Global versus Local Image Expansion in Estimating Time-to-Contact from Complex Optic Flow

Perception ◽  
10.1068/p5271 ◽  
2005 ◽  
Vol 34 (5) ◽  
pp. 577-585 ◽  
Author(s):  
Christos D Giachritsis ◽  
Mike G Harris
Keyword(s):  
Optic Flow ◽  
Local Analysis ◽  
Systematic Effect ◽  
Global Pattern ◽  
Time To Contact ◽  
Local Expansion ◽  
Rotation Rates ◽  
Global And Local ◽  
Local Image ◽  
Image Expansion

Previous work (Harris and Giachritsis 2000, Vision Research40 601–611) has shown that, when global and local image expansion are placed in conflict, estimates of time-to-contact (TTC) are based almost exclusively upon global expansion. Here we extend this finding by demonstrating that global image expansion continues to predominate even under conditions that seem more favourable to a local analysis. We added a global rotation to the stimulus so that the global pattern of expansion was distorted while leaving the local expansion unaffected. Even under relatively high rotation rates (30° s−1), local expansion continued to have little systematic effect upon estimates of TTC.

Global and Local Contributions to the Optical Specification of Time to Contact: Observer Sensitivity to Composite Tau

Perception ◽  
10.1068/p3230 ◽  
2002 ◽  
Vol 31 (8) ◽  
pp. 901-924 ◽  
Author(s):  
Reinoud J Bootsma ◽  
Cathy M Craig
Keyword(s):  
Discrimination Performance ◽  
Forced Choice ◽  
Object Motion ◽  
Time To Contact ◽  
Local Expansion ◽  
First Order ◽  
Optical Distance ◽  
Observer Motion ◽  
Environmental Element ◽  
Global And Local

First-order time remaining until a moving observer will pass an environmental element is optically specified in two different ways. The specification provided by global tau (based on the pattern of change of angular bearing) requires that the element is stationary and that the direction of motion is accurately detected, whereas the specification provided by composite tau (based on the patterns of change of optical size and optical distance) does not require either of these. We obtained converging evidence for our hypothesis that observers are sensitive to composite tau in four experiments involving relative judgments of time to passage with forced-choice methodology. Discrimination performance was enhanced in the presence of a local expansion component, while being unaffected when the detection of the direction of heading was impaired. Observers relied on the information carried in composite tau rather than on the information carried in its constituent components. Finally, performance was similar under conditions of observer motion and conditions of object motion. Because composite tau specifies first-order time remaining for a large number of situations, the different ways in which it may be detected are discussed.

Local image structures and optic flow estimation

2005 ◽  
Vol 16 (4) ◽  
pp. 341-356 ◽  
Author(s):  
S. Kalkan ◽  
D. Calow ◽  
F. Wörgötter ◽  
M. Lappe ◽  
N. Krüger
Keyword(s):  
Optic Flow ◽  
Flow Estimation ◽  
Local Image

scholarly journals Global and local expansion of magnetic clouds in the inner heliosphere

2009 ◽  
Vol 509 ◽  
pp. A39 ◽  
Author(s):  
A. M. Gulisano ◽  
P. Démoulin ◽  
S. Dasso ◽  
M. E. Ruiz ◽  
E. Marsch
Keyword(s):  
Magnetic Clouds ◽  
Local Expansion ◽  
Global And Local ◽  
Inner Heliosphere

scholarly journals Optic Flow: A History

i-Perception ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 204166952110557
Author(s):  
Diederick C. Niehorster
Keyword(s):  
Optic Flow ◽  
Visual Motion ◽  
Scientific Literature ◽  
Archival Research ◽  
Visual World ◽  
Global Pattern ◽  
Self Motion

The concept of optic flow, a global pattern of visual motion that is both caused by and signals self-motion, is canonically ascribed to James Gibson's 1950 book “ The Perception of the Visual World.” There have, however, been several other developments of this concept, chiefly by Gwilym Grindley and Edward Calvert. Based on rarely referenced scientific literature and archival research, this article describes the development of the concept of optic flow by the aforementioned authors and several others. The article furthermore presents the available evidence for interactions between these authors, focusing on whether parts of Gibson's proposal were derived from the work of Grindley or Calvert. While Grindley's work may have made Gibson aware of the geometrical facts of optic flow, Gibson's work is not derivative of Grindley's. It is furthermore shown that Gibson only learned of Calvert's work in 1956, almost a decade after Gibson first published his proposal. In conclusion, the development of the concept of optic flow presents an intriguing example of convergent thought in the progress of science.

Landing with Time-to-Contact and Ventral Optic Flow Estimates

2012 ◽  
Vol 35 (4) ◽  
pp. 1362-1367 ◽  
Author(s):  
Dario Izzo ◽  
Guido de Croon
Keyword(s):  
Optic Flow ◽  
Time To Contact

Adaptive Query Refinement Based on Global and Local Analysis

2005 ◽  
pp. 584-593 ◽  
Author(s):  
Chaoyuan Cui ◽  
Hanxiong Chen ◽  
Kazutaka Furuse ◽  
Nobuo Ohbo
Keyword(s):  
Local Analysis ◽  
Query Refinement ◽  
Global And Local

Classification and Counting of Composite Objects in Traffic Scenes Using Global and Local Image Analysis

2013 ◽  
Vol 14 (1) ◽  
pp. 69-81 ◽  
Author(s):  
Guruprasad Somasundaram ◽  
Ravishankar Sivalingam ◽  
Vassilios Morellas ◽  
Nikolaos Papanikolopoulos
Keyword(s):  
Image Analysis ◽  
Composite Objects ◽  
Global And Local ◽  
Local Image

scholarly journals Systematic differences between visually-relevant global and local image statistics of brain MRI and natural scenes

2018 ◽  
Author(s):  
Yueyang Xu ◽  
Ashish Raj ◽  
Jonathan Victor ◽  
Keyword(s):  
Visual System ◽  
Human Visual System ◽  
Image Formation ◽  
Natural Images ◽  
Natural Image ◽  
Natural Scenes ◽  
Image Statistics ◽  
Processing Technologies ◽  
Global And Local ◽  
Local Image

AbstractAn important heuristic in developing image processing technologies is to mimic the computational strategies used by humans. Relevant to this, recent studies have shown that the human brain’s processing strategy is closely matched to the characteristics of natural scenes, both in terms of global and local image statistics. However, structural MRI images and natural scenes have fundamental differences: the former are two-dimensional sections through a volume, the latter are projections. MRI image formation is also radically different from natural image formation, involving acquisition in Fourier space, followed by several filtering and processing steps that all have the potential to alter image statistics. As a consequence, aspects of the human visual system that are finely-tuned to processing natural scenes may not be equally well-suited for MRI images, and identification of the differences between MRI images and natural scenes may lead to improved machine analysis of MRI.With these considerations in mind, we analyzed spectra and local image statistics of MRI images in several databases including T1 and FLAIR sequence types and of simulated MRI images,[1]–[6] and compared this analysis to a parallel analysis of natural images[7] and visual sensitivity[7][8]. We found substantial differences between the statistical features of MRI images and natural images. Power spectra of MRI images had a steeper slope than that of natural images, indicating a lack of scale invariance. Independent of this, local image statistics of MRI and natural images differed: compared to natural images, MRI images had smaller variations in their local two-point statistics and larger variations in their local three-point statistics – to which the human visual system is relatively insensitive. Our findings were consistent across MRI databases and simulated MRI images, suggesting that they result from brain geometry at the scale of MRI resolution, rather than characteristics of specific imaging and reconstruction methods.

scholarly journals Energy Landscape of the SARS-CoV-2 Reveals Extensive Conformational Heterogeneity

2021 ◽  
Author(s):  
Ghoncheh Mashayekhi ◽  
John Vant ◽  
Abhishek Singharoy ◽  
Abbas Ourmazd
Keyword(s):  
Free Energy ◽  
Energy Landscape ◽  
Binding Pocket ◽  
Minimum Free Energy ◽  
Spike Protein ◽  
Local Analysis ◽  
Interaction Sites ◽  
Density Maps ◽  
The Stability ◽  
Global And Local

Cryo-electron microscopy (cryo-EM) has produced a number of structural models of the SARS-CoV-2 spike, already prompting biomedical outcomes. However, these reported models and their associated electrostatic potential maps represent an unknown admixture of conformations stemming from the underlying energy landscape of the spike protein. As for any protein, some of the spike's conformational motions are expected to be biophysically relevant, but cannot be interpreted only by static models. Using experimental cryo-EM images, we present the energy landscape of the spike protein conformations, and identify molecular rearrangements along the most-likely conformational path in the vicinity of the open (so called 1RBD-up) state. The resulting global and local atomic refinements reveal larger movements than those expected by comparing the reported 1RBD-up and 1RBD-down cryo-EM models. Here we report greater degrees of "openness" in global conformations of the 1RBD-up state, not revealed in the single-model interpretations of the density maps, together with conformations that overlap with the reported models. We discover how the glycan shield contributes to the stability of these conformations along the minimum free-energy pathway. A local analysis of seven key binding pockets reveals that six out them, including those for engaging ACE2, therapeutic mini-proteins, linoleic acid, two different kinds of antibodies, and protein-glycan interaction sites, switch conformations between their known apo- and holo-conformations, even when the global spike conformation is 1RBD-up. This is reminiscent of a conformational pre-equilibrium. We found only one binding pocket, namely antibody AB-C135 to remain closed along the entire minimum free energy path, suggesting an induced fit mechanism for this enzyme.

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