Suprathreshold Contrast Increment Detection is not Affected by Grating Edge-Type

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 271-271
Author(s):  
D R Melmoth ◽  
H T Kukkonen
Keyword(s):  
Fourier Spectrum ◽  
Sinusoidal Grating ◽  
Circular Aperture ◽  
Edge Type ◽  
Spatial Frequencies ◽  
Significant Difference ◽  
Affect Detection ◽  
Sinusoidal Gratings ◽  
Frequency Components ◽  
Subject Performance

We have shown that the spatial frequency components introduced by sharply truncating the edge of a sinusoidal grating do not affect detection thresholds (Kukkonen et al, 1996 Perception25 Supplement, 117). This could be due to the fact that contrast energy at these spatial frequencies is much lower than at the nominal frequency. Any effect upon detection attributable to the broadening of the Fourier spectrum might therefore exert itself most strongly at suprathreshold rather than threshold contrast levels. To establish whether these extra components interfere with performance at higher contrasts, we measured contrast increment thresholds of circular-aperture sinusoidal gratings with a pedestal contrast of 0.5. Gratings were either sharply truncated or Gaussian-edged having a half-contrast diameter equal to that of its corresponding sharp-edged stimulus. Gratings of 0.125 and 0.5 cycle deg−1 were used, each tested with 1 – 8 cycles. There was no significant difference between contrast increment thresholds for the sharp-edged and Gaussian-edged gratings, which were spectrally narrower. The frequency components introduced into the Fourier spectrum by the abrupt edge of the truncated gratings appear to have no effect upon subject performance even in suprathreshold contrast increment detection.

Spatiospectral properties of goldfish retinal ganglion cells

1989 ◽  
Vol 62 (5) ◽  
pp. 1140-1148 ◽  
Author(s):  
J. Bilotta ◽  
I. Abramov
Keyword(s):  
Receptive Field ◽  
Spatial Frequency ◽  
Ganglion Cells ◽  
Spatial Summation ◽  
Relative Sensitivity ◽  
Sinusoidal Grating ◽  
Retinal Ganglion ◽  
Spatial Frequencies ◽  
Sinusoidal Gratings ◽  
Center Cell

1. Responses of single ganglion cells from isolated goldfish retinas were recorded during presentation of various spatial and spectral stimuli. Each cell was classified along several spatial [spatial summation class, spatial contrast sensitivity function (CSF), and response to contrast] and spectral (Red-ON, Red-OFF or Red-ON/OFF, and spectral opponency/nonopponency) dimensions. 2. Linearity of spatial summation was determined from responses to contrast-reversal sinusoidal gratings positioned at various locations across the receptive field of the cell. CSFs were derived from responses to sinusoidal gratings of various spatial frequencies and contrasts, drifting across the cell's receptive field at a rate of 4 Hz. Response to contrast was determined from responses to variations in contrast of a sinusoidal grating of optimal spatial frequency. Spectral classifications were based on responses to monochromatic stimuli presented separately to the center and surround portions of the receptive field. 3. Linearity of spatial summation (X-, Y-, and W-like) was independent of the cell's spectral properties; for example, an X-like cell could be classified as either a Red-ON, Red-OFF, or Red-ON/OFF center cell and as spectrally opponent or nonopponent. 4. There were differences in response to contrast across spectral categories. Red-OFF center cells were very sensitive to contrast compared with Red-ON center cells. Spectrally nonopponent cells were more responsive to contrast than spectrally opponent cells. 5. There were dramatic differences across the spectral categories in relative sensitivity to low spatial frequency stimuli; however, the spatial resolution (i.e., sensitivity to high spatial frequencies) of each spectral classification appeared to be similar.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Aspheric Intraocular Lenses Implantation for Cataract Patients with Extreme Myopia

2014 ◽  
Vol 2014 ◽  
pp. 1-6 ◽  
Author(s):  
Yanwen Fang ◽  
Yi Lu ◽  
Aizhu Miao ◽  
Yi Luo
Keyword(s):  
Contrast Sensitivity ◽  
Visual Quality ◽  
Intraocular Lenses ◽  
Wavefront Aberrations ◽  
Spatial Frequencies ◽  
Aspheric Iol ◽  
Significant Difference ◽  
Composite Scores ◽  
Cataract Patients

Objective. To evaluate the postoperative visual quality of cataract patients with extreme myopia after implantation of aspheric intraocular lenses (IOLs). Methods. Thirty-three eyes were enrolled in this prospectivestudy. Eighteen eyes with an axial length longer than 28 mm were included in the extreme myopia group, and the other 15 eyes were included in the nonextreme myopia group. Phacoemulsification and aspheric IOL implantation were performed. Six months after cataract surgery, best-corrected visual acuity (BCVA), contrast sensitivity, and wavefront aberrations were measured, and subjective visual quality was assessed. Results. The BCVA improved significantly after surgery for both groups, and patients in the nonextreme myopia group achieved better postoperative BCVA due to better retinal status of the eyes. The evaluation of contrast sensitivity without glare was the same in both groups, whereas patients in the nonextreme myopia group performed better at intermediate spatial frequencies under glare conditions. The two groups did not show a significant difference in high-order aberrations. With regard to subjective visual quality, the composite scores of both groups did not differ significantly. Conclusions. Aspheric IOLs provided good visual outcomes in cataract patients with extreme myopia. These patients should undergo careful evaluation to determine the maculopathy severity level before surgery.

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 Contrast Sensitivity Functions Obtained with Colored and Achromatic Gratings

1979 ◽  
Vol 21 (2) ◽  
pp. 225-228 ◽  
Author(s):  
Michael A. Nelson ◽  
Ronald L. Halberg
Keyword(s):  
Contrast Sensitivity ◽  
Spatial Information ◽  
Sensitivity Functions ◽  
Visual Contrast ◽  
Spatial Frequencies ◽  
Sinusoidal Gratings ◽  
Visual Contrast Sensitivity ◽  
Contrast Thresholds

Threshold contrasts for red, green, and achromatic sinusoidal gratings were measured. Spatial frequencies ranged from 0.25 to 15 cycles/deg. No significant differences in contrast thresholds were found among the three grating types. From this finding it was concluded that, under conditions of normal viewing, no significant differences should be expected in the acquisition of spatial information from monochromatic or achromatic displays of equal resolution.

Acuity-sensitivity trade-offs of X and Y cells in the cat lateral geniculate complex: role of the medial interlaminar nucleus in scotopic vision

1992 ◽  
Vol 68 (4) ◽  
pp. 1235-1247 ◽  
Author(s):  
D. Lee ◽  
C. Lee ◽  
J. G. Malpeli
Keyword(s):  
Contrast Sensitivity ◽  
Adaptation Level ◽  
Special Role ◽  
A Cells ◽  
Lateral Geniculate ◽  
Spatial Frequencies ◽  
Wide Range ◽  
Sinusoidal Gratings ◽  
X Cells ◽  
Y Cells

1. The cat medial interlaminar nucleus (MIN) receives inputs almost exclusively from tapetal retina, suggesting that the MIN has a special role in dim-light vision. In this study we compared the sensitivities of cells in the MIN with those in layers A and magnocellular C of the lateral geniculate nucleus (LGNd), using drifting sinusoidal gratings to determine contrast thresholds as a function of spatial frequency and retinal adaptation level over the entire scotopic range. 2. About one-half of the cells recorded in the MIN and layer A had brisk responses that could be nulled by properly positioned, counterphased sinusoidal gratings, and were classified as X cells. The rest of the cells in the MIN and layer A, as well as all cells recorded in layer C, were Y cells. 3. MIN cells had higher contrast sensitivity than layer A cells for low spatial frequencies (0.15 cycles/deg and below) over a wide range of adaptation levels, both overall and for separate comparisons within X or Y cells. Layer C Y cells were intermediate in sensitivity between MIN and layer A Y cells. For low spatial frequencies, Y cells as a group were more sensitive than X cells, whereas the reverse was true for high spatial frequencies. 4. These data enable one to determine the lowest adaptation level at which stimuli of a given contrast can be detected for a given structure. At the lowest spatial frequencies, the MIN can function at adaptation levels approximately 1 log unit below layer A, averaged over all stimulus contrasts. In contrast, the tapetum lowers luminance threshold by at most 0.16 log unit. 5. For scotopic conditions and eccentricities within 15 degrees of the area centralis, contrast sensitivity decreases with eccentricity for low spatial frequencies and remains flat or slightly increases for high spatial frequencies. This relationship, which is opposite to that found for photopic vision, is strongest for MIN Y cells. 6. These data support the hypothesis that the retinal conflict between sensitivity and acuity is ameliorated in the CNS through separate thalamic relays with different degrees of afferent convergence. MIN cells have higher luminance sensitivity than layer A cells, but at the expense of acuity. Layer C appears to occupy an intermediate position in this trade-off.

The Conditions under which Opposing Motion is Seen in Transparency or as Flicker

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 31-31 ◽  
Author(s):  
M M Del Viva ◽  
M C Morrone
Keyword(s):  
Feature Tracking ◽  
Relative Phase ◽  
Phase Relationship ◽  
The Other ◽  
Spatial Frequencies ◽  
Sinusoidal Gratings ◽  
Exact Degree ◽  
Harmonic Components ◽  
Over Time ◽  
Moving Pattern

We present several examples of moving stimuli comprising several harmonic components that can be perceived either as moving independently, or together as a coherent moving pattern. A simple example is two sinusoidal gratings of equal contrast and spatial frequencies moving in opposite directions that are perceived as a single grating modulated sinusoidally over time (counterphase). However, two square waves drifting in opposite directions, while being a superposition of counterphasing pairs, are perceived as two distinct patterns drifting in transparency one over the other. Intermediate situations such as pairs of counterphase gratings can be perceived alternatively as counterphases or as drifting in two directions. We show that the relative phase of the components plays a fundamental role in whether they group or become transparent. The tendency of a component to become part of a pattern is maximal when the phase relationship is 0 deg, and gradually decreases to a minimum at 90 deg. This agrees quantitatively with previous measurements on different stimuli (paper presented at Del Viva and Morrone, ARVO96), suggesting a common computational mechanism. The data were well modelled by a nonlinear model of motion analysis based on feature tracking, showing sensitivity to the exact degree of nonlinearity.

Size Discrimination with Low Spatial Frequencies

Perception ◽  
1982 ◽  
Vol 11 (6) ◽  
pp. 707-720 ◽  
Author(s):  
Robert A Smith
Keyword(s):  
Fourier Spectrum ◽  
Low Frequency ◽  
Current Theory ◽  
Size Perception ◽  
Size Discrimination ◽  
Low Frequencies ◽  
Spatial Frequencies ◽  
Vertical Bars ◽  
The Fourier Transform ◽  
Visual Size

The hypothesis that visual size is determined from the low-frequency Fourier spectrum of the image has been tested in a variety of ways. The fact that size discrimination of vertical bars is unimpaired when high spatial frequencies are filtered out of the image by blurring, and the fact that spatial-frequency adaptation alters perceived size, argue in favor of such hypothesis. However, the hypothesis is weakened by the observation that discrimination is also unimpaired by filtering low frequencies out of the image and by the observation that some manipulations which alter the Fourier transform produce no corresponding perceptual change. No current theory of size perception appears to fit all of these data.

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.

How Reliable is the Pattern Adaptation Technique? A Modeling Study

2009 ◽  
Vol 102 (4) ◽  
pp. 2245-2252 ◽  
Author(s):  
Jay Hegdé
Keyword(s):  
Spatial Frequency ◽  
Frequency Tuning ◽  
Spatial Vision ◽  
Neural Mechanisms ◽  
System Level ◽  
Sinusoidal Grating ◽  
Tuning Parameters ◽  
Neuronal Ensemble ◽  
Spatial Frequency Tuning ◽  
Spatial Frequencies

Upon prolonged viewing of a sinusoidal grating, the visual system is selectively desensitized to the spatial frequency of the grating, while the sensitivity to other spatial frequencies remains largely unaffected. This technique, known as pattern adaptation, has been so central to the psychophysical study of the mechanisms of spatial vision that it is sometimes referred to as the “psychologist's microelectrode.” While this approach implicitly assumes that the adaptation behavior of the system is diagnostic of the corresponding underlying neural mechanisms, this assumption has never been explicitly tested. We tested this assumption using adaptation bandwidth, or the range of spatial frequencies affected by adaptation, as a representative measure of adaptation. We constructed an intentionally simple neuronal ensemble model of spatial frequency processing and examined the extent to which the adaptation bandwidth at the system level reflected the bandwidth at the neuronal level. We find that the adaptation bandwidth could vary widely even when all spatial frequency tuning parameters were held constant. Conversely, different spatial frequency tuning parameters were able to elicit similar adaptation bandwidths from the neuronal ensemble. Thus, the tuning properties of the underlying units did not reliably reflect the adaptation bandwidth at the system level, and vice versa. Furthermore, depending on the noisiness of adaptation at the neural level, the same neuronal ensemble was able to produce selective or nonselective adaptation at the system level, indicating that a lack of selective adaptation at the system level cannot be taken to mean a lack of tuned mechanisms at the neural level. Together, our results indicate that pattern adaptation cannot be used to reliably estimate the tuning properties of the underlying units, and imply, more generally, that pattern adaptation is not a reliable tool for studying the neural mechanisms of pattern analysis.

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.

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