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At least 1,243 records · Page 69Linked to original sources
PubMed2005

Motion in depth from interocular velocity differences revealed by differential motion aftereffect.

There are two possible binocular mechanisms for the detection of motion in depth. One is based on disparity changes over time and the other is based on interocular velocity differences. It has previously been shown that disparity changes over time can produce the perception of motion in depth. However, existing psychophysical and physiological data are inconclusive as to whether interocular velocity differences play a role in motion in depth perception. We studied this issue using the motion aftereffect, the illusory motion of static patterns that follows adaptation to real motion. We induced a differential motion aftereffect to the two eyes and then tested for motion in depth in a stationary random-dot pattern seen with both eyes. It has been shown previously that a differential translational motion aftereffect produces a strong perception of motion in depth. We show here that a rotational motion aftereffect inhibits this perception of motion in depth, even though a real rotation induces motion in depth. A non-horizontal translational motion aftereffect did not inhibit motion in depth. Together, our results strongly suggest that (1) pure interocular velocity differences can produce motion in depth, and (2) the illusory changes in position from the motion aftereffect are generated relatively late in the visual hierarchy, after binocular combination.

Adaptation, Psychological↗
PubMed1978

Geometric transformations of pictured space.

In general, a picture can represent a specific environment of scene only when the picture is seen from a unique viewing point. The determination of this unique point and of the distortions that occur when the picture is viewed from other points is crucial to all aspects of pictorial perception. To clarify the effects of the point of observation on pictorial space, the present paper discusses how the correct point may be calculated, provides a geometric analysis of the effects of altering the viewing point, and briefly reviews the effects of such alterations on space perception.

Depth Perception↗
PubMed1979

Symmetry perception and spatial-frequency channels.

It is known that the sum of a random-dot array with vertical bilateral symmetry and one with horizontal bilateral symmetry appears as a random array. Here we show that if the vertically and horizontally symmetrical arrays are spatially filtered, so that their respective spectra are 2 octaves apart, then their superposition does not appear random, but both symmetries can be simultaneously perceived. The low-band array has a stronger perceptual weight than the high-band array. These demonstrations give further evidence that frequency channels are before symmetry perception.

Depth Perception↗
PubMed1991

The ceiling of the Church of St Ignatius and the perception of concave surfaces.

This research describes two hitherto unobserved phenomena in the frescoes of the seventeenth century architect and painter, Andrea Pozzo, painted on the vaulted ceiling of the central nave of the Church of St Ignatius in Rome. The present research also reports the results of two experimental studies on the problem of the perception of shapes projected on concave surfaces. A quantitative evaluation of the phenomena perceived from various points of observation is made by means of stimuli projected at various angles on a semicylindrical surface. The validity of the assumption of invariance, and in particular of the projective invariant called the cross-ratio, is discussed within the framework of ecological theories on perception.

Architecture↗
PubMed1993

The computation of multiple matching doubly ambiguous stereograms with transparent planes.

Psychophysical experiments have been previously described Weinshall, D. (1989) Nature 341, 737-739; (1991) Vision Research 31, 1731-1748 that involved the perception of many transparent layers, corresponding to multiple matching, in doubly ambiguous random-dot stereograms. Additional experiments are described in the first part of this paper. In one experiment, subjects were required to report the density of dots on each transparent layer. In another experiment, the minimal density of dots on each layer, which is required for the subjects to perceive it as a distinct transparent layer, was measured. The difficulties encountered by stereo matching algorithms, when applied to doubly ambiguous stereograms, are described in the second part of this paper. Algorithms that can be modified to perform consistently with human perception, and the constraints imposed on their parameters by human perception, are discussed.

Algorithms↗
PubMed2000

Neural dynamics of 3-D surface perception: figure-ground separation and lightness perception.

This article develops the FACADE theory of three-dimensional (3-D) vision to simulate data concerning how two-dimensional pictures give rise to 3-D percepts of occluded and occluding surfaces. The theory suggests how geometrical and contrastive properties of an image can either cooperate or compete when forming the boundary and surface representations that subserve conscious visual percepts. Spatially long-range cooperation and short-range competition work together to separate boundaries of occluding figures from their occluded neighbors, thereby providing sensitivity to T-junctions without the need to assume that T-junction "detectors" exist. Both boundary and surface representations of occluded objects may be amodally completed, whereas the surface representations of unoccluded objects become visible through modal processes. Computer simulations include Bregman-Kanizsa figure-ground separation, Kanizsa stratification, and various lightness percepts, including the Münker-White, Benary cross, and checkerboard percepts.

Attention↗
PubMed1986

Infant perception of object unity from translatory motion in depth and vertical translation.

Previous research indicated that 4-month-old infants perceive the unity of a center-occluded object when its visible ends share a common lateral translation in space. The present work investigated the class of motion relationships that can specify object unity to infants, specifically, asking whether it includes all rigid translations. 3 experiments tested the informativeness of 2 axes of translation not previously studied: translation in depth and vertical translation. These motions also allowed assessment of certain interpretations of previous results that invoke specific sensory consequences of lateral movement, rather than perceived motion, as underlying perceived unity. Experiment 1 provided evidence that a small extent of translation in depth specified the unity of an object, but only to the subgroup of infants who detected the motion. Experiment 2 used a greater displacement in depth and found clear evidence for perception of object unity. Experiment 3 indicated that vertical translation, in which the 2 visible areas of the partly hidden object undergo dissimilar changes, also specifies object unity to infants. These results suggest that infants' perception of object unity depends on perceived coherence of motion, no matter how specified, and that the class of informative motions includes all rigid translations.

Depth Perception↗