Orientation-contingent color aftereffects mediated by subjective transparent structures.

We examined whether the orientation-contingent color aftereffect (the McCollough effect) could be mediated by subjective horizontal and vertical structure induced by the perception of transparency. In our experiments, red vertical bars and green horizontal bars were alternated as an adapting stimulus. After adaptation, subjects (n = 6) were asked to adjust the green and red saturation of a test pattern until they obtained a neutral gray. Horizontal and vertical stripes were combined in the test pattern in three different ways: (1) overlapping with a luminance combination that gave rise to a perception of transparent overlays of horizontal and vertical stripes (valid transparency condition), (2) overlapping with luminance combinations that did not induce a perception of transparency (invalid transparency condition) and that appeared more as a patchwork of checks, and (3) presented in adjacent, nonoverlapping areas. Our results showed that the McCollough effect was significantly greater in the valid transparency condition than in the invalid transparency conditions. The effect in the valid transparency condition was nevertheless less strong than was the effect seen with the standard test stimulus made up of nonoverlapping vertical and horizontal stripes. Our results suggest that the McCollough effect can be mediated by the subjective spatial organization (inner representation of vertical and horizontal stripes) that accompanies the perception of transparency in our stimulus.     

Figure-ground perception and random geometry

Constructs of random geometry were applied to the problem of figure-ground perception. Random-dot images of black and white dots with various area fractions and tesselations (square and triangular lattices) were used as stimuli. The constructs of random geometry are correlation functions of n-th order and some functionals defined on them. The only parameter which is independent of the tesselation used is the first-order correlation which is the area fraction. It was first conjectured and then experimentally verified that figure-ground perception is not affected by the various tesselations used. Thus, figure-ground phenomena depend only on the area fraction of the white and black dots in the stimulus. There is a perceptual bias for white, that is, figure-ground reversal is easiest at 40 percent white-black area fraction. It was also experimentally shown that size-constancy prevails in figure-ground perception, but brightness-constancy does not.     

Figure-ground perception and random geometry

Constructs of random geometry were applied to the problem of figure-ground perception. Random-dot images of black and white dots with various area fractions and tesselations (square and triangular lattices) were used as stimuli. The constructs of random geometry are correlation functions of n-th order and some functionals defined on them. The only parameter which is independent of the tesselation used is the first-order correlation which is the area fraction. It was first conjectured and then experimentally verified that figureground perception is not affected by the various tesselations used. Thus, figure-ground phenomena depend only on the area fraction of the white and black dots in the stimulus. There is a perceptual bias for white, that is, figure-ground reversal is easiest at 40 percent white-black area fraction. It was also experimentally shown that size-constancy prevails in figure-ground perception, but brightnes s-constancy does not.     

Role of spatial and temporal coincidence in depth organization

The linking of spatial information is essential for coherent space perception. A study is reported of the contribution of temporal and spatial alignment for the linkage of spatial elements in terms of depth perception. Stereo half-images were generated on the left and right halves of a large-screen video monitor and viewed through a mirror stereoscope. The half-images portrayed a black vertically oriented bar with two brackets immediately flanking this bar and placed in crossed or uncrossed disparity relative to the bar. A pair of thin white 'bridging lines' could appear on the black bar, always at zero disparity. Brackets and bridging lines could be flickered either in phase or out of phase. Observers judged whether the brackets appeared in front of or behind the black bar, with disparity varied. Compared to conditions when the bridging lines were absent, depth judgments were markedly biased toward "in front" when bridging lines and brackets flashed in temporal phase; this bias was much reduced when the bridging lines and brackets flashed out of phase. This biasing effect also depended on spatial offset of lines and brackets. However, perception was uninfluenced by the lateral separation between object and brackets.     

Opponent colours induced by rotating discs

We found a novel visual illusion by using a rotating disc that has some coloured sectors with black arcs. When this disc rotates, illusory colours are seen in the concentric rings that are created by the rotating arcs. The illusory colours are the opponent colours of the sectors that the corresponding arcs are in. Even though we could not differentiate the colours of the individual sectors when the disc rotated quickly, the illusory colours that were the opponent colours of the sector colours could be seen. This visual illusion thus suggests that our visual system can process visual stimuli that we cannot perceive as colours.     

Color And The Duplication Assumption

Susan Hurley has attacked the 'Duplication Assumption', the assumption thatcreatures with exactly the same internal states could function exactly alike inenvironments that are systematically distorted. She argues that the dynamicalinterdependence of action and perception is highly problematic for the DuplicationAssumption when it involves spatial states and capacities, whereas no such problemsarise when it involves color states and capacities. I will try to establish that theDuplication Assumption makes even less sense for lightness than for some ofthe spatial cases. This is due not only to motor factors, but to the basic physicalasymmetry between black and white. I then argue that the case can be extendedfrom lightness perception to hue perception. Overall, the aims of this paper are:(1) to extend Susan Hurley's critique of the Duplication Assumption; (2) to argueagainst highly constrained versions of Inverted Spectrum arguments; (3) to proposea broader conception of the vehicle for color perception.     

Orientation-contingent color aftereffects mediated by subjective transparent structures

We examined whether the orientation-contingent color aftereffect (the McCollough effect) could be mediated by subjective horizontal and vertical structure induced by the perception of transparency. In our experiments, red vertical bars and green horizontal bars were alternated as an adapting stimulus. After adaptation, subjects (n=6) were asked to adjust the green and red saturation of a test pattern until they obtained a neutral gray. Horizontal and vertical stripes were combined in the test pattern in three different ways: (1) overlapping with a luminance combination that gave rise to a perception of transparent overlays of horizontal and vertical stripes (valid transparency condition), (2) overlapping with luminance combinations that did not induce a perception of transparency (invalid transparency condition) and that appeased more as a patchwork of checks, and (3) presented in adjacent, nonoverlapping areas. Our results showed that the McCollough effect was significantly greater in the valid transparency condition than in the invalid transparency conditions. The effect in the valid transparency condition was nevertheless less strong than was the effect seen with the standard test stimulus made up of nonoverlapping vertical and horizontal stripes, Our results suggest that the McCollough effect can be mediated by the subjective spatial organization (inner representation of vertical and horizontal stripes) that accompanies the perception of transparency in our stimulus.     

Cavanagh and Leclerc shape-from-shadow pictures: do line versions fail because of the polarity of the regions or the contour?

Shape-from-shadow perception fails when the contour bordering a shadowed area is reduced to a black line, and the shadow area becomes white. It might be that the polarity of the shadowed and illuminated areas has to be from dark on the shadowed side to light on the illuminated side for successful perception. Or it may be that the line, which has two contours, has one too many for shape-from-shadow processing. Alternatively, the problem might be that one of the contours of the line is incorrectly polarised. To test these explanations, three shape-from-shadow figures were prepared, each depicting the same referent--an elderly person. All three figures had two correctly polarised areas. One figure had a correctly polarised contour at the border between the areas. One had two correctly polarised contours. The other had one correctly polarised contour and one incorrectly polarised contour. The referent of the figure with one incorrectly polarised contour was the one difficult to make out. The result has implications for several theories, including an account of a demonstration by Hering involving penumbra.     

Stereokinetic Anomalous Contours: Demonstrations

Collinearity or correspondence between the contours of the inducing figure to allow `contour continuation' or `figure completion' were, according to G. Kanizsa, the necessary conditions for producing anomalous surfaces or contours. Since Kanizsa's early work various hypotheses have been advanced to explain the phenomenon, but very few examples of anomalous contours that do not satisfy the above conditions have been reported. When two small white discs (1 cm in diameter) are set on a larger black disc in slow rotation, the two discs, after some observation time, will appear as the extremities of a rigid cylinder displaced in depth. The surface of the cylinder, under dim illumination, appears as a whitish transparent surface. However, when the two discs are substituted by a circle and a semicircle of the same size, a clear anomalous contour appears to form the cylinder, even under clear light conditions and when the colours are reversed; i.e., black circles on white disc. The anomalous contours are not apparent when the configuration is stationary. I will demonstrate how the anomalous contours of a stereokinetic cylinder can be obtained even without the “interruption” of the lines in the semicircle. The relationship between the anomalous contours of the stereokinetic cylinder and the vitreous transparency of the surface of the cylinder formed by the two small discs above mentioned, will be discussed as well as their relation to the general theories of anomalous surfaces.     

The structure of memory: Evidence concerning the recall of surface and background colour of shapes

In the first of four experiments, two groups of subjects were shown a series of cards, each displaying a different shape. For one group the shapes were of different colours, and each was located on either a black or a white background. For the other group a shape was black or white, and its background was coloured. Subjects in both groups were instructed to memorize the colour and brightness (black or white) assigned to each shape. Recall of the colours, in response to the names of the shapes, was superior for the group for which the shapes themselves had been coloured. In the other three experiments the finding was extended, with the aim of limiting possible explanations of the effect. One of these experiments showed that the effect is obtained when the relevant stimuli are imagined rather than being physically shown to a subject. This suggests that the effect is not the result of processes of attention that are dependent upon the perceptual analysis of a display. In discussion, it is argued that the effect may shed light on the constraints that govern the process of association. One hypothesis that specifically accounts for the results is that the structure of memory for visually presented information is that of a network of propositions.     

Spatial organization of the diplesthetic and nondiplesthetic areas of the fingers

Cutaneous points on different fingers were brought into contact with each other to ascertain whether one stimulus was perceived to be single or double. The perceptual responses were mapped on the five fingertip pads. The results show that there is an extensive cutaneous area on each fingertip pad which elicits one-stimulus perceptions when a single stimulus is applied between each finger and the thumb. This area decreases when the stimulus is applied to adjacent fingers (2-3, 3-4, 4-5), and even more so when it is applied to nonadjacent fingers (2-4, 2-5, 3-5). In fact, in adjacent and nonadjacent fingers the cutaneous surface eliciting a doubling of the single stimulus (diplesthesia) is very extensive. The spatial arrangement of the cutaneous areas eliciting single perceptions appears to be invariant in the proximo-distal plane. Instead, the shift from one kind of perception to another occurs in the medio-lateral plane. It is suggested that this perceptual organization could reflect a neural organization.     

Perception of illumination

Abstract.— Previous research on the perception of illumination has primarily been occupied with the apparent paradox that "we must know the object colour in order to utilize the reflected light as an index of illumination, while we must know the illumination in order to use the reflected light as an index of object colour". The present study shows this paradox to exist only as a long as the traditional one-dimensional conception of achromatic colours is maintained. Two experiments are reported. In Exp. 1 it is shown that by mere variation of the luminance difference of two adjacent areas, a consistent shift in colourlshadow discrimination is obtained; i.e. within a certain range of luminance differences the observer may find it difficult to decide whether the difference is one of colour (two fields of different greyness in common illumination) or one of illumination (two fields of equal greyness under different illumination), above this range the observer perceives the differences as one of illumination. Taking the bidimensionality of achromatic colours into account in Exp. 2, results are obtained which show the brightness (alternatively termed luminosity) relations of adjacent areas to be the critical factor for the perceptual shift.     

Influence of Value on Spatial Balance of Color Pairs

The spatial balance of the component colors is an important element of color harmony in a design. Munsell (1905) suggested that the area of each color in a composition be inversely proportional to the product of the color's chroma and value. Moon and Spencer (1944) proposed that both chroma and value contribute to spatial balance, but the dominant factor is the contrast of a color with the background or with the adaptation point of the eye. The purpose of the present study was to investigate the predictive power of these two rules for hues of equal chroma, varying in value. The stimuli were presented on three different achromatic backgrounds, and both complementary and adjacent pairs of hues were used. When two colors differed in value, subjects tended to avoid equal areas. With black or white backgrounds subjects seemed to prefer larger areas of the color whose value was nearer that of the background, but with a gray background, their choice was either a narrow band of light or of dark color. These findings fail to support either the Munsell or the Moon and Spencer models.     

Glowing greys and surface-white: the photo-geometric factors of luminosity perception

The perception of luminosity is thought to depend upon the intensity of the stimulus: a surface begins to appear self-luminous when it emits or reflects a certain amount of light. This is known as the luminosity threshold. It is a common opinion among vision scientists that such a threshold is correlated to the intensity of a perceptually white surface, in the sense that only an area of the visual field with luminance higher than perceived surface-white will appear luminous. Here we show grey colours that appear luminous in virtue of surrounding luminance ramps. These ramps are intended to mimic halos seen around light sources in natural environments. The results of three experiments indicate that the phenomenon is in direct contradiction to the aforementioned assumptions and suggest the existence of separate perceptual pathways for self-luminosity perception and for surface-colour perception.     

Spatial and temporal lightness anchoring

Research in the area of lightness perception has not adequately addressed the influence of previously viewed visual fields on perceived surface reflectance. In the spatial realm, a spot-in-a-void will appear darker when a second surface of higher intensity is placed adjacent to it. The brighter surface takes the role of white, the anchor, and the dimmer is scaled accordingly. We find that when a spot-in-a-void is presented to observers in a light controlled chamber it is influenced by nonretinal temporal relationships mediated by the degree of complexity. We also find that the influence cannot be explained in terms of successive contrast at a high or low level in the visual system, but can be explained by an anchoring model. The present results follow the same rules governing spatial integration and anchoring and thereby support the currently proposed concept of temporal anchoring.     

Suprathreshold stereo-depth matches as a function of contrast and spatial frequency

Thresholds for stereoscopic-depth perception increase with decreasing spatial frequency below 2.5 cycles deg-1. Despite this variation of stereo threshold, suprathreshold stereoscopic-depth perception is independent of spatial frequency down to 0.5 cycle deg-1. Below this frequency the perceived depth of crossed disparities is less than that stimulated by higher spatial frequencies which subtend the same disparities. We have investigated the effects of contrast fading upon this breakdown of stereo-depth invariance at low spatial frequencies. Suprathreshold stereopsis was investigated with spatially filtered vertical bars (difference of Gaussian luminance distribution, or DOG functions) tuned narrowly over a broad range of spatial frequencies (0.15-9.6 cycles deg-1). Disparity subtended by variable width DOGs whose physical contrast ranged from 10-100% was adjusted to match the perceived depth of a standard suprathreshold disparity (5 min visual angle) subtended by a thin black line. Greater amounts of crossed disparity were required to match broad than narrow DOGs to the apparent depth of the standard black line. The matched disparity was greater at low than at high contrast levels. When perceived contrast of all the DOGs was matched to standard contrasts ranging from 5-72%, disparity for depth matches became similar for narrow and broad DOGs. 200 ms pulsed presentations of DOGs with equal perceived contrast further reduced the disparity of low-contrast broad DOGs needed to match the standard depth. A perceived-depth bias in the uncrossed direction at low spatial frequencies was noted in these experiments. This was most pronounced for low-contrast low-spatial-frequency targets, which actually needed crossed disparities to make a depth match to an uncrossed standard. This bias was investigated further by making depth matches to a zero-disparity standard (ie the apparent fronto-parallel plane). Broad DOGs, which are composed of low spatial frequencies, were perceived behind the fixation plane when they actually subtended zero disparity. The magnitude of this low-frequency depth bias increased as contrast was reduced. The distal depth bias was also perceived monocularly, however, it was always greater when viewed binocularly. This investigation indicates that contrast fading of low-spatial-frequency stimuli changes their perceived depth and enhances a depth bias in the uncrossed direction. The depth bias has both a monocular and a binocular component.     

Evidence against independent processing of black and white pattern features

Following adaptation to a rectangular grating, subjects observed a shift in the perceived duty cycle of a test grating (Burton, Nagshineh, & Ruddock, 1977; DeValois, 1977). This suggests that size information about black and white pattern components may be analyzed independently. We have tested this hypothesis by combining adaptation to a 2-cpd rectangular wave grating (narrow white bars and wide black bars or vice versa) with adaptation to a 4-cpd sine wave (narrow white and black bars. The data do not support the independent analysis of white and black components, but they may be accounted for by mechanisms sensitive to the relative phase relations among the spatial frequency components of the input.     

The phantom illumination illusion

A novel brightness illusion in planar patterns is reported. The illusion occurs, for example, when surfaces with a luminance ramp shaded from black to white are positioned on a black homogeneous background, so that each white end of the surfaces faces a single point of the plane of the pattern. The illusion consists of the enhancement of the brightness of the background in a relatively wide area around the white ends of the surfaces. A parametric study was conducted in which participants were asked to rate the difference in brightness between the parts of the background inside and outside a virtual circle formed by disks with different luminance ramps. The results show that mean ratings of brightness depended on the luminance of the background, the luminance range of ramps, and the kind of ramp. Discussion of these results with reference to other brightness illusions (assimilation, neon color spreading, anomalous surfaces, visual phantoms, grating induction, and the glare effect) shows that t hephantom illumination illusion derives from processes producing the perception of ambient illumination.     

Visual impressions of interactions between objects when the causal object does not move

Stimuli were presented that consisted of a stationary row of black-bordered white rectangles. As observers watched, each rectangle in turn from left to right changed from white to black. The final rectangle did not change colour but moved off from left to right. The sequential colour change suggested motion from left to right, and observers reliably reported a visual impression that this illusory motion kicked or bumped the last rectangle, thereby making it move. The impression was stronger when the sequential colour change was faster, but was not significantly affected by the number of the rectangles in the row (ranging from 2 to 8). These results support the conclusion that neither contact nor motion of a causal object is necessary for a visual impression of causality to occur.     

Is the acquisition of basic-colour terms in young children constrained?

We investigated whether the learning of colour terms in childhood is constrained by a developmental order of acquisition as predicted by Berlin and Kay [1969 Basic Color Terms (Berkeley, CA: University of California Press)]. Forty-three children, aged between 2 and 5 years and grouped according to language ability, were given two tasks testing colour conceptualisation. Colour comprehension was assessed in a spoken-word-to-colour-matching task in which a target colour was presented in conjunction with two distractor colours. Colour naming was measured in an explicit naming task in which colours were presented individually for oral naming. Results showed that children's knowledge of basic-colour terms varied across tasks and language age, providing little support for a systematic developmental order. In addition, we found only limited support for an advantage for the conceptualisation of primary (red, green, blue, yellow, black, white) compared to non-primary colour terms across tasks and language age. Instead, our data suggest that children acquire reliable knowledge of nine basic colours within a 3-month period (35.6 to 39.5 months) after which there is a considerable lag of up to 9 months before accurate knowledge of the final two colours (brown and grey) is acquired. We propose that children acquire colour term knowledge in two distinct time frames that reflect the establishment of, first, the exterior (yellow, blue, black, green, white, pink, orange, red, and purple) and, second, the interior structure (brown and grey) of conceptual colour space. These results fail to provide significant support for the order predicted by Berlin and Kay, and suggest, instead, that the development of colour term knowledge is largely unconstrained.