Motor programming: does the choice of the limb which is to carry out the response imply a delay?

In many activities, the human being must quickly decide on the response to be produced following a change in the environment. In some of these situations, the limb that the individual chooses to carry out a response seems to be a significant element in performance. Thus, if the individual carries out the response with the limb closest to the target, the performance can improve because it will take less time to achieve the goal. However, it seems that in these situations, the human being does not take this decrease in movement time into consideration and that the response is carried out with the dominant hand. Why is this so? It may be because the reaction is faster when there doesn't have to be a choice as to which limb will carry out the response. The goal of this study was to check this possibility. In order to do so, the subjects performed a two choice reaction-time task. For this task, some subjects knew beforehand which hand they had to use to carry out the response while other subjects were unaware of this fact. The results of two experiments indicated that the choice of the limb which is to carry out the response requires no particular delay when the movement to be produced is externally guided.     

Rhythm and dominance

Subjects were tested by a short experimental procedure involving tapping of a rhythm with one limb with a simultaneous regular beat with another limb. Informal observations had suggested a rhythm dominance effect—that is was dramatically easier with some limb combinations. Notably it was easy when the right hand tapped the rhythm and the left hand the beat but almost impossible the other way round. Equally, both hands dominated both feet. Our tests revealed enormous individual differences, subjects separating neatly into three groups. Some people could not do the task at all, some could do it with any limb combination, the latter group including all the serious musicians tested. For the remainder the rhythm dominance effect was clear. However, the laterality effect was the same (right hand advantage) for a majority (60%) of left handers. We conclude, then, that this effect is linked to language dominance and not handedness. In addition it seems there is a task scheduler which imposes its own view in combining this laterality effect with the dominance of hands over feet.     

Cooperative selection of movements: The optimal selection model

How one selects a movement when faced with alternative ways of doing a task is a central problem in human motor control. Moving the fingertip a short distance can be achieved with any of an infinite number of combinations of knuckle, wrist, elbow, shoulder, and hip movements. The question therefore arises: how is a unique combination chosen? In our model, choice is achieved by consideration of the similarity between the task requirements and the optimal biomechanical performance of each limb segment. Two variants of the model account for the movements that are selected when subjects freely oscillate the fingertip and when they tap against an obstacle. An important feature of both is that the impulse of collision with an obstacle (as in drumming with the hand or tapping with the finger) is assumed to be controlled in part by aiming for a point beyond the surface being struck. Thus, a force-related control variable may be represented and controlled spatially.     

On the type of information used to control and learn an aiming movement after moderate and extensive training

This experiment was conducted to see if, in an aiming task (MT = 550 msec), where subjects received moderate (200 trials) or extensive practice (2000 trials), performance would benefit from vision of the performing limb and the target to be reached when compared to a situation where only the target to be reached was visually available. As a second goal, a transfer paradigm was used to see to what extent learning was specific to the conditions under which practice occurred. The results indicated that performance was enhanced when subjects were permitted vision of the performing limb. Furthermore, the subjects who benefited from vision of the performing limb in the training period were not able, even after extensive training, to maintain performance in the transfer task (i.e., without vision of the performing limb). These results are consistent with the view that vision of the responding limb is particularly important in learning a perceptual-motor task. Moreover, practice does not decrease the importance of this information for guiding the movement as some of the past literature suggests might happen. The results are seen as supporting the notion that movement learning may involve the development of a complex sensorimotor reference mechanism that acts to control and, when necessary, modify the ongoing movement. Further, this would imply that movement learning is relatively specific to the conditions under which practice occurs.     

Manual asymmetries in bimanual reaching: the influence of spatial compatibility and visuospatial attention

The goal of the present investigation was to explore the possible expression of hemispheric-specific processing during the planning and execution of a bimanual reaching task. Participants (N = 9) completed 80 bimanual reaching movements (requiring simultaneous, bilateral production of arm movements) to peripherally presented targets while selectively attending to either their left or right hand. Further, targets were presented in spatially compatible (ipsilateral to the aiming limb) and incompatible (contralateral to the aiming limb) response contexts. It was found that the left hand exhibited temporal superiority over the right hand in the response planning phase of bimanual reaching, indicating a left hand/right hemisphere advantage in the preparation of a bimanual response. During response execution, and consistent with the view that interhemispheric processing time (Barthelemy & Boulinguez, 2002) or biomechanical constraints (Carey, Hargreaves, & Goodale, 1996) generate temporal delays, longer movement times were observed in response to spatially incompatible target positions. However, no hemisphere-specific benefit was demonstrated for response execution. Based on these findings, we propose lateralized processing is present at the time of response planning (i.e., left hand/right hemisphere processing advantage); however, lateralized specialization appears to be annulled during dynamic execution of a bimanual reaching task.     

The effects of temporal-precision and time-minimization constraints on the spatial and temporal accuracy of aimed hand movements

Discrete aimed hand movements, made by subjects given temporal-accuracy and time-minimization task instructions, were compared. Movements in the temporal-accuracy task were made to a point target with a goal movement time of 400 ms. A circular target then was manufactured that incorporated the measured spatial errors from the temporal-accuracy task, and subjects attempted to contact the target with a minimum movement time and without missing the circular target (time-minimization task instructions). This procedure resulted in equal movement amplitude and approximately equal spatial accuracy for the two task instructions. Movements under the time-minimization instructions were completed rapidly (M = 307 ms) without target misses, and tended to be made up of two submovements. In contrast, movements under temporal-accuracy instructions were made more slowly (M = 397 ms), matching the goal movement time, and were typically characterized by a single submovement. These data support the hypothesis that movement times, at a fixed movement amplitude versus target width ratio, decrease as the number of submovements increases, and that movements produced under temporal-accuracy and time-minimization have different control characteristics. These control differences are related to the linear and logarithmic speed-accuracy relations observed for temporal-accuracy and time-minimization tasks, respectively.     

Effect of emotions on the choice of goals and actions

The present paper concerns the influence negative emotions exert on motivational processes, i.e., on the selection of goals and corresponding actions. It is assumed that, in a negative emotional state, the goal to overcome this negative mood state takes precedence over the goal to succeed in a nonemotional task. Correspondingly, emotion-related activities should be preferred to task-related ones. In order to test this assumption, subjects in a negative and a neutral emotional state were given a series of activities, some suited for coping, some suited for task fulfilment. They were instructed to name (Experiment I) or to carry out (Experiment II) those activities they preferred at the very moment and to give a short reason for each choice. Results showed that subjects in a negative mood compared to those of the neutral control group were less occupied with the nonemotional task, but instead more frequently chose emotion-related activities with the explicit reason that these activities served to overcome their negative emotions.     

Combined Effects of Movement Velocity and Duration on Programming Time: Spijkers (1989) Revisited

The goal of the present study was to determine the combined effects of movement velocity and duration on motor programming. Subjects were submitted to a two-choice reaction time task that could be completed by aiming movements differing in the mean velocity at which they were to be produced as well as by their movement time. The results of the present study indicate that, in each pair of responses used, the responses having the higher mean velocity were initiated faster than those having the lower mean velocity. Contrary to Spijkers' (1989) study, the different movement time pairings did not modify the effect of movement velocity on response programming time. Moreover, the same pattern of results was observed whether or not the subjects were permitted to visually guide their ongoing movement. Thus, Spijkers' proposition, that the type of control one may use to guide an aiming movement needs to be determined before movement initiation can take place, was not confirmed.     

Combined effects of movement velocity and duration on programming time: Spijkers (1989) revisited

The goal of the present study was to determine the combined effects of movement velocity and duration on motor programming. Subjects were submitted to a two-choice reaction time task that could be completed by aiming movements differing in the mean velocity at which they were to be produced as well as by their movement time. The results of the present study indicate that, in each pair of responses used, the responses having the higher mean velocity were initiated faster that those having the lower mean velocity. Contrary to Spijkers' (1989) study, the different movement time pairings did not modify the effect of movement velocity on response programming time. Moreover, the same pattern of results was observed whether or not the subjects were permitted to visually guide their ongoing movement. Thus, Spijkers' proposition, that the type of control one may use to guide an aiming movement needs to be determined before movement initiation can take place, was not confirmed.     

Evidence from a response choice task reveals a selection bias in the attentional cueing paradigm

In a typical attentional cueing paradigm, irrelevant peripheral cues produce early facilitation (fast responses) followed by later inhibition (slow responses) to cued locations. Here we examine whether cues not only influence the speed with which responses are produced, but also impact or bias which location is ultimately selected as requiring a response. Specifically, can cues influence not only the speed with which we respond but also influence the behavior produced? To examine this question, a choice localization task was used in which no targets were presented, and subjects were asked to choose which effector (left hand, right hand) to use in response to a centrally presented tone. Thus, following either a left or right peripheral cue, and then a central tone, subjects were free to respond with either their left or right hand. Early facilitation and later inhibition with this choice procedure were found in both response times and the proportion of responses to the cued and uncued locations. These results suggest that there are processes which initially bias response selection toward cued locations and then subsequently bias response selection away from cued locations.     

Achilles Tendon Reflexes and Surface EMG Activity during Anticipation of a Significant Event and Preparation for a Voluntary Movement

Achilles tendon reflexes were evoked bilaterally during and shortly after an interstimulus-interval (ISI) of 4 s and expressed as percentages of an averaged control reflex. Surface EMG of the soleus muscles was recorded continuously during the ISI, and expressed as percentages of a control EMG level. Three types of tasks were introduced, according to a between subjects design. Condition I consisted of a guessing task, involving anticipation of the second stimulus (S2) and not requiring a motor response. Conditions II and III were a warned choice and simple RT task respectively, the motor response to S2 being a plantar flexion of either the left or right foot in Condition II, and a plantar flexion of the right foot in Condition III. The results can be stated as follows: 1. Anticipation of a stimulus is not sufficient for a reflex increase to occur during an ISI. Preparation for a movement seems to be a necessary condition.

2. The reflex increase during preparation is rather independent of the amount of selectivity in the preparatory process; simple and choice RT tasks yield similar results, although the mean RTs do differ.

3. A difference between the involved and non-involved legs in the simple RT task is not found in the present experiment, as opposed to other studies. The particular instruction given to the subjects could be of importance in producing this difference.

4. Reflex changes cannot simply be accounted for by changes in background EMG of the agonist, as the EMG time course shows no changes over time in either condition.

     

Choice reaction time of elbow flexion and extension during passive elbow motions

The effect of passive elbow motions on electromyographic reaction times (EMG-RTs) of the biceps brachii for elbow flexion and the triceps for elbow extension was investigated in 8 normal subjects, using a choice-RT task, in which the subject was uncertain about the response direction to perform until the arrival of response signal after the passive motion started. Compared to the static condition, choice EMG-RTs shortened only when the direction of passive and response movements was the same. It seems that passive motions act as prior information on direction of movement in the choice-RT task.     

Mechanical Efficiency and Metabolic Cost as Measures of Learning a Novel Gross Motor Task

“Efficiency,” or economy of movement with respect to energy expended in achieving the goal of the task, is implicit in many definitions of skilled performance. This study examined changes in mechanical efficiency and transport efficiency on a novel gross motor skill. The subjects were 5 physically fit adult males who were asked to perform 20 3-min trials walking on hands and feet (crawling) on a motor-driven treadmill at constant speed (0.76 mis). Transport efficiency, the metabolic cost of transporting the body mass a given distance at constant speed, improved significantly over practice trials. Mechanical efficiency, derived from the mechanical power output of individual body segments, showed an overall improvement of 13.7% by the last day of practice. Even though this improvement was not statistically significant it appears to be greater than that expected due to physiological training effects. The efficiency measures correlated significantly with changes in limb kinematics. It was concluded that with practice subjects tailored their movement pattern to produce energy efficient adaptations to task constraints. These findings provide empirical support for theoretical perspectives that have emphasized biological principles in the organization of motor coordination and control.     

Mechanical efficiency and metabolic cost as measures of learning a novel gross motor task

"Efficiency, " or economy of movement with respect to energy expended in achieving the goal of the task, is implicit in many definitions of skilled performance. This study examined changes in mechanical efficiency and transport efficiency on a novel gross motor skill. The subjects were 5 physically fit adult males who were asked to perform 20 3-min trials walking on hands and feet (crawling) on a motor-driven treadmill at constant speed (0.76 m/s). Transport efficiency, the metabolic cost of transporting the body mass a given distance at constant speed, improved significantly over practice trials. Mechanical efficiency, derived from the mechanical power output of individual body segments, showed an overall improvement of 13.7% by the last day of practice. Even though this improvement was not statistically significant it appears to be greater than that expected due to physiological training effects. The efficiency measures correlated significantly with changes in limb kinematics. It was concluded that with practice subjects tailored their movement pattern to produce energy efficient adaptations to task constraints. These findings provide empirical support for theoretical perspectives that have emphasized biological principles in the organization of motor coordination and control.     

Achilles tendon reflexes and surface EMG activity during anticipation of a significant event and preparation for a voluntary movement

Achilles tendon reflexes were evoked bilaterally during and shortly after an interstimulus-interval (ISI) of 4 s and expressed as percentages of an averaged control reflex. Surface EMG of the soleus muscles were recorded continuously during the ISI, and expressed as percentages of a control EMG level. Three types of tasks were introduced, according to a between subjects design. Condition I consisted of a guessing task, involving anticipation of the second stimulus (S2) and not requiring a motor response. Conditions II and III were a warned choice and simple RT task respectively, the motor response to S2 being a plantar flexion of either the left or right foot in Condition II, and a plantar flexion of the right foot in Condition III. The results can be stated as follows: 1. Anticipation of a stimulus is not sufficient for a reflex increase to occur during an ISI. Preparation for a movement seems to be a necessary condition. 2. The reflex increase during preparation is rather independent of the amount of selectivity in the preparatory process; simple and choice RT tasks yield similar results, although the mean RTs do differ. 3. A difference between the involved and non-involved legs in the simple RT task is not found in the present experiment, as opposed to other studies. The particular instruction given to the subjects could be of importance in producing this difference. 4. Reflex changes cannot simply be accounted for by changes in background EMG of the agonist, as the EMG time course shows no changes over time in either condition.     

Motor learning of cue-dependent pull-force changes during an isometric precision grip task

The “raspberry task” represents a precision grip task that requires continuous adjustment of grip and pull forces. During this task subjects grip a specialized grip rod and have to increase the pull force linearly while the rod is locked. The aim of this study was to determine whether an associated, initially neutral cue is able to evoke pull-force changes in the raspberry task. A standard delay paradigm was used to study cued pull-force changes during an ongoing movement resulting in unloading. Pull force and EMG activity of hand and arm muscles were recorded from 13 healthy, young subjects. The cue was associated with a complex change in motor behavior.In this task, cued force changes take place more rapidly than in protective reflex systems (in median after the second presentation of the cueing stimulus). A cued force change was detectable in two-thirds of paired trials. Although the force change is produced by a decrease of the EMG activity in several grip- and pull-force-producing muscles, the most significant effect in the majority of the subjects was an increase of the activity of the flexor carpi ulnaris muscle which antagonises corresponding pull-force-producing muscles. Cued force changes require adequately and precisely controlled activation of the muscle groups involved in the movement.     

Is it possible to prepare the second component of a movement before the first one?

Experiment 1 utilized a choice reaction time paradigm to examine whether advance information about the second component of a movement has similar effects upon movement initiation and execution as advance information about the first component. Four stimuli were assigned to four goal keys. Subjects responded with the index finger of their preferred hand. They had to press on of two intermediate keys before pressing the assigned stimulus goal key. Advance information signaled one pair of goal keys in such a way that either the first or the second movement component was unequivocally specified before the response signal appeared. Shorter reaction times resulted when the first component was precued. Further control conditions showed that advance information about the second movement component could not be utilized for movement preparation. Experiment 2 ruled out a perceptual interpretation of this effect. Experiment 3 showed that preparation time for two-component movements are longer than for one-component movements. The study permits the conclusions that speeded two-component movements are controlled by motor programs and that advance information about the first movement component is required before the second movement component can be programmed.     

Explicit Learning of a Dynamic System with a Non-salient Pattern

We examine the hypothesis that a specific goal leads to implicit learning, whereas a nonspecific goal leads to explicit learning, even though the pattern to be learnt is non-salient. Subjects learned a dynamic control task (Berry & Broadbent, 1984). One group of subjects had a specific control goal, the second group had a non-specific pattern-search goal, and the third group had both goals. On measures of learning (control performance, prediction, and general questions), the non-specific group learnt explicitly, outperforming the other two groups on all learning measures. The specific group performed next best on control performance and prediction questions but performed very poorly on general questions. The dual-goal group performed poorly on all measures. Non-specific subjects predicted well on both familiar and unfamiliar situations. Specific-goal subjects predicted well on familiar situations, regardless of whether their previous response had been correct or incorrect. Dual-goal subjects predicted well only on familiar correct situations. We conclude that the non-specific group learned through explicit hypothesis testing, the specific group learned through a mixture of explicit problem solving and implicit instance learning, and the dual-goal group learned instances. Results are discussed in terms of dual-space models of problem solving and hypothesis testing and in terms of implicit instance learning. We consider how the choice of learning goal affects the cognitive processes used during learning and suggest that having subjects learn the same information implicitly or explicitly is potentially useful for drawing clearer distinctions between implicit and explicit modes of learning.     

Risk taking in achievement-oriented situations: Do people really maximize affect or competence information?

Several studies of choice behavior (risk taking) in achievement-oriented situations are reanalyzed. The usual ways of pooling all choices over trials and subjects conceal the series of subjects' decisions and the dynamics inherent in these decisions. A basic strategy of subjects in an achievement-oriented choice situation seems to be to start with an easy task, choose a more difficult one whenever you succeed, and stay mostly at the same difficulty level whenever you fail. A computer model, in which such simple assumptions are made, generates preference functions over the order of difficulty levels that are indistinguishable from those found in empirical studies. It is concluded that the study of choice behavior in achievement-oriented situations should be based on the analysis of the series of single decisions by one subject. For this we need models that allow the predictions of such decisions and the prediction of action-controlling cognitions and emotions.     

Unintentional movements induced by sequential transient perturbations in a multi-joint positional task

We explored the phenomenon of unintentional movements of a multi-joint effector produced by multiple transient changes in the external force. The subjects performed a position-holding task against a constant bias force produced by a robot and were instructed not to intervene voluntarily with arm movements produced by changes in the robot force. The robot produced a smooth force increase leading to hand movement from the trunk, followed by a dwell time. Then, the force dropped to its initial value leading to hand movement toward the initial position but with an undershot. Such perturbation episodes were repeated four times in a row. The accumulated perturbation and undershoot distances kept increasing without saturation within the sequence of four perturbation episode. The limb apparent stiffness before dwell time increased over sequential perturbations while apparent stiffness after dwell time decreased. We interpret the results as consequences of a drift of the hand referent coordinate (RC) caused by a hypothesized RC-back-coupling mechanism and a coupled drift of the apparent stiffness. The results show that RC-back-coupling continues to lead to unintentional movements over repeated perturbations and is accompanied by a relatively slow re-setting process.