Active vision during action execution, observation and imagery: evidence for shared motor representations

Motor imagery drives the effects of combined action observation and motor imagery on corticospinal excitability for coordinative lower-limb actions

Combined action observation and motor imagery (AOMI) facilitates corticospinal excitability (CSE) and may potentially induce plastic-like changes in the brain in a similar manner to physical practice. This study used transcranial magnetic stimulation (TMS) to explore changes in CSE for AOMI of coordinative lower-limb actions. Twenty-four healthy adults completed two baseline (BLH, BLNH) and three AOMI conditions, where they observed a knee extension while simultaneously imagining the same action (AOMICONG), plantarflexion (AOMICOOR-FUNC), or dorsiflexion (AOMICOOR-MOVE). Motor evoked potential (MEP) amplitudes were recorded as a marker of CSE for all conditions from two knee extensor, one dorsi flexor, and two plantar flexor muscles following TMS to the right leg representation of the left primary motor cortex. A main effect for experimental condition was reported for all three muscle groups. MEP amplitudes were significantly greater in the AOMICONG condition compared to the BLNH condition (p = .04) for the knee extensors, AOMICOOR-FUNC condition compared to the BLH condition (p = .03) for the plantar flexors, and AOMICOOR-MOVE condition compared to the two baseline conditions for the dorsi flexors (ps ≤ .01). The study findings support the notion that changes in CSE are driven by the imagined actions during coordinative AOMI.

Online corrections can occur within movement imagery: An investigation of the motor-cognitive model

The motor-cognitive model proposes that movement imagery additionally requires conscious monitoring owing to an absence of veridical online sensory feedback. Therefore, it is predicted that there would be a comparatively limited ability for individuals to update or correct movement imagery as they could within execution. To investigate, participants executed and imagined target-directed aiming movements featuring either an unexpected target perturbation (Exp. 1) or removal of visual sensory feedback (Exp. 2). The results of both experiments indicated that the time-course of executed and imagined movements was equally influenced by each of these online visual manipulations. Thus, contrary to some of the tenets of the motor-cognitive model, movement imagery holds the capacity to interpolate online corrections despite the absence of veridical sensory feedback. The further theoretical implications of these findings are discussed.

Specific Neurodynamic Exercises on Pain and Disability in Old Women with Chronic Mechanical Neck Pain: A Randomized Controlled Trial

Neurodynamic exercise is a specific type of exercise used as a neural treatment that focuses on restoring altered homeostasis in the neuroimmune system by mobilising the nervous system and other structures. A prospective, randomized clinical trial was performed to evaluate the effect of neurodynamic exercises on disability and neck pain in elderly women over four weeks. Participants were randomized into two groups: a neurodynamic (NM) group (n = 28) and a non-specific exercise (NSE) group (n = 28). Inclusion criteria were women over 65 years of age who subjectively admitted to having mechanical neck pain for more than six months. Results showed that specific neurodynamic exercises can improve pain and disability in older women with chronic mechanical neck pain. Improvements were observed in all variables (p < 0.05). Significant between-group differences in favour of the NM group were only found for neck pressure pain thresholds and both tibialis anterior muscles. Larger effect sizes were obtained in favour of the NM group, especially for pain, disability, neck extension and inclination and pressure pain thresholds. Neurodynamic exercises have been shown to be more clinically relevant in disability and neck pain in older women.

Eye movements during motor imagery and execution reveal different visuomotor control strategies in manual interception

Previous research has investigated the degree of congruency in gaze metrics between action execution (AE) and motor imagery (MI) for similar manual tasks. Although eye movement dynamics seem to be limited to relatively simple actions toward static objects, there is little evidence of how gaze parameters change during imagery as a function of more dynamic spatial and temporal task demands. This study examined the similarities and differences in eye movements during AE and MI for an interception task. Twenty-four students were asked to either mentally simulate or physically intercept a moving target on a computer display. Smooth pursuit, saccades, and response time were compared between the two conditions. The results show that MI was characterized by higher smooth pursuit gain and duration while no meaningful differences were found in the other parameters. The findings indicate that eye movements during imagery are not simply a duplicate of what happens during actual performance. Instead, eye movements appear to vary as a function of the interaction between visuomotor control strategies and task demands.

Motor invariants in action execution and perception

The nervous system is sensitive to statistical regularities of the external world and forms internal models of these regularities to predict environmental dynamics. Given the inherently social nature of human behavior, being capable of building reliable predictive models of others' actions may be essential for successful interaction. While social prediction might seem to be a daunting task, the study of human motor control has accumulated ample evidence that our movements follow a series of kinematic invariants, which can be used by observers to reduce their uncertainty during social exchanges. Here, we provide an overview of the most salient regularities that shape biological motion, examine the role of these invariants in recognizing others' actions, and speculate that anchoring socially-relevant perceptual decisions to such kinematic invariants provides a key computational advantage for inferring conspecifics' goals and intentions.

Imagining interceptions: Eye movements as an online indicator of covert motor processes during motor imagery

The analysis of eye movements during motor imagery has been used to understand the influence of covert motor processes on visual-perceptual activity. There is evidence showing that gaze metrics seem to be affected by motor planning often dependent on the spatial and temporal characteristics of a task. However, previous research has focused on simulated actions toward static targets with limited empirical evidence of how eye movements change in more dynamic environments. The study examined the characteristics of eye movements during motor imagery for an interception task. Twenty-four participants were asked to track a moving target over a computer display and either mentally simulate an interception or rest. The results showed that smooth pursuit variables, such as duration and gain, were lower during motor imagery when compared to passive observation. These findings indicate that motor plans integrate visual-perceptual information based on task demands and that eye movements during imagery reflect such constraint.

Utilizing the Variability of Practice in Physical Execution, Action Observation, and Motor Imagery: Similar or Dissimilar Mechanisms?

The simulation theory argues that physical execution, action observation, and imagery share similar underlying mechanisms. Accordingly, applying a high-level psychological variable (variability of practice) should have a similar effect on all three modes. To test this theory, a total of 90 right-handed students participated in this study and were randomly divided into variable versus constant groups in three practice conditions, including physical, observational, and imagery. After a pretest (10 random trials of the putting task), the participants completed 50 practice trials. The groups performed/observed/imagined the task in the variable (different distances to different goals) or constant (fixed distance and goal) practice conditions. Also, there was an extra variable group in the physical and observational conditions, deprived of watching the feedback from the action. The participants completed a retention test 24 hr after the training. The effect of practice variability was observed in physical and observational conditions, but was not seen in the imagery condition. The no-feedback groups did not perform significantly differently from the imagery groups. The reason could be the lack of actual visual feedback during imagery.

There Is an "Eye" in Team: Exploring the Interplay Between Emotion, Gaze Behavior, and Collective Efficacy in Team Sport Settings

Little is understood about the attentional mechanisms that lead to perceptions of collective efficacy. This paper presents two studies that address this lack of understanding. Study one examined participant's (N = 59) attentional processes relating to positive, neutral, or negative emotional facial photographs, when instructed to select their “most confident” or “least confident” team. Eye gaze metrics of first fixation duration (FFD), fixation duration (FD), and fixation count (FC) were measured alongside individual perceptions of collective efficacy and emotional valence of the teams selected. Participants had shorter FFD, longer FD, and more FC on positive faces when instructed to select their most confident team (p < 0.05). Collective efficacy and emotional valence were significantly greater when participants selected their most confident team (p < 0.05). Study two explored the influence of video content familiarity of team-based observation interventions on attentional processes and collective efficacy in interdependent team-sport athletes (N = 34). When participants were exposed to familiar (own team/sport) and unfamiliar (unknown team/sport) team-based performance video, eye tracking data revealed similar gaze behaviors for the two conditions in terms of areas of interest. However, collective efficacy increased most for the familiar condition. Study one results indicate that the emotional expressions of team members influence both where and for how long we look at potential team members, and that conspecifics' emotional expression impacts on our perceptions of collective efficacy. For Study two, given the apparent greater increase in collective efficacy for the familiar condition, the similar attentional processes evident for familiar and unfamiliar team footage suggests that differences in meaning of the observed content dictates collective efficacy perceptions. Across both studies, the findings indicate the importance of positive emotional vicarious experiences when using team-based observation interventions to improve collective efficacy in teams.

Examining the equivalence between imagery and execution within the spatial domain - Does motor imagery account for signal-dependent noise?

Motor imagery is suggested to be functionally equivalent to physical execution as they each utilise a common neural representation. The present study examined whether motor imagery correspondingly reflects the spatial characteristics of physically executed movements, including the signal-dependent noise that typically manifests in more variable end locations (as indicated by effective target width; W_e). Participants executed or imagined a single, upper-limb target-directed aim in the horizontal medio-lateral direction. The start and end of the imagined movements were indexed by the lifting and lowering of the limb over the home position, respectively. Following each imagined movement, participants had to additionally estimate their imagined end location relative to the target. All the movements had to be completed at a pre-specified criterion time (400 ms, 600 ms, 800 ms). The results indicated that the W_e increased following a decrease in movement time for execution, but not imagery. Moreover, the total error of imagined movements was greater than the actual error of executed movements. While motor imagery may comprise a neural representation that also contributes to the execution of movements, it is unable to closely reflect the random sources of variability. This limitation of motor imagery may be attributed to the comparatively limited efferent motor signals.

Central Nervous System Reorganization and Pain After Spinal Cord Injury: Possible Targets for Physical Therapy-A Systematic Review of Neuroimaging Studies

BACKGROUND

Pain is one of the main symptoms associated with spinal cord injury (SCI) and can be associated with changes to the central nervous system (CNS).

PURPOSE

This article provides an overview of the evidence relating to CNS changes (structural and functional) associated with pain in SCIs.

DATA SOURCES

A systematic review was performed, according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) recommendations, on PubMed, Embase, and Web of Science in March 2018.

STUDY SELECTION

Studies were selected if they concerned changes in the CNS of patients with SCI, regardless of the type of imagery.

DATA EXTRACTION

Data were extracted by 2 blinded reviewers.

DATA SYNTHESIS

There is moderate evidence for impaired electroencephalographic function and metabolic abnormalities in the anterior cingulate in patients experiencing pain. There is preliminary evidence that patients with pain have morphological and functional changes to the somatosensory cortex and alterations to thalamic metabolism. There are conflicting data regarding the relationships between lesion characteristics and pain. In contrast, patients without pain can display protective neuroplasticity.

LIMITATIONS AND CONCLUSION

Further studies are required to elucidate fully the relationships between pain and neuroplasticity in patients with SCIs. However, current evidence might support the use of physical therapist treatments targeting CNS plasticity in patients with SCI pain.

Implicit development of gaze strategies support motor improvements during action encoding training of prosthesis use

BACKGROUND

Action observation training has been suggested to facilitate motor improvements in the lives of persons with neural injury. Previous studies have shown that for persons with upper limb amputation, matched limb training, where prosthesis users emulate each other, has shown promise above mismatched training where a prosthesis user emulates actions of a person with sound limbs (most commonly that of a therapist).

OBJECTIVE

The mechanism underlying the matched limb training benefit is unclear. Gaze strategies may reveal unique patterns between matched and mismatched training which could explain improvements in motor function in matched limb training.

METHODS

Twenty persons with sound limbs were trained on how to use a prosthesis simulator using matched or mismatched limb training in a single session. Eye movements were recorded during the training phase. Kinematics were recorded as persons performed the task.

RESULTS

Gaze patterns showed differences between the training groups. The mismatched group demonstrated a higher probability of gaze on the path between the start and end of the action, while the matched group demonstrated a significantly higher probability of focusing on the elements of the path of the action and a trend of focusing on the shoulders. Kinematics also revealed overall improvements in motor control for the matched group.

CONCLUSIONS

This study proposes a putative mechanism that may explain improvements in matched limb training through shifting gaze strategies. Further work is needed to understand whether implicit visual strategies seen during matched limb training might encourage motor learning during functional training with prostheses.

Action dual tasks reveal differential effects of visual imagery perspectives on motor performance

Imagery research has identified two main visual perspectives, external visual imagery (EVI, third person) and internal visual imagery (IVI, first person). Based upon findings from brain imaging literature showing that different neural substrates are recruited for IVI and EVI perspectives, and that IVI activates motor system brain areas, we hypothesised that a concurrent action dual task would cause greater interference in performance for IVI than EVI. In a first experiment, participants were allocated to either an IVI or an EVI group, and were tasked with moving an onscreen marker towards a target in three blocked conditions: imagery, imagery with a concurrent motor dual-task of sequencing, and a math control. An interaction between imagery group and condition was driven by greater root mean square error for participants in the dual-task condition in the IVI group compared with the EVI group. We replicated the experiment with an eye-tracking objective measure of IVI; the results again showed that participants in the IVI group made more errors in motor movements, and an interference effect in eye movements, during the dual-task sequencing condition compared with the EVI group. The results of the two experiments reveal that a secondary motor task does interfere with IVI, providing behavioural evidence that IVI appears to rely on motor system processes more than EVI. These results have important implications for the use of visual imagery perspectives across a number of domains, with this paper being an essential reference for those conducting visual imagery perspectives research.

What Do Eye Gaze Metrics Tell Us about Motor Imagery?

Many of the brain structures involved in performing real movements also have increased activity during imagined movements or during motor observation, and this could be the neural substrate underlying the effects of motor imagery in motor learning or motor rehabilitation. In the absence of any objective physiological method of measurement, it is currently impossible to be sure that the patient is indeed performing the task as instructed. Eye gaze recording during a motor imagery task could be a possible way to "spy" on the activity an individual is really engaged in. The aim of the present study was to compare the pattern of eye movement metrics during motor observation, visual and kinesthetic motor imagery (VI, KI), target fixation, and mental calculation. Twenty-two healthy subjects (16 females and 6 males), were required to perform tests in five conditions using imagery in the Box and Block Test tasks following the procedure described by Liepert et al. Eye movements were analysed by a non-invasive oculometric measure (SMI RED250 system). Two parameters describing gaze pattern were calculated: the index of ocular mobility (saccade duration over saccade + fixation duration) and the number of midline crossings (i.e. the number of times the subjects gaze crossed the midline of the screen when performing the different tasks). Both parameters were significantly different between visual imagery and kinesthesic imagery, visual imagery and mental calculation, and visual imagery and target fixation. For the first time we were able to show that eye movement patterns are different during VI and KI tasks. Our results suggest gaze metric parameters could be used as an objective unobtrusive approach to assess engagement in a motor imagery task. Further studies should define how oculomotor parameters could be used as an indicator of the rehabilitation task a patient is engaged in.

The neural substrates for the different modalities of movement imagery

Research highlights that internal visual, external visual and kinesthetic imagery differentially effect motor performance (White & Hardy, 1995; Hardy & Callow, 1999). However, patterns of brain activation subserving these different imagery perspectives and modalities have not yet been established. In the current study, we applied the Vividness of Movement Imagery Questionnaire-2 (VMIQ-2) to study the brain activation underpinning these types of imagery. Participants with high imagery ability (using the VMIQ-2) were selected to participate in the study. The experimental conditions involved imagining an action (one item from the VMIQ-2) using internal visual imagery, external visual imagery, kinesthetic imagery and a perceptual control condition involved looking at a fixation cross. The imagery conditions were presented using a block design and the participants' brain activation was recorded using 3T fMRI. A post-experimental questionnaire was administered to test if participants were able to maintain the imagery during the task and if they switched between the imagery perspective/modalities. Four participants failed to adhere to the imagery conditions, and their data was excluded from analysis. As hypothesized, the different perspectives and modalities of imagery elicited both common areas of activation (in the right supplementary motor area, BA6) and dissociated areas of activation. Specifically, internal visual imagery activated occipital, parietal and frontal brain areas (i.e., the dorsal stream) while external visual imagery activated occipital ventral stream areas and kinesthetic imagery activated caudate and cerebellum areas. These results provide the first central evidence for the visual perspectives and modalities delineated in the VMIQ-2, and, initial biological validity for the VMIQ-2. However, given that only one item from the VMIQ-2 was employed, future fMRI research needs to explore all items to further examine these contentions.

Abnormal sensory reactivity in preterm infants during the first year correlates with adverse neurodevelopmental outcomes at 2 years of age

BACKGROUND

Sensory experience is the basis for learning in infancy. In older children, abnormal sensory reactivity is associated with behavioural and developmental disorders. We hypothesised that in preterm infants, abnormal sensory reactivity during infancy would be associated with perinatal characteristics and correlate with 2-year neurodevelopmental outcomes.

METHODS

We conducted a prospective observational study of infants with birth weight ≤1500 g using the Test of Sensory Function in Infants (TSFI) in the first year. Infants with gestational age ≤30 weeks were tested with the Bayley Scales of Infant and Toddler Development III (BSID III) at 24 months.

RESULTS

Of the 72 participants evaluated at 4-12 months corrected age (median 8 months), 59 (82%) had a least one TSFI score concerning for abnormal sensory reactivity. Lower gestational age was associated with abnormal reactivity to deep pressure and vestibular stimulation (p<0.001). Poor ocular-motor control predicted worse cognitive and motor scores in early childhood (OR 16.7; p=0.004), but was tightly correlated to the presence of severe white matter injury. Poor adaptive motor function in response to tactile stimuli predicted worse BSID III motor (p=0.01) and language scores (p=0.04) at 2 years, even after adjusting for confounders.

CONCLUSIONS

Abnormal sensory reactivity is common in preterm infants; is associated with immaturity at birth, severe white matter injury and lower primary caregiver education; and predicts neurodevelopmental delays. Early identification of abnormal sensory reactivity of very preterm infants may promote parental support and education and may facilitate improved neurodevelopment.

Effects of short-term experience on anticipatory eye movements during action observation

Recent studies have shown that anticipatory eye movements occur during both action observation and action execution. These findings strongly support the direct matching hypothesis, which states that in observing others' actions, people take advantage of the same action knowledge that enables them to perform the same actions. Furthermore, a connection between action experience and the ability to anticipate action goals has been proposed. Concerning the role of experience, most studies concentrated on motor experts such as athletes and musicians, whereas only few studies investigated whether motor programs can be activated by short-term experience. Applying a pre-post design, we examined whether short-term experience affects anticipatory eye movements during observation. Participants (N = 150 university students) observed scenes showing an actor performing a block stacking task. Subsequently, participants performed either a block stacking task, puzzles, or a pursuit rotor task. Afterward, participants were again provided with the aforementioned block stacking task scenes. Results revealed that the block stacking task group directed their gaze significantly earlier toward the action goals of the block stacking task during posttest trials, compared with Puzzle and pursuit rotor task groups, which did not differ from each other. In accordance with the direct matching hypothesis, our study provides evidence that short-term experience with the block stacking task activates task-specific action knowledge.

The influence of early aging on eye movements during motor simulation

Movement based interventions such as imagery and action observation are used increasingly to support physical rehabilitation of adults during early aging. The efficacy of these more covert approaches is based on an intuitively appealing assumption that movement execution, imagery and observation share neural substrate; alteration of one influences directly the function of the other two. Using eye movement metrics this paper reports findings that question the congruency of the three conditions. The data reveal that simulating movement through imagery and action observation may offer older adults movement practice conditions that are not constrained by the age-related decline observed in physical conditions. In addition, the findings provide support for action observation as a more effective technique for movement reproduction in comparison to imagery. This concern for imagery was also seen in the less congruent temporal relationship in movement time between imagery and movement execution suggesting imagery inaccuracy in early aging.

Congruency of gaze metrics in action, imagery and action observation

The aim of this paper is to provide a review of eye movements during action execution, action observation, and movement imagery. Furthermore, the paper highlights aspects of congruency in gaze metrics between these states. The implications of the imagery, observation, and action gaze congruency are discussed in terms of motor learning and rehabilitation. Future research directions are outlined in order to further the understanding of shared gaze metrics between overt and covert states. Suggestions are made for how researchers and practitioners can structure action observation and movement imagery interventions to maximize (re)learning.