Development of the Correspondence Between Real and Imagined Fine and Gross Motor Actions

The development of the correspondence between real and imagined motor actions was investigated in 2 experiments. Experiment 1 evaluated whether children imagine body position judgments of fine motor actions in the same way as they perform them. Thirty-two 8-year-old children completed a task in which an object was presented in different orientations, and children were asked to indicate the position of their hand as they grasped and imagined grasping the object. Children’s hand position was almost identical for the imagined- and real-grasping trials. Experiment 2 replicated this result with 8-year-olds as well as 6-year-olds and also assessed the development of the correspondence of the chronometry of real and imagined gross motor actions. Sixteen 6-year-old children and seventeen 8-year-old children participated in the fine motor grasping task from Experiment 1 and a gross motor task that measured the time it took for children to walk and imagine walking different distances. Six-year-olds showed more of a difference between real and imagined walking than did 8-year-olds. However, there were strong correlations between real and imagined grasping and walking for both 6- and 8-year-old children, suggesting that by at least 6 years of age, motor imagery and real action may involve common internal representations and that motor imagery is important for motor control and planning.     

When music tempo affects the temporal congruence between physical practice and motor imagery

When people listen to music, they hear beat and a metrical structure in the rhythm; these perceived patterns enable coordination with the music. A clear correspondence between the tempo of actual movement (e.g., walking) and that of music has been demonstrated, but whether similar coordination occurs during motor imagery is unknown. Twenty participants walked naturally for 8 m, either physically or mentally, while listening to slow and fast music, or not listening to anything at all (control condition). Executed and imagined walking times were recorded to assess the temporal congruence between physical practice (PP) and motor imagery (MI). Results showed a difference when comparing slow and fast time conditions, but each of these durations did not differ from soundless condition times, hence showing that body movement may not necessarily change in order to synchronize with music. However, the main finding revealed that the ability to achieve temporal congruence between PP and MI times was altered when listening to either slow or fast music. These data suggest that when physical movement is modulated with respect to the musical tempo, the MI efficacy of the corresponding movement may be affected by the rhythm of the music. Practical applications in sport are discussed as athletes frequently listen to music before competing while they mentally practice their movements to be performed.     

Timing processes in motor imagery

Previous research shows inconsistencies in the timing of imagined and actual actions. Little is known about the timing in imagery, or how it relates to other forms of timing. Two studies examined whether imagery timing followed Weber's law, where variations in judgements grow linearly as the interval duration increases, or Vierordt's law, where short durations are overestimated and longer durations underestimated. In Study 1 participants (n=22) mentally walked and estimated journey times for flat paths and stairways, with and without a load. The timing patterns that emerged did not conform to Weber's law. In Study 2 participants (n=20) completed imagery, reproduction, production, and estimation timing tasks. Timing errors for imagery along a straight path, reproduction, estimation, and production all showed “Vierordt-like” effects. However, when imagining walking in a square participants consistently overestimated. It was concluded that imagery and interval timing processes are similar, but imagery timing is task dependent.     

The metrics of spatial distance traversed during mental imagery

The authors conducted 2 experiments to study the metrics of spatial distance in a mental imagery task. In both experiments, participants first memorized the layout of a building containing 10 rooms with 24 objects. Participants then received mental imagery instructions and imagined how they walked through the building from one room to another. The authors manipulated Euclidean distance involved in these imaginary motions: Spatial distance measured in centimeters on the layout was either short or long. Independently, they varied categorical distance: The motions led through one room or two rooms. The time needed to imagine motions and response times to test probes indicated that both Euclidean distance and categorical distance affected mental imagery. The authors discuss the new finding of categorical distance effects in mental imagery and relate the results to earlier failures to find Euclidean distance effects in formally equivalent studies of narrative comprehension.     

Does Transcranial Direct Current Stimulation Affect the Learning of a Fine Sequential Hand Motor Skill with Motor Imagery?

Learning a fine sequential hand motor skill, like playing the piano or learning to type, improves not only due to physical practice, but also due to motor imagery. Previous studies revealed that transcranial direct current stimulation (tDCS) and motor imagery independently affect motor learning. In the present study, we investigated whether tDCS combined with motor imagery above the primary motor cortex influences sequence-specific learning. Four groups of participants were involved: an anodal, cathodal, sham stimulation, and a control group (without stimulation). A modified discrete sequence production (DSP) task was employed: the Go/NoGo DSP task. After a sequence of spatial cues, a response sequence had to be either executed, imagined, or withheld. This task allows to estimate both non-specific learning and sequence-specific learning effects by comparing the execution of unfamiliar sequences, familiar imagined, familiar withheld, and familiar executed sequences in a test phase. Results showed that the effects of anodal tDCS were already developing during the practice phase, while no effects of tDCS on sequence-specific learning were visible during the test phase. Results clearly showed that motor imagery itself influences sequence learning, but we also revealed that tDCS does not increase the influence of motor imagery on sequence learning.     

Some consequences of visualization in pattern identification and detection

The goal of this study was to establish some of the conditions under which mental imagery facilitates or interferes with the identification and detection of visual patterns. In Experiment 1, subjects identified simple bar patterns presented at orientations 90 degrees apart under normal viewing conditions. Their reaction times were shorter when they had imagined seeing the patterns in advance at the same orientation, but were longer when they had imagined seeing the patterns at orientations that were in-between those of the actual presented patterns, relative to baseline conditions in which they were instructed not to imagine the patterns. In Experiment 2, where the subjects had only to detect the target patterns without identifying them, there was no effect of image formation or image-target alignment. In Experiment 3, where the detection task was repeated but where the target exposure duration was reduced, imagery significantly interfered with detection. In contrast to the results of Experiment 1, reaction time and error rate in this case were greatest when the imagined patterns were perfectly aligned with the target patterns. These findings demonstrate that whether imagery facilitates or interferes with performance on a visual task depends on the nature and difficulty of the task and on how closely the imagined and presented patterns correspond.     

The Influence of Motor Imagery on Postural Sway: Differential Effects of Type of Body Movement and Person Perspective

The present study examined the differential effects of kinesthetic imagery (first person perspective) and visual imagery (third person perspective) on postural sway during quiet standing. Based on an embodied cognition perspective, the authors predicted that kinesthetic imagery would lead to activations in movement-relevant motor systems to a greater degree than visual imagery. This prediction was tested among 30 participants who imagined various motor activities from different visual perspectives while standing on a strain gauge plate. The results showed that kinesthetic imagery of lower body movements, but not of upper body movements, had clear effects on postural parameters (sway path length and frequency contents of sway). Visual imagery, in contrast, had no reliable effects on postural activity. We also found that postural effects were not affected by the vividness of imagery. The results suggest that during kinesthetic motor imagery participants partially simulated (re-activated) the imagined movements, leading to unintentional postural adjustments. These findings are consistent with an embodied cognition perspective on motor imagery.     

Pushing the limits of imagination: mental practice for learning sequences

In 2 experiments, the efficacy of motor imagery for learning to type number sequences was examined. Adults practiced typing 4-digit numbers. Then, during subsequent training, they either typed in the same or a different location, imagined typing, merely looked at each number, or performed an irrelevant task. Repetition priming (faster responses for old relative to new numbers) was observed on an immediate test and after a 3-month delay for participants who imagined typing. Improvement across the delay in typing old and new numbers was found for the imagined and actual typing conditions but not for the other conditions. The findings suggest that imagery can be used to acquire and retain representations of sequences and to improve general typing skill.     

Sensorimotor alignment effects in the learning environment and in novel environments

Four experiments investigated the conditions contributing to sensorimotor alignment effects (i.e., the advantage for spatial judgments from imagined perspectives aligned with the body). Through virtual reality technology, participants learned object locations around a room (learning room) and made spatial judgments from imagined perspectives aligned or misaligned with their actual facing direction. Sensorimotor alignment effects were found when testing occurred in the learning room but not after walking 3 m into a neighboring (novel) room. Sensorimotor alignment effects returned after returning to the learning room or after providing participants with egocentric imagery instructions in the novel room. Additionally, visual and spatial similarities between the test and learning environments were independently sufficient to cause sensorimotor alignment effects. Memory alignment effects, independent from sensorimotor alignment effects, occurred in all testing conditions. Results are interpreted in the context of two-system spatial memory theories positing separate representations to account for sensorimotor and memory alignment effects.     

The man who executed "imagined" movements: evidence for dissociable components of the body schema

We examined the nature of representations underlying motor imagery and execution in a patient (CW) with bilateral parietal lesions. When imagining hand movements, CW executed the imagined motor act but was unaware of the movements. These movements were significantly more accurate than volitional movements for the left but not right hand. CW also exhibited preserved motor imagery for the left but not right hand. Consistent with previous accounts, these findings suggest that motor imagery may normally involve the inhibition of movements. CW's unawareness of movements during motor imagery may reflect inattention or misattribution of the unexpected sensory feedback. Furthermore, in line with current models of motor control, motor imagery may depend on the integrity of a "forward model" derived from motor outflow information to generate a prediction of the consequences of a motor command. Such predictions appear to be preserved for imagery of left but not right hand movements in CW. Action may additionally depend on precise updating of effector position derived from the comparison of predicted and actual sensory information. We propose that CW's impaired volitional movements may be attributable to the degradation of such an updating mechanism.     

基于fNIRS的运动执行与运动想象脑激活模式比较

使用《运动想象问卷−修订版》筛选出的30名被试(男女各半), 采用功能性近红外光谱成像技术(fNIRS)监测被试在执行实际举哑铃(男生, 4磅和8磅; 女生, 2磅和4磅)任务和想象举同等重量哑铃任务时, 其大脑皮层氧合血红蛋白浓度的变化。结果发现：男女被试在运动执行与运动想象任务下都激活了主运动皮层; 且运动执行的大脑激活水平高于运动想象。在执行实际运动任务时, 运动强度显著影响大脑皮层血氧浓度的变化, 表现出左半球偏侧化优势; 在执行想象运动任务时, 运动强度没有影响大脑皮层血氧浓度的变化, 且无偏侧化现象。     

Dynamic locomotor imagery in athletes with severe visual impairments

Motor imagery is a mental process not accompanied by movement and widely studied in healthy subjects, related to hand movements in terms of timing. This study compared static and dynamic motor imagery analyzing temporal and spatial features in different locomotor conditions in three different groups of subjects: high-skilled athletes with visual impairments, a group of sighted unprofessional athletes and a control group of sighted subjects. We found that dynamic motor imagery resulted in timely closer to real performance than static motor imagery. The discrepancies between dynamic motor imagery and real condition, in fact, resulted limited to uncommon locomotion, such as lateral walking. Motor imagery resulted closer to real performance in terms of timing than in terms of step length, with the exception of athletes with visual impairments that, differently from the other groups, did not show any significant differences between the numbers of imagined and performed steps. It opens a new question about the relationship between temporal and spatial imagination of locomotion.     

The representation of pitch in auditory imagery: Evidence from S-R compatibility and distance effects

In three experiments we explored the nature of representations constructed during the perception and imagination of pitch. We employed a same–different task to eliminate the influence of nonauditory information and to minimise use of cognitive strategies on auditory imagery. A reference tone of frequency 1000, 1500, or 2000 Hz, or an imagined tone of a pitch indicated by a visual cue, was followed by a comparison tone (1000, 1500, or 2000 Hz) to which either a speeded same or different response was required. In separate experiments, same–different judgements were mapped to vertically (Experiments 1 and 2) and horizontally arranged responses (Experiment 3). Judgements of tones closer in pitch yielded longer reaction times and higher error rates than more distant tones, indicating a pitch distance effect for perceptual and imagery tasks alike. In addition, in the imagery task, same–different responses were faster when low-pitched tones demanded a bottom or left key response and high-pitched tones a top or right response than vice versa, suggesting that pitch is coded spatially. Together, these behavioural effects support the assumption that both perceived and imagined pitch are translated into an analogical representation in the spatial domain.     

Dissociation between visual perception of allocentric distance and visually directed walking of its extent

Walking without vision to previously viewed targets was compared with visual perception of allocentric distance in two experiments. Experimental evidence had shown that physically equal distances in a sagittal plane on the ground were perceptually underestimated as compared with those in a frontoparallel plane, even under full-cue conditions. In spite of this perceptual anisotropy of space, Loomis et al (1992 Journal of Experimental Psychology. Human Perception and Performance 18 906-921) found that subjects could match both types of distances in a blind-walking task. In experiment 1 of the present study, subjects were required to reproduce the extent of allocentric distance between two targets by either walking towards the targets, or by walking in a direction incompatible with the locations of the targets. The latter condition required subjects to derive an accurate allocentric distance from information based on the perceived locations of the two targets. The walked distance in the two conditions was almost identical whether the two targets were presented in depth (depth-presentation condition) or in the frontoparallel plane (width-presentation condition). The results of a perceptual-matching task showed that the depth distances had to be much greater than the width distances in order to be judged to be equal in length (depth compression). In experiment 2, subjects were required to reproduce the extent of allocentric distance from the viewing point by blindly walking in a direction other than toward the targets. The walked distance in the depth-presentation condition was shorter than that in the width-presentation condition. This anisotropy in motor responses, however, was mainly caused by apparent overestimation of length oriented in width, not by depth compression. In addition, the walked distances were much better scaled than those in experiment 1. These results suggest that the perceptual and motor systems share a common representation of the location of targets, whereas a dissociation in allocentric distance exists between the two systems in full-cue conditions.     

Facilitation of corticospinal excitability during motor imagery of wrist movement with visual or quantitative inspection of EMG activity

The present study investigated facilitation of corticospinal excitability during motor imagery of wrist movement with visual or quantitative inspection of background electromyographic (EMG) activity. Ten healthy participants imagined wrist extension from a first-person perspective in response to a start cue. Transcranial magnetic stimulation was delivered to the motor cortex 2 sec. after the start cue. EMG signals were recorded from the extensor carpi radialis muscle. Trials with background EMG activity were discarded based on visual inspection. Both motor-evoked potential (MEP) and background EMG amplitudes increased during motor imagery. The amount of increase in MEP amplitude was positively correlated with the amount of increase in background EMG amplitude during motor imagery. The statistically significant increase in MEP amplitude during motor imagery disappeared when the effect of muscle activity was statistically eliminated or after trials with background EMG activity were discarded based on strict quantitative criteria. Facilitation of corticospinal excitability during motor imagery of wrist movement depends partially on muscle activity. Discarding background EMG activity during motor imagery based on visual inspection is not sufficient to equalize background EMG amplitude between resting and motor imagery. Discarding trials with background EMG activity through strict quantitative criteria is useful to equalize background EMG amplitude between at rest and during motor imagery.     

Visual perception and the guidance of locomotion without vision to previously seen targets

Two experiments were performed to assess the accuracy and precision with which adults perceive absolute egocentric distances to visible targets and coordinate their actions with them when walking without vision. In experiment 1 subjects stood in a large open field and attempted to judge the midpoint of self-to-target distances of between 4 and 24 m. In experiment 2 both highly practiced and unpracticed subjects stood in the same open field, viewed the same targets, and attempted to walk to them without vision or other environmental feedback under three conditions designed to assess the effects on accuracy of time-based memory decay and of walking at an unusually rapid pace. In experiment 1 the visual judgments were quite accurate and showed no systematic constant error. The small variable errors were linearly related to target distance. In experiment 2 the briskly paced walks were accurate, showing no systematic constant error, and the small, variable errors were a linear function of target distance and averaged about 8% of the target distance. Unlike Thomson's (1983) findings, there was not an abrupt increase in variable error at around 9 m, and no significant time-based effects were observed. The results demonstrate the accuracy of people's visual perception of absolute egocentric distances out to 24 m under open field conditions. The accuracy of people's walking without vision to previously seen targets shows that efferent and proprioceptive information about locomotion is closely calibrated to visually perceived distance. Sensitivity to the correlation of optical flow with efferent/proprioceptive information while walking with vision may provide the basis for this calibration when walking without vision.     

Motor imagery may incorporate trial-to-trial error

The authors tested for 1/f noise in motor imagery (MI). Participants pointed and imagined pointing to a single target (Experiment 1), to targets of varied size (Experiment 2), and switched between pointing and grasping (Experiment 3). Experiment 1 showed comparable patterns of serial correlation in actual and imagined movement. Experiment 2 suggested increased correlation for MI and performance with increased task difficulty, perhaps reflecting adaptation to a more complex environment. Experiment 3 suggested a parallel decrease in correlation with task switching, perhaps reflecting discontinuity of mental set. Although present results do not conclusively reveal 1/f fluctuation, the emergent patterns suggest that MI could incorporate trial-to-trial error across a range of constraints.     

Manipulating perception versus action in recalibration tasks

We conducted six experiments to examine how manipulating perception versus action affects perception–action recalibration in real and imagined blindfolded walking tasks. Participants first performed a distance estimation task (pretest) and then walked through an immersive virtual environment on a treadmill for 10 min. Participants then repeated the distance estimation task (posttest), the results of which were compared with their pretest performance. In Experiments 1a, 2a, and 3a, participants walked at a normal speed during recalibration, but the rate of visual motion was either twice as fast or half as fast as the participants' walking speed. In Experiments 1b, 2b, and 3b, the rate of visual motion was kept constant, but participants walked at either a faster or a slower speed. During pre- and posttest, we used either a blindfolded walking distance estimation task or an imagined walking distance estimation task. Additionally, participants performed the pretest and posttest distance estimation tasks in either the real environment or the virtual environment. With blindfolded walking as the distance estimation task for pre- and posttest, we found a recalibration effect when either the rate of visual motion or the walking speed was manipulated during the recalibration phase. With imagined walking as the distance estimation task, we found a recalibration effect when the rate of visual motion was manipulated, but not when the walking speed was manipulated in both the real environment and the virtual environment. Discussion focuses on how spatial-updating processes operate on perception and action and on representation and action.     

Inhibition in motor imagery: a novel action mode switching paradigm

Motor imagery requires that actual movements are prevented (i.e., inhibited) from execution. To investigate at what level inhibition takes place in motor imagery, we developed a novel action mode switching paradigm. Participants imagined (indicating only start and end) and executed movements from start buttons to target buttons, and we analyzed trial sequence effects. Trial sequences depended on current action mode (imagination or execution), previous action mode (pure blocks/same mode, mixed blocks/same mode, or mixed blocks/other mode), and movement sequence (action repetition, hand repetition, or hand alternation). Results provided evidence for global inhibition (indicated by switch benefits in execution-imagination (E-I)-sequences in comparison to I-I-sequences), effector-specific inhibition (indicated by hand repetition costs after an imagination trial), and target inhibition (indicated by target repetition benefits in I-I-sequences). No evidence for subthreshold motor activation or action-specific inhibition (inhibition of the movement of an effector to a specific target) was obtained. Two (global inhibition and effector-specific inhibition) of the three observed mechanisms are active inhibition mechanisms. In conclusion, motor imagery is not simply a weaker form of execution, which often is implied in views focusing on similarities between imagination and execution.     

Subjective Estimation of Task Time and Task Difficulty of Simple Movement Tasks

It has been demonstrated in previous work that the same neural structures are used for both imagined and real movements. To provide a strong test of the similarity of imagined and actual movement times, 4 simple movement tasks were used to determine the relationship between estimated task time and actual movement time. The tasks were single-component visually controlled movements, 2-component visually controlled, low index of difficulty (ID) moves and pin-to-hole transfer movements. For each task there was good correspondence between the mean estimated times and actual movement times. In all cases, the same factors determined the actual and estimated movement times: the amplitudes of movement and the IDs of the component movements, however the contribution of each of these variables differed for the imagined and real tasks. Generally, the standard deviations of the estimated times were linearly related to the estimated time values. Overall, the data provide strong evidence for the same neural structures being used for both imagined and actual movements.