1,721,097 research outputs found
An Update on Mathematical Models of the Saccadic Mechanism
No full textSaccades are the rapid eye movements that we continuously make to shift gaze from one object of interest to another. These voluntary eye movements not only are exemplary to describe various forms of ocular motor and cognitive function but also have a fundamental role as a prototype for understanding general principles in motor neurosciences. Their production requires most of the information processing steps that are needed in all motor control tasks, yet their understanding is far more detailed than that related to other fields in motor control. Indeed, a great deal has been learned about the anatomy and neurophysiology of saccades thanks to a fruitful collaboration between clinical studies, basic science research, and mathematical modeling. In this non-exhaustive review, I will discuss contemporary computational concepts that describe the current understanding of the physiology of saccades in health and disease
Estimating the time constants of the rVOR. A model-based study.
No full textSingle-unit recordings of vestibular afferents from the semicircular canals of squirrel monkeys have shown that the cupular time constant (T(c)) is between 5 and 6 sec. Such recordings obviously cannot be performed in humans, and the corresponding values have thus been inferred to be somewhat longer based on their size and on the cupula-endolymph system. The ocular motor response of the rotational vestibule-ocular reflex (rVOR) is characterized by longer time constants, typically between 15 and 20 sec, due to the so-called velocity storage mechanism (VSM), which prolongs the time constant of the afferents through central processing. Recent studies have attempted to determine the time constant of the cupola by fitting the slow phase velocity (SPV) of the response to postrotational stimuli using a mathematical model of the rVOR processing. To this goal they considered the processing of head velocity due to the peripheral vestibular organs and to the VSM. The resulting estimates of T. are lower than expected, averaging about 4 sec. These modeling approaches, though, neglect both the processing of the final common pathway and the adaptation shown by the discharge of primary vestibular afferents. Here we argue that such an approach may be bound to underestimate the duration of the rVOR time constants
Latency detection in motor responses: a model based approach with genetic algorithm optimization
No full textThe latency of a response is one of the most frequently reported parameters when describing the characteristics of a motor system. Such measurement provides important information both to the basic researcher investigating the neural circuitry of the underlying physiological system and to the clinician gathering information for diagnosing a patient. Our concern here is that when the latency of a response is determined on experimentally recorded data by using the most commonly referenced techniques to find the onset of a motor response, the resulting figure encompasses both the neural processing time and the dynamics of the system producing the response (e.g., the musculoskeletal apparatus). Therefore, the resulting latency measurement cumulates information relative to two substantially different sources and thus having different implications. The goal of our study is that of suggesting a technique allowing the separation of the relative contributions of neural transmission and processing time from that of the dynamics of the motor system. This is accomplished by using a technique based on fitting a model to the experimentally recorded response, thus allowing to exploit as much as is known with regards to the dynamics of the studied motor system (e.g., model order and constraints on the values of the model parameters). The optimization of the model parameters for fitting the experimental data is carried out using a real-valued genetic algorithm, allowing to avoid trapping in local, suboptimal minima. The use of this approach allows to estimate the pure delay in the response introduced by neural processing more accurately than the traditional latency detection techniques based on adaptive thresholds
A computational framework for the standardization of motion analysis exploiting wearable inertial sensors.
No full textHEAD IMPULSE TESTING DEVICE FOR ASSESSING THE FUNCTIONALITY OF THE SEMICIRCULAR CANALS AND FOR THE REHABILITATION OF VESTIBULAR LOSS
No full textThe device allows: 1) the evaluation of the function of each individual semicircular canal over a range of head accelerations based on the ability to stabilize the visual scene during head impulse tests and 2) the rehabilitation of vestibular function through an adaptive algorithm constantly challenging the vestibular stabilization system and thus promote adaptive compensatory mechanisms
The translational vestibulo ocular reflex (TVOR) in humans: responses to abrupt, high-acceleration stimuli
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