The influence of mixing frequency and depth on phytoplankton functional group composition (mobile versus immobile species) was studied by enclosure experiments in a shallow, stratified lake. Mixing events were artificially induced at intervals from 2-12 d. The mixing depth was increased from the natural level (4 m) to 6 and ...

1. Data on the distributions of pelagic and benthic Chaoborus flavicans larvae were gathered in 1994 and tested for their agreement with the predator avoidance hypotheses. The development of all Chaoborus Life stages, as well as the horizontal and vertical distribution in the four larval instars, was followed from May ...

Movement through an environment produces an optical spatiotemporal pattern, known as a flow field. When visually guiding movement using a flow field, do humans make use of information about the distance of constituent elements? Employing a novel active steering task, we examined the use of depth (height-in-scene and disparity) and ...

Can the motion system selectively process elements at a particular depth? We attempted to answer this question using global coherence tasks in which signal and noise elements could be given different disparities. In experiment 1 we found that, if all the signal elements had a disparity different from that of ...

The contrast dependence of perceived depth was quantified through a series of depth matching experiments. Perceived depth was found to be a power law function of contrast. In addition, subjects exhibited a large uncrossed depth bias indicating that low contrast test patterns appeared much farther away than high contrast patterns ...

Previously (Popple et al, 1998 Vision Research 38 319-326) we found, using random-dot stereograms, that initial vergence increases with the size of a cyclopean disc. A corresponding improvement in stereoacuity within the disc was predicted, because disparities in the disc would be brought closer to the plane of current fixation. ...

The perceived slant of a surface relative to the frontal plane can be reduced when the surface is viewed through a frame between the observer and the surface. Aspects of this framing effect were investigated in three experiments in which observers judged the orientations-in-depth of rectangular and trapezoidal surfaces which ...

Some recent studies on the extraretinal contribution to distance perception are reviewed. These experiments demonstrate that vergence can provide reliable information for judgments on the distance of proximal targets in the absence of all other cues. We argue that, although vergence is an unreliable cue at large fixation distances and ...

The influence of monocular occlusion cues on the perceived direction of motion of barber pole patterns is examined. Unlike previous studies that have emphasized the importance of binocular disparity, we find that monocular cues strongly influence the perceived motion direction and can even override binocular depth cues. The difference in ...

When the product of a vertical square-wave grating (contrast envelope) and a horizontal sinusoidal grating (carrier) are viewed binocularly with different disparity cues they can be perceived transparently at different depths. We found, however, that the transparency was asymmetric; it only occurred when the envelope was perceived to be the ...

Four experiments related human perception of depth-order relations in structure-from-motion displays to current Euclidean and affine theories of depth recovery from motion. Discrimination between parallel and nonparallel lines and relative-depth judgments was observed for orthographic projections of rigidly oscillating random-dot surfaces. We found that (1) depth-order relations were perceived veridically ...

PURPOSE: To test the hypothesis that extraretinal cues related to vergence angle and lens accommodation are used to scale horizontal disparities for fixation distance. METHODS: Depth perception of random dot stereograms was studied in 10 healthy adult subjects with normal visual acuity by modifying retinal disparity, fixation distance, vergence angle, ...

It has been suggested that to resolve ambiguities implicit in binocular perception of complex visual scenes, the brain adopts a continuity constraint assuming that disparities change smoothly with eccentricity. Stereoscopic transparency is characterized by abrupt changes of binocular disparity across retinal locations. The focus of the present study is how ...

Disparity discrimination thresholds are known to increase with both retinal eccentricity and distance from the horopter. However, little is known about how the detectability of cyclopean gratings varies with retinal position. Thresholds for disparity corrugations were measured as a function of corrugation frequency for different visual eccentricities. Subjects viewed annular ...

The depth of focus of light patterns can be extended, within given tolerances, beyond the classical limits. For a quantitative evaluation we introduce a degree of depth-of-focus extension and a three-dimensional energy-distribution efficiency. The basic limitations involved in depth-of-focus extension are discussed. A coherent system in which the input is ...

The allocation of perceived size and perceived motion or displacement in depth resulting from retinal size changes (changes in the visual angle of the stimulus) was investigated in situations in which all other cues of perceived changes in distance were absent. The allocation process was represented by the size-distance invariance ...

PURPOSE: In normal vision, stereoscopic cues are combined with perspective cues to provide veridical depth perception. The relative strengths of these depth cues, however, may be dependent upon context effects. We investigated the role of stimulus context on the interactions of binocular disparity, contrast, and size. METHODS: The subjects, four ...

PURPOSE: To determine the vergence response, if any, in a homogenous group of patients suffering from strabismus and submitted to environmental induction of retinal disparity with respect to a control group of subjects. MATERIALS AND METHODS: A series of 13 subjects was included in the present study (5 normal subjects ...

To understand better the range of conditions supporting stereoscopic vision, we explored the effects of speed, as well as specific optic flow patterns, on judgments of the depth, near or far of fixation, of large targets briefly presented in the upper periphery. They had large disparities (1-6 deg) and moved ...

In a stereoscopic system, both eyes or cameras have a slightly different view. As a consequence, small variations between the projected images exist ('disparities') which are spatially evaluated in order to retrieve depth information (Sanger 1988; Fleet et al. 1991). A strong similarity exists between the analysis of visual disparities ...

Binocular information has been shown to be important for the programming and control of reaching and grasping. But even without binocular vision, people are still able to reach out and pick up objects accurately - albeit less efficiently. As part of a continuing investigation into the role that monocular cues ...

Stereoscopic segregation in depth was studied using two superimposed frontoparallel surfaces displayed in dynamic random dot stereograms. The two patterns were positioned symmetrically in front of and behind a binocular fixation point. They were either stationary, or they could move relative to each other. Sensitivity for segregation was established by ...

Moving plaid patterns composed of component gratings that differ in luminance contrast tend not to cohere perceptually. Plaid patterns configured to mimic one occlusive grating overlying another also fail to cohere. We hypothesized that plaids constructed of components with different luminance contrasts fail to cohere because these components are interpreted ...

Fixation disparities (FD) were measured as a function of forced vergence using binocular scleral search coils and simultaneously with nonius lines. The slope of the objective FD curve was significantly greater than the subjective FD curve for three of five subjects. This indicates an alteration in retinal correspondence of up ...

In four experiments, subjects examined four categories of rotating eight-vertex geometric forms in parallel projection. Some of the figures appeared to deform, even though rigid three-dimensional interpretations were possible mathematically. Our results from several deformation-rating tasks indicated that most of the configurations maintained a rigid appearance throughout their rotations, although ...

Although binocular disparity and motion parallax are powerful cues for depth, neither, in isolation, can specify information about both object size and depth. It has been shown that information from both cues can be combined to specify the size, depth, and distance of an object in a scene (Richards, 1985 ...

The perception of depth and slant in three-dimensional scenes specified by texture was investigated in five experiments. Subjects were presented with computer-generated scenes of a ground and ceiling plane receding in depth. Compression, convergence, and grid textures were examined. The effect of the presence or absence of a gap in ...

Praying mantises are considered to be phylogenetically ancient insects with their roots in the palaeozoic Protoblattoidea. They have evolved two mechanisms for spatial vision: (a) estimating the distance to moving prey objects with the use of binocular disparity [Rossel, 1983] and (b) estimating the distance to stationary target objects with ...

We investigated over what central area disparity in a random dot stereogram is integrated to stimulate an initial vergence response. Vergence was measured subjectively, with a forced choice dichoptic nonius vernier task following a brief (230 msec) stimulus presentation. Stimuli were random-dot stereograms showing a central circular disc of 12.5 ...

A number of researchers have compared the contrast requirements for stereopsis with those for detection of the stereoscopic stimulus, but they have generally failed to allow for the fact that stereopsis requires a detectable stimulus in both eyes at the same time. It is argued that the most appropriate detection ...

Linear transformations (shear or scale transformations) of either horizontal or vertical disparity give rise to the percept of slant or inclination. It has been proposed that the percept of slant induced by vertical size disparity, known as Ogle's induced-size effect, and the analogous induced-shear effect, compensate for scale and shear ...

The linking of spatial information is essential for coherent space perception. A study is reported of the contribution of temporal and spatial alignment for the linkage of spatial elements in terms of depth perception. Stereo half-images were generated on the left and right halves of a large-screen video monitor and ...

The two main questions addressed in this study were (a) what effect does yoking the relative expansion and contraction (EC) of retinal images to forward and backward head movements have on the resultant magnitude and stability of perceived depth, and (b) how does this relative EC image motion interact with ...

The influence of stereoscopic vision on the perception of optic flow fields was investigated in experiments based on a recently described illusion. In this illusion, subjects perceive a shift of the center of an expanding optic flow field when it is transparently superimposed by a unidirectional motion pattern. This illusory ...

The integration of binocular disparity, shading, and texture was measured for two different aspects of three-dimensional structure: (1) shape index, which is a measure of scale-independent structure, and (2) curvedness, which is a measure of scale-dependent structure. Binocular disparity was found to contribute significantly more to judged shape index than ...

Three-dimensional interpretation of simple line drawings, composed of two triangles with a common side, was studied through the quantitative measurement of perceived orientation of the surface indicated by a stimulus figure. In a single triangle, depth perception is ambiguous and is not stable even if perceived. In two triangles with ...

We are surrounded by surfaces that we perceive by visual means. Understanding the basic principles behind this perceptual process is a central theme in visual psychology, psychophysics, and computational vision. In many of the computational models employed in the past, it has been assumed that a metric representation of physical ...

In addition to the conventional luminance spatial frequency-dependent, disparity processing mode, there is a second-order luminance spatial frequency-independent type of processing available to the stereoscopic system. Here we use gaussian-enveloped, amplitude-modulated grating patches to determine how the stereoscopic system responds to the presence of two sources of second-order disparity information ...

The integration of binocular stereopsis and kinetic depth was measured for two distinct aspects of 3-D structure: (1) shape index, which is a measure of scale-independent structure, and (2) curvedness, which is a measure of scale-dependent structure. We found that motion contributes significantly more to judged shape index than it ...

Visual information from binocular disparity and from relative motion provide information about three-dimensional structure and layout of the world. Although the mechanisms that process these cues have typically been studied independently, there is now a substantial body of evidence that suggests that they interact in the visual pathway. This paper ...

Previously it has been reported that horizontal disparity vergence is strongly influenced by subject instructions to vary attention or tracking effort. This paper describes experiments which compared these instruction effects on horizontal and vertical disparity vergence. Within-trial comparisons were made possible by use of oblique (combined horizontal and vertical) disparity ...

We investigated the upper limit of horizontal spatial modulation of vertical-size disparity in a textured surface for the perception of depth. In Experiment 1 subjects matched the appearance of a surface with modulated horizontal-size disparity to that of a surface with modulated vertical-size disparity. In Experiment 2 we determined the ...

In previous work [Meese et al. (1995). Vision Research, 35, 2879-2888)] we showed that one-dimensional (1D) speed gradients are sufficient to produce a compelling impression of surface slant. Summing a 1D vertical shearing gradient or, less intuitively, a 1D horizontal shearing gradient with a random field of horizontally translating dots ...

A mathematical analysis is presented of a model that uses motion-opponent operators similar to neurons found in the primate middle temporal visual area, to determine observer heading and depth from optical flow information. The response of these operators to depth changes in the form of a slanted plane or a ...

Factors limiting binocular fusion were studied using 2-dimensional difference of Gaussian (2D-DOG) stimuli. The proportion of fused stimuli and observer's response time were determined for stimuli that varied in spatial frequency composition between 0.22 and 4.8 cycles per degree. At small disparities, mean fusion response times were short and relatively ...

The 2D projection of a rotating Necker cube yields an ambiguous 3D interpretation based on both 2D shape and kinetic depth information. The present study shows that the alternation rate of the two 3D interpretations is constant with the rotation speed up to some critical value (around 25 turns/min for ...

It has been suggested that breaking camouflage is one of the major functions of stereopsis (Julesz, 1971). In this study, we found that stereopsis is less effective in breaking camouflage for moving targets than for static ones. Observers were asked to detect a single dot moving on a straight trajectory ...

Stereo thresholds for 84% correct detection of sinusoidal disparity corrugations depicted by narrow-band-filtered random dot stereograms were determined for surfaces as a function of (i) luminance center spatial frequency and (ii) disparity modulation frequency. In addition, supra-threshold depth matching functions for two amplitudes of peak-to-trough depth were determined using similar ...

Using monocular observation, open-loop measurements were obtained of the perceptions of linear size, angular size, and sagittal motion associated with the terminal (largest or smallest) stimuli of repetitive optical expansions and contractions using 1-D or 2-D displays produced on a video monitor at a constant distance from the observer. The ...

The relationship between visual space and physical space was investigated by means of the apparent fronto-parallel plane percept. A set of curves in physical space, corresponding to fronto-parallel planes perceived in front or behind a given fixation point, was determined. The curvature at the apex of these curves follows a ...