scholarly journals Optical snow and the aperture problem

2003 ◽  
Author(s):  
R. Mann ◽  
M.S. Langer
Keyword(s):  
Aperture Problem

scholarly journals The aperture problem in stereopsis

1997 ◽  
Vol 37 (19) ◽  
pp. 2737-2744 ◽  
Author(s):  
M.J. Morgan ◽  
E. Castet
Keyword(s):  
Aperture Problem

scholarly journals The Perceived Direction of Textured Gratings and Their Motion Aftereffects

Perception ◽  
1995 ◽  
Vol 24 (12) ◽  
pp. 1383-1396 ◽  
Author(s):  
David Alais ◽  
Maarten J van der Smagt ◽  
Frans A J Verstraten ◽  
Wim A van de Grind
Keyword(s):  
Motion Aftereffect ◽  
Sine Wave ◽  
Circular Aperture ◽  
High Luminance ◽  
One Dimensional ◽  
Square Wave ◽  
Aperture Problem ◽  
Motion Energy ◽  
Motion Aftereffects ◽  
Do So

The stimuli in these experiments are square-wave luminance gratings with an array of small random dots covering the high-luminance regions. Owing to the texture, the direction of these gratings, when seen through a circular aperture, is disambiguated because the visual system is provided with an unambiguous motion energy. Thus, the direction of textured gratings can be varied independently of grating orientation. When subjects are required to judge the direction of textured gratings moving obliquely relative to their orientation, they can do so accurately (experiment 1). This is of interest because most studies of one-dimensional motion perception have involved (textureless) luminance-defined sine-wave or square-wave gratings, and the perceived direction of these gratings is constrained by the aperture problem to be orthogonal to their orientation. Thus, direction and orientation have often been confounded. Interestingly, when subjects are required to judge the direction of an obliquely moving textured grating during a period of adaptation and then the direction of the motion aftereffect (MAE) immediately following adaptation (experiments 2 and 3), these directions are not directly opposite each other. MAE directions were always more orthogonal to the orientation of the adapting grating than the corresponding direction judgments during adaptation (by as much as 25°). These results are not readily explained by conventional MAE models and possible accounts are considered.

The aperture problem for binaural hearing can explain ambiguous lateralization of complex binaural stimuli

2021 ◽  
Vol 150 (4) ◽  
pp. A303-A303
Author(s):  
Daniel J. Tollin ◽  
Matthew J. Goupell ◽  
G. Christopher Stecker
Keyword(s):  
Binaural Hearing ◽  
Aperture Problem

Velocity Computation from Measures of Spatiotemporal Gradients at Multiple Orientations

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 77-77 ◽  
Author(s):  
A Johnston ◽  
P W McOwan
Keyword(s):  
Natural Extension ◽  
Image Brightness ◽  
Motion Patterns ◽  
One Dimensional ◽  
Aperture Problem ◽  
Motion Models ◽  
Temporal Domain ◽  
Moving Stimulus ◽  
Zero Values ◽  
Derivatives Of

Current models of speed and direction of motion which use measures of spatiotemporal gradients can suffer from ill-conditioning. This problem arises either because local measures of the derivatives of image brightness take zero values or because the motion equations cannot be solved for one-dimensional (1-D) signals in two-dimensional (2-D) images—the aperture problem. One way around this predicament is to select image points or introduce constants to deal with ill-conditioned calculations. Here we describe an analytic method that combines measures of speed in a range of directions to provide a well-conditioned measure of velocity at all points in the moving stimulus. This approach is a natural extension of a one-dimensional model which has been successful in predicting perceived motion in a variety of 1-D spatiotemporal motion patterns (Johnston, McOwan and Buxton 1992 Proceedings of the Royal Society of London, Series B250 297 – 306). Speed is computed with the use of biologically plausible filters that are derivatives of Gaussians in the spatial domain and log Gaussians in the temporal domain. Measures of speed and inverse speed are computed for a range of orientations consistent with the number of direction columns in MT/V5. The pattern of velocities measured over this set of orientations is then used to recover the speed and direction of motion of the stimulus. The model can correctly compute the velocity of moving 1-D patterns, such as gratings, patterns that prove a problem for many current 2-D motion models as they form degenerate cases, as well as the motion of rigid 2-D patterns.

A Computational Model of the Perceived Velocity of Moving Plaids

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 87-87
Author(s):  
I Lamouret ◽  
V Cornilleau-Pérès ◽  
J Droulez
Keyword(s):  
Optic Flow ◽  
Type Ii ◽  
Local Velocity ◽  
Local Motion ◽  
Aperture Problem ◽  
Tilted Line ◽  
Short Stimulus ◽  
Detection Mechanisms ◽  
Perceived Velocity ◽  
Gradient Models

Local motion detection mechanisms generally lead to one component of the optic flow becoming indeterminate. One way to solve this ‘aperture problem’ is to compute the optic flow which minimises some smoothing constraint. With iterative schemes the computed velocity array is suboptimal relative to the constraint until the process has converged. Under the original assumption that the iteration rate is sufficiently low to allow the perception of suboptimal flows at short stimulus durations, iterative gradient models give an accurate description of biases in the perception of tilted line velocity. We examine whether this approach can be applied to moving sinusoidal plaids. Our simulations are in agreement with a number of psychophysical results on both speed and direction perception. In particular we show that the effect of stimulus duration on the perceived direction of type II plaids [Yo and Wilson, 1992 Vision Research32(1)] can be accounted for without recourse to second-order mechanisms. The effects of contrast and component directions on the evolution rate of this bias are well reproduced. The model also successfully describes the effect of spatial frequency, and data obtained with gratings. These results suggest that iterative gradient schemes can model the dynamics of interactions between local velocity detectors, as revealed by psychophysical experiments with lines and plaids.

scholarly journals Occlusion and the solution to visual motion ambiguity: Looking beyond the aperture problem

10.1167/8.2.4 ◽  
2008 ◽  
Vol 8 (2) ◽  
pp. 4 ◽  
Author(s):  
Maarten J. van der Smagt ◽  
Gene R. Stoner
Keyword(s):  
Visual Motion ◽  
Aperture Problem
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