scholarly journals Effects of Spatial Frequency Filtering Choices on the Perception of Filtered Images

Vision ◽  
2020 ◽  
Vol 4 (2) ◽  
pp. 29
Author(s):  
Sabrina Perfetto ◽  
John Wilder ◽  
Dirk B. Walther
Keyword(s):  
Spatial Frequency ◽  
Behavioral Outcomes ◽  
High Spatial Frequency ◽  
Frequency Content ◽  
Frequency Filtering ◽  
Image Content ◽  
Specific Choice ◽  
Spatial Frequencies ◽  
Spatial Frequency Filtering ◽  
Frequency Components

The early visual system is composed of spatial frequency-tuned channels that break an image into its individual frequency components. Therefore, researchers commonly filter images for spatial frequencies to arrive at conclusions about the differential importance of high versus and low spatial frequency image content. Here, we show how simple decisions about the filtering of the images, and how they are displayed on the screen, can result in drastically different behavioral outcomes. We show that jointly normalizing the contrast of the stimuli is critical in order to draw accurate conclusions about the influence of the different spatial frequencies, as images of the real world naturally have higher contrast energy at low than high spatial frequencies. Furthermore, the specific choice of filter shape can result in contradictory results about whether high or low spatial frequencies are more useful for understanding image content. Finally, we show that the manner in which the high spatial frequency content is displayed on the screen influences how recognizable an image is. Previous findings that make claims about the visual system’s use of certain spatial frequency bands should be revisited, especially if their methods sections do not make clear what filtering choices were made.

Cortical processing of second-order motion

1999 ◽  
Vol 16 (3) ◽  
pp. 527-540 ◽  
Author(s):  
ISABELLE MARESCHAL ◽  
CURTIS L. BAKER
Keyword(s):  
Spatial Frequency ◽  
High Spatial Frequency ◽  
Second Order ◽  
Spatial Properties ◽  
Processing Stream ◽  
Spatial Frequencies ◽  
Nonlinear Input ◽  
Nonlinear Processing ◽  
Frequency Components ◽  
Optimal Values

Neurons in the mammalian visual cortex have been found to respond to second-order features which are not defined by changes in luminance over the retina (Albright, 1992; Zhou & Baker, 1993, 1994, 1996; Mareschal & Baker, 1998a,b). The detection of these stimuli is most often accounted for by a separate nonlinear processing stream, acting in parallel to the linear stream in the visual system. Here we examine the two-dimensional spatial properties of these nonlinear neurons in area 18 using envelope stimuli, which consist of a high spatial-frequency carrier whose contrast is modulated by a low spatial-frequency envelope. These stimuli would fail to elicit a response in a conventional linear neuron because they are designed to contain no spatial-frequency components overlapping the neuron's luminance defined passband. We measured neurons' responses to these stimuli as a function of both the relative spatial frequencies and relative orientations of the carrier and envelope. Neurons' responses to envelope stimuli were narrowband to the carrier spatial frequency, with optimal values ranging from 8- to 30-fold higher than the envelope spatial frequencies. Neurons' responses to the envelope stimuli were strongly dependent on the orientation of the envelope and less so on the orientation of the carrier. Although the selectivity to the carrier orientation was broader, neurons' responses were clearly tuned, suggesting that the source of nonlinear input is cortical. There was no fixed relationship between the optimal carrier and envelope spatial frequencies or orientations, such that nonlinear neurons responding to these stimuli could perhaps respond to a variety of stimuli defined by changes in scale or orientation.

scholarly journals Hybrid motion illusions as examples of perceptual conflict

2021 ◽  
Vol 2 ◽  
Author(s):  
Arthur Shapiro
Keyword(s):  
Spatial Frequency ◽  
Spatial Scales ◽  
High Spatial Frequency ◽  
Natural World ◽  
Fine Scale ◽  
Frequency Content ◽  
Coarse Scale ◽  
Trade Offs ◽  
Spatial Frequencies ◽  
Contrast Information

Shapiro and Hedjar (2019) proposed a shift in the definition of illusion, from ‘differences between perception and reality’ to ‘conflicts between possible constructions of reality’. This paper builds on this idea by presenting a series of motion hybrid images that juxtapose fine scale contrast (high spatial frequency content) with coarse scale contrast-generated motion (low spatial frequency content). As is the case for static hybrid images, under normal viewing conditions the fine scale contrast determines the perception of motion hybrid images; however, if the motion hybrid image is blurred or viewed from a distance, the perception is determined by the coarse scale contrast. The fine scale contrast therefore masks the perception of motion (and sometimes depth) produced by the coarser scale contrast. Since the unblurred movies contain both fine and coarse scale contrast information, but the blurred movies contain only coarse scale contrast information, cells in the brain that respond to low spatial frequencies should respond equally to both blurred and unblurred movies. Since people undoubtedly differ in the optics of their eyes and most likely in the neural processes that resolve conflict across scales, the paper suggests that motion hybrid images illustrate trade-offs between spatial scales that are important for understanding individual differences in perceptions of the natural world.

scholarly journals Accessing depth-resolved high spatial frequency content from the optical coherence tomography signal

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Sergey Alexandrov ◽  
Anand Arangath ◽  
Yi Zhou ◽  
Mary Murphy ◽  
Niamh Duffy ◽  
...  
Keyword(s):  
Optical Coherence Tomography ◽  
Spatial Frequency ◽  
Structural Changes ◽  
High Spatial Frequency ◽  
Optical Coherence ◽  
Frequency Content ◽  
Structural Alterations ◽  
Spatial Frequencies ◽  
Internal Structures ◽  
Optical Coherence Tomography Signal

AbstractOptical coherence tomography (OCT) is a rapidly evolving technology with a broad range of applications, including biomedical imaging and diagnosis. Conventional intensity-based OCT provides depth-resolved imaging with a typical resolution and sensitivity to structural alterations of about 5–10 microns. It would be desirable for functional biological imaging to detect smaller features in tissues due to the nature of pathological processes. In this article, we perform the analysis of the spatial frequency content of the OCT signal based on scattering theory. We demonstrate that the OCT signal, even at limited spectral bandwidth, contains information about high spatial frequencies present in the object which relates to the small, sub-wavelength size structures. Experimental single frame imaging of phantoms with well-known sub-micron internal structures confirms the theory. Examples of visualization of the nanoscale structural changes within mesenchymal stem cells (MSC), which are invisible using conventional OCT, are also shown. Presented results provide a theoretical and experimental basis for the extraction of high spatial frequency information to substantially improve the sensitivity of OCT to structural alterations at clinically relevant depths.

Depth Interpolation with Sparse Disparity Cues

Perception ◽  
1989 ◽  
Vol 18 (1) ◽  
pp. 39-54 ◽  
Author(s):  
Sofia M Würger ◽  
Michael S Landy
Keyword(s):  
Spatial Frequency ◽  
Narrow Band ◽  
High Spatial Frequency ◽  
Linear Interpolation ◽  
Uniform Field ◽  
Frequency Content ◽  
Apparent Contrast ◽  
Spatial Frequencies ◽  
Basic Stimulus ◽  
Filtered Noise

The interpolation of stereoscopic depth given only sparse disparity information was investigated. The basic stimulus was a rectangle with zero disparity at one edge, and 20 or 30 min visual angle disparity at the other. The depth assigned to the ambiguous intervening locations was measured by means of a small briefly-flashed binocular comparison spot. For a stimulus consisting of a uniform rectangle presented on a background of random dots with zero disparity, interpolated depth was greater for a high mean contrast between rectangle and background than for a low mean contrast. Relative to a linear interpolation between the edges, a larger difference in edge disparity resulted in poorer depth interpolation. Depth interpolation based on rivalrous information was examined by filling the stimulus rectangle with narrow-band filtered noise which was uncorrelated between the two eyes. Four different passbands which were matched in apparent contrast were investigated. The results demonstrate that the rivalrous low-spatial-frequency content was resistant to interpolation; rivalrous high spatial frequencies did not interfere with depth interpolation. High-spatial-frequency stimuli yielded a percept similar to the uniform-field condition, whereas low-spatial-frequency stimuli lay in a depth plane near or even behind the background. In the latter case a transparent plane was perceived which was linearly interpolated between the two edges, and which floated above the rivalrous noise.

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.

On the Variety of Percepts Associated with Dichoptic Viewing of Dissimilar Monocular Stimuli

Perception ◽  
1992 ◽  
Vol 21 (1) ◽  
pp. 47-62 ◽  
Author(s):  
Yuede Yang ◽  
David Rose ◽  
Randolph Blake
Keyword(s):  
Spatial Frequency ◽  
High Spatial Frequency ◽  
Frequency Difference ◽  
The Other ◽  
Frequency Content ◽  
High Transparency ◽  
Frequency Information ◽  
Dichoptic Viewing ◽  
Spatial Frequencies ◽  
Over Time

Upon dichoptic viewing of dissimilar patterns, several distinct perceptual states may be experienced over time. One state is exclusive monocular dominance, wherein the view of only one eye is seen in its entirety for some period of time. Another state is characterized by a mosaic-like collage consisting of portions of the view of each eye. Two other states involve simultaneous perception of both monocular images in their entirety. In one of these states, the two monocular stimuli appear to be superimposed without depth (a phenomenon we shall term ‘superimposition’). In the other state, the two monocular stimuli appear to be located at different depth planes (which we shall term ‘transparency’). This paper documents the stimulus conditions favoring these various perceptual states. Exclusive monocular dominance occurs most often when the two eyes view dissimilar patterns with the same spatial-frequency content, particularly when both patterns consist of low spatial frequencies. Superimposition also occurs most often when the two eyes view the same spatial frequencies, but predominantly when those spatial frequencies are high. Transparency is favored when the spatial-frequency difference between the eyes is great, particularly when the view of one eye consists of high spatial-frequency information.

scholarly journals Contrast thresholds reveal different visual masking functions in humans and praying mantises

2017 ◽  
Author(s):  
Ghaith Tarawneh ◽  
Vivek Nityananda ◽  
Ronny Rosner ◽  
Steven Errington ◽  
William Herbert ◽  
...  
Keyword(s):  
Spatial Frequency ◽  
Motion Detection ◽  
Visual Masking ◽  
High Spatial Frequency ◽  
Visual Noise ◽  
Frequency Noise ◽  
Detection Systems ◽  
Spatial Frequencies ◽  
Summary Statement ◽  
Contrast Thresholds

AbstractRecently, we showed a novel property of the Hassenstein-Reichardt detector: namely, that insect motion detection can be masked by “invisible” noise, i.e. visual noise presented at spatial frequencies to which the animals do not respond when presented as a signal. While this study compared the effect of noise on human and insect motion perception, it used different ways of quantifying masking in two species. This was because the human studies measured contrast thresholds, which were too time-consuming to acquire in the insect given the large number of stimulus parameters examined. Here, we run longer experiments in which we obtained contrast thresholds at just two signal and two noise frequencies. We examine the increase in threshold produced by noise at either the same frequency as the signal, or a different frequency. We do this in both humans and praying mantises (Sphodromantis lineola), enabling us to compare these species directly in the same paradigm. Our results confirm our earlier finding: whereas in humans, visual noise masks much more effectively when presented at the signal spatial frequency, in insects, noise is roughly equivalently effective whether presented at the same frequency or a lower frequency. In both species, visual noise presented at a higher spatial frequency is a less effective mask.Summary StatementWe here show that despite having similar motion detection systems, insects and humans differ in the effect of low and high spatial frequency noise on their contrast thresholds.

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