Illusory occluding contours and surface formation by depth propagation.

A novel kind of depth-spreading effect which should be distinguished in various aspects from the known interpolation, averaging, or 'filling-in' phenomena is reported. The demonstrations and experiments suggest that depth from an uncrossed disparity can be extrapolated from, not just interpolated between, illusory or real contours to form perceptually a background surface. In addition, the form of the illusory contour itself could be drastically changed in configuration and sharpness, contingently with perceptual background-surface formation. No such effects of surface and contour formation were observed in the crossed disparity case. Because the illusory contours were enhanced and perceived as illusory 'occluding contours', these effects may be closely related to the 'occlusion constraints' in the real world.     

Vehicle-representationalism and hallucination

This paper is a new defense of the view that visual hallucinations lack content. The claim is that visual hallucinations are illusory not because their content is nonveridical, but rather because they seem to represent when they fail to represent anything in the first place. What accounts for the phenomenal character of visual experiences is not the content itself (content-representationalism), but rather the vehicle of content (vehicle-representationalism), that is, not the properties represented by visual experience, but rather the relational properties of experience (or of the brain) of representing singular contents, namely particular instantiations of properties. I argue that the Russellian particular-involving proposition is the only appropriate model for the representational content of visual experience and hence that visual hallucinations are just like failed demonstrations.

     

Illusory contours and spatial judgment

We investigated whether, in the human visual system, the mechanisms responsible for relative location judgments are the same when those judgments are made in the context of illusory contours and in the context of mentally joining two points. We asked subjects to align a dot with the oblique contour of an illusory surface or to align a dot with two markers at an oblique orientation. The systematic errors differed in direction for these two conditions. All the systematic errors were orientation dependent. The errors in aligning a dot with an illusory contour seem to be related to the asymmetrical shape of the single objects, which are able to induce an illusory contour, as well as figure-ground segregation.     

The role of early visual input in the development of contour interpolation: the case of subjective contours

We tested the effect of early monocular and binocular deprivation of normal visual input on the development of contour interpolation. Patients deprived from birth by dense central cataracts in one or both eyes, and age‐matched controls, discriminated between fat and thin shapes formed by either illusory or luminance‐defined contours. Thresholds indicated the minimum amount of curvature (the fatness or thinness) required for discrimination of the illusory shape, providing a measure of the precision of interpolation. The results show that individuals deprived of visual input in one eye, but not those deprived in both eyes, later show deficits in perceptual interpolation. The deficits were shown mostly for weakly supported contours in which interpolation of contours between the inducers was over a large distance relative to the size of the inducers. Deficits shown for the unilateral but not for the bilateral patients point to the detrimental effect of unequal competition between the eyes for cortical connections on the later development of the mechanisms underlying contour interpolation.     

错觉轮廓的适应效应

错觉轮廓反映知觉的主动建构过程, 考察其是否存在适应效应有助于理解视觉系统反馈调节的特性。我们采用Kanizsa这种典型的错觉轮廓来研究其适应过程, 结果发现：Kanizsa错觉轮廓具有适应效应, 并且这种适应主要是由主观形成的整体轮廓造成的, 而不是由Pac-Man上的线条引起的。表明依赖于高级视觉皮层反馈调节的主观建构过程和自下而上的神经元信息一样, 会随呈现时间的增加, 神经活动减弱, 体现为适应效应。     

Rolling perception without rolling motion

The texture of a rolling circle depicts the translational and rotational components of its motion. In the case of a homogeneous circle, however, visual cues to the rotational component of motion are absent. To examine how the visual system resolves undetermined motion cues, optically neutral circles were displaced so that changes in their orientation were invisible. Contextual cues systematically triggered the perception of illusory rotation, suggesting that the visual system uses contextual cues along with intrinsic surface cues to compute percepts of rolling objects. This might also explain why people rarely experience the perception of ambiguous motion.     

The effects of curvature on the grid illusions

Grid illusions, including the Hermann grid and scintillating grid (in which light disks are superimposed upon the grid intersections), are diminished by curving the alleys that limn the repeating pattern. Curvature might either disrupt the processes that induce the illusion, or simply make the illusory effects harder to see. To determine which mechanism might be invoked, we examined the effects of curving the alleys upon the vanishing-disk illusion, a phenomenon in which a single disk in a grid intersection is rendered less detectable. This illusion is of reduced visibility, rather than generating an illusory apparition as in the Hermann grid or scintillating grid. Thus, inhibition of illusory influence would enhance disk visibility, while a general reduction of visibility would render disks even harder to detect. We find that thresholds for both scintillation and the disk itself increase in a graded manner with increased curvature. Measuring the effect of curvature upon the vanishing disk with traditional forced-choice staircase methods demonstrates that the effect of curvature is upon detection, not subjective criterion. Furthermore, disks that are easy to detect within a rectilinear grid are more difficult to detect when the alleys are curved. Thus, curvature of the alleys induces a general tendency to inhibit the visibility of features, and is not specifically a repression of illusory effects.     

Apparent motion of subjective surfaces

Apparent motion of an illusory surface was produced by presenting two spatially separated illusory squares in an appropriately timed sequence. Control experiments showed that the effect arose from the illusory contours themselves and not from motion of the cut sectors on the discs. When a template of this movie was superimposed on 'wallpaper' composed of a regular matrix of spots, the spots appeared to move with the illusory surface even though they were physically stationary. This effect ('motion capture') suggests that the motion of certain salient features in the visual field gets spontaneously attributed to even static elements in the vicinity.     

A double dissociation between action and perception in the context of visual illusions: opposite effects of real and illusory size

The idea that there are two distinct cortical visual pathways, a dorsal action stream and a ventral perception stream, is supported by neuroimaging and neuropsychological evidence. Yet there is an ongoing debate as to whether or not the action system is resistant to pictorial illusions in healthy participants. In the present study, we disentangled the effects of real and illusory object size on action and perception by pitting real size against illusory size. In our task, two objects that differed slightly in length were placed within a version of the Ponzo illusion. Even though participants erroneously perceived the physically longer object as the shorter one (or vice versa), their grasping was remarkably tuned to the real size difference between the objects. These results provide the first demonstration of a double dissociation between action and perception in the context of visual illusions and together with previous findings converge on the idea that visually guided action and visual perception make use of different metrics and frames of reference.     

Infants’ perception of curved illusory contour with motion

Recently, Masuda et al. (submitted for publication) showed that adults perceive moving rigid or nonrigid motion from illusory contour with neon color spreading in which the inducer has pendular motion with or without phase difference. In Experiment 1, we used the preferential looking method to investigate whether 3–8-month-old infants can discriminate illusory and non-illusory contour figures, and found that the 7–8-month-old, but not the 3–6-month-old, infants showed significant preference for illusory contour with phase difference. In Experiment 2, we tested the validity of the visual stimuli in the present study, and whether infants could detect illusory contour from the current neon color spreading figures. The results showed that all infants might detect illusory contour figure with neon color spreading figures. The results of Experiments 1 and 2 suggest that 7–8-month-old infants potentially perceive illusory contour from the visual stimulus with phase-different movement of inducers, which elicits the perception of nonrigid dynamic subjective contour in adults.     

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.     

The interpolation of object and surface structure

One of the main theoretical challenges of vision science is to explain how the visual system interpolates missing structure. Two forms of visual completion have been distinguished on the basis of the phenomenological states that they induce. Modal completion refers to the formation of visible surfaces and/or contours in image regions where these properties are not specified locally. Amodal completion refers to the perceived unity of objects that are partially obscured by occluding surfaces. Although these two forms of completion elicit very different phenomenological states, it has been argued that a common mechanism underlies modal and amodal boundary and surface interpolation (the "identity hypothesis"; Kellman & Shipley, 1991; Kellman, 2001). Here, we provide new data, demonstrations, and theoretical principles that challenge this view. We show that modal boundary and surface completion processes exhibit a strong dependence on the prevailing luminance relationships of a scene, whereas amodal completion processes do not. We also demonstrate that the shape of interpolated contours can change when a figure undergoes a transition from a modal to an amodal appearance, in direct contrast to the identity hypothesis. We argue that these and previous results demonstrate that modal and amodal completion do not result from a common interpolation mechanism.     

Early development of object unity: evidence for perceptual completion in newborns

The present study aimed to investigate whether perceptual completion is available at birth, in the absence of any visual experience. An extremely underspecified kinetic visual display composed of four spatially separated fragments arranged to give rise to an illusory rectangle that occluded a vertical rod (illusory condition) or rotated so as not to elicit perceptual grouping (control condition) was constructed. After newborns' ability to detect the particular kind of rod-and-box display used in the present study had been probed (Experiment 1), they were habituated to the illusory rod-and-box display (Experiment 2), to the control display that did not contain illusory contours (Experiment 3), and to a standard real rod-and-box display akin to those used in previous infants' studies (Experiment 4). Newborns perceived the rod as a connected unit either in the illusory condition (Experiment 2) or in the real condition (Experiment 4), as documented by a preference for a broken rod over a complete rod during the test phase, but not when the occluder was absent (Experiment 3). In all experiments newborns showed no preference between the two test stimuli (control condition), avoiding the possibility that newborns have a spontaneous preference for one test display over the other. Overall, the results of the present study provide evidence that the ability to achieve object unity (1) stems from intrinsic properties of the human perceptual system and (2) is operative from birth, given the right conditions.     

Overshoot of curvature in visual apparent motion

If a curved line and a straight line are presented briefly, one above the other, in sequence to the eye, then, under appropriate conditions, visual apparent motion is obtained. Subjects report that the illusory figure moving and changing from the curved line to the straight line appears to overshoot the latter, gaining a small curvature in the opposite sense. Three experiments are described. In the first, the magnitude of this apparent curvature was quantified as a function of the delay between the onsets of the curved line and straight line (the stimulus onset asynchrony, SOA). It is shown that overshoot in curvature cannot be attributed to inappropriate patterns of eye fixations. In the second experiment, the stimulus configuration was modified to reveal the contribution to apparent curvature of classical curvature-contrast effects. Curvature overshoot due to apparent motion alone was thus estimated as a function of SOA. In the third experiment, an analogous position overshoot was measured for apparent motion elicited by two brief sequentially presented parallel line segments. It is argued that a combination of such position overshoots cannot explain curvature overshoot. Two schemes of a more general kind that might be used to interpret curvature overshoot are then outlined. One scheme is based on a neural-net model of apparent motion, and the other on a functional model of apparent motion that operates by laws analogous to those governing real physical motion.     

Surface geometry influences the shape of illusory contours

Geometric and neural models of illusory-contour (IC) synthesis currently use only local contour geometry to derive the shape of ICs. Work on the visual representation of shape, by contrast, points to the importance of both contour and surface geometry. We investigated the influence of surface-based geometric factors on IC shape. The local geometry of inducing-contour pairs was equated in stereoscopic IC displays, and the shape of the enclosed surface was varied by manipulating sign of curvature, cross-axial shape width, and medial-axis geometry. IC shapes were measured using a parametric shape-adjustment task (Experiment 1) and a dot-adjustment task (Experiment 2). Both methods revealed large influences of surface geometry. ICs enclosing locally concave regions were perceived to be systematically more angular than those enclosing locally convex regions. Importantly, the influence of sign of curvature was modulated significantly by shape width and medial-axis geometry: IC shape difference between convex and concave inducers was greater for narrow shapes than wider ones, and greater for shapes with straight axis and symmetric contours (diamond versus bowtie), than those with curved axis and parallel contours (bent tubes). Even at the level of illusory "contours," there is a contribution of region-based geometry which is sensitive to nonlocal shape properties involving medial geometry and part decomposition. Models of IC synthesis must incorporate the role of nonlocal region-based geometric factors in a way that parallels their role in organizing visual shape representation more generally.     

Rapid activation of motor responses by illusory contours

Whereas physiological studies indicate that illusory contours (ICs) are signaled in early visual areas at short latencies, behavioral studies are divided as to whether IC processing can proceed in a fast, automatic, bottom-up manner or whether it requires extensive top-down intracortical feedback or even awareness and cognition. Here, we employ a response priming paradigm to assess two measures of IC processing using identical stimuli: response priming by ICs, which can occur independently of visual awareness, and a measure of visual awareness of the ICs. In three experiments, participants responded to the orientation of illusory and real-contour targets preceded by illusory and real-contour primes at stimulus-onset asynchronies from 35 to 106 ms. Both illusory and real-contour targets were strongly primed by ICs, and this effect was independent of prime visibility. The effect was fully present in the fastest responses and cannot be explained by responses to stimulus features other than the ICs. Results indicate that ICs, regardless of whether they are consciously perceived, activate fast motor responses, indicating that they are processed without time-consuming intracortical feedback. We conclude that conflicting studies were based on qualitatively different measures of IC processing, some depending on visual awareness and others independent of it. (PsycINFO Database Record (c) 2012 APA, all rights reserved).     

When do letter features migrate? A boundary condition for feature-integration theory

Feature-integration theory postulates that a lapse of attention will allow letter features to change position and to recombine as illusory conjunctions (Treisman & Paterson, 1984). To study such errors, we used a set of uppercase letters known to yield illusory conjunctions in each of three tasks. The first, a bar-probe task, showed whole-character mislocations but not errors based on feature migration and recombination. The second, a two-alternative forced-choice detection task, allowed subjects to focus on the presence or absence of subletter features and showed illusory conjunctions based on feature migration and recombination. The third was also a two-alternative forced-choice detection task, but we manipulated the subjects' knowledge of the shape of the stimuli: In the case-certain condition, the stimuli were always in uppercase, but in the case-uncertain condition, the stimuli could appear in either upper- or lowercase. Subjects in the case-certain condition produced illusory conjunctions based on feature recombination, whereas subjects in the case-uncertain condition did not. The results suggest that when subjects can view the stimuli as feature groups, letter features regroup as illusory conjunctions; when subjects encode the stimuli as letters, whole items may be mislocated, but subletter features are not. Thus, illusory conjunctions reflect the subject's processing strategy, rather than the architecture of the visual system.     

Development of illusory-contour perception in infants

We investigated whether infants from 8-22 weeks of age were sensitive to the illusory contour created by aligned line terminators. Previous reports of illusory-contour detection in infants under 4 months old could be due to infants' preference for the presence of terminators rather than their configuration. We generated preferential-looking stimuli containing sinusoidal lines whose oscillating, abutting terminators give a strong illusory contour in adult perception. Our experiments demonstrated a preference in infants 8 weeks old and above for an oscillating illusory contour compared with a stimulus containing equal terminator density and movement. Control experiments excluded local line density, or attention to alignment in general, as the basis for this result. In the youngest age group (8-10 weeks) stimulus velocity appears to be critical in determining the visibility of illusory contours, which is consistent with other data on motion processing at this age. We conclude that, by 2 months of age, the infant's visual system contains the nonlinear mechanisms necessary to extract an illusory contour from aligned terminators.     

The effect of a flashing visual stimulus on the auditory continuity illusion

The effect of a visual stimulus on the auditory continuity illusion was examined. Observers judged whether a tone that was repeatedly alternated with a band-pass noise was continuous or discontinuous. In most observers, a transient visual stimulus that was synchronized with the onset of the noise increased the limit of illusory continuity in terms of maximum noise duration and maximum tone level. The smaller the asynchrony between the noise onset and the visual stimulus onset, the larger the visual effect on this illusion. On the other hand, detection of a tone added to the noise was not enhanced by the visual stimulus. These results cannot be fully explained by the conventional theory that illusory continuity is created by the decomposition of peripheral excitation produced by the occluding sound.     

Contextual illusions reveal the limit of unconscious visual processing

The perception of even the most elementary features of the visual environment depends strongly on their spatial context. In the study reported here, we asked at what level of abstraction such effects require conscious processing of the context. We compared two visual illusions that alter subjective judgments of brightness: the simultaneous brightness contrast illusion, in which two circles of identical physical brightness appear different because of different surround luminance, and the Kanizsa triangle illusion, which occurs when the visual system extrapolates a surface without actual physical stimulation. We used a novel interocular masking technique that allowed us to selectively render only the context invisible. Simultaneous brightness contrast persisted even when the surround was masked from awareness. In contrast, participants did not experience illusory contours when the inducing context was masked. Our findings show that invisible context is resolvable by low-level processes involved in surface-brightness perception, but not by high-level processes that assign surface borders through perceptual completion.