Spatial-Frequency Masking with Briefly Pulsed Patterns

Perception ◽  
1978 ◽  
Vol 7 (2) ◽  
pp. 161-166 ◽  
Author(s):  
Gordon E Legge ◽  
Michael A Cohen ◽  
Charles F Stromeyer
Keyword(s):  
Spatial Frequency ◽  
Frequency Band ◽  
Nonlinear Distortion ◽  
Test Pattern ◽  
Low Frequency ◽  
High Spatial Frequency ◽  
Sinusoidal Grating ◽  
Backward Masking ◽  
Frequency Test ◽  
Test Grating

Spatial-frequency masking was studied with briefly pulsed (25 ms) vertical gratings. The mask was a noise grating, and the test pattern was a sinusoidal grating. A low-frequency band of noise masked a low- but not high-spatial-frequency test grating when the patterns were presented simultaneously. A high-frequency band of noise did not mask a low-frequency test grating when the patterns were presented simultaneously or when the mask was presented after the test pattern (backward masking). Masking was, however, observed when the mask or test pattern was of sufficiently high contrast so that the stimuli had nonlinear distortion and thus produced DC shifts of the field luminance.

Spatial Scale Interactions and Visual-Tracking Performance

Perception ◽  
1997 ◽  
Vol 26 (8) ◽  
pp. 1047-1058 ◽  
Author(s):  
Howard C Hughes ◽  
David M Aronchick ◽  
Michael D Nelson
Keyword(s):  
Spatial Frequency ◽  
High Frequency ◽  
Visual Information ◽  
Low Frequency ◽  
High Spatial Frequency ◽  
Performance Measure ◽  
High Frequency Component ◽  
Stimulus Velocity ◽  
Spatial Frequencies ◽  
Wide Range

It has previously been observed that low spatial frequencies (≤ 1.0 cycles deg−1) tend to dominate high spatial frequencies (≥ 5.0 cycles deg−1) in several types of visual-information-processing tasks. This earlier work employed reaction times as the primary performance measure and the present experiments address the possibility of low-frequency dominance by evaluating visually guided performance of a completely different response system: the control of slow-pursuit eye movements. Slow-pursuit gains (eye velocity/stimulus velocity) were obtained while observers attempted to track the motion of a sine-wave grating. The drifting gratings were presented on three types of background: a uniform background, a background consisting of a stationary grating, or a flickering background. Low-frequency dominance was evident over a wide range of velocities, in that a stationary high-frequency component produced little disruption in the pursuit of a drifting low spatial frequency, but a stationary low frequency interfered substantially with the tracking of a moving high spatial frequency. Pursuit was unaffected by temporal modulation of the background, suggesting that these effects are due to the spatial characteristics of the stationary grating. Similar asymmetries were observed with respect to the stability of fixation: active fixation was less stable in the presence of a drifting low frequency than in the presence of a drifting high frequency.

Effect of repetitive visual stimuli on behaviour and plasma corticosterone of European starlings

2005 ◽  
Vol 55 (3) ◽  
pp. 245-258 ◽  
Author(s):  
◽  
◽  
◽  
Keyword(s):  
Spatial Frequency ◽  
High Frequency ◽  
Temporal Frequency ◽  
Low Frequency ◽  
High Spatial Frequency ◽  
Plasma Corticosterone ◽  
European Starlings ◽  
Fluorescent Lamps ◽  
Spatial Frequencies ◽  
Temporal And Spatial

AbstractFlickering light can cause adverse effects in some humans, as can rhythmic spatial patterns of particular frequencies. We investigated whether birds react to the temporal frequency of standard 100 Hz fluorescent lamps and the spatial frequency of the visual surround in the manner predicted by the human literature, by examining their effects on the preferences, behaviour and plasma corticosterone of European starlings (Sturnus vulgaris). We predicted that high frequency lighting (> 30 kHz) and a relatively low spatial frequency on the walls of their cages (0.1 cycle cm−1) would be less aversive than low frequency lighting (100 Hz) and a relatively high spatial frequency (2.5 cycle cm−1). Birds had strong preferences for both temporal and spatial frequencies. These preferences did not always fit with predictions, although there was evidence that 100 Hz was more stressful than 30 kHz lighting, as birds were less active and basal corticosterone levels were higher under 100 Hz lighting. Our chosen spatial frequencies had no overall significant effect on corticosterone levels. Although there are clearly effects of, and interactions between, the frequency of the light and the visual surround on the behaviour and physiology of birds, the pattern of results is not straightforward.

Predictions of U-Shaped Backward Pattern Masking from Considerations of the Spatio-Temporal Frequency Response

Perception ◽  
1975 ◽  
Vol 4 (3) ◽  
pp. 297-304 ◽  
Author(s):  
Bruno G Breitmeyer
Keyword(s):  
Spatial Frequency ◽  
Temporal Frequency ◽  
High Spatial Frequency ◽  
Stimulus Onset ◽  
Masking Effect ◽  
Time Interval ◽  
Sinusoidal Grating ◽  
Frequency Content ◽  
Pattern Masking ◽  
Spatio Temporal

The threshold detectability of a briefly presented target stimulus consisting of a vertical sinusoidal grating was affected not only by the spatial frequency content of an equally briefly presented, two-octave-wide masking noise, but also by the time interval separating the onsets of the target and its mask. Over a range of stimulus onset asynchronies, in which the mask onset either preceded, coincided with, or followed the target onset, a mask with a low spatial frequency content had its greatest masking effect on a high spatial frequency target grating when the mask followed the target by 120–180 ms. When the mask had a high spatial frequency content and the target was of low spatial frequency, or when the target was entered on the mask frequency band, optimal masking effects occurred when the onsets of the mask and target coincided. The results are discussed in relation to previous masking studies, particuarly those in which U-shaped backward pattern masking functions are obtained.

Diphasic and Polyphasic Temporal Modulations Multiply Apparent Spatial Frequency

Perception ◽  
1974 ◽  
Vol 3 (3) ◽  
pp. 323-336 ◽  
Author(s):  
V Virsu ◽  
G Nyman ◽  
P K Lehtiö
Keyword(s):  
Spatial Frequency ◽  
High Frequency ◽  
Light Adaptation ◽  
Second Harmonic ◽  
Temporal Integration ◽  
Low Frequency ◽  
Integration Time ◽  
Sinusoidal Grating ◽  
Spatial Effects ◽  
Spatial Integration

The effects of diphasic and polyphasic flicker on apparent spatial frequency were studied in several experiments through simultaneous spatial-frequency matches. In diphasic flicker the spatial phase of a sinusoidal grating alternated between two values in a counterphase fashion, and in polyphasic flicker the spatial phases of gratings were varied discretely in time in a variable number of steps. Both forms of flicker increased the apparent spatial frequency at low temporal frequencies, in the same manner as low-frequency monophasic flicker has been found to do. At high temporal frequencies, diphasic flicker doubled the apparent spatial frequency, as reported by Kelly (1966). We found that through high-frequency polyphasic flicker the spatial effect that Kelly mentions can be generalised to spatial frequency multiplication: polyphasic flicker produces not only the apparent second harmonic but also the third and the fourth harmonic, depending on the phase parameters. A numerical analysis showed that the spatial high-frequency effects can be explained through temporal integration of nonlinearly filtered input signals if a value of 200 td(1) is assumed for the nonlinearity constant in [Formula: see text] where B( I) is the brightness, I is the retinal illuminance, K is a scale constant, and I½ is the constant of nonlinearity. A minimum value of 60 ms had to be estimated for integration time. An investigation of the integration time with diphasic flicker indicated that spatial integration time decreases when the level of light adaptation increases, and that the integration time for spatial effects is longer than for flicker fusion. The spatial effects of low-frequency and high-frequency flicker differ in so many respects that different neural processes have to be postulated for their explanation.

Dynamics of Adaptation to Contrast

Perception ◽  
1982 ◽  
Vol 11 (5) ◽  
pp. 505-528 ◽  
Author(s):  
David Rose ◽  
Ivan Lowe
Keyword(s):  
Spatial Frequency ◽  
Visual System ◽  
Power Function ◽  
Single Phase ◽  
Detection Threshold ◽  
High Spatial Frequency ◽  
Sinusoidal Grating ◽  
Dual Phase ◽  
High Contrast ◽  
Inhibitory Interactions

An investigation has been made into the temporal parameters with which the detection threshold for a sinusoidal grating changes during and after adaptation to the same grating at high contrast. Stationary high-spatial-frequency gratings and a phase-reversing low-spatial-frequency grating have been studied separately. It was found that the threshold continues to rise during adaptation for at least 6 min without sign of levelling off, and that full recovery from 6 min of adaptation can take more than 45 min. Intermittent adaptation and continuous adaptation for the same period produce similar effects. Single-phase and dual-phase exponential fits to the data are rejected, and it is concluded that the level of adaptation of the visual system to spatial contrast changes as a power function of time. However, recovery is not always monotonic, especially after adaptation to phase-reversing gratings. This may be due to inhibitory interactions between channels (in particular, those for pattern and movement information).

scholarly journals Monocular blur alters the tuning characteristics of stereopsis for spatial frequency and size

2016 ◽  
Vol 3 (9) ◽  
pp. 160273 ◽  
Author(s):  
Roger W. Li ◽  
Kayee So ◽  
Thomas H. Wu ◽  
Ashley P. Craven ◽  
Truyet T. Tran ◽  
...  
Keyword(s):  
Spatial Frequency ◽  
Narrow Band ◽  
Frequency Tuning ◽  
Low Frequency ◽  
High Spatial Frequency ◽  
Spatial Filters ◽  
Optimum Frequency ◽  
Spatial Frequencies ◽  
Coarse To Fine ◽  
Tuning Function

Our sense of depth perception is mediated by spatial filters at different scales in the visual brain; low spatial frequency channels provide the basis for coarse stereopsis, whereas high spatial frequency channels provide for fine stereopsis. It is well established that monocular blurring of vision results in decreased stereoacuity. However, previous studies have used tests that are broadband in their spatial frequency content. It is not yet entirely clear how the processing of stereopsis in different spatial frequency channels is altered in response to binocular input imbalance. Here, we applied a new stereoacuity test based on narrow-band Gabor stimuli. By manipulating the carrier spatial frequency, we were able to reveal the spatial frequency tuning of stereopsis, spanning from coarse to fine, under blurred conditions. Our findings show that increasing monocular blur elevates stereoacuity thresholds ‘selectively’ at high spatial frequencies, gradually shifting the optimum frequency to lower spatial frequencies. Surprisingly, stereopsis for low frequency targets was only mildly affected even with an acuity difference of eight lines on a standard letter chart. Furthermore, we examined the effect of monocular blur on the size tuning function of stereopsis. The clinical implications of these findings are discussed.

Recognition of Positive and Negative Bandpass-Filtered Images

Perception ◽  
1986 ◽  
Vol 15 (5) ◽  
pp. 595-602 ◽  
Author(s):  
Tony Hayes ◽  
M Concetta Morrone ◽  
David C Burr
Keyword(s):  
Spatial Frequency ◽  
Visual System ◽  
Visual Information ◽  
Recognition Performance ◽  
Low Frequency ◽  
High Spatial Frequency ◽  
Spatial Frequencies ◽  
Negative Images ◽  
Frequency Components

A study is reported in which the significance for vision of low- and high-spatial-frequency components of photographic positive and negative images was investigated by measuring recognition of bandpass-filtered photographs of faces. The results show that a 1.5 octave bandpass-filtered image contains sufficient visual information for good recognition performance, provided the filter is centred close to 20 cycles facewidth−1. At low spatial frequencies negatives are more difficult to recognize than positives, but at high spatial frequencies there is no difference in recognition, implying that it is the low-frequency components of negatives which present difficulties for the visual system.

Temporal summation of moving images by the human visual system

1981 ◽  
Vol 211 (1184) ◽  
pp. 321-339 ◽  
Keyword(s):  
Spatial Frequency ◽  
Visual System ◽  
Human Visual System ◽  
Temporal Summation ◽  
Temporal Integration ◽  
High Spatial Frequency ◽  
Slow Motion ◽  
Sinusoidal Grating ◽  
Moving Images ◽  
Sinusoidal Gratings

Measurements of threshold visibility were made as a function of duration of stimulus exposure for small moving dot targets, drifting sinusoidal gratings and moving patches of sinusoidal gratings, to investigate how the human visual nervous system summates over time signals arising from stimuli in motion. At image speeds of less that 16 deg/s, temporal summation is as strong and as extended for moving as for stationary dots (total summation over to about 100 ms). This summation is about twice that which would be expected from separate consideration of the regions of spatial and temporal integration. Measurements with sinusoidal gratings reveal that the nature of the summation depends critically on the spatial frequency of the stimulus: gratings of low spatial frequency summate well when in motion (and only when in motion), whereas those of high spatial frequency summate well only when stationary or in very slow motion. An analogue simulation with electronic filters showed that these psychophysical results are directly predictable from the known transfer characteristics of the human visual system (with the additional assumption of probability summation at threshold). Finally, with small patches of sinusoidal grating, it was established that translation per se across the retina has little effect on temporal summation. This suggests that the results obtained with sinusoidal gratings of large extent are also relevant to small moving stimuli, allowing the summation results obtained with dot stimuli to be discussed in terms of the temporal transfer properties of spatially selective visual detectors. On the basis of these results it is proposed that the extended temporal summation observed for dots in motion results from summation of energy of low spatial frequency present in these stimuli.

Contrast sensitivity in dyslexia

1995 ◽  
Vol 12 (1) ◽  
pp. 153-163 ◽  
Author(s):  
Karen Gross-Glenn ◽  
Bernt C. Skottun ◽  
William Glenn ◽  
Alex Kushch ◽  
Robert Lingua ◽  
...  
Keyword(s):  
Spatial Frequency ◽  
Contrast Sensitivity ◽  
High Frequency ◽  
Temporal Summation ◽  
Low Frequency ◽  
High Spatial Frequency ◽  
Forward Masking ◽  
Baseline Condition ◽  
Transient System ◽  
Deficit Theory

AbstractContrast sensitivity was determined for dyslexic and normal readers. When testing with temporally ramped (i.e. stimuli with gradual temporal onsets and offsets) gratings of 0.6, 4.0, and 12.0 cycles/deg, we found no difference in contrast sensitivity between dyslexic readers and controls. Using 12.0 cycles/deg gratings with transient (i.e. abrupt) onsets and offsets, we found that dyslexic individuals had, compared to controls, markedly inferior contrast sensitivity at the shortest stimulus durations (i.e. 17, 34, and 102 ms). This deficit may reflect more sluggish temporal summation. There was no difference in sensitivity to 0.6 cycles/deg gratings with transient onsets and offsets. Under these conditions, the two groups showed a consistent and equal increase in sensitivity relative to the ramped baseline condition at 0.6 cycles/deg at the longer stimulus durations. This demonstrates that dyslexic readers have no deficit in their ability to detect stimulus transients, a finding which appears to be inconsistent with a transient system deficit. That detection of the low-frequency stimuli was mediated by the transient system is further indicated by the fact that these stimuli were more susceptible to forward masking than were the high-frequency stimuli. The effects of masking of both high and low spatial-frequency stimuli were about equal for dyslexic readers and controls. This is not in agreement with the transient system deficit theory, according to which one would expect there to be less masking of high spatial-frequency stimuli in the case of dyslexic readers.

Modelling of Polishing Tools for High Spatial Frequency Defect Correction on Aspherical Surfaces

2013 ◽  
Vol 554-557 ◽  
pp. 1232-1241 ◽  
Author(s):  
Antoine Goupil ◽  
Ivan Iordanoff ◽  
Jean Luc Charles ◽  
André Rinchet
Keyword(s):  
Spatial Frequency ◽  
High Frequency ◽  
Ion Beam ◽  
Excitation Frequency ◽  
Low Frequency ◽  
High Spatial Frequency ◽  
Initial Pressure ◽  
Fused Silica ◽  
Pressure Differential ◽  
Machining Parameters

Nowadays, precision Computer Controlled Optical Surfacing (CCOS) and processes like Ion Beam Finishing (IBF) or Magneto-Rheological Finishing (MRF) allow manufacturing of fused silica optics with nanometer precision. However, High spatial frequency defects remain on the optics and need to be previously smoothed. Full aperture semi-flexible polishing tools can be used, as they can guarantee uniform pressure on low frequency patterns to preserve the pre-formed aspherical shape while maintaining a high pressure differential on high frequency defects, thus smoothing them. That behavior can be obtained with tools that combine a continuous flexible layer for low frequency compliance and a fractionate viscoelastic polishing layer for high frequency defect polishing. The main goals of this study are predicting smoothing efficiency and form control of different tools, and then determining the best tool to achieve a good balance between them. To do this, a multiscale model is developed. First, at the whole tool scale, for a given aspherical shape, the largest misfit between tools and surfaces is mathematically determined, depending on machining parameters. Then a finite-element parametric study is performed and yields for the flexible layer the best mechanical properties and thickness as well as the optimal applied force to achieve pressure homogeneity at the global aspherical shape level. Second, at the viscoelastic polishing layer level, the Discrete Element Method (DEM) is used to investigate the tool – workpiece interface. A model based on the viscoelastic cohesive beam method is developed, thus allowing taking into account the polishing layer’s dynamic response depending on the excitation frequency. The optical surface is also modeled by interpenetrated discrete elements, paving the way for a full-DEM model of the polishing layer – workpiece interface. Smoothing simulations are separated in two steps : the first one is the initial pressure application, leading to an initial state of full tool – surface contact with an homogeneous pressure. Then the tool is moved over the surface and the dynamic pressure is calculated depending on defect and polishing layer properties as well as tool kinematics. By analyzing the pressure differential on defects it becomes possible to calculate the smoothing efficiency of a given polishing layer and therefore optimize its properties depending on the defects that need to be smoothed.

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