Spatial Filter Combination in Human Pattern Vision: Channel Interactions Revealed by Adaptation

Perception ◽  
1996 ◽  
Vol 25 (3) ◽  
pp. 255-277 ◽  
Author(s):  
Tim S Meese ◽  
Mark A Georgeson
Keyword(s):  
Spatial Frequency ◽  
Spatial Filter ◽  
Selective Adaptation ◽  
Compound Structure ◽  
Spatial Filters ◽  
Linear Filters ◽  
Combination Process ◽  
Sinusoidal Gratings ◽  
Channel Interactions ◽  
Conventional Models

Above threshold, two superimposed sinusoidal gratings of the same spatial frequency (eg 1 cycle deg−1), of equal moderate contrast (eg C1 = C2 = 6%), and with orientations of ±45°, usually look like a compound structure containing vertical and horizontal edges (ie a blurred checkerboard). These feature orientations are very different from the dominant filter orientations in a wavelet-type (eg simple-cell) transform of the stimulus, and so present a serious challenge to conventional models of orientation coding based on labelled linear filters. Previous experiments on perceived structure in static plaids have led to the view that the outputs of tuned spatial filters are combined in a stimulus-dependent way, before features such as edges are extracted. Here an adaptation paradigm was used to investigate the cross-channel interactions that appear to underlie the spatial-filter-combination process. Reported are two aftereffects of selective adaptation: (i) adaptation to a 1 cycle deg−1 plaid whose component orientations are intermediate to those in a 1 cycle deg−1 test plaid ‘breaks’ perceptual combination of the components in the test plaid; (ii) adapting to a 3 cycles deg−1 plaid whose component orientations match those in a 1 cycle deg−1 test plaid facilitates perceptual combination of the components in the test plaid. The results are taken as evidence that spatial channels remote from those most responsive to a test plaid play a crucial role in determining whether the test plaid segments or coheres perceptually.

Adaptation in single units in visual cortex: The tuning of aftereffects in the spatial domain

1989 ◽  
Vol 2 (6) ◽  
pp. 593-607 ◽  
Author(s):  
A. B. Saul ◽  
M. S. Cynader
Keyword(s):  
Spatial Frequency ◽  
Cortical Neurons ◽  
Frequency Tuning ◽  
Cortical Cell ◽  
Selective Adaptation ◽  
Single Units ◽  
Spatial Frequency Tuning ◽  
Sinusoidal Gratings ◽  
A Cell ◽  
Drift Direction

AbstractCat striate cortical neurons were investigated using a new method of studying adaptation aftereffects. Stimuli were sinusoidal gratings of variable contrast, spatial frequency, and drift direction and rate. A series of alternating adapting and test trials was presented while recording from single units. Control trials were completely integrated with the adapted trials in these experiments.Every cortical cell tested showed selective adaptation aftereffects. Adapting at suprathreshold contrasts invariably reduced contrast sensitivity. Significant aftereffects could be observed even when adapting at low contrasts.The spatial-frequency tuning of aftereffects varied from cell to cell. Adapting at a given spatial frequency generally resulted in a broad response reduction at test frequencies above and below the adapting frequency. Many cells lost responses predominantly at frequencies lower than the adapting frequency.The tuning of aftereffects varied with the adapting frequency. In particular, the strongest aftereffects occurred near the adapting frequency. Adapting at frequencies just above the optimum for a cell often altered the spatial-frequency tuning by shifting the peak toward lower frequencies. The fact that the tuning of aftereffects did not simply match the tuning of the cell, but depended on the adapting stimulus, implies that extrinsic mechanisms are involved in adaptation effects.

Spatial-frequency and orientation tuning in psychophysical end-stopping

1998 ◽  
Vol 15 (4) ◽  
pp. 585-595 ◽  
Author(s):  
CONG YU ◽  
DENNIS M. LEVI
Keyword(s):  
Spatial Frequency ◽  
Frequency Tuning ◽  
Spatial Filter ◽  
Orientation Tuning ◽  
Maximal Strength ◽  
Facilitation Effect ◽  
Spatial Filters ◽  
Spatial Frequency Tuning ◽  
Spatial Frequencies ◽  
Wide Range

A psychophysical analog to cortical receptive-field end-stopping has been demonstrated previously in spatial filters tuned to a wide range of spatial frequencies (Yu & Levi, 1997a). The current study investigated tuning characteristics in psychophysical spatial filter end-stopping. When a D6 (the sixth derivative of a Gaussian) target is masked by a center mask (placed in the putative spatial filter center), two end-zone masks (placed in the filter end-zones) reduce thresholds. This “end-stopping” effect (the reduction of masking induced by end-zone masks) was measured at various spatial frequencies and orientations of end-zone masks. End-stopping reached its maximal strength when the spatial frequency and/or orientation of the end-zone masks matched the spatial frequency and/or orientation of the target and center mask, showing spatial-frequency tuning and orientation tuning. The bandwidths of spatial-frequency and orientation tuning functions decreased with increasing target spatial frequency. At larger orientation differences, however, end-zone masks induced a secondary facilitation effect, which was maximal when the spatial frequency of end-zone masks equated the target spatial frequency. This facilitation effect might be related to certain types of contour and texture perception, such as perceptual pop-out.

Edge Computation in Human Vision: Anisotropy in the Combining of Oriented Filters

Perception ◽  
1995 ◽  
Vol 24 (6) ◽  
pp. 603-622 ◽  
Author(s):  
Tim S Meese ◽  
Tom C A Freeman
Keyword(s):  
Spatial Structure ◽  
Spatial Frequency ◽  
Human Vision ◽  
Contrast Effects ◽  
Compound Structure ◽  
Component Structure ◽  
Zero Crossings ◽  
Coding Scheme ◽  
Two Component ◽  
Sinusoidal Gratings

Above threshold, two superimposed sinusoidal gratings of the same spatial frequency (eg 1 cycle deg−1) and equal contrasts, and with orientations balanced around vertical, usually look like a compound structure containing vertical and horizontal edges. However, at large plaid angles (ie large differences between component orientations) and low plaid contrasts there is a tendency for the stimulus to appear as two overlapping gratings (component structure) with obliquely oriented edges. These dependencies of perceived spatial structure in plaids are incompatible with an edge-coding scheme that uses only circular filters to compute zero-crossings, but instead support the idea that different oriented filters can (compound percept) or cannot (component percept) be combined before edges are represented. Here, further evidence is presented in support of this hypothesis. Two-component plaid stimuli had plaid angles of 45° or 90°, and a range of plaid orientations (ie a range of orientations around which the plaid components were balanced). Observers indicated whether each stimulus was perceived as a compound or component structure for a range of plaid contrasts. In addition to angle and contrast effects, perceived spatial structure was also found to depend on plaid orientation: compound structures were perceived more often when the plaid components were balanced around the cardinal axes of the retina. It is suggested that the principles governing the combination of oriented-filter outputs might be learnt during the development of the visual system by using a Hebb-type rule: coactivated filters are more likely to combine their outputs when activated on future occasions. Given the prominence of vertical and horizontal orientations in a carpentered environment, this simple rule promotes a network that combines filters balanced around cardinal axes more readily than oblique axes, in agreement with the results.

Discrimination between Plaids: Do Oriented Filters Combine Dichoptically?

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 299-299
Author(s):  
L A Olzak ◽  
R L Wong
Keyword(s):  
Spatial Frequency ◽  
Opposite Sign ◽  
Pattern Discrimination ◽  
The Other ◽  
Frequency Content ◽  
Low Contrast ◽  
Combination Process ◽  
Test Conditions ◽  
Sinusoidal Gratings ◽  
Confidence Scale

Two oblique gratings combine perceptually to form a chequerboard appearance under monoptic presentation but not under dichoptic presentation (Georgeson and Meese, 1996 Perception25 Supplement, 121), suggesting an early combination process. Combining processes that operate over orthogonal orientations are also observed in complex pattern discrimination tasks (Olzak and Thomas, 1991 Vision Research31 1885 – 1898). We ask here whether the interactions observed in discrimination tasks occur before or beyond the site of binocular interaction. Observers discriminated between two patterns that differed slightly in their spatial-frequency content. On each trial, one of the two patterns was presented. Observers judged which stimulus had been presented on a 1 – 6 confidence scale. In control conditions, the stimuli were single sinusoidal gratings near 3 cycles deg−1, and were always presented monoptically. In test conditions, a second component was added to the first in each stimulus. The second component was either presented to the same eye as the first component (monoptic presentation), or to the other eye (dichoptic presentation). The second component was either a mask of exactly 3 cycles deg−1, or varied to give a second cue to discrimination. Second cues either varied with the first (both components lower frequency or both higher) or varied in opposite sign (high with low). Rivalry was eliminated by using low contrast (10 × threshold) and small (1.2 deg) patterns. Our results suggest that the combination processes we observe occur beyond the site of binocular combination and differ from those mediating the percept.

Comparison of Deterministic and Linear Cosine Spatial Filtering of Transmission Electron Micrographs

1972 ◽  
Vol 30 ◽  
pp. 596-597
Author(s):  
David A. Ansley
Keyword(s):  
Spherical Aberration ◽  
Focal Length ◽  
Chromatic Aberration ◽  
Spatial Filter ◽  
Operating Conditions ◽  
Objective Lens ◽  
List Type ◽  
Spatial Filters ◽  
Transmission Electron ◽  
Wide Range

The coherence of the electron flux of a transmission electron microscope (TEM) limits the direct application of deconvolution techniques which have been used successfully on unmanned spacecraft programs. The theory assumes noncoherent illumination. Deconvolution of a TEM micrograph will, therefore, in general produce spurious detail rather than improved resolution.A primary goal of our research is to study the performance of several types of linear spatial filters as a function of specimen contrast, phase, and coherence. We have, therefore, developed a one-dimensional analysis and plotting program to simulate a wide 'range of operating conditions of the TEM, including adjustment of the:(1) Specimen amplitude, phase, and separation(2) Illumination wavelength, half-angle, and tilt(3) Objective lens focal length and aperture width(4) Spherical aberration, defocus, and chromatic aberration focus shift(5) Detector gamma, additive, and multiplicative noise constants(6) Type of spatial filter: linear cosine, linear sine, or deterministic

Temporal-Discontinuity Detection with Contrast-Modulated Gratings

Perception ◽  
1995 ◽  
Vol 24 (11) ◽  
pp. 1257-1264
Author(s):  
Shigeru Ichihara ◽  
Kenji Susami
Keyword(s):  
Spatial Frequency ◽  
Modulation Frequency ◽  
Sinusoidal Grating ◽  
Local Contrast ◽  
Staircase Method ◽  
Low Contrast ◽  
Discontinuity Detection ◽  
Temporal Discontinuity ◽  
Sinusoidal Gratings ◽  
The Subject

Three experiments on temporal-discontinuity detection were carried out. In experiment 1, temporal-discontinuity thresholds were measured for sinusoidal gratings by the use of the double-staircase method. A sinusoidal grating was presented twice successively. The subject judged whether or not an interval was present. The temporal-discontinuity threshold increased as the spatial frequency of the grating increased, but decreased as the contrast of the grating increased. In experiment 2, contrast-modulated gratings were used instead of the sinusoidal grating. The temporal-discontinuity threshold increased as the carrier frequency increased, and the threshold for each contrast-modulated grating was similar to that for the no-modulation (sinusoidal) grating whose contrast was the same as the maximum local contrast of the contrast-modulated grating. In experiment 3, temporal-discontinuity thresholds were measured for low-contrast (3%) sinusoidal gratings. The thresholds were very low, even for such low-contrast gratings. These results suggest that the low-spatial-frequency channels are not involved in detecting the modulation frequency of the contrast-modulated grating. Rather, the local contrast seems to be the determinant of the detection of the contrast-modulated grating itself.

Visual Stimuli for Strabismic Suppression

Perception ◽  
1977 ◽  
Vol 6 (5) ◽  
pp. 583-593 ◽  
Author(s):  
Clifton M Schor
Keyword(s):  
Spatial Frequency ◽  
Binocular Vision ◽  
Binocular Rivalry ◽  
Visual Stimuli ◽  
Normal Group ◽  
Sensory Fusion ◽  
Sinusoidal Gratings

The effects of orientation and spatial frequency of grating stimuli upon suppression were examined with a binocular rivalry paradigm in a group of ten strabismic patients and in a control normal group. Duration, frequency, and period of rivalry were examined as functions of differences in orientation and spatial frequency of dichoptic achromatic sinusoidal gratings. Records were made of responses by the sighting and by the nonsighting eye as well as responses during periods of combined binocular vision. Strabismic subjects reported normal binocular rivalry when presented with gratings of dissimilar orientation. Suppression of the deviating eye in strabismic subjects occurred with stimuli of similar orientation and was unaffected by spatial-frequency differences between dichoptic stimuli. Suppression was most intense under conditions that normally stimulate stereopsis and sensory fusion.

Noise Effects in Perceptual Models

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 44-44
Author(s):  
T D Wickens ◽  
L A Olzak
Keyword(s):  
Visual Perception ◽  
Spatial Frequency ◽  
Signal Detection ◽  
Intrinsic Variability ◽  
Noise Sources ◽  
Third Order ◽  
Noise Effects ◽  
Combination Process ◽  
Delta Sigma ◽  
Visual Phenomena

In studies of visual perception performance is often measured by statistics that are ratios of a perceptual magnitude to its intrinsic variability, most commonly the signal-detection measure d'=delta sigma. Many models for visual phenomena treat the variability sigma as a constant and describe performance exclusively by delta. However, in models for the combination of stimulus attributes, the combination process affects both terms, and an observed d' reflects both delta and sigma. For example, we have shown that masking and configural effects with sinusoidal plaids can be at least partially interpreted as noise effects. We have developed methods to analyse these effects. Through a series of concurrent-response experiments using grating stimuli, some reported at earlier ECVP meetings, we have measured the form and magnitude of the noise sources. Our analysis allows us to model the way that primitive Fourier components (spatial frequency by orientation) are integrated to form second-order or third-order combinations (eg spatial frequency pooled over orientation).

The Effect of Spatial Frequency and Contrast on Visual Persistence

Perception ◽  
1979 ◽  
Vol 8 (5) ◽  
pp. 529-539 ◽  
Author(s):  
Alison Bowling ◽  
William Lovegrove ◽  
Barry Mapperson
Keyword(s):  
Spatial Frequency ◽  
Visual Persistence ◽  
Published Data ◽  
High Contrast ◽  
Low Contrast ◽  
Spatial Frequencies ◽  
Sinusoidal Gratings

The visual persistence of sinusoidal gratings of varying spatial frequency and contrast was measured. It was found that the persistence of low-contrast gratings was longer than that of high-contrast stimuli for all spatial frequencies investigated. At higher contrast levels of 1 and 4 cycles deg−1 gratings, a tendency for persistence to be independent of contrast was observed. For 12 cycles deg−1 gratings, however, persistence continued to decrease with increasing contrast. These results are compared with recently published data on other temporal responses, and are discussed in terms of the different properties of sustained and transient channels.

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