Visual Directions of Two Stimuli in Panum's Limiting Case

Perception ◽  
1994 ◽  
Vol 23 (9) ◽  
pp. 1037-1048 ◽  
Author(s):  
Sachio Nakamizo ◽  
Koichi Shimono ◽  
Michiaki Kondo ◽  
Hiroshi Ono
Keyword(s):  
Sagittal Plane ◽  
Visual Direction ◽  
Frontoparallel Plane ◽  
Retinal Disparity ◽  
Limiting Case

Visual directions of the two stimuli in Panum's limiting case with different interstimulus and convergence distances confirmed the predictions from the reformulated Wells—Hering's laws of visual direction. In experiment 1, six observers each converged on the midpoint of the interstimulus axis at 30, 60, and 90 cm from the eyes and adjusted a probe on the fixation plane to be in the same visual direction as that of each stimulus. Visual direction of the far stimulus was always nonveridical whereas that of the near stimulus was veridical only when its retinal disparity was small. In experiment 2, three observers each converged on the intersection of mid-sagittal plane and (a) the frontoparallel plane of the near stimulus, (b) that of the midpoint between the two stimuli, or (c) that of the far stimulus. The midpoint of the interstimulus axis was 60 cm from the eyes. Visual direction of the far stimulus was veridical only with convergence at the far plane. Visual direction of the near stimulus was veridical with convergence at the near plane, and also, only when its retinal disparity was small, with convergence at the two other planes.

Geometric Considerations for Stereoscopic Virtual Environments

1993 ◽  
Vol 2 (1) ◽  
pp. 34-43 ◽  
Author(s):  
Larry F. Hodges ◽  
Elizabeth Thorpe Davis
Keyword(s):  
Virtual Environments ◽  
Virtual Environment ◽  
Visual Direction ◽  
Apparent Depth ◽  
Spatial Unit ◽  
Retinal Disparity ◽  
Relationship Of ◽  
The Relationship

We examine the relationship among the different geometries implicit in a stereoscopic virtual environment. In particular, we examine in detail the relationship of retinal disparity, fixation point, binocular visual direction, and screen parallax. We introduce the concept of a volumetric spatial unit called a stereoscopic voxel. Due to the shape of stereoscopic voxels, apparent depth of points in space may be affected by their horizontal placement.

Dissociation between Visual Perception of Allocentric Distance and Visually Directed Walking of its Extent

Perception ◽  
10.1068/p5444 ◽  
2005 ◽  
Vol 34 (11) ◽  
pp. 1399-1416 ◽  
Author(s):  
Nobuo Kudoh
Keyword(s):  
Visual Perception ◽  
Sagittal Plane ◽  
Human Perception ◽  
Matching Task ◽  
Frontoparallel Plane ◽  
Motor Systems ◽  
Motor Responses ◽  
Presentation Condition ◽  
Perceptual Matching ◽  
Depth Compression

Walking without vision to previously viewed targets was compared with visual perception of allocentric distance in two experiments. Experimental evidence had shown that physically equal distances in a sagittal plane on the ground were perceptually underestimated as compared with those in a frontoparallel plane, even under full-cue conditions. In spite of this perceptual anisotropy of space, Loomis et al (1992 Journal of Experimental Psychology: Human Perception and Performance18 906–921) found that subjects could match both types of distances in a blind-walking task. In experiment 1 of the present study, subjects were required to reproduce the extent of allocentric distance between two targets by either walking towards the targets, or by walking in a direction incompatible with the locations of the targets. The latter condition required subjects to derive an accurate allocentric distance from information based on the perceived locations of the two targets. The walked distance in the two conditions was almost identical whether the two targets were presented in depth (depth-presentation condition) or in the frontoparallel plane (width-presentation condition). The results of a perceptual-matching task showed that the depth distances had to be much greater than the width distances in order to be judged to be equal in length (depth compression). In experiment 2, subjects were required to reproduce the extent of allocentric distance from the viewing point by blindly walking in a direction other than toward the targets. The walked distance in the depth-presentation condition was shorter than that in the width-presentation condition. This anisotropy in motor responses, however, was mainly caused by apparent overestimation of length oriented in width, not by depth compression. In addition, the walked distances were much better scaled than those in experiment 1. These results suggest that the perceptual and motor systems share a common representation of the location of targets, whereas a dissociation in allocentric distance exists between the two systems in full-cue conditions.

Freeze fracture imaging and computer simulation of liposome structure: Membrane geometry and defects

1983 ◽  
Vol 41 ◽  
pp. 646-647
Author(s):  
Joseph A. Zasadzinski
Keyword(s):  
Liquid Crystalline ◽  
Freeze Fracture ◽  
Continuum Theory ◽  
Closed Surfaces ◽  
Straight Line ◽  
Low Weight ◽  
Concentric Spheres ◽  
Membrane Geometry ◽  
Dupin Cyclides ◽  
Limiting Case

At low weight fractions, many surfactant and biological amphiphiles form dispersions of lamellar liquid crystalline liposomes in water. Amphiphile molecules tend to align themselves in parallel bilayers which are free to bend. Bilayers must form closed surfaces to separate hydrophobic and hydrophilic domains completely. Continuum theory of liquid crystals requires that the constant spacing of bilayer surfaces be maintained except at singularities of no more than line extent. Maxwell demonstrated that only two types of closed surfaces can satisfy this constraint: concentric spheres and Dupin cyclides. Dupin cyclides (Figure 1) are parallel closed surfaces which have a conjugate ellipse (r1) and hyperbola (r2) as singularities in the bilayer spacing. Any straight line drawn from a point on the ellipse to a point on the hyperbola is normal to every surface it intersects (broken lines in Figure 1). A simple example, and limiting case, is a family of concentric tori (Figure 1b).To distinguish between the allowable arrangements, freeze fracture TEM micrographs of representative biological (L-α phosphotidylcholine: L-α PC) and surfactant (sodium heptylnonyl benzenesulfonate: SHBS)liposomes are compared to mathematically derived sections of Dupin cyclides and concentric spheres.

Suppression of γ’ Precipitation in a Laser-Melted Nickel-Base Alloy

1977 ◽  
Vol 35 ◽  
pp. 270-271
Author(s):  
J. M. Walsh ◽  
J. C. Whittles ◽  
B. H. Kear ◽  
E. M. Breinan
Keyword(s):  
Cooling Rate ◽  
Base Alloy ◽  
Material Surface ◽  
Intimate Contact ◽  
Absorbed Power ◽  
Perfect Contact ◽  
Nickel Base ◽  
Rapidly Solidified ◽  
Limiting Case ◽  
The Heat Transfer Coefficient

Conventionally cast γ’ precipitation hardened nickel-base superalloys possess well-defined dendritic structures and normally exhibit pronounced segregation. Splat quenched, or rapidly solidified alloys, on the other hand, show little or no evidence for phase decomposition and markedly reduced segregation. In what follows, it is shown that comparable results have been obtained in superalloys processed by the LASERGLAZE™ method.In laser glazing, a sharply focused laser beam is traversed across the material surface at a rate that induces surface localized melting, while avoiding significant surface vaporization. Under these conditions, computations of the average cooling rate can be made with confidence, since intimate contact between the melt and the self-substrate ensures that the heat transfer coefficient is reproducibly constant (h=∞ for perfect contact) in contrast to the variable h characteristic of splat quenching. Results of such computations for pure nickel are presented in Fig. 1, which shows that there is a maximum cooling rate for a given absorbed power density, corresponding to the limiting case in which melt depth approaches zero.

Secondary Fractures Following Internal Fixation in Two Horses

1989 ◽  
Vol 02 (03) ◽  
pp. 125-128
Author(s):  
E. M. Gaughan ◽  
N. G. Duchar
Keyword(s):  
Internal Fixation ◽  
Sagittal Plane ◽  
Proximal Phalanx ◽  
Fracture Repair ◽  
Fracture Line ◽  
Carpal Bone ◽  
Fracture Plane ◽  
The Third ◽  
Lag Screw ◽  
Secondary Fractures

SummaryImplant associated fractures have not been reported in horses. Two horses were evaluated for fractures in the fore limbs, occurring subsequent to previous fracture repair. Previously, the horses had sustained fractures of unusual configurations which were repaired using internal fixation. Following repair and healing of the fractures, secondary fractures occurred in the same bone, but in a different (more common) configuration. The first horse was evaluated ten months following lag screw fixation of a longitudinal fracture of the proximal phalanx in a frontal plane. This horse presented with a more typical comminuted fracture in the sagittal plane with the screws from the first fixation lying in the fracture line. This fracture was successfully treated with a cast. The second horse was examined eightteen months after repair of a medial sagittal slab fracture of the third carpal bone. The horse presented with a more typical dorsal slab fracture of the third carpal bone with the previously placed lag screw lying in the fracture line. The screw was removed and a lag screw was placed perpendicular to the new fracture plane through the dorsal surface of the third carpal bone to repair the fracture.

Cartesian Fingerprints in Beckett's Imagination Dead Imagine

2012 ◽  
Vol 21 (2) ◽  
pp. 223-243
Author(s):  
Irit Degani-Raz
Keyword(s):  
The Self ◽  
Levels Of Abstraction ◽  
The Media ◽  
The Mind ◽  
Limiting Case

The idea that Beckett investigates in his works the limits of the media he uses has been widely discussed. In this article I examine the fiction Imagination Dead Imagine as a limiting case in Beckett's exploration of limits at large and the limits of the media he uses in particular. Imagination Dead Imagine is shown to be the self-reflexive act of an artist who imaginatively explores the limits of that ultimate medium – the artist's imagination itself. My central aim is to show that various types of structural homologies (at several levels of abstraction) can be discerned between this poetic exploration of the limits of imagination and Cartesian thought. The homologies indicated here transcend what might be termed as ‘Cartesian typical topics’ (such as the mind-body dualism, the cogito, rationalism versus empiricism, etc.). The most important homologies that are indicated here are those existing between the role of imagination in Descartes' thought - an issue that until only a few decades ago was quite neglected, even by Cartesian scholars - and Beckett's perception of imagination. I suggest the use of these homologies as a tool for tracing possible sources of inspiration for Beckett's Imagination Dead Imagine.

Body balance in a free-standing position in road and off-road cyclists

2014 ◽  
Vol 6 (4) ◽  
Author(s):  
Paulina Hebisz ◽  
Rafal Hebisz ◽  
Marek Zaton
Keyword(s):  
Sagittal Plane ◽  
Standing Position ◽  
The Body ◽  
Free Standing ◽  
Body Balance ◽  
Eyes Closed ◽  
Road Cycling ◽  
Progressive Exercise ◽  
Before And After ◽  
Road Cyclists

AbstractBackground: The purpose of this study was to compare body balance in road and off-road cyclists, immediately before and after the racing season.Material/Methods: Twenty individuals participated in the study and they were divided into two groups: specialists in road-cycling (n = 10) and in off-road cycling (n = 10). Immediately before and after the five-month racing season stabilographic trials were carried out (at rest and after progressive exercise). In assessing body balance the distance and velocity of the centre shifts (in the anterior-posterior and left-right direction) were analysed. The tests were performed with the cyclists’ eyes open, eyes closed, and in feedback.Results: After the racing season, in the off-road cyclists’ group, distance and velocity of the centre of pressure shifts increased after a progressive exercise.Conclusions: In the off-road cyclists’ group the balance of the body in the sagittal plane deteriorated after the racing season. Moreover, after the racing season off-road cyclists were characterized by a worse balance of the body, compared to road cyclists

Correction of Posture Deviations in the Sagittal Plane Using the Pilates Method

2019 ◽  
pp. 3-13
Author(s):  
Alexandru Cîtea ◽  
George-Sebastian Iacob
Keyword(s):  
Low Back Pain ◽  
Back Pain ◽  
Postural Control ◽  
Human Body ◽  
Sagittal Plane ◽  
The Body ◽  
Lower Limbs ◽  
Low Back ◽  
Pilates Method ◽  
The Relationship

Posture is commonly perceived as the relationship between the segments of the human body upright. Certain parts of the body such as the cephalic extremity, neck, torso, upper and lower limbs are involved in the final posture of the body. Musculoskeletal instabilities and reduced postural control lead to the installation of nonstructural posture deviations in all 3 anatomical planes. When we talk about the sagittal plane, it was concluded that there are 4 main types of posture deviation: hyperlordotic posture, kyphotic posture, rectitude and "sway-back" posture.Pilates method has become in the last decade a much more popular formof exercise used in rehabilitation. The Pilates method is frequently prescribed to people with low back pain due to their orientation on the stabilizing muscles of the pelvis. Pilates exercise is thus theorized to help reactivate the muscles and, by doingso, increases lumbar support, reduces pain, and improves body alignment.

Accurate rebuilding of sagittal plane radian measure for treatment of thoracolumbar vertebrate fracture: a comparative study

2013 ◽  
Vol 33 (9) ◽  
pp. 985-989
Author(s):  
Xiao-jian ZHU ◽  
Jian-hua CAO ◽  
Xiao-peng XIA ◽  
Wei-jun ZHU ◽  
Pu-jian CHEN ◽  
...  
Keyword(s):  
Comparative Study ◽  
Sagittal Plane
Sign in / Sign up

Export Citation Format

Share Document