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

As it can be expected that the effects described in the two-quanta explanation are important for the brightness impression, we performed experiments suitable for the study of these phenomena concerning brightness impression.

The Quanta Explanation of Vision and the Brightness Impression for Various Times of Observation and Visual Angles

In the context of the quantum theory of vision scalers, coincidence scalers, adapting coincidence scalers and dead time mechanisms have been used as basic constituents of network models: van de Grind et al. (1970a), Koenderink et al. (1970a, b). The possibilities that these devices offer to construct network models of vision are presently further analysed. First of all a mechanistic analysis is given of the event rate reduction characteristics of “dead time boxes”. Next the interaction of these devices with scalers is discussed in relation with a number of “fluctuation models” of vision proposed in the literature. A critical evaluation of these fluctuation models shows an important defect of most of them, viz. that unrealizable detection criteria are postulated. Our reconsideration of this detection problem then leads to the proposal of some specific realizable detectors. An application of the developed theory of mechanisms (‘machines’) to the explanation of the flash detection characteristics of Limulus concludes the paper. Applications of the presented ideas to neural theory and modelling are treated hi a separate paper (van de Grind et al., 1970b) and for applications of the theory to psychophysically oriented visual modelling studies the reader is referred to Koenderink et al. (1970a, b) and van de Grind et al. (1970a).

The concepts of scaling and refractoriness in psychophysical theories of vision.

Publisher Summary This chapter deals with the quantum fluctuations in vision. The theoretical concept that visual detectability is governed by chemical mass action laws and chemical equilibrium between intact and bleached regenerating retinal pigment, is instead receiving all the attention. This is remarkable as it can have been clear from the onset that such an approach is incompatible with the “few-quanta-only’’ concept. A whole framework of theoretical ideas and corresponding experimental studies has been founded on the basic concept that the visual detection capacity is limited by quantum fluctuations. Further, light intensities on the retina can be measured by diverting a fixed fraction to a physical light detector but quantal hits on the retina cannot be measured that way, because of their statistical spatial and temporal nature. Therefore, it was of paramount importance when the first announcements of electrophysiological confirmations of so-called quantum bumps appeared. The chapter also discusses the electrophysiological evidence of the quantum events.

II Quantum Fluctuations in Vision

This paper deals with measurements of the pupillary response to several kinds of input signals such as sinusoidal modulated light intensity, flashes, noise and frequency-modulated flicker light. The results are compared with one another. This turns out that the dynamic behaviour of the pupillary response to continuous input signals (sinusoidal, random) differs slightly from the behaviour of the response to flashes, while the shape of the response to frequency-modulated flicker light is quite different and resembles the far-to-near response of the pupil system.

Maarten A. Bouman

Papers

The Quanta Explanation of Vision and the Brightness Impression for Various Times of Observation and Visual Angles

The concepts of scaling and refractoriness in psychophysical theories of vision.

II Quantum Fluctuations in Vision

Dependence of the Dynamic Behaviour of the Human Pupil System on the Input Signal

Quantum coincidence requirements during dark-adaptation.