Use of variable online visual feedback to optimize sensorimotor coding and learning of a motor sequence.

The present study characterized the impact of reliable and/or unreliable online visual feedback and their order of presentation on the coding and learning of a motor sequence. Participants practiced a 12-element motor sequence 200 times. During this acquisition phase, two groups received a single type (i.e., either reliable or unreliable) of online visual feedback, two other groups encountered both types of feedback: either reliable first then unreliable, or unreliable first then reliable. Delayed retention tests and intermanual transfer tests (visuospatial and motor) were administered 24 hours later. Results showed that varying the reliability of online visual information during the acquisition phase allowed participants to use different task coding modalities without damaging their long-term sequence learning. Moreover, starting with reliable visual feedback, replaced halfway through with unreliable feedback promoted motor coding, which is seldom observed. This optimization of motor coding opens up interesting perspectives, as it is known to promote better learning of motor sequences.

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.

PLAViMoP database: A new continuously assessed and collaborative 3D point-light display dataset.

It was more than 45 years ago that Gunnar Johansson invented the point-light display technique. This showed for the first time that kinematics is crucial for action recognition, and that humans are very sensitive to their conspecifics' movements. As a result, many of today's researchers use point-light displays to better understand the mechanisms behind this recognition ability. In this paper, we propose PLAViMoP, a new database of 3D point-light displays representing everyday human actions (global and fine-motor control movements), sports movements, facial expressions, interactions, and robotic movements. Access to the database is free, at https://plavimop.prd.fr/en/motions . Moreover, it incorporates a search engine to facilitate action retrieval. In this paper, we describe the construction, functioning, and assessment of the PLAViMoP database. Each sequence was analyzed according to four parameters: type of movement, movement label, sex of the actor, and age of the actor. We provide both the mean scores for each assessment of each point-light display, and the comparisons between the different categories of sequences. Our results are discussed in the light of the literature and the suitability of our stimuli for research and applications.

The Added Value of Point-Light Display Observation in Total Knee Arthroplasty Rehabilitation Program: A Prospective Randomized Controlled Pilot Study.

Background and Objectives: The present study aimed to assess the potential benefit of the observation of rehabilitation-related point-light display in addition to a conventional 3-week rehabilitation program, the objective being to improve functional capacity in patients having undergone total knee arthroplasty. Materials and Methods: Patients randomized in the control group had conventional rehabilitation treatment with two sessions per day 5 days a week of physical therapy (90 min), whereas patients in the experimental group had a program of conventional rehabilitation combined with a point-light display observation two times per day (5 min) and 3 days a week. Results: The patients of both groups had improved their performances by the end of the program, and the pre- and post-test improvement were superior for the experimental group over the control group concerning the total WOMAC score (p = 0.04), the functional WOMAC score (p = 0.03), and correct recognition of point-light displays (p = 0.003). Conclusions: These findings provide new insight favoring systematic point-light display observation to improve functional recovery in patients with total knee arthroplasty.

Evaluative Threat Increases Effort Expenditure in a Cycling Exercise: An Exploratory Study.

Research shows that negative or threatening emotional stimuli can foster movement velocity and force. However, less is known about how evaluative threat may influence movement parameters in endurance exercise. Based on social self-preservation theory, the authors predicted that evaluative threat would facilitate effort expenditure in physical exercise. In an exploratory study, 27 young men completed a bogus intelligence test and received either low-intelligence-quotient feedback (evaluative threat) or no feedback (control). Next, they were asked to pedal on a stationary bicycle for 30 min at a constant cadence. After 10 min (calibration period), the cadence display was hidden. Findings show that participants under evaluative threat increased cadence more than control participants during the subsequent 20-min critical period. These findings underline the potential importance of unrelated evaluative threat on physical performance.

Physical and observational practices of unusual actions prime action verb processing.

Numerous studies have highlighted a strong relationship between language and sensorimotor processes, showing, for example, that perceiving an action influences subsequent language processing. Moreover, previous studies have demonstrated that the context in which actions are perceived is crucial to enable this action-language relationship. In particular, action verb processing is facilitated when an action is perceived in its usual context (e.g., someone watering a plant) but not in an unusual context (e.g., someone watering a computer). This difference could be explained in terms of experience; because people always practice actions in accordance with the context, they have no (visual or motor) experience related to the unusual context. The aim of the present study was to test this assumption by assessing and comparing the effect of physical practice and observational learning on the action-language relationship. The results of two experiments showed a facilitation effect of both training methods. Whereas usual actions systematically prime action verb processing, the link between action and language appears for unusual actions only after training by practicing (experiment 1, physical practice) or observing (experiment 2, observational learning). Overall, these findings support the role of experience in the activation of sensorimotor representations during action verb processing.

PLAViMoP: How to standardize and simplify the use of point-light displays.

The study of biological point-light displays (PLDs) has fascinated researchers for more than 40 years. However, the mechanisms underlying PLD perception remain unclear, partly due to difficulties with precisely controlling and transforming PLD sequences. Furthermore, little agreement exists regarding how transformations are performed. This article introduces a new free-access program called PLAViMoP (Point-Light Display Visualization and Modification Platform) and presents the algorithms for PLD transformations actually included in the software. PLAViMoP fulfills two objectives. First, it standardizes and makes clear many classical spatial and kinematic transformations described in the PLD literature. Furthermore, given its optimized interface, PLAViMOP makes these transformations easy and fast to achieve. Overall, PLAViMoP could directly help scientists avoid technical difficulties and make possible the use of PLDs for nonacademic applications.

The influence of eye-movements on the development of a movement sequence representation during observational and physical practice.

An experiment was conducted to examine the development of a movement sequence representation and the role of eye-movements during observational and physical practice. The task was to reproduce a 1300ms spatial-temporal pattern of a sequence of elbow flexions and extensions. An inter-manual transfer design with a retention and two effector transfer tests (contralateral limb) was used. The mirror transfer test required the same pattern of homologous muscle activation and a sequence of joint angles as experienced during the acquisition phase, and the non-mirror transfer test required the same visual-spatial pattern as performed or observed during acquisition. Participants were randomly assigned to one of four groups differing in eye-movements (free to use their eyes vs. instruction to fixate) and the practice type (observational practice vs. physical practice). The results indicated that permitting to use eye-movements facilitates sequence learning. This advantage was found on both practice types. The results of the transfer tests indicated that participants of the physical practice group who were permitted to use their eyes demonstrated superior transfer performance in the mirror transfer test, while participants in the observational practice group demonstrated better performance on the non-mirror transfer test. These findings indicated that eye-movements enhanced the development of a visual-spatial representation during observational practice as well as a motor representation during physical practice.

Magnifying visual target information and the role of eye movements in motor sequence learning.

An experiment investigated the influence of eye movements on learning a simple motor sequence task when the visual display was magnified. The task was to reproduce a 1300 ms spatial-temporal pattern of elbow flexions and extensions. The spatial-temporal pattern was displayed in front of the participants. Participants were randomly assigned to four groups differing on eye movements (free to use their eyes/instructed to fixate) and the visual display (small/magnified). All participants had to perform a pre-test, an acquisition phase, a delayed retention test, and a transfer test. The results indicated that participants in each practice condition increased their performance during acquisition. The participants who were permitted to use their eyes in the magnified visual display outperformed those who were instructed to fixate on the magnified visual display. When a small visual display was used, the instruction to fixate induced no performance decrements compared to participants who were permitted to use their eyes during acquisition. The findings demonstrated that a spatial-temporal pattern can be learned without eye movements, but being permitting to use eye movements facilitates the response production when the visual angle is increased.

The role of eye movements in motor sequence learning.

An experiment that utilized a 16-element movement sequence was designed to determine the impact of eye movements on sequence learning. The participants were randomly assigned to two experimental groups: a group that was permitted to use eye movements (FREE) and a second group (FIX) that was instructed to fixate on a marker during acquisition (ACQ). A retention test (RET) was designed to provide a measure of learning, and two transfer tests were designed to determine the extent to which eye movements influenced sequence learning. The results demonstrated that both groups decreased the response time to produce the sequence, but the participants in the FREE group performed the sequence more quickly than participants of the FIX group during the ACQ, RET and the two transfer tests. Furthermore, continuous visual control of response execution was reduced over the course of learning. The results of the transfer tests indicated that oculomotor information regarding the sequence can be stored in memory and enhances response production.

Conscious awareness of action potentiates sensorimotor learning.

Many everyday skills are unconsciously learned through repetitions of the same behaviour by binding independent motor acts into unified sets of actions. However, our ability to be consciously aware of producing newly and highly trained motor skills raises the question of the role played by conscious awareness of action upon skill acquisition. In this study we strengthened conscious awareness of self-produced sequential finger movements by way of asking participants to judge their performance in terms of maximal fluency after each trial. Control conditions in which participants did not make any judgment or performance-unrelated judgments were also included. Findings indicate that conscious awareness of action, enhanced via subjective appraisal of motor efficiency, potentiates sensorimotor learning and skilful motor production in optimising the processing and sequencing of action units, as compared to the control groups. The current work lends support to the claim that the learning and skilful expression of sensorimotor behaviours might be grounded upon our ability to be consciously aware of our own motor capability and efficiency.

Interference effect of body shadow in action control.

Observing actions performed by other persons can subsequently influence our own motor behaviours. However, it is unknown whether the shadows cast by such actions can also have an impact on the observers' actions. Here we show that the mere observation of a cast shadow can influence imitative behaviours. Specifically, participants were shown a hand picture and its associated cast shadow in a neutral position. In a 'compatible trial' the hand and the shadow that followed were turned in the same open or closed direction, whereas in an 'incompatible trial' the hand and the shadow were turned in different directions. We contrasted two experimental conditions: (i) 'hand-shadow' in which participants observed a hand and its cast shadow (the hand covered the shadow); (ii) 'hand-hand' in which participants observed a hand and another black hand (the shadow covered the hand). The participants' task was to imitate (ie by closing or opening their own hands) the hand or the cast shadow of an action. For both conditions results revealed interference (ie longer response latencies) for incompatible trials. This suggests for the first time that the mere observation of a cast shadow of a hand can influence imitative behaviours. However, time courses of the response latencies revealed that imitative effect in the hand-shadow condition was different than the imitative effect in the hand-hand condition. Therefore, we suggest considering the cast shadow of an action as an important feature during motor control for humans.

Retrieval practice in motor learning.

In this study we sought to determine whether testing promotes the generalization of motor skills during the process of encoding and/or consolidation. We used a dynamic arm movement task that required participants to reproduce a spatial-temporal pattern of elbow extensions and flexions with their dominant right arm. Generalization of motor learning was tested by the ability to transfer the original pattern (extrinsic transformation) or the mirrored pattern (intrinsic transformation) to the unpractised left arm. To investigate the testing effects during both encoding and consolidation processing, participants were administered an initial testing session during early practice before being evaluated on a post-practice testing session administered either 10min (Testing-Encoding group) or 24hr apart (Testing-Consolidation group), respectively. Control groups were required to perform a post-practice testing session administered after either a 10-min (Control-Encoding group) or 24-hr delay (Control-Consolidation group). The findings revealed that testing produced rapid, within-practice skill improvements, yielding better effector transfer at the 10-min testing for the Testing-Encoding group on both extrinsic and intrinsic transformation tests when compared with the Control-Encoding group. Furthermore, we found better performance for the Testing-Consolidation group at the 24-hr testing for extrinsic and intrinsic transformations of the movement pattern when compared with the Control-Consolidation group. However, our results did not indicate any significant testing advantage on the latent, between-session development of the motor skill representation (i.e., from the 10-min to the 24-hr testing). The testing benefits expressed at the 10-min testing were stabilised but did not extend during the period of consolidation. This indicates that testing contributes to the generalisation of motor skills during encoding but not consolidation.

Testing promotes effector transfer.

The retrieval of information from memory during testing has recently been shown to promote transfer in the verbal domain. Motor-related research, however, has ignored testing as a relevant method to enhance motor transfer. We thus investigated whether testing has the potential to induce generalised motor memories by favouring effector transfer. Participants were required to reproduce a spatial-temporal pattern of elbow extensions and flexions with their dominant right arm. We tested the ability of participants to transfer the original pattern (extrinsic transformation; i.e., goal-based configuration) or the mirrored pattern (intrinsic transformation; i.e., movement-based configuration) to the unpractised non-dominant left arm. To evaluate how testing affects motor transfer at 24-h testing, participants were either administered an initial testing session during early practice (early testing group) or shortly after the end of practice (late testing group; i.e., no alternation between practice and testing sessions). No initial testing session was completed for the control group. We found better effector transfer at 24-h testing for the early testing group for both extrinsic and intrinsic transformations of the movement pattern when compared with the control group, while no testing benefit was observed for the late testing group. This indicates that testing positively affects motor learning, yielding enhanced long-term transfer capabilities. We thus demonstrate the critical role of retrieval practice via testing during the process of motor memory encoding, and provide the conditions under which testing effectively contributes to the generalisation of motor memories.

Observational training in visual half-fields and the coding of movement sequences.

An experiment was conducted to determine if gating information to different hemispheres during observational training facilitates the development of a movement representation. Participants were randomly assigned to one of three observation groups that differed in terms of the type of visual half-field presentation during observation (right visual half-field (RVF), left visual half-field (LVF), or in central position (CE)), and a control group (CG). On Day 1, visual stimuli indicating the pattern of movement to be produced were projected on the respective hemisphere. The task participants observed was a 1300 ms spatial-temporal pattern of elbow flexions and extensions. On Day 2, participants physically performed the task in an inter-manual transfer paradigm with a retention test, and two contralateral transfer tests; a mirror transfer test which required the same pattern of muscle activation and limb joint angles and a non-mirror transfer test which reinstated the visual-spatial pattern of the sequence. The results demonstrated that participants of the CE, RVF and the LVF groups showed superior retention and transfer performance compared to participants of the CG. Participants of the CE- and LVF-groups demonstrated an advantage when the visual-spatial coordinates were reinstated compared to the motor coordinates, while participants of the RVF-group did not promote specific transfer patterns. These results will be discussed in the context of hemisphere specialization.

Sensory-based mechanism for delayed motor intention.

Prospective motor learning (PML) can be defined as learning an action to be performed in the future. The privileged retrieval mechanism behind this delayed motor performance remains unknown. From a motor control and learning perspective, we may conceive of two forms of retrieval: a stimulus- and an intention-based control. Retrieval from intention-based control is based on the anticipation of intended sensory effects related to an action in order to select and control the appropriate motor procedure (i.e., the ideomotor mechanism). In contrast, in a stimulus-based control a connection between stimuli-features and their related action-features is stored in the memory and serves as the retrieval mechanism. In this view, action retrieval from external stimuli is based on the detection of events in the environment to perform the intended behaviour (i.e., the sensorimotor mechanism). In this study, we report an advantage in the action retrieval for participants who use an intention-based mode of control in comparison to a stimulus-based control. Furthermore, a control task reveals that the intention-based advantage is specific to PML. Our findings show that PML is benefited by mental anticipation of a sensory effect that is efficiently processed through an ideomotor mechanism to fulfil delayed motor intentions.

Scheduling observational and physical practice: influence on the coding of simple motor sequences.

The main purpose of the present experiment was to determine the coordinate system used in the development of movement codes when observational and physical practice are scheduled across practice sessions. The task was to reproduce a 1,300-ms spatial-temporal pattern of elbow flexions and extensions. An intermanual transfer paradigm with a retention test and two effector (contralateral limb) transfer tests was used. The mirror effector transfer test required the same pattern of homologous muscle activation and sequence of limb joint angles as that performed or observed during practice, and the non-mirror effector transfer test required the same spatial pattern movements as that performed or observed. The test results following the first acquisition session replicated the findings of Gruetzmacher, Panzer, Blandin, and Shea (2011) . The results following the second acquisition session indicated a strong advantage for participants who received physical practice in both practice sessions or received observational practice followed by physical practice. This advantage was found on both the retention and the mirror transfer tests compared to the non-mirror transfer test. These results demonstrate that codes based in motor coordinates can be developed relatively quickly and effectively for a simple spatial-temporal movement sequence when participants are provided with physical practice or observation followed by physical practice, but physical practice followed by observational practice or observational practice alone limits the development of codes based in motor coordinates.

Practice makes transfer of motor skills imperfect.

We investigated the practice-effects on motor skill transfer and the associated representational memory changes that occur during the within-practice and between-practice phases. In two experiments, participants produced extension-flexion movements with their dominant right arm for a limited or prolonged practice session arranged in either a single- or multi-session format. We tested the ability of participants to transfer the original pattern (extrinsic transformation) or the mirrored one (intrinsic transformation) to the non-dominant left arm, 10 min and 24 h after the practice sessions. Results showed that practice induces rapid motor skill improvements that are non-transferable irrespective of the amount of acquisition trials. Furthermore, the extrinsic component of the skill develops early and remains the dominant coding system during practice. Conversely, we found distinct between-practice memory changes: a limited practice induces an off-line development of the extrinsic component, whereas a prolonged practice session subserves the off-line development of the intrinsic component (experiment 2). We provided further evidence that the long-term representation of the motor skill also depends on the nature of the practice session itself: the parsing of practice into multiple sessions narrows the effector-transfer capacities in comparison to a single session (experiment 1). These findings yield theoretical and practical implications that are discussed in the context of recent motor skill learning models.

Feedback and intention during motor-skill learning: a connection with prospective memory.

The intention to complete an action in the future can improve the learning of this action, but it is unknown whether this effect persists when feedback is manipulated during encoding. In experiment 1, participants were instructed to learn a motor skill with or without intending to reproduce this learning in the future, and feedback on their movements was administrated by self-decision, that is, participants asked for feedback whenever they wanted it. The results showed that intention increased the frequency with which feedback was requested, but did not improve motor performance. In experiment 2, participants had to learn the task with high or few feedbacks, which they could not control. In these conditions, intention was beneficial in promoting motor learning only for a low feedback schedule. We suggest that the beneficial effect of intention on learning can be overshadowed or emphasised by the feedback processing during encoding. These findings are discussed in light of theories surrounding prospective memory.

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.