Visuomotor Mapping Research Articles

Mapping Shape to Visuomotor Mapping: Generalization to Novel Shapes

The accuracy of visually guided motor movements largely depends on the stability of the sensory environment that defines the required response mapping. Thus, as the environment keeps changing we constantly have to adapt our motor responses to stay accurate. The more sensory information we receive about the current state of the environment the more accurate we may be. Recruitment of additional cues that correlate with the environment can therefore aid in this adaptation process. It has previously been shown that subjects recruit previously irrelevant cues to help them switch between 2 specific visuomotor mappings (e.g. Martin et al., 1996; van Dam et al., 2008). However, in rapidly changing environments additional cues will only be of real benefit if it is possible to learn a more continuous correlation between the cue and required visuomotor response. Here we investigate transfer of explicitly trained cue-element/response-mapping combinations to other cue elements from the same continuous scale (a shape morph). In our experiment subjects performed a rapid pointing task to targets for which we manipulated the visuomotor mapping. During training subject simultaneously learned two mappings to two different target shapes. The target shapes were taken from a set of shape morphs (we morphed between spiky and circular shapes). After five sessions of 180 training trials, using catch trials, we tested subjects' performance on different target shape morphs that could either come from an interpolation or an extrapolation along the shape morph axis. Results show that for 7 out of the 12 subjects learning is not restricted to the trained shapes but interpolates and partially also extrapolates to other shapes along the morph axis. We conclude that participants learned implicitly the newly defined shape axis when trained with two distinct visuomotor mappings and they generalize their visuomotor mappings to this new dimension.

Can cerebellar input calibrate collicular topographic maps?

There is substantial evidence that repeating cerebellar microcircuit implements an adaptive filter algorithm suitable for fine tuning a wide range of sensorimotor skills [1]. Although it is known that multimodal map layer of superior colliculus receives a massive cerebellar input which directly influences collicular output cells [2], there has been little speculation as to function of this influence. We suggest here that these cerebellar inputs play a role in calibrating accuracy of collicular topographic maps. The cerebellum is a plausible candidate for this role for a number of reasons. It is known to be crucial for accuracy of saccades generated by colliculus. It is also known that cerebellar lesions impair prism adaptation of eye movements. A recent imaging study [3] found direct evidence of cerebellar activation during prism adaptation and suggests that the cerebellum is particularly involved in [establishing] a correct spatial mapping among visuomotor and sensorimotor coordinates systems. A modeling study [3] of collicular visuomotor mapping concludes that transformation occurs in brainstem with cerebellum adjusting it for accuracy, stating that ... importance of cerebellum has been neglected in previous modeling studies. Here we investigate whether adaptive filter model of cerebellar microcircuit which has been so successful in conventional sensorimotor contexts can be applied without change to very different computational problem of calibrating a topographic map driving an orienting response. We propose a model in which (i) unimodal sensory topographic maps constitute a probabilistic representation of target position and that these maps are optimally combined to produce a multimodal map [4] whose peak activity drives orienting response, (ii) cerebellar input can bias position of peak map activity (e.g. by a process such as attentional gain modulation [5]), (iii) cerebellum receives sensory information that generates topographic maps on its mossy fibre inputs, and (iv) information about orienting errors caused by miscalibration is made available to cerebellum on its climbing fibre inputs and drives cerebellar learning. We demonstrate in simulation that this mechanism can successfully calibrate topographic maps and go on to investigate its computational properties. For example we investigate a fundamental calibration ambiguity in which sensory maps can be miscalibrated in such a way that their effects on combined estimate cancel. We show that this ambiguity is resolved in a plausible way if error signals are gated whenever a sensor fails to observe target; a similar gating process has been observed in some motor behaviors [6].We also demonstrate that optimality of cerebellar learning rule [7] ensures that Purkinje cell synapses carrying cross-talk between sensors are driven to silence, greatly reducing need to hard-wire connectivity of parallel fiber inputs to cerebellar microzones.

Neural Substrates of Graphomotor Sequence Learning: A Combined fMRI and Kinematic Study

The goal of this study was to characterize the dynamics and functional connectivity of brain networks associated with fast (short-term) learning of handwriting using functional magnetic resonance imaging. Participants (n = 12) performed a graphomotor sequence learning task (naïve subjects learning to draw simple, 3-stroke Chinese word characters), which focused the learning process on the kinematic aspects of sequence learning instead of on the production of the line segments. Learning of the graphomotor sequence was demonstrated by a progressive improvement in movement smoothness as assessed by normalized jerk scores. Examination of the patterns of regional neural activity and functional connectivity during sequence learning demonstrated that cortical regions, which may support visuomotor mapping components of the task, were active prior to subcortical areas that may play a role in encoding and refining the novel sequences. Importantly, differences in the time course of recruitment of basal ganglia and cerebellar networks suggest distinct but integrated roles in the encoding and refining of the handwritten sequences. This implies multiple kinematic representations of graphomotor trajectories may be encoded at various spatiotemporal scales.

Optic flow recalibrates the direction of walking but not throwing

Understanding the visuo-motor calibration of spatially-oriented movements is central to an understanding of perception and action. We investigate whether adaptation of the mapping between visual target direction and walking direction transfers to the direction of underhand throws. In an adaptation phase, participants repeatedly walked to a target in a virtual environment while the heading direction specified by optic flow was displaced 10 deg to the right of the actual walking direction (Bruggeman, Zosh, & Warren, Current Biology, 2007). Within in a few trails, they adapted and walked straight toward the target. Rushton (2004) and others have argued that the exposure to displaced flow leads to adaptation of the visual straight ahead. In contrast, we hypothesized that optic flow acts to recalibrate the visuo-motor mappings from perceived target direction to initial and ongoing walking direction. On the former hypothesis, adaptation of the straight ahead should affect any spatial-oriented movement, including throwing to the target. On the latter hypothesis, adaptation should affect only walking whereas throwing should remain unchanged. We tested these hypotheses by evaluating walking and throwing direction before and after adaptation. Participants first threw a ball to a visually specified target (they could not see the ball's trajectory and landing position) and then walked with their eyes closed to the target, as if to retrieve the ball. Prior to adaptation participants throw and walk in the same direction. However, after adaptation they walked approximately 5 deg to the left of the target, missing it by about .8 m. But their throws remained on target. Surprisingly, participants were not able to retrieve their own throws! Thus, optic flow recalibrates the visual-locomotor mapping, not the direction of visual straight ahead.

Learning not to generalize: modular adaptation of visuomotor gain.

When a new sensorimotor mapping is learned through practice, learning commonly transfers to unpracticed regions of task space, that is, generalization ensues. Does generalization reflect fixed properties of movement representations in the nervous system and thereby limit what visuomotor mappings can and cannot be learned? Or does what needs to be learned determine the shape of generalization? We used the broad generalization properties of visuomotor gain adaptation to address these questions. Adaptation to a single gain for reaching movements is known to generalize broadly across movement directions. By training subjects on two different gains in two directions, we set up a potential conflict between generalization patterns: if generalization of gain adaptation indicates fixed properties of movement amplitude encoding, then learning two different gains in different directions should not be possible. Conversely, if generalization is flexible, then it should be possible to learn two gains. We found that subjects were able to learn two gains simultaneously, although more slowly than when they adapted to a single gain. Analysis of the resulting double-gain generalization patterns, however, unexpectedly revealed that generalization around each training direction did not arise de novo, but could be explained by a weighted combination of single-gain generalization patterns, in which the weighting takes into account the relative angular separation between training directions. Our findings therefore demonstrate that the mappings to each training target can be fully learned through reweighting of single-gain generalization patterns and not through a categorical alteration of these functions. These results are consistent with a modular decomposition approach to visuomotor adaptation, in which a complex mapping results from a combination of simpler mappings in a "mixture-of-experts" architecture.

Learning a visuomotor rotation: simultaneous visual and proprioceptive information is crucial for visuomotor remapping.

Visuomotor adaptation is mediated by errors between intended and sensory-detected arm positions. However, it is not clear whether visual-based errors that are shown during the course of motion lead to qualitatively different or more efficient adaptation than errors shown after movement. For instance, continuous visual feedback mediates online error corrections, which may facilitate or inhibit the adaptation process. We addressed this question by manipulating the timing of visual error information and task instructions during a visuomotor adaptation task. Subjects were exposed to a visuomotor rotation, during which they received continuous visual feedback (CF) of hand position with instructions to correct or not correct online errors, or knowledge-of-results (KR), provided as a static hand-path at the end of each trial. Our results showed that all groups improved performance with practice, and that online error corrections were inconsequential to the adaptation process. However, in contrast to the CF groups, the KR group showed relatively small reductions in mean error with practice, increased inter-trial variability during rotation exposure, and more limited generalization across target distances and workspace. Further, although the KR group showed improved performance with practice, after-effects were minimal when the rotation was removed. These findings suggest that simultaneous visual and proprioceptive information is critical in altering neural representations of visuomotor maps, although delayed error information may elicit compensatory strategies to offset perturbations.

Sex-related differences in the hemispheric laterality of slow cortical potentials during the preparation of visually guided movements

Previous work suggests the presence of sex differences in the laterality of brain activity in the premotor-parietal network during the preparation of visually guided reaching movements. In the current study, electroencephalography was used to test the hypothesis that women would have higher amplitude potentials over frontal and parietal regions ipsilateral to arm movements, relative to men. Event-related slow cortical potentials (SCPs) were collected from 30 participants (15 men and 15 women) during the performance of two visually guided reaching conditions (eyes and arm moved to the same spatial location or moved in opposite directions). The results of the study demonstrate that the amplitudes of SCPs were significantly higher overlying frontal regions of the right hemisphere of women relative to men. These differences were present both during an instructed-delay period prior to receiving a go-signal to initiate movement and during the period just prior to movement initiation. The study also revealed an interaction of Sex and Condition in the parietal region during the pre-movement period. These results suggest that motor preparatory activity in men mainly occurs in the hemisphere contralateral to reaching but that preparatory activity in women is distributed relatively more bilaterally. However, the nature of these differences changes over the time course of the preparatory period and is partially dependent on the type of visuomotor mapping being performed.

Pinna Cues Determine Orienting Response Modes to Synchronous Sounds in Elevation

To program a goal-directed orienting response toward a sound source embedded in an acoustic scene, the audiomotor system should detect and select the target against a background. Here, we focus on whether the system can segregate synchronous sounds in the midsagittal plane (elevation), a task requiring the auditory system to dissociate the pinna-induced spectral localization cues. Human listeners made rapid head-orienting responses toward either a single sound source (broadband buzzer or Gaussian noise) or toward two simultaneously presented sounds (buzzer and noise) at a wide variety of locations in the midsagittal plane. In the latter case, listeners had to orient to the buzzer (target) and ignore the noise (nontarget). In the single-sound condition, localization was accurate. However, in the double-sound condition, response endpoints depended on relative sound level and spatial disparity. The loudest sound dominated the responses, regardless of whether it was the target or the nontarget. When the sounds had about equal intensities and their spatial disparity was sufficiently small, endpoint distributions were well described by weighted averaging. However, when spatial disparities exceeded approximately 45 degrees, response endpoint distributions became bimodal. Similar response behavior has been reported for visuomotor experiments, for which averaging and bimodal endpoint distributions are thought to arise from neural interactions within retinotopically organized visuomotor maps. We show, however, that the auditory-evoked responses can be well explained by the idiosyncratic acoustics of the pinnae. Hence basic principles of target representation and selection for audition and vision appear to differ profoundly.

Poster 13: Huntington's Disease Disrupts Motor Control Mechanisms That Rely on Internal Models

Background Previous studies demonstrated that Huntington's disease (HD) impairs the ability to perform to perform online adjustments during reaching movements. It is not clear whether the difficulty is in responding to errors in observed or predicted trajectory. Do patients have trouble observing deviations of the hand from its goal, or does the difficulty lie in predicting where the hand should be based on internal models of the effects of motor commands? Methods We compared corrections made to two visuomotor perturbations that were equivalent in sensory space, but differed in the nature of the resulting error (goal-related vs effector-related). Subjects made planar reaching movements to guide a screen cursor to a target. Interspersed with baseline trials were perturbation trials, in which either the target jumped to a new location (target jump) or the direction of the cursor was rotated relative to the starting point (rotation). The target jump (to a new direction, ±30 degrees away) and the rotation (±30 degrees) were spatially matched so as to require the same change in hand movement direction in order to acquire the target. The target jump required a change in movement goal (external error), whereas rotation introduced a mismatch between actual hand position and hand position predicted by subject's visuomotor map (internal model error). Results and Discussion The corrections made by patients to target jumps were only slightly abnormal, with increased variability and slight undershoot. Their corrections to visuomotor rotation trials, on the other hand, were considerably abnormal. There was a systematic delay in the onset of the correction, and the amplitude of the correction was incomplete. These findings establish a selective impairment in monitoring errors in computation of predicted hand position. A function of the circuits affected by HD may be to monitor internal motor control models that are necessary to guide movements to their targets.

Inhibition of the anterior intraparietal area and the dorsal premotor cortex interfere with arbitrary visuo-motor mapping

The contribution of the human anterior intraparietal area and the dorsal premotor cortex to arbitrary visuo-motor mapping during grasping were tested. Trained right-handed subjects reached for and pincer-grasped a cube with the right hand in the absence of visual feedback after the cube location had been displayed for 200ms. During the reaching movements, the colour of the cube changed and visual feedback about the change of colour was provided for 100ms at 500ms after movement onset (at the time of peak grasp aperture). Depending on colour, subjects were instructed to either pincer-grasp the cube in a horizontal or vertical grasp position with the latter necessitating wrist rotation (experiment 1) or to pincer-grasp and transport the cube to either a left or right target position (experiment 2). Within two consecutive 200ms time windows (TMS 1 and 2) starting 500ms and 700ms after movement onset, respectively, double pulses of supra-threshold transcranial magnetic stimulation (inter-stimulus interval: 100ms) were delivered over (i) the left primary motor cortex (90 degrees vertically angulated coil position, control stimulation), (ii) the left dorsal premotor cortex or (ii) the left anterior intraparietal area. Compared to control stimulation, stimulation of the anterior intraparietal area, but not of the dorsal premotor cortex, at TMS 1 delayed the times to wrist rotation (experiment 1) and hand transport (experiment 2). Compared to control stimulation, stimulation of the dorsal premotor cortex, but not of the anterior intraparietal area, at TMS 2 delayed both wrist rotation (experiment 1) and hand transport (experiment 2). We contend that the anterior intraparietal area and the dorsal premotor cortex are both involved albeit at different phases during the mapping of arbitrary visual cues with goal directed grasp and transport movements. These data add to the current understanding of how human cortical areas work in concert during manual activities.

Arbitrary visuomotor mapping during object manipulation in Parkinson's disease

The objective of this study is to investigate whether subjects with Parkinson's disease are able to use arbitrary color cues linked to the mass of an object to be lifted allowing for the predictive selection of appropriate grip forces. Fourteen patients with Parkinson's disease used a precision grip to lift two objects of different masses (400 and 600 g) in random order. In a "no cue" condition, a noninformative neutral visual stimulus was presented before each lift, thereby not allowing any judgement about which mass to be lifted. In a "cue" condition an arbitrary color cue provided advance information about which of the two masses patients would have to lift in the subsequent trial. Patients performed the conditions with either hand and by both on and off drugs. In the "no cue" trials patients scaled the predictive grip force output according to the perceived mass of the preceding lift. In the "cue" experiment patients scaled grip force in a predictive manner to mass based on the provided color cues. The ability of arbitrary visuomotor mapping was evident at either hand and not influenced by medication on/off. The precision of arbitrary visuomotor mapping correlated negatively with age, but not with disease duration, severity of motor disability on and off drug, severity of cognitive impairment on and off drug, or the amount of levodopa equivalent daily dosage of dopaminergic drugs. These data imply that Parkinson's disease does not preclude the ability of visuomotor mapping in the grip-lift task.

Real-time error detection but not error correction drives automatic visuomotor adaptation

We investigated the role of visual feedback of task performance in visuomotor adaptation. Participants produced novel two degrees of freedom movements (elbow flexion-extension, forearm pronation-supination) to move a cursor towards visual targets. Following trials with no rotation, participants were exposed to a 60 degrees visuomotor rotation, before returning to the non-rotated condition. A colour cue on each trial permitted identification of the rotated/non-rotated contexts. Participants could not see their arm but received continuous and concurrent visual feedback (CF) of a cursor representing limb position or post-trial visual feedback (PF) representing the movement trajectory. Separate groups of participants who received CF were instructed that online modifications of their movements either were, or were not, permissible as a means of improving performance. Feedforward-mediated performance improvements occurred for both CF and PF groups in the rotated environment. Furthermore, for CF participants this adaptation occurred regardless of whether feedback modifications of motor commands were permissible. Upon re-exposure to the non-rotated environment participants in the CF, but not PF, groups exhibited post-training aftereffects, manifested as greater angular deviations from a straight initial trajectory, with respect to the pre-rotation trials. Accordingly, the nature of the performance improvements that occurred was dependent upon the timing of the visual feedback of task performance. Continuous visual feedback of task performance during task execution appears critical in realising automatic visuomotor adaptation through a recalibration of the visuomotor mapping that transforms visual inputs into appropriate motor commands.

The influence of goals on movement kinematics during imitation

This study took a quantitative approach to investigate movement kinematics during the imitation of goal-directed and non-goal directed movements. Motion tracking equipment was used to record the hand movements of 15 healthy participants during an imitation task involving aiming movements that varied in speed. We predicted that movement kinematics would be most similar to the observed movements in the non-goal condition, as a result of direct visuomotor mapping of the action, and least similar in the goal-directed condition because more importance would be given to the end goal. We also predicted that precues (prior information about the movement) would increase imitation accuracy in the non-goal condition by reducing cognitive demand, and that precues would reduce accuracy in the goal-directed condition, as less attention would be paid to the movement. Results showed that imitation was modulated by the speed of the observed action in the non-goal condition only. Contrary to predictions, precues did not improve imitation in the non-goal condition or improve imitation accuracy in the goal-directed condition. These results demonstrate that visuomotor mapping is favoured in non-goal imitation, regardless of prior information, and that accurate imitation of movement detail is compromised by the presence of goals. Such differences in movement kinematics indicate that different processes mediate the imitation of non-goal and goal-directed actions.

Adaptation to Visuomotor Rotation Through Interaction Between Posterior Parietal and Motor Cortical Areas

Studying how motor adaptation to visuomotor rotation for one reach direction generalizes to other reach directions can provide insight into how visuomotor maps are represented and learned in the brain. Previous psychophysical studies have concluded that postadaptation generalization is restricted to a narrow range of directions around the training direction. A population-coding model that updates the weights between narrow Gaussian-tuned visual units and motor units on each trial reproduced experimental trial-by-trial learning curves for rotation adaptation and the generalization function measured postadaptation. These results suggest that the neurons involved in rotation adaptation have a relatively narrow directional tuning width ( approximately 23 degrees ). Population coding models with units having broader tuning functions (such as cosine tuning in motor cortex and Gaussian sum in the cerebellum) could not reproduce the narrow single-peaked generalization pattern. Visually selective neurons with narrow Gaussian tuning curves have been identified in posterior parietal cortex, making it a possible site of adaptation to visuomotor rotation. We propose that rotation adaptation proceeds through changes in synaptic weights between neurons in posterior parietal cortex and motor cortex driven by a prediction error computed by the cerebellum.

The neural computations of decision-making during arbitrary visuomotor learning

Event Abstract Back to Event The neural computations of decision-making during arbitrary visuomotor learning Andrea Brovelli1* and Driss Boussaoud1 1 CNRS -Universite Aix-Marseille, INCM, France Learning the consequences of our actions in their context is a fundamental cognitive ability, because it allows us and other animals to anticipate relevant events and to adapt to varying environments. If the relation between the visual stimulus, or context, the action, and its outcome is arbitrary and causal, we refer to as arbitrary visuomotor learning (Wise and Murray 2000). Associative theory (Dickinson 1980) postulates that learning the consequences of our actions is represented as stimulus-response-outcome associations that evolve according to prediction error signals (the discrepancy between the observed and predicted outcome). With further training, goal-directed behaviors are transformed into habitual responses that gradually become elicited by the antecedent stimuli (Yin and Knowlton, 2006). The aim of our work is to test these theories on functional magnetic resonance imaging (fMRI) data acquired from human participants and to provide quantitative descriptions of the neural computation mediating the acquisition of instrumental behaviors. Consistent with the Rescorla-Wagner model, prediction-error signals are computed in the human brain and selectively engage the ventral striatum. In addition, we found evidence of computations not formally predicted by the Rescorla-Wagner model. The dorsal frontoparietal network, the dorsal striatum, and the ventrolateral prefrontal cortex are activated both on the incorrect and first correct trials and may reflect the processing of relevant visuomotor mappings during the early phases of learning. The left dorsolateral prefrontal cortex is selectively activated on the first correct outcome (Brovelli et al., 2008).Decision-related brain responses: We tested the hypothesis that the selection of action during the different phases of instrumental leaning is mediated by complementary frontostriatal loops (the associative and sensorimotor newtorks) transforming goal-directed actions into stimulus-driven habits (Yin and Knowlton, 2006). Preliminary results showed that the fMRI activity in the dorsal caudate nucleus increases during the exploratory phase and it correlates with the learning curve. In parallel, the activaty in the putamen increases slower during learning and it correlates with the probability that the stimulus is a good predictor of the correct action. To conclude, the results provide quantitative evidence of the neural computations mediating arbitrary visuomotor learning and suggest new directions for future computational models. Conference: 3rd Mediterranean Conference of Neuroscience , Alexandria, Egypt, 13 Dec - 16 Dec, 2009. Presentation Type: Oral Presentation Topic: Symposium 01 – Neural dynamics, learning and functional recovery Citation: Brovelli A and Boussaoud D (2009). The neural computations of decision-making during arbitrary visuomotor learning. Front. Neurosci. Conference Abstract: 3rd Mediterranean Conference of Neuroscience . doi: 10.3389/conf.neuro.01.2009.16.003 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 18 Nov 2009; Published Online: 18 Nov 2009. * Correspondence: Andrea Brovelli, CNRS -Universite Aix-Marseille, INCM, 13331 Marseille, France, andrea.brovelli@univ-amu.fr Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Andrea Brovelli Driss Boussaoud Google Andrea Brovelli Driss Boussaoud Google Scholar Andrea Brovelli Driss Boussaoud PubMed Andrea Brovelli Driss Boussaoud Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Adaptation to a direction-dependent visuomotor gain in the young and elderly

Consistent with the widely accepted notion of separate specification of movement amplitude and direction, it has been argued that there is also a categorical difference between adaptation to novel visuomotor rotations and to novel visuomotor gains. In line with this view, ageing seems to affect rotation and gain adaptation differently in that age-related impairments are consistently found for the former, but not for the latter. In this study we ask whether the contrasting findings could also be ascribed to differences in the level of difficulty of gain and rotation adaptation tasks, respectively. In order to increase the difficulty of gain adaptation, younger and older participants had to adapt to a direction-dependent gain transformation. Results revealed direction-dependent adaptation in both groups. More importantly, we replicated the typical findings of age-related impairments of adaptation, but not of aftereffects, that were previously only reported for rotation adaptation. Younger participants also showed superior explicit knowledge regarding the novel visuomotor mapping as compared to the older participants. We show that this knowledge was used by younger participants to selectively augment adaptive shifts. Finally, our findings suggest that the difficulty of the novel visuomotor transformation and, related to this, the involvement of explicit knowledge in adaptation is critical for age-related changes to show up, but not the type of adaptation task, rotation and gain adaptation, respectively.

Spatial representation of overlearned arbitrary visuomotor associations

Our movements can be guided directly by spatial information, but also more flexibly through arbitrary rules. We have recently shown that as arbitrary visuomotor mappings became overlearned, they come to rely not only on fronto-striatal circuits, but also on the posterior parietal cortex (PPC). Since this region supports multiple reference frames for hand movements, the question arose whether overlearned visuomotor associations could come to rely on a spatial framework, similar to spatially guided movements. Alternatively, overlearned visuomotor associations could be non-spatial in nature. In this study we investigate the characteristics of the movement representations supporting arbitrary visuomotor mappings by assessing how performance of extensively trained arbitrary visuomotor associations depends on the effector used to provide the response. After extensive training on a set of arbitrary visuomotor associations, subjects were asked to perform the same task in one of two novel settings that varied either the spatial or the motor relationship between visual instructions and finger movements. We found that the change in spatial configuration resulted in a larger amount of interference on the performance of the original mappings than the configuration change in motor coordinates. This result suggests that the visual stimuli became arbitrarily coupled to locations in space and not directly to the finger movements. We infer that overlearned arbitrary visuomotor associations are represented in spatial coordinates, in an effector-independent framework. This result raises the possibility that the previously reported involvement of the posterior parietal cortex in overlearned visuomotor behavior reflects the transition from an arbitrary visuomotor mapping into a spatially based stimulus-location-response mapping.

The efficacy of colour cues in facilitating adaptation to opposing visuomotor rotations

We investigated visuomotor adaptation using an isometric, target-acquisition task. Following trials with no rotation, two participant groups were exposed to a random sequence of 30 degrees clockwise (CW) and 60 degrees counter-clockwise (CCW) rotations, with (DUAL-CUE), or without (DUAL-NO CUE), colour cues that enabled each environment (non-rotated, 30 degrees CW and 60 degrees CCW) to be identified. A further three groups experienced only 30 degrees CW trials or only 60 degrees CCW trials (SINGLE rotation groups) in which each visuomotor mapping was again associated with a colour cue. During training, all SINGLE groups reduced angular deviations of the cursor path during the initial portion of the movements, indicating feedforward adaptation. Consistent with the view that the adaptation occurred automatically via recalibration of the visuomotor mapping (Krakauer et al. 1999), post-training aftereffects were observed, despite colour cues that indicated that no rotation was present. For the DUAL-CUE group, angular deviations decreased with training in the 60 degrees trials, but were unchanged in the 30 degrees trials, while for the DUAL-NO CUE group angular deviations decreased for the 60 degrees CW trials but increased for the 30 degrees CW trials. These results suggest that in a dual adaptation paradigm a colour cue can permit delineation of the two environments, with a subsequent change in behaviour resulting in improved performance in at least one of these environments. Increased reaction times within the training block, together with the absence of aftereffects in the post-training period for the DUAL-CUE group suggest an explicit cue-dependent strategy was used in an attempt to compensate for the rotations.

Eye–hand strategies in copying complex lines

Eye movements and eye–hand interactions have been recorded for 10 beginner art students copying complex lines representing outlines of caricature heads seen in profile. Four copying conditions mimicking real-world drawing situations were tested: Direct copying where the original and copy were placed side by side, Direct Blind copying where the subject could not see the drawing hand and copy, Memory copying where the original was first memorized for drawing and subsequently hidden before drawing commenced, and Non-specific Memory copying where the original was encoded for facial recognition before being hidden and drawn from memory. We observed four very different eye–hand interaction strategies which provide evidence for the eye's dual role in the copying process: acquiring visual information in order to activate the visuomotor transformation and guiding the hand on the paper. The Direct copying strategies were best understood in terms of a Drawing Hypothesis stating that shape is the result of visuomotor mapping alone and, consequently, can be accurately drawn without vision of the drawing hand or paper. A double just-in-time mechanism is proposed whereby the eye refers alternatively to the original for shape and to the copy for spatial position just in time for the drawing action to proceed continuously.

Generalisation between opposing visuomotor rotations when each is associated with visual targets and movements of different amplitude

Previous studies have attempted to identify sources of contextual information which can facilitate dual adaptation to two variants of a novel environment, which are normally prone to interference. The type of contextual information previously used can be grouped into two broad categories: that which is arbitrary to the motor system, such as a colour cue, and that which is based on an internal property of the motor system, such as a change in movement effector. The experiments reported here examined whether associating visuomotor rotations to visual targets and movements of different amplitude would serve as an appropriate source of contextual information to enable dual adaptation. The results indicated that visual target and movement amplitude is not a suitable source of contextual information to enable dual adaptation in our task. Interference was observed in groups who were exposed to opposing visuomotor rotations, or a visuomotor rotation and no rotation, both when the onset of the visuomotor rotations was sudden, or occurred gradually over the course of training. Furthermore, the pattern of interference indicated that the inability to dual adapt was a result of the generalisation of learning between the two visuomotor mappings associated with each of the visual target and movement amplitudes.