A simple method for comparing peripheral and central color vision by means of two smartphones.

Information on peripheral color perception is far from sufficient, since it has predominantly been obtained using small stimuli, limited ranges of eccentricities, and sophisticated experimental conditions. Our goal was to consider the possibility of facilitating technical realization of the classical method of asymmetric color matching (ACM) developed by Moreland and Cruz (1959) for assessing appearance of color stimuli in the peripheral visual field (VF). We adopted the ACM method by employing two smartphones to implement matching procedure at various eccentricities. Although smartphones were successfully employed in vision studies, we are aware that some photometric parameters of smartphone displays are not sufficiently precise to ensure accurate color matching in foveal vision; moreover, certain technical characteristics of commercially available devices are variable. In the present study we provided evidence that, despite these shortages, smartphones can be applied for general and wide investigations of the peripheral vision. In our experiments, the smartphones were mounted on a mechanical perimeter to simultaneously present colored stimuli foveally and peripherally. Trying to reduce essential discomfort and fatigue experienced by most observers in peripheral vision studies, we did not apply bite bars, pupil dilatation, and Maxwellian view. The ACM measurements were performed without prior training of observers and in a wide range of eccentricities, varying between 0 and 95°. The results were presented in the HSV (hue, saturation, value) color space coordinates as a function of eccentricity and stimulus luminance. We demonstrated that our easy-to-conduct method provided a convenient means to investigate color appearance in the peripheral vision and to assess inter-individual differences.

Visual Percepts in the Cases of Binocular and Monocular Viewing Stabilized Test Objects, Ganzfeld Stimuli, and Prolonged Afterimages.

A thorough analysis of the literature on retinal image stabilization, as well as our own experimental data, present evidence that Yarbus's concept, implying inevitable and irreversible fading of a visible image evoked by stabilized retinal stimulus of any size, color, and luminance in 1 to 3 s after its onset, is not valid in a general case. It has been demonstrated that, even with Yarbus's stabilization techniques, the lifetime of visible images varies from fractions of a second to the whole stimulus duration-up to 30 min in our experiments-depending on many factors: monocular or binocular viewing, stimulus parameters, characteristics of subjects, and so forth. The dynamics of perceived images is determined mainly by the processes at the higher levels of the visual system. In the cases of such unusual visual stimuli as stabilized retinal images, it is problematic for the visual brain to find their proper interpretations in terms of everyday natural experience. Usually, the responses of retinal units are determined by three types of coexisting images: (a) the optical projections of external objects, (b) shadows of the blood vessels and other internal eye structures, (c) virtual patterns caused by the traces of previous stimuli. A task of the visual system is to recognize and visualize only external objects separating their projections from all the entoptic images of the two remaining types. To implement separation, visual brain employs a number of approaches--in particular, the eye movements that cause sliding over the retina but only the projection of the external objects. This means that the peculiar phenomena observed in the cases of stabilized retinal images can be determined not by invariability of such stimuli per se but rather by the fact that stabilization eliminates a powerful cue helping to identify the retinal images belonging to the external objects, thereby increasing the probability to treat them as the entoptic ones which should be ignored or canceled rather than perceived. However, the probability of canceling--image fading--can be essentially reduced in conditions of concordant, large, bright, and sharp binocular stimuli.

Yarbus's Conceptions on the General Mechanisms of Color Perception.

In the last series of papers published during 1975 to 1980, Alfred Yarbus tried to formulate general conceptions concerning the basic principles of retinal image processing in the human visual system. The original ideas of Yarbus were based on the results of his numerous and various experiments carried out with extraordinary inventiveness and great skill. Being concentrated primarily on the problems of color vision, Alfred Yarbus dreamed of elaborating a comprehensive model that would simulate visual information processing at the monocular precognitive level in the visual system of humans with normal trichromatic color perception. In this article, the most important of Yarbus' experimental paradigms, findings, statements, and conclusions are systematized and considered in relation to the classical theories of color perception and, in particular, fundamental theses of the Nyberg school. The perceptual model developed by Alfred Yarbus remained incomplete. Nevertheless, it is already evident that some intrinsic contradictions make it inadequate in terms of comprehensive modeling. However, certain partial advantages deserve more thorough appreciation and further investigation.