Pattern recognition in humans: correlations which cannot be perceived.
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Color Perception↗
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Results for “Form Perception”
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Dominance of touch by vision: generalization of the hypothesis to a tactually experienced population.
It is now held that in conditions where there is conflicting sensory information vision dominates touch. The present study was designed to place boundary conditions on the generality of the hypothesis by comparing the performance of tactually experienced subjects - potters - with university students on a form-perception task in which a square was optically distorted so as to appear rectangular. Subjects examined the square haptically and visually, and matched it by touch or vision. Although potters were more accurate than students when not permitted vision, tactual judgements of both were dominated by vision when they were presented with conflicting information. In a supplementary study longer, more active exploration and emphasis on the necessity of matching by touch had no differential effect. In a third study it was found that a range effect produced by the comparison stimuli could explain the lesser accuracy of the students when they were making haptic judgements. The generality of the hypothesis that vision dominates touch is strengthened by our failure to refute it.
Adolescent↗
A figure-density hypothesis and illusory contour brightness.
Perceived figures tend to have surface colour and to be comparatively dense in texture and saturated. These figure characteristics are found in many of the illusory contour figures examined heretofore but new figures presented here do not conform to these characteristics. Consequently, rather than explain subjective brightness effects as offshoots of figural processes, it may be better to begin with concepts of local brightness effects induced by the display, which are made perceptually effective when grouped by the eye.
Color Perception↗
Vision with isoluminant colour contrast: 1.A projection technique and observations.
An optical technique is described for projecting two-colour pictures with controlled brightness contrast, which may be set to zero-at isoluminance. Colour registration is maintained without adjustment or special setting up. It is suggested that colour-and brightness-contour registration in the visual channel is a problem which may be solved neurally be master brightness signals locking slave colour signals. The projection apparatus allows the supposed master brightness signals to be removed-at isoluminance-when contour disturbances should occur. Observation of this kind are reported.
Color Perception↗
Stereopsis and the representation of space.
Four stereoblind and four normal subjects were tested on a mental rotation task. It was hypothesized that, if stereopsis is an important input for building up the perceptual system that represents three-dimensional space, then subjects lacking it ought to be deficient at mental rotations in depth. Stereoblind subjects were equally efficient at picture-plane and depth rotations, and were nonsignificantly better than normal subjects at rotations in depth. It was concluded that in the absence of stereopsis other cues are sufficient for the development of the "three-dimensional" perceptual system. A puzzling paradox was raised, however, by the finding that the introspections of the two groups differed markedly.
Depth Perception↗
Articulation in the context of edge classification.
Many researchers believe the human visual system classifies luminance edges into those produced by reflectance edges or those produced by illumination edges, yet this classification process is not completely understood. One suggestion is that heuristics are used for edge classification. For example. specific contrast relationships at the luminance edge ('codirectional contrast invariance' and 'transversal luminance-ratio preserving') may distinguish an illumination edge from a reflectance edge on the one hand, and from a translucent edge on the other. Distinct from luminance junctions, these features are global characteristics of the luminance pattern that make distinguishing between different types of edge easier with more highly articulated scenes. I demonstrate that apparent translucency, nonreversing X-junctions, and single-reversing X-junctions are insufficient on their own to produce the lightness illusion of Adelson's well-known tile pattern. While tolerating violations of the codirectional contrast invariance and transversal-luminance-ratio presersving without reversing the sign of contrast, the visual system is quite sensitive to such contrast reversal at the luminance edge. I account for this by suggesting that humans process lightness in terms of an ordinal, rather than interval, (or ratio) scale.
Color Perception↗
The role of apparent depth and context in the perception of the Ponzo illusion.
The role of apparent depth features and the proximity of the test lines to the adjacent contours in the actuation of the Ponzo illusion was examined. Six versions of the Ponzo figure were employed: a standard Ponzo figure and five modified figures in which the test lines varied in orientation (horizontal or vertical) and in location (inside or outside the converging contours). Both manipulations resulted in a significant decrease in the magnitude of the illusion in comparison to the standard Ponzo figure. The results suggest that the Ponzo illusion is significantly affected by contextual factors.
Depth Perception↗
A note on the Münsterberg or café wall illusion.
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Color Perception↗
Geometric transformations of pictured space.
In general, a picture can represent a specific environment of scene only when the picture is seen from a unique viewing point. The determination of this unique point and of the distortions that occur when the picture is viewed from other points is crucial to all aspects of pictorial perception. To clarify the effects of the point of observation on pictorial space, the present paper discusses how the correct point may be calculated, provides a geometric analysis of the effects of altering the viewing point, and briefly reviews the effects of such alterations on space perception.
Depth Perception↗
The Penrose triangle and a family of related figures.
Starting from a study of the Penrose triangle, the theory is advanced that our perception of the relative spatial positions of parts of a figure is mediated by a set of significant directions (or axes). Illustration and exploration of the theory in this paper revolves around examples drawn mostly from a family of figures related to the Penrose triangle. This family is defined partly in terms of the common nature of its members' anomalies, and partly by the feature that they are seen as configurations of 'beams'. This feature and the conditions for it are also examined by the use of examples.
Depth Perception↗
Illusory dilatation of square surfaces.
The aim of the present research was to study illusory dilatation of surfaces isolating some factors contributing to this phenomenon. A series of displays (8.5 cm x 8.5 cm) was prepared: a white square card and five square cards with a uniform pattern of black dots, increasing gradually. The displays were presented to two different groups of subjects, according to the method of paired comparisons and according to the method of limits (under conditions of reduced viewing) respectively. The subjects were asked to evaluate the relative magnitude of the displays. The textured cards significantly differed from the white standard and also among themselves. Up to a threshold, as the dots increase, the surfaces expand as well.
Distance Perception↗
The effect of refractive error on size constancy and shape constancy.
The effect of refractive error was determined for both size constancy and shape constancy. Although an error of 1.5 diopters reduces shape constancy, 3.0 diopters of blur had no effect on size constancy. The results are discussed in terms of the multiple mechanisms subserving the perceptual constancies. The importance of cues from the peripheral visual fields for size constancy and the role of foveally mediated texture and stereopsis cues for shape constancy are emphasized.
Adult↗
Perspectives in open spaces. A geometrical application of the Thouless index.
A geometrical model for computing 'general perspectives' is discussed. It is based on the power function r = p(d/t) 1 -i, where i is the Thouless index for the phenomenal regression to the real object, r is the real size of the object, p is the apparent size, d is the distance between the subject and the object, and t is the distance between the subject and the projection plane. This model assumes that i is invariant for different distances and this was verified in seventy children and adults at distances of 15 or 120 m. A computer program draws families of curved perspectives which are well-fitted to the actual shape of large visual alleys produced by experiment in open fields.
Adult↗
An additional dimension to grating perception.
Visual acuity (A) for a two-dimensional multiplicative sinusoidal contrast grid (sinusoidal chessboard) was measured as a function of spatial frequency (omega) of modulation in one of the dimensions. The reduction in acuity as frequency was increased was well described by the equation: A = -2pikomega + c, where k and c are constants. At suprathreshold contrasts, the frequency of modulation appeared to be doubled relative to the underlying modulation frequency. This doubling is not related to the frequency of the harmonic components of the chessboard, but suggests the existence of a perceptual mechanism sensitive to areas of sinusoidal modulation which are seen at twice the frequency of the variation in contrast.
Depth Perception↗
Second-order statistics of colour codes modulate transformations that effectuate varying degrees of scene invariance and illumination invariance.
We argue, from an ethology-inspired perspective, that the internal concepts 'surface colours' and 'illumination colours' are part of the data format of two different representational primitives. Thus, the internal concept of 'colour' is not a unitary one but rather refers to two different types of 'data structure', each with its own proprietary types of parameters and relations. The relation of these representational structures is modulated by a class of parameterised transformations whose effects are mirrored in the idealised computational achievements of illumination invariance of colour codes, on the one hand, and scene invariance, on the other hand. Because the same characteristics of a light array reaching the eye can be physically produced in many different ways, the visual system, then, has to make an 'inference' whether a chromatic deviation of the space-averaged colour codes from the neutral point is due to a 'non-normal', ie chromatic, illumination or due to an imbalanced spectral reflectance composition. We provide evidence that the visual system uses second-order statistics of chromatic codes of a single view of a scene in order to modulate corresponding transformations. In our experiments we used centre surround configurations with inhomogeneous surrounds given by a random structure of overlapping circles, referred to as Seurat configurations. Each family of surrounds has a fixed space-average of colour codes, but differs with respect to the covariance matrix of colour codes of pixels that defines the chromatic variance along some chromatic axis and the covariance between luminance and chromatic channels. We found that dominant wavelengths of red-green equilibrium settings of the infield exhibited a stable and strong dependence on the chromatic variance of the surround. High variances resulted in a tendency towards 'scene invariance', low variances in a tendency towards 'illumination invariance' of the infield.
Adult↗
Frequency, phase, and colour coding in apparent motion.
We present some results which indicate that the known spatiotemporal limits for apparent motion are consistent with the motion being sinusoidal or a result of filtering. Given this we investigated how two such motions interact as a function of their relative temporal phase differences. This was accomplished by inducing two independent motions from complementary coloured event pairs. Results indicated critical phase limits for perceiving the two motions (red and green) which were consistent with the frequency specificity of the effect. The results are discussed within the framework of a filtering process for the perception of apparent motion.
Color Perception↗
The contribution of colour to three-dimensional ambiguities in paintings and drawings.
This paper is about kinds of visual ambiguity that concern the author as a painter. Some effects of incompatible depth cues on the experience of looking at paintings and drawings are discussed. Particular attention is given to the role of colour as a depth cue. It is suggested that areas of identical pigmentation on different parts of a picture surface tend to be interpreted as being on the same plane. Where this interpretation is incompatible with other depth cues 'visual tension' results, the degree of tension being dependent on the relative strength of the cues involved. This hypothesis is illustrated and elaborated with the help of a number of line drawings.
Art↗
Sensory conditions for the occurrence of the neon spreading illusion.
The neon effect, i.e. an illusion of light projected onto a homogeneous lattice, may occur in line patterns made up of elements of different color or brightness. Particular luminance relations between the different line elements in the patterns and between these line elements and their background appear to be critical for the occurrence of the effect.
Color Perception↗