Multiple 3-D Interpretations in a Classic Stereokinetic Effect

Perception ◽  
1986 ◽  
Vol 15 (4) ◽  
pp. 405-408 ◽  
Author(s):  
Paola Bressan ◽  
Giorgio Vallortigara
Keyword(s):  
Prolonged Exposure ◽  
Frontal Plane ◽  
Circular Disc ◽  
Frontoparallel Plane ◽  
Circular Trajectory ◽  
Axis Ratio ◽  
Stereokinetic Effect ◽  
Flat Pattern

It is known that a flat ellipse rotating in the frontoparallel plane sooner or later appears as a rigid circular disc tilting in 3-D space. An experiment is reported in which prolonged exposure to the same flat pattern produces a second previously unnoticed 3-D percept: an elongated egg slanted in 3-D space, which points towards the observer and the end parts of which describe a circular trajectory in the frontal plane. It is shown that the achievement of this alternative percept is not affected by the particular shape of the ellipse, although the time needed to reach it increases with an ellipse with a 2:3 axis ratio.

Perceptual Alternations in Stereokinesis

Perception ◽  
1988 ◽  
Vol 17 (1) ◽  
pp. 31-34 ◽  
Author(s):  
Giorgio Vallortigara ◽  
Paola Bressan ◽  
Marco Bertamini
Keyword(s):  
Frontal Plane ◽  
Circular Disc ◽  
Frontoparallel Plane ◽  
Circular Trajectory ◽  
Size Change ◽  
Prolonged Observation ◽  
Stimulation Of

When a flat ellipse is slowly rotated in the frontoparallel plane, two different 3-D percepts can be obtained: (i) a rigid circular disc tilting back and forth in 3-D space, and (ii) an elongated egg, slanted into 3-D space, whose end parts seem to be located at different distances from the observer and describe a circular trajectory with respect to the frontal plane. Under prolonged observation, the two 3-D percepts alternate in time, separated by brief intervals in which either the rotation of a rigid flat ellipse in the frontal plane or an amoeba-like distortion of a 2-D shape can be perceived. An experiment is reported in which the sequence of perceptual alternations was investigated. Results show that the 3-D disc is mostly preceded by impressions of elastic amoeba-like deformations, whereas the 3-D egg is mostly preceded by the percept of a rotating flat ellipse. Direct transitions from egg to disc are not as frequent as transitions from disc to egg. Results are discussed in relation to Braunstein and Andersen's hypothesis that phenomena of this sort might result from the stimulation of automatic mechanisms for perceiving size change (changing—size neural channels).

Learning to See Stereokinetic Effects

Perception ◽  
1987 ◽  
Vol 16 (2) ◽  
pp. 187-192 ◽  
Author(s):  
Paola Bressan ◽  
Giorgio Vallortigara
Keyword(s):  
Rigid Body ◽  
Structure From Motion ◽  
Incubation Time ◽  
Stimulus Pattern ◽  
Circular Ring ◽  
Frontoparallel Plane ◽  
Stereokinetic Effect ◽  
Flat Pattern

The Saturn illusion is a stereokinetic effect that occurs when a flat pattern composed of a full ellipse with two symmetrical semirings is rotated slowly in the frontoparallel plane. Subjects report seeing an egg-shaped object inserted into a circular ring, and the two objects move solidly into 3-D space as a single rigid body. Inexperienced observers show a conspicuous delay before reaching this percept. Two experiments are reported in which it is shown that this incubation time progressively decreases with repeated exposures to the stimulus pattern. A certain amount of time (14 s on average) is, however, required to obtain the effect, even after six successive exposures. It is argued that this time, which is independent of the speed of rotation and is not further reducible, is a fixed entity and is needed to compute the most rigid 3-D solution from deformations in the 2-D image. The results are discussed in relation to current theories of perception of structure from motion.

Perception of Depth in Rotating Objects: 3. Asymmetry and Velocity as the Determinants of the Stereokinetic Effect

1968 ◽  
Vol 26 (3) ◽  
pp. 671-681 ◽  
Author(s):  
Betty A. Wieland ◽  
Roy B. Mefferd
Keyword(s):  
Internal Structure ◽  
Horizontal Axis ◽  
Apparent Depth ◽  
Frontoparallel Plane ◽  
Stereokinetic Effect ◽  
Rotating Objects

When a flat stimulus is rotated in the frontoparallel plane about a horizontal axis that is an extension of O's line of regard, the apparent depth of the stimulus is enhanced. The enhancement was entirely a function of peripheral asymmetry. The apparent depth in the static figure, internal structure, or taper in the periphery did not augment the rotation-enhanced depth. The magnitude of the enhancement was constant for any series of stimuli, such as a series of overlapping circles with increasing overlap. The apparent depth also increased as a function of the speed of rotation.

Stereokinesis with Moving Visual Phantoms

Perception ◽  
1987 ◽  
Vol 16 (1) ◽  
pp. 73-78 ◽  
Author(s):  
Paola Bressan ◽  
Giorgio Vallortigara
Keyword(s):  
Dimensional Space ◽  
Three Dimensional ◽  
Major Axis ◽  
Circular Ring ◽  
Frontoparallel Plane ◽  
Flat Pattern ◽  
Three Dimensional Space

When a flat pattern composed of a solid ellipse with two symmetrical semirings (corresponding to the visible parts of a contour ellipse whose major axis is perpendicular to that of the solid ellipse) is slowly rotated in the frontoparallel plane, a compelling three-dimensional impression occurs. Subjects report seeing an egg-shaped object that is inserted into a circular ring: the two objects move solidly into three-dimensional space and a moving visual phantom is generated so that the ring appears completed by an illusory curved bar in the region closest to the observer during rotation. A number of variations of this illusion are presented. It is shown that stereokinetic phantoms (i) maintain the shape of the inducing elements; (ii) appear only after the stereokinetic transformation has taken place; and (iii) depend on the organization of the three-dimensional percept as a whole. Relations between stereokinetic phantoms and other completion phenomena are presented and discussed.

Methods for three-dimensional reconstruction of cellular components within a thick section

1986 ◽  
Vol 44 ◽  
pp. 18-21
Author(s):  
J. Frank ◽  
B. F. McEwen ◽  
M. Radermacher ◽  
C. L. Rieder
Keyword(s):  
Tilt Angle ◽  
Tomographic Reconstruction ◽  
3D Structure ◽  
Three Dimensional ◽  
Thick Section ◽  
Three Dimensional Reconstruction ◽  
Axis Ratio ◽  
Dimensional Reconstruction ◽  
Cellular Components

The tomographic reconstruction from multiple projections of cellular components, within a thick section, offers a way of visualizing and quantifying their three-dimensional (3D) structure. However, asymmetric objects require as many views from the widest tilt range as possible; otherwise the reconstruction may be uninterpretable. Even if not for geometric obstructions, the increasing pathway of electrons, as the tilt angle is increased, poses the ultimate upper limitation to the projection range. With the maximum tilt angle being fixed, the only way to improve the faithfulness of the reconstruction is by changing the mode of the tilting from single-axis to conical; a point within the object projected with a tilt angle of 60° and a full 360° azimuthal range is then reconstructed as a slightly elliptic (axis ratio 1.2 : 1) sphere.

A Therapist's Guide to Prolonged Exposure

PsycCRITIQUES ◽  
2008 ◽  
Vol 53 (30) ◽  
Author(s):  
Susan P. Stevens ◽  
Maha H. Zayed
Keyword(s):  
Prolonged Exposure
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