8,055 research outputs found
Adaptive intermittent control: A computational model explaining motor intermittency observed in human behavior
It is a fundamental question how our brain performs a given motor task in a real-time fashion with the slow sensorimotor system. Computational theory proposed an influential idea of feed-forward control, but it has mainly treated the case that the movement is ballistic (such as reaching) because the motor commands should be calculated in advance of movement execution. As a possible mechanism for operating feed-forward control in continuous motor tasks (such as target tracking), we propose a control model called "adaptive intermittent control" or "segmented control," that brain adaptively divides the continuous time axis into discrete segments and executes feed-forward control in each segment. The idea of intermittent control has been proposed in the fields of control theory, biological modeling and nonlinear dynamical system. Compared with these previous models, the key of the proposed model is that the system speculatively determines the segmentation based on the future prediction and its uncertainty. The result of computer simulation showed that the proposed model realized faithful visuo-manual tracking with realistic sensorimotor delays and with less computational costs (i.e., with fewer number of segments). Furthermore, it replicated "motor intermittency", that is, intermittent discontinuities commonly observed in human movement trajectories. We discuss that the temporally segmented control is an inevitable strategy for brain which has to achieve a given task with small computational (or cognitive) cost, using a slow control system in an uncertain variable environment, and the motor intermittency is the side-effect of this strategy
Low Speed Flap-bounding in Ornithopters and its Inspiration on the Energy Efficient Flight of Quadrotors
Flap-bounding, a form of intermittent flight, is often exhibited by small birds over their entire range of flight speeds. The purpose of flap-bounding is unclear during low to medium speed (2 - 8 m/s) flight from a mechanical-power perspective: aerodynamic models suggest continuous flapping would require less power output and lower cost of transport. This thesis works towards the understanding of the advantages of flap-bounding and tries to employ the underlining principle to design quadrotor maneuver to improve power efficiency. To explore the functional significance of flap-bounding at low speeds, I measured body trajectory and kinematics of wings and tail of zebra finch (Taeniopygia guttata, N=2) during flights in a laboratory between two perches. The flights consist of three phases: initial, descending and ascending. Zebra finch first accelerated using continuous flapping, then descended, featuring intermittent bounds. The flight was completed by ascending using nearly-continuous flapping. When exiting bounds in descending phase, they achieved higher than pre-bound forward velocity by swinging body forward similar to pendulum motion with conserved mechanical energy. Takeoffs of black-capped chickadees (Poecile atricapillus, N=3) in the wild was recorded and I found similar kinematics. Our modeling of power output indicates finch achieves higher velocity (13%) with lower cost of transport (9%) when descending, compared with continuous flapping in previously-studied pigeons. To apply the findings to the design of quadrotor motion, a mimicking maneuver was developed that consisted of five phases: projectile drop, drop transition, pendulum swing, rise transition and projectile rise. The quadrotor outputs small amount (4 N) of thrust during projectile drop phase and ramps up the thrust while increasing body pitch angle during the drop transition phase until the thrust enables the quadrotor to advance in pendulum-like motion in the pendulum swing phase. As the quadrotor reaches the symmetric point with respect to the vertical axis of the pendulum motion, it engages in reducing the thrust and pitch angle during the rise transition phase until the thrust is lowered to the same level as the beginning of the maneuver and the body angle of attack minimized (0.2 deg) in the projectile rise phase. The trajectory of the maneuver was optimized to yield minimum cost of transport. The quadrotor moves forward by tracking the cycle of the optimized trajectory repeatedly. Due to the aggressive nature of the maneuver, we developed new algorithms using onboard sensors to determine the estimated position and attitude. By employing nonlinear controller, we showed that cost of transport of the flap-bounding inspired maneuver is lower (28%) than conventional constant forward flight, which makes it the preferable strategy in high speed flight (≥15 m/s)
Effects of the CPAP Treatment on the NON-REM Sleep Microstructures in Patients with Severe Apnea-Hypoapnea Syndrome
Sleep quality is affected in patients with sleep apnea- hypopnea syndrome (SAHS) with nocturnal and diurnal consequences. Most of these patients who are treated with positive airway pressure (CPAP) return to normal sleep patterns. We could consider good sleepers those patients who present more sleep spindles in stage II, and slower wave sleep as a good sign of better sleep quality. The objective in this research study was to compare the microstructure of stage II using the number of spindles and the increase of slow wave sleep before and after CPAP night titration. We developed a wavelet filter using a spline cubic function from a wavelet mother, which was appropriate to be used over electroencephalographic signal. By means of this filter in a multi-resolution mode, the spindles were detected from the increase of the IV band power; the sampling rate of the device determined the filter characteristics. The staging of polysomnographic studies was made by an expert according AASM (American Academy of Sleep Medicine) and then processed by the filter to get the index of sleep spindles before-and-after CPAP during stage II as well as the relationship between fast and slow powers from the EEG signal. An increase in the power of the slow waves vs. fast activity was observed in all the cases as a feature of better sleep. The neuroprotective effect described in previous research works regarding the density of the sleep spindles seems to be detected in patients improving their sleep quality after the correction of the apnea-hypopnea syndrome using CPAP.Fil: Smurra, Marcela. Gobierno de la Ciudad de Buenos Aires. Hospital General de Agudos Dr. Enrique Tornú; ArgentinaFil: Blanco, Susana Alicia Ana. Universidad de Belgrano. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Eguiguren, Veronica. Gobierno de la Ciudad de Buenos Aires. Hospital General de Agudos Dr. Enrique Tornú; ArgentinaFil: Di Risio, Cecilia Diana. Universidad de Belgrano. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
Aerospace Medicine and Biology: A continuing bibliography with indexes (supplement 141)
This special bibliography lists 267 reports, articles, and other documents introduced into the NASA scientific and technical information system in April 1975
A robot model of the basal ganglia: Behavior and intrinsic processing
The existence of multiple parallel loops connecting sensorimotor systems to the basal ganglia has given rise to proposals that these nuclei serve as a selection mechanism resolving competitions between the alternative actions available in a given context. A strong test of this hypothesis is to require a computational model of the basal ganglia to generate integrated selection sequences in an autonomous agent, we therefore describe a robot architecture into which such a model is embedded, and require it to control action selection in a robotic task inspired by animal observations. Our results demonstrate effective action selection by the embedded model under a wide range of sensory and motivational conditions. When confronted with multiple, high salience alternatives, the robot also exhibits forms of behavioral disintegration that show similarities to animal behavior in conflict situations. The model is shown to cast light on recent neurobiological findings concerning behavioral switching and sequencing
Postural instability via a loss of intermittent control in elderly and patients with Parkinson's disease: a model-based and data-driven approach
Postural instability is one of the major symptoms of Parkinson's disease. Here, we assimilated a model of intermittent delay feedback control during quiet standing into postural sway data from healthy young and elderly individuals as well as patients with Parkinson's disease to elucidate the possible mechanisms of instability. Specifically, we estimated the joint probability distribution of a set of parameters in the model using the Bayesian parameter inference such that the model with the inferred parameters can best-fit sway data for each individual. It was expected that the parameter values for three populations would distribute differently in the parameter space depending on their balance capability. Because the intermittent control model is parameterized by a parameter associated with the degree of intermittency in the control, it can represent not only the intermittent model but also the traditional continuous control model with no intermittency. We showed that the inferred parameter values for the three groups of individuals are classified into two major groups in the parameter space: one represents the intermittent control mostly for healthy people and patients with mild postural symptoms and the other the continuous control mostly for some elderly and patients with severe postural symptoms. The results of this study may be interpreted by postulating that increased postural instability in most Parkinson's patients and some elderly persons might be characterized as a dynamical disease
The dynamics of pattern matching in camouflaging cuttlefish
Many cephalopods escape detection using camouflage. This behaviour relies on a visual assessment of the surroundings, on an interpretation of visual-texture statistics and on matching these statistics using millions of skin chromatophores that are controlled by motoneurons located in the brain. Analysis of cuttlefish images proposed that camouflage patterns are low dimensional and categorizable into three pattern classes, built from a small repertoire of components. Behavioural experiments also indicated that, although camouflage requires vision, its execution does not require feedback, suggesting that motion within skin-pattern space is stereotyped and lacks the possibility of correction. Here, using quantitative methods, we studied camouflage in the cuttlefish Sepia officinalis as behavioural motion towards background matching in skin-pattern space. An analysis of hundreds of thousands of images over natural and artificial backgrounds revealed that the space of skin patterns is high-dimensional and that pattern matching is not stereotyped-each search meanders through skin-pattern space, decelerating and accelerating repeatedly before stabilizing. Chromatophores could be grouped into pattern components on the basis of their covariation during camouflaging. These components varied in shapes and sizes, and overlay one another. However, their identities varied even across transitions between identical skin-pattern pairs, indicating flexibility of implementation and absence of stereotypy. Components could also be differentiated by their sensitivity to spatial frequency. Finally, we compared camouflage to blanching, a skin-lightening reaction to threatening stimuli. Pattern motion during blanching was direct and fast, consistent with open-loop motion in low-dimensional pattern space, in contrast to that observed during camouflage.journal articl
Constriction Behavior, a Key Innovation In Snake Evolution: The Integration of Ethology and Physiology
Among living tetrapod vertebrates, snakes exhibit the most radical shifts in feeding biology and among limbless squamate reptiles, only snakes have undergone a substantial adaptive radiation. The behavioral innovation, constriction, has been associated with the success of this clade. Constriction is a prey restraint behavior that enabled snakes to immobilize and subdue extremely large prey items relative to their own body mass. This behavior pattern is associated with the incredible shifts observed in snake feeding biology from consuming small meals frequently to less frequent feeding on large prey. Although constriction is an ethological homology for the majority of snakes, variations of constriction postures have been documented in many derived snake lineages. Nevertheless, the mechanisms driving behavioral variation are not well understood. In this dissertation, I attempt to use a comparative hierarchical approach to examine constriction behavior at both the ethological and physiological levels in order to better understand the behavioral variation of this key innovation.
As reviewed in Part 1, derived snake lineages seem to have several methods with which to restrain prey. Prey restraint methods appear to vary with respect to prey characteristics (size, shape, activity level). On the other hand, intermediate taxa (boas and pythons) are thought to be less variable in the prey restraint phase of feeding. The kinematics of loop application pattern also appears to differ between intermediate and derived snake groups. Derived snakes use the lateral part of their body to wind prey whereas boas tend to bend ventrally around prey. The polarity for variable prey restraint behavior and loop application patterns have not been determined as observations on feeding behavior for basal snake taxa are lacking.
I report on stimulus control studies evaluating prey restraint behavior and loop application pattern for basal and intermediate snake taxa in Part 2. Testing for the effects of prey size and status on the prey restraint behavior enabled me to polarize variable prey restraint behavior and loop application pattern. Prey size and status had varying effects on the capture position, prey restraint method, prey restraint time and swallowing time for basal and semi-fossorial boas while individuals of B. constrictor only constricted prey. Looping one or more times around prey was observed during the intraoral transport (swallowing) phase of feeding in the majority of trials for L. bicolor and Erycine snakes (Eryx muelleri, Charina bottae, Lichanura triviragata). Loop application patterns varied across snake taxa with basal and semi-fossorial boas applying loops laterally around prey. Individuals of B. constrictor bent ventrally around prey. The ability to vary prey restraint behavior, in response to prey characteristics and applying loops laterally around prey is probably the ancestral condition in snakes. Intermediate taxa, such a boas exhibit a derived simplified behavioral repertoire.
Examining the underlying physiology of a complex motor pattern, such as constriction behavior, can provide a better understanding of the hierarchical structure of organisms in nature. As an ethological homology, constriction behavior provides us with the opportunity to trace evolutionary change at other levels of biological organization and to examine how various levels within a hierarchy relate to one another.
Although constriction is an important key innovation associated with the adaptive radiation of snakes, few studies have examined the underlying physiological patterns of this complex motor pattern that may account for the kinematic variability of constriction postures among snakes. In Parts 3 & 4, I comparatively examine the muscle activity patterns during constriction for basal and intermediate snake lineages. I specifically investigated how the underlying physiological mechanisms of constriction correspond to the postural changes observed at the behavioral level using electromyography. Lateral bending and unilateral muscle activity patterns were predominant in the basal taxon, Loxocemus bicolor. Lateral bending and unilateral muscle activity patterns were also observed in derived snake taxa previously documented. Ventral bending and bilateral epaxial muscle activity patterns were predominant in intermediate lineages and present in derived snake lineages. Therefore, similar to prey restraint behaviors, three epaxial muscle activity patterns were observed: 1) mostly lateral bending with unilateral epaxial muscle activity, 2) mostly ventral bending with bilateral muscle activity and 3) mostly lateral and some bilateral bends associated with both unilateral and bilateral epaxial muscle activity, “mixed”. The kinematic and muscle activity patterns correspond with the ethological data in Part 2.
Lateral bending and unilateral epaxial muscle activity support the more variable prey restraint behaviors observed in basal and derived snake taxa. Ventral bending and bilateral activity supports the highly stereotyped behavior patterns observed in intermediate snake taxa. A ‘mixed’ kinematic and epaxial activity pattern supports highly variable prey restraint methods as observed from previous research on gopher snakes and kingsnakes. Thus the patterns of epaxial muscle activity underlying constriction behavior can be correlated with the variability in prey restraint postures.
In Part 5, I integrate the behavioral, physiological, and ecological differences reported for L. bicolor and Boid snakes, from the stimulus control data and the physiological data collected in this study, to further discuss the origin and evolution of feeding behavior among basal, intermediate and derived snake taxa
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