica): relations to anatomical differences in motor systems

Traditional anatomical/behavioral classifications suggest that rats and opossums have simple motor systems and are impoverished with respect to their ability to make prehensile movements. Nevertheless, the motor system in rats and opossums represent extremes in relative size and complexity suggesting that a behavioral analysis of the movement competencies of these species will provide insights into the significance of such anatomical differences. This paper examines the movements that the two species use in catching crickets and in reaching for food items. Both species could use a single limb to reach out and grasp prey during prey catching and both could use a single limb to take food from a shelf. Both species could transport the food to the mouth by using a single paw. The food handling behavior of the rats was more complex than that of the opossums, however. They used a variety of prey catching movements and extensively manipulated the prey to remove the legs and wings before eating only the head and body. Additionally the rats made rotatory limb movements of aiming, pronation, and supination, when reaching. For both cricket catching and reaching, they used their digits more than did the opossums. The suggestion also emerged from the results that the movements of the opossums were more fixed and species-typical whereas those of the rats were more plastic and individualistic. Thus, the skilled movements of both species are more complex than is generally recognized and the greater complexity of the rat movements parallels their more complex motor system. These results are discussed in relation to anatomical differences in the motor system and, specifically, to differences in the terminal fields of the pyramidal tract. It is concluded that the motor abilities of nonprimate mammals have been vastly underrated.