White's effect: removing the junctions but preserving the strength of the illusion

White's effect (also known as the Munker White effect) is a lightness illusion in which, contrary to expectations based on simultaneous contrast and Wallach's rule, a gray rectangle predominantly surrounded by white appears lighter than an identical rectangle that is mainly surrounded by black. The illusion is often explained in terms of T-junctions that are formed by the three-way intersection of the gray rectangle, a black stripe, and a white stripe. I present a circular variant of White's effect in which all the junctions have been removed without significantly affecting the strength of the illusion, suggesting that junctions are not an important consideration in all versions of White's effect.     

Stereoscopic depth and the occlusion illusion

In the occlusion illusion, the visible portion of a partly occluded object appears larger than a physically identical nonoccluded region. Stereoscopic displays allowed for a direct test of the apparent-distance hypothesis. In Experiments 1A and 1B, we measured both the perceived size and the perceived depth of partly occluded targets when the binocular disparity of both targets and occluders was varied. Stereoscopic occlusion greatly increased perceived target size but not perceived target distance. A reduced illusion was still present when the target was stereoscopically in front of the abutting rectangle, however. Experiments 2A and 2B showed similar results, even when the occluding figures were illusory rectangles that formed no explicit T-junctions. Experiment 3 showed that an unexpected negative size illusion on control trials was primarily due to adaptation to the occlusion illusion on other trials. The present findings eliminate apparent-distance explanations of the occlusion illusion but are consistent with other hypotheses, such as partial modal completion and selective dimensional expansion.     

Phantom arcs: now you see them..

A new visual illusion is reported and illustrated. The illusion, dubbed 'phantom arcs', survives manipulations of contrast, scale, and hue. The arcs can be seen in printed versions as well as in images displayed on CRT or LCD monitors. Data collected in an undergraduate perception class reveal that the illusion can be seen by untrained observers.     

Interaction space of Müller-Lyer with filled-unfilled illusion: An explanation of Müller-Lyer asymmetry

The filled-unfilled space illusion was investigated as a possible explanation for the asymmetry (difference in strength) between tails-out and tails-in versions of the Müller -Lyer illusion. Previous work has shown that removal of the horizontal shaft makes both configurations look shorter, but affects them unequally and only partially reduces the asymmetry. In two experiments, illusion strength was varied by use of either different tail lengths or single- vs. double-ended figures. Subjects used method of adjustment with stimuli presented by computer. When the Müller -Lyer was sufficiently weak, shaft removal had equal effects on both tails-in and tails-out configurations, but less effect on plain lines. This produced a reversal of the usual asymmetry, that is, tails-in was stronger than tails-out. It is concluded that the asymmetry is caused by the filled-unfilled illusion. This may require reassessment of the view that the two Müller -Lyer versions are different illusions.     

Illusions of bent line

A recent paper offered an explanation of the Poggendorf illusion, assuming that it results from a failure of the visual system to make a perfect resolution of acute angles. Variations of the illusion were drawn eliminating all acute angles, and the illusion was shown to remain in full strength. A variation of the figure preserving the acute angle was drawn, and the illusion was found to reverse in direction. Several theoretical interpretations are considered but none accepted, and it is concluded that the illusion remains unexplained.     

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.     

人际互动中的被洞悉错觉

被洞悉错觉是人际互动中的一种认知偏差。文章回顾了被洞悉错觉在不同领域存在的证据;介绍了被洞悉错觉在旁观者冷漠、刑事审讯、社交障碍、自我泄露感和亲密关系中的相关应用;分析了锚定及其调节效应、知识之祸、自我关注和朴素实在论对被洞悉错觉的理论解释;讨论了以往研究在对象、方法及跨文化比较方面的不足。     

Framing effects and the reversed Müller-Lyer illusion.

The enclosure hypothesis of the reversed Müller-Lyer illusion was examined in three experiments. In Experiment 1, the ingoing- and outgoing-wings forms of the illusion were measured separately, as a function of the size of the gap between the ends of the shaft and the apices of the wings. In Experiments 2 and 3, the effects of a square frame and of complete and amputated versions of a rectangle on the perceived length of an enclosed horizontal line were examined. For all non-Müller-Lyer illusion figures, an inverted U-shaped function describes the relationship between illusion magnitude and the length of the test line. The peak overestimation of the test line's length was obtained when the ratio of total figure length to test line length was about 3:2. Taken together, the results of the three experiments suggest that the reversed Müller-Lyer illusion can be explained within current theoretical frameworks, such as assimilation theory, without recourse to a special factor of enclosure.     

The hollow-face illusion: object-specific knowledge, general assumptions or properties of the stimulus?

The hollow-face illusion, in which a mask appears as a convex face, is a powerful example of binocular depth inversion occurring with a real object under a wide range of viewing conditions. Explanations of the illusion are reviewed and six experiments reported. In experiment 1 the detrimental effect of figural inversion, evidence for the importance of familiarity, was found for other oriented objects. The inversion effect held for masks lit from the side (experiment 2). The illusion was stronger for a mask rotated by 90 degrees lit from its forehead than from its chin, suggesting that familiar patterns of shading enhance the illusion (experiment 2). There were no effects of light source visibility or any left/right asymmetry (experiment 3). In experiments 4-6 we used a 'virtual' hollow face, with illusion strength quantified by the proportion of noise texture needed to eliminate the illusion. Adding characteristic surface colour enhanced the illusion, consistent with the familiar face pigmentation outweighing additional bottom-up cues (experiment 4). There was no difference between perspective and orthographic projection. Photographic negation reduced, but did not eliminate, the illusion, suggesting shading is important but not essential (experiment 5). Absolute depth was not critical, although a shallower mask was given less extreme convexity ratings (experiment 6). We argue that the illusion arises owing to a convexity preference when the raw data have ambiguous interpretations. However, using a familiar object with typical orientation, shading, and pigmentation greatly enhances the effect.     

Attenuating the haptic horizontal—vertical curvature illusion

In a number of experiments, blindfolded subjects traced convex curves whose verticals were equal to their horizontal extent at the base. Overestimation of verticals, as compared with horizontals, was found, indicating the presence of a horizontal-vertical illusion with haptic curves, as well as with visible curves. Experiment 1 showed that the illusion occurred with stimuli in the frontal plane and with stimuli that were flat on the table surface in vision and touch. In the second experiment, the stimuli were rotated, and differences between vision and touch were revealed, with a stronger illusion in touch. The haptic horizontal-vertical illusion was virtually eliminated when the stimuli were bimanually touched using free exploration at the body midline, but a strong illusion was obtained when curves were felt with two index fingers or with a single hand at the midline. Bimanual exploration eliminated the illusion for smaller 2.5- through 10.2-cm stimuli, but a weakened illusion remained for the largest 12.7-cm patterns. The illusion was present when the stimuli were bimanually explored in the left and right hemispace. Thus, the benefits of bimanual exploration derived from the use of the two hands at the body midline combined with free exploration, rather than from bimanual free exploration per se. The results indicate the importance of haptic exploration at the body midline, where the body can serve as a familiar reference metric for size judgments. Alternative interpretations of the results are discussed, including the impact of movement-based heuristics as a causal factor for the illusion. It was suggested that tracing the curve’s peak served to bisect the curve in haptics, because of the change in direction.     

Framing effects and the reversed Müller-Lyer illusion

The enclosure hypothesis of the reversed Müller-Lyer illusion was examined in three experiments. In Experiment 1, the ingoing- and outgoing-wings forms of the illusion were measured separately, as a function of the size of the gap between the ends of the shaft and the apices of the wings. In Experiments 2 and 3, the effects of a square frame and of complete and amputated versions of a rectangle on the perceived length of an enclosed horizontal line were examined, For all non-Müller-Lyer illusion figures, an inverted U-shaped function describes the relationship between illusion magnitude and the length of the test line. The peak overestimation of the test line’s length was obtained when the ratio of total figure length to test line length was about 3:2. Taken together, the results of the three experiments suggest that the reversed Müller-Lyer illusion can be explained within current theoretical frameworks, such as assimilation theory, without recourse to a special factor of enclosure.     

Visual perception in domestic dogs: susceptibility to the Ebbinghaus–Titchener and Delboeuf illusions

Susceptibility to geometrical visual illusions has been tested in a number of non-human animal species, providing important information about how these species perceive their environment. Considering their active role in human lives, visual illusion susceptibility was tested in domestic dogs (Canis familiaris). Using a two-choice simultaneous discrimination paradigm, eight dogs were trained to indicate which of two presented circles appeared largest. These circles were then embedded in three different illusory displays; a classical display of the Ebbinghaus–Titchener illusion; an illusory contour version of the Ebbinghaus–Titchener illusion; and the classical display of the Delboeuf illusion. Significant results were observed in both the classical and illusory contour versions of the Ebbinghaus–Titchener illusion, but not the Delboeuf illusion. However, this susceptibility was reversed from what is typically seen in humans and most mammals. Dogs consistently indicated that the target circle typically appearing larger in humans appeared smaller to them, and that the target circle typically appearing smaller in humans, appeared larger to them. We speculate that these results are best explained by assimilation theory rather than other visual cognitive theories explaining susceptibility to this illusion in humans. In this context, we argue that our findings appear to reflect higher-order conceptual processing in dogs that cannot be explained by accounts restricted to low-level mechanisms of early visual processing.     

The use of realistic and mechanical hands in the rubber hand illusion,and the relationship to hemispheric differences

Embodiment, as measured through the rubber-hand illusion (RHI), depends on the similarity between object to be embodied and part of the body it replaces. We compared a fake hand similar to a real hand, and one matched in size but made of wires (mechanical). Left and right versions were tested to investigate whether the effect of appearance was stronger in the left hand. We found that the mechanical hand induced embodiment, though to a reduced degree relative to the realistic hand (N = 120). Left and right versions of the mechanical hand did not differ in strength of the illusion. However, with the left realistic hand there was a stronger relationship between drift (an objective measure of the illusion) and agreement on the questionnaire (subjective experience). With the mechanical hand, objective and subjective measures were unrelated. We discuss the results in relation to factors that influence the RHI and hemispheric differences.     

Ponzo错觉解释的合理性：倾斜恒常性理论的局限

倾斜恒常性理论是一种新的解释Ponzo错觉的理论,但是似乎存在一些局限。本研究采用调节法通过两个实验考察了四种Ponzo错觉版本在各种条件(视角和水平线段间距)下的错觉量情况,以此来检验倾斜恒常性理论。实验一中,对称Ponzo错觉变异版本在50mm时的错觉量情况和Prinzmetal(2001)的结果相似,但是在85mm和120mm时得到了较多的错觉量,这和倾斜恒常性理论的理论预期不符。实验二对不对称Ponzo错觉的考察得到了和实验一类似的结果,只有50mm时的情形符合倾斜恒常性理论预期。通过以上实验得到水平线间距和视角因素都是产生Ponzo错觉的重要因素,而倾斜恒常性理论过分强调了背景线的倾斜诱导效应,忽略了其他结构因素对Ponzo错觉的影响,所以倾斜恒常性理论具有一定的局限性,不能有效地解释Ponzo错觉的产生机制。     

A comparison of length-matching and length-fractionation measures of Müller-lyer distortions

Two experiments were performed to evaluate the informational equivalence of length-matching (e.g., reproduction) and length-fractionation (e.g., bisection) procedures that are frequently used to quantify geometrical size distortions, such as the Müller-Lyer (M-L) illusion. In Experiment 1, the distortion in the apparent length of a horizontal test line was measured as a function of the angle between it and an abutting inducing line, and in Experiment 2 distortion was measured in the apparent length of the shaft of one-angle versions of the M-L illusion. Both procedures indexed the expansion of the obtuse-angle and the wings-out M-L illusion and the contraction of the acute-angle and the wings-in M-L illusion. However, whereas the reproduction measures indicated substantially greater expansion than contraction distortion, the bisection measures indicated greater contraction distortion. Some possible reasons for this difference, particularly the possibility that the reproduction and bisection procedures are unequally sensitive to the outputs of the mechanisms producing the M-L illusion, are discussed.     

Visual context integration is not fully developed in 4-year-old children

Long-range horizontal interactions supporting contour integration were found to be weaker in children than in adults (Kovács et al, 1999 Proceedings of the National Academy of Sciences of the USA 96 12204-12209). In the present study, integration on a larger scale, between a target and its context was investigated. Contextual modulation of the percept of a local target can be directly measured in the case of geometric illusions. We compared the magnitude of a size contrast illusion (Ebbinghaus illusion or Titchener circles) in children and adults. 4-year-old children and adults performed 2AFC size comparisons between two target disks in the classical Ebbinghaus illusion display and in two other modified versions. We found that the magnitude of the illusion effect was significantly smaller in children than in adults. Our interpretation is that context integration is not fully developed in 4-year-old children. Closer-to-veridical-size estimations by children demonstrate that the perception of the local target is less affected by stimulus context in their case. We suggest that immature cortical connectivity is behind the reduced contextual sensitivity in children.     

Geometrical illusions in solid objects under ordinary viewing conditions.

The Müller-Lyer and Ponzo illusions were obtained under free binocular viewing of three-dimensional objects, and the function relating magnitude of illusion to fin angle, characteristic of converging-line versions of the Müller-Lyer pattern, was closely paralleled by volumetric (three-cone), line-free objects (but not with an erect, planar "walk-through" construction and moving observers). Illusions cannot be dismissed as artifacts of static, impoverished viewing, therefore, but must be explained within any general theory of perception. Perspective explanations have difficulties with such three-dimensional manifestations, and seem completely inapplicable to our further finding that approximately the same amount of illusion occurred in objects and patterns with no oblique lines or edges. Confusion or averaging theories, not themselves tested here, remain unthreatened by these data.     

Geometrical illusions in solid objects under ordinary viewing conditions

The Müller-Lyer and Ponzo illusions were obtained under free binocular viewing of three-dimensional objects, and the function relating magnitude of illusion to fin angle, characteristic of converging-line versions of the Müller-Lyer pattern, was closely paralleled by volumetric (three-cone), line-free objects (but not with an erect, planar “walk-through” construction and moving observers). Illusions cannot be dismissed as artifacts of static, impoverished viewing, therefore, but must be explained within any general theory of perception. Perspective explanations have difficulties with such three-dimensional manifestations, and seem completely inapplicable to our further finding that approximately the same amount of illusion occurred in objects and patterns with no oblique lines or edges. Confusion or averaging theories, not themselves tested here, remain unthreatened by these data.     

Straightness as the main factor of the hErmann grid illusion

The generally accepted explanation of the Hermann grid illusion is Baumgartner's hypothesis that the illusory effect is generated by the response of retinal ganglion cells with concentric ON-OFF or OFF-ON receptive fields. To challenge this explanation, we have introduced some simple distortions to the grid lines which make the illusion disappear totally, while all preconditions of Baumgartner's hypothesis remain unchanged. To analyse the behaviour of the new versions of the grid, we carried out psychophysical experiments, in which we measured the distortion tolerance: the level of distortion at which the illusion disappears at a given type of distortion for a given subject. Statistical analysis has shown that the distortion tolerance is independent of grid-line width within a wide range, and of the type of distortion, except when one side of each line remains straight. We conclude that the main cause of the Hermann grid illusion is the straightness of the edges of the grid lines, and we propose a theory which explains why the illusory spots occur in the original Hermann grid and why they disappear in curved grids.     

Distortions of perceived length in the frontoparallel plane: tests of perspective theories

The perceived length of a line segment in a frontoparallel plane is sometimes affected by the presence of other line segments in the visual field. Perspective theories attribute such interactions to size-constancy scaling: The configuration of line segments present in the visual field includes depth cues that trigger size scaling of each line segment. In three experiments, we test this claim for a range of simple configurations composed of two line segments joined at a point. These configurations include the inverted T configuration of the bisection illusion, as well as the L configuration of the horizontal-vertical illusion. We conclude that the available depth cues, even when supplemented by known biases in perspective interpretations, do not account for observed distortions in judgments of relative length.