Perceptual depth synthesis in the visual system as revealed by selective adaptation.

Selective adaptation was used to determine the degree of interactions between channels processing relative depth from stereopsis, motion parallax, and texture. Monocular adaptations with motion parallax or binocular stationary adaptation caused test surfaces, viewed either stationary binocularly or monocularly with motion parallax, to appear to slant in the opposite direction compared with the slant initially adapted to. Monocular adaptations on frontoparallel surfaces covered with a pattern of texture gradients caused a subsequently viewed test surface, viewed either monocularly with motion parallax or stationary binocularly, to appear to slant in the opposite direction as the slant indicated by the texture in the adaptation condition. No aftereffect emerged in the monocular stationary test condition. A mechanism of independent channels for relative depth perception is dismissed in favor of a view of an asymmetrical interactive processing of different information sources. The results suggest asymmetrical inhibitory interactions among habituating slant detector units receiving inputs from static disparity, dynamic disparity, and texture gradients. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The stereoscopic anisotropy: Individual differences and underlying mechanisms.

Observers are more sensitive to variations in the depth of stereoscopic surfaces in a vertical than in a horizontal direction; however, there are large individual differences in this anisotropy. The authors measured discrimination thresholds for surfaces slanted about a vertical axis or inclined about a horizontal axis for 50 observers. Orientation and spatial frequency discrimination thresholds were also measured. For most observers, thresholds were lower for inclination than for slant and lower for orientation than for spatial frequency. There was a positive correlation between the 2 anisotropies, resulting from positive correlations between (a) orientation and inclination thresholds and (b) spatial frequency and slant thresholds. These results support the notion that surface inclination and slant perception is in part limited by the sensitivity of orientation and spatial frequency mechanisms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Types of size disparity and the perception of surface slant

We examined (i) perceived slant of a textured surface about a vertical axis as a function of disparity magnitude for horizontal-size disparity, vertical-size disparity, and overall-size disparity; and (ii) interactions between patterns with various types and magnitudes of size disparity and superimposed or adjacent zero-disparity stimuli. Horizontal-size disparity produced slant which increased with increasing disparity, was enhanced by superimposed zero-disparity stimuli, and induced contrasting slant in superimposed or adjacent zero-disparity stimuli. Vertical-size disparity produced opposite slant (induced effect) which was reduced to near zero by a superimposed zero-disparity pattern and both patterns appeared as one surface. Adjacent vertical-size-disparity and zero-disparity patterns appeared as separate surfaces with a wide curved boundary. Overall-size disparity produced slant which was enhanced by a superimposed zero-disparity pattern and less so by a zero-disparity line, and induced more slant in a zero-disparity line than in a zero-disparity pattern. The results are discussed in terms of depth underestimation of isolated surfaces, depth enhancement, depth contrast, and the processing of deformation disparity.     

Atomic-force microscopic study of dimensional changes in human dentine during drying

Six 1-mm thick sections of human dentine, three parallel to the occlusal surface and three perpendicular to the buccal surface, were prepared from non-carious third molars. The enamel was ground off, and the sections were polished with alumina powder to remove the smear layer. Each section was imaged by atomic-force microscopy with 20 nm horizontal and 0.1 nm vertical resolutions, initially while the samples were immersed in deionized water and then periodically during drying at room temperature. No dimensional changes over microscopic fields of view (scanned areas smaller than 50 x 50 microns) could be detected within the precision of the measurements (< 0.5%). Across the entire sample, however, vertical displacements of 10-20 microns were measured. Elasticity (Bernoulli beam) theory was used to calculate the engineering strain required to produce these displacements. The magnitude of the strain was 0.04% (SD = 0.01) in the buccal sections in the direction of the tubule axis and 0.09% (SD = 0.02) in the direction normal to the tubule axis. Also, the strain alternated between tension and compression across the samples. It was concluded that, as determined by using microscopic techniques, drying-induced strain is too small to require corrections for tubule size and tubule density.     

Postfusional latency in stereoscopic slant perception and the primitives of stereopsis.

Random dot stereograms of slanted surfaces were constructed, each representing one or two slanted surfaces in different relative arrangements and with different axes. Latency to fusion and from fusion to stereoscopic resolution was measured for each stimulus. It was found that latency to fusion was always very brief but that latency to stereoscopic resolution varied markedly, depending upon the orientation and arrangement of the stereoscopic surfaces. A gradient of discontinuities at a surface boundary produced an instant slant response for that surface, whereas a gradient of absolute disparities across the surface did not, except under conditions where vertical declination (a form of orientation disparity) was present. We conclude that stereopsis is not based on the primitives used in matching the images for fusion and that it is, at least initially, a response to disparity discontinuities which play no role in the fusion process. We also conclude that vertical declination is responded to globally as a slant around a horizontal axis but that other forms of orientation disparity are ineffective. The evidence from our experiments does not support the existence of a stereoscopic ability to respond globally to differences in magnification (or spatial frequency). It is suggested that stereoscopic perception of slant around a vertical axis is slow because it results from the integration of local processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visualizing 3D objects from 2D cross sectional images displayed in-situ versus ex-situ.

The present research investigates how mental visualization of a 3D object from 2D cross sectional images is influenced by displacing the images from the source object, as is customary in medical imaging. Three experiments were conducted to assess people’s ability to integrate spatial information over a series of cross sectional images in order to visualize an object posed in 3D space. Participants used a hand-held tool to reveal a virtual rod as a sequence of cross-sectional images, which were displayed either directly in the space of exploration (in-situ) or displaced to a remote screen (ex-situ). They manipulated a response stylus to match the virtual rod’s pitch (vertical slant), yaw (horizontal slant), or both. Consistent with the hypothesis that spatial colocation of image and source object facilitates mental visualization, we found that although single dimensions of slant were judged accurately with both displays, judging pitch and yaw simultaneously produced differences in systematic error between in-situ and ex-situ displays. Ex-situ imaging also exhibited errors such that the magnitude of the response was approximately correct but the direction was reversed. Regression analysis indicated that the in-situ judgments were primarily based on spatiotemporal visualization, while the ex-situ judgments relied on an ad hoc, screen-based heuristic. These findings suggest that in-situ displays may be useful in clinical practice by reducing error and facilitating the ability of radiologists to visualize 3D anatomy from cross sectional images. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceived orientation of axis of rotation in structure-from-motion

Perceived orientation of axis of rotation and accuracy in discriminating fixed-axis from nonfixed-axis rotations were investigated for orthographic projections of three-dimensional rotating objects. The principal findings were (a) the slant of the axis of rotation was systematically misperceived; (b) in both two-view and multiview displays, the perceived slant of the axis of rotation was well-predicted by the ratio between the deformation (a property of the first-order optic flow) and the component parallel to the image plane of the global velocity vector; (c) if this ratio was kept constant in each frame transition of the stimulus sequence (or it was varied), then the stimuli tended to be judged as fixed-axis rotations (or as nonfixed-axis rotations), regardless of whether they simulated a fixed-axis rotation or not; and (d) the tilt of the axis of rotation was perceived in two-view displays with a very small error.     

Perceived orientation of axis rotation in structure-from-motion.

Perceived orientation of axis of rotation and accuracy in discriminating fixed-axis from nonfixed-axis rotations were investigated for orthographic projections of three-dimensional rotating objects. The principal findings were (1) the slant of the axis of rotation was systematically misperceived; (2) in both two-view and multiview displays, the perceived slant of the axis of rotation was well-predicted by the ratio between the deformation (a property of the first-order optic flow) and the component parallel to the image plane of the global velocity vector; (3) if this ratio was kept constant in each frame transition of the stimulus sequence (or it was varied), then the stimuli tended to be judged as fixed-axis rotations (or as nonfixed-axis rotations), regardless of whether they simulated a fixed-axis rotation or not; and (4) the tilt of the axis of rotation was perceived in two-view displays with a very small error. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Extent and effect of surface tilt on the data display of the EyeSys videokeratoscope

AIMS: This study examined the occurrence, magnitude, and the consequences of a possible tilt between the corneal surface and optical axis of the EyeSys videokeratoscope. METHODS: Initially, a theoretical model was developed to calculate the angle of tilt. The predictions of the model were verified empirically using a convex conicoid surface and were found to predict the tilt to within 0.5 degree of the actual tilt. The likely effects of the tilt on the corneal power were also examined. The angle of tilt was then measured on the human cornea and the effect of neutralising the tilt on the videokeratoscopic data display was observed. RESULTS: The angle of tilt was found to lie between 1 degree and 6 degrees in a temporal direction. CONCLUSION: When the corneal tilt on the human subjects was neutralised, then a reduction in the nasal/temporal asymmetry was observed.     

Gradients as visual primitives.

Following J. J. Gibson (1950), it is implicitly assumed in the literature that texture gradients are directly available as perceptual primitives. Yet, the depth response to compression gradients is poor compared with gradients of linear perspective. This may indicate that mechanisms for directly detecting the differential structure that constitutes a compression gradient do not exist. We tested this hypothesis outside the context of depth perception by measuring the speed with which participants could detect a gradient anomaly as a function of the number of elements in the gradient. Only in the case of linear perspective did anomalies "pop out." This was attributable to the emergent feature of alignment of the ends of the elements forming the gradient rather than the direct detection of its differential structure. It is argued that gradients are not perceptual primitives and that the poor depth response to compression in a variety of contexts (motion parallax, stereo, and perspective) therefore is not surprising. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The effect of head-to-trunk position on the direction of arm movements before, during, and after space flight

This contribution deals with the examination of the consequences of different head-to-trunk positions on arm movements under normal gravity and during prolonged space flight. One of the objectives of this study was to investigate the influence of weightlessness on the condition of the spatial analysis system. Aimed arm movements in the horizontal plane (pointings towards two visual targets) were recorded, first with eyes open, head straight (learning part), then with eyes closed, head straight and during yaw or roll position of the head (performance part). Measurements related to these different head-to-trunk-positions were taken in one short-term and nine long-term cosmonauts preflight, inflight, and postflight. Terrestrial control experiments were carried out with an extended experimental design in 14 healthy volunteers. The analysis of these experiments revealed that, with eyes closed and the head in yaw position, cosmonauts before flight and control subjects exhibit significant slants of the movement plane of the arm. Contrary to terrestrial measurements, in space experiments roll tilt of the head to the right is correlated with considerable counterclockwise slant of the movement plane. This slant of the movement plane of the arm was interpreted as tilt of the internal representation of the horizontal coordinate. The effect is larger with greater distortion induced by the changed head position and with larger muscular involvement to keep this position. This effect is also increased by the reduction of information (for example, in microgravity). The amount and the direction of the horizontal offset of the arm movements are shown to be dependent on the head-to-trunk position, too. Additionally, we have found changes in the amplitude and in the duration of the arm movement, in the vertical offset, and in the curvature of the movement paths, depending on the experimental conditions.     

Perceiving surface slant from deformation of optic flow.

Perceived surface orientation and angular velocity were investigated for orthographic projections of 3-D rotating random-dot planes. It was found that (a) tilt was accurately perceived and (b) slant and angular velocity were systematically misperceived. It was hypothesized that these misperceptions are the product of a heuristic analysis based on the deformation, one of the differential invariants of the first-order optic flow. According to this heuristic, surface attitude and angular velocity are recovered by determining the magnitudes of these parameters that most likely produce the deformation of the velocity field, under the assumption that all slant and angular velocity magnitudes have the same a priori probability. The results of the present investigation support this hypothesis. Residual orientation anisotropies not accounted for by the proposed heuristic were also found. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Three-dimensional organization of otolith-ocular reflexes in rhesus monkeys. I. Linear acceleration responses during off-vertical axis rotation

1. The dynamic properties of otolith-ocular reflexes elicited by sinusoidal linear acceleration along the three cardinal head axes were studied during off-vertical axis rotations in rhesus monkeys. As the head rotates in space at constant velocity about an off-vertical axis, otolith-ocular reflexes are elicited in response to the sinusoidally varying linear acceleration (gravity) components along the interaural, nasooccipital, or vertical head axis. Because the frequency of these sinusoidal stimuli is proportional to the velocity of rotation, rotation at low and moderately fast speeds allows the study of the mid-and low-frequency dynamics of these otolith-ocular reflexes. 2. Animals were rotated in complete darkness in the yaw, pitch, and roll planes at velocities ranging between 7.4 and 184 degrees/s. Accordingly, otolith-ocular reflexes (manifested as sinusoidal modulations in eye position and/or slow-phase eye velocity) were quantitatively studied for stimulus frequencies ranging between 0.02 and 0.51 Hz. During yaw and roll rotation, torsional, vertical, and horizontal slow-phase eye velocity was sinusoidally modulated as a function of head position. The amplitudes of these responses were symmetric for rotations in opposite directions. In contrast, mainly vertical slow-phase eye velocity was modulated during pitch rotation. This modulation was asymmetric for rotations in opposite direction. 3. Each of these response components in a given rotation plane could be associated with an otolith-ocular response vector whose sensitivity, temporal phase, and spatial orientation were estimated on the basis of the amplitude and phase of sinusoidal modulations during both directions of rotation. Based on this analysis, which was performed either for slow-phase eye velocity alone or for total eye excursion (including both slow and fast eye movements), two distinct response patterns were observed: 1) response vectors with pronounced dynamics and spatial/temporal properties that could be characterized as the low-frequency range of "translational" otolith-ocular reflexes; and 2) response vectors associated with an eye position modulation in phase with head position ("tilt" otolith-ocular reflexes). 4. The responses associated with two otolith-ocular vectors with pronounced dynamics consisted of horizontal eye movements evoked as a function of gravity along the interaural axis and vertical eye movements elicited as a function of gravity along the vertical head axis. Both responses were characterized by a slow-phase eye velocity sensitivity that increased three- to five-fold and large phase changes of approximately 100-180 degrees between 0.02 and 0.51 Hz. These dynamic properties could suggest nontraditional temporal processing in utriculoocular and sacculoocular pathways, possibly involving spatiotemporal otolith-ocular interactions. 5. The two otolith-ocular vectors associated with eye position responses in phase with head position (tilt otolith-ocular reflexes) consisted of torsional eye movements in response to gravity along the interaural axis, and vertical eye movements in response to gravity along the nasooccipital head axis. These otolith-ocular responses did not result from an otolithic effect on slow eye movements alone. Particularly at high frequencies (i.e., high speed rotations), saccades were responsible for most of the modulation of torsional and vertical eye position, which was relatively large (on average +/- 8-10 degrees/g) and remained independent of frequency. Such reflex dynamics can be simulated by a direct coupling of primary otolith afferent inputs to the oculomotor plant. (ABSTRACT TRUNCATED)     

Discrimination of the direction and speed of motion in depth of a monocularly visible target from binocular information alone

Thresholds for discriminating a monocularly visible object's direction of motion in depth and speed of motion in depth were measured using only binocular cues. Observers could discriminate the direction of motion in depth while totally ignoring speed and discriminate the speed of motion in depth while totally ignoring direction. Direction discrimination thresholds were the same for motion in depth within the vertical and horizontal meridians, even though a cue to trajectory was available for motion within the horizontal meridian that is not available for motion within the vertical meridian. Speed discrimination thresholds also were the same for motion in depth within the vertical and horizontal meridians. For the 3 observers the lowest direction discrimination thresholds were 0.14 degree, 0.18 degree, and 0.22 degree (means of horizontal and vertical thresholds).     

Confinement Effects in Shallow-Water Jets

This paper documents measurements of the mean velocity field and turbulence statistics of an isothermal, round jet entering a shallow layer of water. The lower boundary of the jet was a solid wall and the upper boundary a free surface. The jet axis was midway between the solid wall and the free surface in all cases. Experiments were performed at a Reynolds number of 22,500 for water layer depths 15, 10, and 5?times the jet exit diameter (9?mm). Particle image velocimetry measurements were made on vertical and horizontal planes—both containing the axis of the jet. The measurements were taken from 10 to 80 jet diameters downstream. Results showed that, for the highly confined cases at downstream locations, the axial velocity was quite uniform over the depth, with a mild peak below the jet axis. In the horizontal plane, the velocity profiles were slightly narrower than the free jet profile, but in the vertical plane, they were wider. The mean vertical velocity profiles showed that entrainment was suppressed in the vertical direction. At the same time, the lateral velocity profiles indicate that fluid flows from the sides toward the jet centerline. For the shallow cases, the mean vertical velocity becomes negative over most of the depth at downstream locations, indicating that this inflow from the sides is directed downward toward the solid wall. The relative turbulence intensity results were suppressed in the axial and vertical directions and mildly enhanced in the lateral direction. As well, the Reynolds shear stress in the vertical plane was significantly reduced by the vertical confinement, while in the horizontal plane it was only slightly affected by the confinement.     

三山岛海底金矿开采充填体与围岩变形规律的数值模拟

为合理解释三山岛金矿新立矿区海底开采充填体和围岩变形特征,建立了假二维的矿山开挖充填力学模型,并将其简化为平面应变问题。根据对充填体力学特性的研究,在模型建立过程中,对充填体采用了双屈服模型,对矿柱及围岩采用了应变硬化/软化塑性模型。利用FLAC3D数值模拟软件,并在模型中的相应位置设置位移监测点,分析了真实矿山开采过程中上下各采场充填体和围岩的移动变形规律。研究结果表明,新立矿区充填体变形主要为水平方向上的压缩变形,且具有累积效应,当充填体达到垂直方向的最大压缩量后,顶板围岩在水平构造应力作用下有向充填体上山方向滑动的趋势。     

The observer-relative velocity field as the basis for effective motion parallax.

Earlier studies of motion parallax found unambiguous relative depth perception when random dot patterns were systematically translated in accordance with either motion of the observer's head or motion of the display scope. The need for such relative motion between an observer and a flow field was examined by placing a flow field in a limited area (window) in a large scope and translating the window relative to the observer. Accuracy in judging surface orientation and quantitative depth estimates were determined by the velocity field relative to the observer and were not measurably affected by whether this field was produced with a stationary or a moving window. Accuracy was consistently higher for smaller ratios of maximum to minimum projected velocities, reaching 100% in one experiment with a 1.12:1 ratio. We conclude that fully effective motion parallax does not require relative motion between the observer's head and the contours of a flow field. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Orientation of slit pupil and visual streak in the eye of the cat

The orientation of the visual streak of the cat's retina was compared to that of the long axis of the slit pupil in the same eye. In five paralyzed, anesthetized cats, the retinal projection to the superior colliculus was mapped with electrophysiological techniques. The orientation of the visual streak was estimated from the projection in visual space of the collicular region of high magnification which corresponds to the central projection of the streak. The angle by which the streak was tilted from absolute horizontal was always within one or two degree of the angle by which the pupil axis was tilted from absolute vertical. This relationship was confirmed in three of the animals in which small retinal lesions were placed a known distance from the histologically determined axis of the streak. From the visual coordinates of these lesions, an independent estimate of the streak's orientation was obtained. In each case, the tilt of streak axis from horizontal differed by no more than 0.5 degrees from the tilt of the pupil axis from vertical. The results support the hypothesis that planes containing the long axis of the cat's slit pupil are perpendicular to planes containing the long axis of the visual streak of the same eye.     

Iron supplementation

BACKGROUND: Besides decentration of the graft/host trephination and "horizontal torsion" "vertical tilt" is an important factor for reduced visual outcome after penetrating keratoplasty (PK). The purpose of this study was to evaluate the time course of vertical tilt in absolute value and direction and to correlate it with functional results after PK. PATIENTS AND METHODS: Fifty patients each (20 primary dystrophies, 30 keratoconus) underwent nonmechanical trephination (NMT) (excimer laser MEL60, Aesculap-Meditec, Heroldsberg, Germany) or mechanical motor trephination (MT) (Geuder, Heidelberg, Germany) in penetrating keratoplasty. All procedures (7.5 mm in dystrophies, 8.0 mm in keratoconus, 8 orientation teeth in NMT, double-running 10-0 nylon suture) were performed by one surgeon (GOHN). At a postoperative gate of 6 weeks, 6 months, before partial suture removal and after complete suture removal, corneal topography analysis (TMS-1, Tomey, Tennenlohe, Germany) was performed. After a Gram-Schmidt-orthogonalization corneal topography height data of 25 noncentric rings in 256 hemimeridians were decomposed into Zernike components of radial order n = 16 in the sense of minimizing the root mean square error. The tilt of the surface relative to the videokeratoscope axis was calculated from the Zernike components Z1(1) and Z1(-1). The meridional power at the cardinal meridians was derived from all parabolic Zernike terms. Tilt and the difference between both meridians of the Zernike representation (ZA) were correlated with the results of Zeiss keratometry (KA). Simulated Keratometry (SimK) of the TMS-1, subjective refraction (RZ) and best-corrected visual acuity. RESULTS: After NMT, vertical tilt of the graft was 3 degrees without significant change over time. Following MT, an equivalent time course could be observed before partial suture removal. However, after complete suture removal, a significant increase of the tilt was measured to 5 degrees (p = 0.02). No significant difference could be detected comparing keratoconus and Fuchs' dystrophy both in NMT and MT. The direction of the vertical tilt component piled up to the hemimeridian defined by the knot of the first running suture. At all postoperative follow-up examinations, the ZA of the Zernike decomposition showed a good correlation to the RZ, whereas the KA and the SimK did not. At the end of the follow-up, best-corrected visual acuity after NMT was 2 decimal lines better than after MT. CONCLUSIONS: The Zernike decomposition of topographic height data is a suitable tool for extraction and quantifying vertical tilt of the graft following penetrating keratoplasty. In contrast to conventional keratometry with its 4-point measurement, a decomposition of topographic height data into orthogonal polynomials enables a detection of both cardinal meridians even in corneas with a high degree of local irregularities.     

Suction Caisson Capacity in Anisotropic, Purely Cohesive Soil

This paper presents a plastic limit analysis of the lateral load capacity of suction caissons in an anisotropic, purely cohesive soil assuming conditions of rotational symmetry about the vertical or gravity axis. The formulation utilizes a form of the Hill yield criterion that is modified to allow for different soil strengths in triaxial compression and extension. Using this yield criterion, energy dissipation relationships are formulated for continuous and discontinuous deformation fields. These dissipation relationships are then applied to a postulated caisson failure mechanism comprising a wedge near the free soil surface (mudline), a two-dimensional flow-around failure at depth, and a hemispherical slip surface at the base of the rotating caisson. The plastic limit analysis predictions compared favorably to predictions obtained from finite-element simulations employing a Hill yield criterion. For the range of anisotropic undrained strength properties commonly reported for normally K0-consolidated clays, parametric studies indicate that suction caisson horizontal load capacities predicted using a conventional approach (a von Mises yield surface fitted to the soil simple shear strength) will differ from anisotropic predictions by less than 10%.