The Effects of Temporal Modulation on the Orientation Channels of the Human Visual System

Perception ◽  
1973 ◽  
Vol 2 (1) ◽  
pp. 23-29 ◽  
Author(s):  
C R Sharpe ◽  
D J Tolhurst
Keyword(s):  
Visual System ◽  
Human Visual System ◽  
Adaptation Effect ◽  
Half Width ◽  
Temporal Modulation ◽  
Spatial Adaptation ◽  
Temporal Properties ◽  
Spatial Frequencies ◽  
Sinusoidal Gratings ◽  
Orientation Specificity

The orientation specificity of spatial adaptation was quantified by using an equivalent-contrast transformation. The half-width at half-amplitude of the adaptation effect was 6·5° when the sinusoidal gratings were stationary, but was increased to 11° when the gratings drifted laterally. Another type of temporal modulation, flashing the gratings on and off repetitively, also increased the half-width, but only at low spatial frequencies where these stimuli actually appeared to be flickering back and forth at threshold. At higher spatial frequencies the flashing stimuli appeared to be stationary at threshold and the half-width was as small as that for truly stationary gratings. It is suggested that there are two types of channel in the visual system: they differ in their orientation specificities, in their temporal properties, and in their roles in the analysis of a spatiotemporal stimulus.

Contrast Constancy Revisited: The Perceived Contrast of Sinusoidal Gratings above Threshold

2015 ◽  
Vol 68 (2) ◽  
pp. 363-380 ◽  
Author(s):  
Wayne S. Smith
Keyword(s):  
Visual System ◽  
Contrast Sensitivity ◽  
Local Adaptation ◽  
Significant Role ◽  
Stimulus Duration ◽  
Human Visual System ◽  
Sensitivity Function ◽  
Contrast Sensitivity Function ◽  
Spatial Frequencies ◽  
Sinusoidal Gratings

The contrast sensitivity function of the human visual system, measured with sinusoidal luminance gratings, has an inverted U shape with a peak around 2–4 c/deg. Above threshold, it is thought that luminance gratings of equal physical contrasts but of distinguishably different spatial frequencies are all perceived as having similar contrasts, a phenomenon that has been termed contrast constancy. However, when suprathreshold contrast matches were measured for pairs of luminance gratings whose spatial frequencies were indistinguishable, the matching curves were not flat and followed a similar inverted U shape form as the contrast sensitivity function at threshold. It was therefore suggested that contrast constancy may only be revealed when matching the contrasts of clearly distinguishable spatial frequencies. Here, observers matched the perceived contrasts of suprathreshold luminance gratings of similar but visibly different spatial frequencies between 0.25 and 16 c/deg. The results show that, much like the contrast sensitivity function at threshold, observers are more sensitive to intermediate spatial frequencies (1–6 c/deg) than they are to either higher or to lower spatial frequencies. This tuning is evident when matching reference contrasts of 30–80%, implying a significant role in everyday vision. To demonstrate that these results were not due to local adaptation, the experiment was repeated with shorter stimulus duration, producing the same results. The extent of departure from contrast constancy found in the present study is compared to previously reported suprathreshold measurements. The results are also discussed with consideration to limitations with display apparatus such as monitor blur.

Orientation Specificity and Spatial Selectivity in Human Vision

Perception ◽  
1973 ◽  
Vol 2 (1) ◽  
pp. 53-60 ◽  
Author(s):  
J A Movshon ◽  
C Blakemore
Keyword(s):  
Spatial Frequency ◽  
Human Visual System ◽  
Human Vision ◽  
Orientation Tuning ◽  
High Contrast ◽  
Vertical Grating ◽  
Spatial Frequencies ◽  
High Contrast Grating ◽  
Orientation Specificity ◽  
Adaptation Method

An adaptation method is used to determine the orientation specificity of channels sensitive to different spatial frequencies in the human visual system. Comparison between different frequencies is made possible by a data transformation in which orientational effects are expressed in terms of equivalent contrast (the contrast of a vertical grating producing the same adaptational effect as a high-contrast grating of a given orientation). It is shown that, despite great variances in the range of orientations affected by adaptation at different spatial frequencies (±10° to ±50°), the half-width at half-amplitude of the orientation channels does not vary systematically as a function of spatial frequency over the range tested (2·5 to 20 cycles deg−1). Two subjects were used and they showed significantly different orientation tuning across the range of spatial frequencies. The results are discussed with reference to previous determinations of orientation specificity, and to related psychophysical and neurophysiological phenomena.

A Test of the Spatial-Frequency Explanation of the Müller-Lyer Illusion

Perception ◽  
1986 ◽  
Vol 15 (5) ◽  
pp. 553-562 ◽  
Author(s):  
Marisa Carrasco ◽  
Jesus G Figueroa ◽  
J Douglas Willen
Keyword(s):  
Spatial Frequency ◽  
Visual System ◽  
Human Visual System ◽  
Lyer Illusion ◽  
Lower Spatial Frequency ◽  
Spatial Frequencies ◽  
Frequency Components ◽  
Fourier Spectra

Previous investigations have shown that the response of spatial-frequency-specific channels in the human visual system is differentially affected by adaptation to gratings of distinct spatial frequencies and/or orientations. A study is reported of the effects of adaptation to vertical or horizontal gratings of a high or a low spatial frequency on the extent of the Brentano form of the Müller-Lyer illusion in human observers. It is shown that the illusion decreases after adaptation to vertical gratings of low spatial frequency, but seems unaffected otherwise. These results are consistent with the notion of visual channels that are spatial-frequency and orientation specific, and support the argument that the Müller-Lyer illusion may be due primarily to lower-spatial-frequency components in the Fourier spectra of the image.

A Demonstration of the Visual Importance and Flexibility of Spatial-Frequency Amplitude and Phase

Perception ◽  
1982 ◽  
Vol 11 (3) ◽  
pp. 337-346 ◽  
Author(s):  
Leon N Piotrowski ◽  
Fergus W Campbell
Keyword(s):  
Spatial Frequency ◽  
Visual System ◽  
Human Visual System ◽  
Retinal Image ◽  
Fourier Domain ◽  
Spatial Frequencies ◽  
Visual Importance ◽  
Visual Scenes ◽  
Phase Relationships

To establish how little information the human visual system requires for recognition, common objects were digitally manipulated in the Fourier domain. The results demonstrate that it is not only possible, but also quite efficient, for a (biological) visual system to exist with very few phase relationships among the component spatial frequencies of the (retinal) image. A visual example is then presented which illustrates how certain phase relationships can hinder, or completely eliminate, the recognition of visual scenes.

The Square-Wave Illusion and Phase Anisotropy of the Human Visual System

Perception ◽  
1982 ◽  
Vol 11 (5) ◽  
pp. 547-556 ◽  
Author(s):  
Lawrence E Leguire ◽  
Randolph Blake ◽  
Michael Sloane
Keyword(s):  
Visual System ◽  
Human Visual System ◽  
Relative Phase ◽  
Adaptation Effect ◽  
Phase Relations ◽  
Phase Anisotropy ◽  
Triangular Wave ◽  
Square Wave ◽  
Frequency Components ◽  
Over Time

A triangular-wave grating is perceived to fluctuate over time: at one moment it may appear veridical (ie triangular), at another it may more closely resemble a square-wave grating with rounded edges. In addition, the square-wave illusion itself is bistable, in that it sometimes appears to shift in phase by 180 deg. Experiments in which the phase and amplitude of the first three frequency components of the triangular-wave grating were independently varied showed that the square-wave illusion results from the relative phase of the frequency components. Adaptation to two frequency components in square-wave (sine) phase was found to reduce the illusion strength, and adaptation to triangular-wave (cosine) phase was found to increase the illusion strength. In addition, the square-wave adaptation effect spreads to nonadapted retinal areas. It is concluded that the square-wave illusion reflects a phase anisotropy in the human visual system that favors square-wave phase over other phase relations.

Masking by Uniform Field Flicker: Some Practical Problems

Perception ◽  
1987 ◽  
Vol 16 (5) ◽  
pp. 641-647 ◽  
Author(s):  
David R Badcock ◽  
Elizabeth Sevdalis
Keyword(s):  
Visual System ◽  
Contrast Sensitivity ◽  
Human Visual System ◽  
Sensitivity Function ◽  
Relative Performance ◽  
Contrast Sensitivity Function ◽  
Uniform Field ◽  
Spatial Frequencies ◽  
The Mean ◽  
Mean Luminance

The technique of uniform field flicker (UFF) masking has frequently been used to address issues concerning the relative performance of sustained and transient neural channels in the human visual system. Unfortunately there has been an artifact in the implementation of this method in most published experiments which has meant that the contrast of the target has been flickered in synchrony with the mean luminance. A study is reported in which the artifact was corrected and the effects of UFF masking on the contrast sensitivity function then examined. With this correction, masking was still restricted to low spatial frequencies but it was much weaker than reported originally. It is argued that the original evidence suggesting that UFF masking can be used to examine the functioning of transient and sustained channels has not been interpreted correctly and that the basis for such a claim is weak.

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.

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