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

Measurements of the chance of interaction for a light perception of two stimuli projected at various distances in time and place from each other in the dark-adapted human peripheral retina are presented. The two separate test stimuli were about 2′ of angular size and each lasted 0.01 second. The time τ between these two was varied from 0 to 0.21 second, the distance δ between them 0–25 minutes of arc. The chance of interaction was measured by determination of the chances of observation for each test stimulus apart and for τ=δ=0. The colors of the light from the separated stimuli were red and green, for red chiefly the cones being active and for green, the rods. In the study, one test stimulus activated the rods; in the other the cones were included. It proved that the chance for interaction is described by p(τ)·q(δ); p(τ) does not depend on the place on the retina used or on the kind of receptors stimulated by the two test flashes. q(δ) depends on the position of the retina and the kind of receptors concerned in agreement with the well-known facts of the validity of Ricco’s law. For mixed-rod cone vision q(δ) is situated intermediately between q(δ) for pure cone and pure rod vision on the position of the retina under consideration. Eccentricities from 5° up to 27° from the fovea are used. The results are discussed in relation to outstanding details of the two quanta explanation of the absolute thresholds.

On the Integrate Capacity in Time and Space of the Human Peripheral Retina

The interaction of subliminal effects arising in the retina from two stimuli presented at adjustable time and distance apart from each other is studied (with the aid of measurements of frequencies of seeing) for each stimulus separately and for the combined flash. The chance for successful interaction as a function of time and distance between the stimuli is deduced quantitatively. Experiments refer to red and green flashes on red and green adapting fields, in peripheral and foveal vision. Except for integrate capacity in space in the fovea, a considerable decrease in these capacities is demonstrated for higher levels of adapting brightness. The amplitude of variation in sensitivity during adaptation is estimated.

Variation of integrative actions in the retinal system; an adaptational phenomenon.

Fluctuation theory of colour discrimination of normal trichromats

From the fact that the retina is rather inhomogeneous, it can be inferred that the perception of spatial patterns of appreciable extent will be dependent on the retinal location. Anatomical, electrophysiological and psychophysical findings substantiate the claim that the retina is very inhomogeneous of composition. In order to investigate the influence of this inhomogeneity on the perception of patterns, a model of spatiotemporal signal processing in the retina was developed on the basis of a paradigm for the Weber type adaptation. Such “scaling-ensembles” proved successful in the prediction of spatiotemporal modulation transfer in the human fovea (Koenderink et al., 1971). One prediction of the present model is that certain spatial patterns are optimally detected at well defined retinal locations, dependent on the spatial frequency content of the stimulus. A confrontation of the model's predictions with measurements published by Bryngdahl (1966) enabled us to estimate some of the relevant parameters of the retinal receptive fields as a function of the eccentricity. We obtained estimates that compare reasonably well with previously known values; for instance with values of acuity and anatomical measurements. The present discussion bears relevance on the question of whether the retina is composed of independently tuned spatial frequency filters at any retinal location, or whether the tuning is with respect to the eccentricity.

The influence of the retinal inhomogeneity on the perception of spatial patterns.

The transfer function of the human lens system appears to be strongly influenced by the possibility to predict the input signal. Owing to this the accommodating system can respond very rapidly to a change in target distance when anticipation is used, and it is relatively slow when the subject is unable to anticipate the input signal. An optimal and a minimal transfer function is determined assuming that possibility to anticipate the input signal is relevant. The two aforementioned transfer functions are compared with sinusoidal responses which were strongly influenced by the extent of training and the attention of the subject.

Maarten A. Bouman

Papers

On the Integrate Capacity in Time and Space of the Human Peripheral Retina

Variation of integrative actions in the retinal system; an adaptational phenomenon.

Fluctuation theory of colour discrimination of normal trichromats

The influence of the retinal inhomogeneity on the perception of spatial patterns.

The Effect of Anticipation on the Transfer Function of the Human Lens System