Infants' perception of transparency

Four- and 7-month-old infants' perception of transparency was investigated with computer-generated achromatic or color displays depicting a semitransparent box occluding the center of a rod. Following habituation, infants viewed test displays consisting of either a two-color rod (corresponding to the habituation display's proximal characteristics) or a solid rod (corresponding to the distal characteristics of the event depicted by the habituation display). Looking-time results from 4-month-olds suggested perception of transparency in color displays but not in an achromatic display. An additional condition indicated that transparency perception may rely on the visibility of background texture through the transparent surface. Seven-month-olds, in contrast, provided some evidence of transparency perception in the achromatic display. Implications for the development of infants' responses to object properties and perceptual segregation are discussed.     

Flank transparency: transparent filters seen in dynamic two-color displays

Flank transparency is the perception of a colored transparent filter evoked by apparent-motion displays containing as few as two colors. Displays of flank transparency contain a random array of line segments placed on a uniform background. Small flanks are added to the line segments if the segments fall in the interior of a moving virtual shape, such as a virtual disk. This leads to the perception of a colored transparent disk with well-defined boundaries moving over the array of lines. Current qualitative and quantitative models of luminance and color conditions for perceptual transparency do not account for flank transparency as they require displays containing at least three different colors.     

At first glance, transparency enhances assimilation

We investigated the role of transparency, perceptual grouping, and presentation time on perceived lightness. Both transparency and perceptual grouping have been found to result in assimilation effects, but only for ambiguous stimulus displays and with specific attentional instructions. By varying the presentation times of displays with two partly overlapping transparent E-shaped objects, we measured assimilation in unambiguous stimulus displays and without specific attentional instructions. The task was to judge which of two simultaneously presented E-shaped objects was darker. With unrestrained presentation times, if a transparency interpretation was possible, assimilation was not found. Inhibiting a transparency interpretation by occluding the local junctions between the two E-shaped objects, did lead to assimilation. With short presentation times, if a transparency interpretation was possible, assimilation was now also found. Thus, we conclude that, although transparency appears to enhance assimilation, with unambiguous stimulus displays and without specific attentional instructions, perceptual grouping is more important for assimilation to occur.     

Competition between color salience and perceptual load during visual selection can be biased by top-down set

Visual salience and perceptual load may both influence the efficiency of visual selection. Recently, Gibson and Bryant (2008) showed that perceptual load can dominate color salience in a distractor interference paradigm. The purpose of the present study was to investigate the possibility that knowledge (of color or load) may modulate the relative operation of these two mechanisms. Consistent with previous findings, perceptual load dominated color salience, but only in certain contexts in which display load was mixed and high-load displays preceded other high-load displays. More important, color salience dominated perceptual load in other contexts in which display load was mixed and low-load displays preceded high-load displays. In addition, color salience also dominated perceptual load in contexts in which display load was fixed and advance knowledge of load was available. Altogether, the present findings suggest that the competition between color salience and perceptual load can vary as a function of task context, thereby supporting top-down accounts, although the precise aspect of task context remains to be identified.     

Transparency: relation to depth, subjective contours, luminance, and neon color spreading

The perception of transparency is highly dependent on luminance and perceived depth. An image region is seen as transparent if it is of intermediate luminance relative to adjacent image regions, and if it is perceived in front of another region and has a boundary which provides information that an object is visible through this region. Yet, transparency is not just the passive end-product of these required conditions. If perceived transparency is triggered, a number of seemingly more elemental perceptual primitives such as color, contour, and depth can be radically altered. Thus, with the perception of transparency, neon color spreading becomes apparent, depth changes, stereoscopic depth capture can be eliminated, and otherwise robust subjective contours can be abolished. In addition, we show that transparency is not coupled strongly to real-world chromatic constraints since combinations of luminance and color which would be unlikely to arise in real-world scenes still give rise to the perception of transparency. Rather than seeing transparency as a perceptual end-point, determined by seemingly more primitive processes, we interpret perceived transparency as much a 'cause', as an 'effect'. We speculate that the anatomical substrate for such mutual interaction may lie in cortical feed-forward connections which maintain modular segregation and cortical feedback connections which do not.     

The Relationship Between Visual Illusion and Aesthetic Preference – an Attempt to Unify Experimental Phenomenology and Empirical Aesthetics

Experimental phenomenology has demonstrated that perception is much richer than stimulus. As is seen in color perception, one and the same stimulus provides more than several modes of appearance or perceptual dimensions. Similarly, there are various perceptual dimensions in form perception. Even a simple geometrical figure inducing visual illusion gives not only perceptual impressions of size, shape, slant, depth, and orientation, but also affective or aesthetic impressions. The present study reviews our experimental phenomenological work on visual illusion and experimental aesthetics, and examines how aesthetic preference is influenced by stimulus factors determining visual illusions including anomalous surface and transparency as well as geometrical illusion. Along with line figures producing geometrical illusions, illusory surface figures inducing neon color spreading and transparency effects were used as test patterns. Participants made both of psychophysical judgments and of aesthetic judgments for the same test pattern. Both of geometrical illusions and aesthetic preferences were found to change similarly as a function of stimulus variables such as the number of filling lines and the size ratio of the inner and outer figural components. Also, following specific stimulus variables such as lightness contrast ratio and spatial interval between inducing figural elements (so called ``packmen''), strong effects of color spreading and transparency were accompanied with strong preferences. It seems that the paradigm to investigate aesthetic phenomena along with perceptual dimensions is useful to bridge the gap between experimental phenomenology and experimental aesthetics.     

A purely temporal transparency mechanism in the visual system.

I report evidence for a purely temporal perceptual transparency mechanism. Rapid alternation of two images in the same location can result in the simultaneous experience of both, accompanied by a sense of transparency. This is true even when the sum of the two images does not appear transparent, which suggests that the percept is not mediated by the static transparency processes. At slow rates, alternating gratings were experienced as successive. As the rate was increased, by 8 Hz observers experienced the gratings as simultaneous. The rapidly alternating gratings are apparently processed separately before being combined for awareness by a process that integrates over about 120 ms. A final experiment tested whether the common presentation time of different parts of an image in alternation with another would cause the parts to perceptually bind. Observers did not distinguish between a rapidly alternating intact grating display and one in which halves of the display were exchanged in time. In other words, temporal binding across space did not occur. The temporal transparency phenomenon, in addition to informing theories of transparency and the dynamics of visual processing, may also be useful for the creation of transparent displays for electronic devices.     

Constructing surfaces and contours in displays of color from motion: the role of nearest neighbors and maximal disks

Color-from-motion displays consist of a sparse array of dots which never move but change color according to various algorithms. Yet such displays can trigger human vision to construct apparent motion of a subjective surface which is uniformly colored and bounded by a subjective contour. We show that the perceptual strength of this construction depends on the density and regularity of dot placement. We studied three objective measures of density and regularity: nearest-neighbor distance, mean of maximal disks, and variance of maximal disks. We found that nearest-neighbor mechanisms alone are inadequate to account for the perceptual strength of the subjective surfaces and contours. Mechanisms sensitive to areal gaps provide a more adequate account.     

Associative grouping: Perceptual grouping of shapes by association

Perceptual grouping is usually defined by principles that associate distinct elements by virtue of image properties, such as proximity, similarity, and occurrence within common regions. What role does learning play in forming a perceptual group? This study provides evidence that learning of shape associations leads to perceptual grouping. Subjects were repeatedly exposed to pairs of unique shapes that co-occurred within a common region. The common region cue was later removed in displays composed of these shapes, and the subjects searched the display for two adjacent shapes of the same color. The subjects were faster at locating the color repetition when the adjacent shapes with the same color came from the same trained groups than when they were composed of two shapes from different trained groups. The effects were perceptual in nature: Learned pairings produced spatial distortions similar to those observed for groups defined by perceptual similarity. A residual grouping effect was observed even when the shapes in the trained group switched their relative positions but was eliminated when each shape was inverted. These results indicate that statistical co-occurrence with explicit grouping cues may form an important component of perceptual organization, determining perceived scene structure solely on the basis of past experience.     

Revisitation of the luminance conditions for the occurrence of the achromatic neon color spreading illusion

This paper develops the idea (Bressan, 1993) that neon spreading derives from the perceptual scissioning of ordinary assimilation color, a process identical to that occurring with nonillusory colors in phenomenal transparency. It is commonly held that the critical elements in achromatic neon spreading patterns must be of luminance intermediate between that of the embedding lines and of the background. The interpretation of neon spreading on the basis of color scissioning, however, predicts that neon spreading should also be observed for different luminance hierarchies, provided that these are compatible with transparency. This prediction found experimental support in the present work. The results suggest that (1) the widespread notion that chromatic and achromatic neon spreading must be mediated by separate mechanisms is unwarranted; (2) the widespread notion that color spreading in ordinary assimilation patterns and color spreading in neon patterns must be mediated by separate mechanisms is unwarranted; and (3) other than pointing to the way in which the overall organization of a scene affects the mode of color appearance, the neon spreading effect may not convey any extra theoretical relevance.     

Test of a convergence model for color transparency perception

Models of color transparency suggest that a region in which colors of surfaces converge in color space will appear transparent. The convergence is described by a transparency parameter alpha and a target of convergence. To test such models psychophysically, observers were presented a display with four colored areas. The colors of three of the areas were chosen in advance by the experimenter. The task of the observer was to choose the color of the fourth area to make a central region appear transparent. Settings for the fourth color were collected for a total of twenty-four color combinations chosen from three planes in color space. Observers' settings agreed well with the model, which predicts that choices for the fourth color lie along a line segment in color space that is parameterized by alpha. The results suggest further that color discriminability and color opponency also influence transparency judgment.     

Toward a perceptual theory of transparency

Theories of perceptual transparency have typically been developed within the context of a physical model that generates the percept of transparency (F. Metelli's episcotister model, 1974b). Here 2 fundamental questions are investigated: (a) When does the visual system initiate the percept of one surface seen through another? (b) How does it assign surface properties to a transparent layer? Results reveal systematic deviations from the predictions of Metelli's model, both for initiating image decomposition into multiple surfaces and for assigning surface attributes. Specifically, results demonstrate that the visual system uses Michelson contrast as a critical image variable to initiate percepts of transparency and to assign transmittance to transparent surfaces. Findings are discussed in relation to previous theories of transparency, lightness, brightness, and contrast-contrast.     

Perceptual transparency in 3- to 4-month-old infants

We examined perceptual transparency in infants. In a previous study, Johnson and Aslin (2000 Developmental Psychology 36 808 - 816) found that 4-month-olds could perceive transparency in a moving chromatic display, but not in an achromatic display. In this study, we further examined perceptual transparency in infants using a static achromatic display. Considering the development of figural organisation and contrast sensitivity, we assumed that 3- to 4-month-olds would perceive transparency even in a static achromatic display. We created a transparency and a non-transparent display composed of a partially overlapping circle and square, by switching the colours. Infants aged 3 to 4 months (n = 24) were familiarised with the transparency display (experiment 1) or with the non-transparent display (experiment 2). Then, they were confronted with a uniform colour and a two-colour figure. Infants showed novelty preference for the two-colour figure after they had been familiarised with the transparency display (experiment 1), but not after they had been familiarised with the non-transparent display (experiment 2). These results suggest that 3- to 4-month-old infants can perceive transparency in a static achromatic display.     

The repetition discrimination task: an objective method for studying perceptual grouping

Five experiments are reported that demonstrate the use of the repetition discrimination task (RDT) to study perceptual grouping effects objectively and quantitatively. Experiments 1 and 3 validate the method by measuring grouping based on proximity, color similarity, common region, and element connectedness. Experiment 2 compares the RDT effects for proximity grouping to explicit subjective ratings of grouping strength in identical displays. Experiments 4 and 5 investigate the effects of size and orientation of surrounding ovals in displays in which competing organizations are present. In each case, the RDT produces clear, consistent patterns of response times that are consistent with predictions based on grouping. It thus represents an objective method for studying the full range of grouping phenomena originally described by Wertheimer.     

Perceptual continuation and depth in visual phantoms can be explained by perceptual transparency

We try to explain perceptual continuation and depth in the visual-phantom illusion in terms of perceptual transparency. Perceptual continuation of inducing gratings across the occluder in stationary phantoms could be explained with unique transparency, a notion proposed by Anderson (1997 Perception 26 419-453). This view is consistent with a number of previous reports including that of McCourt (1994 Vision Research 34 1609-1617) who criticized the stationary phantom illusion from the viewpoint of his counterphase lightness induction or grating induction, which might involve invalid transparency. Here we confirm that the photopic phantom illusion (Kitaoka et al, 1999 Perception 28 825-834) really gives in-phase lightness induction and involves bistable transparency. It is thus suggested that perceptual continuation and depth in the visual-phantom illusion depend on perceptual transparency.     

Role of perceptual organization while attending in depth

Seven experiments were conducted in order to explore the conditions under which visual attention can be allocated in depth. In each experiment, observers were cued to the most likely target location in stereoscopic depth displays, and targets could appear in either the cued location or in another location. In Experiments 1 and 2, we show that previous failures to observe effects of cuing in depth may have depended on the specific timing characteristics of the displays. In Experiments 3, 4, and 5, we eliminated the hypothesis, suggested by Experiments 1 and 2, that in order to allocate attention in depth, attention must be allocated to a specific object token. Experiment 6 provides evidence that, in the absence of other organizing information (e.g., color), attention can be allocated in depth on the basis of the surface information available in the display. Finally, in Experiment 7, we demonstrate that, although sufficient, surface information is not necessary for the allocation of attention; color supported the allocation of attention across multiple items that failed to fall on a single coherent surface in depth. Together, these findings suggest that attention in depth, like attention in two-dimensional displays, is determined by the perceptual organization of the display.     

Low-Level Properties in Perceptual Experience

Whether perceptual experience represents high-level properties like causation and natural-kind in virtue of its phenomenology is an open question in philosophy of mind. While the question of high-level properties has sparked disagreement, there is widespread agreement that the sensory phenomenology of perceptual experience presents us with low-level properties like shape and color. This paper argues that the relationship between the sensory character of experience and the low-level properties represented therein is more complex than most assume. Careful consideration of mundane examples, like looking at a coin from an oblique angle, show that the low-level properties represented in experience do not necessarily figure in the sensory character of the experience. Furthermore, the sensible properties invoked when characterizing the sensory character of a perceptual experience are not necessarily included in the sensible properties represented in a perceptual experience. On this basis it is argued that perceptual experience has a disunified metaphysics, consisting in distinct sensory and cognitive components. The account is developed in relation to existing unified and disunified accounts, and discussed in terms of its implications for cognitive penetration, the reliability of introspection, the transparency of experience, and cognitive phenomenology.     

Achieving Transparency: An Argument For Enactivism

The transparency of perceptual experience has been invoked in support of many views about perception. I argue that it supports a form of enactivism—the view that capacities for perceptual experience and for intentional agency are essentially interdependent. I clarify the perceptual phenomenon at issue, and argue that enactivists should expect to find a parallel instance of transparency in our agentive experience, and that the two forms of transparency are constitutively interdependent (Section 1). I then argue that i) we do indeed find such parallels: the way in which an action is directed towards its goal through our bodily movements parallels the way in which an experience is directed towards its object through our perceptual sensation (Section 2), and ii) reflecting on sensorimotor skills shows why the two instances of transparency are constitutively interdependent (Section 3). Section 4 gives reasons for generalizing beyond the cases considered so far by applying the enactive view to Kohler's landmark studies of perceptual adaptation. The final section clarifies the form of enactivism to which the previous sections point. The view that emerges is one whereby our perceptual and practical skills are interrelated aspects of a single capacity to have one's mind intentionally directed upon the world. The transparency of experience, on this view, is achieved in virtue of our capacities as agents as much as it is given in virtue of our capacities as perceivers.     

Visual detection and perceptual independence: Assessing color and form

Visual stimuli are multidimensional. One important perceptual problem is to determine how the dimensions are combined. One important aspect of dimensional combination is whether the dimensions are perceptually independent or perceptually correlated. A new task is presented—the visual detection task—that directly assesses the degree of perceptual correlation between any two dimensions. Two experiments were conducted that assess the degree of perceptual correlation between form and color during the early stages of perceptual analysis. The results show that form and color are not perceptually independent. In addition, the pattern of perceptual correlation found indicates that form and color are not processed independently. The pattern of results constrains all models of early vision. A model of early vision based on active signal modulation is proposed.