Visuomotor Transformation Research Articles

Cerebral cortical dynamics during visuomotor transformation: Adaptation to a cognitive‐motor executive challenge

EEG was employed during cognitive-motor adaptation to a visuomotor transformation that required inhibition of an established motor plan. Performance was positively related to frontal alpha and theta power during both planning and execution of reaching movements to visual targets. EEG changes suggest initial involvement of frontal executive functioning to suppress established visuomotor mappings followed by progressive idling (i.e., alpha synchrony). Also, progressive idling of the temporal and parietal sites over the trials was observed, suggesting a decreasing role of working memory and encoding of the new visuomotor map, respectively. The regional changes in the cortical dynamics translated into the quality of motor behavior. This study expands our understanding of the role of frontal executive processes beyond the cognitive domain to the cognitive-motor domain.

Implicit and explicit adjustments to extrinsic visuo-motor transformations and their age-related changes

Humans have unique abilities in using tools. The skilled and goal-directed use of a tool implies that processes of motor control can be adjusted to the transformation of the movement of a part of the body into the movement of the effective part of the tool. A common example is the transformation of a hand movement in the motion of a cursor on a computer monitor. In part the adjustments to such transformations are implicit, that is, without conscious awareness of the novel transformation and the appropriate change of one’s own movements. However, the adjustments can also be explicit and intentional. We review a series of experiments which show that implicit and explicit adjustments to a novel visuo-motor gain are additive. This finding suggests that the processes which generate different types of adjustment are functionally independent. In a second series of experiments it turned out that at older adult age explicit adjustments to novel visuo-motor transformations are impaired, whereas implicit adjustments remain unaffected across working age.

Coordination deficits in ideomotor apraxia during visually targeted reaching reflect impaired visuomotor transformations

Ideomotor limb apraxia, commonly defined as a disorder of skilled, purposeful movement, is characterized by spatiotemporal deficits during a variety of actions. These deficits have been attributed to damage to, or impaired retrieval of, stored representations of learned actions, especially object-related movements. However, such deficits might also arise from impaired visuomotor transformation mechanisms that operate in parallel to or downstream from mechanisms for storage of action representations. These transformation processes convert extrinsic visual information into intrinsic neural commands appropriate for the desired motion. These processes are a key part of the movement planning process and performance errors due to inadequate transformations have been shown to increase with the dynamic complexity of the movement. This hypothesis predicts that apraxic patients should show planning deficits when reaching to visual targets, especially when the coordination and/or dynamic requirements of the task increase. Three groups (18 healthy controls, 9 non-apraxic and 9 apraxic left hemisphere damaged patients) performed reaching movements to visual targets that varied in the degree of interjoint coordination required. Relative to the other two groups, apraxic patients made larger initial direction errors and showed higher variability during their movements, especially when reaching to the target with the highest intersegmental coordination requirement. These problems were associated with poor coordination of shoulder and elbow torques early in the movement, consistent with poor movement planning. These findings suggest that the requirement to transform extrinsic visual information into intrinsic motor commands impedes the ability to accurately plan a visually targeted movement in ideomotor limb apraxia.

Human Muscle Spindles Act as Forward Sensory Models

Modern theories of motor control incorporate forward models that combine sensory information and motor commands to predict future sensory states. Such models circumvent unavoidable neural delays associated with on-line feedback control. Here we show that signals in human muscle spindle afferents during unconstrained wrist and finger movements predict future kinematic states of their parent muscle. Specifically, we show that the discharges of type Ia afferents are best correlated with the velocity of length changes in their parent muscles approximately 100-160 ms in the future and that their discharges vary depending on motor sequences in a way that cannot be explained by the state of their parent muscle alone. We therefore conclude that muscle spindles can act as "forward sensory models": they are affected both by the current state of their parent muscle and by efferent (fusimotor) control, and their discharges represent future kinematic states. If this conjecture is correct, then sensorimotor learning implies learning how to control not only the skeletal muscles but also the fusimotor system.

Rapid Online Correction Is Selectively Suppressed During Movement With a Visuomotor Transformation

Reaching movements to visual targets are under fast feedback control, which can rapidly correct an ongoing movement for errors. This study investigates how this online correction is affected by the application of a new visuomotor transformation. Thirty-two subjects made planar pointing movements to visual targets. Vision of the arm was prevented, and hand position was represented by a cursor displayed in the movement plane. In some trials, the target abruptly changed location at the onset of arm movement, which required a rapid correction of movement direction. After performing baseline trials, some subjects were required to adapt to a mirror-image transformation that inverted the visual feedback of their hand position across the body midline, whereas others were not familiarized with the transformation. Afterward, subjects' online correction was tested with target jumps in the presence of the mirror transformation. Results show that after short-term motor adaptation to the mirror transformation there was a selective suppression of the rapid non-mirror correction in the direction of visual target displacement but no mirror reversal. The suppression occurred within the first few trials after the introduction of the mirror transformation, and it was strongest for the movements in which the transformation caused the largest dissociation between the target location and hand movement. Finally, whether or not the short-latency non-mirror correction was suppressed in a given trial, the mirror correction occurred at the same latency as the onset time of voluntary correction in subjects who had not experienced the mirror transformation.

Sensory-Spatial Transformations in the Left Posterior Parietal Cortex May Contribute to Reach Timing

The posterior parietal cortex (PPC) contains viewer-centered spatial maps important for reaching movements. It is known that spatial reaching deficits emerge when this region is damaged, yet less is known about temporal deficits that may also emerge because of a failure in sensory-spatial transformations. This work introduces a new geometric measure to quantify multimodal sensory transformation and integration deficits affecting the tempo of reaching trajectories that are induced by injury to the left PPC. Erratic rates of positional change involving faulty maps from rotational angular displacements to translational linear displacements contributed to temporal abnormalities in the reach. Such disruptions were quantified with a time-invariant geometric measure. This measure, paired with an experimental paradigm that manipulated the source of visual guidance for reaches, was used to compare the performance of normal controls to those from a patient (T.R.) who had a lesion in his left-PPC. For controls, the source of visual guidance significantly scaled the tempo of target-directed reaches but did not change the geometric measure. This was not the case in patient T.R., who altered this measure. With continuous, extrapersonal visual feedback of the target, however, these abnormalities improved. Vision of the target rather than vision of his moving hand also improved his arm-joint rotations for posture control. These results show that the left PPC is critically important for visuo-motor transformations that specifically rely on extrapersonal cues to align rotational-arm and linear-hand displacements and to continuously integrate their rates of change. The intactness of this system contributes to the fluidity of the reach's tempo.

Interruption of visually perceived forward motion in depth evokes a cortical activation shift from spatial to intentional motor regions

Forward locomotion generates a radially expanding flow of visual motion which supports goal-directed walking. In stationary mode, wide-field visual presentation of optic flow stimuli evokes the illusion of forward self-motion. These effects illustrate an intimate relation between visual and motor processing. In the present fMRI study, we applied optic flow to identify distinct interfaces between circuitries implicated in vision and movement. The dorsal premotor cortex (PMd) was expected to contribute to wide-field forward motion flow (FFw), reflecting a pathway for externally triggered motor control. Medial prefrontal activation was expected to follow interrupted optic flow urging internally generated action. Data of 15 healthy subjects were analyzed with Statistical Parametric Mapping and confirmed this hypothesis. Right PMd activation was seen in FFw, together with activations of posterior parietal cortex, ventral V5, and the right fusiform gyrus. Conjunction analysis of the transition from wide to narrow forward flow and reversed wide-field flow revealed selective dorsal medial prefrontal activation. These findings point at equivalent visuomotor transformations in locomotion and goal-directed hand movement, in which parietal–premotor circuitry is crucially implicated. Possible implications of an activation shift from spatial to intentional motor regions for understanding freezing of gait in Parkinson's disease are discussed: impaired medial prefrontal function in Parkinson's disease may reflect an insufficient internal motor drive when visual support from optic flow is reduced at the entrance of a narrow corridor.

The Impact of Augmented Information on Visuo-Motor Adaptation in Younger and Older Adults

BackgroundAdjustment to a visuo-motor rotation is known to be affected by ageing. According to previous studies, the age-related differences primarily pertain to the use of strategic corrections and the generation of explicit knowledge on which strategic corrections are based, whereas the acquisition of an (implicit) internal model of the novel visuo-motor transformation is unaffected. The present study aimed to assess the impact of augmented information on the age-related variation of visuo-motor adjustments.Methodology/Principal FindingsParticipants performed aiming movements controlling a cursor on a computer screen. Visual feedback of direction of cursor motion was rotated 75° relative to the direction of hand motion. Participants had to adjust to this rotation in the presence and absence of an additional hand-movement target that explicitly depicted the input-output relations of the visuo-motor transformation. An extensive set of tests was employed in order to disentangle the contributions of different processes to visuo-motor adjustment. Results show that the augmented information failed to affect the age-related variations of explicit knowledge, adaptive shifts, and aftereffects in a substantial way, whereas it clearly affected initial direction errors during practice and proprioceptive realignment.ConclusionsContrary to expectations, older participants apparently made no use of the augmented information, whereas younger participants used the additional movement target to reduce initial direction errors early during practice. However, after a first block of trials errors increased, indicating a neglect of the augmented information, and only slowly declined thereafter. A hypothetical dual-task account of these findings is discussed. The use of the augmented information also led to a selective impairment of proprioceptive realignment in the younger group. The mere finding of proprioceptive realignment in adaptation to a visuo-motor rotation in a computer-controlled setup is noteworthy since visual and proprioceptive information pertain to different objects.

Perceiving affordances: A computational investigation of grasping affordances

The Grasping Affordance Model (GAM) introduced here provides a computational account of perceptual processes enabling one to identify grasping action possibilities from visual scenes. GAM identifies the core of affordance perception with visuo-motor transformations enabling one to associate features of visually presented objects to a collection of hand grasping configurations. This account is coherent with neuroscientific models of relevant visuo-motor functions and their localization in the monkey brain. GAM differs from other computational models of biological grasping affordances in the way of modeling focus, functional account, and tested abilities. Notably, by learning to associate object features to hand shapes, GAM generalizes its grasp identification abilities to a variety of previously unseen objects. Even though GAM information processing does not involve semantic memory access and full-fledged object recognition, perceptions of (grasping) affordances are mediated there by substantive computational mechanisms which include learning of object parts, selective analysis of visual scenes, and guessing from experience.

Implicit and explicit components of dual adaptation to visuomotor rotations

Concurrent adaptation to two different visuomotor transformations has been shown to be possible as long as discriminative contextual cues are available. The authors examined explicit and implicit components of visually cued dual adaptation in younger and older adults. They found that only young adults, but not old adults, produced appropriate adaptive shifts of hand-movement direction to compensate for the visuomotor rotations. Aftereffects, conceived as a measure of implicit knowledge, were only poorly developed. Furthermore, only participants in the younger group exhibited systematic explicit knowledge of the visuomotor rotations. Subsequent analyses revealed strong correlations between the quality of explicit knowledge and the overall visuomotor adaptation. Thus, visually cued dual adaptation to two opposite visuomotor rotations is primarily mediated by conscious strategic corrections based on explicit knowledge of the transformations, a process, which is selectively impaired in older adults.

Limb apraxia in corticobasal syndrome

Corticobasal syndrome (CBS) is a progressive neurodegenerative disorder with asymmetric presentation and course characterized by degeneration of basal ganglia and cortical structures. Limb apraxia is a commonly observed deficit in CBS. Few studies have examined comprehensively the nature of deficits in limb apraxia. The goal of our study was to investigate the severity of deficits in various conceptual and gesture production task modalities. CBS patients were divided in two groups based on the side of brain that was initially affected by the disease. Ten patients with right hemisphere presentation (RHP) and seven with left hemisphere presentation (LHP) were included. The results showed that while selective conceptual tasks deficits were present in both groups, the overall picture suggests preserved conceptual representations of tools and actions in CBS patients with either LHP or RHP. Both groups were impaired relative to controls on gesture production tasks. Performance on transitive gestures was more severely affected in both groups than intransitive gestures. Imitation was more severely affected than pantomime, suggesting deficits in visuomotor transformations. The addition of verbal cuing during concurrent imitation affected only the LHP patients, rendering them more impaired relative to controls in their imitation with verbal cuing as opposed to their imitation only performance. Imitation of non-representational gestures was least accurate and intransitive gestures were most accurate. Patients were more severely impaired relative to controls when holding the object and when they were shown pictures of tools to pantomime.

Brain mechanisms of visuomotor transformation based on deficits in tracing and copying

AbstractThe neural mechanisms underlying visuomotor transformation are examined based on deficits in tracing and copying, as well as functional neuroimaging studies. The developmental process of copying and tracing, as well as lesion studies with adults showing disability in drawing, are reviewed, then two experiments are introduced. In Experiment 1, a behavioral analysis of copying and tracing by individuals with Williams Syndrome (WS) was presented. In Experiment 2, the brain activity involved in copying and tracing was measured in normal adults using functional magnetic resonance imaging. Based on these findings, we propose a model of visuomotor transformation to explain the neural basis of tracing and copying, as well as to provide a possible neural mechanism underlying the copying deficits and closing‐in phenomenon observed in WS.

Examining Procedural Consolidation with Visuomotor Learning in the Lower Limb

ABSTRACTTo investigate the effects of interference tasks in the early stages of motor learning, we used a computerized motor skill analyzer (CMSA) for the lower limb that evaluates the accuracy and speed of movements in tracking tasks. Forty-five healthy subjects were randomly divided into three groups: a control group without an interference task, a mirror image interference group, and a point symmetry interference group. The practice and measurement of motor-learning trials were carried out as follows: (1) 10 practice trials followed by 10 measurement trials in the morning of the first day. (2) 10 measurement trials 6–7 awake hours after the first measurement. (3) 10 measurement trials on the morning of day 2. In the learning interference groups, 10 trials of the mirror image or point symmetry task were performed immediately after the first measurement. Although motor skills of the control group improved, those of the learning interference groups did not. This suggests that a second task performed immediately after the first task interferes with the consolidation of motor skill learning demanding complex visuomotor transformation.

Manipulation After Object Rotation Reveals Independent Sensorimotor Memory Representations of Digit Positions and Forces

Planning of object manipulations is dependent on the ability to generate, store, and retrieve sensorimotor memories of previous actions associated with grasped objects. However, the sensorimotor memory representations linking object properties to the planning of grasp are not well understood. Here we use an object rotation task to gain insight into the mechanisms underlying the nature of these sensorimotor memories. We asked subjects to grasp a grip device with an asymmetrical center of mass (CM) anywhere on its vertical surfaces and lift it while minimizing object roll. After subjects learned to minimize object roll by generating a compensatory moment, they were asked to rotate the object 180 degrees about a vertical axis and lift it again. The rotation resulted in changing the direction of external moment opposite to that experienced during the prerotation block. Anticipatory grasp control was quantified by measuring the compensatory moment generated at object lift onset by thumb and index finger forces through their respective application points. On the first postrotation trial, subjects failed to generate a compensatory moment to counter the external moment caused by the new CM location, thus resulting in a large object roll. Nevertheless, after several object rotations subjects reduced object roll on the initial postrotation trials by anticipating the new CM location through the modulation of digit placement but not tangential forces. The differential improvement in modulating these two variables supports the notion of independent memory representations of kinematics and kinetics and is discussed in relation to neural mechanisms underlying visuomotor transformations.

Multiple Motor Learning Strategies in Visuomotor Rotation

BackgroundWhen exposed to a continuous directional discrepancy between movements of a visible hand cursor and the actual hand (visuomotor rotation), subjects adapt their reaching movements so that the cursor is brought to the target. Abrupt removal of the discrepancy after training induces reaching error in the direction opposite to the original discrepancy, which is called an aftereffect. Previous studies have shown that training with gradually increasing visuomotor rotation results in a larger aftereffect than with a suddenly increasing one. Although the aftereffect difference implies a difference in the learning process, it is still unclear whether the learned visuomotor transformations are qualitatively different between the training conditions.Methodology/Principal FindingsWe examined the qualitative changes in the visuomotor transformation after the learning of the sudden and gradual visuomotor rotations. The learning of the sudden rotation led to a significant increase of the reaction time for arm movement initiation and then the reaching error decreased, indicating that the learning is associated with an increase of computational load in motor preparation (planning). In contrast, the learning of the gradual rotation did not change the reaction time but resulted in an increase of the gain of feedback control, suggesting that the online adjustment of the reaching contributes to the learning of the gradual rotation. When the online cursor feedback was eliminated during the learning of the gradual rotation, the reaction time increased, indicating that additional computations are involved in the learning of the gradual rotation.Conclusions/SignificanceThe results suggest that the change in the motor planning and online feedback adjustment of the movement are involved in the learning of the visuomotor rotation. The contributions of those computations to the learning are flexibly modulated according to the visual environment. Such multiple learning strategies would be required for reaching adaptation within a short training period.

The effects of mechanical transparency on adjustment to a complex visuomotor transformation at early and late working age.

Mechanical tools are transparent in the sense that their input-output relations can be derived from their perceptible characteristics. Modern technology creates more and more tools that lack mechanical transparency, such as in the control of the position of a cursor by means of a computer mouse or some other input device. We inquired whether an enhancement of transparency by means of presenting the shaft of a virtual sliding lever, which governed the transformation of hand position into cursor position, supports performance of aimed cursor movement and the acquisition of an internal model of the transformation in both younger and older adults. Enhanced transparency resulted in an improvement of visual closed-loop control in terms of movement time and curvature of cursor paths. The movement-time improvement was more pronounced at older working age than at younger working age, so that the enhancement of transparency can serve as a means to mitigate age-related declines in performance. Benefits for the acquisition of an internal model of the transformation and of explicit knowledge were absent. Thus, open-loop control in this task did not profit from enhanced mechanical transparency. These findings strongly suggest that environmental support of transparency of the effects of input devices on controlled systems might be a powerful tool to support older users. Enhanced transparency may also improve simulator-based training by increasing motivation, even if training benefits do not transfer to situations without enhanced transparency.

Anterior intraparietal cortex codes complexity of observed hand movements

Human and monkey studies clearly show that the anterior intraparietal area (AIP) is crucial for hand-related visuomotor transformations. Human AIP activates also during observation of hand actions, involving it in the mirror system. It is not known, however, whether its activation can also reflect a difference in the complexity of the observed action. In the present study we used functional magnetic resonance imaging (fMRI) to explore the activation of human area AIP during the observation of complex object-manipulation tasks (e.g. inserting a key in a lock and turning it) as compared to simple tasks (whole hand grasping of an object) executed with the left and the right hand in a first person perspective. The results show that, in general, both complex and simple tasks produced an activation of the fronto-parietal mirror system and that the activity of AIP in each hemisphere was higher during observation of the contralateral hand (hand identity effect). A Region-Of-Interest (ROI) analysis of the parietal activations responding to hand identity showed that each AIP was more active during the observation of complex with respect to simple tasks. In the right AIP this effect was stronger during observation of the contralateral hand, in the left AIP was strong during observation of both hands. This complexity-related property was not observed in the other activated areas. These findings support the concept that the observation of motor acts retrieves the internal representation of those same acts in the observer's motor system (direct-matching hypothesis based on the mirror neuron mechanism).

Robust Coding of Ego-Motion in Descending Neurons of the Fly

In many species, motion-sensitive neurons responding to optic flow at higher processing stages are well characterized; however, less is known how this representation of ego-motion is further transformed into an appropriate motor response. Here, we analyzed in the blowfly Calliphora vicina the visuomotor transformation from motion-sensitive neurons in the lobula plate [V2 and vertical system (VS) cells] onto premotor descending neurons [descending neurons of the ocellar and vertical system (DNOVS) cells] feeding into the motor circuit of the fly thoracic ganglion. We found that each of these cells is tuned to rotation of the fly around a particular body axis. Comparing the responses of presynaptic and postsynaptic cells revealed that DNOVS cells have approximately the same tuning widths as V2 and VS cells. However, DNOVS signals cells are less corrupted by fluctuations arising from the spatial structure of the visual input than their presynaptic elements. This leads to a more robust representation of ego-motion at the level of descending neurons. Thus, when moving from lobula plate cells to descending neurons, the selectivity for a particular optic flow remains unaltered, but the robustness of the representation increases.

The trajectory of adaptation to the visuo-motor transformation of virtual and real sliding levers

We studied adaptation to the visuo-motor transformation of a virtual and a real two-sided sliding lever. In a previous study (Sülzenbrück and Heuer in Exp Brain Res 195:153-165, 2009) we had found essentially no differences. However, adaptation had been restricted to a simplified symmetry approximation of the transformation. In the present study practice conditions were designed to facilitate adaptation (e.g., terminal rather than continuous visual feedback). In visual open-loop tests, differences between the effects of practice with a virtual and a real lever were found for curvature of hand movements, whereas movement end positions were not different. Curved hand movements induced by the use of the real lever persisted in subsequent open-loop tests with the virtual lever. Early in practice end-position errors were strongly biased toward the simplified symmetry approximation, but this bias was reduced later on. Thus, the symmetry approximation is a transient state in the trajectory of adaptation that is reached quickly and from which there is a slow and gradual transition to an accurate internal representation of the visuo-motor transformation of the sliding lever.

Insights into the control of arm movement during body motion as revealed by EMG analyses

Recent studies have revealed that vestibulomotor transformations contribute to maintain the hand stationary in space during trunk rotation. Here we tested whether these vestibulomotor transformations have the same latencies and whether they are subject to similar cognitive control than the visuomotor transformations during manual tracking of a visual target. We recorded hand displacement and shoulder–muscle activity in two tasks: a stabilization task in which subjects stabilized their hand during passive 30° body rotations, and a tracking task in which subjects tracked with their finger a visual target as it moved 30° around them. The EMG response times recorded in the stabilization task (∼ 165 ms) were twice as short as those observed for the tracking task (∼ 350 ms). Tested with the same paradigm, a deafferented subject showed EMG response times that closely matched those recorded in healthy subjects, thus, suggesting a vestibular origin of the arm movements. Providing advance information about the direction of the required arm movement reduced the response times in the tracking task (by ∼ 115 ms) but had no significant effect in the stabilization task. Generally, when providing false information about movement direction in the tracking task, an EMG burst first appeared in the muscle moving the arm in the direction opposite to the actual target motion (i.e., in accord with the precueing). This behavior was rarely observed in the stabilization task. These results show that the sensorimotor transformations that move the arm relative to the trunk have shorter latencies when they originate from vestibular inputs than from visual information and that vestibulomotor transformations are more resistant to cognitive processes than visuomotor transformations.