Effector independence

Learning a covert sequence of effector movements: limits to its acquisition

Sequence learning in serial reaction time (SRT) tasks is an established, lab-based experimental paradigm to study acquisition and transfer of skills based on the detection of predictable regularities in stimulus and motor response sequences. Participants learn a sequence of targets and responses to these targets by associating the responses with subsequently presented targets. In the traditional paradigm, however, actions and response targets are directly related. In contrast, the present study asked whether participants would demonstrate acquisition of a sequence of effector movements of the left vs. right hand (e.g., hand sequence learning), whilst the actual targets and associated finger responses are unpredictable. Twenty-seven young adults performed a SRT task to visually presented characters with the index or middle fingers of both hands. While the specific fingers to respond with were randomly selected for each target presentation, both hands followed a covert sequence. We asked whether participants would learn the underlying hand sequence as demonstrated by shortened response latencies and increased accuracy compared to a fully randomized hand sequence. The results show sequence-specific learning effects. However, categorization of hand responses depending on the previous response suggested that learning occurred predominantly for subsequent finger responses of the same hand, which added to general hand-based priming. Nevertheless, a marginally significant effect was observed even for predictable shifts between hands when homologous fingers were involved. Our results thus suggest that humans are able to benefit from predictable within-hand finger shifts but less so for predicted shifts between hands.

Reliability of on-line visual feedback influences learning of continuous motor task of healthy young adults

A continuous task was used to determine how the reliability of on-line visual feedback during acquisition impacts motor learning. Participants performed a right hand pointing task of a repeated sequence with a visual cursor that was either reliable, moderately unreliable, or largely unreliable. Delayed retention tests were administered 24 h later, as well as intermanual transfer tests (performed with the left hand). A visuospatial transfer test was performed with the same targets' sequence (same visuospatial configuration) while a motor transfer test was performed with the visual mirror of the targets' sequence (same motor patterns). Results showed that pointing was slower and long-term learning disrupted in the largely unreliable visual cursor condition, compared with the reliable and moderately unreliable conditions. Also, analysis of transfers revealed classically better performance on visuospatial transfer than on motor transfer for the reliable condition. However, here we first show that such difference disappears when the cursor was moderately or largely unreliable. Interestingly, these results indicated a difference in the type of sequence coding, depending on the reliability of the on-line visual feedback. This recourse to mixed coding opens up interesting perspectives, as it is known to promote better learning of motor sequences.

Simulated practice effects on the transfer and retention of gait sequences from the upper to the lower extremity

This study investigated transfer of training from upper extremity limbs (the index fingers) to the lower extremity limbs (the legs) for performance of three gait sequences of different difficulty. Fifteen subjects participated in the study. Subjects in an iPad training group practiced by sequentially moving their left-and right-hand index fingers across tiles to each of three targets displayed on an iPad for 20 trials. Subjects in a gait training group practiced by sequentially walking across tiles to each of the 3 targets displayed on a screen for 20 trials. A no practice group did not receive practice trials. Immediately following practice of each level of difficulty, a transfer test (20 trials) was given for which subjects walked to the target just practiced. A retention test of 36 trials (12 trials at each difficulty level) was administered 20 min following performance of the last transfer test trial. The retention test showed that reaction times were shorter for the iPad training than gait training and no training groups; anticipatory postural adjustment times were equivalent for the iPad and gait training groups, but shorter than for the no training group; and movement times were shorter for the iPad training group than for the gait training and no training groups. These results suggest that iPad training (upper extremity) followed by performance of gait training (lower extremity) had greater benefits for learning (as measured by the delayed retention test) the gait sequences than practicing the actual gait sequences themselves.

Bimanual coordination associated with left- and right-hand dominance: testing the limb assignment and limb dominance hypothesis

In an experiment conducted by Kennedy et al. (Exp Brain Res 233:181–195, 2016), dominant right-handed individuals were required to produce a rhythm of isometric forces in a 2:1 or 1:2 bimanual coordination pattern. In the 2:1 pattern, the left limb performed the faster rhythm, while in the 1:2 pattern, the right limb produced the faster pattern. In the 1:2 pattern, interference occurred in the limb which had to produce the slower rhythm of forces. However, in the 2:1 condition, interference occurred in both limbs. The conclusion was that interference was not only influenced by movement frequency, but also influenced by limb dominance. The present experiment was designed to replicate these findings in dynamic bimanual 1:2 and 2:1 tasks where performers had to move one wrist faster than the other, and to determine the influence of limb dominance. Dominant left-handed (N = 10; LQ = − 89.81) and dominant right-handed (N = 14; LQ = 91.25) participants were required to perform a 2:1 and a 1:2 coordination pattern using Lissajous feedback. The harmonicity value was calculated to quantify the interference in the trial-time series. The analysis demonstrated that regardless of limb dominance, harmonicity was always lower in the slower moving limb than in the faster moving limb. The present results indicated that for dominant left- and dominant right-handers the faster moving limb influenced the slower moving limb. This is in accordance with the assumption that movement frequency has a higher impact on limb control in bimanual 2:1 and 1:2 coordination tasks than handedness.

The effect of how to perform movement sequences on absolute and relative timing transfer

Depending on the difficulty of the task in terms of movement duration and the number of elements forming the sequence, recent research has shown that movement sequences are coded in visual-spatial coordinates or motor coordinates. An interesting question that arises is how a specific manner of performance without a change in such functional difficulties affects the representation of movement sequences. Accordingly, the present study investigated how the way in which a movement sequence is performed affects the transfer of timing properties (absolute and relative timing) from the practised to unpractised hand under mirror (same motor commands as those used in practice) and non-mirror (the same visual-spatial coordinates as those present during practice) conditions in two experiments each with segment movement time goals that were arranged differently. The study showed that after a limited amount of practice, the pattern of results obtained for relative timing differed between the two experiments. In the first experiment, there was no difference between retention and non-mirror transfer, but performance on these tasks was significantly better than that for mirror transfer, whereas in the second experiment, there was no difference between the mirror and non-mirror transfer. For total errors, no significant difference was found between the retention and transfer tests in both experiments. It was concluded that the way in which a sequence is performed could affect the representation of the task and the transfer of relative timing, while absolute timing could purposefully be maintained if necessary.

BDNF Val66Met polymorphism is associated with altered activity-dependent modulation of short-interval intracortical inhibition in bilateral M1

The BDNF Val66Met polymorphism is associated with impaired short-term plasticity in the motor cortex, short-term motor learning, and intermanual transfer of a procedural motor skill. Here, we investigated the impact of the Val66Met polymorphism on the modulation of cortical excitability and interhemispheric inhibition through sensorimotor practice of simple dynamic skills with the right and left first dorsal interosseous (FDI) muscles. To that end, we compared motor evoked potentials (MEP) amplitudes and short-interval intracortical inhibition (SICI) in the bilateral representations of the FDI muscle in the primary motor cortex (M1), and interhemispheric inhibition (IHI) from the left to right M1, before and after right and left FDI muscle training in an alternated sequence. Val66Met participants did not differ from their Val66Val counterparts on motor performance at baseline and following motor training, or on measures of MEP amplitude and IHI. However, while the Val66Val group displayed significant SICI reduction in the bilateral M1 in response to motor training, SICI remained unchanged in the Val66Met group. Further, Val66Val group's SICI decrease in the left M1, which was also observed following unimanual training with the right hand in the Control Right group, was correlated with motor improvement with the left hand. The potential interaction between left and right M1 activity during bimanual training and the implications of altered activity-dependent cortical excitability on short-term motor learning in Val66Met carriers are discussed.

Sequence Learning: Response Structure and Effector Transfer

Two experiments are reported that investigate the response structure and effector transfer of repeated movement sequences. Participants moved a lever to targets sequentially presented on the computer monitor. In Experiment 1 the learning of 10- and 16-element sequences (identical movement pattern) was contrasted. After 1 day of practice the 10-element sequence was organized into fewer subsequences and, thus, performed more rapidly than the 16-element sequence. The imposed organization appeared to be coded in a relatively abstract way, as evidenced by effector transfer that was as good as that on the retention test. In Experiment 2 the 16-element sequence was studied after more extensive practice. By the end of 4 days of practice the participants produced relatively seamless responses void of obvious transitions between subsequences, but the control of the movement was less effector independent than observed earlier in practice. The results suggest that the process of consolidating the sequence, which led to more fluent response production, also resulted in the utilization of effector specific information.

Proportional and nonproportional transfer of movement sequences

Two experiments were designed to determine participants’ ability to transfer a learned movement sequence to new spatial locations. A 16-element dynamic arm movement sequence was used in both experiments. The task required participants to move a horizontal lever to sequentially projected targets. Experiment 1 included 2 groups. One group practised a pattern in which targets were located at 20, 40, 60, and 80° from the start position (long sequence). The other group practised a pattern with targets at 20, 26.67, 60, and 80° (mixed sequence). Both groups were tested 24 hours later on the long, mixed, and short sequence. The short sequence was considered a proportional transfer for the long acquisition group because all the amplitudes between targets were reduced by the same proportion. Nonproportional transfer occurred when the amplitudes between targets did not have the same proportions as those for their practice sequence (e.g., long sequence to mixed sequence or vice versa). The results indicated that participants could effectively transfer to new target configurations regardless of whether the transfer required proportional or nonproportional spatial changes to the movement pattern. Experiment 2 assessed the effects of extended practice on proportional and nonproportional spatial transfer. The data indicated that while participants can effectively transfer to both proportional and nonproportional spatial transfer conditions after 1 day of practice, they are only effective at transferring to proportional transfer conditions after 4 days of practice. The results are discussed in terms of the mechanism by which response sequences become increasingly specific over extended practice in an attempt to optimize movement production.

Influence of Inter-Training Intervals on Intermanual Transfer Effects in Upper-Limb Prosthesis Training: A Randomized Pre-Posttest Study

Improvement in prosthetic training using intermanual transfer (the transfer of motor skills from the trained, “unaffected” hand to the untrained, “affected” hand) has been shown in previous studies. The aim of this study is to determine the influence of the inter-training interval on the magnitude of the intermanual transfer effects. This was done using a mechanistic, randomized, single-blinded pretest-posttest design. Sixty-four able-bodied, right-handed participants were randomly assigned to the Short and Long Interval Training Groups and the Short and Long Interval Control Groups. The Short and Long Interval Training Groups used a prosthesis simulator in their training program. The Short and Long Interval Control Groups executed a sham training program, that is, a dummy training program in which the same muscles were trained as with the prosthesis simulator. The Short Interval Training Group and the Short Interval Control Groups trained on consecutive days, while the Long Interval Training Group and Long Interval Control Group trained twice a week. To determine the improvement in skills, a test was administered before, immediately after, and at two points in time after the training. Training was performed with the “unaffected” arm; tests were performed with the “affected” arm. The outcome measurements were: the movement time (the time from the beginning of the movement until completion of the task); the duration of maximum hand opening, (the opening of the prosthetic hand while grasping an object); and the grip-force control (the error from the required grip-force during a tracking task). Intermanual transfer was found in movement times, but not in hand opening or grip-force control. The length of the inter-training interval did not affect the magnitude of intermanual transfer effects. No difference in the intermanual transfer effect in upper-limb prosthesis training was found for training on a daily basis as compared to training twice a week.

TRIAL REGISTRATION

Nederlands Trial Register NTR3888.

Limb Dominance and Its Effects on the Benefits of Intralimb Transfer of Learning: A Visuomotor Aiming Task

Research has attempted to address what characteristics benefit from transfer of learning; however, it is still unclear which characteristics are effector dependent or independent. Furthermore, it is not clear if intralimb transfer shows, similarly to interlimb transfer, an asymmetry of benefits between the upper limbs. The purpose of the current study is to examine if effector independence effects emerge, as observed in interlimb transfer studies, when transfer to new effector group within the same limb occurs, and whether the pattern of intralimb transfer benefits differ between the limbs. Our results suggest that a visuomotor task transfers within both limbs, even though the transfer benefits within the limbs seem to differ. This was supported by more transfer occurring in the dominant limb than the nondominant limb. Potential control mechanisms used for intralimb transfer are discussed.

Bilateral transfer for learning to control timing but not for learning to control fine force

This study examined the characteristics of bilateral transfer of learning to control timing and fine force from a dominant limb to a nondominant limb. 20 right-handed college students (12 women, 8 men; M age = 21.5 yr., SD = 2.3) learned a sequential task consisting of timing and force control. Each participant completed a pre-test of the task with both hands and then performed 100 practice trials with the dominant hand. A post-test was conducted 1 hr. later. The results showed that after training, participants learned to control the timing and force. Nevertheless, only the time-control learning was transferred to the untrained hand, whereas the force-control learning did not transfer to the untrained hand.

Left visual field preference for a bimanual grasping task with ecologically valid object sizes

Grasping using two forelimbs in opposition to one another is evolutionary older than the hand with an opposable thumb (Whishaw and Coles in Behav Brain Res 77:135-148, 1996); yet, the mechanisms for bimanual grasps remain unclear. Similar to unimanual grasping, the localization of matching stable grasp points on an object is computationally expensive and so it makes sense for the signals to converge in a single cortical hemisphere. Indeed, bimanual grasps are faster and more accurate in the left visual field, and are disrupted if there is transcranial stimulation of the right hemisphere (Le and Niemeier in Exp Brain Res 224:263-273, 2013; Le et al. in Cereb Cortex. doi: 10.1093/cercor/bht115, 2013). However, research so far has tested the right hemisphere dominance based on small objects only, which are usually grasped with one hand, whereas bimanual grasping is more commonly used for objects that are too big for a single hand. Because grasping large objects might involve different neural circuits than grasping small objects (Grol et al. in J Neurosci 27:11877-11887, 2007), here we tested whether a left visual field/right hemisphere dominance for bimanual grasping exists with large and thus more ecologically valid objects or whether the right hemisphere dominance is a function of object size. We asked participants to fixate to the left or right of an object and to grasp the object with the index and middle fingers of both hands. Consistent with previous observations, we found that for objects in the left visual field, the maximum grip apertures were scaled closer to the object width and were smaller and less variable, than for objects in the right visual field. Our results demonstrate that bimanual grasping is predominantly controlled by the right hemisphere, even in the context of grasping larger objects.

Generalisation of new sequence knowledge depends on response modality

New visuomotor skills can guide behaviour in novel situations. Prior studies indicate that learning a visuospatial sequence via responses based on manual key presses leads to effector- and response-independent knowledge. Little is known, however, about the extent to which new sequence knowledge can generalise, and, thereby guide behaviour, outside of the manual response modality. Here, we examined whether learning a visuospatial sequence either via manual (key presses, without eye movements), oculomotor (obligatory eye movements), or perceptual (covert reorienting of visuospatial attention) responses supported generalisation to direct and indirect tests administered either in the same (baseline conditions) or a novel response modality (transfer conditions) with respect to initial study. Direct tests measured the use of conscious knowledge about the studied sequence, whereas the indirect tests did not ostensibly draw on the study phase and measured response priming. Oculomotor learning supported the use of conscious knowledge on the manual direct tests, whereas manual learning supported generalisation to the oculomotor direct tests but did not support the conscious use of knowledge. Sequence knowledge acquired via perceptual responses did not generalise onto any of the manual tests. Manual, oculomotor, and perceptual sequence learning all supported generalisation in the baseline conditions. Notably, the manual baseline condition and the manual to oculomotor transfer condition differed in the magnitude of general skill acquired during the study phase; however, general skill did not predict performance on the post-study tests. The results demonstrated that generalisation was only affected by the responses used to initially code the visuospatial sequence when new knowledge was applied to a novel response modality. We interpret these results in terms of response-effect distinctiveness, the availability of integrated effector- and motor-plan based information, and discuss their implications for neurocognitive accounts of sequence learning.

Intermanual transfer in training with an upper-limb myoelectric prosthesis simulator: a mechanistic, randomized, pretest-posttest study

BACKGROUND

Intermanual transfer may improve prosthetic handling and acceptance if used in training soon after an amputation.

OBJECTIVE

The purpose of this study was to determine whether intermanual transfer effects can be detected after training with a myoelectric upper-limb prosthesis simulator.

DESIGN

A mechanistic, randomized, pretest-posttest design was used.

PARTICIPANTS

A total of 48 right-handed participants (25 women, 23 men) who were able-bodied were randomly assigned to an experimental group or a control group.

INTERVENTION

The experimental group performed a training program of 5 days' duration using the prosthesis simulator. To determine the improvement in skill, a test was administered before, immediately after, and 6 days after training. The control group only performed the tests. Training was performed with the unaffected arm, and tests were performed with the affected arm (the affected arm simulating an amputated limb). Half of the participants were tested with the dominant arm and half with the nondominant arm.

MEASUREMENTS

Initiation time was defined as the time from starting signal until start of the movement, movement time was defined as the time from the beginning of the movement until completion of the task, and force control was defined as the maximal applied force on a deformable object.

RESULTS

The movement time decreased significantly more in the experimental group (F₂,₉₂=7.42, P=.001, η²(G)=.028) when compared with the control group. This finding is indicative of faster handling of the prosthesis. No statistically significant differences were found between groups with regard to initiation time and force control. We did not find a difference in intermanual transfer between the dominant and nondominant arms.

LIMITATIONS

The training utilized participants who were able-bodied in a laboratory setting and focused only on transradial amputations.

CONCLUSIONS

Intermanual transfer was present in the affected arm after training the unaffected arm with a myoelectric prosthesis simulator, and this effect did not depend on laterality. This effect may improve rehabilitation of patients with an upper-limb amputation.

A right hemisphere dominance for bimanual grasps

To find points on the surface of an object that ensure a stable grasp, it would be most effective to employ one area in one cortical hemisphere. But grasping the object with both hands requires control through both hemispheres. To better understand the control mechanisms underlying this "bimanual grasping", here we examined how the two hemispheres coordinate their control processes for bimanual grasping depending on visual field. We asked if bimanual grasping involves both visual fields equally or one more than the other. To test this, participants fixated either to the left or right of an object and then grasped or pushed it off a pedestal. We found that when participants grasped the object in the right visual field, maximum grip aperture (MGA) was larger and more variable, and participants were slower to react and to show MGA compared to when they grasped the object in the left visual field. In contrast, when participants pushed the object we observed no comparable visual field effects. These results suggest that grasping with both hands, specifically the computation of grasp points on the object, predominantly involves the right hemisphere. Our study provides new insights into the interactions of the two hemispheres for grasping.

The coding and inter-manual transfer of movement sequences

The manuscript reviews recent experiments that use inter-manual transfer and inter-manual practice paradigms to determine the coordinate system (visual-spatial or motor) used in the coding of movement sequences during physical and observational practice. The results indicated that multi-element movement sequences are more effectively coded in visual-spatial coordinates even following extended practice, while very early in practice movement sequences with only a few movement elements and relatively short durations are coded in motor coordinates. Likewise, inter-manual practice of relatively simple movement sequences show benefits of right and left limb practice that involves the same motor coordinates while the opposite is true for more complex sequences. The results suggest that the coordinate system used to code the sequence information is linked to both the task characteristics and the control processes used to produce the sequence. These findings have the potential to greatly enhance our understanding of why in some conditions participants following practice with one limb or observation of one limb practice can effectively perform the task with the contralateral limb while in other (often similar) conditions cannot.

Age-related effects in interlimb practice on coding complex movement sequences

Hikosaka et al. (1999) proposed that sequential movements are acquired in independent visual-spatial and motor coordinate systems with coding initially represented in visual-spatial coordinates, and later after extended practice in motor coordinates. One aspect of sequence learning that has not been systematically studied, however, is the question of whether or not older adults show the same pattern of coding in inter-limb practice as younger learners. In the present experiment an inter-limb practice paradigm was designed to determine the role that visual-spatial (Cartesian) and motor (joint angles, activation patterns) coordinates play in the coding and learning of a complex movement sequence. Younger and older adults practiced a 16-element movement sequence with one limb on Day 1 and the contra-lateral limb on Day 2. Practice involved the same sequence with either the same visual-spatial or motor coordinates on the two days. Retention tests were conducted on Day 3. Results indicated that keeping the visual-spatial coordinates the same during acquisition resulted in superior retention only for younger adults. Results also indicated the overall slowing of sequential movement production for older adults which appears to result from these participants inability to impose a structure on the sequence. This provides strong evidence that the visual-spatial code plays a dominant role in complex movement sequences and this code is represented in an effector-independent manner for younger adults, but not for older adults.

Observation and physical practice: coding of simple motor sequences

An experiment was conducted to determine the coordinate system used in the development of movement codes during observation and utilized on later physical practice performance of a simple spatial-temporal movement sequence. The task was to reproduce a 1.3-s spatial-temporal pattern of elbow flexions and extensions. An intermanual transfer paradigm with a retention test and two transfer tests was used: a mirror transfer test where the same pattern of muscle activation and limb joint angles was required and a nonmirror transfer test where the visual-spatial pattern of the sequence was reinstated on the transfer test. The results indicated a strong advantage for participants in the physical practice condition when transferred to the mirror condition in which the motor coordinates (e.g., pattern of muscle activation and joint angles) were reinstated relative to transfer performance when the visual-spatial coordinates were reinstated (visual and spatial location of the target waveform). The observation group, however, demonstrated an advantage when the visual-spatial coordinates were reinstated. These results demonstrate that codes based in motor coordinates can be developed relatively quickly for simple rapid movement sequences when participants are provided physical practice, but observational practice limits the system to the development of codes based in visual-spatial coordinates. Performances of control participants, who were not permitted to practise or observe the task, were quite poor on all tests.

Attention and time constraints in perceptual-motor learning and performance: instruction, analogy, and skill level

We sought to gain more insight into the effects of attention focus and time constraints on skill learning and performance in novices and experts by means of two complementary experiments using a table tennis paradigm. Experiment 1 showed that skill-focus conditions and slowed ball frequency disrupted the accuracy of experts, but dual-task conditions and speeded ball frequency did not. For novices, only speeded ball frequency disrupted accuracy. In Experiment 2, we extended these findings by instructing novices either explicitly or by analogy (implicit motor learning technique). Explicitly instructed novices were less accurate in skill-focused and dual-task conditions than in single-task conditions. Following analogy instruction novices were less accurate in the skill-focused condition, but maintained accuracy under dual-task conditions. Participants in both conditions retained accuracy when ball frequency was slowed, but lost accuracy when ball frequency was speeded, suggesting that not attention, but motor dexterity, was inadequate under high temporal constraints.

Sensory-motor equivalence: manual aiming in C6 tetraplegics following musculotendinous transfer surgery at the elbow

Cervical spinal lesions at C6 result in paralysis of the triceps brachii while leaving deltoid and elbow flexor function intact. We examined the spatial-temporal characteristics of goal-directed aiming movements performed by C6 tetraplegics who had undergone musculotendinous transfer surgery in which the posterior deltoid replaces the triceps as the elbow extensor. On some trials, liquid crystal goggles were used to eliminate vision of the limb and target upon movement initiation. Although tetraplegic participants achieved the same degree of movement accuracy/consistency as control participants, their movement times were longer regardless of whether the movements were made away from (elbow extension) or towards the body (elbow flexion). Longer movement times were related to lower peak velocities, and not the symmetry of the aiming profiles. The tetraplegic participants were no more dependent on visual feedback for limb regulation than control participants. Although the characteristics of the movement trajectories were surprisingly similar, in both vision conditions, tetraplegics required more real and proportional time to reduce spatial variability in the limb's trajectory for elbow extensions. Our results indicate that the sensorimotor system is adaptable and that the representations governing limb control are not muscle specific.

Intermanueller Transfer und Händigkeit

Zusammenfassung. In dem Experiment wurde der intermanuelle Transfer auf eine neue dynamische Anforderung und Händigkeit untersucht. Gegenstand ist das Lernen einer Bewegungssequenz. Die Aufgabe der Lerner bestand in dem Erwerb einer 16-Elementigen Bewegungssequenz. Nach einem anfänglichen Training einer Bewegungssequenz für Rechts- und Linkshänder in Abhängigkeit der Starthand (dominante, nicht-dominante Hand) wurden nach einem Intervall von 24 Stunden ein Behaltenstest und zwei Transfertests appliziert. In dem Behaltenstest musste die gelernte Sequenz mit der trainierten Hand ohne Zusatzlast (0 kg) reproduziert werden. In den beiden ausbalancierten Transfertests sollte sowohl mit der trainierten als auch mit der untrainierten kontralateralen Hand eine zusätzliche Masse von 1 kg bewegt werden. Die Ergebnisse zeigen, dass sowohl Rechts- als auch Linkshänder auf unterschiedliche dynamische Eigenschaften mit ihrer dominanten Hand transferieren können. Rechtshänder können sowohl mit der rechten als auch der linken Hand unabhängig von ihrer Starthand auf neue dynamische Anforderungen transferieren (Symmetrie). Eine Asymmetrie in dem Übertrag zeigt sich bei den Linkshändern, die unabhängig von ihrer trainierten Hand nicht auf ihre rechte Hand und auf eine veränderte dynamische Anforderung transferieren können.

Asymmetric effector transfer of complex movement sequences

An experiment was designed to determine if the addition of a load altered the effector transfer profile observed in earlier experiments using multi-element movement sequences. The acquisition task required participants to move a horizontal lever (with 0.567kg load) to 16 sequentially projected targets. One group practiced the movement sequence with their right (dominant) limb and another group practiced with their left (non-dominant) limb. Approximately 24h after completion of the acquisition session both groups were administered test blocks (0kg, 0.567kg, and 1.134kg) using their practiced and unpracticed limbs. Decreased and increased loads had minimal effect on test performance. The results indicated that the group trained with their left limb were able to perform the right limb tests as well as the group that trained with the right limb. However, the group that trained with their right limb were significantly slower performing the tests with the left limb than the group that practiced with their left limb. Importantly, the left acquisition limb group maintained the pattern of element durations used during practice on the various tests including transfer to the dominant limb. However, the pattern of element durations for the right acquisition limb group on the left limb transfer tests was altered such that the production of only the fastest produced elements were disrupted. These results suggest that one of the reasons for poor sequence performance when transferring from the right to left is because the sequence structure developed during acquisition and used on the tests lacked access to the appropriate commands or the controller lacked the ability to implement codes that effectively manage the movement dynamics.

Changes in speed of information processing in the brain following tendon repair

The objective of this study was to measure the "preparation time" that is the speed of information processing in the brain, and discuss the relevance of this parameter in the restoration of hand function following flexor tendon repair. The preparation time of 48 healthy adult participants was measured twice at a 6-week interval and compared with that of 12 patients after flexor tendon repair. There was no difference between the left and right hands of the healthy participants. The correlation between repeated measurements was high, although healthy participants performed 2.6% faster 6 weeks after the first measurement. After 6 weeks of immobilisation, patients showed a significant deterioration with respect to the speed of information processing by the brain on both the injured and uninjured sides compared with healthy participants, who had improved between the first and the second measurements. The results indicate that a period of lack of normal use of the hand leads to a change in cerebral control of hand movements.

The effects of sequence difficulty and practice on proportional and nonproportional transfer

Two experiments were designed to determine participants' ability to transfer a learned movement sequence to new spatial locations. A 16-element dynamic arm movement sequence was used in both experiments. The task required participants to move a horizontal lever to sequentially projected targets. Experiment 1 included two groups. One group practised a relatively easy 16-element movement sequence (easy long). The other group practised a more difficult 16-element movement sequence (difficult long). Approximately 24 hours after practice with their respective sequence both groups were administered a retention and two transfer tests. The only difference between the retention and transfer tests was the location of the targets. The short transfer target configuration was considered a proportional transfer because all the amplitudes between targets were reduced by the same proportion. The mixed transfer configuration was considered a nonproportional transfer because the targets did not have the same proportional distances between targets as the sequence they practised. The results indicated that participants could effectively transfer the difficult long sequence to the new target configurations regardless of whether the transfer required proportional and nonproportional spatial changes to the movement pattern. However, the easy long sequence was only effectively transferred in the proportional transfer condition. Experiment 2 assessed the effects of extended practice of the easy long sequence on proportional and nonproportional spatial transfer. The data indicated that participants could again effectively transfer the easy long sequence to proportional but not the nonproportional spatial transfer conditions regardless of the amount of practice (1 or 4 days). The results are discussed in terms of the mechanism by which response sequences become increasingly specific over extended practice in an attempt to optimize movement production and how this process interacts with the difficulty of the sequence.

Transfer of movement sequences: bigger is better

Experiment 1 was conducted to determine if proportional transfer from "small to large" scale movements is as effective as transferring from "large to small." We hypothesize that the learning of larger scale movement will require the participant to learn to manage the generation, storage, and dissipation of forces better than when practicing smaller scale movements. Thus, we predict an advantage for transfer of larger scale movements to smaller scale movements relative to transfer from smaller to larger scale movements. Experiment 2 was conducted to determine if adding a load to a smaller scale movement would enhance later transfer to a larger scale movement sequence. It was hypothesized that the added load would require the participants to consider the dynamics of the movement to a greater extent than without the load. The results replicated earlier findings of effective transfer from large to small movements, but consistent with our hypothesis, transfer was less effective from small to large (Experiment 1). However, when a load was added during acquisition transfer from small to large was enhanced even though the load was removed during the transfer test. These results are consistent with the notion that the transfer asymmetry noted in Experiment 1 was due to factors related to movement dynamics that were enhanced during practice of the larger scale movement sequence, but not during the practice of the smaller scale movement sequence. The findings that the movement structure is unaffected by transfer direction but the movement dynamics are influenced by transfer direction is consistent with hierarchal models of sequence production.

The transfer of movement sequences: effects of decreased and increased load

A number of recent experiments have demonstrated that a movement structure develops during the course of learning a movement sequence that provides the basis for transfer. After learning a movement sequence participants have been shown to be able to effectively produce the sequence when movement demands require that the sequence be rescaled in amplitude or produced with an unpractised set of effectors. The purpose of the present experiment was to determine whether participants, after learning a complex 16-element movement sequence with a 0.567-kg load, could also effectively produce the sequence when the load was decreased (0.0 kg) or increased (1.134 kg). The results indicated that participants were able to effectively compensate for decreased and increased load with virtually no changes in performance characteristics (displacement, velocity, acceleration, and pattern of element durations) while electromyographic (EMG) signals demonstrated that smaller (reduced load) or larger forces (increased load) were spontaneously generated to compensate for the change in load. The muscle activation patterns of the biceps and triceps as well as the level of coactivation appeared to be generally upscaled to generate and dissipate the changes in force requirement needed to compensate for the increased load.

Learning and transfer of a relative phase pattern and a joint amplitude ratio in a rhythmic multijoint arm movement

According to the coordination dynamics perspective, one can characterize the learning of novel relative phase patterns as the formation of a stable attractor in the coordination landscape of the order parameter relative phase. The authors examined 18 participants' learning and transfer of a 90 degrees relative phase pattern and a 0.6-joint-amplitude ratio between the elbow and wrist. Variability in the relative phasing and the joint amplitude ratio between the elbow and wrist decreased with practice. Positive transfer of the 90 degrees relative phase pattern was not dependent on the learning arm (dominant or nondominant). Positive transfer of the joint amplitude ratio was dependent on the learning arm and the direction of transfer. The results demonstrated that relative phase is an order parameter that characterizes the coordination dynamics of learning and transferring multijoint arm movements, and they provide preliminary evidence that joint amplitude ratios act as order parameters in the learning and transfer of multijoint arm movements.

Error detection processes during observational learning

The purpose of this experiment was to determine whether a faded knowledge of results (KR) frequency during observation of a model's performance enhanced error detection capabilities. During the observation phase, participants observed a model performing a timing task and received KR about the model's performance on each trial or on one of two trials. Delayed retention and transfer tests were used to assess the observer's ability to detect error in the model's performance and in the participant's performance while physically practicing the task. Results indicated a beneficial effect of a reduced KR frequency for performance stability and the ability to detect errors in both the model and the participant's own performance. The results suggest that aspects of the processing mechanism(s) developed in observational learning and related to KR are probably similar to those developed through physical practice.

Learning and transfer of an ipsilateral coordination task: evidence for a dual-layer movement representation

The present study addressed the nature of the memory representation for interlimb coordination tasks. For this purpose, the acquisition of a multifrequency (2:1) task with the ipsilateral limbs and transfer to the ipsilateral and contralateral body side was examined. In particular, subjects practiced a 2:1 coordination pattern whereby the right arm moved twice as fast as the right leg, or vice versa. Subsequently, they transferred the practiced 2:1 task to three different conditions: (1) the converse partner (i.e., the slow-moving limb had to move fast, and vice versa) at the ipsilateral body side, and (2) the identical and (3) converse 2:1 pattern at the contralateral body side. Findings revealed positive transfer of the identical and converse 2:1 pattern to the contralateral body side. However, no transfer of the learned pattern to its converse partner at the same body side was revealed. We propose a new memory representation model for coordination patterns, composed of an effector-independent and effector-specific component (dual-layer model). It is hypothesized that the general movement goal (i.e., moving one limb twice as fast as the other) constitutes the abstract, higher-level representation that may account for positive contralateral transfer. Conversely, the effector-specific component contains task-specific lower-level muscle synergies that are acquired through practice, prohibiting positive transfer when shifting task allocation within the same effectors. These findings are consistent with recent neuroscientific evidence for neuroplastic changes in distributed brain areas.

Schema Theory: A Critical Appraisal and Reevaluation

The authors critically review a number of the constructs and associated predictions proposed in schema theory (R. A. Schmidt, 1975). The authors propose that new control and learning theories should include a reformulated (a) notion of a generalized motor program that is not based on motor program but still accounts for the strong tendency for responses to maintain their relative characteristics; (b) mechanism or processes whereby an abstract movement structure based on proportional principles (e.g., relative timing, relative force) is developed through practice; and (c) explanation for parameter learning that accounts for the benefits of parameter variability but also considers how variability is scheduled. Furthermore, they also propose that new theories of motor learning must be able to account for the consistent findings spawned as a result of the schema theory proposal and must not be simply discounted because of some disfavor with the motor program notion, in general, or schema theory, more specifically.

Is the learning of goal-directed displacement effector-independent?

The present experiment was designed to investigate whether the learning of goal-directed locomotion is effector independent. To answer this question a bilateral transfer of learning paradigm was used. We wanted to find out whether learning can be transferred from a trained effector system to an untrained one. Sixteen participants were asked to proceed through virtual hallways, while walking on a treadmill or handling of a joystick, in order to cross a pair of oscillating doors. Participants received 1050 training trials on the specific effector system before being transferred to the untrained one. Results indicated a clear transfer from handling to walking and only a moderate transfer from walking to handling. This asymmetrical transfer provides partial support in favor of the effector independent hypothesis. Both the theoretical implications of this work and the possible mediating effect of calibration are discussed.

Learning a single limb multijoint coordination pattern: the impact of a mechanical constraint on the coordination dynamics of learning and transfer

The coordination dynamics of learning and transfer were studied in a single limb multijoint task requiring rhythmic elbow and wrist motions. Participants were required to learn a continuous 90 degrees relative phase pattern between the elbow and wrist such that an angle-angle plot of elbow and wrist motion produced a circle with a diameter of 80 degrees. Joint motion was restricted to elbow and wrist flexion-extension on the sagittal plane and the to-be-learned 90 degrees relative phase pattern was always practiced with the learning arm supine. Cycling frequency was controlled by a pacing metronome set at 0.75 Hz. Issues regarding effector-independent and effector-specific transfer were addressed with three transfer conditions: (1). learning arm prone (LP), (2). non-learning arm supine (NS), and (3). non-learning arm prone (NP). Four subjects learned the required relative phase (90 degrees ) and amplitude (80 degrees ) pattern with their dominant arm and four with their non-dominant arm. The experiment produced three main findings with regard to elbow-wrist control processes: First, seven of eight participants spontaneously produced a wrist-lagging coordination pattern (wrist motion lagged elbow motion) in learning to produce a continuous relative phase pattern of 90 degrees between the elbow and wrist. The wrist-lagging pattern may emerge as a result of the central nervous system exploiting the transfer of angular momentum from the elbow to the wrist as the elbow rotates up and down. The influence of interactive torque on elbow-wrist coordination represents an important mechanical constraint on the selection of intralimb coordination strategies during learning. The transfer conditions revealed that this mechanical constraint was effector-independent with regard to ipsilateral limb transfer (LP) and contralateral limb transfer (NS and NP). Second, consistent transfer of the learned relative phase pattern across ipsilateral and contralateral conditions demonstrates an effector-independent representation for this control variable. The effector-independent and effector-specific nature of joint amplitude transfer was dependent to some degree on learning arm, dominant or non-dominant, and the amount of practice, 1 day versus 5 days. Third, learning of the required 90 degrees relative phase pattern may be characterized as a phase transition leading to the formation of a stable attractor in the elbow-wrist coordination landscape. The above findings are discussed with respect to motor programming and coordination dynamic viewpoints on effector-independent and effector-specific aspects of motor equivalence.

The independence of response structure and element production in timing sequences

In three experiments, participants were asked to produce a prescribed temporal sequence of key presses. The number of elements in a key press sequence, the movement time of the elements, and uniformity of the timing elements comprising the sequence were manipulated. If the processing of the sequence structure was independent of the processing of elements comprising the sequence, increasing the number of the elements in the sequence should affect the production of the sequence but not the proficiency with which the individual elements are, produced. Increasing the movement time of the elements, however, should affect the production of the elements but have little, if any, effect on the integrity of the sequence. The findings indicated that increasing the number of elements negatively affected sequence production when the elements were nonuniform but had little or no effect when elements were uniform. Alternatively, element production was affected by movement time but not number of elements. The results of these experiments appear to confirm the independence of sequence and element production. However, Experiment 3, in which the uniformity of the elements was directly contrasted, found strong evidence for coarticulatory influences in the learning processes, whereby the longer and shorter than average elements in the sequence negatively affected the sequence integrity and the production of the individual elements. When faced with a nonuniformn timing pattern, participants appear to elongate or shrink individual elements of a uniform timing pattern to fit the desired sequence requirements. The result is that the longer or shorter than average elements require more practice to produce correctly, tend to regress across retention intervals, and are generally less stable than the elements nearer the average.

Intermanual transfer of force control is modulated by asymmetry of muscular strength

Interlateral transfer of learning is conceptualized as an index of the degree to which learning takes place at a lower level of motor control, with strong dependence on the effector system, or at a higher effector-independent level in the movement organization hierarchy. In this study, the locus of motor learning was investigated by increasing lateral asymmetry of force between the wrist flexor muscles, and comparing the amount of interlateral transfer of force control in relation to a condition of symmetric force. To perform this contrast, the participants were assigned to one of three groups: symmetric force (SM), who were left with original asymmetries of muscular strength; asymmetric force (AS), who had unilateral training for increment of maximum strength for the wrist flexor muscles; or a control condition (CO). The learning task consisted of launching a small cart across a metallic trackway with the preferred hand, aiming at making the cart achieve an instantaneous velocity of 70 cm/s. This action was practiced for 300 trials by the SM and AS group, while the CO group had active rest. The groups, then, were submitted to a transfer task requiring a mirrored action with the contralateral hand. The results indicated that the SM group achieved significantly higher interlateral transfer of learning as compared to the AS group, which presented response variability similar to the CO group. Analysis of directional trend of error revealed that the AS group presented a significant target overshoot as compared with the symmetric force groups. These findings suggest that an absolute force is learnt at a higher level in the action hierarchy, and that decline in interlateral transfer of learning in the asymmetric force condition was motivated by a resetting in the interplay between higher and lower levels of movement control.

Effect of practice on effector independence

The authors' primary purpose in the present experiment was to determine if practice changes the extent to which simple motor sequences are effector independent. Contralateral and ipsilateral effector transfers were assessed in 24 participants after 1 (200 trials) and 4 (800 trials) days of practice. The response sequence became increasingly effector dependent; the response structure and the scaling of force on the effector transfer tests were no better after 4 days of practice than after only 1 day, even though retention performance improved substantially. Those results are consistent with the notion that participants refine their movements over extended practice by exploiting the unique characteristics of the effectors. The additional practice results in a more effective movement when the same effectors are used but is of little value when different effectors are required.