Up–down Asymmetry in Vertical Induced Motion

Perception ◽  
1993 ◽  
Vol 22 (5) ◽  
pp. 527-535 ◽  
Author(s):  
Lori A Lott ◽  
Robert B Post
Keyword(s):  
Optokinetic Nystagmus ◽  
Motion Path ◽  
Optokinetic Stimulation ◽  
Stimulus Motion ◽  
Real Motion ◽  
Illusory Movement ◽  
Induced Motion ◽  
The Asymmetry ◽  
The Difference ◽  
Direction Opposite

Induced motion (IM) is the illusory movement of an object in the direction opposite to the real motion of adjacent detail. One theory of IM suggests that it results, in part, from suppression of optokinetic nystagmus (OKN) by fixational (smooth-pursuit) effort. In several studies an asymmetry in human vertical OKN has been reported, with upward optokinetic stimulation eliciting higher OKN gain than downward motion. This provides a test of the nystagmus-suppression theory of IM. If suppression of OKN contributes significantly to IM, upward inducing stimuli should result in a greater magnitude of the illusion than should downward stimulus motion. Additionally, the asymmetry of vertical OKN should become more pronounced at higher stimulus velocities. Therefore, the asymmetry of vertical IM should be greater at higher inducing-stimulus velocities. Twelve subjects viewed a large, random-dot stimulus, which moved either upward or downward at a velocity of 10, 40, or 70 deg s−1. Subjects fixated a horizontally moving laser spot and adjusted a rod to match the apparent slope of the motion path of the spot. IM magnitude was derived from these measures. Mean IM velocity was significantly higher with upward than with downward stimulation, and the difference was maximal at velocities of 40 and 70 deg s−1. The results are discussed within the context of the nystagmus-suppression theory and other theories of IM.

Induced Motion Considered as a Visually Induced Oculogyral Illusion

Perception ◽  
1986 ◽  
Vol 15 (2) ◽  
pp. 131-138 ◽  
Author(s):  
Robert B Post
Keyword(s):  
Optokinetic Nystagmus ◽  
Optokinetic Stimulation ◽  
Fixation Target ◽  
Illusory Motion ◽  
Reverse Phase ◽  
Ocular Pursuit ◽  
Stationary Stimulus ◽  
Oculogyral Illusion ◽  
Induced Motion ◽  
Perceived Motion

The possibility that nystagmus suppression contributes to illusory motion was investigated by measuring perceived motion of a stationary stimulus following the removal of an optokinetic stimulus. This was done because optokinetic nystagmus typically outlasts cessation of an optokinetic stimulus. Therefore, it would be expected that a stationary fixated stimulus should appear to move after removal of an optokinetic stimulus if illusory motion results from nystagmus suppression. Illusory motion was reported for a stationary fixation target following optokinetic stimulation. This motion was reported first in the same direction as the preceding induced motion, then in the opposite direction. The two directions of illusory motion following optokinetic stimulation are interpreted as resulting from the use of smooth ocular pursuit to suppress first one phase of optokinetic afternystagmus and then the reverse phase. Implications for the origins of induced motion are discussed.

Modification of Parameters in Vertical Optokinetic Nystagmus after Repeated Vertical Optokinetic Stimulation in Patients with Vestibular Lesions

1995 ◽  
Vol 115 (sup520) ◽  
pp. 419-422 ◽  
Author(s):  
Toshihiro Tsuzuku ◽  
Elisabeth Vitte ◽  
Alain Sémont ◽  
Alain Berthoz
Keyword(s):  
Optokinetic Nystagmus ◽  
Optokinetic Stimulation

Neural Processing of Gravito-Inertial Cues in Humans. IV. Influence of Visual Rotational Cues During Roll Optokinetic Stimuli

2003 ◽  
Vol 89 (1) ◽  
pp. 390-400 ◽  
Author(s):  
L. H. Zupan ◽  
D. M. Merfeld
Keyword(s):  
Visual Cues ◽  
Gravitational Force ◽  
Sensory Information ◽  
Inertial Force ◽  
Linear Acceleration ◽  
Otolith Organs ◽  
Optokinetic Stimulation ◽  
The Difference ◽  
The Right ◽  
Roll Tilt

Sensory systems often provide ambiguous information. For example, otolith organs measure gravito-inertial force (GIF), the sum of gravitational force and inertial force due to linear acceleration. However, according to Einstein's equivalence principle, a change in gravitational force due to tilt is indistinguishable from a change in inertial force due to translation. Therefore the central nervous system (CNS) must use other sensory cues to distinguish tilt from translation. For example, the CNS might use dynamic visual cues indicating rotation to help determine the orientation of gravity (tilt). This, in turn, might influence the neural processes that estimate linear acceleration, since the CNS might estimate gravity and linear acceleration such that the difference between these estimates matches the measured GIF. Depending on specific sensory information inflow, inaccurate estimates of gravity and linear acceleration can occur. Specifically, we predict that illusory tilt caused by roll optokinetic cues should lead to a horizontal vestibuloocular reflex compensatory for an interaural estimate of linear acceleration, even in the absence of actual linear acceleration. To investigate these predictions, we measured eye movements binocularly using infrared video methods in 17 subjects during and after optokinetic stimulation about the subject's nasooccipital (roll) axis (60°/s, clockwise or counterclockwise). The optokinetic stimulation was applied for 60 s followed by 30 s in darkness. We simultaneously measured subjective roll tilt using a somatosensory bar. Each subject was tested in three different orientations: upright, pitched forward 10°, and pitched backward 10°. Five subjects reported significant subjective roll tilt (>10°) in directions consistent with the direction of the optokinetic stimulation. In addition to torsional optokinetic nystagmus and afternystagmus, we measured a horizontal nystagmus to the right during and following clockwise (CW) stimulation and to the left during and following counterclockwise (CCW) stimulation. These measurements match predictions that subjective tilt in the absence of real tilt should induce a nonzero estimate of interaural linear acceleration and, therefore, a horizontal eye response. Furthermore, as predicted, the horizontal response in the dark was larger for Tilters ( n = 5) than for Non-Tilters ( n= 12).

Correction method for the asymmetry of the tangential beam in Couette (or Searle) geometry used in rheo-small-angle neutron scattering

2004 ◽  
Vol 37 (3) ◽  
pp. 438-444 ◽  
Author(s):  
Florian Nettesheim ◽  
Ulf Olsson ◽  
Peter Lindner ◽  
Walter Richtering
Keyword(s):  
Neutron Scattering ◽  
Cross Sections ◽  
Small Angle ◽  
Small Angle Neutron Scattering ◽  
Correction Method ◽  
Shear Cell ◽  
The Asymmetry ◽  
The Difference ◽  
Scattering Cross Sections ◽  
Final Expression

A method of correcting the asymmetry in the scattering of the tangential beam configuration in a rheo-small-angle neutron scattering experiment is proposed. The asymmetry of the scattering in the tangential beam configuration can be attributed to the difference in pathlength for neutrons that are scattered toward compared with those which are scattered away from the axis of rotation of the shear cell. The pathlength problem is solved and a final expression for the two-dimensional scattering intensity is given. The results from these calculations are compared with experimental data, which offer a different option to correct this asymmetry, namely by just measuring the scattering of H2O/D2O mixtures with absolute scattering cross sections identical to those of the respective samples. However, the situation for anisotropic media is more complex and the correction procedure described here is less effective.

scholarly journals Breaking the symmetry of geminates in diachrony and synchrony

2017 ◽  
Vol 2 ◽  
pp. 164-202 ◽  
Author(s):  
Michela Russo ◽  
Shanti Ulfsbjorninn
Keyword(s):  
Consonant Cluster ◽  
Structural Units ◽  
True Nature ◽  
Internal Forces ◽  
The Asymmetry ◽  
The Difference ◽  
Control Relation

Autosegmentalism invariably represents geminates in a symmetrical one-to-many relationship — as feature bundles or root nodes attached to two structural units: x-slots, moras, or C-slots. This symmetry, however, is often not reflected in their diachronic origin. For instance, in Blevins’ (2008) Type 1 pathway, only the second C of a consonant cluster (CC) ever determines the geminate: CxCy > CyCy, *CxCx (e.g. Latin > Italian). Moreover, although most synchronic processes identify geminates as symmetrical, there is an exception: geminate integrity. Unlike CCs and long vowels (LVs), geminates never ‘break’ by epenthesis: *CyCy > CyVCy. We propose that this is central to understanding the true nature of geminates, and present analyses in two frameworks. The first is ‘control by contiguity’, which uses head-dependent ‘control chains’ (Russo 2013). A control relation applies between a specified and an unspecified position: -C. Inalterability and integrity result from the asymmetry of the geminate’s positions. The second is based on Strict CV. This restricts a geminate’s melody to one of its two skeletal positions. Unlike CC and LVs, geminates do not involve a ‘trapped’ empty V position that could host epenthesis and cause breaking; the difference between LVs and geminates follows from framework-internal forces and suggests that melodic branching always requires licensing. These two approaches share the insight that the representation of geminates is not symmetrical, like that of long vowels.

scholarly journals A New Semisubmersible Design for Improved Heave Motion, Vortex-Induced Motion and Quayside Stability

2011 ◽  
Author(s):  
Qi Xu
Keyword(s):  
Floating Platform ◽  
Natural Period ◽  
Suppression Effect ◽  
Structural Rigidity ◽  
Hull Design ◽  
Induced Motion ◽  
Steel Catenary Risers ◽  
The Difference ◽  
Touchdown Point ◽  
Heave Motion

Recently the semisubmersible has become a favorable choice as a wet-tree floating platform supporting steel catenary risers (SCRs), mainly due to its capability of quayside topside integration and cost-effectiveness. However, it is still a challenge for a conventional semisubmersible to support SCRs, particularly large ones, in harsh environment and relatively shallow water due to its large heave motion. To answer this challenge, a new semisubmersible design has been developed at Technip as a wet-tree floater which achieves significantly improved heave motion and vortex-induced-motion (VIM) performance through hull form optimization while maintaining the simplicity of a conventional semisubmersible design. The difference between the NexGen semi-submersible design and a conventional semi-submersible design is in the blisters attached to the columns, distribution of pontoon volume, and pontoon cross section shape. In the NexGen semi-submersible design, the pontoon volume is re-distributed to minimize heave loading while maintaining sufficient structural rigidity, a long heave natural period and adequate quayside buoyancy. The blisters attached to the columns effectively break the vortex shedding coherence along the column length and therefore suppresses VIM. The blisters also provide much needed stability at quayside and during the hull deployment process, making the hull design less sensitive to topside weight increase. In the present paper the hydrodynamic aspects of this new design are discussed in detail. A benchmark case is presented in which the new design is compared against a more conventional design with the same principal dimensions. It is shown that the heave response in extreme sea states (100-yr hurricane) at the platform center of gravity is reduced by about 30–40%, and at the SCR hang-off locations by about 25–30%. Due to the reduced heave motion, SCRs experience about one third less stress at the touchdown point. A qualitative VIM analytical model is used to predict the VIM suppression effect of the new design. A highlight of a VIM model test for the proposed design is also presented. The reduced heave and VIM significantly improve the riser stress and fatigue near the touchdown point. This new design makes the semisubmersible a more robust wet-tree floater concept, and even a potentially good candidate as a dry-tree host concept in relatively benign environment.

Can Illusory Motion Disrupt Tracking Real Motion?

Perception ◽  
1997 ◽  
Vol 26 (3) ◽  
pp. 269-275 ◽  
Author(s):  
Timothy J Andrews ◽  
Allison N McCoy
Keyword(s):  
Motion Perception ◽  
Retinal Image ◽  
Optokinetic Nystagmus ◽  
Neural Representation ◽  
Illusory Motion ◽  
Brain Areas ◽  
Critical Rate ◽  
Real Motion ◽  
Actual Motion ◽  
Perceived Motion

When rotating stripes or other periodic stimuli cross the retina at a critical rate, a reversal in the direction of motion of the stimuli is often seen. This illusion of motion perception was used to explore the roles of retinal and perceived motion in the generation of optokinetic nystagmus. Here we show that optokinetic nystagmus is disrupted during the perception of this illusion. Thus, when perceived and actual motion are in conflict, subjects fail to track the veridical movement. This observation suggests that the perception of motion can directly influence optokinetic nystagmus, even in the presence of a moving retinal image. A conflict in the neural representation of motion in different brain areas may explain these findings.

Investigation of the tyre characteristics under non-steady-state conditions on the basis of road tests

2016 ◽  
Vol 231 (1) ◽  
pp. 3-15 ◽  
Author(s):  
Hubert Sar ◽  
Andrzej Reński ◽  
Janusz Pokorski
Keyword(s):  
Steady State ◽  
Computer Simulations ◽  
Dynamic Characteristics ◽  
Slip Angle ◽  
Real Motion ◽  
Side Force ◽  
The Real ◽  
Different Types ◽  
Non Linear ◽  
The Difference

This paper presents a method of identifying the dynamic characteristics of tyres for non-steady-state conditions on the basis of road measurements on a vehicle. The side force acting on the tyre is presented as a function of not only the slip angle but also the slip angle derivative (i.e. the velocity of the change in the slip angle). Hence, the influence of the manoeuvre dynamics on the tyre characteristics and the difference between the characteristics obtained for steady-state conditions and the characteristics for non-steady-state conditions are shown. Also the results of computer simulations prepared for different types of tyre characteristics are presented in this paper. It is evident from the presented graphs that applying dynamic non-linear tyre characteristics for computer simulations instead of steady-state characteristics enables us to describe the real motion of a vehicle better.

scholarly journals Determination of mass hierarchy with νμ → ντ appearance and the effect of nonstandard interactions

2017 ◽  
Vol 32 (11) ◽  
pp. 1750060 ◽  
Author(s):  
Ahmed Rashed ◽  
Alakabha Datta
Keyword(s):  
Asymmetry Parameter ◽  
Transition Probabilities ◽  
New Physics ◽  
Mass Hierarchy ◽  
Normal Hierarchy ◽  
Inverted Hierarchy ◽  
Leptonic Sector ◽  
The Asymmetry ◽  
The Difference

Crucial developments in neutrino physics would be the determination of the mass hierarchy (MH) and measurement of the CP phase in the leptonic sector. The patterns of the transition probabilities [Formula: see text] and [Formula: see text] are sensitive to these oscillation parameters. An asymmetry parameter can be defined as the difference of these two probabilities normalized to their sum. The profile of the asymmetry parameter gives a clear signal of the mass ordering as it is found to be positive for inverted hierarchy and negative for normal hierarchy. The asymmetry parameter is also sensitive to the CP phase. We consider the effects of nonstandard neutrino interactions (NSI) on the determination of the mass hierarchy. Since we assume the largest new physics effects involve the [Formula: see text] sector only, we ignore NSI in production and study the NSI effects in detection as well as along propagation. We find that the NSI effects can significantly modify the prediction of the asymmetry parameter though the MH can still be resolved.

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