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.     

Visual mental imagery influences attentional guidance in a visual-search task

Visual mental imagery resembles visual working memory (VWM). Because both visual mental imagery and VWM involve the representation and manipulation of visual information, it was hypothesized that they would exert similar effects on visual attention. Several previous studies have demonstrated that working-memory representations guide attention toward a memory-matching task-irrelevant stimulus during visual-search tasks. Therefore, mental imagery may also guide attention toward imagery-matching stimuli. In the present study, five experiments were conducted to investigate the effects of visual mental imagery on visual attention during a visual-search task. Participants were instructed to visualize a color or an object clearly associated with a specific color, after which they were asked to detect a colored target in the visual-search task. Reaction times for target detection were shorter when the color of the target matched the imagined color, and when the color of the target was similar to that strongly associated with the imagined object, than when the color of the target did not match that of the mental representation. This effect was not observed when participants were not instructed to imagine a color. These results suggest that similar to VWM, visual mental imagery guides attention toward imagery-matching stimuli.     

The influence of imagery ability on color aftereffects produced by physically present and imagined induction stimuli

Two methods of induction were used to produce orientation-contingent color aftereffects for observers assigned to one of three groups (high, medium, and low) on the basis of self-rated imagery ability. In Experiment 1, observers were required to make magnitude estimates of color aftereffects following inspection of stimulus patterns normally used to produce McCollough effects (e.g., red vertical contours, green horizontal contours). Experiment 2 was a partial replication of Experiment 1, with additional induction conditions in which observers were required to imagine the presence of appropriately oriented contours when particular homogeneous color patches were presented. The results indicated that self-rated imagery ability was not a significant factor in differentiating between observers’ performance when orthodox induction procedures were used (Experiment 1). In addition, there were no reliable indications (Experiment 2) that imagined stimulus attributes can be effectively substituted for real stimulus attributes in order to produce orientation-contingent color aftereffects. The results are discussed in terms of their implications for the use of imagery-induced perceptual phenomena as a paradigm for investigating the possibility of common neural mechanisms in perception and imagination; in addition, the general implications of the results for understanding the functional significance of self-reported imagery ability are examined.     

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。     

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.     

The visual accommodation response during concurrent mental activity

Concurrent mental activity seems to be a significant, nonvisual factor affecting the human accommodation response. Two experiments were conducted to determine the direction and magnitude of this accommodation response. Experiment 1 employed a concurrent, written backwards counting task. Experiment 2 employed a concurrent, mental imagery task of “thinking near” and “thinking far.” In both experiments, the concurrent secondary task effected a cumulative accommodative shift toward the visual far point of from .25 to .75 diopter away from a near (3.0 diopter) target. This accommodative shift was observed only in the presence of a stimulus field and not in open-loop (analogous to empty-field) conditions. In addition, a long-term instability in the open-loop method of obtaining the dark focus was observed. Similarities between this accommodative shift and the pupillary response are noted. The accommodation response is discussed in relationship to both an attention-sharing and an involuntary autonomic response model.     

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.     

Evidence of imagined passive self-motion through imagery-perception interaction

The existence of whole-body passive self-motion mental imagery was investigated by examining whether the perception of passive body accelerations can be affected by passive self-motion imagery. Twenty healthy subjects recognised target passive body acceleration. This recognition task was performed under three conditions: (1) a baseline condition without imagery; (2) a compatible imagery condition during which subjects imagined themselves passively moving in the same direction as the target acceleration; (3) a non-compatible imagery condition during which subjects imagined themselves passively moving in the direction opposite to that of the target acceleration. The recognition of the target acceleration was improved under compatible and degraded under non-compatible imagery. This interaction implies that perception and imaginary share common representations, and supports the existence of passive self-motion imagery.     

Effect of worrisome and relaxing thinking on fearful emotional processing

This study replicated and extended previous data suggesting that worry inhibits emotional processing of fearful imagery. Female participants categorized as either victimization-fearful (N = 24) or victimization and speech-fearful (N = 27) completed trials of worrisome or relaxing thinking and tone-cued imagery. For each trial, participants engaged in 30 s of relaxing or worrisome (speech or victimization) thinking and then imagined speech or victimization fear scenes for 15 s. Heart rate and facial electromyography activity at the corrugator supercilii region were measured during the think and imagery periods to estimate degree of emotional processing of the fear imagery. Consistent with earlier findings, there was greater heart rate suppression during fearful imagery after a period of worry as opposed to relaxation. This finding, however, may have been the result of physiological differences between worrisome and relaxation thinking. Corrugator activation during thinking showed a similar pattern as the heart rate data while corrugator activation during fearful imagery was dependent on the baseline employed. These data, in combination with the imagery ratings data, suggest that worry may be an unsuccessful strategy for avoiding the physiological activation associated with emotional processing.     

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.     

When the brain simulates stopping: Neural activity recorded during real and imagined stop-signal tasks

It has been suggested that mental rehearsal activates brain areas similar to those activated by real performance. Although inhibition is a key function of human behavior, there are no previous reports of brain activity during imagined response cancellation. We analyzed event-related potentials (ERPs) and time–frequency data associated with motor execution and inhibition during real and imagined performance of a stop-signal task. The ERPs characteristic of stop trials—that is, the stop-N2 and stop-P3—were also observed during covert performance of the task. Imagined stop (IS) trials yielded smaller stop-N2 amplitudes than did successful stop (SS) and unsuccessful stop (US) trials, but midfrontal theta power similar to that in SS trials. The stop-P3 amplitude for IS was intermediate between those observed for SS and US. The results may be explained by the absence of error-processing and correction processes during imagined performance. For go trials, real execution was associated with higher mu and beta desynchronization over motor areas, which confirms previous reports of lower motor activation during imagined execution and also with larger P3b amplitudes, probably indicating increased top-down attention to the real task. The similar patterns of activity observed for imagined and real performance suggest that imagination tasks may be useful for training inhibitory processes. Nevertheless, brain activation was generally weaker during mental rehearsal, probably as a result of the reduced engagement of top-down mechanisms and limited error processing.     

Pupillometric decoding of high-level musical imagery

Humans report imagining sound where no physical sound is present: we replay conversations, practice speeches, and “hear” music all within the confines of our minds. Research has identified neural substrates underlying auditory imagery; yet deciphering its explicit contents has been elusive. Here we present a novel pupillometric method for decoding what individuals hear “inside their heads”. Independent of light, pupils dilate and constrict in response to noradrenergic activity. Hence, stimuli evoking unique and reliable patterns of attention and arousal even when imagined should concurrently produce identifiable patterns of pupil-size dynamics (PSDs). Participants listened to and then silently imagined music while eye-tracked. Using machine learning algorithms, we decoded the imagined songs within- and across-participants following classifier-training on PSDs collected during both imagination and perception. Echoing findings in vision, cross-domain decoding accuracy increased with imagery strength. These data suggest that light-independent PSDs are a neural signature sensitive enough to decode imagination.     

Electrophysiological evidence for a shared representational medium for visual images and visual percepts

Does mental imagery involve the activation of representations in the visual system? Systematic effects of imagery on visual signal detection performance have been used to argue that imagery and the perceptual processing of stimuli interact at some common locus of activity (Farah, 1985). However, such a result is neutral with respect to the question of whether the interaction occurs during modality-specific visual processing of the stimulus. If imagery affects stimulus processing at early, modality-specific stages of stimulus representation, this implies that the shared stimulus representations are visual, whereas if imagery affects stimulus processing only at later, amodal stages of stimulus representation, this implies that imagery involves more abstract, postvisual stimulus representations. To distinguish between these two possibilities, we repeated the earlier imagery-perception interaction experiment while recording event-related potentials (ERPs) to stimuli from 16 scalp electrodes. By observing the time course and scalp distribution of the effect of imagery on the ERP to stimuli, we can put constraints on the locus of the shared representations for imagery and perception. An effect of imagery was seen within 200 ms following stimulus presentation, at the latency of the first negative component of the visual ERP, localized at the occipital and posterior temporal regions of the scalp, that is, directly over visual cortex. This finding provides support for the claim that mental images interact with percepts in the visual system proper and hence that mental images are themselves visual representations.     

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.     

EEG and fMRI agree: Mental arithmetic is the easiest form of imagery to detect

fMRI and EEG during mental imagery provide alternative methods of detecting awareness in patients with disorders of consciousness (DOC) without reliance on behaviour. Because using fMRI in patients with DOC is difficult, studies increasingly employ EEG. However, there has been no verification that these modalities provide converging information at the individual subject level. The present study examined simultaneous EEG and fMRI in healthy volunteers during six mental imagery tasks to determine whether one mental imagery task generates more robust activation across subjects; whether activation can be predicted from familiarity with the imagined activity; and whether EEG and fMRI converge upon the same conclusions about individual imagery performance. Mental arithmetic generated the most robust activation in the majority of subjects for both EEG and fMRI, and level of activation could not be predicted from familiarity, with either modality. We conclude that overall, EEG and fMRI agree regarding individual mental imagery performance.     

Similar effects of visual perception and imagery on simple reaction time

A longstanding issue is whether perception and mental imagery share similar cognitive and neural mechanisms. To cast further light on this problem, we compared the effects of real and mentally generated visual stimuli on simple reaction time (RT). In five experiments, we tested the effects of difference in luminance, contrast, spatial frequency, motion, and orientation. With the intriguing exception of spatial frequency, in all other tasks perception and imagery showed qualitatively similar effects. An increase in luminance, contrast, and visual motion yielded a decrease in RT for both visually presented and imagined stimuli. In contrast, gratings of low spatial frequency were responded to more quickly than those of higher spatial frequency only for visually presented stimuli. Thus, the present study shows that basic dependent variables exert similar effects on visual RT either when retinally presented or when imagined. Of course, this evidence does not necessarily imply analogous mechanisms for perception and imagery, and a note of caution in such respect is suggested by the large difference in RT between the two operations. However, the present results undoubtedly provide support for some overlap between the structural representation of perception and imagery.     

Similar effects of visual perception and imagery on simple reaction time

A longstanding issue is whether perception and mental imagery share similar cognitive and neural mechanisms. To cast further light on this problem, we compared the effects of real and mentally generated visual stimuli on simple reaction time (RT). In five experiments, we tested the effects of difference in luminance, contrast, spatial frequency, motion, and orientation. With the intriguing exception of spatial frequency, in all other tasks perception and imagery showed qualitatively similar effects. An increase in luminance, contrast, and visual motion yielded a decrease in RT for both visually presented and imagined stimuli. In contrast, gratings of low spatial frequency were responded to more quickly than those of higher spatial frequency only for visually presented stimuli. Thus, the present study shows that basic dependent variables exert similar effects on visual RT either when retinally presented or when imagined. Of course, this evidence does not necessarily imply analogous mechanisms for perception and imagery, and a note of caution in such respect is suggested by the large difference in RT between the two operations. However, the present results undoubtedly provide support for some overlap between the structural representation of perception and imagery.     

Examining the Relation Between Visual Imagery and Spatial Ability Tests

Research evidence indicates that self-report imagery ability is psychometrically distinct from objective, spatial test measures. One hypothesis put forward in the literature to explain this finding is that the nature of the stimulus is important. The aim of this article was to examine the relation between spatial abilities and measures of visual imagery obtained using different types of stimulus material. The main finding was that imagery tasks that required the mental synthesis or transformation of visual forms, such as alphanumeric characters and simple geometric shapes, correlated strongly with tests of spatial ability. In contrast, images of familiar items retrieved from long-term memory did not correlate with spatial test performance. It is argued that tasks that better control the stimuli imagined and the standards used to rate the quality of the image provide more objective measures of imagery ability. The implications of these findings are discussed.