Bimanual Tracking Task Research Articles

Toward methodologies for motor imagery enhancement: a tDCS-BCI study

ABSTRACT Motor imagery (MI) becomes a powerful rehabilitation tool, particularly when combined with brain–computer interfaces (BCI). Therefore, methods to improve MI accuracy are a trending topic in the BCI field. Here, we examined the effects of transcranial direct current stimulation (tDCS) and MI priming on the MI signature in an EEG-based MI-BCI triple-blind study. Thirty healthy younger adults participated in this study and were designated to one of two priming groups: A bimanual tracking task and a MI task as primers for MI-BCI. During the performance of the primer task, participants received anodal and sham tDCS in two randomized sessions with a one-week wash-out period between sessions. Subsequently, participants performed an EEG-driven BCI-MI task. EEG time–frequency analyses revealed that desynchronization of the Beta Region precedes desynchronization in the Alpha Region, implying that the Beta frequency band might be best-suited to extract MI signatures as it could lead to faster MI-BCI. Contrary to our hypotheses, no effect of tDCS or priming task on EEG activity during the BCI-MI task was found. Future research should carefully consider the added value of tDCS and priming tasks BCI performance improvement. Electric field modeling studies and high-definition tDCS motor cortex stimulation might be promising avenues.

Interactions between the aging brain and motor task complexity across the lifespan: balancing brain activity resource demand and supply.

The Compensation Related Utilization of Neural Circuits Hypothesis (CRUNCH) proposes a framework for understanding task-related brain activity changes as a function of healthy aging and task complexity. Specifically, it affords the following predictions: (i) all adult age groups display more brain activation with increases in task complexity, (ii) older adults show more brain activation compared with younger adults at low task complexity levels, and (iii) disproportionately increase brain activation with increased task complexity, but (iv) show smaller (or no) increases in brain activation at the highest complexity levels. To test these hypotheses, performance on a bimanual tracking task at 4 complexity levels and associated brain activation were assessed in 3 age groups (20-40, 40-60, and 60-80years, n = 99). All age groups showed decreased tracking accuracy and increased brain activation with increased task complexity, with larger performance decrements and activation increases in the older age groups. Older adults exhibited increased brain activation at a lower complexity level, but not the predicted failure to further increase brain activity at the highest complexity level. We conclude that older adults show more brain activation than younger adults and preserve the capacity to deploy increased neural resources as a function of task demand.

How virtual and mechanical coupling impact bimanual tracking.

Bilateral training systems look to promote the paretic hand's use in individuals with hemiplegia. Although this is normally achieved using mechanical coupling (i.e., a physical connection between the hands), a virtual reality system relying on virtual coupling (i.e., through a shared virtual object) would be simpler to use and prevent slacking. However, it is not clear whether different coupling modes differently impact task performance and effort distribution between the hands. We explored how 18 healthy right-handed participants changed their motor behaviors in response to the uninstructed addition of mechanical coupling, and virtual coupling using a shared cursor mapped to the average hands' position. In a second experiment, we then studied the impact of connection stiffness on performance, perception, and effort imbalance. The results indicated that both coupling types can induce the hands to actively contribute to the task. However, the task asymmetry introduced by using a cursor mapped to either the left or right hand only modulated the hands' contribution when not mechanically coupled. The tracking performance was similar for all coupling types, independent of the connection stiffness, although the mechanical coupling was preferred and induced the hands to move with greater correlation. These findings suggest that virtual coupling can induce the hands to actively contribute to a task in healthy participants without hindering their performance. Further investigation on the coupling types' impact on the performance and hands' effort distribution in patients with hemiplegia could allow for the design of simpler training systems that promote the affected hand's use.NEW & NOTEWORTHY We showed that the uninstructed addition of a virtual and/or a mechanical coupling can induce both hands to actively contribute in a continuous redundant bimanual tracking task without impacting performance. In addition, we showed that the task asymmetry can only alter the effort distribution when the hands are not connected, independent of the connection stiffness. Our findings suggest that virtual coupling could be used in the development of simpler VR-based training devices.

Aging and Complexity Effects on Hemisphere-Dependent Movement-Related Beta Desynchronization during Bimanual Motor Planning and Execution.

With aging comes degradation of bimanual movement performance. A hallmark feature of bimanual movements is movement-related beta desynchronization (MRBD), an attenuation in the amplitude of beta oscillations associated with sensorimotor activation. Here, we investigated MRBD in 39 healthy adults (20 younger and 19 older adults) in frontal, central, and parietal regions across both hemispheres, during the planning and execution of a bimanual tracking task. Task accuracy decreased with age and during more difficult conditions when both hands had to move at different relative speeds. MRBD was mostly situated in the central region, and increased in older versus younger adults during movement execution but not planning. Irrespective of age, motor planning and execution were associated with increased MRBD in the left and right hemispheres, respectively. Notably, right central MRBD during motor planning was associated with bimanual task performance, particularly in older adults. Specifically, persons who demonstrated high MRBD during motor planning performed better on the bimanual tracking task. Our results highlight the importance of lateralized MRBD during motor planning, thereby shining new light on previous research and providing a promising avenue for future interventions.

Is a Robot Needed to Modify Human Effort in Bimanual Tracking?

Robotic bimanual training can benefit from understanding how to modify human motor effort in bimanual tasks. We addressed this issue by carrying out a study to investigate whether and how penalizing the use of one hand could alter the hands’ effort distribution. Actuated haptic perturbations and alterations of the visual feedback of the right hand were tested on a bimanual tracking task with 16 healthy right-handed participants. For each feedback modality (haptic or visual), both a disturbance and a perturbation requiring additional effort from the right hand were implemented. The results showed that the participants were able to adjust to these four perturbations, and perceived them correctly as something that disturbed the dominant hand. Contrary to our expectations, the bimanual effort distribution changes induced by the haptic perturbations were not uniform across subjects. However, the visual disturbance induced most participants to use only their unperturbed left hand (with only 2/16 participants reporting a different behaviour). This suggests that a visual disturbance could be used to alter the effort distribution among the two hands. Clinical validation of these findings on hemiplegic patients may help simplify the design of robotic training interfaces.

The effect of aging on inter-limb coordination: Establishing a novel transcranial alternating current stimulation (tACS) protocol by means of electroencephalography (EEG)

Abstract Healthy aging is a societal challenge with a significant socioeconomic impact. Gaining knowledge about neurodegenerative changes that impact functional independence is thus of high scientific importance. Age-related structural and functional neural changes have consequences for inter-limb coordination, which forms an intrinsic part of everyday life (e.g., driving, buttoning a shirt). Research has demonstrated that transcranial alternating current stimulation (tACS) targeting neural oscillations can alter behavioral performance. Nevertheless, profound understanding of tACS in the context of inter-limb coordination is yet to be achieved. In order to accomplish this, a more thorough understanding of the neural oscillations underlying inter-limb coordination is of utmost importance. The current study used electroencephalography (EEG) in healthy right-handed participants during two inter-limb coordination tasks; the bimanual tracking task (BTT) and the multi-limb reaction time task (MLT). The BTT consists of rotating two dials with both hands in a coordinated fashion. Three conditions were used, differing in left- and right-hand movement frequency. The MLT requires participants to lift multiple limbs in a correct manner. Six conditions were used, differing in required motor response (e.g., lifting right arm and left leg, lifting left arm and both legs). Twenty healthy right-handed young adults (age: 22.3 ± 1.0 (mean ± standard deviation)) and nineteen older adults (age: 70.7 ± 3.0) participated. Laplacian filtered EEG data will be analyzed in the time-frequency domain using morlet wavelet convolution. EEG time-frequency data between 4 and 35 hertz will be analyzed by means of repeated measures ANOVA, investigating differences across conditions and groups for each task respectively. In addition, bivariate channel-level functional connectivity will be analyzed using inter-site phase clustering. Behavioral data will be analyzed with a mixed model approach. These insights will be used to establish novel tACS protocols. If significant differences between young and older adults are present, these findings can lead to age-adapted tACS protocols. Keywords: Electroencephalography, Transcranial alternating current stimulation, Ageing, Functional connectivity

Fiber-specific variations in anterior transcallosal white matter structure contribute to age-related differences in motor performance

Age-related differences in bimanual motor performance have been extensively documented, but their underlying neural mechanisms remain less clear. Studies applying diffusion MRI in the aging population have revealed evidence for age-related white matter variations in the corpus callosum (CC) which are related to bimanual motor performance. However, the diffusion tensor model used in those studies is confounded by partial volume effects in voxels with complex fiber geometries which are present in up to 90% of white matter voxels, including the bilateral projections of the CC. A recently developed whole-brain analysis framework, known as fixel-based analysis (FBA), enables comprehensive statistical analyses of white matter quantitative measures in the presence of such complex fiber geometries. To investigate the contribution of age-related fiber-specific white matter variations to age-related differences in bimanual performance, a cross-sectional lifespan sample of healthy human adults (N ​= ​95; 20–75 years of age) performed a bimanual tracking task. Furthermore, diffusion MRI data were acquired and the FBA metrics associated with fiber density, cross-section, and combined fiber density and cross-section were estimated. Whole-brain FBA revealed significant negative associations between age and fiber density, cross-section, and combined metrics of multiple white matter tracts, including the bilateral projections of the CC, indicative of white matter micro- and macrostructural degradation with age. More importantly, mediation analyses demonstrated that age-related variations in the combined (fiber density and cross-section) metric of the genu, but not splenium, of the CC contributed to the observed age-related differences in bimanual coordination performance. These findings highlight the contribution of variations in interhemispheric communication between prefrontal (non-motor) cortices to age-related differences in motor performance.

Age-related differences in network flexibility and segregation at rest and during motor performance

Brain networks undergo widespread changes in older age. A large body of knowledge gathered about those changes evidenced an increase of functional connectivity between brain networks. Previous work focused mainly on cortical networks during the resting state. Subcortical structures, however, are of critical importance during the performance of motor tasks. In this study, we investigated age-related changes in cortical, striatal and cerebellar functional connectivity at rest and its modulation by motor task execution. To that end, functional MRI from twenty-five young (mean age 21.5 years) and eighteen older adults (mean age 68.6 years) were analysed during rest and while performing a bimanual tracking task practiced over a two-week period. We found that inter-network connectivity among cortical structures was more positive in older adults both during rest and task performance. Functional connectivity within striatal structures decreased with age during rest and task execution. Network flexibility, the changes in network composition from rest to task, was also reduced in older adults, but only in networks with an age-related increase in connectivity. Finally, flexibility of areas in the prefrontal cortex were associated with lower error scores during task execution, especially in older adults. In conclusion, our findings indicate an age-related reduction in the ability to suppress irrelevant network communication, leading to less segregated and less flexible cortical networks. At the same time, striatal connectivity is impaired in older adults, while cerebellar connectivity shows heterogeneous age-related effects during rest and task execution. Future research is needed to clarify how cortical and subcortical connectivity changes relate to one another.

S149. Improved bimanual control in elderly after motor cortex stimulation

Introduction Accompanying the natural advancing of age is a decline in cognitive and motor functions, which may be the result of altered neuroplasticity, due to changes in synaptic function and neurotransmission. Successful performance of routine, but complex motor tasks such as bimanual movements may require optimal synchronization of motor cortical areas, which decline with ageing. On the other hand, recent work has shown that transcranial direct current stimulation (tDCS) may be a useful tool to restitute these altered mechanisms, and improve performance of motor skills. Presently, we address the question of identifying physiological markers of age-related differences during acquisition of new bimanual motor control tasks, based on induced oscillatory changes, using EEG. Second, we assess whether performance of complex bimanual skills can be improved in the elderly using tDCS. Methods Experiment 1 : 43 healthy subjects (21 elderly) performed the bimanual tracking task (BTT), which is a complex task requiring multiple cognitive domains, as well as the skilled use of in-phase and anti-phase movements, at various frequencies. Three blocks of the task were performed (180 total trials) while EEG was recorded to measure task-induced power changes. Experiment 2 : An additional 40 subjects (20 elderly) were recruited for evaluating whether right M1 anodal tDCS (1.0 mA, 20 min) may improve performance in the task, particularly in the non-dominant left hand. The study was double-blinded, sham-controlled, and employed a randomized crossover design in order to assess tDCS-induced performance and task-induced synchronization differences between young and elderly groups. Results Experiment 1: Overall task performance in younger subjects was more accurate than in elderly. Younger subjects showed significantly stronger desynchronization in the mu and beta band, whereas older subjects showed greater gamma band activity in motor cortical areas. In addition, these patterns were also found to correlate inter-individually with accurate performance in the task. Experiment 2: ANOVA revealed a main effect of stimulation, which was significant between active and sham tDCS conditions in the elderly but not in young. Further exploratory analyses revealed significant improvements in both left and right hand coordination in active stimulation conditions for both groups of subjects, with the greatest improvement found in left-hand dominant motor movements in the elderly group. Conclusion We show that both task-induced oscillatory synchronization and inter-limb kinematics underlying bimanual motor coordination are different between the young and elderly. Further, a single session of tDCS applied to the motor cortex could significantly improve bimanual performance in the elderly. Although further studies are needed to optimize tDCS parameters for enhanced and prolonged effects, tDCS may be a viable tool in restituting the learning of complex motor functions in the aging or other vulnerable populations.

Age-Dependent Modulations of Resting State Connectivity Following Motor Practice.

Recent work in young adults has demonstrated that motor learning can modulate resting state functional connectivity. However, evidence for older adults is scarce. Here, we investigated whether learning a bimanual tracking task modulates resting state functional connectivity of both inter- and intra-hemispheric regions differentially in young and older individuals, and whether this has behavioral relevance. Both age groups learned a set of complex bimanual tracking task variants over a 2-week training period. Resting-state and task-related functional magnetic resonance imaging scans were collected before and after training. Our analyses revealed that both young and older adults reached considerable performance gains. Older adults even obtained larger training-induced improvements relative to baseline, but their overall performance levels were lower than in young adults. Short-term practice resulted in a modulation of resting state functional connectivity, leading to connectivity increases in young adults, but connectivity decreases in older adults. This pattern of age differences occurred for both inter- and intra-hemispheric connections related to the motor network. Additionally, long-term training-induced increases were observed in intra-hemispheric connectivity in the right hemisphere across both age groups. Overall, at the individual level, the long-term changes in inter-hemispheric connectivity correlated with training-induced motor improvement. Our findings confirm that short-term task practice shapes spontaneous brain activity differentially in young and older individuals. Importantly, the association between changes in resting state functional connectivity and improvements in motor performance at the individual level may be indicative of how training shapes the short-term functional reorganization of the resting state motor network for improvement of behavioral performance.

P315 Investigating bimanual motor coordination in healthy young and older adults using EEG and transcranial direct current stimulation (tDCS)

Introduction Accompanying the natural advancing of age is a decline in cognitive and motor functions, which can significantly impact the daily life activities in the elder demographic (>65 y). Such declines may involve altered neuroplasticity, due to changes in synaptic function and neurotransmission. Successful performance of complex motor tasks may also entail distinct patterns in motor cortical functional connectivity, which may also be subject to age related changes. On the other hand, recent work has shown that transcranial direct current stimulation (tDCS) may be a useful tool to restitute these altered mechanisms, and improve performance of motor skills. Objectives The present study first addresses the question of identifying physiological markers of age-related differences during acquisition and performance of bimanual motor movements, based on motor cortical functional connectivity using EEG. Second, the study assesses whether performance of complex bimanual motor skills can be improved in the elderly using tDCS. Methods Experiment 1 : 42 healthy, non-smoking subjects (20 young/22 elderly) were recruited. Subjects performed a bimanual tracking task similar to the classic “Etch-a-Sketch” game, which requires in-phase and anti-phase movements, and at various frequencies. Three blocks of the task were performed (180 total trials) in the single-session design to evaluate both kinematic and EEG metrics (phase lag functional connectivity) between the young and elderly. Experiment 2 : An additional 40 subjects (20 young/20 elderly) were recruited for evaluating whether right M1 anodal tDCS (1.0 mA, 20 min) may improve performance in the task. A double-blinded, sham-controlled, randomized crossover design was implemented to assess kinematic and functional connectivity differences between young and elderly. Data was statistically analyzed within the framework of mixed-design ANOVAs, in order to assess overall group differences in performance, as well as main effects of stimulation, across three incrementing levels of task difficulty. Results Experiment 1 : Task performance in younger subjects was more accurate than elderly. Elderly showed higher beta power during planning and performance periods. Lateralized motor cortical functional connectivity to prefrontal cortical areas was also greater in younger subjects, whereas elderly subjects showed no discrimination in activation during tasks that relied more on one hand. Experiment 2 : ANOVA revealed a main effect of stimulation in elderly but not in young. Post hoc analyses revealed significant improvements in both left and right hand coordination in real stimulation conditions. Younger subjects tended to improve performance as well, although ceilings effects may have been a constraint. In further post hoc analyses, we observed that older subjects favored slower, but accurate movement coordination whereas younger participants divided evenly in the speed vs. accuracy dichotomy. Conclusion We show that both functional connectivity and inter-limb kinematics underlying bimanual motor coordination are different between the young and elderly. Such differences may be due to constraints in muscular strength, degeneration of the gray matter, and/or differences in cortical connectivity as a result of the aging process. We further show that a single session of tDCS applied to the motor cortex was able to significantly improve the bimanual performance in both young and elderly. Although further studies are needed to optimize tDCS parameters for enhanced and prolonged effects, this non-invasive stimulation technique may be a viable tool in restituting and even further optimizing motor functioning. Download high-res image (183KB) Download full-size image

Movement preparation and execution: differential functional activation patterns after traumatic brain injury.

Years following the insult, patients with traumatic brain injury often experience persistent motor control problems, including bimanual coordination deficits. Previous studies revealed that such deficits are related to brain structural white and grey matter abnormalities. Here, we assessed, for the first time, cerebral functional activation patterns during bimanual movement preparation and performance in patients with traumatic brain injury, using functional magnetic resonance imaging. Eighteen patients with moderate-to-severe traumatic brain injury (10 females; aged 26.3 years, standard deviation = 5.2; age range: 18.4-34.6 years) and 26 healthy young adults (15 females; aged 23.6 years, standard deviation = 3.8; age range: 19.5-33 years) performed a complex bimanual tracking task, divided into a preparation (2 s) and execution (9 s) phase, and executed either in the presence or absence of augmented visual feedback. Performance on the bimanual tracking task, expressed as the average target error, was impaired for patients as compared to controls (P < 0.001) and for trials in the absence as compared to the presence of augmented visual feedback (P < 0.001). At the cerebral level, movement preparation was characterized by reduced neural activation in the patient group relative to the control group in frontal (bilateral superior frontal gyrus, right dorsolateral prefrontal cortex), parietal (left inferior parietal lobe) and occipital (right striate and extrastriate visual cortex) areas (P's < 0.05). During the execution phase, however, the opposite pattern emerged, i.e. traumatic brain injury patients showed enhanced activations compared with controls in frontal (left dorsolateral prefrontal cortex, left lateral anterior prefrontal cortex, and left orbitofrontal cortex), parietal (bilateral inferior parietal lobe, bilateral superior parietal lobe, right precuneus, right primary somatosensory cortex), occipital (right striate and extrastriate visual cortices), and subcortical (left cerebellum crus II) areas (P's < 0.05). Moreover, a significant interaction effect between Feedback Condition and Group in the primary motor area (bilaterally) (P < 0.001), the cerebellum (left) (P < 0.001) and caudate (left) (P < 0.05), revealed that controls showed less overlap of activation patterns accompanying the two feedback conditions than patients with traumatic brain injury (i.e. decreased neural differentiation). In sum, our findings point towards poorer predictive control in traumatic brain injury patients in comparison to controls. Moreover, irrespective of the feedback condition, overactivations were observed in traumatically brain injured patients during movement execution, pointing to more controlled processing of motor task performance.

Cortical grey matter content is associated with both age and bimanual performance, but is not observed to mediate age-related behavioural decline.

Declines in both cortical grey matter and bimanual coordination performance are evident in healthy ageing. However, the relationship between ageing, bimanual performance, and grey matter loss remains unclear, particularly across the whole adult lifespan. Therefore, participants (N=93, range 20-80years) performed a complex Bimanual Tracking Task, and structural brain images were obtained using magnetic resonance imaging. Analyses revealed that age correlated negatively with task performance. Voxel-based morphometry analysis revealed that age was associated with grey matter declines in task-relevant cortical areas and that grey matter in these areas was negatively associated with task performance. However, no evidence for a mediating effect of grey matter in age-related bimanual performance decline was observed. We propose a new hypothesis that functional compensation may account for the observed absence of mediation, which is in line with the observed pattern of increased inter-individual variance in performance with age.

Vision of the active limb impairs bimanual motor tracking in young and older adults.

Despite the intensive investigation of bimanual coordination, it remains unclear how directing vision toward either limb influences performance, and whether this influence is affected by age. To examine these questions, we assessed the performance of young and older adults on a bimanual tracking task in which they matched motor-driven movements of their right hand (passive limb) with their left hand (active limb) according to in-phase and anti-phase patterns. Performance in six visual conditions involving central vision, and/or peripheral vision of the active and/or passive limb was compared to performance in a no vision condition. Results indicated that directing central vision to the active limb consistently impaired performance, with higher impairment in older than young adults. Conversely, directing central vision to the passive limb improved performance in young adults, but less consistently in older adults. In conditions involving central vision of one limb and peripheral vision of the other limb, similar effects were found to those for conditions involving central vision of one limb only. Peripheral vision alone resulted in similar or impaired performance compared to the no vision (NV) condition. These results indicate that the locus of visual attention is critical for bimanual motor control in young and older adults, with older adults being either more impaired or less able to benefit from a given visual condition.

Reduced Neural Differentiation Between Feedback Conditions After Bimanual Coordination Training with and without Augmented Visual Feedback

It has been established that bimanual coordination with augmented feedback (FB) versus no augmented feedback (NFB) is associated with activity in different brain regions. It is unclear however, whether this distinction remains after practice comprising both these conditions. Functional magnetic resonance imaging was used in humans to compare visual FB versus NFB conditions for a bimanual tracking task, and their differential evolution across learning. Scanning occurred before (Pre) and after 2 weeks (Post) of mixed FB and NFB training using an event-related design, allowing differentiation between the planning and execution phase of the task. Activations at the whole-brain level initially differed for FB versus NFB movements but this differentiation diminished with training for the movement execution phase. Specifically, in right dorsal premotor cortex and right dorsolateral prefrontal cortex activation increased for NFB and decreased for FB trials to converge toward the end of practice. This suggests that learning led to a decreased need to adjust the ongoing movement on the basis of FB, whereas online monitoring became more pronounced in NFB trials as discrepancies between the required and the produced motor output were detected more accurately after training, due to a generic internal reference of correctness supporting movement control under varying conditions.

Dual Arm Manipulation using Constraint Based Programming

In this paper, we present a technique for online generation of dual arm trajectories using constraint based programming based on bound margins. Using this formulation, we take both equality and inequality constraints into account, in a way that incorporates both feedback and feedforward terms, enabling e.g. tracking of timed trajectories in a new way. The technique is applied to a dual arm manipulator performing a bi-manual task. We present experimental validation of the approach, including comparisons between simulations and real experiments of a complex bimanual tracking task. We also show how to add force feedback to the framework, to account for modeling errors in the systems. We compare the results with and without feedback, and show how the resulting trajectory is modified to achieve the prescribed interaction forces.

White matter organization in relation to upper limb motor control in healthy subjects: exploring the added value of diffusion kurtosis imaging

Diffusion tensor imaging (DTI) characterizes white matter (WM) microstructure. In many brain regions, however, the assumption that the diffusion probability distribution is Gaussian may be invalid, even at low b values. Recently, diffusion kurtosis imaging (DKI) was suggested to more accurately estimate this distribution. We explored the added value of DKI in studying the relation between WM microstructure and upper limb coordination in healthy controls (N=24). Performance on a complex bimanual tracking task was studied with respect to the conventional DTI measures (DKI or DTI derived) and kurtosis metrics of WM tracts/regions carrying efferent (motor) output from the brain, corpus callosum (CC) substructures and whole brain WM. For both estimation models, motor performance was associated with fractional anisotropy (FA) of the CC-genu, CC-body, the anterior limb of the internal capsule, and whole brain WM (r s range 0.42-0.63). Although DKI revealed higher mean, radial and axial diffusivity and lower FA than DTI (p<0.001), the correlation coefficients were comparable. Finally, better motor performance was associated with increased mean and radial kurtosis and kurtosis anisotropy (r s range 0.43-0.55). In conclusion, DKI provided additional information, but did not show increased sensitivity to detect relations between WM microstructure and bimanual performance in healthy controls.

Age-related decline of peripheral visual processing: the role of eye movements

Earlier work suggests that the area of space from which useful visual information can be extracted (useful field of view, UFoV) shrinks in old age. We investigated whether this shrinkage, documented previously with a visual search task, extends to a bimanual tracking task. Young and elderly subjects executed two concurrent tracking tasks with their right and left arms. The separation between tracking displays varied from 3 to 35 cm. Subjects were asked to fixate straight ahead (condition FIX) or were free to move their eyes (condition FREE). Eye position was registered. In FREE, young subjects tracked equally well at all display separations. Elderly subjects produced higher tracking errors, and the difference between age groups increased with display separation. Eye movements were comparable across age groups. In FIX, elderly and young subjects tracked less well at large display separations. Seniors again produced higher tracking errors in FIX, but the difference between age groups did not increase reliably with display separation. However, older subjects produced a substantial number of illicit saccades, and when the effect of those saccades was factored out, the difference between young and older subjects’ tracking did increase significantly with display separation in FIX. We conclude that the age-related shrinkage of UFoV, previously documented with a visual search task, is observable with a manual tracking task as well. Older subjects seem to partly compensate their deficit by illicit saccades. Since the deficit is similar in both conditions, it may be located downstream from the convergence of retinal and oculomotor signals.

Transfer of Motor Learning in a Visuomotor Tracking Task for Healthy Old and Young Adults

Using a continuous bimanual tracking task with three different movement speeds, we examined motor learning and transfer in older adults. Three groups of subjects within each age group learned only one particular trajectory during training of 40 trials, while the other two trajectories were not practiced during this period. Motor learning (measured as absolute and relative reduction in tracking error) was identified in all subjects. The most important finding was that motor learning was present even for the trajectories that were not practiced to almost the same degree as for practiced trajectories and motor skills for visuomotor tracking show the same amount of improvement and transfer in young and older adults.

Bimanual co-ordination in callosal agenesis and partial commissurotomy

Studies of bilateral motor coordination in commissurotomy patients pointed to the importance of direct interhemispheric integration for the fine regulation of the lower motor system within each hemisphere. When external visual feedback was withdrawn in the performance of a bimanual tracking task, partial commissurotomy patients, in whom the anterior portions of the callosum were cut, deviated significantly when drawing lines which required asymmetrical input from the two hands. The task devised by Preilowski was given to two adult acallosals, an 11 yr old acallosal boy, and an 11 yr old girl in whom the centre one-third of the corpus callosum had been sectioned. The acallosals performed in a manner similar to Preilowski's partial commissurotomy patients. The results were interpreted as confirming the interhemispheric integrative function of the corpus callosum. It is argued that they constitute further evidence for the existence of hemispheric dominance for motor control in acallosals. The partial commissurotomy patient did not differ in performance from normals. Her results were consistent with the view that it is the anterior parts of the callosum which are crucial for the interhemispheric integration of the lower motor system in each hemisphere.