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An important window into sensorimotor function is how humans interact and stop moving projectiles, such as stopping a door from closing shut or catching a ball. Previous studies have suggested that humans time the initiation and modulate the amplitude of their muscle activity based on the momentum of the approaching object. However, real-world experiments are constrained by laws of mechanics, which cannot be manipulated experimentally to probe the mechanisms of sensorimotor control and learning. An augmented-reality variant of such tasks allows for experimental manipulation of the relationship between motion and force to obtain novel insights into how the nervous system prepares motor responses to interact with moving stimuli. Existing paradigms for studying interactions with moving projectiles use massless objects and are primarily focused on quantifying gaze and hand kinematics. Here, we developed a novel collision paradigm using a robotic manipulandum where participants mechanically stopped a virtual object moving in the horizontal plane. On each block of trials, we varied the virtual object's momentum by increasing either its velocity or mass. Participants stopped the object by applying a force impulse that matched the object momentum. We observed that hand force increased as a function of object momentum linked to changes in virtual mass or velocity, similar to results from studies involving catching free-falling objects. In addition, increasing object velocity resulted in later onset of hand force relative to the impending time-to-contact. These findings show that the present paradigm can be used to determine how humans process projectile motion for hand motor control. [ABSTRACT FROM AUTHOR]

While reaching and grasping are highly prevalent manual actions, neuroimaging studies provide evidence that their neural representations may be shared between different body parts, i.e., effectors. If these actions are guided by effector-independent mechanisms, similar kinematics should be observed when the action is performed by the hand or by a cortically remote and less experienced effector, such as the foot. We tested this hypothesis with two characteristic components of action: the initial ballistic stage of reaching, and the preshaping of the digits during grasping based on object size. We examined if these kinematic features reflect effector-independent mechanisms by asking participants to reach toward and to grasp objects of different widths with their hand and foot. First, during both reaching and grasping, the velocity profile up to peak velocity matched between the hand and the foot, indicating a shared ballistic acceleration phase. Second, maximum grip aperture and time of maximum grip aperture of grasping increased with object size for both effectors, indicating encoding of object size during transport. Differences between the hand and foot were found in the deceleration phase and time of maximum grip aperture, likely due to biomechanical differences and the participants' inexperience with foot actions. These findings provide evidence for effector-independent visuomotor mechanisms of reaching and grasping that generalize across body parts. [ABSTRACT FROM AUTHOR]

Precise foot placement is dependent on changes in spatial and temporal coordination between two legs in response to a perturbation during walking. Here, we used a 'virtual' split-belt adaptation task to examine the effects of reinforcement (reward and punishment) feedback about foot placement on the changes in error, step length and step time asymmetry. Twenty-seven healthy adults (20 ± 2.5 years) walked on a treadmill with continuous feedback of the foot position and stepping targets projected on a screen, defined by a visuomotor gain for each leg. The paradigm consisted of a baseline period (same gain on both legs), visuomotor adaptation period (split: one high = 'fast', one low = 'slow' gain) and post-adaptation period (same gain). Participants were divided into 3 groups: control group received no score, reward group received increasing score for each target hit, and punishment group received decreasing score for each target missed. Re-adaptation was assessed 24 ± 2 h later. During early adaptation, the slow foot undershot and fast foot overshot the stepping target. Foot placement errors were gradually reduced by late adaptation, accompanied by increasing step length asymmetry (fast < slow step length) and step time asymmetry (fast > slow step time). Only the punishment group showed greater error reduction and step length re-adaptation on the next day. The results show that (1) explicit feedback of foot placement alone drives adaptation of both step length and step time asymmetry during virtual split-belt walking, and (2) specifically, step length re-adaptation driven by visuomotor errors may be enhanced by punishment feedback. [ABSTRACT FROM AUTHOR]

Relative visual information has been shown to mediate grasping responses directed to an area previously occupied by a target object (i.e., pantomime-grasping) and is an information type functionally distinct from the absolute visual information supporting naturalistic grasping (i.e., grasping a physical target). Pantomime- and naturalistic grasps differ not only in terms of their visual properties, but also because the former lacks physical interaction with a target object (i.e., no-haptic feedback). The absence of haptic feedback may represent a reason why pantomime- and naturalistic grasps differ. To address this issue, participants completed pantomime-grasps to objects embedded in fins-in and fins-out configurations of the Müller-Lyer (ML) illusion following a 2000-ms visual delay when haptic feedback was unavailable (H− condition), and when experimentally induced (H+ condition). In particular, in the H+ condition the experimenter placed a physical target object between participants' thumb and forefinger after they completed their grasping response. H− and H+ conditions were performed when online vision was available (i.e., Experiment 1) and when withdrawn (i.e., Experiment 2). If haptic feedback influences grasping, then the absolute information afforded from physically touching a target object (i.e., the H+ condition) should result in aperture metrics that are refractory-or attenuated-to the relative properties of the ML figures. Grip apertures in H− and H+ conditions were 'tricked' in a direction consistent with the perceptual effects of the ML illusion; however, Experiment 2 showed that illusory effects were attenuated in the H+ condition. In other words, responses without online vision showed evidence of a visuo-haptic calibration. These results provide convergent evidence that haptic and visual feedback play a salient role in considering the extant literature's documented report of kinematic differences between pantomime- and naturalistic grasps. [ABSTRACT FROM AUTHOR]

The neural systems responsible for postural control are separate from the neural substrates that underpin control of the hand. Nonetheless, postural control and eye-hand coordination are linked functionally. For example, a stable platform is required for precise manual control tasks (e.g. handwriting) and thus such skills often cannot develop until the child is able to sit or stand upright. This raises the question of the strength of the empirical relationship between measures of postural stability and manual motor control. We recorded objective computerised measures of postural stability in stance and manual control in sitting in a sample of school children ( n = 278) aged 3-11 years in order to explore the extent to which measures of manual skill could be predicted by measures of postural stability. A strong correlation was found across the whole sample between separate measures of postural stability and manual control taken on different days. Following correction for age, a significant but modest correlation was found. Regression analysis with age correction revealed that postural stability accounted for between 1 and 10 % of the variance in manual performance, dependent on the specific manual task. These data reflect an interdependent functional relationship between manual control and postural stability development. Nevertheless, the relatively small proportion of the explained variance is consistent with the anatomically distinct neural architecture that exists for 'gross' and 'fine' motor control. These data justify the approach of motor batteries that provide separate assessments of postural stability and manual dexterity and have implications for therapeutic intervention in developmental disorders. [ABSTRACT FROM AUTHOR]

Previous research has demonstrated faster reaction times in response to appropriately oriented action-inducing stimuli (affordance effect, e.g. Tucker and Ellis in J Exp Psychol Hum Percept Perform 24:830-846, ). However, it has been argued that faster responses may be due to a spatial compatibility effect. In the current investigation, we aimed to dissociate the affordance and spatial compatibility effects. Moreover, we explored these effects beyond button-press responses by measuring detailed kinematics of the arms and hands during a naturalistic reach response. Participants were presented with images of a door handle (affording) or an abstract (non-affording) stimulus and made a pantomimed reach response with either hand depending on a colour change of the stimulus (i.e. Blue = left, Green = right). Stimuli could be aligned as spatially compatible or incompatible with the responding hand. The colour change occurred after a delay of 0, 500 or 1,000 ms. Only spatially compatible affordance stimuli facilitated reach onset compared to other stimuli and compatibility combinations, replicating previous reaction time studies. Therefore, in the absence of graspable stimuli, spatial compatibility alone was not sufficient to facilitate reach onset. There was also a larger outwards deviation of reach trajectory for spatially incompatible abstract stimuli compared to spatially compatible abstract stimuli, which waned with stimulus onset delay. However, no such affect was observed for the affording stimuli. Accordingly, later kinematics of the reaching action was influenced by the spatial compatibility of the stimulus alone. Overall, the dissociation of affordance and spatial compatibility effects suggests that these effects are driven by visuomotor priming and the inhibition of the incompatible spatial location, respectively. [ABSTRACT FROM AUTHOR]

Right-hand preference has been demonstrated for visually guided reaching and grasping. Grasping, however, requires the integration of both visual and haptic cues. To what extent does vision influence hand preference for grasping? Is there a hand preference for haptically guided grasping? Two experiments were designed to address these questions. In Experiment 1, individuals were tested in a reaching-to-grasp task with vision (sighted condition) and with hapsis (blindfolded condition). Participants were asked to put together 3D models using building blocks scattered on a tabletop. The models were simple, composed of ten blocks of three different shapes. Starting condition (Vision-First or Hapsis-First) was counterbalanced among participants. Right-hand preference was greater in visually guided grasping but only in the Vision-First group. Participants who initially built the models while blindfolded (Hapsis-First group) used their right hand significantly less for the visually guided portion of the task. To investigate whether grasping using hapsis modifies subsequent hand preference, participants received an additional haptic experience in a follow-up experiment. While blindfolded, participants manipulated the blocks in a container for 5 min prior to the task. This additional experience did not affect right-hand use on visually guided grasping but had a robust effect on haptically guided grasping. Together, the results demonstrate first that hand preference for grasping is influenced by both vision and hapsis, and second, they highlight how flexible this preference could be when modulated by hapsis. [ABSTRACT FROM AUTHOR]

The temporal delay between sensory input and motor execution is a fundamental constraint in interactions with the environment. Predicting the temporal course of a stimulus and dynamically synchronizing the required action with the stimulus are critical for offsetting this constraint, and this prediction-synchronization capacity can be tested using visual tracking of a target with predictable motion. Although the role of temporal prediction in visual tracking is assumed, little is known of how internal predictions interact with the behavioral outcome or how changes in the cognitive state influence such interaction. We quantified and compared the predictive visual tracking performance of military volunteers before and after one night of sleep deprivation. The moment-to-moment synchronization of visual tracking during sleep deprivation deteriorated with sensitivity changes greater than 40 %. However, increased anticipatory saccades maintained the overall temporal accuracy with near zero phase error. Results suggest that acute sleep deprivation induces instability in visuomotor prediction, but there is compensatory visuomotor adaptation. Detection of these visual tracking features may aid in the identification of insufficient sleep. [ABSTRACT FROM AUTHOR]

The underlying neural mechanisms of a perceptual bias for in-phase bimanual coordination movements are not well understood. In the present study, we measured brain activity with functional magnetic resonance imaging in healthy subjects during a task, where subjects performed bimanual index finger adduction-abduction movements symmetrically or in parallel with real-time congruent or incongruent visual feedback of the movements. One network, consisting of bilateral superior and middle frontal gyrus and supplementary motor area (SMA), was more active when subjects performed parallel movements, whereas a different network, involving bilateral dorsal premotor cortex (PMd), primary motor cortex, and SMA, was more active when subjects viewed parallel movements while performing either symmetrical or parallel movements. Correlations between behavioral instability and brain activity were present in right lateral cerebellum during the symmetric movements. These findings suggest the presence of different error-monitoring mechanisms for symmetric and parallel movements. The results indicate that separate areas within PMd and SMA are responsible for both perception and performance of ongoing movements and that the cerebellum supports symmetric movements by monitoring deviations from the stable coordination pattern. [ABSTRACT FROM AUTHOR]

Visual information about the hand, the reach space, and a target can all contribute to the control of a reaching movement. When visual information is removed, both feedforward mechanisms (involved in planning the movement) and feedback mechanisms (involved in correcting errors) may be affected. This study looks at how 4- to 5-year-old children use visual information to guide reaching movements. Children reached for a toy object in four conditions-in the light, in the dark while the toy was glowing, and in complete darkness after a 0-s delay and a 4-s delay. When a reach in the glowing condition was compared with a reach in the light, reaches were more curved, had a longer duration, and earlier time-to-peak-velocity than a reach in the light but the number of grasping responses were comparable to in the light condition. When a reach in the two dark conditions (0- and 4-s) was compared with a reach in the light, the number of grasping responses decreased and 14 and 31 % of reaches resulted in a miss, that is, no contact was made with the object. While we did not find any significant kinematic differences between the 0- and 4-s dark conditions, there was a significantly larger number of misses in the 4-s dark condition, suggesting that memory of target position may decay over time. Overall, removing vision of the hand and reach space in the glowing condition appears to affect the planning of a reach (as vision of the hand was not available at reach initiation) and feedback control, while removing vision of the object in the dark conditions has an effect on endpoint response as we found that children experience difficulty retrieving the object in the dark. While young children demonstrate more adult-like reach control (i.e., relatively longer deceleration time, increased reach duration) under reduced feedback conditions, they have difficulty retrieving the object in the dark, particularly after a 4-s delay, and it is possible that mechanisms guiding predictive control and visual memory are still developing. [ABSTRACT FROM AUTHOR]

Visuomotor-adaptation experiments devoted to the study of plasticity are also used to indirectly test hypotheses about how the brain encodes the spatio-temporal characteristics of arm movement directed at a visual target. A current major theory, the vectorial coding hypothesis, postulates that arm movements are processed differentially for direction and amplitude. This approach, at first developed in an extrinsic Cartesian frame of references, has been also adopted in an intrinsic joint space. In the present paper, we report an experiment that corroborates this last point of view. Subjects performed pointing movements in a one degree of freedom condition, while systematic self-attributed endpoint errors were introduced. Through an observation of motor behavior in a battery of pre- and post-tests, we suggested that adaptation consisted in an increase in the motor gain in the adapted direction, with a perfect transfer to all starting points in the experimental reaching space. We explained the results by the absence of intersensory conflict and of correlative sensory adaptive component. As this paradigm was adapted from the saccadic adaptation paradigm, we eventually compared the two paradigms and highlighted that both induced mostly motor effects. [ABSTRACT FROM AUTHOR]

Studies on visuomotor adaptation provide crucial clues on the functional properties of the human motor system. The widely studied saccadic adaptation paradigm is a major example of such a fruitful field of investigation. Magescas and Prablanc (J Cogn Neurosci 18(1):75-83, ) proposed a transposition of this protocol to arm pointing behavior, by designing an experiment in which the informational context of the upper limb visuomotor system is comparable to that of the saccadic system. Subjects were given terminal only visual feedback in a hand pointing task, assumed to produce a purely terminal visual error signal. Importantly, this paradigm has been shown to induce no saccadic adaptation. Although the saccadic adaptation paradigm is known to induce a predominantly motor adaptation with minor sensory effects, the lack of sensory changes has not been tested in its transposition to pointing. The present study was a partial replication of Magescas and Prablanc's (J Cogn Neurosci 18(1):75-83, ) study with additional control tests. A first experiment searched for a possible change in the static visual-to-proprioceptive congruency. A second experiment, based on an anti-pointing task, aimed at separating the sensory and motor effects of the adaptation in a dynamic condition. Consistent with most results on saccadic adaptation, we found a predominant adaptation of the motor components, with little if any involvement of the sensory components. Results are interpreted by proposing a causal relationship between the type of error signal and its adaptive effects. [ABSTRACT FROM AUTHOR]

Recent research has demonstrated that adaptation to a visuomotor distortion systematically influenced movements to auditory targets in adults and typically developing (TD) children, suggesting that the adaptation of spatial-to-motor transformations for reaching movements is multisensory (i.e., generalizable across sensory modalities). The multisensory characteristics of these transformations in children with developmental coordination disorder (DCD) have not been examined. Given that previous research has demonstrated that children with DCD have deficits in sensorimotor integration, these children may also have impairments in the formation of multisensory spatial-to-motor transformations for target-directed arm movements. To investigate this hypothesis, children with and without DCD executed discrete arm movements to visual and acoustic targets prior to and following exposure to an abrupt visual feedback rotation. Results demonstrated that the magnitudes of the visual aftereffects were equivalent in the TD children and the children with DCD, indicating that both groups of children adapted similarly to the visuomotor perturbation. Moreover, the influence of visuomotor adaptation on auditory-motor performance was similar in the two groups of children. This suggests that the multisensory processes underlying adaptation of spatial-to-motor transformations are similar in children with DCD and TD children. [ABSTRACT FROM AUTHOR]

The premotor-parietal network for preparation of visually guided reaching demonstrates activity mainly contralateral to the reaching arm in men but bilaterally in women. These sex differences are most prominent in the dorsal premotor cortex (PMd); however, the functional implications of these differences remain unclear. Therefore, in the experiments described here, we used continuous theta burst stimulation (cTBS) to test hypotheses regarding the roles of PMd both contralateral and ipsilateral to the reaching arm in men and in women. Inhibitory cTBS of the ipsilateral PMd did not have a significant effect on reaction time in either men or women. However, cTBS of the contralateral PMd resulted in a slowed mean reaction time in men but not in women. Movement times were unaffected by stimulation applied to either hemisphere. These results suggest the presence of sex differences in processing within the left PMd during visually guided reaching movements using the right arm. Further, when taken together, the results suggest that ipsilateral PMd activity in women may not be functionally necessary for reaching movements. Rather, this ipsilateral activity may provide a protective redundancy that can compensate for decreased activity from the contralateral PMd. The observation of sex differences in reaction times but not in movement times following cTBS to the contralateral hemisphere suggests that these sex differences are more strongly associated with movement planning than with motor execution. [ABSTRACT FROM AUTHOR]

The ability to correct reaching movements for changes in target position has been described as the hand's 'automatic pilot'. These corrections are preconscious and occur by default in double-step reaching tasks, even if the goal is to react to the target jump in some other way, for instance by stopping the movement (STOP instruction). Nonetheless, corrections are strongly modulated by conscious intention: participants make more corrections when asked to follow the target (GO instruction) and can suppress them when explicitly asked not to follow the target (NOGO instruction). We studied the influence of a cognitively demanding (auditory 1-back) task upon correction behaviour under GO, STOP and NOGO instructions. Correction rates under the STOP instruction were unaffected by cognitive load, consistent with the assumption that they reflect the default behaviour of the automatic pilot. Correction rates under the GO instruction were also unaffected, suggesting that minimal cognitive resources are required to enhance online correction. By contrast, cognitive load impeded the ability to suppress online corrections under the NOGO instruction. These data reveal a constitutional bias in the automatic pilot system: intentional suppression of the default correction behaviour is cognitively demanding, but enhancement towards greater responsiveness is seemingly effortless. [ABSTRACT FROM AUTHOR]

The observer’s motor system has been shown to be involved in observing the actions of another person. Recent findings suggest that people with Parkinson’s disease do not show the same motor facilitatory effects when observing the actions of another person. We studied whether Parkinson’s patients were able to make unspeeded judgements about another person’s action. Participants were asked to watch video clips of an actor lifting a box containing different weights (100, 200, 300 or 400 g) and to guess the weight that was being lifted on a 9-point scale. We compared the performance of 16 patients with PD with 16 healthy age-matched controls. Both groups were able to do the task, showing a significant relationship between the real weight and the guessed weight, albeit with a tendency to overestimate the lowest weight and underestimate the heaviest weight. The PD patients, however, showed a reduced slope value. These results show that despite their own motor deficits, PD patients are still able to judge the weight being lifted by another person, albeit with a slight reduction in accuracy. Further research will be required to determine whether PD patients use a motor simulation or a visual compensatory strategy to achieve this. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

It is well established that listening to music can modify subjects’ cognitive performance. The present study evaluates whether this so-called Mozart Effect extends beyond cognitive tasks and includes sensorimotor adaptation. Three subject groups listened to musical pieces that in the author’s judgment were serene, neutral, or sad, respectively. This judgment was confirmed by the subjects’ introspective reports. While listening to music, subjects engaged in a pointing task that required them to adapt to rotated visual feedback. All three groups adapted successfully, but the speed and magnitude of adaptive improvement was more pronounced with serene music than with the other two music types. In contrast, aftereffects upon restoration of normal feedback were independent of music type. These findings support the existence of a “Mozart effect” for strategic movement control, but not for adaptive recalibration. Possibly, listening to music modifies neural activity in an intertwined cognitive–emotional network. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Recent work by our group reported that mirror-symmetrical reaching movements (i.e., antipointing) are supported by perception-based visual information (Heath et al. ). The present study was designed to determine if the perception-based visual information supporting antipointing results in a primarily offline mode of control; that is, a mode of control wherein the response unfolds with few—if any—online limb corrections. Participants reached directly to (propointing) or mirror-symmetrical (antipointing) to targets presented in the left and right visual fields. To examine the extent reaches were controlled online versus offline, we computed the proportion of variance ( R2) explained by the position of the limb at 75% of movement time relative to the response’s ultimate movement endpoint. The endpoints for propointing in left and right visual fields demonstrated robust endpoint accuracy and stability and were tied to low R2 values. In contrast, antipointing elicited a marked degree of endpoint variability and were characterized by a visual-field specific pattern of endpoint bias. Moreover, the R2 values for antipointing were more robust than propointing counterparts. Therefore, we propose that the metrical visual information supporting stimulus-driven propointing results in a primarily online mode of control whereas the relative nature of the perception-based visual information supporting antipointing results in an offline mode of control. More directly, we propose that the offline control of antipointing is attributed to the “slow” cognitive processing of visuoperceptual networks. [ABSTRACT FROM AUTHOR]

When searching for a target with eye movements, saccades are planned and initiated while the visual information is still being processed, so that subjects often make saccades away from the target and then have to make an additional return saccade. Presumably, the cost of the additional saccades is outweighed by the advantage of short fixations. We previously showed that when the cost of passing the target was increased, by having subjects manually move a window through which they could see the visual scene, subjects still passed the target and made return movements (with their hand). When moving a window in this manner, the eyes and hand follow the same path. To find out whether the hand still passes the target and then returns when eye and hand movements are uncoupled, we here compared moving a window across a scene with moving a scene behind a stationary window. We ensured that the required movement of the hand was identical in both conditions. Subjects found the target faster when moving the window across the scene than when moving the scene behind the window, but at the expense of making larger return movements. The relationship between the return movements and movement speed when comparing the two conditions was the same as the relationship between these two when comparing different window sizes. We conclude that the hand passing the target and then returning is not directly related to the eyes doing so, but rather that moving on before the information has been fully processed is a general principle of visuomotor control. [ABSTRACT FROM AUTHOR]

We often complete step downs in the absence of visual feedback of the lower-limbs, and/or of the area on the ground where we intend to land (e.g. when descending a step whilst carrying a laundry basket). Therefore, the present study examined whether information from lower visual field (lvf) provides any advantage to the control of step descent. Ten healthy subjects (age 24.4 ± 9.4 years) completed repeated step downs over three-step heights with visual information available from either full or upper visual fields (lvf occluded), and for specific intervals relative to step initiation. Visuomotor control of step descent was assessed by determining pre-landing kinematic measures and landing mechanic variables for the initial landing period. Findings indicate that whilst there were only limited effects on pre-landing kinematic measures under lvf occlusion, individual’s ability to plan/control landing mechanics was significantly different in such conditions compared to when they had access to full field vision. These changes were consistent with participants being uncertain regarding precise floor height when access to lvf was restricted, and consequently led them to adapt their landing behaviour but without fundamentally altering their stepping strategy. Compared to when vision was available throughout, the occlusion of vision (full or upper visual field) from toe-off or mid-swing onwards caused very few differences in landing behaviour. This suggests that the contribution of information from lvf to the control of landing behaviour occurs predominantly prior to or during movement initiation and that ‘online’ vision is used only in the latter portion of the descent phase to subtly ‘fine tune’ landings. [ABSTRACT FROM AUTHOR]

Despite early neurological reports of gait abnormalities in Williams syndrome (WS), a rare genetically based neurodevelopmental disorder, there has not yet been any systematic investigation of gait dysfunction in this disorder. The current study examined the gait characteristics in adults with WS and a neurologically normal control group as they walked at self-selected slow, preferred and fast speeds using the GAITRite walkway. The WS group showed hypokinetic gait, which manifested as reduced gait speed and stride length, but with a disproportionate increase in cadence (stepping frequency) as speed was increased. The WS group also showed increased variability of stride length and a broad based stepping pattern implicating a compensatory strategy for postural instability. Performance IQ correlated significantly with stride length in the WS group. While these results should be considered preliminary due to the small sample size, these findings have implications for our understanding of the neural basis of gait dysfunction in WS. [ABSTRACT FROM AUTHOR]

We sought to determine whether mirror-symmetrical limb movements (so-called anti-pointing) elicit a pattern of endpoint bias commensurate with perceptual judgments. In particular, we examined whether asymmetries related to the perceptual over- and under-estimation of target extent in respective left and right visual space impacts the trajectories of anti-pointing. In Experiment 1, participants completed direct (i.e. pro-pointing) and mirror-symmetrical (i.e. anti-pointing) responses to targets in left and right visual space with their right hand. In line with the anti-saccade literature, anti-pointing yielded longer reaction times than pro-pointing: a result suggesting increased top-down processing for the sensorimotor transformations underlying a mirror-symmetrical response. Most interestingly, pro-pointing yielded comparable endpoint accuracy in left and right visual space; however, anti-pointing produced an under- and overshooting bias in respective left and right visual space. In Experiment 2, we replicated the findings from Experiment 1 and further demonstrate that the endpoint bias of anti-pointing is independent of the reaching limb (i.e. left vs. right hand) and between-task differences in saccadic drive. We thus propose that the visual field-specific endpoint bias observed here is related to the cognitive (i.e. top-down) nature of anti-pointing and the corollary use of visuo-perceptual networks to support the sensorimotor transformations underlying such actions. [ABSTRACT FROM AUTHOR]

Even though there have been extensive investigations of the temporal integration limits of binocular vision in perceptual tasks, relatively little is known about temporal integration limits during the completion of visuomotor tasks. To assess the temporal integration limits of binocular disparity within the action domain, accuracy of reach kinematics in a reaching and grasping task under continuous binocular and monocular viewing conditions were compared with those obtained under alternating monocular viewing conditions with interocular delays ranging from 14 to 58 ms. Even the shortest of the interocular delays resulted in larger grip apertures than those in the continuous monocular and binocular viewing conditions. The short temporal integration interval of stereovision obtained in this study cannot be accounted for by differential visual feedback in the binocular and interocular delay conditions, nor is it likely to be a consequence of visual disruption due to the interocular delays. Our findings suggest that the visuomotor system has little tolerance to interocular delay. [ABSTRACT FROM AUTHOR]

A recent study by our group showed that the scaling of reach trajectories to target size is independent of conscious visual awareness of that intrinsic target property (Binsted et al. in Proc Natl Acad Sci USA 104:12669–12672, ). The present investigation sought to extend previous work and determine whether unconscious target information represents a temporally durable or evanescent visuomotor characteristic. To accomplish that objective, we employed Di Lollo et al’s (J Exp Psychol Gen 129:481–507, ) object substitution masking paradigm and asked participants to complete verbal reports and reaching responses to different sized (1.5, 2.5, 3.5, 4.5, 5.5 cm) targets under masked and non-masked target conditions. To determine whether visuomotor networks retain unconscious target information, reaching trials were cued concurrent with target presentation or 1,000 or 2,000 ms after target presentation. For the perceptual trials, participants readily identified the size of non-masked trials but demonstrated only chance success identifying target size during masked trials. Interestingly, however, reaches directed to non-masked and masked targets exhibited comparable and robust scaling with target size; that is, lawful speed-accuracy relations related to movement planning and execution times were observed regardless of whether participants were aware (i.e., non-masked trials) or unaware (i.e., masked trials) of target size. What is more, the length of the visual delay period used here did not differentially influence the scaling of reach trajectories. These results indicate that a conscious visual percept is not necessary to support motor output and that unconscious visual information persists in visuomotor networks to support the kinematic parameterization of action. [ABSTRACT FROM AUTHOR]

Visual guidance of forwards, sideways, and upwards stepping has been investigated, but there is little knowledge about the visuomotor processes underlying stepping down actions. In this study we investigated the visual control of a single vertical step. We measured which aspects of the stepping down movement scaled with visual information about step height, and how this visual control varied with binocular versus monocular vision. Subjects stepped down a single step of variable and unpredictable height. Several kinematic measures were extracted including a new measure, “kneedrop”. This describes a transition in the movement of the lower leg, which occurs at a point proportional to step height. In a within-subjects design, measurements were made with either full vision, monocular vision, or no vision. Subjects scaled kneedrop relative to step height with vision, but this scaling was significantly impaired in monocular and no vision conditions. The study establishes a kinematic marker of visually controlled scaling in single-step locomotion which will allow further study of the visuomotor control processes involved in stepping down. [ABSTRACT FROM AUTHOR]

We sought to determine the extent to which colour (and luminance) signals contribute towards the visuomotor localization of targets. To do so we exploited the movement-related illusory displacement a small stationary window undergoes when it has a continuously moving carrier grating behind it. We used drifting (1.0–4.2 Hz) red/green-modulated isoluminant gratings or yellow/black luminance-modulated gratings as carriers, each curtailed in space by a stationary, two-dimensional window. After each trial, the perceived location of the window was recorded with reference to an on-screen ruler (perceptual task) or the on-screen touch of a ballistic pointing movement made without visual feedback (visuomotor task). Our results showed that the perceptual displacement measures were similar for each stimulus type and weakly dependent on stimulus drift rate. However, while the visuomotor displacement measures were similar for each stimulus type at low drift rates (<4 Hz), they were significantly larger for luminance than colour stimuli at high drift rates (>4 Hz). We show that the latter cannot be attributed to differences in perceived speed between stimulus types. We assume, therefore, that our visuomotor localization judgements were more susceptible to the (carrier) motion of luminance patterns than colour patterns. We suggest that, far from being detrimental, this susceptibility may indicate the operation of mechanisms designed to counter the temporal asynchrony between perceptual experiences and the physical changes in the environment that give rise to them. We propose that perceptual localisation is equally supported by both colour and luminance signals but that visuomotor localisation is predominantly supported by luminance signals. We discuss the neural pathways that may be involved with visuomotor localization. [ABSTRACT FROM AUTHOR]

In the present study, we measured spontaneous hand preference in a “natural” grasping task. We asked right- and left-handed subjects to put a puzzle together or to create different LEGO© models, as quickly and as accurately as possible, without any instruction about which hand to use. Their hand movements were videotaped and hand preference for grasping in ipsilateral and contralateral space was measured. Right handers showed a marked preference for their dominant hand when picking up objects; left handers, however, did not show this preference and instead used their right hand 50% of the time. Furthermore, compared to right handers, left handers used their non-dominant hand significantly more often to pick up objects in ipsilateral as well as contralateral space. Our results show that handedness in left handers does not extend to precision grasp and suggest that right handedness for visuomotor control may reflect a universal left-hemisphere specialization for this class of behaviour. [ABSTRACT FROM AUTHOR]

During the last 10 years a considerable number of neurophysiological and functional imaging studies have provided evidence that observation and execution of movements activate common representations. Furthermore, several behavioural studies suggest that action observation can influence the performance of movements. Recently it was shown that viewing incongruent movements interferes with the execution of non-object oriented sinusoidal arm movements (Kilner et al. in Curr Biol 13:522–525, ). In the current study, we investigated whether interference of action observation also occurs during goal-directed prehension movements. Participants were required to grasp cubes of different sizes while simultaneously observing an actor performing grasping or pointing movements. The actors’ movement could be directed at objects that were identical, or different in size to the cube grasped by the participant. The results showed that maximum grip aperture was affected by observation of grasping towards larger objects. No effect of object size was found during observation of pointing movements. These results suggest that observation of grasping movements can interfere with the on-line control of prehension movements and provides further evidence for overlapping networks for grasping observation and execution. [ABSTRACT FROM AUTHOR]

Movement of the body, head, or eyes with respect to the world creates one of the most common yet complex situations in which the visuomotor system must localize objects. In this situation, vestibular, proprioceptive, and extra-retinal information contribute to accurate visuomotor control. The utility of retinal motion information, on the other hand, is questionable, since a single pattern of retinal motion can be produced by any number of head or eye movements. Here we investigated whether retinal motion during a smooth pursuit eye movement contributes to visuomotor control. When subjects pursued a moving object with their eyes and reached to the remembered location of a separate stationary target, the presence of a moving background significantly altered the endpoints of their reaching movements. A background that moved with the pursuit, creating a retinally stationary image (no retinal slip), caused the endpoints of the reaching movements to deviate in the direction of pursuit, overshooting the target. A physically stationary background pattern, however, producing retinal image motion opposite to the direction of pursuit, caused reaching movements to become more accurate. The results indicate that background retinal motion is used by the visuomotor system in the control of visually guided action. [ABSTRACT FROM AUTHOR]

Ample evidence exists that the cerebellum is involved in associative motor learning, particularly in eyeblink-conditioning. In visuomotor associative learning the role of the cerebellum is less clear. One open question is whether cerebellar patients’ deficits in visuomotor learning are present both in a stimulus-response and a stimulus-stimulus-response association task. Twelve patients with cerebellar degeneration and 12 healthy matched control subjects participated. A magnetic resonance imaging (MRI) volumetric analysis of the cerebellum was performed to assess the degree of cerebellar atrophy. In a blocked design, subjects had to learn the association between one color square or two color squares and a right or left key press. In the latter condition, the two colors were shown one after the other in the same sequence except for two blocks at the end of the experiment. Overall, cerebellar subjects reacted significantly slower than controls. In both groups, reaction time decreased over blocks, and the learning effect was more pronounced in the stimulus-response than in the stimulus-stimulus-response condition.Post hocanalyses revealed that learning differences between conditions were significant in cerebellar patients but not control subjects. Furthermore, only healthy subjects were irritated, i.e., they significantly increased reaction times in the blocks with reversed sequence in the stimulus-stimulus-response condition. Cerebellar subjects tended to name less correct stimulus-stimulus-response associations after the experiment. Finally, cerebellar volume correlated with parameters of motor performance, but not learning. In conclusion, cerebellar patients showed deficits in stimulus-stimulus-response, but not stimulus-response learning. Future experiments are needed to differentiate between possible deficits in learning the stimulus-stimulus association, use of sequence information, and/or impaired motor performance interfering with learning. [ABSTRACT FROM AUTHOR]

In various studies subjects have been shown to misperceive the positions of targets that are flashed during pursuit eye movements. They mislocalise them in the direction of pursuit. Nevertheless, Hansen (1979) found that subjects accurately hit targets that are flashed during pursuit with a quick hammer blow. We examined whether this is because there is a fundamental difference between the information that determines our perceptual judgements of a target’s position and the information that is used to guide our hand to a similar target. Subjects were asked to quickly tap targets that were flashed during pursuit with their index finger. They systematically tapped ahead of the position of the flash, in accordance with the above-mentioned perceptual mislocalisations. Thus the lack of systematic errors in Hansen’s study is not a general property of fast motor responses. [ABSTRACT FROM AUTHOR]

The pedunculopontine tegmental nucleus (PPT) projects its cholinergic fibers to both the lateralis medialis-suprageniculate nucleus (LM-Sg) and the superior colliculus (SC). For the purpose of verification of whether a single neuron in the PPT projects to both the LM-Sg and the SC, we injected dextran tetramethylrhodamine (DR) into the LM-Sg and dextran fluorescein (DF) into the ipsilateral SC. The DR-positive neurons labeled retrogradely in the PPT are small (mean: 27.13±1.22 µm) and distributed in the rostral two-thirds of this nucleus, whereas the DF-positive neurons are small (mean: 27.54±1.16 µm) or medium-sized (mean: 40.18±1.43 µm), and are located throughout the PPT. Thirty-five percent of all labeled neurons are double-labeled and small. The present study indicates that the PPT projection to the LM-Sg in part involves neurons bifurcating to the SC. [ABSTRACT FROM AUTHOR]

Eye–hand coordination is geometrically complex. To compute the location of a visual target relative to the hand, the brain must consider every anatomical link in the chain from retinas to fingertips. Here we focus on the first three links, studying how the brain handles information about the angles of the two eyes and the head. It is known that people, even in darkness, reach more accurately when the eye looks toward the target, rather than right or left of it. We show that reaching is also impaired when the binocular fixation point is displaced from the target in depth: reaching becomes not just sloppy, but systematically inaccurate. Surprisingly, though, in normal Gaze-On-Target reaching we found no strong correlations between errors in aiming the eyes and hand onto the target site. We also asked people to reach when the head was not facing the target. When the eyes were on-target, people reached accurately, but when gaze was off-target, performance degraded. Taking all these findings together, we suggest that the brain's computational networks have learned the complex geometry of reaching for well-practiced tasks, but that the networks are poorly calibrated for less common tasks such as Gaze-Off-Target reaching. [ABSTRACT FROM AUTHOR]

Many authors have performed experiments in which subjects grasp objects in illusory surroundings. The vast majority of these studies report that illusions affect the maximum grip aperture less than they affect the perceived size. This observation has frequently been regarded as experimental evidence for separate visual systems for perception and action. In order to make this conclusion, one assumes that the grip aperture is based on a visual estimate of the object's size. We believe that it is not, and that this is why size illusions fail to influence grip aperture. Illusions generally do not affect all aspects of space perception in a consistent way, but mainly affect the perception of specific spatial attributes. This applies not only to object size, but also to other spatial attributes such as position, orientation, displacement, speed, and direction of motion. Whether an illusion influences the execution of a task will therefore depend on which spatial attributes are used rather than on whether the task is perceptual or motor. To evaluate whether illusions affect actions when they influence the relevant spatial attributes we review experimental results on various tasks with inconsistent spatial processing in mind. Doing so shows that many actions are susceptible to visual illusions. We argue that the frequently reported differential effect of illusions on perceptual judgements and goal-directed action is caused by failures to ensure that the same spatial attributes are used in the two tasks. Illusions only affect those aspects of a task that are based on the spatial attributes that are affected by the illusion. [ABSTRACT FROM AUTHOR]

In order to assess the effect of rehearsal by eye movement alone on visuomotor performance, the eye movements and visually guided stepping of two cerebellar patients were monitored before and after a first and second batch of eye-movement rehearsals, in which patients made saccadic eye movements to the first 6 footfall targets (in a sequence of 18) whilst standing stationary at the start of the walkway. There was a marked improvement in oculomotor and locomotor performance following the second batch of eye-movement rehearsal. Both patients showed reduced occurrence of saccadic dysmetria, evident as a significant increase in the proportion of single to multi-saccadic eye movements (from 46 to 77% for DB and from 75 to 94% for TP). This was accompanied by increased regularity and accuracy of stepping in both patients, and decreased stance and double support phase durations (one patient only). Separate testing confirmed that these improvements in eye movements and stepping did not result from simple repetition of the task. This is the first demonstration of a technique – rehearsal by eye movement – that improves the visuomotor performance of cerebellar patients. It is compelling evidence for our proposal that during visually guided stepping the locomotor control system is dependent on assistance from the oculomotor control system. [ABSTRACT FROM AUTHOR]

In a series of three separate experiments, we studied two different orientation illusions, in both of which vertical lines appear tilted as a result of being set against a tilted background pattern. The 'simultaneous tilt illusion' (STI), in which a target grating is viewed within an abutting tilted grating surround, is thought to originate early in the cortical processing of visual contours. In contrast, the 'rod-and-frame' illusion (RFI), which is induced by a distant tilted frame, is thought to originate much later in the perceptual processing system. In the first two experiments we found that orientation-guided action was virtually impervious to the RFI, whereas both perceptual experience and action were equally influenced by the STI. In the third experiment, in which the two illusions were pitted one against the other, an opposite pattern of effects emerged, such that visuomotor performance was now deceived by the illusion much more than was perceptual experience. This pattern of association and dissociation in the effects of visual illusions on perception versus action can best be explained within a two-visual-systems model of cortical processing. [ABSTRACT FROM AUTHOR]

Eight patients suffering from primary cerebellar degenerative diseases undertook a walkway task, demanding precise foot placement at each step, and a visual fixation task, requiring only eye movements. Step cycle and horizontal eye movements were recorded throughout the tasks and compared to those of healthy adults (including age- and sex-matched controls). Cerebellar patients displayed both locomotor and oculomotor deficits. Increases in duration of the stance, swing and double support phases of the step cycle were all shown to contribute to ataxic gait. Dysmetric saccades to fixate the footfall targets were seen more frequently in patients than in controls. These hypometric saccades were followed by one or more corrective saccades (patients: >45% accompanied by one or more corrective saccades; controls: <10% accompanied by a single corrective saccade). Similarities between the oculomotor deficits displayed by patients during the visual fixation task and when walking indicate that the latter are not merely a consequence of ataxic gait. The existence of several links between these locomotor and oculomotor deficits provides evidence for considerable interaction between the two control systems in the production of patterned eye and stepping movements. These results also suggest that the cerebellum plays an active role in the co-ordination of visually guided eye and limb movements during visually guided stepping. [ABSTRACT FROM AUTHOR]

Neurons in the premotor cortex of macaques respond to tactile, visual and auditory stimuli. The distribution of these responses was studied in five anesthetized monkeys. In each monkey, multiunit activity was studied at a grid of locations across the precentral gyrus. A cluster of sites with polysensory responses was found posterior to the genu of the arcuate sulcus. Tactile and visual responses were represented in all five monkeys, while auditory responses were rarer and found in only two monkeys. This polysensory zone (PZ) was located in the caudal part of premotor cortex. It varied in extent among the monkeys. It was mainly ventral to the genu of the arcuate, in the dorsal and caudal part of the ventral premotor cortex (PMv). In some monkeys it extended more dorsally, into the caudal part of dorsal premotor cortex (PMd). Sensory responses were almost never found in the rostral part of PMd. We suggest that the polysensory zone may contribute to the guidance of movement on the basis of tactile, visual and auditory signals. [ABSTRACT FROM AUTHOR]

Dysfunction of the cerebellum leads to significant deterioration of movements performed under visual guidance and of co-ordinated eye and hand movement. Visually guided tracking tasks combine both of these control features, as the eyes and hand together track a visual target. To better understand the involvement of the cerebellum in tracking tasks, we used functional magnetic-resonance imaging to study the activation of cerebellar structures in visually guided tracking movements of the eye and hand. Subjects were tested performing ocular tracking, manual tracking without eye movement or combined eye and hand tracking of a smoothly moving visual target. Three areas were activated in the cerebellum: a bilateral region in the ansiform lobule of the lateral hemisphere, a region in the ipsilateral paramedian lobule and a region in the oculomotor vermis. The ansiform and paramedian areas were most strongly activated by hand movement, although the vermal site was also active. The reverse was found for ocular tracking, with predominantly vermal activation. Activation of these cerebellar cortical areas related to movement of eyes or hand alone was significantly enhanced when the subjects performed co-ordinated eye and hand tracking of a visual target. These results provide the first direct evidence from a functional-imaging study for cerebellar activation in eye and hand co-ordination. [ABSTRACT FROM AUTHOR]

The aim of this study was to: (1) quantify errors in open-loop pointing toward a spatially central (but retinally peripheral) visual target with gaze maintained in various eccentric horizontal, vertical, and oblique directions; and (2) determine the computational source of these errors. Eye and arm orientations were measured with the use of search coils while six head-fixed subjects looked and pointed toward remembered targets in complete darkness. On average, subjects made small exaggerations in both the vertical and horizontal components of retinal displacement (tending to overshoot the target relative to current gaze), but individual subjects showed considerable variations in this pattern. Moreover, pointing errors for oblique retinal targets were only partially predictable from errors for the cardinal directions, suggesting that most of these errors did not arise within independent vertical and horizontal coordinate channels. The remaining variance was related to nonhomogeneous, direction-dependent distortions in reading out the magnitudes and directions of retinal displacement. The largest and most consistent nonhomogeneities occurred as discontinuities between adjacent points across the vertical meridian of retinotopic space, perhaps related to the break between the representations of space in the left and right cortices. These findings are consistent with the hypothesis that at least some of these visuomotor distortions are due to miscalibrations in quasi-independent visuomotor readout mechanisms for "patches" of retinotopic space, with major discontinuities existing between patches at certain anatomic and/or physiological borders. [ABSTRACT FROM AUTHOR]

We recently reported that subjects performing a task that requires visual guidance of each step onto irregularly placed 'stepping stones' usually fixate the next target of footfall just before they lift the foot to be repositioned, i.e. towards the end of that limb's stance phase. When negotiating the same walkway without ambient lighting, and with each stone's location indicated by a central light spot (LED), stepping and eye movements were unchanged. Under conditions of intermittent visual denial, in which all LEDs (the only visual cues) were temporarily extinguished at irregular intervals, temporal changes in the normal stepping pattern were sometimes observed, but stepping was not always affected. The primary effect of visual denial was on the leg that was in stance (foot in place on a stepping stone) at the moment of LED extinction, rather than on the leg that was in swing, and was an increase in stance duration, suggesting an effect on planning during this stance of the next swing towards the next target rather than on execution of the ongoing swing of the other leg. Subjects rarely failed to step onto the targets. Prolongations of stance under visual denial lasting 400 or 500 ms were less than 200 ms, much less than the duration of denial; subjects did not simply wait for the footfall target to reappear. There was no effect for denial lasting 300 ms; subjects performed as well as with a constantly visible target. Under 400 and 500 ms denial, there was no effect when the targets disappeared in the first 100 ms of stance (of the foot to be repositioned); stance durations were indistinguishable from control. This suggests that there is no crucial visuomotor processing by the control system(s) for eye and limb guidance until the target reappeared near the usual end of stance, when feedforward planning of the next saccade and/or swing to a target reaches a crucial stage, and is affected by intrusion of the period of visual denial. With longer (800 ms) denial there was an effect regardless of when in stance it began. A smaller effect of 800 ms denial sometimes visible in swing duration is attributable to interlimb coordination. Accurate saccades, followed by accurate steps, to the next target are almost always made, even when the target is invisible. Our results demonstrate that uninterrupted on-line visual information is not necessary for accurate stepping even when (as here) each step requires visual guidance. Also, since stance prolongations did not always result, and they were always much shorter than the periods of denial, we conclude that the visuomotor control mechanism(s) are robust in the face of substantial denial of all visual information including normally preferred inputs (foveal or peripheral images) at the normally preferred times. The fact that a saccade is still made to an invisible target location implies that this is useful in itself, since it does not result in a visible foveal image. We propose that skilled, visually guided stepping onto irregularly placed targets is executed under predominantly feedforward visuomotor control mechanisms, and suggest that the ability to function effectively in this way is dependent upon the integrity of the lateral cerebellum. [ABSTRACT FROM AUTHOR]

The pattern of the nigrotectal projection in Galago crassicaudatus was determined using retrograde and anterograde transport methods. These experiments revealed that pars reticulata and pars lateralis of the substantia nigra project to all layers of the ipsilateral and contralateral superior colliculus, except to layer I. The nigrotectal projection is not homogeneous, but is concentrated in particular collicular layers and sublayers, and the intensity and laminar distribution of the projection varies along the rostral-caudal dimension of the superior colliculus. The ipsilateral and contralateral nigrotectal projections are generally similar, except that a tier of dense label which is prominent in the ventral part of much of the ipsilateral layer IV is not obvious contralaterally; moreover, the contralateral projection is much sparser than the ipsilateral. Deposits of tracers at different medial-lateral locations within the substantia nigra did not result in different laminar patterns of anterogradely transported label in the superior colliculus. Based on the known connections and functions of the collicular layers and sublayers, the pattern and distribution of the nigrotectal projection suggests that the substantia nigra may use this pathway to gain access to particular components of vision- and visuomotor-related networks. [ABSTRACT FROM AUTHOR]

Movement of large visual scenes induces an illusion of self-motion (vection) and postural responses. We investigated if the conscious perception of self-motion influences the magnitude and directional accuracy of visually evoked postural responses. Five normal subjects fixated the centre of a large disk rotating in the roll (coronal) plane. The disk was placed either in front of the subjects or obliquely 30 deg to their right or left; in these oblique positions disk fixation was achieved by horizontal ocular deviation alone (i.e. no neck deviation). Subjects indicated their subjective perceptual status, either vection or object motion, with a push button. The results confirmed that the direction of the visually evoked postural response was reoriented according to the different eye-disk positions. In addition, both the magnitude of the postural response and the accuracy of its alignment with the disk rotational plane were significantly increased during vection periods. The results show that conscious perception of self-motion enhances visuopostural performance. Since conscious perception is likely to arise at cortical levels, the findings indicate that the cortex is one of the sites where gaze direction interacts with retinal motion signals to provide a self-motion signal in body-centric co-ordinates. Such interaction provides a substrate for spatial representation during motion in the environment. [ABSTRACT FROM AUTHOR]