Postural costs of performing cognitive tasks in non-coincident reference frames

An extensive literature exists attesting to the limited-capacity performance of everyday tasks, such as looking and mental manipulation. Only relatively recently has empirical interest turned towards the capacity limitations of the body coordinations (such as posture control) that provide the physical substrate for cognitive operations (and so mandatorily coexist with cognition). What are the capacity implications for the body’s safety and mobility, for example, in accommodating the need to stabilize the eye-head apparatus for looking, or when mentally manipulating objects in 3-D space? Specifically, what are the postural costs in having to position and orientate the body in its own task space while supporting spatial operations in cognitive task space? What are the performance implications, in turn, for everyday cognitive tasks when posture control is challenged in this way? The purpose of this thesis was to establish a theoretical and methodological basis for examining any postural costs that may arise from the sharing or partitioning of spatial reference frames between these two components (a frame co-registration cost hypothesis). In 7 experiments, young adults performed either conjunction visual search or mental rotation tasks (cognitive component) while standing upright (postural component). Visual search probed cognitive operations in extrapersonal space and mental rotation probed operations in representational space. Immersive visualization was used to operationalise postural and cognitive task contexts, by arranging for the two tasks (under varying postural and cognitive task-load conditions) to be carried out with respect to two spatial reference frames that were either coincident or noncoincident with each other. Aside from the expected performance trade-offs due to task-load manipulations, non-coincidence of reference frames was found to significantly add to postural costs for cognitive operations in extrapersonal space (visual search) and for representational space (mental rotation). These results demonstrate that the maintenance of multiple task-spaces can be a source of interference in posture-cognition dual-tasking. Such interference may arise, it is suggested, from the dynamics of time-sharing between underlying spatial coordinations required for these tasks. Beyond its importance within embodied cognition research, this work may have theoretical and methodological relevance to the study of posture-cognition in the elderly, and to the study of balance and coordination problems in learning difficulties such as those encountered in dyslexia and the autistic spectrum.EThOS - Electronic Theses Online ServiceEconomic and Social Research Council (ESRC)Warwick Postgraduate Research FellowshipGBUnited Kingdo

Understanding motor control in humans to improve rehabilitation robots

Recent reviews highlighted the limited results of robotic rehabilitation and the low quality of evidences in this field. Despite the worldwide presence of several robotic infrastructures, there is still a lack of knowledge about the capabilities of robotic training effect on the neural control of movement. To fill this gap, a step back to motor neuroscience is needed: the understanding how the brain works in the generation of movements, how it adapts to changes and how it acquires new motor skills is fundamental. This is the rationale behind my PhD project and the contents of this thesis: all the studies included in fact examined changes in motor control due to different destabilizing conditions, ranging from external perturbations, to self-generated disturbances, to pathological conditions. Data on healthy and impaired adults have been collected and quantitative and objective information about kinematics, dynamics, performance and learning were obtained for the investigation of motor control and skill learning. Results on subjects with cervical dystonia show how important assessment is: possibly adequate treatments are missing because the physiological and pathological mechanisms underlying sensorimotor control are not routinely addressed in clinical practice. These results showed how sensory function is crucial for motor control. The relevance of proprioception in motor control and learning is evident also in a second study. This study, performed on healthy subjects, showed that stiffness control is associated with worse robustness to external perturbations and worse learning, which can be attributed to the lower sensitiveness while moving or co-activating. On the other hand, we found that the combination of higher reliance on proprioception with \u201cdisturbance training\u201d is able to lead to a better learning and better robustness. This is in line with recent findings showing that variability may facilitate learning and thus can be exploited for sensorimotor recovery. Based on these results, in a third study, we asked participants to use the more robust and efficient strategy in order to investigate the control policies used to reject disturbances. We found that control is non-linear and we associated this non-linearity with intermittent control. As the name says, intermittent control is characterized by open loop intervals, in which movements are not actively controlled. We exploited the intermittent control paradigm for other two modeling studies. In these studies we have shown how robust is this model, evaluating it in two complex situations, the coordination of two joints for postural balance and the coordination of two different balancing tasks. It is an intriguing issue, to be addressed in future studies, to consider how learning affects intermittency and how this can be exploited to enhance learning or recovery. The approach, that can exploit the results of this thesis, is the computational neurorehabilitation, which mathematically models the mechanisms underlying the rehabilitation process, with the aim of optimizing the individual treatment of patients. Integrating models of sensorimotor control during robotic neurorehabilitation, might lead to robots that are fully adaptable to the level of impairment of the patient and able to change their behavior accordingly to the patient\u2019s intention. This is one of the goals for the development of rehabilitation robotics and in particular of Wristbot, our robot for wrist rehabilitation: combining proper assessment and training protocols, based on motor control paradigms, will maximize robotic rehabilitation effects

What Is the Contribution of Ia-Afference for Regulating Motor Output Variability During Standing?

Motor variability is an inherent feature of all human movements, and describes the system‘s stability and rigidity during the performance of functional motor tasks such as balancing. In order to ensure successful task execution, the nervous system is thought to be able to flexibly select the appropriate level of variability. However, it remains unknown which neurophysiological pathways are utilized for the control of motor output variability. In responding to natural variability (in this example sway), it is plausible that the neuro-physiological response to muscular elongation contributes to restoring a balanced upright posture. In this study, the postural sway of 18 healthy subjects was observed while their visual and mechano-sensory system was perturbed. Simultaneously, the contribution of Ia-afferent information for controlling the motor task was assessed by means of H-reflex. There was no association between postural sway and Ia-afference in the eyes open condition, however up to 4%of the effects of eye closure on themagnitude of sway can be compensated by increased reliance on Ia-afference. Increasing the biomechanical demands by adding up to 40% bodyweight around the trunk induced a specific sway response, such that the magnitude of sway remained unchanged but its dynamic structure became more regular and stable (by up to 18%). Such regular sway patterns have been associated with enhanced cognitive involvement in controlling motor tasks. It therefore appears that the nervous system applies different control strategies in response to the perturbations: The loss of visual information is compensated by increased reliance on other receptors; while the specific regular sway pattern associated with additional weight-bearing was independent of Ia-afferent information, suggesting the fundamental involvement of supraspinal centers for the control of motor output variability

Computational and Robotic Models of Human Postural Control

Currently, no bipedal robot exhibits fully human-like characteristics in terms of its postural control and movement. Current biped robots move more slowly than humans and are much less stable. Humans utilize a variety of sensory systems to maintain balance, primary among them being the visual, vestibular and proprioceptive systems. A key finding of human postural control experiments has been that the integration of sensory information appears to be dynamically regulated to adapt to changing environmental conditions and the available sensory information, a process referred to as "sensory re-weighting." In contrast, in robotics, the emphasis has been on controlling the location of the center of pressure based on proprioception, with little use of vestibular signals (inertial sensing) and no use of vision. Joint-level PD control with only proprioceptive feedback forms the core of robot standing balance control. More advanced schemes have been proposed but not yet implemented. The multiple sensory sources used by humans to maintain balance allow for more complex sensorimotor strategies not seen in biped robots, and arguably contribute to robust human balance function across a variety of environments and perturbations. Our goal is to replicate this robust human balance behavior in robots.In this work, we review results exploring sensory re-weighting in humans, through a series of experimental protocols, and describe implementations of sensory re-weighting in simulation and on a robot

Postural costs of performing cognitive tasks in non-coincident reference frames

An extensive literature exists attesting to the limited-capacity performance of everyday tasks, such as looking and mental manipulation. Only relatively recently has empirical interest turned towards the capacity limitations of the body coordinations (such as posture control) that provide the physical substrate for cognitive operations (and so mandatorily coexist with cognition). What are the capacity implications for the body’s safety and mobility, for example, in accommodating the need to stabilize the eye-head apparatus for looking, or when mentally manipulating objects in 3-D space? Specifically, what are the postural costs in having to position and orientate the body in its own task space while supporting spatial operations in cognitive task space? What are the performance implications, in turn, for everyday cognitive tasks when posture control is challenged in this way? The purpose of this thesis was to establish a theoretical and methodological basis for examining any postural costs that may arise from the sharing or partitioning of spatial reference frames between these two components (a frame co-registration cost hypothesis). In 7 experiments, young adults performed either conjunction visual search or mental rotation tasks (cognitive component) while standing upright (postural component). Visual search probed cognitive operations in extrapersonal space and mental rotation probed operations in representational space. Immersive visualization was used to operationalise postural and cognitive task contexts, by arranging for the two tasks (under varying postural and cognitive task-load conditions) to be carried out with respect to two spatial reference frames that were either coincident or noncoincident with each other. Aside from the expected performance trade-offs due to task-load manipulations, non-coincidence of reference frames was found to significantly add to postural costs for cognitive operations in extrapersonal space (visual search) and for representational space (mental rotation). These results demonstrate that the maintenance of multiple task-spaces can be a source of interference in posture-cognition dual-tasking. Such interference may arise, it is suggested, from the dynamics of time-sharing between underlying spatial coordinations required for these tasks. Beyond its importance within embodied cognition research, this work may have theoretical and methodological relevance to the study of posture-cognition in the elderly, and to the study of balance and coordination problems in learning difficulties such as those encountered in dyslexia and the autistic spectrum

The effects of peripheral nerve impairments on postural control and mobility among people with peripheral neuropathy

Approximately 20 million Americans are suffering Peripheral Neuropathy (PN). It is estimated that the prevalence of all-cause PN is about 2.4% in the entire adult population, whereas over 8-10% in the population segment over the age of 55 (Martyn & Hughes, 1997). Peripheral Neuropathy leads to a high risk of falling, resulting from the deficits of postural control caused by the impaired peripheral nerves, especially the degenerative somatosensory system. To date, there is no effective medical treatment for the disease but pain managements. The deficits of postural control decrease the life quality of this population. The degeneration of peripheral nerves reduces sensory inputs from the somatosensory system to central nervous system via spinal reflexive loop, which should provide valuable real-time information for balance correction. Therefore, it is necessary to investigate how PN affects the somatosensory system regarding postural control. Besides that, people with PN may develop a compensatory mechanism which could be reinforced by exercise training, ultimately to improve balance and mobility in their daily life. The neuroplasticity may occur within somatosensory system by relying on relative intact sensory resources. Hence, unveiling the compensatory mechanism in people with PN may help in understanding (a) essential sensations or function of peripheral nerves to postural control, (b) effective strategy of physical treatments for people with PN, and (c) task-dependent sensory information requirements. Therefore, this dissertation discussed the roles of foot sole sensation, ankle proprioception, and stretch reflex on balance as well as gait among people with PN. Furthermore, the discussion of the coupling between small and large afferent reflexive loops may spot the compensatory mechanism in people with PN

Effect of Aging on Human Postural Control and the Interaction with Attention

The ability to stand upright and walk is generally taken for granted, yet control of balance utilizes many processes involving the neuromuscular and sensory systems. As we age, balance function begins to decline and can become problematic for many older adults. In particular, adults 65 years of age and older exhibit a higher incidence of falls than younger adults, and falls are a leading cause of injury in older adults, contributing to significant medical costs. Without better understanding of the impact of aging on balance and means to ameliorate those effects, this problem is expected to grow as life expectancy continues to increase.In addition to sensori-motor declines with age that impact balance, another factor known to affect balance, particularly in older adults, is attention, meaning the amount of cognitive resources utilized for a particular task. When two or more tasks vie for cognitive resources, performance in one or more tasks can be compromised (a common example today is driving while talking on a cell phone). Attention has been observed to be a critical factor in many falls reported by older adults. However, it is still not fully understood how aging and attentional demand affect balance and how they interact with each other.In this dissertation, we conducted dual-task experiments and model-based analyses to study upright standing and the interaction of the effects of age and attention on postural control. The effect of age was investigated by testing two age groups (young and older adults) with no evident balance and cognitive impairment and by comparing results of the two groups. The effect of attention and its interaction with age was studied by comparing body sway in the two age groups in response to a moving platform, while either concurrently performing a cognitive task (dual-task) or not (single-task). Our findings highlight postural control differences between young and older adults, as quantified by experimental measures of body motion as well as by model parameter values, such as stiffness, damping and processing delay

Does dual tasking affect the ability to generate anticipatory postural adjustments?

Introduction: To date, little is known about the impact of additional cognitive tasks on perturbed balance and whether different types of cognitive tasks can generate different balance mechanisms. The aim of the study was to investigate how two different cognitive tasks (Stroop test and counting backwards task) would influence young adults’ ability to generate appropriate postural responses. Methods: Twenty young adults (25.95 ± 2.97 years) were asked to stand eyes open, bare feet shoulder-width apart on a moving platform which was translated in the anterior-posterior direction at three different frequencies (0.1, 0.25, 0.5 Hz) and perform either a counting backwards task, a Stroop task, or no cognitive task. Tonic activity and muscle onset latencies of the Rectus Femoris, Bicep Femoris, Tibialis Anterior and Gastrocnemius Medialis muscles were measured through surface electromyography (1000 Hz), and the number of cognitive errors was recorded. Results: Results showed no significant differences in muscle onset latencies and tonic activity between dual tasking and single tasking conditions, nor between the two dual tasking conditions. More cognitive errors were made in the counting backwards task (238 total cognitive errors across all frequencies) compared to the Stroop task where no errors were recorded. A frequency effect was identified with participants, regardless of condition, showing greater tonic activity in the Rectus Femoris (p= 0.012, M= 177% baseline, SD= 79.2), the Gastrocnemius Medialis (p= 0.016, M= 274.8% baseline, SD= 201.4) and the Bicep Femoris (p= 0.043, M= 291%, SD= 3.5) at 0.5 Hz, as well as earlier muscle activation in the Tibialis Anterior (p< 0.001, M= -2.7, SD= 8.1% half cycle), the Gastrocnemius Medialis (p< 0.001, M= -9.54, SD= 3.3% half cycle) and the Bicep Femoris (p< 0.001, M= -1.34, SD= 3.9% half cycle) at 0.5 Hz compared to the other frequencies. Transition and steady state muscle onset latencies were only significantly different for the Gastrocnemius Medialis at 0.25 Hz (p= 0.001), possibly because the 0.1 Hz frequency was too easy to require adaptation and the 0.5 Hz frequency was large enough to trigger earlier muscle activation from transition state which was then carried to steady state. Dual tasking did not seem to influence anticipatory postural adjustments, however perturbation intensities did. Discussion: It is assumed that due to the ‘threatening’ nature of the 0.5 Hz perturbation, a stiffer position was adopted as seen by the increased tonic activity, and anticipatory mechanisms were triggered sooner than the other frequencies, as seen by earlier muscle activation. Since posture was unchanged between single and dual tasking, it is suggested that participants’ postural control was automated and the cognitive errors in the two mental tasks could reflect their difficulty level. Future research should explore body kinematics to identify the balance strategies adopted, as well as take into account the reaction time of the cognitive task to better understand participants’ allocation of attention during perturbed balance dual tasking