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D M Merfeld - One of the best experts on this subject based on the ideXlab platform.

  • Vestibulo-ocular reflex of the squirrel monkey during eccentric rotation with Centripetal Acceleration along the naso-occipital axis.
    Brain research bulletin, 1996
    Co-Authors: D M Merfeld
    Abstract:

    The vestibulo-ocular reflexes (VOR) are determined not only by angular Acceleration, but also by the presence of gravity and linear Acceleration. This phenomenon was studied by measuring three-dimensional nystagmic eye movements, with implanted search coils, in four male squirrel monkeys. Monkeys were rotated in the dark at 200 degrees/s, centrally or 79 cm off-axis, with the axis of rotation always aligned with gravity and the spinal axis of the upright monkeys. The monkey's position relative to the Centripetal Acceleration (facing center or back to center) had a dramatic influence on the VOR. These studies show that a torsional response was always elicited that acted to shift the axis of eye rotation toward alignment with gravito-inertial force. On the other hand, a slow phase downward vertical response usually existed, which shifted the axis of eye rotation away from the gravito-inertial force. These findings were consistent across all monkeys. In another set of tests, the same monkeys were rapidly tilted about their interaural (pitch) axis. Tilt orientations of 45 degrees and 90 degrees were maintained for 1 min. Other than a compensatory angular VOR during the rotation, no consistent eye velocity response was ever observed during or following the tilt. The absence of any response following tilt proves that the observed torsional and vertical responses were not a positional nystagmus. Model simulations qualitatively predict all components of these eccentric rotation and tilt responses. These simulations support the conclusion that the VOR during eccentric rotation may consist of two components: a linear VOR and a rotational VOR. The model predicts a slow phase downward, vertical, linear VOR during eccentric rotation even though there was never a change in the force aligned with monkey's spinal (Z) axis. The model also predicts the torsional components of the response that shift the rotation axis of the angular VOR toward alignment with gravito-inertial force.

  • Spatial orientation of VOR to combined vestibular stimuli in squirrel monkeys.
    Acta oto-laryngologica. Supplementum, 1991
    Co-Authors: D M Merfeld, Laurence R. Young, David L. Tomko, Gary D. Paige
    Abstract:

    The interaction of angular and linear stimuli produces a complex alignment of spatial orientation and the VOR. This phenomenon was studied by measuring three dimensional eye movements in 6 squirrel monkeys during centrifugation in the dark. The axis of eye rotation was always aligned with gravity and with the spinal axis of the upright monkeys. The erect monkeys were oriented such that they were either facing toward the direction of motion or were facing away from the motion. Angular velocity trapezoids were utilized as the motion stimuli with a ramp Acceleration of 10°/s2 to a constant velocity of 200°/s. This yields a final Centripetal Acceleration of 1 g. The orientation of Centripetal Acceleration dramatically altered the VOR by changing the axis of eye rotation, the peak value of slow phase eye velocity, and the time constant of per-rotary decay. The axis of eye rotation always tended to align with gravito-inertial force, the peak value of slow phase eye velocity was greater when the monkey faced the...

Hidenori Inohara - One of the best experts on this subject based on the ideXlab platform.

  • Three-dimensional analysis of the vestibulo-ocular reflex and the ability to distinguish the direction of Centripetal Acceleration in humans during eccentric rotation with the right ear facing downwards.
    Neuroscience research, 2018
    Co-Authors: Xiuwen Jiang, Takao Imai, Tomoko Okumura, Yumi Ohta, Yasuhiro Osaki, Takashi Sato, Hidenori Inohara
    Abstract:

    Abstract This study was conducted to evaluate the linear vestibulo-ocular reflex (lVOR) mediated by the saccule, and to investigate the relationship between the lVOR and the ability to distinguish the direction of Centripetal Acceleration during centric and eccentric rotation. Participants sat on a chair in darkness, with the right ear facing downwards, either directly above the center of rotation, or with their nose out, nose in, right shoulder out, or left shoulder out against the center of rotation (eccentric rotation). Participants were given no information about the chair position, and were rotated sinusoidally at 0.1–0.7 Hz. Three-dimensional eye movements during rotation were analyzed. Participants were asked to describe the position of the chair after rotation. Correctly reporting the five possible chair positions requires recognition of the direction of Centripetal Acceleration. We analyzed the rate of correct answers to assess participants’ ability to identify the direction of Centripetal Acceleration. lVOR mediated by the saccule was observed only at high rotational frequencies. The rate of correct answers was higher at high rotational frequencies than that at low rotational frequencies. These results indicate that high rotational frequency is important for both lVOR mediated by the saccule and distinguishing the direction of Centripetal Acceleration.

Xinmin Yang - One of the best experts on this subject based on the ideXlab platform.

  • Training GANs with predictive projection Centripetal Acceleration.
    arXiv: Machine Learning, 2020
    Co-Authors: Ke Zhang, Qiang Liu, Xinmin Yang
    Abstract:

    Although remarkable successful in practice, training generative adversarial networks(GANs) is still quite difficult and iteratively prone to cyclic behaviors, as GANs need to solve a non-convex non-concave min-max game using a gradient descent ascent (GDA) method. Motivated by the ideas of simultaneous Centripetal Acceleration (SCA) and modified predictive methods (MPM), we propose a novel predictive projection Centripetal Acceleration (PPCA) methods to alleviate the cyclic behaviors. Besides, under suitable assumptions, we show that the difference between the signed vector of partial derivatives at t + 1 and t is orthogonal to the signed vector of partial derivatives at t for GDA, and the last-iterate exponential convergence on the bilinear game. Finally, numerical simulations are conducted by PPCA in GANs setting, and the results illustrate the effectiveness of our approach.

Carolin Curtze - One of the best experts on this subject based on the ideXlab platform.

  • inertial sensor based Centripetal Acceleration as a correlate for lateral margin of stability during walking and turning
    IEEE Transactions on Neural Systems and Rehabilitation Engineering, 2020
    Co-Authors: Peter C Fino, Fay B Horak, Carolin Curtze
    Abstract:

    There is growing interest in using inertial sensors to continuously monitor gait during free-living mobility. Inertial sensors can provide many gait measures, but they struggle to capture the spatial stability of the center-of-mass due to limitations estimating sensor-to-sensor distance. While the margin of stability (MoS) is an established outcome describing the instantaneous mechanical stability of gait relating to fall-risk, methods to estimate the MoS from inertial sensors have been lacking. Here, we developed and tested a framework, based on Centripetal Acceleration, to determine a correlate for the lateral MoS using inertial sensors during walking with or without turning. Using three synchronized sensors located bilaterally on the feet and lumbar spine, the average Centripetal Acceleration over the subsequent step can be used as a correlate for lateral MoS. Relying only on a single sensor on the lumbar spine yielded similar results if the stance foot can be determined from other means. Additionally, the Centripetal Acceleration correlate of lateral MoS demonstrates clear differences between walking and turning, inside and outside turning limbs, and speed. While limitations and assumptions need to be considered when implemented in practice, this method presents a novel correlate for the lateral MoS during walking and turning using inertial sensors, although further validation is required for other activities and populations.

  • Estimating the lateral margin of stability during walking and turning using inertial sensors
    2019
    Co-Authors: Peter C Fino, Fay B Horak, Carolin Curtze
    Abstract:

    Abstract There is growing interest in using inertial sensors to continuously monitor gait during free-living mobility. Inertial sensors can provide many gait measures, but they struggle to capture the spatial stability of the center-of-mass due to limitations estimating sensor-to-sensor distance. While the margin of stability (MoS) is an established outcome describing the instantaneous mechanical stability of gait relating to fall-risk, methods to estimate the MoS from inertial sensors have been lacking. Here, we developed and tested a construct, based on Centripetal Acceleration, to estimate the lateral MoS using inertial sensors during walking and turning. Using three sensors located bilaterally on the feet and lumbar spine, the lateral MoS can be consistently and reliably estimated based on the average Centripetal Acceleration over the subsequent step. Relying only on a single sensor on the lumbar spine yielded similar results at the expense of identifying left versus right stance foot. Additionally, the Centripetal Acceleration estimate of lateral MoS demonstrates clear differences between walking and turning, inside and outside turning limbs, and speed. While limitations and assumptions need to be considered when implemented in practice, this method presents a novel, reliable way to estimate the lateral MoS during free-living community ambulation using inertial sensors.

David F. Crawford - One of the best experts on this subject based on the ideXlab platform.

  • A static stable universe
    The Astrophysical Journal, 1993
    Co-Authors: David F. Crawford
    Abstract:

    A static and stable solution to a Newtonian cosmological model is described where the Centripetal Acceleration of high-temperature particles moving in a three-sphere embedded in a four-dimensional Euclidian space balances the gravitational Acceleration. This model is used to show a possible deficiency in the equations of general relativity in that the Newtonian model contains a term corresponding to Centripetal Accelerations that is not present in Friedmann's equations. Together with a gravitational interaction that can explain the Hubble redshift it provides a viable cosmological model