Contrast masking was studied psychophysically. A two-alternative forced-choice procedure was used to measure contrast thresholds for 2.0 cpd sine-wave gratings in the presence of masking sine-wave gratings. Thresholds were measured for 11 masker contrasts spanning three log units, and seven masker frequencies ranging +/- one octave from the signal frequency. Corresponding measurements were made for gratings with horizontal widths of 0.75 degrees (narrow fields) and 6.0 degrees (wide fields). For high contrast maskers at all frequencies, signal thresholds were related to masking contrast by power functions with exponents near 0.6. For a range of low masking contrasts, signal thresholds were reduced by the masker. For the wide fields, high contrast masking tuning functions peaked at the signal frequency, were slightly asymmetric, and had approximately invariant half-maximum frequencies that lie 3/4 octave below and 1 octave above the signal frequency. The corresponding low contrast tuning functions exhibited peak threshold reduction at the signal frequency, with half-minimum frequencies at roughly +/- 0.25 octaves. For the narrow fields, the masking tuning functions were much broader at both low and high masking contrasts. A masking model is presented that encompasses contrast detection, discrimination, and masking phenomena. Central constructs of the model include a linear spatial frequency filter, a nonlinear transducer, and a process of spatial pooling that acts at low contrasts only.

https://courses.washington.edu/psy448/pdf/Legge_JOSA80.pdf

Contrast masking in human vision

We propose a model of how humans sense the velocity of moving images. The model exploits constraints provided by human psychophysics, notably that motion-sensing elements appear tuned for two-dimensional spatial frequency, and by the frequency spectrum of a moving image, namely, that its support lies in the plane in which the temporal frequency equals the dot product of the spatial frequency and the image velocity. The first stage of the model is a set of spatial-frequency-tuned, direction-selective linear sensors. The temporal frequency of the response of each sensor is shown to encode the component of the image velocity in the sensor direction. At the second stage, these components are resolved in order to measure the velocity of image motion at each of a number of spatial locations and spatial frequencies. The model has been applied to several illustrative examples, including apparent motion, coherent gratings, and natural image sequences. The model agrees qualitatively with human perception.

Model of human visual-motion sensing

A method of producing red-green and blue-yellow sinusoidal chromatic gratings is used which permits the correction of all chromatic aberrations. A quantitative criterion is adopted to choose the intensity match of the two colours in the stimulus: this is the intensity ratio at which contrast sensitivity for the chromatic grating differs most from the contrast sensitivity for a monochromatic luminance grating. Results show that this intensity match varies with spatial frequency and does not necessarily correspond to a luminance match between the colours. Contrast sensitivities to the chromatic gratings at the criterion intensity match are measured as a function of spatial frequency, using field sizes ranging from 2 to 23 deg. Both blue-yellow and red-green contrast sensitivity functions have similar low-pass characteristics, with no low-frequency attenuation even at low frequencies below 0.1 cycles/deg. These functions indicate that the limiting acuities based on red-green and blue-yellow colour discriminations are similar at 11 or 12 cycles/deg. Comparisons between contrast sensitivity functions for the chromatic and monochromatic gratings are made at the same mean luminances. Results show that, at low spatial frequencies below 0.5 cycles/deg, contrast sensitivity is greater to the chromatic gratings, consisting of two monochromatic gratings added in antiphase, than to either monochromatic grating alone. Above 0.5 cycles/deg, contrast sensitivity is greater to monochromatic than to chromatic gratings.

The contrast sensitivity of human colour vision to red‐green and blue‐yellow chromatic gratings.

Chapter 9 Visual adaptation and retinal gain controls

Perceptual visual quality metrics: A survey

A model describing the processing of quantal effects at low luminance levels is evaluated with respect to generally known experimental results for the temporal domain. The model consists of two sequential stages: a square-root scaler and a simple integrate-to-threshold detector. It is shown that with this model the experimental behavior of the absolute light threshold in relation to the flash duration and to the interval for periodic stimuli can be correctly described. When the detection mechanism is changed to a mechanism that detects a fixed minimum number of changes per time unit, the model can describe experimental data obtained at low luminance levels on the increment and decrement thresholds, the modulation transfer function, and the flicker experiments with varying light–dark ratio. From the data fitting it is concluded that in the near-peripheral visual field, adaptation processes have typical time constants of the order of 100 msec, whereas in the far periphery these processes have typical time constants ranging from 50 to 5000 msec, depending on stimulus size. The sampling time of the visual system for the above mentioned stimuli lies between 350 and 1500 msec.

Detection of light and flicker at low luminance levels in the human peripheral visual system. II. A mechanistic model.

In 194zt, three independent approaches were developed, towards establishing the number of quanta effectively absorbed by the visual purple and necessary for light-perception (van der Velden, 1944. These methods were independent of the loss of light caused by reflection and absorption in the various parts of the eye, so that the absolute values of the energies employed' are of no importance. The methods are: A. Determination of the relation between the chance of o,bservation of a flash and the average number of quanta in the flash for very small visual angles and for short flash-times. After the war we received' the p-pers by Hecht and his co-workers (1942), who had already used this method in 1942. These results indicated that a co-operation of at least 5, 6 or 7 quanta (dependent on the observer) were necessary for the perception of light. Our results (van der Velden, 1944, 1946; Bouman O van der Velden (1947)), on the other hand, suggested a co-operation of two quanta, independent of the observer. B. Determination of the dependence of the average number of quanta for a fixed chance of observation on the duration of the flash for a small visual angle. It is obvious, that when more than one quantum is necessary for light-perception, one has to ex,pect a dependence of the average number of quanta m the flash N, necessary for a certain chance of observation, on the duration of the flash t. Assuming that tl~e retinal condition existing after the absorption of the first quantum will have a finite life-time r it is possible to calculate the number N as a function of t, at least to give the slope

The two-quanta explanation of the dependence of the threshold values on the visual angle and the time of observation.

Ricco’s Law and the Quanta-Explanation of Vision

Thresholds for seeing light from a stimulus are determined by a mechanism that pairs subliminal excitations from both halves of a twin unit Such excitations stem from a package of k ≥ 1 receptor responses A half-unit contains one red or one green cone and P rods The receptor's "Weber machine" controls the receptor's gain Each half of a twin unit contains a "de Vries machine," which controls the half's k number In the dark the receptor's dark noise events reset its Weber machine and the receptor's relation to its de Vries machine A pairing product for light perception also represents a direction event The local time signs of the two subliminal excitations are crucial for the polarity, size, and pace of the direction event In relation to the time when and the area in which the stimulus is presented, these signs have average latency periods that depend on intensity and average locations that depend on movement Polarity depends on which of the two subliminal excitations happens to arrive first at the twin's pairing facility The intra- and inter-twin pairings in a persepton for the perceptions of light, edge and movement and the probability summation of the pairing products of the mutually independent three sets of twins of the retrinet improve intensity discrimination Cross-pairings of intra-receptor pairings in red and green cones of a trion for yellow improve visual discrimination further Discrimination of stimuli that exploit the model's entire summation mechanisms and pairing facilities represents "what the perfect human eye sees best" For the model this threshold of modulation in quantum absorption is the ideal limit that is prescribed by statistical physics The lateral and meta interaction in a twin unit enhance the contrast of an edge and of a temporal transient The precision of the local time sign of a half's stimulation determines the spatiotemporal hyperfunctions for location and speed The model's design for the perfect retinal mosaic consists of red twins situated along clockwise and counterclockwise spirals and green twins along circles that are concentric with the fovea The model's descriptions of discrimination, adaptation, and hyperfunctions agree with experimental data © 2002 Optical Society of America

De Vries-Weber gain control and dark adaptation in human vision.

When the frequency of seeing light from a pair of point flashes is beyond the probability summation of the separate flashes, the surplus is due to the successful interaction of subliminal responses from the different flashes. Experiments with various distances and various periods of the pair show thet successful interaction occurs when in each of two successive time-quanta of 0.04 seconds and in each of two adjacent distinct receptor groups at least one subliminal receptor response occurs. An autonomous source produces the time-quanta. It serves the time-processing of the central nervous system and of the motor system. Posdsibly, action potentials from the purkinje cells of the myocardium play a role. Hyper acuity in direction and in depth, flicker fusion, perceptual rivalry and ather phenomena follow from the quantized spatiotemporal signal processing.

/pdf/the-stroboscopic-human-vision-49xj0f1o6q.pdf

Maarten A. Bouman

Papers

Detection of light and flicker at low luminance levels in the human peripheral visual system. II. A mechanistic model.

The two-quanta explanation of the dependence of the threshold values on the visual angle and the time of observation.

Ricco’s Law and the Quanta-Explanation of Vision

De Vries-Weber gain control and dark adaptation in human vision.

The stroboscopic human vision