scholarly journals Effect of Spatial Frequency on Perceived Speed

2004 ◽  
Vol 58 (10) ◽  
pp. 1449-1452
Author(s):  
Haoming Shen ◽  
Yoshifumi Shimodaira ◽  
Gosuke Ohashi
Keyword(s):  
Spatial Frequency ◽  
Perceived Speed

Perceived Speed of Moving Cyclopean Corrugations Increases with Increasing Disparity Amplitude

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 195-195
Author(s):  
A M Johns ◽  
B J Rogers ◽  
R A Eagle
Keyword(s):  
Spatial Frequency ◽  
Feature Tracking ◽  
Temporal Frequency ◽  
Reference Stimulus ◽  
Experimental Control ◽  
The Poor ◽  
Random Dot Stereograms ◽  
Matching Performance ◽  
Perceived Speed ◽  
Central Fixation

In order to investigate how cyclopean motion is coded by the visual system, the points of subjective equality (PSEs) were measured for (i) speed, (ii) spatial frequency (SF), and (iii) temporal frequency (TF) as a function of peak-to-trough disparity amplitude for cyclopean corrugations. Two panels (3.0 deg × 7.0 deg) of dynamic random-dot stereograms were located 0.5 deg on either side of a central fixation spot. Each panel contained a horizontally oriented sinusoidal cyclopean corrugation whose SF, TF, and disparity amplitude were under experimental control. On each trial, the cyclopean corrugations were displaced vertically in opposite directions. Subjects judged which panel contained the higher SF, TF, or speed depending on condition. The reference stimulus was a sinusoidal corrugation with SF=0.4 cycles deg−1, TF=0.8 Hz, speed of 2.0 deg s−1, and peak-to-trough disparity amplitude of 8 min arc around fixation. We found that, as the peak-to-trough disparity amplitude of the test stimulus increased from 2 min arc to 32 min arc, the PSE for speed decreased from 2.21 deg s−1 to 1.67 deg s−1, compared to a reference speed of 2.00 deg s−1. However, across the same levels of disparity amplitude, the PSE for SF remained constant and the PSE for TF varied but with no consistent pattern. Thus, perceived speed increases with increased disparity amplitude. As all levels of disparity amplitude were above threshold, cyclopean speed cannot be detected by a purely ‘feature-tracking’ mechanism. These metamers and the poor TF matching performance suggest that cyclopean speed is coded by a sparse number of temporal mechanisms.

Influence of Temporal Frequency on Perceived Speed

1977 ◽  
Vol 45 (1) ◽  
pp. 39-50 ◽  
Author(s):  
André Delorme ◽  
Jean-Yves Frigon
Keyword(s):  
Visual Perception ◽  
Spatial Frequency ◽  
Temporal Frequency ◽  
Stable Fixation ◽  
Ocular Pursuit ◽  
The Third ◽  
Contextual Elements ◽  
Moving Stimulus ◽  
Perceived Speed ◽  
Moving Line

The visual perception of velocity was studied in three experiments. The stimulus used in the first experiment was an endless striped belt moving behind a stable fixation line. In the second experiment a vertical moving line was presented in front of a stable striped background. In the third experiment the same moving line was pursued by the eye but the background was stable or moving either with the moving stimulus or in the opposite direction. The variables studied were the speed of the moving stimulus, the speed of the background, and the density (spatial frequency) of the stripes. Two theoretical explanations of the perceptual effects obtained are compared. The first explains variations of perceptual velocity in terms of density. The second asserts effects of perceptual velocity are contingent upon temporal frequency of encounters between the moving stimulus and the stable or moving contextual elements. The results favor the latter interpretation in the three experiments, but part of the results of Exp. 3 could be explained by the influence of ocular pursuit.

Determination of the Best Emulsion for the Microscopy of Crystals

1981 ◽  
Vol 39 ◽  
pp. 32-33
Author(s):  
David A. Grano ◽  
Kenneth H. Downing
Keyword(s):  
Spatial Frequency ◽  
Information Transfer ◽  
Signal To Noise Ratio ◽  
Experimental Situation ◽  
Photographic Emulsion ◽  
Modulation Transfer ◽  
Signal To Noise ◽  
Frequency Space ◽  
Noise Ratio

The retrieval of high-resolution information from images of biological crystals depends, in part, on the use of the correct photographic emulsion. We have been investigating the information transfer properties of twelve emulsions with a view toward 1) characterizing the emulsions by a few, measurable quantities, and 2) identifying the “best” emulsion of those we have studied for use in any given experimental situation. Because our interests lie in the examination of crystalline specimens, we've chosen to evaluate an emulsion's signal-to-noise ratio (SNR) as a function of spatial frequency and use this as our critereon for determining the best emulsion.The signal-to-noise ratio in frequency space depends on several factors. First, the signal depends on the speed of the emulsion and its modulation transfer function (MTF). By procedures outlined in, MTF's have been found for all the emulsions tested and can be fit by an analytic expression 1/(1+(S/S0)2). Figure 1 shows the experimental data and fitted curve for an emulsion with a better than average MTF. A single parameter, the spatial frequency at which the transfer falls to 50% (S0), characterizes this curve.

Density-based discrimination of protein and RNA in the ribosome

1992 ◽  
Vol 50 (1) ◽  
pp. 464-465
Author(s):  
Joachim Frank
Keyword(s):  
Transfer Function ◽  
Spatial Frequency ◽  
Three Dimensional ◽  
Wiener Filter ◽  
Dark Field Image ◽  
Dark Field ◽  
Frequency Range ◽  
Bright Field ◽  
Contrast Transfer Function ◽  
Pass Filter

Cryo-electron microscopy combined with single-particle reconstruction techniques has allowed us to form a three-dimensional image of the Escherichia coli ribosome.In the interior, we observe strong density variations which may be attributed to the difference in scattering density between ribosomal RNA (rRNA) and protein. This identification can only be tentative, and lacks quantitation at this stage, because of the nature of image formation by bright field phase contrast. Apart from limiting the resolution, the contrast transfer function acts as a high-pass filter which produces edge enhancement effects that can explain at least part of the observed variations. As a step toward a more quantitative analysis, it is necessary to correct the transfer function in the low-spatial-frequency range. Unfortunately, it is in that range where Fourier components unrelated to elastic bright-field imaging are found, and a Wiener-filter type restoration would lead to incorrect results. Depending upon the thickness of the ice layer, a varying contribution to the Fourier components in the low-spatial-frequency range originates from an “inelastic dark field” image. The only prospect to obtain quantitatively interpretable images (i.e., which would allow discrimination between rRNA and protein by application of a density threshold set to the average RNA scattering density may therefore lie in the use of energy-filtering microscopes.

Three-fold astigmatism: An important TEM aberration

1993 ◽  
Vol 51 ◽  
pp. 972-973 ◽  
Author(s):  
O.L. Krivanek ◽  
M.L. Leber
Keyword(s):  
High Resolution ◽  
Spatial Frequency ◽  
Field Emission ◽  
Azimuthal Angle ◽  
Hollow Cone ◽  
Small Probe ◽  
Wide Range ◽  
High Resolution Images ◽  
Image Position

Three-fold astigmatism resembles regular astigmatism, but it has 3-fold rather than 2-fold symmetry. Its contribution to the aberration function χ(q) can be written as:where A3 is the coefficient of 3-fold astigmatism, λ is the electron wavelength, q is the spatial frequency, ϕ the azimuthal angle (ϕ = tan-1 (qy/qx)), and ϕ3 the direction of the astigmatism.Three-fold astigmatism is responsible for the “star of Mercedes” aberration figure that one obtains from intermediate lenses once their two-fold astigmatism has been corrected. Its effects have been observed when the beam is tilted in a hollow cone over a wide range of angles, and there is evidence for it in high resolution images of a small probe obtained in a field emission gun TEM/STEM instrument. It was also expected to be a major aberration in sextupole-based Cs correctors, and ways were being developed for dealing with it on Cs-corrected STEMs.

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