Chromosome 6 abnormalities in ovarian surface epithelial tumors of borderline malignancy suggest a genetic continuum in the progression model of ovarian neoplasms.

PURPOSE: We used conventional cytogenetics, molecular cytogenetics, and molecular genetic analyses to study the pattern of allelic loss on chromosome 6q in a cohort of borderline epithelial ovarian tumors. EXPERIMENTAL DESIGN: Fifteen tumor samples were collected from patients undergoing surgery for ovarian tumors. The tumors of borderline malignancy, classified according to the standard criteria, included 4 mucinous and 11 serous tumors. Cytogenetic and molecular cytogenetic (with yeast artificial chromosome clones from 6q26-27) studies were performed on tumor areas contiguous to those used for histological examination ensuring the appropriate sampling. Moreover loss of heterozygosity analysis was performed using PCR amplification of eight microsatellite markers mapping on 6q27 (D6S193, D6S297), 6q26 (D6S305, D6S415, D6S441), 6q21 (D6S287), 6q16 (D6S311), and 6q14 (D6S300). RESULTS: Deletions of this chromosome arm, in particular of 6q24-27, were the most frequent lesions found in this set of tumors. In a tumor with a normal karyotype the only detectable alteration was a deletion of approximately 300 kb within the D6S149-D6S193 interval at band 6q27. This is, to date, the smallest deletion described for borderline tumors. CONCLUSION: Alterations in the above-mentioned interval are a common finding in advanced ovarian carcinomas but also in benign ovarian cysts, implying that some tumors of borderline malignancy may arise from benign tumors and that malignant ones may evolve from tumors of borderline malignancy. Genes located in 6q27 seem to be crucial for this mechanism of early events in ovarian tumorigenesis.

Explaining lightness illusions.

Grey looks darker when set against white than when set against black. In some complex figures this illusion becomes startling, and can be shown to depend on the perceptual organisation of regions within the image. The most widely accepted explanations of such effects are based on the analysis of the junctions formed where the boundaries of nearby regions meet. Even theories where junctions are not the subject of special concern underline their importance as grouping cues. In this paper I present several new families of figures that challenge both views, and conclude that junctions do not play any crucial role in lightness estimation.

Simultaneous lightness contrast with double increments.

In this paper we demonstrate the existence of simultaneous lightness contrast in displays in which the target patches are both more luminant than their surrounds. These effects are not predicted by theories of lightness that assume that the highest luminance in a scene is perceived as white, and anchors all the other luminances. We show that the strength of double-increment illusions depends crucially on the luminance of both the surrounds and the target patches. Such luminance prerequisites were not met in previous studies, which explains why simultaneous contrast with incremental targets has so far been regarded as extremely weak or nonexistent.

Melanoma of the choroid above the optic disc: considerations concerning a clinical case.

The authors report the case of a patient suffering from melanoma of the choroid above the optic disc. Given the good level of visual acuity and the location and extent of the damage, he was given a radiotherapy treatment with proton beams. At an interval of 6 months from this treatment, the neoformation appeared limited, and no vascular changes due to irradiation were observed.

A closer look at the dependence of neon colour spreading on wavelength and illuminance.

Ejima, Redies, Takahashi and Akita [(1984) Vision Research, 24, 1719-1726], studying the dependence of the neon colour spreading effect on wavelength and illuminance, found a number of relationships that appeared of difficult interpretation. This paper shows that these relationships can all be logically predicted within Grossberg and Mingolla's [(1985) Psychological Review, 92, 173-211] approach to the neon spreading problem, with no need of making ad hoc assumptions.

Solving occlusion indeterminacy in chromatically homogeneous patterns.

Overlapping figures can produce consistent depth stratification even when chromatically homogeneous. Since neither T-junctions nor X-junctions are present in these patterns, the problem arises of what rules determine the direction of depth stratification, ie which surfaces appear in front and which behind. In a series of demonstrations and formal experiments involving perception of stereopsis, motion, transparency, motion in depth, and reversible figures, the validity of the principle that the visual system tends to minimise the formation of interpolated modal contours was tested. The reason why larger surfaces tend to be seen modally in front, rather than behind, would reflect the geometrical property that when, in overlapping objects, larger surfaces are closer there will be shorter occluding boundaries than when smaller surfaces are closer. It is shown that this constraint is independent of the empirical depth cue of relative size. An example is also given of a simple computational strategy that extracts, from chromatically homogeneous patterns, occluding subjective contours corresponding to those perceived by human observers.

A new motion illusion related to the aperture problem.

A previously unreported motion illusion is described. Oblique lines that drift smoothly on the retina in a vertical direction appear to be displaced laterally. The effect occurs both for moving lines under fixation and for stationary lines under ocular tracking of an external target. Orientation, length, and homogeneity of the obliques affect the magnitude of illusory displacement. We propose that this illusion is associated with a misregistration of the direction of displacement occurring, in lines slanted relative to the axis of their motion, because of the aperture problem.

Occlusion, transparency, and stereopsis: a new explanation for stereo capture.

Stereo capture occurs when a regular pattern of repeating elements with zero disparity is superimposed on a disparate subjective figure. The elements enclosed within the subjective contours, but not those outside them, are perceptually captured and pulled on the same depth plane of the disparate figure. The phenomenon has been interpreted as the result either of a spreading of disparity signals from the subjective figure or of the attribution of the depth of certain salient image features to the finer texture elements enclosed in them. We suggest here that, instead, the fact that stereo capture is limited to the texture elements lying within the boundaries of the subjective figure is simply due to ambiguous occlusion information at the monocular level. When the texture elements occlude the inducers of the subjective figure as well, the elements lying outside the boundaries of the subjective figure are also captured. We propose that stereo capture arises as the solution to a conflict between information provided by retinal disparity and occlusion, and show how this effect is related to other previously observed phenomena of conflicting cues to depth.

What induces capture in motion capture?

The phenomenon of "motion capture" has been demonstrated by presenting, one after the other, two identical Kanizsa squares spatially separated and superimposed on a regular matrix of dots. For appropriate temporal intervals, one illusory square is seen to jump from one location to the other and the dots in it appear to move with it even though they are physically stationary. The standard explanation of the effect is that motion signals from the subjective figure are spontaneously attributed to the static elements laying on it. We have found, however, that if alternative removal of right-angle sectors (required to obtain apparent motion of the illusory square) is not accompanied by alternative appearance and disappearance of a few dots, motion capture does not occur. This suggests that the basic mechanism underlying capture is not the motion of the subjective figure per se, but the spreading of motion signals arising from those texture elements that alternately go on and off between frames. On the other hand, subjective contours do play a role by confining the spreading of motion signals to the texture elements located on the figure.

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.

Neon colour spreading with and without its figural prerequisites.

Neon colour spreading has been shown to disappear if certain figural conditions are not met. Evidence is presented which suggests that these conditions are only incidentally related to the neon spreading effect; in particular, that they can be violated as long as the structure remains compatible with the interpretation of a transparent surface. It is proposed that neon spreading and classical colour assimilation share the same basic mechanism, and that the peculiar perceptual attributes of the former derive from the perceptual scissioning of ordinary assimilation colour. This process is identical to that occurring with nonillusory colours in phenomenal transparency.

The role of depth stratification in the solution of the aperture problem.

When a plaid pattern composed of a stationary vertical grating and a horizontally drifting diagonal grating is shown behind a circular aperture, the pattern appears to move coherently in a vertical direction. When the bars of the stationary grating are narrower than those of the moving grating, only the latter is seen to move, in a direction orthogonal to its orientation (ie diagonal); but when the bars of the stationary grating are wider than those of the moving grating, vertical motion of the whole plaid predominates. It is argued that, in the absence of occlusion information, the motion of a plaid within an aperture depends on the unambiguous displacement of inner line terminators at the crossings of the two gratings. Relative motion and differences in bar width between the two gratings provide information about which set of bars is in front of the other. When these sources of information are consistent with each other, separation of the two gratings in depth occurs: inner line terminators no longer perceptually exist and the direction of motion becomes determined only by terminators at the edges, which causes a shift from vertical to orthogonal motion. Differences in luminance also provide (asymmetrical) information about depth relationships: when darker bars occlude lighter bars, the probability of orthogonal motion increases as a function of the difference in luminance, whereas when lighter bars are over darker bars, vertical motion prevails.

Motion aftereffects with rotating ellipses.

The perceptual outcome and the motion-aftereffect duration generated by the rotation on the frontal plane of an ellipse with a bar depend on whether the bar is placed along the major or the minor axis. When the bar is placed along the minor axis, a stereokinetic transformation occurs, and the pattern looks like a tilting ring with a perpendicular bar moving rigidly with it. Placing the bar along the major axis prevents the stereokinetic transformation: subjects report deformations and relative motion of the bar with respect to the ellipse. We found that motion aftereffects last longer when the bar is placed along the minor rather than along the major axis. A series of experiments was carried out to investigate whether differences in aftereffect duration are related to the stereokinetic transformation. Results seem to suggest that they are not.

A context-dependent illusion in the perception of velocity.

It has so far been assumed that velocity contrast effects can be explained by local lateral inhibition processes which act to enhance the difference in velocity between a target and its immediate surround. A new velocity illusion is here reported that seriously questions this notion.

Occlusion and the perception of coherent motion.

Recent work (Shimojo, Silverman & Nakayama, 1989; Vision Research, 29, 619-626) suggests that the visual system must discriminate between extrinsic boundaries (boundaries created by front occluding surfaces) and intrinsic boundaries (real object boundaries) in order to recognize objects and that this would importantly affect the way it solves the so-called "aperture problem" in motion. With the aid of a series of demonstrations (plus two formal experiments) we (1) propose a new explanation for the fact that edge line terminators in a "barber pole" display are perceived as intrinsic; (2) show that inner line terminators in a plaid pattern (i.e. those resulting from the intersection of the two sets of bars) specify coherent or incoherent motion depending on the availability of occlusion-related depth information; and (3) suggest a unitary scheme integrating the two current alternative solutions to the aperture problem, the one based on line terminators and the one based on a velocity space combination of orthogonal components.

Illusory depth from moving subjective figures and neon colour spreading.

If a pattern of concentric circles, interrupted so as to produce the perception of a subjective bar extending from the centre to the periphery of the pattern, was slowly rotated in a plane perpendicular to the line of sight, observers reported seeing the bar slanted in depth and moving over complete and stationary concentric circles. When the interrupted concentric circles were completed by red segments--thereby giving rise to a neon colour-spreading effect--observers reported seeing a reddish bar, which sometimes appeared to be slanted in depth, moving behind the plane of the concentric circles. A combination of the two patterns was found to originate a compelling percept of a unitary bar slanted in depth: part of the bar (the subjective half) appeared to be located in front of its inducing elements, whereas the other part (the neon-like half) appeared to continue behind them. When translatory instead of rotary motion was used, the bars did not look slanted in depth: however, the neon bar appeared either behind or in front of the inducing lines, depending on the luminance contrast between the segments and the inducing lines themselves.

The perception of 3-dimensional affine structure from minimal apparent motion sequences.

The research described in the present article was designed to identify the minimal conditions for the visual perception of 3-dimensional structure from motion by comparing the theoretical limitations of ideal observers with the perceptual performance of actual human subjects on a variety of psychophysical tasks. The research began with a mathematical analysis, which showed that 2-frame apparent motion sequences are theoretically sufficient to distinguish between rigid and nonrigid motion and to identify structural properties of an object that remain invariant under affine transformations, but that 3 or more distinct frames are theoretically necessary to adequately specify properties of euclidean structure such as the relative 3-dimensional lengths or angles between nonparallel line segments. A series of four experiments was then performed to verify the psychological validity of this analysis. The results demonstrated that the determination of structure from motion in actual human observers may be restricted to the use of first order temporal relations, which are available within 2-frame apparent motion sequences. That is to say, the accuracy of observers' judgments did not improve in any of these experiments as the number of distinct frames in an apparent motion sequence was increased from 2 to 8, and performance on tasks involving affine structure was of an order of magnitude greater than performance on similar tasks involving euclidean structure.

Wheels: a new illusion in the perception of rolling objects.

A new illusory effect is described which consists of a conspicuous perceptual overestimation of the speed at which a wheel rolling across an observer's visual field appears to be rotating. Wheels appear to revolve much faster than is compatible with their linear displacement. Experimental verification of the genuineness and magnitude of the effect is reported, along with a discussion of some of the variables upon which it may depend.