Koffka's effect is mediated by figure thickness at the joining region

Three-quarters of a century ago Gestalt psychologist Kurt Koffka described a remarkable effect: when a contiguous gray ring is placed on a background half one shade of gray, half another, the ring appears homogeneous. However, if the ring is divided, the two halves of the ring appear different shades of gray, the half of the ring on the darker background appearing lighter than the half of the ring on the lighter background. The Gestalt principle of continuity is used to explain this effect. But what microscopic principles might be mediating this effect? Recently we found sufficiently thin rings (annuli) appear heterogeneous even when geometrically continuous. Here, using crescent-shaped figures instead of the circular annuli used for the traditional Koffka effect, we show that this effect of thickness of the ring is mediated by the thickness at the boundary of the region where the halves of the figure are joined.     

Lightness of grays: Effects of Background reflectance

The influence of background reflectance was determined for lightness judgments relative to white of small gray patches. The effect of prior stimulus-context was avoided by considering only first judgments. It was found that lightness was proportional to the square root of reflectance when the background was a gray darker than the stimulus, but not when the background was lighter gray or white. In general, a small difference in reflectance between the stimulus and and background produced the same effect as a larger difference.     

Induction in variants of White's effect: common or separate mechanisms?

In White's display the gray target surrounded more by black than white appears darker than the target of the same physical luminance surrounded more by white than black. Several subsequent studies have shown that this effect occurs only when the luminance of the test regions lies between the minimum and maximum luminance values of the inducing stripes. With targets either lighter or darker than both inducing stripes, the direction of the effect is reversed and the effect is known as the 'inverted' White's effect. Views differ on whether the classical and inverted White's effects are mediated by common or separate underlying mechanisms. We varied the aspect ratio of the test and inducing regions in the classical and inverted White's effects. Consistent with previously reported findings, we found that the direction of the classical effect did not depend on the amount of black or white border in immediate contact with the test patch. On the other hand, perceived lightness in the inverted White's effect was affected by such variations, suggesting that induction in classical and inverted White's configurations is governed by different mechanisms. These results confirm the critical importance of the interaction between luminance and geometric relationships in induced brightness.     

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.     

Lightness effects in Delboeuf and Ebbinghaus size-contrast illusions

We examined lightness effects observed in Delboeuf and Ebbinghaus size-contrast illusions. Results of four experiments are reported. Experiment 1 was conducted with Delboeuf-like stimuli and shows that the disk that appears bigger appears either lighter or darker than the disk that appears smaller, depending on the contrast polarity between disks and background. Experiment 2 shows that the direction of these lightness effects is not influenced by the luminance of the size-contrast inducers. Experiment 3 shows that a similar lightness effect is also observed in modified Ebbinghaus size-contrast displays. Experiment 4 tested the presence of the size-contrast illusion in the stimuli used in experiments 2 and 3.     

The perception of assimilation and brightness contrast as derived from code theory

It is shown that assimilation and brightness contrast effects are evoked by structural aspects of patterns. In a pilot experiment, variously shaped gray patterns were used as stimuli. The backgrounds used with each of these shapes were identical: half black and half white. If the gray area against the black part was judged to be more black than the gray area against the white part, an assimilation effect will have occurred; when the reverse occurred, this was called a contrast effect. The task was to rank-order the stimuli on the assimilation-contrast scale. It is argued that the two effects are due to two different interpretations, each derivable from a different code of a pattern. The simpler the contrast code is with respect to the assimilation code, the more it will be perceptually preferred. In the specification of pattern complexity, structural information theory was used. A significant correlation was discovered between the theoretical preference for the contrast interpretation and the contrast preference of subjects.     

Illusions of size change in dynamic displays

A line of constant width viewed against an expanding or contracting grating appears to become narrower or wider, respectively. This effect was studied using a computer-controlled video system with a motorized zoom lens. The magnitude of the illusory size (width) change with a vertical line did not differ when viewed against a horizontal or an oblique background, and the size change was not due to static size contrast between the line and the background. The illusory narrowing observed with an expanding background was equivalent to the widening observed with a contracting background. The apparent change in the width of lines that actually expanded was consistently underestimated, either on a similarly changing background or when viewed against a gray field. Although the transformation of the background and line produced changes in their perceived distance, this did not occur for a constant line against a transforming background, even though this condition induced the perceived size change.     

Multistability of overlapped face stimuli is dependent upon orientation

Stimuli composed of two overlapped faces, one rotated 45 degrees clockwise and the other 45 degrees counterclockwise, produce perceptual rivalry whereby both faces cannot be simultaneously perceived. We obtained subjective and quantitative measures of this rivalry effect and examined if it persists with inverted stimuli. Our results show that upright stimuli are multistable, with alternations occurring from one face to the other within 2 s. Inverted stimuli were instead perceived as ambiguous in half of the trials, indicating weaker perceptual rivalry in that condition. We suggest that overlapped faces produce perceptual rivalry because each face is readily interpreted into a Gestalt, an effect that in turn is dependent upon orientation.     

T-junctions,apparent depth,and perceived lightness contrast

Observers performed lightness matches for physically equivalent gray targets of a simultaneous lightness contrast display and displays in which both targets were on the same background. Targets either shared a common line-texture pattern with their respective backgrounds or did not. Results indicate that when targets share a line-texture pattern with their respective backgrounds, a contrast effect is obtained. However, when the target's pattern is different than the background's pattern, perceived contrast is significantly reduced and the target appears as a separate 3-D entity. This result applies to both vertically and horizontally oriented displays, to targets that are increments or decrements, and to line-texture patterns that are black or white. Line patterns that are shared by targets and backgrounds result in T-junctions that provide occlusion information. We conclude that targets and backgrounds perceived to be on separate planes because of T-junctions are less likely to be perceptually grouped together and that their luminance values are less likely to be compared with one another.     

Visual masking and the recovery phenomenon

Two experiments were carried out to investigate visual masking and target recovery. In the first experiment it was found that with superimposed disks of various sizes masking increases with increasing target-mask similarity and contour proximity. The results of the second study show that the extent of masking produced by a disk, which is slightly larger than the target, is drastically reduced when the mask in turn is followed by a ring, the inner contour of which is contiguous with the contour of the mask. This “facilitation effect” decreases as the interval between the mask and the third stimulus is increased. Target recovery in this situation appears to be brought about as a result of the reduction or elimination of the contour of the mask, which, as the first study has shown, is critical in bringing about the masking effect. The results are discussed in terms of some of the known physiological properties of the visual system.     

Emergence of perceptual Gestalts in the human visual cortex: the case of the configural-superiority effect

Many Gestalt phenomena have been described in terms of perception of a whole being not equal to the sum of its parts. It is unclear how these phenomena emerge in the brain. We used functional MRI to study the neural basis of the behavioral configural-superiority effect (i.e., visual search is more efficient when an odd element is part of a configuration than when it is presented by itself). We found that searching for the odd element in a display of four line segments (parts) was facilitated by adding two additional line segments to each of them (creating whole shapes). Functional MRI-based decoding of neural responses to the position of the odd element revealed a neural configural-superiority effect in shape-selective regions but not in low-level retinotopic areas, where decoding of parts was more pronounced. These results show how at least some Gestalt phenomena in vision emerge only at the higher stages of visual information processing and suggest that feed-forward processing might be sufficient to produce such phenomena.     

Successive responses to simultaneous stimuli

Previous work had shown that, when a memory-span experiment is performed with half the items presented to one ear, and half simultaneously to the other, a certain order of response appears. Either one ear or the other is dealt with first, and then the remaining items produce a response afterwards. The present results extend this finding to the eye and the ear rather than the two ears, and also to two voices distinguished by their frequency characteristics. For the latter condition, it is also shown that alternation of attention can take place at a speed faster than between the two ears. The effect thus appears to be a general one, and not merely a peculiarity of binaural hearing.     

Luminance determinants of perceived surface stratification in two-dimensional achromatic transparent patterns

Two overlapping transparent surfaces forming a two-dimensional pattern stand out in front of each other alternately. Let y denote the luminance of the region where these surfaces overlap and b the luminance of the background. In achromatic patterns, the probability that the lighter transparent surface appears to be in front of the other surface is known to increase with y and with b. The present results show that grouping by achromatic colour similarity cannot explain the effect of b. An alternative conjecture is that the luminance factors that control perceived surface segregation can explain the effects of y and b. Such an explanation predicts a new effect: the probability that one transparent surface appears to be in front increases with the absolute difference in luminance between the surface and the background. The present results confirm this prediction.     

Interactions between perceptual organization based on Gestalt laws and those based on hierarchical processing

Our recent research with compound stimuli (Han, Humphreys, & Chen, 1999a) suggests that grouping between local elements facilitates the perception of global structure, whereas encoding closure in local elements enhances their segmentation. The present study presents further evidence supporting this assertion. Experiment 1 first developed a new paradigm in which grouping between local elements was manipulated. Subjects responded to the orientations of perceptual groups consisting of local arrows or triangles embedded in background crosses. Responses to the orientations of the groups were slowed as a function of the increased contrast of the crosses, indicating that the strength of grouping between local arrows or triangles was gradually weakened by increasing the contrast of the crosses. Using a similar paradigm, Experiments 2 and 3 investigated the role of Gestalt factors in hierarchical analysis. Global arrows or triangles made up of local arrows, or triangles were embedded in background crosses. Subjects responded to global or local stimuli in terms of orientation or closure. Increasing the contrast of the background crosses produced stronger effects on global responses than on local responses and resulted in elimination of the global precedence effect and emerging of a local precedence effect, which was stronger for closure discrimination than for orientation discrimination. These results provide new evidence supporting our previous claim about the role of Gestalt factors in hierarchical analysis.     

The rod-and-frame effect: the whole is less than the sum of its parts

Since the discovery of the influence of the tilted frame on the visual perception of the orientation perceived as vertical (VPV), the frame has been treated as a unitary object-a Gestalt. We evaluated the effect of 1-line, 2-line, 3-line, and 4-line (square frame) stimuli of two different sizes, and asked whether the influence of the square frame on VPV is any greater than the additive combination of separate influences produced by the individual lines constituting the frame. We found that, for each size, the square frame is considerably less influential than the additive combination of the influences of the individual lines. The results conform to a mass action rule, in which the lengths and orientations of the individual line components are what matters and the organization of the lines into a square does not-no higher-level Gestalt property is involved in the induction effect on VPV.     

Do bantams (Gallus gallus domesticus) amodally complete partly occluded lines? An analysis of line classification performance

Humans perceive a line touching an edge of a large rectangle longer than the reality. Kanizsa (1979) has suggested that this illusion occurs because we perceive that the line is partly "hidden" behind the rectangle and automatically completes it. We tested whether bantams (Gallus gallus domesticus) would experience this perceptual phenomenon using a line classification task on the touch monitor, which was used in our previous study with rhesus monkeys and pigeons (Fujita, 2001). We trained three bantams to classify six lengths of black target lines into two categories, "short" or "long," ignoring a gray rectangle (Experiment 1) or a gray area (i.e., a left or a right half of the monitor was filled with gray; Experiment 2) located at the same distance (8 pixels) from the target line. In the test, the gap between the line and the gray rectangle (or area) sometimes changed (0, 4, or 8 pixels; we labeled these stimuli as G0, G4, and G8 respectively). Both of the two successfully trained bantams showed an illusion for G0, but the direction of illusion was reversed; that is, they judged the line in G0 to be "shorter" than that in G4 and G8. Further analyses proved that neither the gaps between the target line and the gray rectangle nor the total widths of the stimuli could account for the bantams' responses. These results suggest that bantams do not complete the "occluded" portion even when identification of its shape is not required.     

On intelligence education and religious beliefs

A number of authors have suggested that education mediates the negative effect of intelligence on religiosity. However, there is very little direct evidence for this mediation, and the indirect evidence is contradictory. The results of the current paper suggest that, by and large, education does not mediate the effect of intelligence on religiosity. However, the results also suggest that since education has a positive effect on religiosity when religious background is strong and a negative effect when religious background is weak, and since intelligence has a positive effect on education, the negative effect of intelligence on religiosity is stronger when religious background is strong than when it is weak. We examine this mediated moderation model in two large, nationally representative, databases.     

Gestalt psychology: the forgotten paradigm in abnormal psychology

Gestalt views of psychopathology are almost completely ignored in mainstream psychology and psychiatry. However, a review of available evidence indicates a remarkable consistency between these views and current data from experimental psychopathology and cognitive neuroscience. This consistency is especially pronounced in the area of schizophrenia. In addition, there is a convergence of cognitive and neurobiological evidence regarding the validity of early Gestalt views of both normal brain-behavior relationships and disordered ones, as in schizophrenia. This article reviews some contributions of Gestalt psychology regarding schizophrenia and examines these views in light of more recent findings from cognitive psychology, cognitive neuroscience, and experimental psychopathology. We conclude that Gestalt theory is a viable theoretical framework from which to understand schizophrenia. Specifically, it appears that a breakdown of Gestalt organizational processes may characterize both the cognitive and the brain processes in schizophrenia.     

The spoke brightness illusion originates at an early motion processing stage

When a bright white disk revolves around a fixation point on a gray background, observers perceive a "spoke": a dark gray region that connects the disk with the fixation point. Our first experiment suggests that motion across the retina is both necessary and sufficient for spokes: The illusion occurs when a disk moves across the retina even though it is perceived to be stationary, but the illusion does not occur when the disk appears to move while remaining stationary on the retina. A second experiment shows that the strength of the illusion decreases with decreasing luminance contrast until subjective equiluminance, where little or no spoke is perceived. These results suggest that spokes originate at an early, predominantly luminance-based stage of motion processing, before the visual system discounts retinal motion caused by smooth pursuit.     

Reference frame effects on shape perception in two versus three dimensions

Three experiments are reported in which it is tested whether the Gestalt effect of configural orientation on shape perception operates on two-dimensional (2-D) or three-dimensional (3-D) representations of space. It is known that gravitationally defined squares and diamonds take longer to discriminate in diagonal arrays than in horizontal or vertical arrays. In the first experiment it is shown that this interference effect decreases dramatically in magnitude when pictorial depth information is added so that subjects perceive the target shapes in different depth planes. In the second experiment this difference is shown not to be due to relative size of the target shapes or to occlusion of a background plane. It is also shown, in the final experiment, that this difference is not due to linear perspective information or merely to perception of the target figures in a 3-D scene. The overall pattern of results supports the position that this configural reference frame effect arises primarily when the elements of the configuration are coplanar, and that the principal organization underlying it is the structure of the perceived 3-D environment rather than that of the 2-D image. In all three experiments, however, there is also a small interference effect in the noncoplanar 3-D conditions. This might be due either to some aspect of reference frame selection operating on the 2-D image representation or to the failure of subjects to see depth in the 3-D stimuli on some proportion of the trials.