The "Little Circles Test" (LCT): a dusted-off tool for assessing fine visuomotor function

BACKGROUND

The fine visuomotor function is commonly impaired in several neurological conditions. However, there is a scarcity of reliable neuropsychological tools to assess such a critical domain.

AIMS

The aim of this study is to explore the psychometric properties and provide normative data for the Visual-Motor Speed and Precision Test (VMSPT).

RESULTS

Our normative sample included 220 participants (130 females) aged 18-86 years (mean education = 15.24 years, SD = 3.98). Results showed that raw VMSPT scores were affected by higher age and lower education. No effect of sex or handedness was shown. Age- and education-based norms were provided. VMSPT exhibited weak-to-strong correlations with well-known neuropsychological tests, encompassing a wide range of cognitive domains of clinical relevance. By gradually intensifying the cognitive demands, the test becomes an indirect, performance-oriented measure of executive functioning. Finally, VMSPT seems proficient in capturing the speed-accuracy trade-off typically observed in the aging population.

CONCLUSIONS

This study proposes the initial standardization of a versatile, time-efficient, and cost-effective neuropsychological tool for assessing fine visuomotor coordination. We propose renaming the VMSPT as the more approachable "Little Circles Test" (LCT).

Melvyn A. Goodale: A visual neuroscientist in action

Mel Goodale has had a multi-faceted career in cognitive neuroscience, principally in the areas of perception, visually-guided action, and visual consciousness. This short article presents a personal reflection on his career from the point of view of a long-time colleague and friend.

Object motion influences feedforward motor responses during mechanical stopping of virtual projectiles: a preliminary study

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.

Hand movements in Mild Cognitive Impairment: clinical implications and insights for future research

Decreased upper-extremity/visuomotor abilities are frequently encountered in healthy aging. However, few studies have assessed hand movements in the prodromal stage of dementia. The evaluation of visuomotor skills in patients with Mild Cognitive Impairment (PwMCI) may have non-negligible clinical relevance both in diagnostic and prognostic terms, given the strong relationships with executive functioning and functional autonomies. In the present review paper, these issues will be disclosed by describing general pathophysiological and neuropsychological mechanisms responsible for visuomotor deficits, and by reporting the available experimental results on differences in visuomotor functioning between PwMCI, healthy controls and/or patients with dementia. Moreover, the relationships binding visuomotor and executive domains to functional autonomies will be then addressed. Finally, we will propose insights for future research.

Visuomotor errors drive step length and step time adaptation during 'virtual' split-belt walking: the effects of reinforcement feedback

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.

Predictive eye movements are adjusted in a Bayes-optimal fashion in response to unexpectedly changing environmental probabilities

This study examined the application of active inference to dynamic visuomotor control. Active inference proposes that actions are dynamically planned according to uncertainty about sensory information, prior expectations, and the environment, with motor adjustments serving to minimise future prediction errors. We investigated whether predictive gaze behaviours are indeed adjusted in this Bayes-optimal fashion during a virtual racquetball task. In this task, participants intercepted bouncing balls with varying levels of elasticity, under conditions of higher or lower environmental volatility. Participants' gaze patterns differed between stable and volatile conditions in a manner consistent with generative models of Bayes-optimal behaviour. Partially observable Markov models also revealed an increased rate of associative learning in response to unpredictable shifts in environmental probabilities, although there was no overall effect of volatility on this parameter. Findings extend active inference frameworks into complex and unconstrained visuomotor tasks and present important implications for a neurocomputational understanding of the visual guidance of action.

Context dependence of head bobs in gerbils and potential neural contributions

Headbobs are up-down movements of the cranium associated with the use of motion parallax for depth perception. Mongolian gerbils (aka jirds; Meriones unguiculatus) often execute a series of headbobs prior to jumping between surfaces. Gerbils were tested in a jumping stand task and headbobs videotaped under three light levels approximating low daylight, dawn/dusk, and moonlight across a range of distances to target. Headbobs per trial increased linearly with increasing distance to the target platform, whereas headbob frequency (rate of headbobbing pre-jump on the start platform) increased with gap distance up to an intermediate level and then decreased. Overall, gerbils made the most headbobs per trial under the darkest conditions, whereas their headbobbing rate was highest for medium illumination, especially for medium-long gap distances. There was a positive correlation between headbob frequency and volume of the superior colliculus (SC), but no relationship between headbobs and relative size of the temporo-posterior (TP) visual cortex. The results suggest that gerbils employ a specific visuomotor strategy for depth perception differentially under different conditions. We suggest that the deployment of headbobs under specific conditions may be part of an SC-driven vigilant state, of which more rapid sampling of the visual environment using headbobs for depth estimation is one component. Moreover, the findings highlight the importance of considering ecological factors in designing studies of visual behavior and its underpinnings in rodents.

The effect of explicit cues on smooth pursuit termination

Predictive deceleration of eye motion during smooth pursuit is induced by explicit cues indicating the timing of the visual target offset. The first aim of this study (experiment 1) was to determine whether the timing of the onset of cue-based predictive pursuit termination depends on spatial or temporal information using three target velocities. The second aim (experiment 2) was to examine whether an unexpected offset of the target affects the pursuit termination. We conducted a pursuit termination task where participants tracked a moving target and then stopped tracking after the target disappeared. The results of experiment 1 showed that the onset times of predictive eye deceleration were consistent regardless of target velocity, indicating that its timing is controlled by the temporal estimation, rather than the spatial distance between the target and cue positions. In experiment 2, we compared pursuit termination between the following two conditions. One condition did not present any cues (unknown condition), whereas a second condition included a same cue as experiment 1 but the target disappeared 500 ms before the timing indicated by the cue unpredictably (unexpected condition). As a result, the unexpected condition showed significant delays in the onset of eye deceleration, but no difference in the total time for completion of pursuit termination. Therefore, our findings suggest that the cue-based pursuit termination is controlled by the predictive pursuit system, and an unexpected offset of the target yields delays in the onset of eye deceleration, while does not affect the duration of pursuit termination.

Lower extremity prism adaptation in individuals with anterior cruciate ligament reconstruction

BACKGROUND

Emerging research has proposed a growing reliance on visual processing during motor performance in individuals following anterior cruciate ligament reconstruction. Reconstructed individuals display increased activation of visual processing areas during task execution and exhibit dramatic performance decrements when vision is completely removed, however the effect of visual information manipulation on performance remains unknown. The purpose of this study was to determine how manipulation of visual information changes performance in persons with anterior cruciate ligament reconstruction.

METHODS

Twenty-one persons with anterior cruciate ligament reconstruction and 21 matched healthy adults reached to a target with the toe of the involved limb 50 times while wearing prism goggles that vertically shifted their visual field. Toe kinematics were collected to quantify endpoint error and reaching behavior.

FINDINGS

Statistical analyses failed to detect significant differences, evidencing both groups performed similarly with respect to endpoint error, movement duration, peak and maximum endpoint velocities, and initial direction error.

INTERPRETATION

When provided inaccurate information via a visual field perturbation, both groups demonstrated comparable adaptation and post-adaptation behavior. These results suggest this sample of persons with anterior cruciate ligament reconstruction are able to effectively integrate information across sensory systems as well as non-injured individuals.

Multiple processes independently predict motor learning

Background

Our ability to acquire, refine and adapt skilled limb movements is a hallmark of human motor learning that allows us to successfully perform many daily activities. The capacity to acquire, refine and adapt other features of motor performance, such as visual search, eye-hand coordination and visuomotor decisions, may also contribute to motor learning. However, the extent to which refinements of multiple behavioral features and their underlying neural processes independently contribute to motor learning remains unknown. In the current study, we used an ethological approach to test the hypothesis that practice-related refinements of multiple behavioral features would be independently predictive of motor learning.

Methods

Eighteen healthy, young adults used an upper-limb robot with eye-tracking to practice six trials of a continuous, visuomotor task once a week for six consecutive weeks. Participants used virtual paddles to hit away 200 “Targets” and avoid hitting 100 “Distractors” that continuously moved towards them from the back of the workspace. Motor learning was inferred from trial-by-trial acquisition and week-by-week retention of improvements on two measures of task performance related to motor execution and motor inhibition. Adaptations involving underlying neural processes were inferred from trial-by-trial acquisition and week-by-week retention of refinements on measures of skilled limb movement, visual search, eye-hand coordination and visuomotor decisions. We tested our hypothesis by quantifying the extent to which refinements on measures of multiple behavioral features (predictors) were independently predictive of improvements on our two measures of task performance (outcomes) after removing all shared variance between predictors.

Results

We found that refinements on measures of skilled limb movement, visual search and eye-hand coordination were independently predictive of improvements on our measure of task performance related to motor execution. In contrast, only refinements of eye-hand coordination were independently predictive of improvements on our measure of task performance related to motor inhibition.

Conclusion

Our results provide indirect evidence that refinements involving multiple, neural processes may independently contribute to motor learning, and distinct neural processes may underlie improvements in task performance related to motor execution and motor inhibition. This also suggests that refinements involving multiple, neural processes may contribute to motor recovery after stroke, and rehabilitation interventions should be designed to produce refinements of all behavioral features that may contribute to motor recovery.

Properties of smooth pursuit adaptation induced by theta motion

Current study attempted to determine whether repeated smooth pursuit trials using theta motion, in which the directions of retinal image-motion and object-motion are opposed, yield pursuit adaptation. Adaptation trials consisted of 350 step-ramp trials using theta motion, and pre- and post-trials using first-order motion were conducted. As a result, initial acceleration in post-adaptation increased significantly than pre-adaptation trials. This was the case even though there was no adaptive change throughout adaptation (350 trials) using theta motion. Our results suggest that smooth pursuit could adapt to theta motion even with challenges associated with opposite retinal slip.

Temporal dynamics of sequential motor activation in a dual-prime paradigm: Insights from conditional accuracy and hazard functions

In response priming experiments, a participant has to respond as quickly and as accurately as possible to a target stimulus preceded by a prime. The prime and the target can either be mapped to the same response (consistent trial) or to different responses (inconsistent trial). Here, we investigate the effects of two sequential primes (each one either consistent or inconsistent) followed by one target in a response priming experiment. We employ discrete-time hazard functions of response occurrence and conditional accuracy functions to explore the temporal dynamics of sequential motor activation. In two experiments (small-N design, 12 participants, 100 trials per cell and subject), we find that (1) the earliest responses are controlled exclusively by the first prime if primes are presented in quick succession, (2) intermediate responses reflect competition between primes, with the second prime increasingly dominating the response as its time of onset is moved forward, and (3) only the slowest responses are clearly controlled by the target. The current study provides evidence that sequential primes meet strict criteria for sequential response activation. Moreover, it suggests that primes can influence responses out of a memory buffer when they are presented so early that participants are forced to delay their responses.

Motor control drives visual bodily judgements

The 'embodied cognition' framework proposes that our motor repertoire shapes visual perception and cognition. But recent studies showing normal visual body representation in individuals born without hands challenges the contribution of motor control on visual body representation. Here, we studied hand laterality judgements in three groups with fundamentally different visual and motor hand experiences: two-handed controls, one-handers born without a hand (congenital one-handers) and one-handers with an acquired amputation (amputees). Congenital one-handers, lacking both motor and first-person visual information of their missing hand, diverged in their performance from the other groups, exhibiting more errors for their intact hand and slower reaction-times for challenging hand postures. Amputees, who have lingering non-visual motor control of their missing (phantom) hand, performed the task similarly to controls. Amputees' reaction-times for visual laterality judgements correlated positively with their phantom hand's motor control, such that deteriorated motor control associated with slower visual laterality judgements. Finally, we have implemented a computational simulation to describe how a mechanism that utilises a single hand representation in congenital one-handers as opposed to two in controls, could replicate our empirical results. Together, our findings demonstrate that motor control is a driver in making visual bodily judgments.

You Snooze, You Win? An Ecological Dynamics Framework Approach to Understanding the Relationships Between Sleep and Sensorimotor Performance in Sport

Sleep has a widespread impact across different domains of performance, including sensorimotor function. From an ecological dynamics perspective, sensorimotor function involves the continuous and dynamic coupling between perception and action. Sport performance relies on sensorimotor function as successful movement behaviors require accurate and efficient coupling between perceptions and actions. Compromised sleep impairs different aspects of sensorimotor performance, including perceptual attunement and motor execution. Changes in sensorimotor performance can be related to specific features of sleep, notably sleep spindles and slow waves. One unaddressed area of study is the extent to which specific sleep features contribute to overall sport-specific performance.

Unanticipated jump-landing quality in patients with anterior cruciate ligament reconstruction: How long after the surgery and return to sport does the re-injury risk factor persist?

BACKGROUND

Inadequate reactions to unforeseen external stimuli are regarded as a major cause for non-contact anterior cruciate ligament (ACL) injuries. We aimed to delineate a potential deficit in the ability to perform unanticipated jump-landing manoeuvres, its sustainability and potential as a new outcome measure after ACL-reconstruction.

METHODS

Physically active adults (n = 27, 13 females, 14 males, 29.7 standard deviation 3.1 years) with a history of unilateral ACL rupture and subsequent reconstruction (6 months to 7 years ago), cleared for return to sports, were included. All participants performed counter-movement jumps with unanticipated single leg landings. Visual information shown after jump take-off indicated the required landing leg. Jump time [s] and successfulness [yes/no], vertical peak ground reaction forces at landing [N], as well as time to stabilisation after landing [s] and path length of the centre of pressure (CoP, [mm]) were calculated. Limb symmetry ratios were determined and analysed for their association with the time since surgery.

FINDINGS

Time since ACL reconstruction was logarithmically (basis 10) associated with side symmetry improvements in peak ground reaction force (R² = 0.23, p < .01) and time to stabilisation (R² = 0.18, p < .01) during and after landing in unanticipated/unpredictable single-leg jump landing tasks. The asymmetry found persists up to 18-26 months post-surgery.

INTERPRETATION

A deficit in unanticipated jump-landing ability seems to persist far beyond surgical restoration of mechanical stability and resumption of initial physical activities levels. The assessment of the ability to suddenly adapt movements to unanticipated visual stimuli may be a relevant complementary component within current functional testing canon in monitoring therapy success and return to sport testing.

Children with cerebral palsy display altered neural oscillations within the visual MT/V5 cortices

Cortical visual processing in visual MT/V5 is necessary for tracking movement and performing reliable visuomotor transformations. Although the role of this cortical area is well recognized, the activity of the visual MT/V5 cortical area in children with cerebral palsy (CP) has not been examined nor has its potential role in the atypical motor actions of these children been considered. This study used magnetoencephalography to image the neural activity in the motion-sensitive MT/V5 cortices of typically developing (TD) children (n = 21; mean age 14 yrs. ± 2, 12 males) and children with CP (n = 21; mean age 16 yrs. ± 4, 13 males) as they viewed a horizontally moving stimulus. Behavioral measures of visual perception were additionally assessed by having the participants press a button when the visual stimulus changed to moving in vertical direction. Our results showed that the horizontal movement of the visual stimulus evoked changes in the strength of the theta-alpha (5-10 Hz) and alpha-beta (8-20 Hz) oscillations in the visual MT/V5 area of all participants. Compared with the TD children, the children with CP had weaker alpha-beta oscillations in the visual MT/V5 cortices. In addition, the children with CP took longer to perceive a directional change of the visual stimulus and made more errors in detecting the change. Lastly, weaker alpha-beta oscillations were correlated with slower detection of the change in motion direction and less accuracy in identifying the change. This study shows that the uncharacteristic neural oscillations in the visual MT/V5 cortical area may partially account for the abnormal perceptions and motor decisions seen in children with CP.

Sensorimotor lateralization scaffolds cognitive specialization

In this chapter, we review hemispheric differences for sensorimotor function and cognitive abilities. Specifically, we examine the left-hemisphere specialization for visuomotor control and its interplay with language, executive function, and musical training. Similarly, we discuss right-hemisphere lateralization for haptic processing and its relationship to spatial and numerical processing. We propose that cerebral lateralization for sensorimotor functions served as a foundation for the development of higher cognitive abilities and their hemispheric functional specialization. We further suggest that sensorimotor and cognitive functions are inextricably linked. Based on the studies discussed in this chapter our view is that sensorimotor control serves as a loom upon which the fibers of language, executive function, spatial, and numerical processing are woven together to create the fabric of cognition.

Voluntarily controlled but not merely observed visual feedback affects postural sway

Online stabilization of human standing posture utilizes multisensory afferences (e.g., vision). Whereas visual feedback of spontaneous postural sway can stabilize postural control especially when observers concentrate on their body and intend to minimize postural sway, the effect of intentional control of visual feedback on postural sway itself remains unclear. This study assessed quiet standing posture in healthy adults voluntarily controlling or merely observing visual feedback. The visual feedback (moving square) had either low or high gain and was either horizontally flipped or not. Participants in the voluntary-control group were instructed to minimize their postural sway while voluntarily controlling visual feedback, whereas those in the observation group were instructed to minimize their postural sway while merely observing visual feedback. As a result, magnified and flipped visual feedback increased postural sway only in the voluntary-control group. Furthermore, regardless of the instructions and feedback manipulations, the experienced sense of control over visual feedback positively correlated with the magnitude of postural sway. We suggest that voluntarily controlled, but not merely observed, visual feedback is incorporated into the feedback control system for posture and begins to affect postural sway.

Rapid decrement in the effects of the Ponzo display dissociates action and perception

It has been demonstrated that pictorial illusions have a smaller influence on grasping than they do on perceptual judgments. Yet to date this work has not considered the reduced influence of an illusion as it is measured repeatedly. Here we studied this decrement in the context of a Ponzo illusion to further characterize the dissociation between vision for perception and for action. Participants first manually estimated the lengths of single targets in a Ponzo display with their thumb and index finger, then actually grasped these targets in another series of trials, and then manually estimated the target lengths again in a final set of trials. The results showed that although the perceptual estimates and grasp apertures were equally sensitive to real differences in target length on the initial trials, only the perceptual estimates remained biased by the illusion over repeated measurements. In contrast, the illusion's effect on the grasps decreased rapidly, vanishing entirely after only a few trials. Interestingly, a closer examination of the grasp data revealed that this initial effect was driven largely by undersizing the grip aperture for the display configuration in which the target was positioned between the diverging background lines (i.e., when the targets appeared to be shorter than they really were). This asymmetry between grasping apparently shorter and longer targets suggests that the sensorimotor system may initially treat the edges of the configuration as obstacles to be avoided. This finding highlights the sensorimotor system's ability to rapidly update motor programs through error feedback, manifesting as an immunity to the effects of illusion displays even after only a few trials.

Speed, resistance, and unexpected accelerations modulate feed forward and feedback control during a novel weight bearing task

We developed a method to investigate feed-forward and feedback movement control during a weight bearing visuomotor knee tracking task. We hypothesized that a systematic increase in speed and resistance would show a linear decrease in movement accuracy, while unexpected perturbations would induce a velocity-dependent decrease in movement accuracy. We determined the effects of manipulating the speed, resistance, and unexpected events on error during a functional weight bearing task. Our long term objective is to benchmark neuromuscular control performance across various groups based on age, injury, disease, rehabilitation status, and/or training. Twenty-six healthy adults between the ages of 19-45 participated in this study. The study involved a single session using a custom designed apparatus to perform a single limb weight bearing task under nine testing conditions: three movement speeds (0.2, 0.4, and 0.6Hz) in combination with three levels of brake resistance (5%, 10%, and 15% of individual's body weight). Individuals were to perform the task according to a target with a fixed trajectory across all speeds, corresponding to a∼0 (extension) to 30° (flexion) of knee motion. An increase in error occurred with speed (p<0.0001, effect size (eta²): η²=0.50) and resistance (p<0.0001, η²=0.01). Likewise, during unexpected perturbations, the ratio of perturbed/non-perturbed error increased with each increment in velocity (p<0.0014, η²=0.08), and resistance (p<0.0001, η²=0.11). The hierarchical framework of these measurements offers a standardized functional weight bearing strategy to assess impaired neuro-muscular control and/or test the efficacy of therapeutic rehabilitation interventions designed to influence neuromuscular control of the knee.

Haptic feedback attenuates illusory bias in pantomime-grasping: evidence for a visuo-haptic calibration

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.

Reaction time norms as measured by ruler drop method in school-going South Asian children: A cross-sectional study

This study aimed to estimate normative range for reaction time using ruler drop method for school-going South Asian children between 6 and 12 years of age. A cross-sectional study was used to evaluate the reaction time for 204 children. Normal values for each age group were obtained. The results of multiple linear regressions showed a decrease in the reaction time values with age, and a significant change occurring between six and eight years of age. No difference in reaction time was obtained between boys and girls. Ruler drop method is an easy to use test and the results of this study provide a normative data for age groups 6-12 years ranging from 214.2ms to 248.8ms. These values can serve as a reference to screen children with delayed reaction time.

Memory-guided reaching in a patient with visual hemiagnosia

The two-visual-systems hypothesis (TVSH) postulates that memory-guided movements rely on intact functions of the ventral stream. Its particular importance for memory-guided actions was initially inferred from behavioral dissociations in the well-known patient DF. Despite of rather accurate reaching and grasping movements to visible targets, she demonstrated grossly impaired memory-guided grasping as much as impaired memory-guided reaching. These dissociations were later complemented by apparently reversed dissociations in patients with dorsal damage and optic ataxia. However, grasping studies in DF and optic ataxia patients differed with respect to the retinotopic position of target objects, questioning the interpretation of the respective findings as a double dissociation. In contrast, the findings for reaching errors in both types of patients came from similar peripheral target presentations. However, new data on brain structural changes and visuomotor deficits in DF also questioned the validity of a double dissociation in reaching. A severe visuospatial short-term memory deficit in DF further questioned the specificity of her memory-guided reaching deficit. Therefore, we compared movement accuracy in visually-guided and memory-guided reaching in a new patient who suffered a confined unilateral damage to the ventral visual system due to stroke. Our results indeed support previous descriptions of memory-guided movements' inaccuracies in DF. Furthermore, our data suggest that recently discovered optic-ataxia like misreaching in DF is most likely caused by her parieto-occipital and not by her ventral stream damage. Finally, multiple visuospatial memory measurements in HWS suggest that inaccuracies in memory-guided reaching tasks in patients with ventral damage cannot be explained by visuospatial short-term memory or perceptual deficits, but by a specific deficit in visuomotor processing.

Beery VMI performance in autism spectrum disorder

Few studies have examined the visuomotor integration (VMI) abilities of individuals with autism spectrum disorder (ASD). An all-male sample consisting of 56 ASD participants (ages 3-23 years) and 36 typically developing (TD) participants (ages 4-26 years) completed the Beery-Buktenica Developmental Test of Visual-Motor Integration (Beery VMI) as part of a larger neuropsychological battery. Participants were also administered standardized measures of intellectual functioning and the Social Responsiveness Scale (SRS), which assesses autism and autism-like traits. The ASD group performed significantly lower on the Beery VMI and on all IQ measures compared to the TD group. VMI performance was significantly correlated with full scale IQ (FSIQ), performance IQ (PIQ), and verbal IQ (VIQ) in the TD group only. However, when FSIQ was taken into account, no significant Beery VMI differences between groups were observed. Only one TD participant scored 1.5 standard deviations (SDs) below the Beery VMI normative sample mean, in comparison to 21% of the ASD sample. As expected, the ASD group was rated as having significantly higher levels of social impairment on the SRS compared to the TD group across all major domains. However, level of functioning on the SRS was not associated with Berry VMI performance. These findings demonstrate that a substantial number of individuals with ASD experience difficulties compared to TD in performing VMI-related tasks, and that VMI is likely affected by general cognitive ability. The fact that lowered Beery VMI performance occurred only within a subset of individuals with ASD and did not correlate with SRS would indicate that visuomotor deficits are not a core feature of ASD, even though they present at a higher rate of impairment than observed in TD participants.

Rate control and quality assurance during rhythmic force tracking

Movement characteristics can be coded in the single neurons or in the summed activity of neural populations. However, whether neural oscillations are conditional to the frequency demand and task quality of rhythmic force regulation is still unclear. This study was undertaken to investigate EEG dynamics and behavior correlates during force-tracking at different target rates. Fourteen healthy volunteers conducted load-varying isometric abduction of the index finger by coupling the force output to sinusoidal targets at 0.5 Hz, 1.0 Hz, and 2.0 Hz. Our results showed that frequency demand significantly affected EEG delta oscillation (1-4 Hz) in the C3, CP3, CPz, and CP4 electrodes, with the greatest delta power and lowest delta peak around 1.5 Hz for slower tracking at 0.5 Hz. Those who had superior tracking congruency also manifested enhanced alpha oscillation (8-12 Hz). Alpha rhythms of the skilled performers during slow tracking spread through the whole target cycle, except for the phase of direction changes. However, the alpha rhythms centered at the mid phase of a target cycle with increasing target rate. In conclusion, our findings clearly suggest two advanced roles of cortical oscillation in rhythmic force regulation. Rate-dependent delta oscillation involves a paradigm shift in force control under different time scales. Phasic organization of alpha rhythms during rhythmic force tracking is related to behavioral success underlying the selective use of bimodal controls (feedback and feedforward processes) and the timing of attentional focus on the target's peak velocity.

Modulation of frontal and parietal neuronal activity by visuomotor learning. An ERP analysis of implicit and explicit pursuit tracking tasks

The present study investigated changes in frontal and parietal activity related to visuomotor learning. Improvement in task performance should be achieved by a transition from feedback control to feedforward control. Event-related potential (ERP) activity related to visual feedback analysis of successful error corrections was expected to decrease at parietal scalp locations. (Pre-) motor activity related to the execution of directional changes should increase and begin earlier. While using a mouse or a joystick for cursor control, subjects performed four different conditions of a pursuit tracking task in a between-subject design. To increase task difficulty, and to set up an implicit learning condition, the gain between mouse/joystick movement and cursor movement increased during the middle of each tracking trial. Subjects were informed about this manipulation in the explicit task only. Within the continuous movement of 12s duration, ERPs were assigned to phasic changes of target and cursor direction. Visuomotor learning was mainly achieved by a continuous reduction of target and cursor distance. A fronto-central positive ERP component related to the execution of a directional change increased earlier after learning. This indicates an anticipated directional change, improving task performance. ERP activity after error corrections decreased after learning, indicating either a higher efficiency or a reduced demand in visual feedback control. Activity difference was shifted from parietal to fronto-central sites later indicating a relation to improved feedforward control. No clear difference between implicit and explicit learning was observed for behavioural and ERP data.

Activity in ventral premotor cortex is modulated by vision of own hand in action

Parietal and premotor cortices of the macaque monkey contain distinct populations of neurons which, in addition to their motor discharge, are also activated by visual stimulation. Among these visuomotor neurons, a population of grasping neurons located in the anterior intraparietal area (AIP) shows discharge modulation when the own hand is visible during object grasping. Given the dense connections between AIP and inferior frontal regions, we aimed at investigating whether two hand-related frontal areas, ventral premotor area F5 and primary motor cortex (area F1), contain neurons with similar properties. Two macaques were involved in a grasping task executed in various light/dark conditions in which the to-be-grasped object was kept visible by a dim retro-illumination. Approximately 62% of F5 and 55% of F1 motor neurons showed light/dark modulations. To better isolate the effect of hand-related visual input, we introduced two further conditions characterized by kinematic features similar to the dark condition. The scene was briefly illuminated (i) during hand preshaping (pre-touch flash, PT-flash) and (ii) at hand-object contact (touch flash, T-flash). Approximately 48% of F5 and 44% of F1 motor neurons showed a flash-related modulation. Considering flash-modulated neurons in the two flash conditions, ∼40% from F5 and ∼52% from F1 showed stronger activity in PT- than T-flash (PT-flash-dominant), whereas ∼60% from F5 and ∼48% from F1 showed stronger activity in T- than PT-flash (T-flash-dominant). Furthermore, F5, but not F1, flash-dominant neurons were characterized by a higher peak and mean discharge in the preferred flash condition as compared to light and dark conditions. Still considering F5, the distribution of the time of peak discharge was similar in light and preferred flash conditions. This study shows that the frontal cortex contains neurons, previously classified as motor neurons, which are sensitive to the observation of meaningful phases of the own grasping action. We conclude by discussing the possible functional role of these populations.