TMS over dorsolateral prefrontal cortex affects the timing of motor imagery but not overt action: Further support for the motor-cognitive model.

The Motor-Cognitive model suggests a functional dissociation between motor imagery and overt action, in contrast to the Functional Equivalence view of common processes between the two behaviours. According to the Motor-Cognitive model, motor imagery differs from overt action primarily through the use of executive resources to monitor and elaborate a motor image during execution, which can result in a lack of correspondence between motor imagery and its overt action counterpart. The present study examined the importance of executive resources in motor imagery by using TMS to impair the function of the dorsolateral prefrontal cortex while measuring the time to complete imagined versus overt actions. In two experiments, TMS over the dorsolateral prefrontal cortex slowed motor imagery but did not affect overt actions. TMS over the same region also interfered with performance of a mental calculation task, though it did not reliably affect less demanding cognitive tasks also thought to rely on executive functions. Taken together, these results were consistent with the Motor-Cognitive model but not with the idea of functional equivalence. The implications of these results for the theoretical understanding of motor imagery, and potential applications of the Motor-Cognitive model to the use of motor imagery in training and rehabilitation, are discussed.

Assessing evidence for replication: A likelihood-based approach.

How to evaluate replications is a fundamental issue in experimental methodology. We develop a likelihood-based approach to assessing evidence for replication. In this approach, the design of the original study is used to derive an estimate of a theoretically interesting effect size. A likelihood ratio is then calculated to contrast the match of two models to the data from the replication attempt: (1) a model based on the derived theoretically interesting effect size, and (2) a null model. This approach provides new insights not available with existing methods of assessing replication. When applied to data from the Replication Project (Open Science Collaboration, 2015), the procedure indicates that a large portion of the replications failed to find evidence for a theoretically interesting effect.

Executive functions in motor imagery: support for the motor-cognitive model over the functional equivalence model.

The motor-cognitive model holds that motor imagery relies on executive resources to a much greater extent than do overt actions. According to this view, engaging executive resources with an interference task during motor imagery or overt actions will lead to a greater lengthening of the time required to imagine a movement than to execute it physically. This model is in contrast to a currently popular view, the functional equivalence model, which holds that motor imagery and overt action use identical mental processes, and thus should be equally affected by task manipulations. The two competing frameworks were tested in three experiments that varied the amount and type of executive resources needed to perform an interference task concurrent with either an overt or imagined version of a grasping and placing action. In Experiment 1, performing a concurrent calculation task led to a greater lengthening of the time required to execute motor imagery than overt action relative to a control condition involving no interference task. Further, an increase in the number of responses used to index performance affected the timing of motor imagery but not overt actions. In Experiment 2, a low-load repetition task interfered with the timing of motor imagery, but less so than a high load calculation task; both tasks had much smaller effects on overt actions. In Experiment 3, a word generation task also interfered with motor imagery much more than with overt actions. The results of these experiments provide broad support for the motor-cognitive model over the functional equivalence model in showing that interfering with executive functions had a much greater impact on the timing of motor imagery than on overt actions. The possible roles of different executive processes in motor imagery are discussed.

Solo versus joint bimanual coordination.

Understanding the differences between solo and joint action control is an important goal in psychology. The present study represented a novel approach in which participants performed a bimanual finger oscillation task, either alone or in pairs. It was hypothesized that performance of this task relies heavily on attention and utilizes two independent processes that differentially affect solo and joint performance. One process attempts to align the fingers correctly regardless of oscillation speed, and this is reflected in an alignment error evident even at slow oscillations. A second process attempts to minimize the time lag between the fingers as the oscillation speed increases, reflected in a temporal error indexed by the rate of error increase with increasing movement speed. In three experiments, alignment and temporal error in the finger oscillation task were compared in solo and joint actors. Overall, solo actors had much lower alignment error than joint actors. Solo actors also showed a reduction in temporal error when the fingers moved in a symmetrical rather than parallel fashion, consistent with previous research showing an increase in error with increasing movement speed. However, the effect of symmetry on temporal error did not occur with joint actors. Similar results were found with one hand inverted, suggesting that the pattern of results was not due to the use of homologous muscles. To test the role of visual feedback, we examined the effect of denying visual feedback to one of the actors in the joint condition. Paradoxically, under these conditions, there was lower temporal error in the symmetrical condition. These results are interpreted in terms of the organization of solo versus joint actions and the control of bimanual tasks in general.

The motor-cognitive model of motor imagery: Evidence from timing errors in simulated reaching and grasping.

Motor imagery represents an important but theoretically underdeveloped area of research in psychology. The motor-cognitive model of motor imagery was presented, and contrasted with the currently prevalent view, the functional equivalence model. In 3 experiments, the predictions of the two models were pitted against each other through manipulations of task precision and the introduction of an interference task, while comparing their effects on overt actions and motor imagery. In Experiments 1a and 1b, the motor-cognitive model predicted an effect of precision whereby motor imagery would overestimate simulated movement times when a grasping action involved a high level of precision; this prediction was upheld. In Experiment 2, the motor-cognitive model predicted that an interference task would slow motor imagery to a much greater extent than it would overt actions; this prediction was also upheld. Experiment 3 showed that the effects observed in the previous experiments could not be due to failures to match the motor imagery and overt action tasks. None of the above results were explainable by either a strong version of the functional equivalence model, or any reasonable adaptations thereof. It was concluded that the motor-cognitive model may represent a theoretically viable advance in the understanding of motor imagery. (PsycINFO Database Record

The role of predictability in cooperative and competitive joint action.

Predictability may be an important component of cooperative action, or it may arise as a by-product of involuntary entrainment with another's behavior. Further, differences previously observed in cooperative versus competitive actions may represent a fundamental distinction between behaviors with opposite goals, or they may simply reflect the output of different physical actions. The role of predictability in cooperative versus competitive behavior was directly tested using a joint sequential button-pressing task in which Participant 1 (P1) pressed a key followed by P2 pressing a key. In the cooperative condition, both actors shared the goal of minimizing P2's response times (RTs). In the competitive condition, P1 tried to maximize P2's RTs, whereas P2 continued to try to minimize them. It was found that P1 was much more predictable in the timing of his or her presses in the cooperative condition than in the competitive condition, and this coincided with faster P2 responses when cooperating than when competing. A 2nd experiment showed the effects of the predictability of P1's responses on the speed of P2 responses were similar when P1 was replaced by a schematic hand, showing the responses could not have been due to the transmission of subtle nonverbal cues by P1. These results demonstrate that being predictable is an important strategy in the timing of cooperative joint action, whereas being unpredictable is an important strategy in competition, and that they have opposite effects on a coactor's ability to respond quickly. (PsycINFO Database Record

Perseveration effects in reaching and grasping rely on motor priming and not perception.

Perseveration effects in grasping were examined in two experiments. In both experiments, participants reached and grasped different versions of a novel object with their thumb and forefinger using either a horizontal or vertical pincer grasp. The dependent variable was the choice of grasp. In Experiment 1, trials were performed either with or without visual feedback. In Experiment 2, trials were performed either physically or using motor imagery. In both experiments, participants tended to perseverate in their choice of grip. Further, there was no evidence that either the availability of visual feedback during the preceding or current action modulated this effect; mode of responding was similarly inconsequential. The results were interpreted as evidence for a motor priming explanation of perseveration and against an account that relies on perceptual priming.

Context and vision effects on real and imagined actions: support for the common representation hypothesis of motor imagery.

Motor imagery may use the same mental representations as overt actions, or it may be performed using a nonmotoric cognitive estimation strategy. These competing hypotheses were tested by having participants perform either simple overt pointing tasks or analogous motor imagery tasks while manipulating the visual context and the availability of visual information. In three pairs of experiments, visual illusions, word labels, and numeric labels were all found to have comparable effects on overt pointing and motor imagery. In each case, effects of the contextual variables on overt performance and imagery were larger when vision was removed and a delay imposed before movement initiation. These findings support the hypothesis that a common mental representation is used in both motor imagery and overt actions. In contrast, the results were inconsistent with the view that motor imagery is performed using a cognitive estimation strategy. Limitations in the ability of motor imagery to faithfully simulate overt actions are discussed.

Distinct cortical networks support the planning and online control of reaching-to-grasp in humans.

A number of brain imaging studies have identified regions involved in the planning and control of complex actions. Here we attempt to contrast activity related to planning and online control in the human brain during simple reaching and grasping movements. In four conditions, participants did one of the following: passively observed a grasp target; planned a grasping movement without executing; planned and then executed a grasp; or immediately executed a grasp. Neural activity was measured using functional magnetic resonance imaging and activity in the various conditions compared. Two large, independent networks of brain activity were identified: (i) a planning network including the premotor cortex, basal ganglia, anterior cingulate, posterior medial parietal area, superior parietal occipital cortex and middle intraparietal sulcus; and (ii) a control network including sensorimotor cortex, the cerebellum, the supramarginal gyrus and the superior parietal lobule. These findings provide evidence that the planning and control of even simple reaching and grasping actions use different brain regions, including different parts of the frontal and parietal lobes.

Perseveration and contrast effects in grasping.

In order to assess sequential effects in grasping a disc, grip aperture was measured as a function of whether the previous disc was smaller or larger than the current target. In Experiment 1, a biphasic sequential effect was found over the course of the reach: Early in the movement, a contrast effect was observed in which grip aperture was wider following a smaller target; later in the movement, a perseveration effect was observed in which grip aperture was smaller following a smaller target. In Experiment 2, the target was accompanied by context discs that were larger and smaller than the range of target sizes. In this case, there was no contrast effect, and a perseveration effect was observed over the course of the movement trajectory. In a third experiment, a sequential contrast effect was found when subjects did not grasp the disc but merely estimated its size. Our interpretation is that there are two mechanisms producing sequential effects: a perceptual contrast effect in which the target appears larger following a smaller disc, and a motor perseveration effect in which subjects tend to reuse similar motor control parameters from trial to trial. These effects were overlaid in Experiment 1, producing the observed biphasic response. However, in Experiment 2, the context eliminated sequential perceptual contrast, and grip aperture only showed an effect of perseveration. In Experiment 3, only the perceptual effect was found because subjects did not need to grasp the disc.

Different action patterns for cooperative and competitive behaviour.

The aim of the present study is to elucidate the influence of context on the kinematics of the reach-to-grasp movement. In particular, we consider two basic modes of social cognition, namely cooperation and competition. In two experiments kinematics of the very same action - reaching-to-grasp a wooden block - were analyzed in two different contexts provided by a cooperative task and competitive task. For the 'cooperation' tasks two participants were required to reach and grasp their respective objects and to cooperate to join the two objects in specific configurations in the middle of the working surface. For the 'competition' tasks, the two participants had to compete to place their own object first in the middle of the working surface. Results revealed specific kinematic patterns for cooperation and competition which were distinct from similar actions performed by each participant in isolation. Further, during the cooperation tasks, a high level of correlation between key kinematical parameters of the two participants was found. In accordance with evidence from neuroimaging, developmental and social psychology our results suggest the existence of motor patterns which reflect the intention to act in a social context.

Recovering space in unilateral neglect: a neurological dissociation revealed by virtual reality.

Neglect patients often show deficits in responding to targets in the contra-lesional side of space. Past studies were able to ameliorate these deficits through manipulation of visual input. Here, the neural bases of the recovery of space following virtual reality (VR) training in neglect patients were investigated. Neglect patients were trained to respond to targets in the left side of space that appeared in the central or in the right side of space in a VR system. It was found that only patients with lesions that spared the inferior parietal/superior temporal regions were able to benefit from the VR training. It was concluded that these regions play a crucial role in the recovery of space that underlies the improvement of neglect patients when trained with VR. The implications of these results for determining the neural bases of a higher order attentional and/or spatial representation and for treating patients with unilateral neglect are discussed.

Adjusting reach to lift movements to sudden visible changes in target's weight.

People can adjust their reach-to-grasp movements online to sudden changes in the spatial properties of a target. We investigated whether they can also do this when a non-spatial property, weight, suddenly changes. Guiding your movement by using visual cues about an object's weight depends heavily on experience and is expected to be processed by the (slow) ventral stream rather than the (fast) 'online control' dorsal stream. In the first experiment, participants reached out and lifted an object with an expected or an unexpected weight. As predicted, there was an effect of expected weight on the time between the end of the reaching phase and the object's lift-off. In the second experiment, the object sometimes visibly changed weight after the participants had started their movement. The lifting time did not depend on whether the object had changed weight. Thus, participants can make online adjustments to a visually indicated change in weight. These results are interpreted as being contrary to existing theories of online control.

Failure to read motor intentions from gaze in children with autism.

A core feature of autism is the abnormal use of gaze to attribute mental states to others, and thus to predict others' behaviour. An untested idea is whether this dysfunction is confined to mental states having a propositional content, such as beliefs and desire or extends to motor intentional states which allow one to make inferences about the actions of others. This study used kinematics to examine the ability to use gaze to inform one about the motor states of another in normal and autistic children. In each trial two participants, a model and an observer, were seated facing each other at a table. In three experimental blocks the model was requested to grasp a stimulus, to gaze towards the same stimulus, and to gaze away from the stimulus without performing any action. The task for the observer was to grasp the stimulus after having watched the model perform her task. We observed that normal children showed facilitation effects in terms of movement speed following the observation of the model grasping or simply gazing at the object. In contrast, autistic children did not show any evidence of facilitation in these conditions. Neither normal nor autistic children showed evidence of facilitation when the model's gaze was not directed towards the stimulus. These findings demonstrate that, in contrast to normal children, children with autism fail to use information from the model's action or gaze to plan their subsequent action, and that in autism the inability to use of another person's gaze produces a lack of understanding of the motor intention of others.

Effects of an orientation illusion on motor performance and motor imagery.

Although the effect of visual illusions on overt actions has been an area of keen interest in motor performance, no study has yet examined whether illusions have similar or different effects on overt and imagined movements. Two experiments were conducted that compared the effects of an orientation illusion on an overt posture selection task and an imagined posture selection task. In Experiment 1 subjects were given a choice of grasping a bar with the thumb on the left side or right side of the bar. In Experiment 2 subjects were instructed to only imagine grasping the bar while remaining motionless. Subjects then reported which side of the bar their thumb had been placed in imagined grasping. Both the overt selection and imagined selection tasks were found to be sensitive to the orientation illusion, suggesting that similar visual information is used for overt and imagined movements, with both being sensitive to an orientation illusion. The results are discussed in terms of the visual processing and representation of real and imagined actions.

Effects of increasing visual load on aurally and visually guided target acquisition in a virtual environment.

The aim of the present study is to investigate interactions between vision and audition during a target acquisition task performed in a virtual environment. We measured the time taken to locate a visual target (acquisition time) signalled by auditory and/or visual cues in conditions of variable visual load. Visual load was increased by introducing a secondary visual task. The auditory cue was constructed using virtual three-dimensional (3D) sound techniques. The visual cue was constructed in the form of a 3D updating arrow. The results suggested that both auditory and visual cues reduced acquisition time as compared to an uncued condition. Whereas the visual cue elicited faster acquisition time than the auditory cue, the combination of the two cues produced the fastest acquisition time. The introduction of secondary visual task differentially affected acquisition time depending on cue modality. In conditions of high visual load, acquiring a target signalled by the auditory cue led to slower and more error-prone performance than acquiring a target signalled by either the visual cue alone or by both the visual and auditory cues.

Parietal rTMS disrupts the initiation but not the execution of on-line adjustments to a perturbation of object size.

Previous studies have implicated the human parietal lobes in the on-line guidance of action. However, no study to date has examined at what stage in the on-line adjustment process do the parietal lobes play their most critical role. Repetitive transcranial magnetic stimulation (rTMS) was applied over the left intraparietal sulcus as participants reached to grasp a small or large illuminated cylinder. On some trials, the illumination could suddenly switch from the small to large cylinder, or vice-versa. Small-Large switches were associated with relatively early grip aperture adjustments, whereas Large-Small switches were associated with relatively late grip aperture adjustments. When rTMS was applied early in the movement, it disrupted on-line adjustments to Small-Large target switches, but not to Large-Small switches. Conversely, when rTMS was applied late in the movement, it disrupted adjustments to Large-Small target switches but not to Small-Large switches. The timing of the disruption by rTMS appeared linked to the initiation of the adjustment. It was concluded that the left parietal lobe plays a critical role in initiating an on-line adjustment to a change in target size, but not in executing that adjustment. The implications of these results for current views of on-line control are discussed.

Separate visual representations in the planning and control of action.

Evidence for a dichotomy between the planning of an action and its on-line control in humans is reviewed. This evidence suggests that planning and control each serve a specialized purpose utilizing distinct visual representations. Evidence from behavioral studies suggests that planning is influenced by a large array of visual and cognitive information, whereas control is influenced solely by the spatial characteristics of the target, including such things as its size, shape, orientation, and so forth. Evidence from brain imaging and neuropsychology suggests that planning and control are subserved by separate visual centers in the posterior parietal lobes, each constituting part of a larger network for planning and control. Planning appears to rely on phylogenetically newer regions in the inferior parietal lobe, along with the frontal lobes and basal ganglia, whereas control appears to rely on older regions in the superior parietal lobe, along with the cerebellum.

What causes scale errors in children?

A recent article by DeLoache et al. has documented an intriguing phenomenon in the development of action planning in young children. When children act on toy replicas of larger objects they make scale errors that are consistent with the full-sized object. Although the actions selected are inappropriate, their execution accurately takes into account the true size of the target. This phenomenon permits tests of the predictions of the perception-action and planning-control models of vision for action.