Accommodation and Apparent Distance

Perception ◽  
1988 ◽  
Vol 17 (5) ◽  
pp. 609-621 ◽  
Author(s):  
S Kay Fisher ◽  
Kenneth J Ciuffreda
Keyword(s):  
Linear Function ◽  
Apparent Distance ◽  
Optical Range ◽  
Egocentric Distance ◽  
Distance Information ◽  
Accommodative Response ◽  
The Poor ◽  
Tonic Level ◽  
Limiting Case ◽  
Source Of Information

The ability to judge egocentric distance was assessed in sixteen normal observers under conditions where monocular blur-driven accommodation provided the only source of information regarding changes in target dioptric distance. Accommodation and apparent distance were measured over an optical range of 2 to 6 D for each of three targets which differed in their effectiveness as accommodative stimuli (excellent, moderate, and poor). For the excellent and moderate accommodative targets, apparent distance decreased as accommodation increased, with both targets sharing a common linear function. Apparent distance, however, tended to exceed accommodative distance and was relatively compressed in scale. As expected, accommodative response and apparent distance diminished in range as target effectiveness was reduced. The poor accommodative target represented the limiting case wherein accommodation failed to deviate from the tonic level, and apparent distance remained constant. There were considerable intersubject differences in the ability to judge distances on the basis of accommodation. The results indicate that accommodation can indeed serve as a source of distance information, particularly for some individuals.

Who Were the Poor? The Recipients of Relief

2018 ◽  
pp. 167-186
Author(s):  
John McCallum
Keyword(s):  
Early Modern ◽  
Recent Literature ◽  
Internal Dynamics ◽  
The Poor ◽  
Fixed Model ◽  
Local Patterns ◽  
The Subject ◽  
Relief System ◽  
Source Of Information

This chapter analyses the poor themselves. Although recent literature has made valuable attempts to study the poor in their own right rather than simply through the prism of relief (and therefore elites), welfare records remain the richest source of information on the poor, especially in an area such as Scotland where very little previous work has been undertaken. Therefore the chapter opens up the subject of who received relief and why, shedding light not just on the internal dynamics of this most neglected group within Scottish society, but also on the agenda and priorities of the relief system itself. The chapter draws attention to variations in the demographics of relief recipients, and argues that there was no fixed model or ‘type’ of recipient, and that kirk sessions were responding to local patterns of need. The chapter also emphasises the complexity and range of (overlapping) reasons why early modern Scots might find themselves in need of welfare.

Monocular Egocentric Distance Information Generated by Head Movement

1994 ◽  
Vol 6 (3) ◽  
pp. 219-238 ◽  
Author(s):  
Geoffrey P. Bingham ◽  
Michael G. Stassen
Keyword(s):  
Head Movement ◽  
Egocentric Distance ◽  
Distance Information

Vertical disparity, egocentric distance and stereoscopic depth constancy: a new interpretation

1989 ◽  
Vol 237 (1289) ◽  
pp. 445-469 ◽  
Keyword(s):  
Visual System ◽  
Striate Cortex ◽  
Stereoscopic Depth ◽  
Published Data ◽  
Threshold Values ◽  
Egocentric Distance ◽  
Distance Information ◽  
Independent Information ◽  
New Interpretation ◽  
Depth Constancy

There has long been a problem concerning the presence in the visual cortex of binocularly activated cells that are selective for vertical stimulus disparities because it is generally believed that only horizontal dis­parities contribute to stereoscopic depth perception. The accepted view is that stereoscopic depth estimates are only relative to the fixation point and that independent information from an extraretinal source is needed to scale for absolute or egocentric distance. Recently, however, theor­etical computations have shown that egocentric distance can be esti­mated directly from vertical disparities without recourse to extraretinal sources. There has been little impetus to follow up these computations with experimental observations, because the vertical disparities that normally occur between the images in the two eyes have always been regarded as being too small to be of significance for visual perception and because experiments have consistently shown that our conscious appre­ciation of egocentric distance is rather crude and unreliable. Neverthe­less, the veridicality of stereoscopic depth constancy indicates that accurate distance information is available to the visual system and that the information about egocentric distance and horizontal disparity are processed together so as to continually recalibrate the horizontal dis­parity values for different absolute distances. Computations show that the recalibration can be based directly on vertical disparities without the need for any intervening estimates of absolute distance. This may partly explain the relative crudity of our conscious appreciation of egocentric distance. From published data it has been possible to calculate the magnitude of the vertical disparities that the human visual system must be able to discriminate in order for depth constancy to have the observed level of veridicality. From published data on the induced effect it has also been possible to calculate the threshold values for the detection of vertical disparities by the visual system. These threshold values are smaller than those needed to provide for the recalibration of the horizontal disparities in the interests of veridical depth constancy. An outline is given of the known properties of the binocularly activated cells in the striate cortex that are able to discriminate and assess the vertical disparities. Experi­ments are proposed that should validate, or otherwise, the concepts put forward in this paper.

scholarly journals Effect of Vertical Disparities on Depth Representation in Macaque Monkeys: MT Physiology and Behavior

2008 ◽  
Vol 99 (2) ◽  
pp. 876-887 ◽  
Author(s):  
Syed A. Chowdhury ◽  
Daniel L. Christiansen ◽  
Michael L. Morgan ◽  
Gregory C. DeAngelis
Keyword(s):  
Viewing Distance ◽  
Horizontal Disparity ◽  
Egocentric Distance ◽  
Physiological Mechanisms ◽  
Distance Information ◽  
Vertical Disparity ◽  
Mt Neurons ◽  
Behavioral Studies ◽  
Early Visual Cortex ◽  
And Behavior

Horizontal binocular disparities provide information about the distance of objects relative to the point of ocular fixation and must be combined with an estimate of viewing distance to recover the egocentric distance of an object. Vergence angle and the gradient of vertical disparities across the visual field are thought to provide independent sources of viewing distance information based on human behavioral studies. Although the effect of vergence angle on horizontal disparity selectivity in early visual cortex has been examined (with mixed results), the effect of the vertical disparity field has not been explored. We manipulated the vertical disparities in a large random-dot stimulus to simulate different viewing distances, and we examined the effect of this manipulation on both the responses of neurons in the middle temporal (MT) area and on the psychophysical performance of the animal in a curvature discrimination task. We report here that alterations to the vertical disparity field have no effect on the horizontal disparity tuning of MT neurons. However, the same manipulation strongly and systematically biases the monkey's judgments of curvature, consistent with previous human studies. We conclude that monkeys, like humans, make use of the vertical disparity field to estimate viewing distance, but that the physiological mechanisms for this effect occur either downstream of MT or in a different pathway.

Apparent Relative Size in the Judgement of Apparent Distance

Perception ◽  
1983 ◽  
Vol 12 (6) ◽  
pp. 683-700 ◽  
Author(s):  
Denis K Burnham
Keyword(s):  
Linear Function ◽  
Stimulus Pair ◽  
Relative Size ◽  
Apparent Distance ◽  
Relative Area ◽  
The Real ◽  
Comparison Figure ◽  
Series Of Experiments ◽  
Different Shapes ◽  
Real Area

In experiment 1 judgements of the apparent distance of comparison figures (squares or triangles) were obtained under reduction conditions. These comparison figures were either shaped the same as or different from equidistant standard figures, and were half, equal to, or double the area of the standard figures. Apparent distance was found to be a linear function of the relative area of the comparison figure both in same-shape and different-shape stimulus pair conditions. In addition, apparent distance was found to be a function of perceived area, because in different-shape conditions triangles were generally seen to be closer than squares even when the real area of the standard and comparison was equal. The results of experiment 2 and 3 provide some evidence that the effect of different shapes of standard and comparison on apparent distance is due to the observers' perception of the height rather than the area of figures. The series of experiments shows that the traditional transactionalists' explanation of relative size as a cue for distance is inadequate.

Convergence as a Cue for Distance

Perception ◽  
1994 ◽  
Vol 23 (2) ◽  
pp. 207-217 ◽  
Author(s):  
Alexander D Logvinenko ◽  
Viktor I Belopolskii
Keyword(s):  
Eye Movements ◽  
Apparent Distance ◽  
Convergence Angle ◽  
Source Of Information ◽  
Physical Displacement

Binocular eye movements were measured in subjects experiencing the wallpaper illusion. It was found that a physical displacement of the fixation point by more than 1 m out of the plane of apparent localisation of the strips had no influence on the illusory location of these strips. Hence, illusory localisation in the wallpaper illusion is independent of the actual magnitude of the subject's convergence angle, once the illusion has come into existence. This result suggests that convergence does not serve as a source of information about apparent distance, at least in the wallpaper illusion.

Magnetic-field strengths from optical polarization data

1967 ◽  
Vol 31 ◽  
pp. 381-383
Author(s):  
J. M. Greenberg
Keyword(s):  
Magnetic Field ◽  
Optical Polarization ◽  
Polarization Data ◽  
Term Model ◽  
Source Of Information ◽  
Field Strengths

Van de Hulst (Paper 64, Table 1) has marked optical polarization as a questionable or marginal source of information concerning magnetic field strengths. Rather than arguing about this–I should rate this method asq+-, or quarrelling about the term ‘model-sensitive results’, I wish to stress the historical point that as recently as two years ago there were still some who questioned that optical polarization was definitely due to magnetically-oriented interstellar particles.

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.

High-Resolution, Low-Voltage SEM of Cell Wall Regeneration of Yeast Shizosaccharomyces Pombe Protoplasts

1988 ◽  
Vol 46 ◽  
pp. 208-211
Author(s):  
M. Osumi ◽  
N. Yamada ◽  
T. Nagatani
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Low Voltage ◽  
Cell Wall Regeneration ◽  
The Past ◽  
The Poor ◽  
Probe Size ◽  
Beam Damage ◽  
Biological Field ◽  
Scanning Electron

Even though many early workers had suggested the use of lower voltages to increase topographic contrast and to reduce specimen charging and beam damage, we did not usually operate in the conventional scanning electron microscope at low voltage because of the poor resolution, especially of bioligical specimens. However, the development of the “in-lens” field emission scanning electron microscope (FESEM) has led to marked inprovement in resolution, especially in the range of 1-5 kV, within the past year. The probe size has been cumulated to be 0.7nm in diameter at 30kV and about 3nm at 1kV. We have been trying to develop techniques to use this in-lens FESEM at low voltage (LVSEM) for direct observation of totally uncoated biological specimens and have developed the LVSEM method for the biological field.

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