Planning an action

Communicative modulations of early action components support the prediction of distal goals

The successful unfolding of many social interactions relies on our capacity to predict other people's action goals, whether these are proximal (i.e., immediate) or distal (i.e., upcoming). The present set of studies asks whether observers can predict the distal goal of two-step action sequences when presented with communicative modulations of the first movement component of the sequence. We conducted three online experiments in which we presented participants with animations of a box moving to a first target location before moving onwards to a final, either near or far, target location. The second movement component and the target locations were occluded. After observing the first movement, participants were asked to select the most likely final target location, i.e., the distal goal of the sequence. Experiment 1 showed that participants relied on the velocity modulations of the first movement to infer the distal goal. The results of Experiment 2 indicated that such predictions of distal goals are possible even when the second movement in the sequence does not contain any velocity information, thus suggesting that the information present in the first movement plays the major role in the process of linking movements to their distal goals. However, Experiment 3 showed that under some circumstances the second movement can also contribute to how observers predict a distal goal. We discuss these results in terms of the underlying simulation processes that enable observers to predict a distal goal from the observation of proximal communicative modulations.

Sowing the seeds of intentionality: Motor intentions in plants

Motor intention/intentionality has been investigated from a wide variety of perspectives: some researchers have, for example, been focusing on the purely physical and mechanical aspects underlying the control of action, while others have been concentrating on subjective intentionality. Basically, all approaches ranging from the neuroscientific to phenomenological-inspired ones have been used to investigate motor intentions. The current study set out to examine motor intentions in connection to plant behavior utilizing the final goal of plant action as the definition of its motor intention. Taking a wide-angle approach, the first part of the review is dedicated to examining philosophical and psychological studies on motor intentions. Recent data demonstrating that plant behavior does indeed seem goal-directed will then be reviewed as we ponder the possibility of purposeful or intentional plant responses to stimuli and stress conditions in their environment. The article will draw to a close as we examine current theories attempting to explain plants' overt behavior and corresponding covert representations.

Predictable real-time constraints reveal anticipatory strategies of coupled planning in a sequential pick and place task

Planning a sequence of two motor elements is much more than concatenating two independent movements. However, very little is known about the cognitive strategies that are used to perform fluent sequences for intentional object manipulation. In this series of studies, the participants’ task was to reach for and pick to place a wooden cylinder to set it on a place pad of three different diameters, which served to modify terminal accuracy constraints. Participants were required to perform the sequences (1) at their preferred speed or (2) as fast as possible. Action kinematics were recorded with the Qualisys motion-capture system in order to implement a real-time protocol to get participants to engage in a true interactive relation. Results revealed that with low internal constraints (at preferred speed), low coupling between the two elements of the motor sequence was observed, suggesting a step-by-step planning strategy. Under high constraints (at fastest speed), an important terminal accuracy effect back propagated to modify early kinematic parameters of the first element, suggesting strong coupling of the parameters in an encapsulated planning strategy. In Studies 2 and 3, we further manipulated instructions and timing constraints to confirm the importance of time and predictability of external information for coupled planning. These findings overall sustain the hypothesis that coupled planning can take place in a pick and place task when anticipatory strategies are possible. This mode of action planning may be the key reason why motor intention can be read through the observation of micro variations in body kinematics.

Observer-Agent Kinematic Similarity Facilitates Action Intention Decoding

It is well known that the kinematics of an action is modulated by the underlying motor intention. In turn, kinematics serves as a cue also during action observation, providing hints about the intention of the observed action. However, an open question is whether decoding others’ intentions on the basis of their kinematics depends solely on how much the kinematics varies across different actions, or rather it is also influenced by its similarity with the observer motor repertoire. The execution of reach-to-grasp and place actions, differing for target size and context, was recorded in terms of upper-limb kinematics in 21 volunteers and in an actor. Volunteers had later to observe the sole reach-to-grasp phase of the actor’s actions, and predict the underlying intention. The potential benefit of the kinematic actor-participant similarity for recognition accuracy was evaluated. In execution, both target size and context modulated specific kinematic parameters. More importantly, although participants performed above chance in intention recognition, the similarity of motor patterns positively correlated with recognition accuracy. Overall, these data indicate that kinematic similarity exerts a facilitative role in intention recognition, providing further support to the view of action intention recognition as a visuo-motor process grounded in motor resonance.

Kinematic characteristics of second-order motor planning and performance in 6- and 10-year-old children and adults: Effects of age and task constraints

This study explored age-related differences in motor planning as expressed in arm-hand kinematics during a sequential peg moving task with varying demands on goal insertion complexity (second-order planning). The peg was a vertical cylinder with either a circular or semicircular base. The task was to transport the peg between two positions and rotate it various amounts horizontally before fitting into its final position. The amount of rotation required was either 0°, 90°, 180°, or -90°. The reaching for the peg, the displacement of it, and the way the rotation was accomplished was analyzed. Assessments of end state comfort, goal interpretation errors, and type of grip used were also included. Participants were two groups of typically developing children, one younger (M_age  = 6.7 years) and one older (M_age  = 10.3 years), and one adult group (M_age  = 34.9 years). The children, particularly 6-year-olds, displayed less efficient prehensile movement organization than adults. Related to less efficient motor planning, 6-year-olds, mainly, had shorter reach-to-grasp onset latencies, higher velocities, and shorter time to peak velocities, and longer grasp durations than adults. Importantly, the adults rotated the peg during transport. In contrast, the children made corrective rotations after the hand had arrived at the goal.

Aim and Plausibility of Action Chains Remap Peripersonal Space

Successful interaction with objects in the peripersonal space requires that the information relative to current and upcoming positions of our body is continuously monitored and updated with respect to the location of target objects. Voluntary actions, for example, are known to induce an anticipatory remapping of the peri-hand space (PHS, i.e., the space near the acting hand) during the very early stages of the action chain: planning and initiating an object grasp increase the interference exerted by visual stimuli coming from the object on touches delivered to the grasping hand, thus allowing for hand-object position monitoring and guidance. Voluntarily grasping an object, though, is rarely performed in isolation. Grasping a candy, for example, is most typically followed by concatenated secondary action steps (bringing the candy to the mouth and swallowing it) that represent the agent’s ultimate intention (to eat the candy). However, whether and when complex action chains remap the PHS remains unknown, just as whether remapping is conditional to goal achievability (e.g., candy-mouth fit). Here we asked these questions by assessing changes in visuo-tactile interference on the acting hand while participants had to grasp an object serving as a support for an elongated candy, and bring it toward their mouth. Depending on its orientation, the candy could potentially enter the participants’ mouth (plausible goal), or not (implausible goal). We observed increased visuo-tactile interference at relatively late stages of the action chain, after the object had been grasped, and only when the action goal was plausible. These findings suggest that multisensory interactions during action execution depend upon the final aim and plausibility of complex goal-directed actions, and extend our knowledge about the role of peripersonal space in guiding goal-directed voluntary actions.

The left hand disrupts subsequent right hand grasping when their actions overlap

Adaptive motor control is premised on the principle of movement minimization, which in turn is premised on a form of sensorimotor memory. But what is the nature of this memory and under what conditions does it operate? Here, we test the limits of sensorimotor memory in an intermanual context by testing the effect that the action performed by the left hand has on subsequent right hand grasps. Target feature-overlap predicts that sensorimotor memory is engaged when task-relevant sensory features of the target are similar across actions; partial effector-overlap predicts that sensorimotor memory is engaged when there is similarity in the task-relevant effectors used to perform an action; and the action-goal conjunction hypotheses predicts that sensorimotor memories are engaged when the action goal and the action type overlap. In three experiments, participants used their left hand to reach out and pick up an object, manually estimate its size, pinch it, look at it, or merely rest the left hand before reaching out to pick up a second object with their right hand. The in-flight anticipatory grip aperture of right-hand grasps was only influenced when it was preceded by grasps performed by the left-hand. Overlap in the sizes of the objects, partial overlap in the effectors used, and in the availability of haptic feedback bore no influence on this metric. These results support the hypothesis that intermanual transfer of sensorimotor memory on grasp execution is dependent on a conjunction of action type and goal.

Shaping of Reach-to-Grasp Kinematics by Intentions: A Meta-Analysis

When we reach to grasp something, we need to take into account both the properties of the object we are grasping and the intention we have in mind. Previous research has found these constraints to be visible in the reach-to-grasp kinematics, but there is no consensus on which kinematic parameters are the most sensitive. To examine this, a systematic literature search and meta-analyses were performed. The search identified studies assessing how changes in either an object property or a prior intention affect reach-to-grasp kinematics in healthy participants. Hereafter, meta-analyses were conducted using a restricted maximum likelihood random effect model. The meta-analyses showed that changes in both object properties and prior intentions affected reach-to-grasp kinematics. Based on these results, the authors argue for a tripartition of the reach-to-grasp movement in which the accelerating part of the reach is primarily associated with transporting the hand to the object (i.e., extrinsic object properties), the decelerating part of the reach is used as a preparation for object manipulation (i.e., prepare the grasp or the subsequent action), and the grasp is associated with manipulating the object's intrinsic properties, especially object size.

Grasping the Agent's Perspective: A Kinematics Investigation of Linguistic Perspective in Italian and German

Every day, we primarily experience actions as agents, by having a concrete perspective on our actions, their means and goals. This peculiar perspective is what allows us to successfully plan and execute our actions in a dense social environment. Nevertheless, in this environment actions are also perceived from an observer's perspective. Adopting such a perspective helps us to understand and respond to other's people actions and their outcomes. Importantly, similar experiences of being agent and observer occur also when actions are not physically acted/perceived but are merely linguistically shared. In this paper we present two exploratory studies, one in Italian and one in German, in which we applied a direct comparison of three singular perspectives in combination with different verb categories. First, second and third person pronouns were combined with action and interaction verbs, i.e., verbs implying an interaction with an object - e.g., grasp - or an interaction with an object and another person - e.g., give. By means of kinematics recording, we analyzed participants' reaching-grasping responses to a mouse while they were presented with the different combinations of linguistic stimuli (pronouns and verb type). Results of Experiment 1 on reaching show that, when they are preceded by YOU, interaction verbs reached the velocity peak earlier than action verbs, since a further motor act will follow. Thus pronouns influence perspective taking and while comprehending language we are sensitive to the motor chain organization of verbs. The absence of the same effects in Experiment 2 is likely due to the fact that, being the pronoun in German mandatory, it is perceived as less salient than in Italian. Overall our result supports the idea that language is grounded in the motor system in a flexible way, and highlights the need for cross-linguistic studies in the field of embodied language processing.

Habit outweighs planning in grasp selection for object manipulation

Object-directed grasping movements are adapted to intended interactions with an object. We address whether adjusting the grasp for object manipulation is controlled habitually, based on past experiences, or by goal-directed planning, based on an evaluation of the expected action outcomes. Therefore, we asked participants to grasp and rotate a dial. In such tasks, participants typically grasp the dial with an excursed, uncomfortable arm posture, which then allows to complete the dial rotation in a comfortable end-state. We extended this task by manipulating the contingency between the orientation of the grasp and the resulting end-state of the arm. A one-step (control) group rotated the dial to a single target. A two-step group rotated the dial to an initial target and then in the opposite direction. A three-step group rotated the dial to the initial target, then in the opposite direction, and then back to the initial target. During practice, the two-step and three-step groups reduced the excursion of their grasps, thus avoiding overly excursed arm postures after the second rotation. When the two-step and three-step groups were asked to execute one-step rotations, their grasps resembled those that were acquired during the two-step and three-step rotations, respectively. However, the carry-over was not complete. This suggests that adjusting grasps for forthcoming object manipulations is controlled by a mixture of habitual and goal-directed processes. In the present experiment, the former contributed approximately twice as much to grasp selection than the latter.

Performance of Motor Sequences in Children at Heightened vs. Low Risk for ASD: A Longitudinal Study from 18 to 36 Months of Age

Recent research shows that motor difficulties are a prominent component of the behavioral profile of autism spectrum disorder (ASD) and are also apparent from early in development in infants who have an older sibling with ASD (High Risk; HR). Delays have been reported for HR infants who do and who do not receive an eventual diagnosis of ASD. A growing body of prospective studies has focused on the emergence of early motor skills primarily during the first year of life. To date, however, relatively little work has examined motor skills in the second and third years. Thus, the present research was designed to investigate motor performance in object transport tasks longitudinally in HR and LR (Low Risk) children between the ages of 18 and 36 months. Participants (15 HR children and 14 LR children) were observed at 18, 24, and 36 months. Children completed two motor tasks, the Ball Task and the Block Task, each of which included two conditions that varied in terms of the precision demands of the goal action. Kinematic data were acquired via two magneto inertial sensors worn on each wrist. In the Block Task, HR children reached more slowly (i.e., mean acceleration was lower) compared to LR children. This finding is in line with growing evidence of early delays in fine motor skills in HR children and suggests that vulnerabilities in motor performance may persist into the preschool years in children at risk for ASD.

Eating interrupted: the effect of intent on hand-to-mouth actions

Evidence from recent neurophysiological studies on nonhuman primates as well as from human behavioral studies suggests that actions with similar kinematic requirements but different end-state goals are supported by separate neural networks. It is unknown whether these different networks supporting seemingly similar reach-to-grasp actions are lateralized, or if they are equally represented in both hemispheres. Recently published behavioral evidence suggests certain networks are lateralized to the left hemisphere. Specifically, when participants used their right hand, their maximum grip aperture (MGA) was smaller when grasping to eat food items than when grasping to place the same items. Left-handed movements showed no difference between tasks. The present study investigates whether the differences between grasp-to-eat and grasp-to-place actions are driven by an intent to eat, or if placing an item into the mouth (sans ingestion) is sufficient to produce asymmetries. Twelve right-handed adults were asked to reach to grasp food items to 1) eat them, 2) place them in a bib, or 3) place them between their lips and then toss them into a nearby receptacle. Participants performed each task with large and small food items, using both their dominant and nondominant hands. The current study replicated the previous finding of smaller MGAs for the eat condition during right-handed but not left-handed grasps. MGAs in the eat and spit conditions did not significantly differ from each other, suggesting that eating and bringing a food item to the mouth both utilize similar motor plans, likely originating within the same neural network. Results are discussed in relation to neurophysiology and development.

Concatenation of observed grasp phases with observer's distal movements: a behavioural and TMS study

The present study aimed at determining how actions executed by two conspecifics can be coordinated with each other, or more specifically, how the observation of different phases of a reaching-grasping action is temporary related to the execution of a movement of the observer. Participants observed postures of initial finger opening, maximal finger aperture, and final finger closing of grasp after observation of an initial hand posture. Then, they opened or closed their right thumb and index finger (experiments 1, 2 and 3). Response times decreased, whereas acceleration and velocity of actual finger movements increased when observing the two late phases of grasp. In addition, the results ruled out the possibility that this effect was due to salience of the visual stimulus when the hand was close to the target and confirmed an effect of even hand postures in addition to hand apparent motion due to the succession of initial hand posture and grasp phase. In experiments 4 and 5, the observation of grasp phases modulated even foot movements and pronunciation of syllables. Finally, in experiment 6, transcranial magnetic stimulation applied to primary motor cortex 300 ms post-stimulus induced an increase in hand motor evoked potentials of opponens pollicis muscle when observing the two late phases of grasp. These data suggest that the observation of grasp phases induced simulation which was stronger during observation of finger closing. This produced shorter response times, greater acceleration and velocity of the successive movement. In general, our data suggest best concatenation between two movements (one observed and the other executed) when the observed (and simulated) movement was to be accomplished. The mechanism joining the observation of a conspecific's action with our own movement may be precursor of social functions. It may be at the basis for interactions between conspecifics, and related to communication between individuals.

Tailoring reach-to-grasp to intended action: the role of motor practice

Motor learning results from repeated exposure to the same movement and allows a mover to increase movement optimality. Typically, this has only been considered in single-step movements. In sequential movements, an initial reach movement is tailored to the demands of the onward movement. However, the exact role of motor practice in the tailoring to onward task demands is unknown. Eighteen adults performed blocks of 15 movements; each movement consisted of a reach phase and an onward phase (the object was placed in a tight-fitting hole, placed in a loose-fitting hole or thrown). Simple practice effects were seen; for the reach phase, the amount of time spent decelerating decreased over trials, and for the onward phase, the accuracy of the place/throw movements increased over trials. Furthermore, approximately 30 % of variance in the practice effect of the onward phase could be explained by the practice effect in the reach phase. Therefore, we suggest that the changes in the reach phase are directly linked to the changes in the efficiency of action and that this is necessary but not sufficient for explaining the calibration of the onward action.

Prospective and retrospective effects in a virtual pointing task

Over two decades ago prospective and retrospective effects of posture selection in a sequential task were described for the first time. Since then, both effects have been reproduced in a number of reaching studies. We asked (1) whether retrospective effects would also be found in a sequential pointing task and (2) whether pro/retrospective effects of posture selection would transfer to the end-effector position in the absence of haptic feedback. To this end, we created a sequential, perceptual-motor task in a virtual environment. Participants had to point to a row of targets in the frontal plane in sequential order. In a control experiment, physical targets were placed at the same locations. Results showed that kinematic parameters were similar in the virtual and real environment. Retrospective effects of posture/position were found in neither environment, indicating that pointing movements require lower cognitive planning costs than reaching movements. Prospective effects of posture were found both in the virtual and real environment. Prospective effects of position, on the other hand, were present in the virtual but not in the real environment, indicating that the absence of haptic feedback may result in unconscious shifts of the end-effector position.

Oral hapsis guides accurate hand preshaping for grasping food targets in the mouth

Preshaping the digits and orienting the hand when reaching to grasp a distal target is proposed to be optimal when guided by vision. A reach-to-grasp movement to an object in one's own mouth is a natural and commonly used movement, but there has been no previous description of how it is performed. The movement requires accuracy but likely depends upon haptic rather than visual guidance, leading to the question of whether the kinematics of this movement are similar to those with vision or whether the movement depends upon an alternate strategy. The present study used frame-by-frame video analysis and linear kinematics to analyze hand movements as participants reached for ethologically relevant food targets placed either at a distal location or in the mouth. When reaching for small and medium-sized food items (blueberries and donut balls) that had maximal lip-to-target contact, hand preshaping was equivalent to that used for visually guided reaching. When reaching for a large food item (orange slice) that extended beyond the edges of the mouth, hand preshaping was suboptimal compared to vision. Nevertheless, hapsis from the reaching hand was used to reshape and reorient the hand after first contact with the large target. The equally precise guidance of hand preshaping under oral hapsis is discussed in relation to the idea that hand preshaping, and its requisite neural circuitry, may have originated under somatosensory control, with secondary access by vision.

The bottle and the glass say to me: "pour!"

The present study aimed at determining whether the observation of two functionally compatible artefacts, that is which potentially concur in achieving a specific function, automatically activates a motor programme of interaction between the two objects. To this purpose, an interference paradigm was used during which an artefact (a bottle filled with orange juice), target of a reaching-grasping and lifting sequence, was presented alone or with a non-target object (distractor) of the same or different semantic category and functionally compatible or not. In experiment 1, the bottle was presented alone or with an artefact (a sphere), or a natural (an apple) distractor. In experiment 2, the bottle was presented with either the apple or a glass (an artefact) filled with orange juice, whereas in experiment 3, either an empty or a filled glass was presented. In the control experiment 4, we compared the kinematics of reaching-grasping and pouring with those of reaching-grasping and lifting. The kinematics of reach, grasp and lift was affected by distractor presentation. However, no difference was observed between two distractors that belonged to different semantic categories. In contrast, the presence of the empty rather filled glass affected the kinematics of the actual grasp. This suggests that an actually functional compatibility between target (the bottle) and distractor (the empty glass) was necessary to activate automatically a programme of interaction (i.e. pouring) between the two artefacts. This programme affected the programme actually executed (i.e. lifting). The results of the present study indicate that, in addition to affordances related to intrinsic object properties, "working affordances" related to a specific use of an artefact with another object can be activated on the basis of functional compatibility.

Motor planning is facilitated by adopting an action's goal posture: an fMRI study

Motor planning is a hierarchical process that is typically organized around an action's goal (e.g., drinking from a cup). However, the motor plan depends not only on the goal but also on the current body state. Here, we investigated how one's own body posture interacts with planning of goal-directed actions. Participants engaged in a grasp selection (GS) task while we manipulated their arm posture. They had to indicate how they would grasp a bar when transporting it from a start to goal position and orientation. We compared situations in which one's body posture was in-congruent with the start posture and/or goal posture of the planned movement. Behavioral results show that GS took longer when one's own body state was incongruent with the goal posture of the planned movement. Correspondingly, neural activity in the intraparietal sulcus (IPS) and extrastriate body area (EBA) was modulated by congruency between the body state and the action plan. IPS was sensitive to overall congruency between body posture and action plan, while the EBA was sensitive specifically to goal posture congruency. Together, our results suggest that IPS maintains an internal state of one's own body posture, while EBA contains a representation of the goal posture of the action plan.

Typical and atypical (cerebral palsy) development of unimanual and bimanual grasp planning

In the present study we tested 13 children with cerebral palsy (CP) and 24 typically developing children (7-12 years old) in a unimanual and bimanual motor planning task. We focused on two research questions: (1) How does motor planning develop in children with and without CP? and (2) Is motor planning facilitated when the task is performed with both hands? Participants had to grasp one or two vertical oriented cylinder(s) and transport it/them to a platform that had different heights. As a measure of motor planning, we registered the height at which participants grasped the cylinder. Here, anticipation of grasp height upon the height of the upcoming target(s) is reflective of proper forward motor planning as it leads to a comfortable posture at the end of the task. In the unimanual task the typically developing children showed a significant grasp height effect, which increased with age. In contrast, no grasp height effect, or age related changes therein were found for the children with CP, suggesting a compromised development of motor planning in these children. Interestingly, when children had to transport one cylinder to a high shelf and one cylinder to a low shelf, the more affected hand of the CP children clearly anticipated the grasp height to the upcoming target height. The less affected hand did not show such anticipation. Taken collectively, these findings suggest a delayed or compromised development of motor planning in children with CP compared to typically developing children. At the same time, the facilitated motor planning of the more affected arm in the bimanual task offers a valuable entry point for intervention to improve motor planning in CP.

Social requests and social affordances: how they affect the kinematics of motor sequences during interactions between conspecifics

The present study aimed at determining whether and what factors affect the control of motor sequences related to interactions between conspecifics. Experiment 1 demonstrated that during interactions between conspecifics guided by the social intention of feeding, a social affordance was activated, which modified the kinematics of sequences constituted by reaching-grasping and placing. This was relative to the same sequence directed to an inanimate target. Experiments 2 and 4 suggested that the related-to-feeding social request emitted by the receiver (i.e. the request gesture of mouth opening) is prerequisite in order to activate a social affordance. Specifically, the two experiments showed that the social request to be fed activated a social affordance even when the sequences directed towards a conspecific were not finalized to feed. Experiment 3 showed that moving inside the peripersonal space of a conspecific, who did not produce any social request, marginally affected the sequence. Finally, experiments 5 and 6 indicated that the gaze of a conspecific is necessary to make a social request effective at activating a social affordance. Summing up, the results of the present study suggest that the control of motor sequences can be changed by the interaction between giver and receiver: the interaction is characterized by a social affordance that the giver activates on the basis of social requests produced by the receiver. The gaze of the receiver is a prerequisite to make a social request effective.

Behavioral evidence for left-hemisphere specialization of motor planning

Recent studies suggest that the left hemisphere is dominant for the planning of motor actions. This left-hemisphere specialization hypothesis was proposed in various lines of research, including patient studies, motor imagery studies, and studies involving neurophysiological techniques. However, most of these studies are primarily based on experiments involving right-hand-dominant participants. Here, we present the results of a behavioral study with left-hand-dominant participants, which follows up previous work in right-hand-dominant participants. In our experiment, participants grasped CD casings and replaced them in a different, pre-cued orientation. Task performance was measured by the end-state comfort effect, i.e., the anticipated degree of physical comfort associated with the posture that is planned to be adopted at movement completion. Both left- and right-handed participants showed stronger end-state comfort effects for their right hand compared to their left hand. These results lend behavioral support to the left-hemisphere-dominance motion-planning hypothesis.

Compromised motor planning and Motor Imagery in right Hemiparetic Cerebral Palsy

We investigated whether motor planning problems in people with Hemiparetic Cerebral Palsy (HCP) are paralleled by impaired ability to use Motor Imagery (MI). While some studies have shown that individuals with HCP can solve a mental rotation task, it was not clear if they used MI or Visual Imagery (VI). In the present study, motor planning and MI were examined in individuals with right HCP (n=10) and controls. Motor planning was measured using an object manipulation task, where participants had to anticipate the end of the motor action. MI was measured using a mental rotation paradigm, where participants judged laterality of hands presented from a back view and a palm view. To test if participants used MI or VI we compared reaction times of lateral versus medial rotations, under the assumption that MI is subject to biomechanical constraints of rotated hands, but VI is not. Individuals with HCP had a higher proportion of task failures due to inappropriate grip choice, exemplifying impaired planning. Second, individuals with HCP did not show a reaction time difference between lateral and medial rotations, indicating an impaired ability to use MI. These findings show that compromised motor planning in HCP is paralleled by an impairment in the ability to use MI. Training of MI may be a useful entry-point for rehabilitation of motor planning problems.

Changes of locomotion in old age depend on task setting

BACKGROUND

Laboratory settings may differ from everyday life with respect to factors such as attention, motivation, intention, and self-efficacy. Since those factors are likely to influence subjects' performance on locomotor tasks, we evaluated whether the age-related changes of locomotion previously observed under laboratory conditions are equally present in a real life-like scenario.

METHODS

15 young and 15 older subjects walked along a marked path of 25 m length and 0.3m width in a laboratory environment. 14 young and 13 older subjects walked in a community park along a 3 km path, with a straight and level registration section located after 1.5 km.

RESULTS

Step duration was longer, angular limb excursion was smaller, and the spatio-temporal gait variability was higher in the laboratory than in the park. Analysis of co-variance revealed that these changes cannot be traced back to a single cause. The variability of step duration and of limb excursion increased in old age under laboratory conditions, but only the latter parameter increased under real life-like conditions.

DISCUSSION

Our laboratory setting destabilized the gait pattern more than our real life-like setting, thus accentuating age-related changes.

Advance Planning in Sequential Pick–and–Place Tasks

It has been suggested that the kinematics of a reach–to–grasp movement, performed within an action sequence, vary depending on the action goal and the properties of subsequent movement segments (action context effect). The aim of this study was to investigate whether the action context also affects action sequences that consist of several grasping movements directed toward different target objects. Twenty participants were asked to perform a sequence in which they grasped a cylinder, placed it into a target area, and subsequently grasped and displaced a target bar of a certain orientation. We specifically tested whether the orientation of the target bar being grasped in the last movement segment influenced the grip orientation adapted to grasp and place the cylinder in the preceding segments. When all movement segments within the sequence were easy to perform, results indeed showed that grip orientation chosen in the early movement segments depended on the forthcoming motor demands, suggesting a holistic planning process. In contrast, high accuracy demands in specifying a movement segment reduced the ability of the motor system to plan and organize the movement sequence into larger chunks, thus causing a shift toward sequential performance. Additionally, making the placing task more difficult resulted in prolonged reaction times and increased the movement times of all other movement segments.

Planning and control of hand orientation in grasping movements

Humans grasp objects in a way that facilitates the intended use of the object. We examined how humans grasp a circular control knob in order to turn it in different directions and by different extents. To examine the processes involved in anticipatory planning of grasps, we manipulated advance information about the location of the control knob and the target of the knob-turn. The forearm orientation at the time of grasping depended strongly on the knob-turn, with the direction of the knob-turn having a stronger effect than the extent of the knob-turn. However, the variability of the forearm orientations after the knob-turn remained considerable. Anticipatory forearm orientations began early during the grasping movement. Advance information had no influence on the trajectory of the grasp but affected reaction times and the duration of the grasp. From the results, we conclude that (1) grasps are selected in anticipation of the upcoming knob rotation, (2) the desired hand location and forearm orientation at the time of grasping are specified before the onset of the grasp, and (3) an online programming strategy is used to schedule the preparation of the knob-turn during the execution of the grasp.

Transcranial magnetic stimulation to the frontal operculum and supramarginal gyrus disrupts planning of outcome-based hand-object interactions

Behavioral data suggest that goals inform the selection of motor commands during planning. We investigated the neural correlates that mediate planning of goal-oriented actions by asking 10 healthy subjects to prepare either a goal-specific movement toward a common object (a cup), with the intent of grasping-to-pour (liquid into it) or grasping-to-move (to another location) the object, or performing a non-object-oriented stimulus-response task (move a finger). Single-pulse transcranial magnetic stimulation was administered on 50% of trials to the supramarginal gyrus (SMG), anterior intraparietal sulcus, inferior frontal gyrus opercularis (IFGo), and triangularis during motor planning. Stimulation to SMG and IFGo caused a significant delay in planning goal-oriented actions but not responses to an arbitrary stimulus. Despite the delay, movement execution was not affected, suggesting that the motor plan remained intact. Our data implicate the SMG and IFGo in planning goal-oriented hand-object interactions.

Visual information for action planning in left and right congenital hemiparesis

Converging evidence suggests that compromised motor abilities in hemiparetic cerebral palsy are not solely due to impairments in motor execution, but are also related to deficits in action planning. The present study had two aims. First, we compared grip planning in a sequential task between participants with left-sided (n=12) or right-sided (n=10) congenital hemiparesis. Second, we studied the use of visual information for grip planning by having participants grasp a rod embedded in a 'rod-and-frame' illusion. The results showed that especially participants with right hemiparesis revealed planning problems as most of them did not switch between different grip types at all or they switched in an inconsistent manner. In contrast, the majority of participants with left hemiparesis showed consistent planning of the first part of the task. Second, the results indicated that visual information provided by the illusion had an effect on grip planning in participants that used a consistent planning strategy, suggesting that the use of visual information in action planning was not affected in these participants. The results are discussed in relation to hemispheric differences in motor planning and visuo-motor integration in congenital hemiparesis.

The effect of the "rod-and-frame" illusion on grip planning in a sequential object manipulation task

We investigated the effect of visual context (i.e., a visual illusion) on the planning of a sequential object manipulation task. Participants (n = 13) had to grasp a rod embedded in a “rod-and-frame” illusion and insert the rod-end into a tight hole in a pre-defined way. The grip type (defined by start posture, either pronated or supinated; and end posture, either comfortable or uncomfortable) used to grasp the rod was registered as a macroscopic variable of motor planning. Different rod orientations forced the participants to switch between grip types. As expected, most participants switched between pronated and supinated start postures, such that they ended the movement with a comfortable end posture. As it has been argued that planning is dependent on visual context information, we hypothesized that the visual illusion would affect the specific rod orientation at which participants would switch into a different grip type. This hypothesis was confirmed. More specifically, the illusion affected the critical spatial information that is used for action planning. Collectively, these findings are the first to show an effect of an illusion on motor planning in a sequential object manipulation task.

An object for an action, the same object for other actions: effects on hand shaping

Objects can be grasped in several ways due to their physical properties, the context surrounding the object, and the goal of the grasping agent. The aim of the present study was to investigate whether the prior-to-contact grasping kinematics of the same object vary as a result of different goals of the person grasping it. Subjects were requested to reach toward and grasp a bottle filled with water, and then complete one of the following tasks: (1) Grasp it without performing any subsequent action; (2) Lift and throw it; (3) Pour the water into a container; (4) Place it accurately on a target area; (5) Pass it to another person. We measured the angular excursions at both metacarpal-phalangeal (mcp) and proximal interphalangeal (pip) joints of all digits, and abduction angles of adjacent digit pairs by means of resistive sensors embedded in a glove. The results showed that the presence and the nature of the task to be performed following grasping affect the positioning of the fingers during the reaching phase. We contend that a one-to-one association between a sensory stimulus and a motor response does not capture all the aspects involved in grasping. The theoretical approach within which we frame our discussion considers internal models of anticipatory control which may provide a suitable explanation of our results.

Evidence for a distributed hierarchy of action representation in the brain

Complex human behavior is organized around temporally distal outcomes. Behavioral studies based on tasks such as normal prehension, multi-step object use and imitation establish the existence of relative hierarchies of motor control. The retrieval errors in apraxia also support the notion of a hierarchical model for representing action in the brain. In this review, three functional brain imaging studies of action observation using the method of repetition suppression are used to identify a putative neural architecture that supports action understanding at the level of kinematics, object centered goals and ultimately, motor outcomes. These results, based on observation, may match a similar functional-anatomic hierarchy for action planning and execution. If this is true, then the findings support a functional-anatomic model that is distributed across a set of interconnected brain areas that are differentially recruited for different aspects of goal-oriented behavior, rather than a homogeneous mirror neuron system for organizing and understanding all behavior.

Deployment of visual attention before sequences of goal-directed hand movements

We examined the allocation of attention during the preparation of sequences of manual pointing movements in a dual task paradigm. As the primary task, the participants had to perform a sequence of two or three reaching movements to targets arranged on a clock face. The secondary task was a 2AFC discrimination task in which a discrimination target (digital 'E' or '3') was presented among distractors either at one of the movement goals or at any other position. The data show that discrimination performance is superior at the location of all movement targets while it is close to chance at the positions that were not relevant for the movement. Moreover, our findings demonstrate that all movement-relevant locations are selected in parallel rather than serially in time, and that selection involves spatially distinct, non-contiguous foci of visual attention. We conclude that during movement preparation--well before the actual execution of the hand movement--attention is allocated in parallel to each of the individual movement targets.

Higher blood pressure predicts lower regional grey matter volume: Consequences on short-term information processing

Hypertension is a risk factor for diffuse brain atrophy. Yet, there is little evidence that higher blood pressure predicts focal brain atrophy, as indicated by a lower volume of regional brain tissue. This voxel-based morphometry study tested (a) whether higher blood pressure predicts lower regional grey or white matter volume and (b) whether a blood-pressure-related reduction in regional brain tissue volume predicts poorer neuropsychological test performance. Participants were 76 men (M age = 61.33, SD = 4.95 years) and 58 women (M age = 59.86, SD = 5.10 years) without a cardiovascular, cerebrovascular, or neuropsychiatric disease. Results showed that among men, higher resting systolic blood pressure predicted lower grey matter volume in the supplementary motor area and adjacent superior frontal gyrus, the anterior cingulate cortex, and middle temporal gyrus. Among men, lower grey matter volume in the supplementary motor area also predicted a slower time to complete the Trail Making Part B Test of executive control and a poorer recall of items from the Four-word Short-term Memory Test of working memory. These relationships were independent of age, total brain tissue volume, educational history, severity of carotid atherosclerosis, and the extent of periventricular and subcortical white matter lesions. Among women, no statistically significant relationships were found between blood pressure, regional brain tissue volume, and cognitive function. These findings suggest a functional relationship among men between higher blood pressure, lower regional grey matter volume, and poorer cognitive function that is independent of other risk factors and confounding medical conditions.

Effects of end-goal on hand shaping

The aim of the present study was to determine whether hand shaping was affected by planning of an action subsequent to object contact. Ten subjects (5 females and 5 males, ages 19-33) were requested to reach toward and grasp a convex object between the thumb and the four fingers of the right hand and to perform one of the following actions: 1) lift up the object; 2) insert the object into a niche of a similar shape and size as the object, or 3) insert the object into a rectangular niche much larger than the object. Flexion/extension at the metacarpal-phalangeal and proximal interphalangeal joints of all digits were measured using resistive sensors embedded in a glove. Although all experimental conditions required grasping the same object, we found different covariation patterns among finger joint angles across conditions. Gradual preshaping of the hand occurred only when planning object lift or when the end-goal required object placement into the tight niche. In contrast, for the larger niche, gradual preshaping was not evident for the ring and the little finger. Further, reaching movements were faster for movements ending with the larger niche than for the other movement conditions. The present results suggest that hand shaping takes into account end-goal in addition to object geometry. We discuss these findings in the context of forward internal models that allow the prediction of the sensorimotor consequences of motor commands in advance to their execution.

Planning short pointing sequences

An experiment tested the hypothesis that fast, short sequences of movements are planned as a whole, before movement inception. The experimental task consisted of pointing to either one (one-step condition), or two (two-step condition) visual targets aligned along the mid-sagittal axis in a horizontal plane. There were nine possible arrangements of the targets resulting from all combinations of three distances (5, 10, 15 cm), and two trial orders (blocked or random). Performances were characterised by reaction time (RT), movement kinematics, and spatial accuracy. Compared with one-step trials, the first movements of two-step trials had longer RTs (length effect), particularly in random sessions, and when the sequences included short-distance targets. There were also differences in duration (one-target advantage), velocity profile and spatial accuracy that did not depend on the characteristics of the second movement. The results are inconsistent with the assumption that two-step sequences are planned as a whole. Instead, they are in keeping with the alternative hypothesis that part of the preparation of the second step takes place during the execution of the first step.

Execution and observation of bringing a fruit to the mouth affect syllable pronunciation

Kinematic analysis of lip and voice spectrum analysis were used to assess the influence of both execution and observation of arm-mouth-related actions on speech production. In experiments 1 and 2 participants brought either a cherry or an apple to their mouth and either pronounced the syllable BA (experiment 1) or emitted a nonspeech-related vocalization (experiment 2). In the other three experiments participants observed arm actions performed by the experimenter and pronounced the syllable BA. In experiment 3, they observed the action of bringing the cherry or apple to the mouth. In experiments 4 and 5, they observed a pantomime of the same action performed by the experimenter with his own arm (experiment 4) or with a nonbiological arm (experiment 5). The results showed that the formant 2 of the vowel 'a' increased when participants executed the bringing-to-the-mouth act with the apple or observed its execution or pantomime with the experimenter's arm (experiments 1, 3 and 4). In contrast, no modification in the vowel formants was found during a nonspeech-related vocalization (experiment 2) and during observation of an action with a nonbiological arm (experiment 5). Finally, the opening of the lips was larger when the participant brought the apple rather than the cherry to the mouth and pronounced BA (experiment 1). Taken together, the results of the present study suggest that the execution and observation of the bringing-to-the-mouth action activate a mouth articulation posture (probably due to the act of food manipulation with the mouth) which selectively influences speech production. They support the idea that the system involved in speech production shares and may derive from the neural substrate which is involved in the control of arm-mouth interactions and, in general, of arm actions.