Orienting the finger opposition space during prehension movements

Two experiments are reported that examined the act of prehension when subjects were asked to grasp with their thumb and index finger pads an elongated object resting horizontally on a surface and placed at different orientations with respect to the subject. In Experiment 1, the pad opposition preferences were determined for the six angles of orientation examined. For angles of 90 degrees (object parallel to frontal plane) or less, no rotation of the wrist (pronation) was used; for angles 110 degrees or greater, pronation was systematically employed to reorient the finger opposition space. Only one angle, 100 degrees , produced any evidence of ambiguity in how to grasp the object: Approximately 60% of these grasps involved pronation and 40% did not. Using the foregoing grasp preference data, in Experiment 2 we examined the kinematics of the wrist and elbow trajectories during prehension movements directed at an object in different orientations. Movement time, time to peak acceleration, velocity, and deceleration were measured. No kinematic differences were observed when the object orientation either required (110 degrees ) or did not require (80 degrees ) a pronation. By contrast, if the orientation was changed at the onset of the movement, such that an unpredicted pronation had to be introduced to achieve the grasp, kinematics were affected: Movement time was increased, and the time devoted to deceleration was lengthened. These data are interpreted as evidence that when natural prehension occurs, pronation can be included in the motor plan without affecting the movement kinematics. When constraints are imposed on the movement execution as a consequence of a perturbation, however, the introduction of a pronation component requires kinematic rearrangement.     

Attention and suppression affect tactile perception in reach-to-grasp movements

Reaching with the hand is characterized by a decrease in sensitivity to tactile stimuli presented to the moving hand. Here, we investigated whether tactile suppression can be canceled by attentional orienting. In a first experiment, participants performed a dual-task involving a goal-directed movement paired with the speeded detection of a tactile pulse. The pulse was either delivered to the moving or stationary hand, during movement preparation, execution, or the post-movement phase. Furthermore, stimulation was delivered with equal probability to either hand, or with a higher probability to either the moving or resting hand. The results highlighted faster RTs under conditions of higher probability of stimulation delivery to both moving and resting hands, thus indicating an attentional effect. For the motor preparation period, RTs were faster only at the resting hand under conditions where tactile stimulation was more likely to be delivered there. In a second experiment, a non-speeded perceptual task was used as a secondary task and tactile discrimination thresholds were recorded. Tactile stimulation was delivered concomitantly at both index fingers either in the movement preparation period (both before and after the selection of the movement effector had taken place), in the motor execution period, or, in a control condition, in the time-window of motor execution, but the movement of the hand was restrained. In the preparation period, tactile thresholds were comparable for the two timings of stimulation delivery; i.e., before and after the selection of the movement effector had taken place. These results therefore suggest that shortly prior to, and during, the execution of goal-directed movements, a combined facilitatory and inhibitory influence acts on tactile perception.     

Functional coupling between the limbs during bimanual reach-to-grasp movements

While it is frequently advantageous to be able to use our hands independently, many actions demand that we use our hands co-operatively. In this paper we present two experiments that examine functional binding between the limbs during the execution of bimanual reach-to-grasp movements. The first experiment examines the effect of gaze direction on unimanual and bimanual reaches. Even when subjects' eye movements are restricted during bimanual reaches so that they may only foveate one target object, the limbs remain tightly synchronized to a common movement duration. In contrast, grip aperture is independently scaled to the size of the target for each hand. The second experiment demonstrates however, that the independent scaling of grip aperture is task dependent. If the two target objects are unified so that they appear to be part of a single object, grip apertures become more similar across the hands (i.e., grip aperture to the large target object is reduced in size while peak aperture to the small target item is increased in size). These results suggest that the coupling of the limbs can operate at a functional level.     

Co-ordination of bimanual movements in a centrally deafferented patient executing open loop reach-to-grasp movements

Many everyday tasks require that we use our hands co-operatively. For tasks where both hands are required to perform the same action, a common motor program can be used. But, where each hand must perform a different action, some degree of independent control of each hand is required. In this paper we examine the co-ordination of bimanual movement kinematics in a female patient recovering from brain injury involving anterior regions of the parietal lobe of the right hemisphere, which has resulted in a dense hemianaesthesia of her left arm. A particular focus of this paper is the co-ordination of bimanual movements for reaches executed without visual feedback. Specifically we present new data, which quantify the synchronisation of patient D.B.'s hands by comparing their relative time lag at the start and the end of her bimanual reaches. The results are discussed with particular reference to the role played by limb proprioception in the planning and control of prehension movements.     

Testing the effects of end-goal during reach-to-grasp movements in Parkinson’s disease

Previous evidence suggests that hand shaping during reaching is modulated by the presence and the nature of the end-goal following object’s grasp. Here we test whether such modulation is maintained in Parkinson’s disease (PD). Six participants with PD and six healthy participants took part in the study. Participants were requested to reach towards a bottle filled with water, and then: (1) grasp it without performing any subsequent action; (2) grasp it and place it accurately on a target area; (3) grasp it and pour its contents within a container. The results showed that participants shaped their hand differently depending on the presence or absence of an action following object’s grasp. However, the request to perform an action after grasp determined a modulation of hand kinematics which was delayed for PD than for control participants. Further, whereas for control participants the nature of the end-goal determined a modulation of hand shaping, for PD patients such modulation was not evident. Data are discussed in terms of the role played by basal ganglia in implementing anticipatory mechanisms for the control of manipulative activities. We contend that in PD patients these mechanisms are not totally compromised, but their implementation depends on the action information that has to be anticipated.     

Observing repetitive finger movements modulates response times of auditorily cued finger movements

Our motor and perceptual representations of actions seem to be intimately linked and the human mirror neuron system (MNS) has been proposed as the mediator. In two experiments, we presented biological or non-biological movement stimuli that were either congruent or incongruent to a required response prompted by a tone. When the tone occurred with the onset of the last movement in a series, i.e., it was perceived during the movement presentation, congruent biological stimuli resulted in faster reaction times than congruent non-biological stimuli. The opposite was observed for incongruent stimuli. When the tone was presented after visual movement stimulation, however, no such interaction was present. This implies that biological movement stimuli only affect motor behaviour during visual processing but not thereafter. These data suggest that the MNS is an "online" system; longstanding repetitive visual stimulation (Experiment 1) has no benefit in comparison to only one or two repetitions (Experiment 2).     

Temporal coordination during bimanual reach-to-grasp movements: The role of vision

The performance of bimanual movements involving separate objects presents an obvious challenge to the visuo-motor system: Visual feedback can only be obtained from one target at a time. To overcome this challenge overt shifts in visual attention may occur so that visual feedback from both movements may be used directly (Bingham, Hughes, & Mon-Williams, 2008; Riek, Tresilian, Mon-Williams, Coppard, & Carson, 2003). Alternatively, visual feedback from both movements may be obtained in the absence of eye movements, presumably by covert shifts in attention (Diedrichsen, Nambisan, Kennerley, & Ivry, 2004). Given that the quality of information falls with increasing distance from the fixated point, can we obtain the level of information required to accurately guide each hand for precision grasping of separate objects without moving our eyes to fixate each target separately? The purpose of the current study was to examine how the temporal coordination between the upper limbs is affected by the quality of visual information available during the performance of a bimanual task. A total of 11 participants performed congruent and incongruent movements towards near and/or far objects. Movements were performed in natural, fixate-centre, fixate-left, and fixate-right vision conditions. Analyses revealed that the transport phase of incongruent movements was similar across vision conditions for the temporal aspects of both the transport and grasp, whereas the spatial aspects of grasp formation were influenced by the quality of visual feedback. We suggest that bimanual coordination of the temporal aspects of reach-to-grasp movements are not influenced solely by overt shifts in visual attention but instead are influenced by a combination of factors in a task-constrained way.     

The preparation of reach-to-grasp movements in adults, children, and children with movement problems

This study explored the use of advance information in the control of reach-to-grasp movements. The paradigm required participants to reach and grasp illuminated blocks with their right hand. Four target blocks were positioned on a table surface, two each side of the mid-saggital plane. In the complete precue condition, advance information precisely specified target location. In the partial precue condition, advance information indicated target location relative to the midsaggital plane (left or right). In the null condition, the advance information was entirely ambiguous. Participants produced fastest responses in the complete precue condition, intermediate response times in the partial condition, and the slowest responses in the null condition. This result was observed in adults and four groups of children including a group aged 4-6 years. In contrast, children with Developmental Coordination Disorder (DCD, n = 11, aged 7-13 years) showed no advantage of partial precueing. Movement duration was determined by target location but was unaffected by precue condition. Movement duration was a clear function of age apart from children in the DCD group who showed equivalent movement times to those of the youngest children. These findings provide important insights into the control of reach-to-grasp movements and highlight that partial cues are exploited by children as young as 4 years but are not used in situations of abnormal development.     

Inhibitory component of externally controlled covert orienting in visual space

Four experiments are reported that investigate an inhibitory effect associated with externally controlled orienting and first identified by Posner and Cohen (1980, 1984). The effect takes the form of an inability to respond quickly to a stimulus appearing in the same location in the visual periphery as a previous one that produced covert orienting. Several characteristics of the effect are revealed that eliminate possible explanations in terms of response inhibition, masking, and sensory habituation. The inhibitory component of orienting occurs whether or not the first stimulus requires a response (Experiment 1), lasts at least a second (Experiments 1, 2, and 3), affects not only the originally stimulated location but also nearby locations (Experiment 2), is determined by environmental coordinates (Experiment 3), and occurs both in the periphery and at the fovea (Experiment 4). It is concluded that inhibition may act together with an early facilitatory component (Posner & Cohen, 1984) in directing the attention and eye movement systems in order to maintain efficient spatial sampling.     

Effect of age and gender in the control of elbow flexion movements

In previous studies of rapid elbow movements in young healthy men, characteristic task-dependent changes in the patterns of muscle activation when movement speed or distance was varied have been reported. In the present study, the authors investigated whether age or gender is associated with changes in the patterns of muscle activity previously reported in young men. Arm movements of 10 healthy older and 10 healthy younger participants (5 men and 5 women in each group) were studied. Surface electromyograms (EMGs) from agonist (biceps) and antagonist (triceps) muscles, kinematic and kinetic parameters, as well as anthropometric and strength measures were recorded. All 4 groups of participants showed similar task- (distance or speed) dependent changes in biphasic EMG activity. Similar modulation of the initial rate of rise of the EMG, integrated agonist and antagonist EMG activity, as well as their relative timing were observed in all 4 groups. Those results suggest that older individuals of both genders retain the control strategies for elbow movements used by young individuals. Despite the qualitative similarities in the patterns of muscle activation, the men moved more quickly than the women, and younger participants moved more quickly than older participants. Those performance differences could not be explained in terms of differences in body size and strength alone.     

Learning to imitate individual finger movements by the human neonate

Imitation in human neonates, unlike imitation in young infants, is still regarded as controversial. Four studies with 203 newborns are presented to examine the imitation of index finger, two‐ and three‐finger movements in human neonates. Results found differential imitations of all three modelled gestures, a left‐handed pattern, and a rapid learning mechanism. The lateralized behavioural pattern suggests the involvement of a right lateralized neural network, and the mechanisms described in this study – (i) the accurate imitation of all aspects of the model's movements, (ii) the rapid learning component, and the (iii) the early sensitive period might fulfil the criteria for filial imprinting.     

Control of goal-directed movements: the contribution of orienting of visual attention and motor preparation.

Three experiments investigated the role of attention and motor preparation for the control of goal-directed movements. In Experiment 1 (double step paradigm), a movement correction was required on 25% of the trials towards the left or right of the initial target. Within these 25% of trials, the probability of location of the second target was manipulated. The efficiency of movement control increased when increasing the probability of correcting the movement in a given direction. In Experiment 2, attentional processes were isolated by asking the subjects to verbally detect the more or less probable target displacement, without correcting their movement. Subjects were able to orient visual attention during movement execution, thus improving the processing of visual feedbacks from target displacement. In Experiment 3, motor preparation processes were isolated by asking the subjects to correct their movement towards a fixed target in response to a more or less probable mechanical perturbation. It was shown that motor preparation not only specifies the initial movement parameters but may also include some parameters of the most probable movement modulations. Overall, these results highlight the role of both attentional and motor preparation processes in the control of goal-directed movements and suggest that the feedback-based corrections of the movement are modulated by a feedforward control.     

Coordination between breathing and mental grouping of pianistic finger movements

6 pianists (age 22 to 43 years) performed a simple finger exercise at a spontaneously chosen most comfortable tempo on a Yamaha-Disklavier piano. Five versions of the exercise, notated in quarter notes, were presented with different types of meters: (1) 3/4, (2) 4/4, (3) 5/4, (4) 6/4, and (5) 7/4. The onsets of finger strokes were measured while respiration was recorded in parallel by means of a thermistor placed at the front of the dominant nostril. The chosen tempo (finger-beat-rate) was about 3 Hz on all trials but not exactly constant. Correspondingly, the meter-rate chosen was faster for 3/4 and 4/4 meter (around 1 Hz), slower for 5/4, 6/4, and 7/4 meter (around 0.5 Hz). Mean breathing rate while playing the piano (0.38 Hz) was significantly higher than while resting (0.22 Hz, p<.05). Pooling the data of all subjects, the ratios of instantaneous meter and breathing rates clustered around different integer values, depending on the type of meter. Also the individual data indicated integer ratios between instantaneous meter and breathing rates. Even periods of constant phase relations between onsets of the meter and of inspiration could be observed. Thus, the mental process of grouping the same piece of music by various musical meters interacts with unconscious breathing rhythm.     

Updating target location at the end of an orienting saccade affects the characteristics of simple point-to-point movements

Six results are reported. (a) Reaching accuracy increases when visual capture of the target is allowed (e.g., target on vs. target off at saccade onset). (b) Whatever the visual condition, trajectories diverge only after peak acceleration, suggesting that accuracy is improved through feedback mechanisms. (c) Feedback corrections are smoothly implemented, causing the corrected and uncorrected velocity profiles to exhibit similar shapes. (d) Initial kinematics poorly predict final accuracy whatever the condition, indicating that target capture is not the only critical input for feedback control. (e) Hand and eye final variability are unrelated, suggesting that gaze direction is not a target signal for arm control. (f) Extent errors are corrected without modification of movement straightness; direction errors cause path curvature to increase. Together these data show that movements with straight paths and bell-shaped velocity profiles are not necessarily ballistic.     

Intermanual interactions during simultaneous execution and programming of finger movements

In bimanual movements, some differences between the movements performed by the two hands cause interference, while others do not. Similarly, in choice between responses with the left and right hand some differences between the two movements increase RT, while others do not. It is suggested that both kinds of effects are, at least in part, due to the incompatibility between processes that determine characteristics of movements jointly for both hands and that are present during preparation as well as during execution. This hypothesis implies that during execution of one movement, programming of a different movement to be performed with the other hand should be impaired, as compared to a condition in which the successive movements of both hands are the same. this expectation was confirmed for finger movements of different forms where an effect on choice RT had been shown previously. On the other hand, interference between execution and programming is not to be expected when successive movements differ in characteristics that are likely to be specified separately for each hand, as indicated by a lacking effect in choice experiments. This expectation was confirmed for successive movements performed with different fingers of either hand as compared to movements performed with the same fingers.     

不同熟练双语儿童注意定向中的抑制控制

研究目的：探讨不同熟练双语儿童“注意定向”成分中抑制控制的差异,及这一差异是否依赖于双语儿童第二语言的熟练程度。方法：采用IOR范式的行为实验。被试为平衡、未平衡双语儿童和单语儿童。结果：SOA600ms时,三组被试均出现了IOR,平衡双语儿童与单语儿童的IOR效应量差异显著,其余被试间差异均不显著。结论：（1）双语学习促进了平衡双语儿童抑制控制能力的发展。（2）双语学习对抑制控制能力的促进作用依赖于双语儿童第二语言的熟练程度。     

The development of exogenous orienting: mechanisms of control

The present study examined exogenous orienting in children ages 6 years (n=14), 10 years (n=13), 14 years (n=14), and adults (n=13). The main purpose was to identify which of the attentional operations underlying exogenous orienting (disengaging, shifting, and/or engaging) improves with age. A simple detection task was used in which single targets were correctly (80%) or incorrectly (20%) cued. The main finding was that disengaging attention alone distinguished the performance of younger children from that of older children and adults, regardless of whether attention alone (covert attention) or attention and associated sensory and motor systems (overt attention) were involved. In addition, our data, in contrast to those reported previously, raise the possibility that even the youngest children tested were able to use the predictability of the cue to enhance their performance. These and related neuroanatomical findings are taken as evidence for the development with age of more flexible control in orienting visual attention.